Astrophysics
New submissions
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New submissions for Wed, 4 Nov 09
- [1] arXiv:0911.0409 [ps, pdf, other]
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Title: What is a Cool-Core Cluster? A Detailed Analysis of the Cores of the X-ray Flux-Limited HIFLUGCS Cluster SampleAuthors: Daniel S. Hudson, Rupal Mittal, Thomas H. Reiprich, Paul E. J. Nulsen, Heinz Andernach, Craig L. SarazinComments: 45 pages, 19 figures, 7 tables. Accepted for publication in A&A. Contact Person: Rupal Mittal (rmittal@astro.rit.edu)Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We use the largest complete sample of 64 galaxy clusters (HIghest X-ray FLUx Galaxy Cluster Sample) with available high-quality X-ray data from Chandra, and apply 16 cool-core diagnostics to them, some of them new. We also correlate optical properties of brightest cluster galaxies (BCGs) with X-ray properties. To segregate cool core and non-cool-core clusters, we find that central cooling time, t_cool, is the best parameter for low redshift clusters with high quality data, and that cuspiness is the best parameter for high redshift clusters. 72% of clusters in our sample have a cool core (t_cool < 7.7 h_{71}^{-1/2} Gyr) and 44% have strong cool cores (t_cool <1.0 h_{71}^{-1/2} Gyr). For the first time we show quantitatively that the discrepancy in classical and spectroscopic mass deposition rates can not be explained with a recent formation of the cool cores, demonstrating the need for a heating mechanism to explain the cooling flow problem. [Abridged]
- [2] arXiv:0911.0413 [ps, pdf, other]
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Title: Enhanced Dense Gas Fraction in Ultra-Luminous Infrared GalaxiesAuthors: S. Juneau (1), D. T. Narayanan (2), J. Moustakas (3), Y. L. Shirley (1), R. S. Bussmann (1), R. C. Kennicutt Jr (4), P. A. Vanden Bout (5) ((1) Steward Observatory, Tucson AZ (2) Harvard-Smithsonian CfA, Cambridge MA (3) Center for Astrophysics and Space Sciences, UCSD, CA (4) Institute of Astronomy, Cambridge UK, (5) NRAO, Charlottesville VA)Comments: 20 pages, 10 figures. To be published in The Astrophysical Journal (accepted)Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
We present a detailed analysis of the relation between infrared luminosity and molecular line luminosity, for a variety of molecular transitions, using a sample of 34 nearby galaxies spanning a broad range of infrared luminosities (10^{10} < L_{IR} < 10^{12.5} L_sun). We show that the power-law index of the relation is sensitive to the critical density of the molecular gas tracer used, and that the dominant driver in observed molecular line ratios in galaxies is the gas density. As most nearby ultraluminous infrared galaxies (ULIRGs) exhibit strong signatures of active galactic nuclei (AGN) in their center, we revisit previous claims questioning the reliability of HCN as a probe of the dense gas responsible for star formation in the presence of AGN. We find that the enhanced HCN(1-0)/CO(1-0) luminosity ratio observed in ULIRGs can be successfully reproduced using numerical models with fixed chemical abundances and without AGN-induced chemistry effects. We extend this analysis to a total of ten molecular line ratios by combining the following transitions: CO(1-0), HCO+(1-0), HCO+(3-2), HCN(1-0), and HCN(3-2). Our results suggest that AGNs reside in systems with higher dense gas fraction, and that chemistry or other effects associated with their hard radiation field may not dominate (NGC 1068 is one exception). Galaxy merger could be the underlying cause of increased dense gas fraction and the evolutionary stage of such mergers may be another determinant of the HCN/CO luminosity ratio.
- [3] arXiv:0911.0414 [ps, pdf, other]
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Title: Hierarchy in the Phase Space and Dark Matter AstronomyComments: 5 pages, 4 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
We develop a theoretical framework for describing the hierarchical structure of the phase space of cold dark matter haloes, due to gravitationally bound substructures. Because it includes the full hierarchy of the cold dark matter initial conditions and is hence complementary to the halo model, the stable clustering hypothesis is applied for the first time here to the small-scale phase space structure. As an application, we show that the particle dark matter annihilation signal could be up to two orders of magnitude larger than that of the smooth halo within the Galactic virial radius. The local boost is inversely proportional to the smooth halo density, and thus is O(1) within the solar radius, which could translate into interesting signatures for dark matter direct detection experiments: The temporal correlation of dark matter detection can change by a factor of 2 in the span of 10 years, while there will be significant correlations in the velocity space of dark matter particles. This can introduce O(1) uncertainty in the direction of local dark matter wind, which was believed to be a benchmark of directional dark matter searches or the annual modulation signal.
- [4] arXiv:0911.0416 [ps, pdf, other]
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Title: Surface Detonations in Double Degenerate Binary Systems Triggered by Accretion Stream InstabilitiesAuthors: James Guillochon (1), Marius Dan (2), Enrico Ramirez-Ruiz (1), Stephan Rosswog (2), ((1) Univ. of California Santa Cruz, (2) Jacobs University Bremen)Comments: 6 pages, 4 figures, 1 table. Submitted to ApJL. For a high-resolution version, movies, and other supporting material see this http URLSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We present three-dimensional simulations on a new mechanism for the detonation of a sub-Chandrasekhar CO white dwarf in a dynamically unstable system where the secondary is either a pure He white dwarf or a He/CO hybrid. For dynamically unstable systems where the accretion stream directly impacts the surface of the primary, the final tens of orbits can have mass accretion rates that range from $10^{-5}$ to $10^{-3} M_{\odot}$ s$^{-1}$, leading to the rapid accumulation of helium on the surface of the primary. After $\sim 10^{-2}$ $M_{\odot}$ of helium has been accreted, the ram pressure of the hot helium torus can deflect the accretion stream such that the stream no longer directly impacts the surface. The velocity difference between the stream and the torus produces shearing which seeds large-scale Kelvin-Helmholtz instabilities along the interface between the two regions. These instabilities eventually grow into dense knots of material that periodically strike the surface of the primary, adiabatically compressing the underlying helium torus. If the temperature of the compressed material is raised above a critical temperature, the timescale for triple-$\alpha$ reactions becomes comparable to the dynamical timescale, leading to the detonation of the primary's helium envelope. This detonation drives shockwaves into the primary which tend to concentrate at one or more focal points within the primary's CO core. If a relatively small amount of mass is raised above a critical temperature and density at these focal points, the CO core may itself be detonated.
- [5] arXiv:0911.0417 [ps, pdf, other]
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Title: Evolution of the Halpha luminosity functionAuthors: Eduard Westra (1), Margaret J. Geller (1), Michael J. Kurtz (1), Daniel G. Fabricant (1), Ian Dell'Antonio (2) ((1) Smithsonian Astrophysical Observatory, (2) Brown University)Comments: 26 pages, 23 figures, submitted to ApJ; version with high resolution figures available at this http URLSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The Smithsonian Hectospec Lensing Survey (SHELS) is a window on the star formation history over the last 4 Gyr. SHELS is a spectroscopically complete survey for Rtot < 20.3 over 4 square degrees. We use the 10k spectra to select a sample of pure star forming galaxies based on their Halpha emission line. We use the spectroscopy to determine extinction corrections for individual galaxies and to remove active galaxies in order to reduce systematic uncertainties. We use the large volume of SHELS with the depth of a narrowband survey for Halpha galaxies at z ~ 0.24 to make a combined determination of the Halpha luminosity function at z ~ 0.24. The large area covered by SHELS yields a survey volume big enough to determine the bright end of the Halpha luminosity function from redshift 0.100 to 0.377 for an assumed fixed faint-end slope alpha = -1.20. The bright end evolves: the characteristic luminosity L* increases by 0.84 dex over this redshift range. Similarly, the star formation density increases by 0.11 dex. The fraction of galaxies with a close neighbor increases by a factor of 2-5 for L(Halpha) >~ L* in each of the redshift bins. We conclude that triggered star formation is an important influence for star forming galaxies with Halpha emission.
