Where Galaxies Go to Die: The Environments of Massive Quiescent Galaxies at $3<z<5$

TL;DR

This study investigates how environment shapes the formation and quenching of massive quiescent galaxies (MQGs) at $3<z<5$ by combining spectroscopic MQG samples with three-dimensional overdensity maps constructed via Monte Carlo Voronoi Tessellation in the UDS and EGS fields. It identifies 12 robust overdense peaks and several protoclusters, finding that MQGs preferentially inhabit the most massive structures, with roughly half residing in peaks of $ ext{log}(M_{ ext{Peak}}/ ext{M}_igodot)\geq 13$ and 75% of the most massive MQGs within overdense regions. Prospector-based SFH modeling reveals that MQG progenitors inferred from their SFHs often exceed the observed high-redshift stellar mass function, implying substantial ex-situ mass growth through mergers in overdense environments. Together, these results indicate that environmental effects, via enhanced merger activity and structure formation, drive rapid mass assembly and early quenching of MQGs, underscoring the importance of high-$z$ cosmic structures in shaping the MQG population. The work also identifies key protoclusters, such as UDS-PCl-z3.2 and Cosmic Vine, demonstrating that MQG-environment links extend to large-scale structure at $z>3$.

Abstract

At low redshift, massive quiescent galaxies (MQGs) are most frequently found in massive, rich galaxy clusters, but at high redshift the trend is less clear. Here, we present spectroscopic evidence of the effects of environment on the formation and assembly of high-redshift MQGs. We identify 25 (5) $\log (M_*/\mathrm{M_\odot}\geq10.5$ ($10.0\leq\log (M_*/\mathrm{M_\odot}<10.5$) spectroscopically-confirmed quiescent galaxies in the UDS and EGS fields at $3<z<5$ with NIRSpec PRISM spectroscopy from RUBIES and other public JWST NIRSpec programs. We measure the density contrast in these fields by applying a Monte Carlo Voronoi Tesselation density mapping technique to photometric and spectroscopic redshifts of $m_\mathrm{F444W}<27.5$ sources. We robustly detect 12 massive overdense peaks with $\log (M_\mathrm{Peak}/\mathrm{M_\odot})\geq13$ and six extended massive protoclusters ($\log (M_\mathrm{Struct}/\mathrm{M_\odot})\geq13.85$). We observe that MQGs are preferentially found in these massive peaks and within these massive structures: $\approx50\%$ of MQGs are found in massive peaks, compared to $\approx20\%$ of massive star forming galaxies (MSFGs) and $\approx15\%$ of the overall spectroscopically-confirmed population. We also find an apparent dependence on both quiescent galaxy mass and environment, with $75\%$ of the most massive ($\log (M_*/\mathrm{M_\odot}\geq10.75$) residing inside overdense peaks. We compare the star formation histories (SFHs) of the MQGs with the high-redshift galaxy stellar mass function from observations and simulated quiescent galaxies at $z>5$, finding that the masses from the inferred MQG SFHs regularly exceed either observed or simulated high-redshift galaxies, which suggests indicates that mergers and ex-situ star formation play a key role in the mass assembly of MQGs in overdense environments.

Figures (14)

• Figure 1: 14 of the 25 spectroscopically-confirmed $\log (M_*/\mathrm{M_\odot})\geq10.5$ quiescent galaxies which form our sample. In each panel the PRISM spectrum and uncertainty are shown in black and gray with the MAP Prospector model spectrum overlaid in red (pink for marginally quiescent galaxies). Green open circles with error bars show the photometry. To scale the observed, error, and model spectra to observed photometry, the inverted calibration vector is applied. Each major (minor) tick along the vertical axis is $(0.25\times)10^{-19}\ \mathrm{erg\ s^{-1}\ cm^{-2}\ \AA^{-1}}$. In each panel we give the spectrum ID, field, redshift, stellar mass and SFR (see also Table \ref{['tab:prospector_output']}). Sources from Glazebrook2024Carnall2024DeGraaff2024 have their names from the literature given in parentheses; we use these names hereafter.
• Figure 2: Figure \ref{['fig:prisms1']}, continued. The remaining 11 massive quiescent galaxies, plus one $\log (M_*/\mathrm{M_\odot})\geq10.5$ marginally quiescent galaxy (pink model).
• Figure 3: As Figures \ref{['fig:prisms1']} and \ref{['fig:prisms2']} but for low-mass QGs ($10\leq\log (M_*/\mathrm{M_\odot})<10.5$.
• Figure 4: Left: A 2D histogram of $\log (M_*/\mathrm{M_\odot})$ and $\log\mathrm{(sSFR/yr^{-1})}$ from the posterior draws of all $m_\mathrm{F444W}<24$ spectroscopically-confirmed galaxies modeled with Prospector. The individual galaxies and their uncertainties are indicated by black/blue/red for galaxies classified as $\log (M_*/\mathrm{M_\odot})<10.5$/$\log (M_*/\mathrm{M_\odot})\geq10.5$ star-forming/$\log (M_*/\mathrm{M_\odot})\geq10.5$ quiescent based on their inferred posterior medians. The red box denotes the region we use to define MQGs. Middle: As left, but for $\log\mathrm{(sSFR/yr^{-1})}$ and optical depth $\tau_{\mathrm{dust}}$. Galaxies with high $\tau_{\mathrm{dust}}$ and low sSFR appear to be dusty star-forming galaxies based on visual inspection of their spectra and SEDs. Right: As left, but for $\log (M_*/\mathrm{M_\odot})$ and dust optical depth $\tau_\mathrm{dust}$.
• Figure 5: Left: Specific star formation rate versus redshift for spectroscopically-confirmed galaxies modeled with Prospector. The dashed red line indicates the $\log (\mathrm{sSFR/yr^{-1}})<-10$ selection we use in this work and the dotted red line shows the alternative $\mathrm{sSFR < 0.2\ yr^{-1}}$ selection. Our results are robust to the choice in sSFR cut. The top histogram shows the non-normalized distribution of redshifts of all galaxies (black), massive star-forming galaxies (blue), and MQGs (red). Right: Stellar mass versus redshift, with points colored by F444W magnitude to demonstrate the mass completeness limit selected.