The evolution of compact massive quiescent and star-forming galaxies derived from the Re–Rh and Mstar–Mh relations

Abstract

The mean size ( effective radius Re) of Massive Galaxies (MGs, Mstar > 1011.2M⊙) is observed to increase steadily with cosmic time. It is still unclear whether this trend originates from the size growth of individual galaxies (via, e.g., mergers and/or AGN feedback) or from the inclusion of larger galaxies entering the selection at later epochs (progenitor bias). We here build a data-driven, flexible theoretical framework to probe the structural evolution of MGs. We assign galaxies to dark matter haloes via stellar mass-halo mass (SMHM) relations with varying high-mass slopes and scatters σSMHM in stellar mass at fixed halo mass, and assign sizes to galaxies using an empirically-motivated, constant and linear relationship between Re and the host dark matter halo radius Rh. We find that: 1) the fast mean size growth of MGs is well reproduced independently of the shape of the input SMHM relation; 2) the numbers of compact MGs grow steadily until z ≳ 2 and fall off at lower redshifts, suggesting a lesser role of progenitor bias at later epochs; 3) a time-independent scatter σSMHM is consistent with a scenario in which compact starforming MGs transition into quiescent MGs in a few 108yr with a negligible structural evolution during the compact phase, while a scatter increasing at high redshift implies significant size growth during the starforming phase. A robust measurement of the size function of MGs at high redshift can set strong constraints on the scatter of the SMHM relation and, by extension, on models of galaxy evolution.

The role of scatter and satellites in shaping the large-scale clustering of X-ray AGN as a function of host galaxy stellar mass

“…When assuming the covariant scatter method instead, the AGN bias predicted by the Savorgnan & Graham (2016) relation is slightly lower (by ∼ 0.1 dex) at lower stellar masses as compared to assuming the relation proposed by Shankar et al (2016). 2016) relation shows the bias weighted additionally by the probability of a galaxy of being quenched as a function of the DM halo mass and redshift (assuming 𝜇 = 2.5) as given by Zanisi et al (2021). The limits correspond to AGN host galaxies consisting solely of quenched (upper limit), and non-quenched (lower limit) galaxies.…”

“…We can relax this assumption and explore the effect on the AGN bias as a function of stellar mass of having all AGNs in quenched galaxies. To this purpose, we assign to each AGN a probability of being in a quenched host galaxy 𝑓 𝑞𝑢𝑒𝑛𝑐ℎ as a function of halo mass and redshift following Rodríguez-Puebla et al (2015) and Zanisi et al (2021). In detail, we use 𝑓 quench = 1/[𝑏 0 + (𝑀 (𝑧, 𝜇) × 10 12 /𝑀 halo )], where 𝑀 (𝑧, 𝜇) = 𝑀 0 + (1 + 𝑧) 𝜇 , with 𝑀 halo given in units of solar masses, 𝑀 0 = 0.68, 𝑏 ∼ 1, and 𝜇 ∼ 2.5 (see Zanisi et al 2021 for the details).…”

“…To this purpose, we assign to each AGN a probability of being in a quenched host galaxy 𝑓 𝑞𝑢𝑒𝑛𝑐ℎ as a function of halo mass and redshift following Rodríguez-Puebla et al (2015) and Zanisi et al (2021). In detail, we use 𝑓 quench = 1/[𝑏 0 + (𝑀 (𝑧, 𝜇) × 10 12 /𝑀 halo )], where 𝑀 (𝑧, 𝜇) = 𝑀 0 + (1 + 𝑧) 𝜇 , with 𝑀 halo given in units of solar masses, 𝑀 0 = 0.68, 𝑏 ∼ 1, and 𝜇 ∼ 2.5 (see Zanisi et al 2021 for the details). We note that variations in 𝜇 = 1 − 4 affect the large-scale bias at most at the ∼ 5% level as compared to 𝜇 = 2.5.…”

Active Galactic Nuclei Abundance in Cosmic Voids

“…According to the model that the inflow of cold gas toward the center of the galaxy and accretion onto the central engine regulates black hole growth (e.g. Di Matteo et al 2005;Hopkins et al 2005;Zanisi et al 2021), the availability of gas in these systems would determine the AGN activity. Since we have selected the luminous galaxies ( M r < −20) in both inner and outer void regions, they have more matter available to feed the central AGN.…”

Quiescent Galaxy Size, Velocity Dispersion, and Dynamical Mass Evolution

“…Studies of quiescent galaxy structural evolution invoke this additional effect to explain the observed size evolution of M * < 10 11 M e galaxies fully (e.g., Carollo et al 2013;Fagioli et al 2016;Faisst et al 2017;Gargiulo et al 2017;Damjanov et al 2019). However, at z < 1, dry mergers that enlarge the effective radii of individual quiescent galaxies appear to play a more dominant role in size growth (and the consistent increase in dynamical mass) of the M *  10 10.5 M e quiescent population (e.g., Zahid et al 2019;Zanisi et al 2021).…”