- [6] arXiv:0911.0418 [ps, pdf, other]
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Title: Cosmological Problems with Multiple Axion-like FieldsAuthors: Katherine J. Mack (1 and 2), Paul J. Steinhardt (2) ((1) IoA/KICC, University of Cambridge, (2) Princeton University)Comments: 17 pages, 2 figures. Submitted to Phys Rev DSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Incorporating the QCD axion and simultaneously satisfying current constraints on the dark matter density and isocurvature fluctuations requires non-minimal fine-tuning of inflationary parameters or the axion misalignment angle (or both) for Peccei-Quinn symmetry-breaking scales $f_a > 10^{12}$ GeV. To gauge the degree of tuning in models with many axion-like fields at similar symmetry-breaking scales and masses, as may occur in string theoretic models that include a QCD axion, we introduce a figure of merit ${\cal F}$ that measures the fractional volume of allowed parameter space: the product of the slow roll parameter $\epsilon$ and each of the axion misalignment angles, $\theta_0$. For a single axion, $\mathcal{F} \lesssim 10^{-11}$ is needed to avoid conflict with observations. We show that the fine tuning of $\mathcal{F}$ becomes exponentially more extreme in the case of numerous axion-like fields. Anthropic arguments are insufficient to explain the fine tuning because the bulk of the anthropically allowed parameter space is observationally ruled out by limits on the cosmic microwave background isocurvature modes. Therefore, this tuning presents a challenge to the compatibility of string-theoretic models with light axions and inflationary cosmology.
- [7] arXiv:0911.0419 [ps, pdf, other]
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Title: Ly-alpha emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshiftComments: 5 pages, 5 figures, 1 table, re-submitted after referees comments to A&A Letters, Table 1 can be requested in full from the authorsSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The traditional view that Ly-alpha emission and dust should be mutually exclusive has been questioned more and more often, notably the observations of Ly-alpha emission from ULIRGs seems to counter this view. In this paper we seek to address the reverse question: How large a fraction of Ly-alpha selected galaxies are ULIRGs? Using two samples of 24/25 Ly-alpha emitting galaxies at z = 0.3/2.3 we perform this test, also including results at z = 3.1, and find that whereas the ULIRG fraction at z = 3.1 is very small, it systematically increases towards lower redshifts. There is a hint that this evolution may be quite sudden and that it happens around a redshift of z ~ 2.5. Measuring the infrared luminosities of the Ly-alpha emitters, we find that they are in the normal to ULIRG range in the lower redshift sample, whereas the higher redshift galaxies all have luminosities in the ULIRG category. The Ly-alpha escape fractions for these infrared bright galaxies are in the range 1-100 % in the low redshift galaxies, but are very low, 0.4 % on average, in the high redshift galaxies. The unobscured star formation rates are very high, ranging from 500 to more than 5000 Msun / yr. The dust attenuation derived are in the range 0.0 < A_V < 3.5.
- [8] arXiv:0911.0420 [ps, pdf, other]
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Title: The globular cluster system of NGC 1399 V. dynamics of the cluster system out to 80 kpcAuthors: Y. Schuberth, T. Richtler, M. Hilker, B. Dirsch, L. P. Bassino, A. J. Romanowsky, L. InfanteComments: 31 pages, accepted for publication in A&A. Online material will be available from the CDSSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
(Abridged) We use the largest set of globular cluster velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies. Our sample now comprises velocities for almost 700 GCs with projected galactocentric radii between 6 and 100 kpc. In addition, we use velocities published by Bergond et al. (2007). We study the kinematics of the metal-poor and metal-rich subpopulations and perform spherical Jeans modelling.
The most important results are: The metal-rich (red) GCs resemble the stellar field population of NGC 1399 in the region of overlap. Both subpopulations are kinematically distinct and do not show a smooth transition. It is not possible to find a common dark halo which reproduces simultaneously the properties of both subpopulations. Some velocities of blue GCs are only to be explained by orbits with very large apogalactic distances, thus indicating a contamination with GCs which belong to the entire Fornax cluster rather than to NGC 1399. Stripped GCs from nearby elliptical galaxies, particularly NGC 1404, may also contaminate the metal-poor sample. We argue in favour of a scenario in which the majority of the blue cluster population has been accreted during the assembly of the Fornax cluster. The red cluster population shares the dynamical history of the galaxy itself. Therefore we recommend to use a dark halo based on the red GCs alone. The dark halo which fits best is marginally less massive than the halo quoted by Richtler et al. (2004). The comparison with X-ray analyses is satisfactory in the inner regions, but without showing evidence for a transition from a galaxy to a cluster halo, as suggested by X-ray work. - [9] arXiv:0911.0421 [ps, pdf, other]
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Title: Axions, Inflation and the Anthropic PrincipleAuthors: Katherine J. Mack (1 and 2) ((1) IoA/KICC, University of Cambridge, (2) Princeton University)Comments: 19 pages, 3 figures. Submitted to Phys Rev DSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)
The QCD axion is the leading solution to the strong-CP problem, a dark matter candidate, and a possible result of string theory compactifications. However, for axions produced before inflation, symmetry-breaking scales of $f_a \gtrsim 10^{12}$ GeV (which are favored in string-theoretic axion models) are ruled out by cosmological constraints unless both the axion misalignment angle $\theta_0$ and the inflationary Hubble scale $H_I$ are extremely fine-tuned. We show that attempting to accommodate a high-$f_a$ axion in inflationary cosmology leads to a fine-tuning problem that is worse than the strong-CP problem the axion was originally invented to solve. We also show that this problem remains unresolved by anthropic selection arguments commonly applied to the high-$f_a$ axion scenario.
- [10] arXiv:0911.0423 [ps, pdf, other]
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Title: Optically Selected BL Lacertae Candidates from the Sloan Digital Sky Survey Data Release SevenAuthors: Richard M. Plotkin, S. F. Anderson, W. N. Brandt, A. M. Diamond-Stanic, X. Fan, P. B. Hall, A. E. Kimball, M. W. Richmond, D. P. Schneider, O. Shemmer, W. Voges, D. G. York, N. A. Bahcall, S. Snedden, D. Bizyaev, H. Brewington, V. Malanushenko, E. Malanushenko, D. Oravetz, K. Pan, A. SimmondsComments: 24 pages, 14 figures, 8 tables. Accepted for publication in AJSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
We present a sample of 723 optically selected BL Lac candidates from the SDSS DR7 spectroscopic database encompassing 8250 deg^2 of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts. Approximately 80% of our BL Lac candidates match to a radio source in FIRST/NVSS, and ~40% match to a ROSAT X-ray source. The homogeneous multiwavelength coverage allows subdivision of the sample into 637 radio-loud BL Lac candidates and 86 weak-featured radio-quiet objects. The radio-loud objects broadly support the standard paradigm unifying BL Lac objects with beamed radio galaxies. We propose that the majority of the radio-quiet objects may be lower-redshift (z<2.2) analogs to high-redshift weak line quasars (i.e., AGN with unusually anemic broad emission line regions). These would constitute the largest sample of such objects, being of similar size and complementary in redshift to the samples of high-redshift weak line quasars previously discovered by the SDSS. However, some fraction of the weak-featured radio-quiet objects may instead populate a rare and extreme radio-weak tail of the much larger radio-loud BL Lac population. Serendipitous discoveries of unusual white dwarfs, high-redshift weak line quasars, and broad absorption line quasars with extreme continuum dropoffs blueward of rest-frame 2800 Angstroms are also briefly described.
- [11] arXiv:0911.0424 [ps, pdf, other]
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Title: The Origin of Enhanced Activity in the Suns of M67Comments: accepted by ApJSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We report the results of the analysis of high resolution photospheric line spectra obtained with the UVES instrument on the VLT for a sample of 15 solar-type stars selected from a recent survey of the distribution of H and K chromospheric line strengths in the solar-age open cluster M67. We find upper limits to the projected rotation velocities that are consistent with solar-like rotation (i.e., v sini ~< 2-3 km/s) for objects with Ca II chromospheric activity within the range of the contemporary solar cycle. Two solar-type stars in our sample exhibit chromospheric emission well in excess of even solar maximum values. In one case, Sanders 1452, we measure a minimum rotational velocity of vsini = 4 +/- 0.5 km/s, or over twice the solar equatorial rotational velocity. The other star with enhanced activity, Sanders 747, is a spectroscopic binary. We conclude that high activity in solar-type stars in M67 that exceeds solar levels is likely due to more rapid rotation rather than an excursion in solar-like activity cycles to unusually high levels. We estimate an upper limit of 0.2% for the range of brightness changes occurring as a result of chromospheric activity in solar-type stars and, by inference, in the Sun itself. We discuss possible implications for our understanding of angular momentum evolution in solar-type stars, and we tentatively attribute the rapid rotation in Sanders 1452 to a reduced braking efficiency.
