Galaxy formation and evolution

Abstract:

© 2016 The Authors. We use the Lya Mass Association Scheme (LyMAS) to predict cross-correlations at z = 2.5 between dark matter haloes and transmitted flux in the Lya forest, and compare to crosscorrelations measured for quasars and damped Lya systems (DLAs) from the Baryon Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al. We calibrate LyMAS using Horizon-AGN hydrodynamical cosmological simulations of a (100 h -1 Mpc) 3 comoving volume. We apply this calibration to a (1 h -1 Gpc) 3 simulation realized with 2048 3 dark matter particles. In the 100 h -1 Mpc box, LyMAS reproduces the halo-flux correlations computed from the full hydrodynamic gas distribution very well. In the 1 h -1 Gpc box, the amplitude of the large-scale cross-correlation tracks the halo bias b h as expected. We provide empirical fitting functions that describe our numerical results. In the transverse separation bins used for the BOSS analyses, LyMAS cross-correlation predictions follow linear theory accurately down to small scales. Fitting the BOSS measurements requires inclusion of random velocity errors; we find best-fitting rms velocity errors of 399 and 252 km s-1 for quasars and DLAs, respectively. We infer bias-weighted mean halo masses of M h /10 12 h -1 M⊙ = 2.19 +0.16 -0.15 and 0.69 +0.16 -0.14 for the host haloes of quasars and DLAs, with ~0.2 dex systematic uncertainty associated with redshift evolution, intergalactic medium parameters, and selection of data fitting range.

Abstract:

Observations of galaxy isophotes, long-slit kinematics, and high-resolution photometry suggested a possible dichotomy between two distinct classes of elliptical galaxies. But these methods are expensive for large galaxy samples. Instead, integral field spectroscopy can efficiently recognize the shape, dynamics, and stellar population of complete samples of early-type galaxies (ETGs). These studies showed that the two main classes, the fast and slow rotators, can be separated using stellar kinematics. I show that there is a dichotomy in the dynamics of the two classes. The slow rotators are weakly triaxial and dominate above Mcrit ≈ 2 1011 M . Below Mcrit, the structure of fast rotators parallels that of spiral galaxies. There is a smooth sequence along which the age, the metal content, the enhancement in α-elements, and the weight of the stellar initial mass function all increase with the central mass density slope, or bulge mass fraction, while the molecular gas fraction correspondingly decreases. The properties of ETGs on galaxy scaling relations, in particular the (M*, Re) diagram, and their dependence on environment, indicate two main independent channels for galaxy evolution. Fast-rotator ETGs start as star-forming disks and evolve through a channel dominated by gas accretion, bulge growth, and quenching, whereas slow rotators assemble near the centers of massive halos via intense star formation at high redshift and remain as such for the rest of their evolution via a channel dominated by gas poor mergers. This is consistent with independent studies of the galaxies redshift evolution.