These are the latest articles published in The Astrophysical Journal.

• Open/close HUBBLE SPACE TELESCOPE NEAR-INFRARED SNAPSHOT SURVEY OF 3CR RADIO SOURCE COUNTERPARTS. III. RADIO GALAXIES AND QUASARS IN CONTEXT

  David J. E. Floyd et al  2010 ApJ 713 66 Tag this article

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  We compare the near-infrared (NIR) H-band photometric and morphological properties of low- z ( z < 0.3) 3CR radio galaxies with samples of BL Lac objects and quasar host galaxies, merger remnants, quiescent elliptical galaxies, and brightest cluster galaxies drawn from the literature. In general, the 3CR host galaxies are consistent with luminous (~ L ) elliptical galaxies. The vast majority of FR II's (~80%) occupy the most massive ellipticals and form a homogeneous population that is comparable to the population of radio-loud quasar (RLQ) host galaxies in the literature. However, a significant minority (~20%) of the 3CR FR II's appears under-luminous with respect to quasar host galaxies. All FR II objects in this faint tail are either unusually red, or appear to be the brightest objects within a group. We discuss the apparent differences between the radio galaxy and RLQ host galaxy populations. RLQs appear to require 10 ¹¹ M host galaxies (and ~10 ⁹ M black holes), whereas radio galaxies and radio-quiet quasars can exist in galaxies down to ~3 × 10 ¹⁰ M . This may be due to biases in the measured quasar host galaxy luminosities or populations studied, or due to a genuine difference in host galaxy. If due to a genuine difference, it would support the idea that radio and optical active galactic nuclei are two separate populations with a significant overlap.

• Open/close A MEASUREMENT OF ARCMINUTE ANISOTROPY IN THE COSMIC MICROWAVE BACKGROUND WITH THE SUNYAEV-ZEL'DOVICH ARRAY

  Matthew K. Sharp et al  2010 ApJ 713 82 Tag this article

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  We present 30 GHz measurements of the angular power spectrum of the cosmic microwave background (CMB) obtained with the Sunyaev-Zel'dovich Array. The measurements are sensitive to arcminute angular scales, where secondary anisotropy from the Sunyaev-Zel'dovich effect (SZE) is expected to dominate. For a broad bin centered at multipole 4066, we find 67 ⁺⁷⁷ _–50 μK ²; of which 26 ± 5 μK ² is the expected contribution from primary CMB anisotropy and 80 ± 54 μK ² is the expected contribution from undetected radio sources. These results imply an upper limit of 155 μK ² (95% CL) on the secondary contribution to the anisotropy in our maps. This level of SZE anisotropy power is consistent with expectations based on recent determinations of the normalization of the matter power spectrum, i.e., σ ₈ ~ 0.8.

• Open/close THE IMPACT OF THE UNCERTAINTY IN SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATES ON THE OBSERVED EVOLUTION OF THE BLACK HOLE-BULGE SCALING RELATIONS

  Yue Shen and Brandon C. Kelly  2010 ApJ 713 41 Tag this article

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  Recent observations of the black hole (BH)-bulge scaling relations usually report positive redshift evolution, with higher redshift galaxies harboring more massive BHs than expected from the local relations. All of these studies focus on broad line quasars with BH mass estimated from virial estimators based on single-epoch spectra. Since the sample selection is largely based on quasar luminosity, the cosmic scatter in the BH-bulge relation introduces a statistical bias leading to on average more massive BHs given galaxy properties at high redshift (i.e., the Lauer et al. bias). We here emphasize a previously underappreciated statistical bias resulting from the uncertainty of single-epoch virial BH mass estimators and the shape of the underlying (true) BH mass function, which leads to on average overestimation of the true BH masses at the high-mass end. We demonstrate that the latter virial mass bias can contribute a substantial amount to the observed excess in BH mass at fixed bulge properties, comparable to the Lauer et al. bias. The virial mass bias is independent of the Lauer et al. bias; hence if both biases are at work, they can largely (or even fully) account for the observed BH mass excess at high redshift.

• Open/close SUSTAINED MAGNETOROTATIONAL TURBULENCE IN LOCAL SIMULATIONS OF STRATIFIED DISKS WITH ZERO NET MAGNETIC FLUX

  Shane W. Davis et al  2010 ApJ 713 52 Tag this article

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  We examine the effects of density stratification on magnetohydrodynamic turbulence driven by the magnetorotational instability in local simulations that adopt the shearing box approximation. Our primary result is that, even in the absence of explicit dissipation, the addition of vertical gravity leads to convergence in the turbulent energy densities and stresses as the resolution increases, contrary to results for zero net flux, unstratified boxes. The ratio of total stress to midplane pressure has a mean of ~0.01, although there can be significant fluctuations on long ( 50 orbits) timescales. We find that the time-averaged stresses are largely insensitive to both the radial and the vertical aspect ratios of our simulation domain. For simulations with explicit dissipation, we find that stratification extends the range of Reynolds and magnetic Prandtl numbers for which turbulence is sustained, but the behavior of such simulations on long timescales is highly variable. Confirming the results of previous studies, we find oscillations in the large-scale toroidal field with periods of ~10 orbits and describe the dynamo process that underlies these cycles. We discuss possible origins for the different convergence properties of the stratified and unstratified domains and identify open questions that remain to be answered.

• Open/close EMPIRICAL DELAY-TIME DISTRIBUTIONS OF TYPE Ia SUPERNOVAE FROM THE EXTENDED GOODS/HUBBLE SPACE TELESCOPE SUPERNOVA SURVEY

  Louis-Gregory Strolger et al  2010 ApJ 713 32 Tag this article

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  Using the Hubble Space Telescope (HST) Advanced Camera for Surveys imaging of the GOODS North and South fields during Cycles 11, 12, and 13, we derive empirical constraints on the delay-time distribution function for type Ia supernovae (SNe Ia). We extend our previous analysis to the three-year sample of 56 SNe Ia over the range 0.2 < z < 1.8, using a Markov chain Monte Carlo to determine the best-fit unimodal delay-time distribution function. The test, which ultimately compares the star formation rate density history to the unbinned volumetric SN Ia rate history from the GOODS/ HST SN survey, reveals a SN Ia delay-time distribution that is tightly confined to 3-4 Gyr (to >95% confidence). This result is difficult to resolve with any intrinsic delay-time distribution function (bimodal or otherwise), in which a substantial fraction (e.g., >10%) of events are "prompt," requiring less than approximately 1 Gyr to develop from formation to explosion. The result is, however, strongly motivated by the decline in the number of SNe Ia at z > 1.2. Sub-samples of the HST SN data confined to lower redshifts ( z < 1) show plausible delay-time distributions that are dominated by prompt events, which is more consistent with results from low-redshift supernova samples and supernova host galaxy properties. Scenarios in which a substantial fraction of z > 1.2 supernovae are extraordinarily obscured by dust may partly explain the differences in low- z and high- z results. Other possible resolutions may include environmental dependences (such as gas-phase metallicity) that affect the progenitor mechanism efficiency, especially in the early universe.