- [12] arXiv:0911.0426 [ps, pdf, other]
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Title: Making the Earth: Combining Dynamics and Chemistry in the Solar SystemComments: 61 pages (including online material), 12 figures (7 in paper, 5 online). Accepted to IcarusSubjects: Earth and Planetary Astrophysics (astro-ph.EP)
No terrestrial planet formation simulation completed to date has considered the detailed chemical composition of the planets produced. While many have considered possible water contents and late veneer compositions, none have examined the bulk elemental abundances of the planets produced as an important check of formation models. Here we report on the first study of this type. Bulk elemental abundances based on disk equilibrium studies have been determined for the simulated terrestrial planets of O'Brien et al. (2006). These abundances are in excellent agreement with observed planetary values, indicating that the models of O'Brien et al. (2006) are successfully producing planets comparable to those of the Solar System in terms of both their dynamical and chemical properties. Significant amounts of water are accreted in the present simulations, implying that the terrestrial planets form "wet" and do not need significant water delivery from other sources. Under the assumption of equilibrium controlled chemistry, the biogenic species N and C still need to be delivered to the Earth as they are not accreted in significant proportions during the formation process. Negligible solar photospheric pollution is produced by the planetary formation process. Assuming similar levels of pollution in other planetary systems, this in turn implies that the high metallicity trend observed in extrasolar planetary systems is in fact primordial.
- [13] arXiv:0911.0435 [ps, pdf, other]
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Title: Discovery of a 205.89 Hz accreting-millisecond X-ray pulsar in the globular cluster NGC 6440Authors: D. Altamirano, A. Patruno, C. Heinke, C. Markwardt, T. Strohmayer, M. Linares, R. Wijnands, M. van der Klis, J. SwankComments: 5 pages, 3 figures, submitted to Astrophysical Journal LettersSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
We report the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with the Rossi X-Ray Timing Explorer on August 30th and October 1st, 2009, during the decay of ~4 days outburst of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semi-major axis of 6.22 light-milliseconds. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M_sun (assuming a 1.4 M_sun neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs (~1 month). If this behaviour does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicates that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster.
- [14] arXiv:0911.0436 [pdf, other]
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Title: The Substructure Hierarchy in Dark Matter HaloesAuthors: Carlo Giocoli (ZAH/ITA University of Heidelberg), Giuseppe Tormen (Dipartimento di Astronomia, Universita' degli Studi di Padova), Ravi K. Sheth (Center for Particle Cosmology, University of Pennsylvania), Frank C. van den Bosch (Department of Physics and Astronomy, University of Utah)Comments: 17 pages, 24 figures, submitted to MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present a new algorithm for identifying the substructure within simulated dark matter haloes. The method is an extension of that proposed by Tormen et al. (2004) and Giocoli et al. (2008a), which identifies a subhalo as a group of self-bound particles that prior to being accreted by the main progenitor of the host halo belonged to one and the same progenitor halo (hereafter satellite). However, this definition does not account for the fact that these satellite haloes themselves may also have substructure, which thus gives rise to sub-subhaloes, etc. Our new algorithm identifies substructures at all levels of this hierarchy, and we use it to determine the mass function of all substructure (counting sub-haloes, sub-subhaloes, etc.). On average, haloes which formed more recently tend to have a larger mass fraction in substructure and to be less concentrated than average haloes of the same mass. We provide quantitative fits to these correlations. Even though our algorithm is very different from that of Gao et al. (2004), we too find that the subhalo mass function per unit mass at redshift z = 0 is universal. This universality extends to any redshift only if one accounts for the fact that host haloes of a given mass are less concentrated at higher redshifts, and concentration and substructure abundance are anti-correlated. This universality allows a simple parametrization of the subhalo mass function integrated over all host halo masses, at any given time. We provide analytic fits to this function which should be useful in halo model analyses which equate galaxies with halo substructure when interpreting clustering in large sky surveys. Finally, we discuss systematic differences in the subhalo mass function that arise from different definitions of (host) halo mass.
- [15] arXiv:0911.0444 [ps, pdf, other]
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Title: Discovery of a Second Transient Low-Mass X-ray Binary in the Globular Cluster NGC 6440Authors: C. O. Heinke, D. Altamirano, H. N. Cohn, P. M. Lugger, S. A. Budac, M. Servillat, M. Linares, T. E. Strohmayer, C. B. Markwardt, R. Wijnands, J. H. Swank, C. Knigge, C. Bailyn, J. E. GrindlayComments: 21 pages, 8 (color) figures, submitted to ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)
We have identified a new transient luminous low-mass X-ray binary, NGC 6440 X-2, with Chandra/ACIS, RXTE/PCA, and Swift/XRT observations of the globular cluster NGC 6440. The discovery outburst (July 28-31, 2009) peaked at L_X~1.5*10^36 ergs/s, and lasted for <4 days above L_X=10^35 ergs/s. Three other outbursts (May 29-June 4, Aug. 29-Sept. 1, and Oct. 1-3, 2009) have been observed with RXTE/PCA (identifying millisecond pulsations, Altamirano et al. 2009a) and Swift/XRT (confirming a positional association with NGC 6440 X-2). Optical and infrared imaging did not detect a clear counterpart, with best limits of V>21, B>22 in quiescence from archival HST imaging, g'>22 during the third outburst from Gemini-South GMOS imaging, and J>~18.5$ and K>~17 during the second outburst from CTIO 4-m ISPI imaging.
Archival Chandra X-ray images of the core do not detect the quiescent counterpart, and place a bolometric luminosity limit of L_{NS}< 5.6*10^31 ergs/s (one of the lowest measured) for a hydrogen atmosphere neutron star. A followup Chandra observation finds marginal evidence of enhanced quiescent emission at L_X (0.5-10 keV)~6*10^31 ergs/s 10 days into quiescence.
NGC 6440 X-2 currently shows the shortest recurrence time (32 days) of any known X-ray transient, although regular outbursts were not visible in the bulge scans before early 2009. Fast, low-luminosity transients like NGC 6440 X-2 may be easily missed by current X-ray monitoring. - [16] arXiv:0911.0447 [pdf, other]
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Title: The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star ClustersAuthors: Amy E. Reines (1), David L. Nidever (1), David G. Whelan (1), Kelsey E. Johnson (1,2) ((1) University of Virginia, (2) NRAO)Comments: 13 pages, 11 figures, Accepted for Publication in ApJSubjects: Galaxy Astrophysics (astro-ph.GA)
In this spectroscopic study of infant massive star clusters, we find that continuum emission from ionized gas rivals the stellar luminosity at optical wavelengths. In addition, we find that nebular line emission is significant in many commonly used broad-band HST filters including the F814W I-band, the F555W V-band and the F435W B-band. Two young massive clusters (YMCs) in NGC 4449 were targeted for spectroscopic observations after Reines et al. (2008a) discovered an F814W I-band excess in their photometric study of radio-detected clusters in the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the 3.5 m APO telescope. We supplement these data with HST and SDSS photometry. By comparing our data to the Starburst99 and GALEV models, we find that nebular continuum emission competes with the stellar light in our observations and that the relative contribution is largest in the U- and I-bands, where the Balmer and Paschen jumps are located. The spectra also exhibit strong line emission including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the combination of nebular continuum and line emission can account for the F814W I-band excess found by Reines et al. (2008a). In an effort to provide a benchmark for estimating the impact of ionized gas emission on photometric observations of YMCs, we compute the relative contributions of the stellar continuum, nebular continuum, and emission lines to the total flux of a 3 Myr-old cluster through various HST filter/instrument combinations, including filters in the WFC3. We urge caution when comparing observations of YMCs to evolutionary synthesis models since nebular emission can have a large impact on magnitudes and colors of young (< 5 Myr) clusters, significantly affecting inferred properties such as ages, masses and extinctions. (Abridged)
- [17] arXiv:0911.0474 [ps, pdf, other]
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Title: The X-ray Energy Dependence of the Relation between Optical and X-ray Emission in QuasarsComments: 27 pages preprint style, 10 figures, submitted to ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We develop a new approach to the well-studied anti-correlation between the optical-to-X-ray spectral index, alpha_ox, and the monochromatic optical luminosity, l_opt. By cross-correlating the SDSS DR5 quasar catalog with the XMM-Newton archive, we create a sample of 327 quasars with X-ray S/N > 6, where both optical and X-ray spectra are available. This allows alpha_ox to be defined at arbitrary frequencies, rather than the standard 2500 Angstroms and 2 keV. We find that while the choice of optical wavelength does not strongly influence the alpha_ox-l_opt relation, the slope of the relation does depend on the choice of X-ray energy. The slope of the relation becomes steeper when alpha_ox is defined at low (~ 1 keV) X-ray energies. This change is significant when compared to the slope predicted by a decrease in the baseline over which alpha_ox is defined. The slopes are also marginally flatter than predicted at high (~ 10 keV) X-ray energies. Partial correlation tests show that while the primary driver of alpha_ox is l_opt, the Eddington ratio correlates strongly with alpha_ox when l_opt is taken into account, so accretion rate may help explain these results. We combine the alpha_ox-l_opt and Gamma -L_bol/L_Edd relations to naturally explain two results: 1) the existence of the Gamma-l_x relation as reported in Young et al. (2009) and 2) the lack of a Gamma-l_opt relation. The consistency of the optical/X-ray correlations establishes a more complete framework for understanding the relation between quasar emission mechanisms.
