Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

The Nature of High-Redshift Massive Quiescent Galaxies -- Searching for RUBIES-UDS-QG-z7 in FLARES

Jack C. Turner, Will J. Roper, Aswin P. Vijayan, Sophie L. Newman, Stephen M. Wilkins, Christopher C. Lovell, Shihong Liao, Louise T. C. Seeyave

Abstract

RUBIES-UDS-QG-z7 (RQG) is the earliest massive quiescent galaxy identified to date, inferred to have formed its abundant stellar mass in a single burst that ceases rapidly before $z\sim8$. An object of such extreme nature challenges our understanding of galaxy formation, requiring rapid growth and quenching mechanisms only $0.6 \ \rm{Gyr}$ after the Big Bang and implying number densities $2 \ \rm{dex}$ higher than currently predicted by simulations. We use synthetic observables to identify analogous systems within the First Light And Reionisation Epoch Simulations (FLARES) and find two massive galaxies ($M_{\ast}>10^{9} \ \mathrm{M_{\odot}}$) dominated by rapidly quenched bursts. One of these demonstrates excellent agreement with the inferred physical properties of RQG and implies a number density of analogous systems $\log_{10}(\mathrm{N_{Q}} \ / \ \mathrm{Mpc}^{-3}) = -7.92^{\ +0.52}_{\ -0.76}$. Beyond demonstrating that the current FLARES model is capable of producing RQG-like systems, these analogues provide a laboratory within which to study the underlying physics. Their active galactic nuclei (AGN) heat and expel gas, inducing rapid quenching and preventing timely rejuvenation. This causes above-average chemical enrichment at a given stellar mass, with super solar levels predicted for RQG. These metallicities are underestimated by spectral energy distribution fitting and we show that $α$-enhancement cannot be solely responsible. Degeneracies with age and dust attenuation appear the more likely causes. Tensions between observed and simulated number densities can be alleviated in part by considering systematics, but adjustments to AGN feedback, such as allowing super-Eddington accretion rates, may be required for full agreement.

The Nature of High-Redshift Massive Quiescent Galaxies -- Searching for RUBIES-UDS-QG-z7 in FLARES

Abstract

RUBIES-UDS-QG-z7 (RQG) is the earliest massive quiescent galaxy identified to date, inferred to have formed its abundant stellar mass in a single burst that ceases rapidly before . An object of such extreme nature challenges our understanding of galaxy formation, requiring rapid growth and quenching mechanisms only after the Big Bang and implying number densities higher than currently predicted by simulations. We use synthetic observables to identify analogous systems within the First Light And Reionisation Epoch Simulations (FLARES) and find two massive galaxies () dominated by rapidly quenched bursts. One of these demonstrates excellent agreement with the inferred physical properties of RQG and implies a number density of analogous systems . Beyond demonstrating that the current FLARES model is capable of producing RQG-like systems, these analogues provide a laboratory within which to study the underlying physics. Their active galactic nuclei (AGN) heat and expel gas, inducing rapid quenching and preventing timely rejuvenation. This causes above-average chemical enrichment at a given stellar mass, with super solar levels predicted for RQG. These metallicities are underestimated by spectral energy distribution fitting and we show that -enhancement cannot be solely responsible. Degeneracies with age and dust attenuation appear the more likely causes. Tensions between observed and simulated number densities can be alleviated in part by considering systematics, but adjustments to AGN feedback, such as allowing super-Eddington accretion rates, may be required for full agreement.

Paper Structure

This paper contains 16 sections, 3 equations, 12 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data
  3. Observations
  4. The First Light And Reionisation Epoch Simulations
  5. Identifying Analogues
  6. Matching SEDs
  7. Observable Properties
  8. Physical Properties
  9. Star Formation History
  10. Discussion
  11. Forming an RQG-like Galaxy
  12. Metallicity and $\alpha$-enhancement
  13. Number Density Implications
  14. Conclusions
  15. Matching to FSPS Photometry
  16. ...and 1 more sections

Figures (12)

  • Figure 1: Top: The SEDs of RQG (black) and the potential Flares analogues as observed at $z_{\rm{RQG}}$ after normalising by the total flux. The best matches FRA-1 and FRA-2 are indicated by green and orange lines respectively. Dashed red lines show the weaker matches. The grey line is a median Flares SED, constructed by taking the median value in each filter individually after normalisation. Shaded regions indicate $1\sigma$ confidence limits. Straight lines join the wavelength dependent measurements of each galaxy for readability, but are not physically representative. Bottom: The absolute SEDs of the same galaxies.
  • Figure 2: Top: The Balmer break strength measured using the definition of Wang_2024 as a function of F150W-F444W colour, quantifying the redness of the SED. RQG is represented by a black star, its closest analogues by green and yellow points and the weak candidates by red crosses. Other Flares galaxies are coloured by their sSFR, averaged over the most recent $50 \ \rm{Myr}$. Bottom: AB-magnitude in F444W as a function of redness for the same galaxies. All observational quantities are measured at $z_{\rm{RQG}}$.
  • Figure 3: A portion of the NIRSpec/PRISM resolution spectrum of RQG (black) and the best two Flares matches (green and orange). These are as observed at $z_{\rm{RQG}}$ and normalised by the total flux. Weak matches are omitted for readability. The shaded region indicates the $1\sigma$ confidence limits on the RQG spectrum and the locations of key absorption and emission features are indicated by dashed lines.
  • Figure 4: Top: The sSFR-stellar mass relation as predicted by Flares. The position of RQG is shown for both the fiducial (black) and high-Z (brown) Prospector models. The two best matches are denoted by green and orange points and the weak matches by red crosses. The grey box indicates the selection region for quiescent galaxies at $z_{\rm{RQG}}$, using the time dependent criterion defined by Pacifici_2016. Bottom: The mass-metallicity relation of the same objects. Flares metallicities are averaged over all stellar particles, after weighting by their current masses. Grey lines indicate the median value of each quantity as a function of stellar mass.
  • Figure 5: The star formation history of RQG as a function of lookback time inferred by the fiducial (black) and high-Z (brown) Prospector models. Shaded regions indicate the $1\sigma$ confidence limits reported by Weibel_2025 and the two Flares analogues are shown by green and orange lines. Each history is normalised such that it integrates to one, representing the relative rate in each time interval.
  • ...and 7 more figures