Day 950

Friday.


1508.04771
Galaxy structure as a driver of the star formation sequence slope and scatter
Whitaker, Franx, et al

It is well established that (1) SF galaxies follow a relation between their SFR and stellar mass M*, the "star-formation sequence", and (2) the SFRs of galaxies correlate with their structure, where SF galaxies are less concentrated than quiescent galaxies at fixed mass.  Here, consider whether the scatter and slope of the SF sequence is correlated with systematic variations in the Sersic indices, n, of galaxies across the SFR-M* plane.  Use a mass-complete sample of 23,848 galaxies at 0.5<z<2.5 selected from the 3D-HST photometric catalogs.  Galaxy light profiles parameterized by n are based on HST CANDELS NIR imaging.  Use a single SFR indicator empirically-calibrated from stacks of Spitzer/MIPS 24um imaging, adding the unobscured and obscured SF.  Find that the scatter of the SF sequence is related in part to galaxy structure; the scatter due to variations in n at fixed mass for SF galaxies ranges from 0.14±0.02 dex at z~2 to 0.30±0.04 dex at z<1.  While the slope of the log(SFR)-log(M*) relation is of order unity for disk-like galaxies, galaxies with n>2 (implying more dominant bulges) have significantly lower SFR/M*  than the main ridgeline of the SF sequence.  These results suggest that bulges in massive z~2 galaxies are actively building up, where the stars in the central concentration are relatively young.  At z<1, the presence of older bulges within star-forming galaxies lowers global SFR/M*, decreasing the slope and contributing significantly to the scatter of the SF sequence.


1508.04842
Is main sequence galaxy star formation controlled by halo mass accretion?
Rodriguez-Puebla, Primack, Behroozi, Faber

It is known that the galaxy stellar-to-halo mass ratio (SHMR) is nearly independent of redshift from z=0-4.  This motivates to construct a toy model in which it is assumed that the SMHR for central galaxies measured at z~0 is independent of z, which implies that the SFR is determined by the halo mass accretion rate, a phenomenon termed Stellar-Halo Accretion Rate Coevolution (SHARC).  Moreover, show here that the ~0.3 dex dispersion of the halo mass accretion rate (MAR) is similar to the observed dispersion of the SFR on the main sequence.  In the context of bathtub-type models of galaxy formation, SHARC leads to mass-dependent constraints on the relation between SFR and MAR.  The SHARC assumption is no doubt over-simplified, but it is expected to be possibly valid for central galaxies with stellar masses of 1e9-10.5 Msun that are on the SF MS.  Such galaxies represent most of the life history of M* galaxies, and therefore most of the SF in the Universe.  The predictions from SHARC agree remarkably well with the observed SFR of galaxies on the main sequence at low z and fairly well out to higher z, although the predicted SFR exceeds observations at z<4.  Assuming that the interstellar gas mass is constant for each galaxy, equilibrium condition, the SHARC model allows calculation of mass loading factors for inflowing and outflowing gas.  With assumptions about preventive feedback based on simulations, the model allows calculation of galaxy metallicity evolution.  If the SFR in SF galaxies is indeed largely regulated by halo mass accretion, especially at low z, that may help to explain the success of models that tie galaxy properties to those of their host halos, such as age matching and the relation between two-halo galaxy conformity and halo mass accretion conformity.


1508.04901
Galaxy clustering using photometric redshifts
Soltan, Chodorowski

Investigate the evolution of the galaxy 2PCF over a wide redshift range, 0.2<z<3.  For the first time the systematic analysis covers the redshifts above 1-1.5.  The catalogue of ~250k galaxies with i+<25 and known photo-z in the Subaru Deep field is used.  The galaxies are divided into 3 luminosity classes and several distance/redshift bins.  First, the 2D CF is determined for each luminosity class and distance bin.  Calculations are based on the quantitative differences between the surface distributions of galaxy pairs with comparable and distinctly different photometric redshifts.  The power law approximation for the CF is used.  A limited accuracy of photo-z as compared to the spectroscopic ones has been examined and taken into account.  Then, the 3D functions for all the selected luminosities and distances are calculated.  The power-law parameters of the CF, the slope and the correlation length, are determined.  Both parameters do not show strong variations over the whole investigated redshift range.  The slope of the luminous galaxies appears to be consistently steeper than that for the fainter ones.  The linear bias factor, b(z), grows systematically with redshift; assuming the local normalization b(0)=1.1-1.2, the bias reaches 3-3.5 at the high redshift limit.