- [18] arXiv:0911.0502 [ps, pdf, other]
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Title: Pulsar magnetic alignment and the pulsewidth-age relationComments: 13 pages, 11 figures, Accepted for publication in MNRASSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Using pulsewidth data for 872 isolated radio pulsars we test the hypothesis that pulsars evolve through a progressive narrowing of the emission cone combined with progressive alignment of the spin and magnetic axes. The new data provide strong evidence for the alignment over a time-scale of about 1 Myr with a log standard deviation of around 0.8 across the observed population. This time-scale is shorter than the time-scale of about 10 Myr found by previous authors, but the log standard deviation is larger. The results are inconsistent with models based on magnetic field decay alone or monotonic counter-alignment to orthogonal rotation. The best fits are obtained for a braking index parameter n_gamma approximately equal to 2.3, consistent the mean of the six measured values, but based on a much larger sample of young pulsars. The least-squares fitted models are used to predict the mean inclination angle between the spin and magnetic axes as a function of log characteristic age. Comparing these predictions to existing estimates it is found that the model in which pulsars are born with a random angle of inclination gives the best fit to the data. Plots of the mean beaming fraction as a function of characteristic age are presented using the best-fitting model parameters.
- [19] arXiv:0911.0505 [ps, pdf, other]
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Title: Scientific Data Mining in AstronomyAuthors: Kirk Borne (1) ((1) George Mason University)Comments: 26 pagesJournal-ref: Borne, K., in Next Generation of Data Mining (Taylor & Francis: CRC Press), pp. 91-114 (2009)Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
We describe the application of data mining algorithms to research problems in astronomy. We posit that data mining has always been fundamental to astronomical research, since data mining is the basis of evidence-based discovery, including classification, clustering, and novelty discovery. These algorithms represent a major set of computational tools for discovery in large databases, which will be increasingly essential in the era of data-intensive astronomy. Historical examples of data mining in astronomy are reviewed, followed by a discussion of one of the largest data-producing projects anticipated for the coming decade: the Large Synoptic Survey Telescope (LSST). To facilitate data-driven discoveries in astronomy, we envision a new data-oriented research paradigm for astronomy and astrophysics -- astroinformatics. Astroinformatics is described as both a research approach and an educational imperative for modern data-intensive astronomy. An important application area for large time-domain sky surveys (such as LSST) is the rapid identification, characterization, and classification of real-time sky events (including moving objects, photometrically variable objects, and the appearance of transients). We describe one possible implementation of a classification broker for such events, which incorporates several astroinformatics techniques: user annotation, semantic tagging, metadata markup, heterogeneous data integration, and distributed data mining. Examples of these types of collaborative classification and discovery approaches within other science disciplines are presented.
- [20] arXiv:0911.0506 [ps, pdf, other]
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Title: Quantitative measure of evolution of bright cluster galaxies at moderate redshiftsComments: 5 pages, 3 figures, Accepted for publication in MNRAS: LettersSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Using archival data from the Hubble Space Telescope, we study the quantitative morphological evolution of spectroscopically confirmed bright galaxies in the core regions of nine clusters ranging in redshift from $z = 0.31$ to $z = 0.84$. We use morphological parameters derived from two dimensional bulge-disk decomposition to study the evolution. We find an increase in the mean bulge-to-total luminosity ratio $B/T$ as the Universe evolves. We also find a corresponding increase in the fraction of early type galaxies and in the mean S\'ersic index. We discuss these results and their implications to physical mechanisms for evolution of galaxy morphology.
- [21] arXiv:0911.0521 [ps, pdf, other]
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Title: Possible cosmogenic neutrino constraints on Planck-scale Lorentz violationAuthors: David M. Mattingly (New Hampshire University), Luca Maccione (DESY), Matteo Galaverni (INAF-IASF, Bologna), Stefano Liberati (SISSA & INFN, Trieste), Guenter Sigl (Hamburg University)Comments: 19 pages, 5 figures. Submitted to JCAPSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We study, within an effective field theory framework, $O(E^{2}/\Mpl^{2})$ Planck-scale suppressed Lorentz invariance violation (LV) effects in the neutrino sector, whose size we parameterize by a dimensionless parameter $\eta_{\nu}$. We find deviations from predictions of Lorentz invariant physics in the cosmogenic neutrino spectrum. For positive O(1) coefficients no neutrino will survive above $10^{19} \eV$. The existence of this cutoff generates a bump in the neutrino spectrum at energies of $10^{17} \eV$. Although at present no constraint can be cast, as current experiments do not have enough sensitivity to detect ultra-high-energy neutrinos, we show that experiments in construction or being planned have the potential to cast limits as strong as $\eta_{\nu} \lesssim 10^{-4}$ on the neutrino LV parameter, depending on how LV is distributed among neutrino mass states. Constraints on $\eta_{\nu} < 0$ can in principle be obtained with this strategy, but they require a more detailed modeling of how LV affects the neutrino sector.
- [22] arXiv:0911.0523 [ps, pdf, other]
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Title: Properties and environment of Radio Emitting Galaxies in the VLA-zCOSMOS surveyAuthors: S.Bardelli, E.Schinnerer, V.Smolcic, G.Zamorani, E.Zucca, M.Mignoli, C.Halliday, K.Kovac, P.Ciliegi, K.Caputi, A.M.Koekemoer, A.Bongiorno, M.Bondi, M.Bolzonella, D.Vergani, L.Pozzetti, C.M.Carollo, T.Contini, J.-P.Kneib, O.LeFevre, S.Lilly, V.Mainieri, A.Renzini, M.Scodeggio, G.Coppa, O.Cucciati, S.delaTorre, L.deRavel, P.Franzetti, B.Garilli, A.Iovino, P.Kampczyk, C.Knobel, F.Lamareille, J.-F.LeBorgne, V.LeBrun, C.Maier, R.Pello`, Y.Peng, E.Perez-Montero, E.Ricciardelli, J.D.Silverman, M.Tanaka, L.Tasca, L.Tresse, U.Abbas, D.Bottini, A.Cappi, P.Cassata, A.Cimatti, L.Guzzo, A.Leauthaud, D.Maccagni, C.Marinoni, H.J.McCracken, P.Memeo, B.Meneux, P.Oesch, C.Porciani, R.Scaramella, P.Capak, D.Sanders, N.Scoville, Y.Taniguchi, K.JahnkeComments: 17 pages, 17 figures, A&A in pressSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We investigate the properties and the environment of radio sources with optical counterpart from the combined VLA-COSMOS and zCOSMOS samples. The advantage of this sample is the availability of optical spectroscopic information, high quality redshifts, and accurate density determination.
