Day 784

Wednesday.

1411.2590
The suppression of direct collapse black hole formation by soft X-ray irradiation
Inayoshi, Tanaka

The origins of SMBHs: hypothesis is that they grew from >1e5 Msun BHs that formed in the 'direct collapse' of massive gas clouds that have low concentrations of both metals and H2.  Such clouds could form in the early (z>10) Universe if pre-galactic gas is irradiated by H2-photodissociating, FUV light from a nearby SF galaxy.  The key uncertainties with this scenario are (1) how strong the FUV flux must be to sufficiently suppress the H2 abundance to prevent fragmentation and ordinary SF, and (2) whether the requisite conditions arise frequently enough in nature to account for the observed number density of SMBHs (luminous quasars) at high z.  In this work, re-examine the critical FUV flux J_crit that is required to keep H2 photo dissociated and lead to direct collapse.  Show that J_crit could be much higher than previously believed if the same FUV sources also produce X-rays, which can work to offset H2 photodissociation by increasing the ionization fraction and promoting H2 formation via electron-catalyzed reactions.  Stress that soft (~1 keV) X-rays are far more effective at promoting H2 formation than hard (~10 keV) X-rays.  Further, estimate how much soft X-rays can suppress the number density of direct-collapse BHs compared to previous calculations.  Find that, even for conservative sets of assumptions, if J_crit is higher than 400-1000 then direct collapse would occur too rarely to explain the observed abundance of z>6 quasars.

1411.2597
On the intermediate-redshift central stellar mass-halo mass relation, and implications for the evolution of the most massive galaxies since z~1
Schankar, et al

The stellar mass-halo mass relation is a key constraint in all SAM, numerical, and semi-empirical models of galaxy formation and evolution.  However, its exact shape and redshift dependence remain debated.  Several recent works support a relation in the local Universe steeper than previously thought.  Based on the comparisons with a variety of data on massive central galaxies, show that this steepening holds up to z~1, for stellar masses M*>2e11Msun.  Specifically, find significant evidence for a high-mass end slope of beta>0.35-0.70, instead of the usual beta~0.20-0.30 reported by a number of previous results.  When including the independent constraints from the recent BOSS clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (<0.15 dex) in stellar mass at fixed halo mass, in the redshift range z<0.8 and for M*>3e11 Msun, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs.  Discuss the implications of the results with respect to the evolution of the most massive galaxies since z~1.

1411.2608
Hierarchical probabilistic inference of cosmic shear
Schneider, Hogg, Marshall, Dawson, Meyers, Bard, Lang

Point estimators for the shearing of galaxy images induced by gravitational lensing involve a complex inverse problem in the presence of noise, pixelization, and model uncertainties.  Present a probabilistic forward model approach to gravitational lensing inference that has the potential to mitigate the biased inferences in most common point estimators and is practical for upcoming lensing surveys.  The first part of the statistical framework requires specification of a likelihood function for the pixel data in an imaging survey given parameterized models for the galaxies in the images.  Derive the lensing shear posterior by marginalizing over all intrinsic galaxy properties that contribute to the pixel data (i.e., not limited to galaxy ellipticities) and learn the distributions for the intrinsic galaxy preprocess via hierarchical inference with a suitable flexible conditional probability distribution specification.  Use importance sampling to separate the modeling of small imaging areas from the global shear inference, thereby rendering the algorithm computationally tractable for large surveys.  With simple numerical examples, demonstrate the improvements in accuracy from the importance sampling approach, as well as the significance of the conditional distribution specification for the intrinsic galaxy properties when the data are generated from an unknown number of distinct galaxy populations with different morphological characteristics.
[MBI submission of GREAT3 challenge]

1411.2626
Observational properties of galaxies in overdone and average regions at high redshifts z=6-12
Yajima, Sholsman, Romano-Diaz, Nagamine

Use high-res zoom-in cosmo sims and post-process with panchromatic 3D radiation transfer code to obtain the galaxy UV LF at z=6-12.  A rare, heavily overdense region with a 5-sigma density peak evolve at a substantially accelerated pace.  Most massive galaxy in this region has grown th M*~8.4e10 Msun by z=6.3, contains a dust mass of Mdust~4.1e8 Msun, and is associated with a very high SFR~745 Msun/yr.  At the same time, the most massive object n the 'normal' region has M*~3e8 Msun and Mdust < 1e7 Msun.  The attained SFR - M* correlation results in the sSFR slowly increasing with M*.  Find that most of the UV stellar radiation in high-z massive galaxies is absorbed by the surrounding dust, and their escape fraction f_esc is low.  Galaxies in the average region appear to be more transparent for the UV photons owing to a lower dust column, and they agree with the observed UV LF at z~6-10.  Also show that the UV spectra properties of disky galaxies depend significantly upon the viewing angle.  Find that the massive galaxies are bright in the IR band due to the dust thermal emission, with L_IR~3.6e12 Lsun at z=6.3, while L_IR<1e11 Lsun for the low-mass galaxies.  Therefore, ALMA can probe the massive galaxies in the overdense region up to z~10 with a reasonable integration time.  The stellar and dust masses of the most massive galaxy in the overdense region are comparable to those of the sub-millimeter galaxy recently discovered at z=6.3, while the modeled SFR and the sub-millimeter flux fall below the observed one.