Where Giants Dwell: Probing the Environments of Early Massive Quiescent Galaxies

Abstract

We investigate the environments of massive quiescent galaxies at 3 < z < 5 using the GAlaxy Evolution and Assembly (GAEA) theoretical model. We select galaxies with stellar mass ~10^10.8 Msun and specific star formation rate below 0.3x t_Hubble, yielding in a sample of about 5,000 galaxies within a simulated volume of ~685 Mpc. These galaxies have formation times that cover well the range inferred from recent observational data, including a few rare objects with very short formation time-scales and early formation epochs. Model high-z quiescent galaxies are alpha-enhanced and exhibit a wide range of stellar metallicity, in broad agreement with current observational estimates. Massive high-z quiescent galaxies in our model occupy a wide range of environments, from void-like regions to dense knots at the intersections of filaments. Quiescent galaxies in underdense regions typically reside in halos that collapsed early and grew rapidly at high redshift, though this trend becomes difficult to identify observationally due to large intrinsic scatter in star formation histories. The descendants of high-z massive quiescent galaxies display a broad distribution in mass and environment by z=0, reflecting the stochastic nature of mergers. About one-third of these systems remain permanently quenched, while most rejuvenation events are merger-driven and more common in overdense regions. Our results highlight the diversity of early quiescent galaxies and caution against assuming that all such systems trace the progenitors of present day most massive clusters.

Figures (14)

• Figure 1: Top panel: relation between stellar mass and parent halo virial mass for all galaxies selected at $z \gtrsim 3.1$ and $z \lesssim 5.3$ (trends are similar when considering galaxies in smaller redshift ranges). Gray and cyan contours show the regions enclosing (from thicker to thinner lines) 30, 60, and 90 per cent of the quiescent and star forming galaxies, respectively. Bottom panel: same as above but including an estimate of the observational uncertainty ($0.25$ dex) in the galaxy stellar mass.
• Figure 2: Halo mass distribution for quiescent model galaxies (solid lines) and the corresponding halo mass function (dashed lines). Different colors correspond to different redshifts (as indicated in the legend in the bottom panel), ranging from $\sim 3.1$ (blue) to $\sim 5.3$ (brown). The top and bottom panels are for all quiescent galaxies and for quiescent satellites only, respectively.
• Figure 3: Spatial distribution of galaxies selected at $z\sim 4.5$ and with over-densities over a 3 Mpc scale in the lowest 15th (top panels) and highest 85th (bottom panels) percentiles of the distribution. Galaxies in our sample of massive quiescent galaxies are at the center of each panel and are marked by a red cross, while the other symbols mark the position of all galaxies more massive than $10^{9}\,{\rm M}_{\sun}$ in a projected region of 100x100 Mpc comoving with a dept of $20$ Mpc comoving. The o$3$ value corresponding to each field is indicated in the top left corner of each box. The color of the symbols scales with the galaxy star formation rate as indicated by the color bar on the right, while symbol size scales with galaxy stellar mass. We note that we have plotted the most massive galaxies at the end to emphasize their position, so they can hide other galaxies that lie close in projection.
• Figure 4: Evolution of the parent halo mass, galaxy stellar mass, star formation rate, and black hole mass for the massive quiescent galaxies at $z\sim 4.5$ considered in Fig. \ref{['fig:xypos']}. Green and magenta lines refer to the top and bottom panel respectively, with thickness of the lines and color shade increasing with over-density values as indicated in the legend included in the left panel. $\rm {M}_{200}$ and ${\rm M_{BH}}$ are shown for the main progenitor at each previous cosmic epoch, while for the galaxy stellar mass and SFR we show the sum of all progenitors at the corresponding epoch.
• Figure 5: Correlation between two different estimates of the galaxy environment and the parent halo mass (left column), the intrinsic galaxy stellar mass (middle column), and the galaxy stellar including an estimate for its uncertainty (right column). The top panels are for n$3$, i.e. the local density (in physical Mpc$^{-2}$) estimated considering the three closest neighbors for each galaxy in our quiescent (black) and star forming (cyan) samples. The bottom panels are for o3, i.e. the over-density estimated considering a scale of 3 Mpc. The numbers in each panel correspond to the Spearman's correlation coefficient and relative significance (a small value indicates a significant correlation) for quiescent galaxies (top left) and for star forming galaxies (bottom right).