By comparing the star formation rates estimated from the optical spectral energy distribution with those based on the radio luminosity, we divide the radio sources in three families, passive AGN, non-passive AGN and star forming galaxies. These families occupy specific regions of the 8.0-4.5 $\mu$m infrared color--specific star formation plane, from which we extract the corresponding control samples.
Only the passive AGN have a significantly different environment distribution from their control sample. The fraction of radio-loud passive AGN increases from ~2% in underdense regions to ~15% for overdensities (1+delta) greater than 10. This trend is also present as a function of richness of the groups hosting the radio sources. Passive AGN in overdensities tend to have higher radio luminosities than those in lower density environments. Since the black hole mass distribution is similar in both environments, we speculate that, for low radio luminosities, the radio emission is controlled (through fuel disponibility or confinement of radio jet by local gas pressure) by the interstellar medium of the host galaxy, while in other cases it is determined by the structure (group or cluster) in which the galaxy resides. - [23] arXiv:0911.0531 [ps, pdf, other]
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Title: Stellar Encounters in the Context of Outburst PhenomenaAuthors: Duncan Forgan (1), Ken Rice (1) ((1) SUPA, Institute for Astronomy, University of Edinburgh)Comments: 8 pages, 11 figures, 1 table, accepted for publication in MNRASSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Young stellar systems are known to undergo outbursts, where the star experiences an increased accretion rate, and the system's luminosity increases accordingly. The archetype is the FU Orionis (FU Ori) outburst, where the accretion rate can increase by three orders of magnitude (and the brightness of the system by five magnitudes). The cause appears to be instability in the circumstellar disc, but there is currently some debate as to the nature of this instability (e.g. thermal, gravitational, magneto-rotational). This paper details high resolution Smoothed Particle Hydrodynamics (SPH) simulations that were carried out to investigate the influence of stellar encounters on disc dynamics. Star-star encounters (where the primary has a self-gravitating, marginally stable protostellar disc) were simulated with various orbital parameters to investigate the resulting disc structure and dynamics. Crucially, the simulations include the effects of radiative transfer to realistically model the resulting thermodynamics. Our results show that the accretion history and luminosity of the system during the encounter displays many of the features of outburst phenomena. In particular, the magnitudes and decay times seen are comparable to those of FU Ori. There are two caveats to this assertion: the first is that these events are not expected to occur frequently enough to explain all FU Ori or EX Lupi; the second is that the inner discs of these simulations are subject to numerical viscosity, which will act to reduce the accretion rate (although it has less of an effect on the total mass accreted). In short, these results cannot rule out binary interactions as a potential source of some FU Ori-esque outbursts.
- [24] arXiv:0911.0532 [ps, pdf, other]
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Title: Ice chemistry in embedded young stellar objects in the Large Magellanic CloudAuthors: J.M. Oliveira (Keele University), J. Th. van Loon (Keele), C.-H. R. Chen (U. Virginia), A. G. G. M. Tielens (Leiden), G. C. Sloan (Cornell), P. M. Woods (U. Manchester), F. Kemper (U. Manchester), R. Indebetouw (U. Virginia), K. D. Gordon (STScI), M. L. Boyer (STScI), B. Shiao (STScI), S. Madden (CEA), A. K. Speck (U. Missouri), M. Meixner (STScI), M. Marengo (Iowa)Comments: Accepted for publication in ApJ, 66 pages, 9 figures (some in color), 4 tablesSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)
We present spectroscopic observations of a sample of 15 embedded young stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS spectral range: the bending mode of CO_2 ice at 15.2 micron and the ice band between 5 and 7 micron that includes contributions from the bending mode of water ice at 6 micron amongst other ice species. The 5-7 micron band is difficult to identify in our LMC sample due to the conspicuous presence of PAH emission superimposed onto the ice spectra. We identify water ice in the spectra of two sources; the spectrum of one of those sources also exhibits the 6.8 micron ice feature attributed to ammonium and methanol. We model the CO_2 band in detail, using the combination of laboratory ice profiles available in the literature. We find that a significant fraction (> 50%) of CO_2 ice is locked in a water-rich component, consistent with what is observed for Galactic sources. The majority of the sources in the LMC also require a pure-CO_2 contribution to the ice profile, evidence of thermal processing. There is a suggestion that CO_2 production might be enhanced in the LMC, but the size of the available sample precludes firmer conclusions. We place our results in the context of the star formation environment in the LMC.
- [25] arXiv:0911.0536 [ps, pdf, other]
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Title: An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. II. Spectroscopic classes and accretion modes in radio-loud AGNAuthors: Sara Buttiglione (1), Alessandro Capetti (2), Annalisa Celotti (1), David J. Axon (3,4), Marco Chiaberge (5,6), F. Duccio Macchetto (5), William B. Sparks (5) ((1) SISSA-ISAS, Trieste, Italy, (2) INAF - Osservatorio Astronomico di Torino, Italy, (3) Rochester Institute of Technology, USA, (4) University of Sussex, UK, (5) Space Telescope Science Institute, Baltimore, U.S.A. (6) INAF-Istituto di Radio Astronomia, Bologna, Italy)Comments: Accepted for publication in A&ASubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We use the emission line measurements of 3CR radio sources with redshift < 0.3, to explore their spectroscopic properties. The 3CR sources show a bimodal distribution of Excitation Index, a new spectroscopic indicator that measures the relative intensity of low and high excitation lines. This unveils the presence of two main sub-populations of radio-loud AGN, High and Low Excitation Galaxies (HEG and LEG, respectively). All broad-line objects are HEG from the point of view of their narrow emission line ratios and all HEG are FRII radio-galaxies with log L(178) [erg/s] > 32.8. Conversely LEG cover the whole range of radio power encompassed by this 3CR subsample (30.7 < log L(178) < 35.4) and they are of both FRI and FRII type. The brightest LEG are all FRII. HEG and LEG obey to two (quasi) linear correlations between the optical line and extended radio luminosities, with HEG being brighter than LEG in the [OIII] line by a factor of ~10. HEG and LEG are offset also in a plane that compares the black hole mass and the ionizing nuclear luminosity. However, although HEG are associated with higher nuclear luminosities, we find LEG among the brightest radio sources of the sample and with a clear FRII morphology, indistinguishable from those seen in HEG. This suggests that LEG are not simply objects with a lower level of accretion. We speculate that the differences between LEG and HEG are related to a different mode of accretion: LEG are powered by hot gas, while HEG require the presence of cold accreting material. The high temperature of the accreting gas in LEG accounts for the lack of "cold" structures (i.e. molecular torus and Broad Line Region), for the reduced radiative output of the accretion disk, and for the lower gas excitation. [ABRIDGED]
- [26] arXiv:0911.0554 [ps, pdf, other]
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Title: Absolute properties of the main-sequence eclipsing binary FM LeoAuthors: M. Ratajczak, T. Kwiatkowski, A. Schwarzenberg-Czerny, W. Dimitrov, M. Konacki, K.G. Helminiak, P. Bartczak, M. Fagas, K. Kaminski, P. Kankiewicz, W. Borczyk, A. RozekComments: 5 pages, 4 figures, to appear in MNRASSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
First spectroscopic and new photometric observations of the eclipsing binary FM Leo are presented. The main aims were to determine orbital and stellar parameters of two components and their evolutionary stage. First spectroscopic observations of the system were obtained with DDO and PST spectrographs. The results of the orbital solution from radial velocity curves are combined with those derived from the light-curve analysis (ASAS-3 photometry and supplementary observations of eclipses with 1 m and 0.35 m telescopes) to derive orbital and stellar parameters. JKTEBOP, Wilson-Devinney binary modelling codes and a two-dimensional cross-correlation (TODCOR) method were applied for the analysis. We find the masses to be M_1 = 1.318 $\pm$ 0.007 and M_2 = 1.287 $\pm$ 0.007 M_sun, the radii to be R_1 = 1.648 $\pm$ 0.043 and R_2 = 1.511 $\pm$ 0.049 R_sun for primary and secondary stars, respectively. The evolutionary stage of the system is briefly discussed by comparing physical parameters with current stellar evolution models. We find the components are located at the main sequence, with an age of about 3 Gyr.
