We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs), that encompasses their high-z star-forming progenitors, their high-z quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises: biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star-formation takes place and most of the stellar mass is accumulated; ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations, to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size R e , on the ratio v/σ between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum j of the stellar component; we find good consistency with the available multi-band data in average values and dispersion, both for local ETGs and for their z ∼ 1 − 2 star-forming and quiescent progenitors. The outcomes of our analysis can provide hints to gauge sub-grid recipes implemented in simulations, to tune numerical experiments focused on specific processes, and to plan future multi-band, high-resolution observations on high-redshift star-forming and quiescent galaxies with next generation facilities.

ALMA measurements for 93 Herschel -selected galaxies at 1.1 z 1.7 in COSMOS reveal a sizable (> 29%) population with compact star formation (SF) sizes, lying on average > ×3.6 below the optical stellar mass (M )-size relation of disks. This sample widely spans the star-forming Main Sequence (MS), having 10 8 M 10 11.5 M and 20 SF R 680 M yr −1 . The 32 size measurements and 61 upper limits are measured on ALMA images that combine observations of CO(5-4), CO(4-3), CO(2-1) and λ obs ∼ 1.1−1.3 mm continuum, all tracing the star-forming molecular gas. These compact galaxies have instead normally extended K band sizes, suggesting strong specific SF R gradients. Compact galaxies comprise the 50 ± 18% of MS galaxies at M > 10 11 M . This is not expected in standard bi-modal scenarios where MS galaxies are mostly steadily-growing extended disks. We suggest that compact MS objects are early post-starburst galaxies in which the merger-driven boost of SF has subsided. They retain their compact SF size until either further gas accretion restores pre-merger galaxy-wide SF, or until becoming quenched. The fraction of merger-affected SF inside the MS seems thus larger than anticipated and might reach ∼ 50% at the highest M . The presence of large galaxies above the MS demonstrates an overall poor correlation between galaxy SF size and specific SF R.

No abstract

We present STEEL a STatistical sEmi-Empirical modeL designed to probe the distribution of satellite galaxies in groups and clusters. Our fast statistical methodology relies on tracing the abundances of central and satellite haloes via their mass functions at all cosmic epochs with virtually no limitation on cosmic volume and mass resolution. From mean halo accretion histories and subhalo mass functions the satellite mass function is progressively built in time via abundance matching techniques constrained by number densities of centrals in the local Universe. By enforcing dynamical merging timescales as predicted by high-resolution N-body simulations, we obtain satellite distributions as a function of stellar mass and halo mass consistent with current data. We show that stellar stripping, star formation, and quenching play all a secondary role in setting the number densities of massive satellites above M * 3 × 10 10 M . We further show that observed star formation rates used in our empirical model over predict low-mass satellites below M * 3 × 10 10 M , whereas, star formation rates derived from a continuity equation approach yield the correct abundances similar to previous results for centrals.

The mass and structural assembly of galaxies is a matter of intense debate. Current theoretical models predict the existence of a linear relationship between galaxy size (R e ) and the host dark matter halo virial radius (R h ). By making use of semi-empirical models compared to the size distributions of central galaxies from the Sloan Digital Sky Survey, we provide robust constraints on the normalization and scatter of the R e − R h relation. We explore the parameter space of models in which the R e − R h relation is mediated by either the spin parameter or the concentration of the host halo, or a simple constant the nature of which is in principle unknown. We find that the data require extremely tight relations for both early-type and latetype galaxies (ETGs,LTGs), especially for more massive galaxies. These constraints challenge models based solely on angular momentum conservation, which predict significantly wider distributions of galaxy sizes and no trend with stellar mass, if taken at face value. We discuss physically-motivated alterations to the original models that bring the predictions into better agreement with the data. We argue that the measured tight size distributions of SDSS disk galaxies can be reproduced by semi-empirical models in which the R e − R h connection is mediated by the stellar specific angular momenta j st ar . We find that current cosmological models of galaxy formation broadly agree with our constraints for LTGs, and justify the strong link between R e and j st ar that we propose, however the tightness of the R e − R h relation found in such ab-initio theoretical models for ETGs is in tension with our semi-empirical findings.