- [27] arXiv:0911.0570 [ps, pdf, other]
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Title: The Galactic Thick Disk: An Observational PerspectiveAuthors: Bacham Eswar Reddy (IIA, Bengaluru)Comments: 11 pages including 2 figures, 2 tables an invited review to be published in Proc. of IAU 265 Symp. "Chemical Abundances in the Universe: Connecting First Stars to Planets" eds: K. Cunha, M. Spite & B. BarbuySubjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
In this review, we present a brief description of observational efforts to understand the Galactic thick disk and its relation to the other Galactic components. This review primarily focused on elemental abundance patterns of the thick disk population to pin down the process or processes that were responsible for its existence and evolution. Kinematic and chemical properties of disk stars establish that the thick disk is a distinct component in the Milky Way. The chemical enrichment and star formation histories hold clues to the bigger picture of understanding the Galaxy formation.
- [28] arXiv:0911.0573 [ps, pdf, other]
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Title: Galactic halos in cosmology with long-range scalar DM interactionAuthors: Wojciech A. HellwingComments: 4 pages, 2 figures, to appear in Annalen der Physik issue dedicated to proceedings of the Grassmannian Conference in Fundamental Cosmology (Grasscosmofun'09)Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Based on a set of cosmological N-body simulations we analyze properties of the dark matter haloes (DM) in a galaxy mass range ($10^{11} - 10^{13} h^{-1}M_{\odot}$) in modified $\lcdm$ cosmology with additional dynamically screened scalar interactions in DM sector. Our simulations show that scalar interactions support picture of the Island Universe. Rapid structure formation processes are shifted into higher redshifts resulting in a much smaller accretion and merging rates for galactic haloes at low redshifts. Finally, we present how this "fifth" force affects halo properties, like density profile, triaxiality, ellipticities and the spin parameter.
- [29] arXiv:0911.0582 [ps, pdf, other]
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Title: Positron Annihilation on Polycyclic Aromatic Hydrocarbon molecules in the Interstellar MediumAuthors: N. Guessoum (1), P. Jean (2), W. Gillard (3) ((1) American University of Sharjah, (2) CESR CNRS/Universite de Toulouse, (3) KTH AlbaNova University Centre Stockholm)Comments: Accepted in MNRAS, 10 pages, 5 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)
We examine the annihilation of positrons on polycyclic aromatic hydrocarbon (PAH) molecules in interstellar medium conditions. We estimate the annihilation rates of positrons on PAHs by a semi-empirical approach. We show that PAHs can play a significant role in the overall galactic positron annihilation picture and use the annihilation rates and INTEGRAL galactic emission measurements to constrain the amount of PAHs present in the ISM. We find an upper limit of 4.6 x 10^-7 for the PAH abundance.
- [30] arXiv:0911.0585 [ps, pdf, other]
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Title: Axion-like particles and circular polarisation of active galactic nucleiComments: Contributed to the "5th Patras Workshop on Axions, WIMPs and WISPs", Durham 13-17 July 2009Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The measurements of the linear polarisation of visible light from quasars give strong evidence for large-scale coherent orientations of their polarisation vectors in some regions of the sky. We show that these observations can be explained by the mixing of the photons with very light pseudoscalar (axion-like) particles in extragalactic magnetic fields during their propagation. We present a new treatment in terms of wave packets and discuss the circular polarisation.
- [31] arXiv:0911.0608 [ps, pdf, other]
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Title: The Crab pulsar and its pulsar-wind nebula in the optical and infraredComments: 8 pages, 5 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We investigate the emission mechanism and evolution of pulsars that are associated with supernova remnants.
We used imaging techniques in both the optical and near infrared, using images with very good seeing (<0.6) to study the immediate surroundings of the Crab pulsar. In the case of the infrared, we took two data sets with a time window of 75 days, to check for variability in the inner part of the Crab nebula. We also measure the spectral indices of all these wisps, the nearby knot, and the interwisp medium, using our optical and infrared data. We then compared the observational results with the existing theoretical models.
We report variability in the three nearby wisps located to the northwest of the pulsar and also in a nearby anvil wisp in terms of their structure, position, and emissivity within the time window of 75 days. All the wisps and the inner knot display red spectra with similar spectral indices. Similarly, the interwisp medium regions also show red spectra similar to those of the wisps. Also, based on archival HST data and our IR data, we find that the inner knot remains stationary for a time period of 13.5 years. The projected average velocity relative to the pulsar for this period is < 8 km/s.
By comparing the spectral indices of the structures in the inner Crab with the current theoretical models, we find that the Del Zanna et al. (2006) model for the synchrotron emission fits our observations, although the spectral index is at the flatter end of their modelled spectra. - [32] arXiv:0911.0611 [ps, pdf, other]
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Title: Bound on induced gravitational wave background from primordial black holesComments: 5 pages, 1 figureSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The today's energy density of the induced (second order) gravitational wave background in the frequency region $\sim 10^{-3} - 10^3$ Hz is constrained using the existing limits on primordial black hole production in the early Universe. It is shown, in particular, that at frequencies near $\sim 40$ Hz (which is the region explored by LIGO detector), the value of the induced part of $\Omega_{GW}$ cannot exceed $(1-3)\times 10^{-7}$. The spread of values of the bound is caused by the uncertainty in parameters of the gravitational collapse of black holes.
- [33] arXiv:0911.0612 [ps, pdf, other]
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Title: Weak lensing of the CMBComments: 21 pages, 5 figures. Invited review for GRG special issue on gravitational lensingSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The cosmic microwave background (CMB) represents a unique source for the study of gravitational lensing. It is extended across the entire sky, partially polarized, located at the extreme distance of z=1100, and is thought to have the simple, underlying statistics of a Gaussian random field. Here we review the weak lensing of the CMB, highlighting the aspects which differentiate it from the weak lensing of other sources, such as galaxies. We discuss the statistics of the lensing deflection field which remaps the CMB, and the corresponding effect on the power spectra. We then focus on methods for reconstructing the lensing deflections, describing efficient quadratic maximum-likelihood estimators and delensing. We end by reviewing recent detections and observational prospects.
- [34] arXiv:0911.0622 [ps, pdf, other]
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Title: Quantized fields and gravitational particle creation in f(R) expanding universesComments: 14 pages, 2 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The problem of cosmological particle creation for a spatially flat, homogeneous and isotropic Universes is discussed in the context of f(R) theories of gravity. Different from cosmological models based on general relativity theory, it is found that a conformal invariant metric does not forbid the creation of massless particles during the early stages (radiation era) of the Universe.
- [35] arXiv:0911.0647 [ps, pdf, other]
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Title: On the influence of non-thermal pressure on the mass determination of galaxy clustersComments: Submitted to A&A, 12 pgs, 5 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
(Abridged) The main purpose of this paper is to consider the contribution of all three non-thermal components to total mass measurements of galaxy clusters: cosmic rays, turbulence and magnetic pressures. To estimate the thermal pressure we used public XMM-\textit{Newton} archival data of 5 Abell clusters. To describe the magnetic pressure, we assume a radial distribution for the magnetic field, $B(r) \propto \rho_{g}^{\alpha}$, to seek generality we assume $\alpha$ within the range of 0.5 to 0.9, as indicated by observations and numerical simulations. For the turbulent component, we assumed an isotropic pressure, $P_{\rm turb} = {1/3}\rho_{\rm g}(\sigma_{r}^{2}+\sigma_{t}^{2})$. We also consider the contribution of cosmic ray pressure, $P_{cr}\propto r^{-0.5}$. It follows that a consistent description for the non-thermal component could yield variation in mass estimates that vary from 10% up to $\sim$30%. We verified that in the inner parts of cool-core clusters the cosmic ray component is comparable to the magnetic pressure, while in non cool-core cluster the cosmic ray component is dominant. For cool-core clusters the magnetic pressure is the dominant component, contributing with more than 50% of total mass variation due to non-thermal pressure components. However, for non cool-core clusters, the major influence comes from the cosmic ray pressure that accounts with more than 80% of total mass variation due to non-thermal pressure effects. For our sample, the maximum influence of the turbulent component to total mass variation can be almost 20%. We show that this analysis can be regarded as a starting point for a more detailed and refined exploration of the influence of non-thermal pressure in the intra-cluster medium (ICM).
- [36] arXiv:0911.0663 [ps, pdf, other]
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Title: The subcritical baroclinic instability in local accretion disc modelsComments: 12 pages, 17 figures, submitted to A&A. High quality figures and animations available on the author's websiteSubjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
(abridged) Aims: We present new results exhibiting a subcritical baroclinic instability (SBI) in local shearing box models. We describe the 2D and 3D behaviour of this instability using numerical simulations and we present a simple analytical model describing the underlying physical process.
Results: A subcritical baroclinic instability is observed in flows stable for the Solberg-Hoiland criterion using local simulations. This instability is found to be a nonlinear (or subcritical) instability, which cannot be described by ordinary linear approaches. It requires a radial entropy gradient weakly unstable for the Schwartzchild criterion and a strong thermal diffusivity (or equivalently a short cooling time). In compressible simulations, the instability produces density waves which transport angular momentum outward with typically alpha<3e-3, the exact value depending on the background temperature profile. Finally, the instability survives in 3D, vortex cores becoming turbulent due to parametric instabilities.
Conclusions: The subcritical baroclinic instability is a robust phenomenon, which can be captured using local simulations. The instability survives in 3D thanks to a balance between the 2D SBI and 3D parametric instabilities. Finally, this instability can lead to a weak outward transport of angular momentum, due to the generation of density waves by the vortices. - [37] arXiv:0911.0665 [ps, pdf, other]
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Title: H91$\alpha$ Radio Recombination Line and 3.5 cm Continuum Observations of the Planetary Nebula NGC 3242Comments: 7 pages, 4 figuresSubjects: Galaxy Astrophysics (astro-ph.GA)
We present high sensitivity H91$\alpha$ and 3.5 cm radio continuum observations toward the planetary nebula NGC 3242. The electron temperature determined assuming local thermodynamic equilibrium is consistent within $\sim$10% with that derived from optical lines and the Balmer discontinuity. The line emission and the continuum emission have very similar spatial distribution, suggesting that at this wavelength there is no other continuum process present in a significant manner. In particular, we conclude that emission from spinning dust is not important at this wavelength. In this radio recombination line the nebula presents a radial velocity structure consistent with that obtained from observations of optical lines.
- [38] arXiv:0911.0666 [ps, pdf, other]
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Title: Exploring the inner region of Type 1 AGNs with the Keck interferometerAuthors: Makoto Kishimoto (1), Sebastian F. Hoenig (1), Robert Antonucci (2), Takayuki Kotani (3), Richard Barvainis (4), Konrad R.W. Tristram (1), Gerd Weigelt (1) ((1) MPIfR, (2) UCSB, (3) ISAS, (4) NSF)Comments: accepted for publication in A&A LettersSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The exploration of extragalactic objects with long-baseline interferometers in the near-infrared has been very limited. Here we report successful observations with the Keck interferometer at K-band (2.2 um) for four Type 1 AGNs, namely NGC4151, Mrk231, NGC4051, and the QSO IRAS13349+2438 at z=0.108. For the latter three objects, these are the first long-baseline interferometric measurements in the infrared. We detect high visibilities (V^2 ~ 0.8-0.9) for all the four objects, including NGC4151 for which we confirm the high V^2 level measured by Swain et al.(2003). We marginally detect a decrease of V^2 with increasing baseline lengths for NGC4151, although over a very limited range, where the decrease and absolute V^2 are well fitted with a ring model of radius 0.45+/-0.04 mas (0.039+/-0.003 pc). Strikingly, this matches independent radius measurements from optical--infrared reverberations that are thought to be probing the dust sublimation radius. We also show that the effective radius of the other objects, obtained from the same ring model, is either roughly equal to or slightly larger than the reverberation radius as a function of AGN luminosity. This suggests that we are indeed partially resolving the dust sublimation region. The ratio of the effective ring radius to the reverberation radius might also give us an approximate probe for the radial structure of the inner accreting material in each object. This should be scrutinized with further observations.
- [39] arXiv:0911.0669 [ps, pdf, other]
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Title: Probing dark energy with future redshift surveys: A comparison of emission line and broad band selection in the near infraredComments: submitted to MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Future galaxy surveys will map the galaxy distribution in the redshift interval $0.5<z<2$ using near-infrared cameras and spectrographs. The primary science goal of such surveys is to constrain the nature of the dark energy by measuring the large-scale structure of the Universe. This requires a tracer of the underlying dark matter which maximizes the useful volume of the survey. We investigate two potential survey selection methods: an emission line sample based on the \ha line and a sample selected in the H-band. We present predictions for the abundance and clustering of such galaxies, using two published versions of the \galform galaxy formation model. Our models predict that \ha selected galaxies tend to avoid massive dark matter haloes and instead trace the surrounding filamentary structure; H-band selected galaxies, on the other hand, are found in the highest mass haloes. This has implications for the measurement of the rate at which fluctuations grow due to gravitational instability. We use mock catalogues to compare the effective volumes sampled by a range of survey configurations. To give just two examples: a redshift survey down to $H_{\rm AB}=22$ samples an effective volume that is $\sim 5-10$ times larger than that probed by an \ha survey with $\logfha > -15.4$; a flux limit of at least $\logfha = -16$ is required for an \ha sample to become competitive in effective volume.
- [40] arXiv:0911.0670 [pdf, other]
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Title: Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron StarsComments: 12 pages, 16 figures. To appear in the Astrophysical JournalSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
This paper presents a numerical study over a wide parameter space of the likelihood of the dynamical bar-mode instability in differentially rotating magnetized neutron stars. The innovative aspect of this study is the incorporation of magnetic fields in such a context, which have thus far been neglected in the purely hydrodynamical simulations available in the literature. The investigation uses the Cosmos++ code which allows us to perform three dimensional simulations on a cylindrical grid at high resolution. A sample of Newtonian magneto-hydrodynamical simulations starting from a set of models previously analyzed by other authors without magnetic fields has been performed, providing estimates of the effects of magnetic fields on the dynamical bar-mode deformation of rotating neutron stars. Overall, our results suggest that the effect of magnetic fields are not likely to be very significant in realistic configurations. Only in the most extreme cases are the magnetic fields able to suppress growth of the bar mode.
Cross-lists for Wed, 4 Nov 09
- [41] arXiv:0910.4594 (cross-list from gr-qc) [pdf, other]
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Title: Gravitational-Wave Recoil from the Ringdown Phase of Coalescing Black Hole BinariesComments: 9 pages, 5 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
The gravitational recoil or "kick" of a black hole formed from the merger of two orbiting black holes, and caused by the anisotropic emission of gravitational radiation, is an astrophysically important phenomenon. We combine (i) an earlier calculation, using post-Newtonian theory, of the kick velocity accumulated up to the merger of two non-spinning black holes, (ii) a "close-limit approximation" calculation of the radiation emitted during the ringdown phase, and based on a solution of the Regge-Wheeler and Zerilli equations using initial data accurate to second post-Newtonian order. We prove that ringdown radiation produces a significant "anti-kick". Adding the contributions due to inspiral, merger and ringdown phases, our results for the net kick velocity agree with those from numerical relativity to 10-15 percent over a wide range of mass ratios, with a maximum velocity of 180 km/s at a mass ratio of 0.38.
- [42] arXiv:0910.5488 (cross-list from nucl-th) [ps, pdf, other]
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Title: Thermalisation time and specific heat of neutron stars crustComments: 7 pages, 5 figures, submitted to Phys. Rev. CSubjects: Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
We discuss the thermalisation process of the neutron stars crust described by solving the heat transport equation with a microscopic input for the specific heat of baryonic matter. The heat equation is solved with initial conditions specific to a rapid cooling of the core. To calculate the specific heat of inner crust baryonic matter, i.e., nuclear clusters and unbound neutrons, we use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach at finite temperature. In this framework we analyse the dependence of the crust thermalisation on pairing properties and on cluster structure of inner crust matter. It is shown that the pairing correlations reduce the crust thermalisation time by a very large fraction. The calculations show also that the nuclear clusters have a non-negligible influence on the time evolution of the surface temperature of the neutron star.
- [43] arXiv:0910.5755 (cross-list from gr-qc) [ps, pdf, other]
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Title: Spherically symmetric models with pressure: separating expansion from contraction and generalizing TOV conditionAuthors: José Pedro Mimoso (DFUL, CFTC), Morgan Le Delliou (CFTC, Ift), Filipe C. Mena (CMAT, DM/Ist)Comments: submitted to PRD, 16pp, 9 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
We investigate spherically symmetric perfect fluid spacetimes and discuss the existence and stability of a dividing shell separating expanding and collapsing regions. We perform a 3+1 splitting and obtain gauge invariant conditions relating the intrinsic spatial curvature of the shells to the ADM mass and to a function of the pressure which we introduce and that generalises the Tolman-Oppenheimer-Volkoff equilibrium condition. We analyse the particular cases of the Lema\^itre-Tolman-Bondi dust models with a cosmological constant as an example of a $\Lambda$-CDM model and its generalization to contain a central perfect fluid core. These models provide simple, but physically interesting illustrations of our results.
- [44] arXiv:0911.0131 (cross-list from gr-qc) [ps, pdf, other]
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Title: Inferring physical parameters of compact stars from their f-mode gravitational wave signalsComments: 8 pages, 5 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
We propose here a robust scheme to infer physical parameters of compact stars from their f-mode gravitational wave signals. We first show that the frequency and the damping rate of f-mode oscillation of compact stars can be expressed in terms of universal functions of stellar mass and moment of inertia, whereas various previous proposals made use of mass and radius instead. By employing the new universality in the f-mode one can then infer accurate values of the mass, the moment of inertia and the radius of a compact star. In contrast to previous works, we demonstrate that our new scheme works well for both realistic neutron stars and quark stars, and hence provides a unifying way to infer the physical parameters of compact stars.
- [45] arXiv:0911.0241 (cross-list from gr-qc) [ps, pdf, other]
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Title: Separating expansion from contraction: generalized TOV condition, LTB models with pressure and $\Lambda$CDMComments: Proceedings of 'Invisible Universe International Conference', Paris, June 29- July 3, 2009 ; 5pp, 4 figsSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
We discuss the existence of a dividing shell separating expanding and collapsing regions in spherically symmetric solutions with pressure. We obtain gauge invariant conditions relating not only the intrinsic spatial curvature of the shells to the ADM mass, but also a function of the pressure which we introduce that generalises the Tolman-Oppenheimer-Volkoff equilibrium condition, in the framework of a 3+1 spacetime splitting. We consider the particular case of a Lema\^itre-Tolman-Bondi dust models with a cosmological constant (a $\Lambda$-CDM model) as an example of our results.
Replacements for Wed, 4 Nov 09
- [46] arXiv:0801.0215 (replaced) [ps, pdf, other]
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Title: The Role of Type Ia Supernovae in Chemical Evolution I: Lifetime of Type Ia Supernovae and Galactic Supernova RatesComments: 56 pages, 20 figures, accepted to ApJSubjects: Astrophysics (astro-ph)
- [47] arXiv:0808.3384 (replaced) [ps, pdf, other]
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Title: Deducing the nature of dark matter from direct and indirect detection experiments in the absence of collider signatures of new physicsComments: 19 pages, 7 figuresJournal-ref: Phys.Rev.D80:043509,2009Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph)
- [48] arXiv:0812.0419 (replaced) [ps, pdf, other]
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Title: Cosmological constraints from 21cm surveys after reionizationComments: 12 pages, 4 figures; Replaced with version accepted by JCAP; Significant changes regarding treatment of scale dependent bias due to UV backgroundJournal-ref: Journal of Cosmology and Astroparticle Physics, Issue 10, pp. 030 (2009)Subjects: Astrophysics (astro-ph)
- [49] arXiv:0905.0001 (replaced) [ps, pdf, other]
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Title: The Host Galaxies of Swift Dark Gamma-Ray Bursts: Observational Constraints on Highly Obscured and Very High-Redshift GRBsAuthors: D. A. Perley, S. B. Cenko, J. S. Bloom, H.-W. Chen, N. R. Butler, D. Kocevski, J. X. Prochaska, M. Brodwin, K. Glazebrook, M. M. Kasliwal, S. R. Kulkarni, S. Lopez, E. O. Ofek, M. Pettini, A. M. Soderberg, D. StarrComments: 21 pages, 10 figures. Published in AJJournal-ref: The Astronomical Journal 138 (2009) 1690-1708Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [50] arXiv:0905.4003 (replaced) [ps, pdf, other]
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Title: Determination of the Neutrino Flavor Ratio at the Astrophysical SourceComments: Figures corrected, Discussions on the feasibility of measuring various flux ratios added; version to appear in Phys. Rev. DSubjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
- [51] arXiv:0907.1191 (replaced) [ps, pdf, other]
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Title: A note on observational signatures in superluminal unified dark matter modelsComments: 7 pages, 6 figures, revised versionSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
- [52] arXiv:0907.4268 (replaced) [ps, pdf, other]
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Title: On the saturation of the centrifugally excited curvature drift instability in AGN magnetospheresAuthors: Z. OsmanovComments: 13 pages, 5 figuresSubjects: Galaxy Astrophysics (astro-ph.GA)
- [53] arXiv:0907.4857 (replaced) [ps, pdf, other]
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Title: Implications of Broken Symmetry for Superhorizon Conservation Theorems in CosmologyAuthors: Katherine Jones-Smith (1), Lawrence M. Krauss (2), Harsh Mathur (1) ((1) CERCA, Department of Physics, Case Western Reserve University, Cleveland, OH, (2) School of Earth and Space Exploration, Physics Department, and Beyond Center, Arizona State University, Tempe, AZ)Comments: changed titleSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [54] arXiv:0910.1698 (replaced) [ps, pdf, other]
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Title: INTEGRAL probes the morphology of the Crab nebula in hard X-rays/soft gamma-raysComments: 7 pages, 8 figures, accepted for publication in A&ASubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
- [55] arXiv:0910.3771 (replaced) [ps, pdf, other]
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Title: The spectral energy distribution of the central parsecs of the nearest AGNAuthors: M. A. Prieto (IAC, Tenerife), J. Reunanen (Tuorla Observatory, University of Turku), K. R. W. Tristram (MPIfR, Bonn), N. Neumayer (ESO, Garching), J. A. Fernandez-Ontiveros (IAC, Tenerife), M. Orienti (IAC, Tenerife), K. Meisenheimer (MPIA, Heidelberg)Comments: 50 pages, 14 figures. Accepted for publication in MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
- [56] arXiv:0910.4532 (replaced) [ps, pdf, other]
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Title: Black hole gas in the early universeComments: 14 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
- [57] arXiv:0910.4905 (replaced) [ps, pdf, other]
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Title: Molecular gas, CO, and star formation in galaxies: emergent empirical relations, feedback, and the evolution of very gas-rich systemsComments: 32 pages, 9 figures, accepted for publication in ApJSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [58] arXiv:0910.5005 (replaced) [ps, pdf, other]
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Title: High-precision predictions for the acoustic scale in the non-linear regimeAuthors: Hee-Jong Seo, Jonathan Eckel, Daniel J. Eisenstein, Kushal Mehta, Marc Metchnik, Nikhil Padmanabhan, Phillip Pinto, Ryuichi Takahashi, Martin White, Xiaoying XuComments: Submitted to ApJ, 17 emulated apj pages with 12 figures and 3 tables, Fixed the axis labels of Fig 9Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [59] arXiv:0910.5476 (replaced) [ps, pdf, other]
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Title: Spitzer and HHT observations of starless cores: masses and environmentsAuthors: Amelia M. Stutz, George H. Rieke, John H. Bieging, Zoltan Balog, Fabian Heitsch, Miju Kang, William L. Peters, Yancy L. Shirley, Michael W. WernerComments: 41 pages, 28 figures, 5 tables; accepted by ApJSubjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
- [60] arXiv:0910.5818 (replaced) [ps, pdf, other]
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Title: Light-time computations for the BepiColombo radioscience experimentComments: 14 pages, 7 figures, corrected referencesSubjects: General Relativity and Quantum Cosmology (gr-qc); Earth and Planetary Astrophysics (astro-ph.EP)
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