Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

The $M_{\rm BH}-M_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots

Brenda L. Jones, Dale D. Kocevski, Fabio Pacucci, Anthony J. Taylor, Steven L. Finkelstein, Johannes Buchner, Jonathan R. Trump, Rachel S. Somerville, Michaela Hirschmann, L. Y. Aaron Yung, Guillermo Barro, Eric F. Bell, Laura Bisigello, Antonello Calabro, Nikko J. Cleri, Avishai Dekel, Mark Dickinson, Giovanni Gandolfi, Mauro Giavalisco, Norman A. Grogin, Kohei Inayoshi, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Lorenzo Napolitano, Masafusa Onoue, Swara Ravindranath, Giulia Rodighiero, Stephen M. Wilkins

TL;DR

The paper tackles whether the local $M_{ m BH}-M_igstar$ relation holds at $3<z<7$ by analyzing 70 JWST broad-line AGN with a forward-modeling Bayesian approach to correct for biases. It finds a significant overmassive BH population at high redshift, with an intrinsic scatter of about $0.9$ dex and a ~$2.3$ dex increase in $M_{ m BH}/M_igstar$ from $z\sim3.5$ to $z\sim6.5$; the trend is driven largely by an increasing fraction of LRDs at $z>4$. The results challenge simple evolutionary scenarios and favor scenarios with heavy seeding or rapid early BH growth, though they emphasize caution due to LRD-related ambiguities and BH mass calibrations. Overall, the study provides robust evidence that early BH growth outpaced host galaxy growth and offers important constraints for seeding models and high-$z$ galaxy–BH co-evolution.

Abstract

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at $3<z<7$ using a sample of 70 broad-line AGN identified using NIRSpec/G395M spectroscopy from the CEERS, JADES, and RUBIES surveys. Roughly half (43\%) of our sample appear heavily reddened and are classified as little red dots (LRDs). We estimate BH masses ($M_{\rm BH}$) using single-epoch virial techniques, while host stellar masses ($M_{\star}$) are inferred using a combination of two-dimensional surface brightness profile fitting and spectral energy distribution modeling. We find that a majority of our sources (50/70) have $M_{\rm BH}/M_{\star}$ ratios that are 1-2 dex higher than that observed in AGN locally. Using a forward-modeling Bayesian framework that accounts for uncertainties, intrinsic scatter, and selection effects, we infer a $M_{\rm BH}-M_{\star}$ relationship that is $>3σ$ above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of $0.9$ dex, which does not vary over the redshift range of our sample. We also find that the $M_{\rm BH}/M_{\star}$ ratio increases by $2.3$ dex from $z = 3.5$ and $z = 6.5$ with a confidence level of $ > 3σ$. We attribute this trend with the increasing fraction of LRDs in our sample at $z>4$ as their host masses are $\sim1$ dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST's broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

The $M_{\rm BH}-M_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots

TL;DR

The paper tackles whether the local relation holds at by analyzing 70 JWST broad-line AGN with a forward-modeling Bayesian approach to correct for biases. It finds a significant overmassive BH population at high redshift, with an intrinsic scatter of about dex and a ~ dex increase in from to ; the trend is driven largely by an increasing fraction of LRDs at . The results challenge simple evolutionary scenarios and favor scenarios with heavy seeding or rapid early BH growth, though they emphasize caution due to LRD-related ambiguities and BH mass calibrations. Overall, the study provides robust evidence that early BH growth outpaced host galaxy growth and offers important constraints for seeding models and high- galaxy–BH co-evolution.

Abstract

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at using a sample of 70 broad-line AGN identified using NIRSpec/G395M spectroscopy from the CEERS, JADES, and RUBIES surveys. Roughly half (43\%) of our sample appear heavily reddened and are classified as little red dots (LRDs). We estimate BH masses () using single-epoch virial techniques, while host stellar masses () are inferred using a combination of two-dimensional surface brightness profile fitting and spectral energy distribution modeling. We find that a majority of our sources (50/70) have ratios that are 1-2 dex higher than that observed in AGN locally. Using a forward-modeling Bayesian framework that accounts for uncertainties, intrinsic scatter, and selection effects, we infer a relationship that is above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of dex, which does not vary over the redshift range of our sample. We also find that the ratio increases by dex from and with a confidence level of . We attribute this trend with the increasing fraction of LRDs in our sample at as their host masses are dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST's broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

Paper Structure

This paper contains 17 sections, 4 equations, 9 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Data Description & Reduction
  3. NIRCam Imaging
  4. NIRSpec Spectroscopy
  5. Sample Description
  6. Methodology
  7. Black Hole Mass Measurements
  8. Host Galaxy Morphologies
  9. Host Galaxy Stellar Mass Measurements
  10. Inferring the High-z $M_{\rm BH}-M_{\star}$ Relation
  11. Results
  12. Evolution of the $M_{\rm BH}-M_{\rm \star}$ Relation with Redshift
  13. Discussion
  14. Comparison to Previous Results
  15. Comparison to Cosmological Simulations and Semi-Analytical Models
  16. ...and 2 more sections

Figures (9)

  • Figure 1: The redshift distribution of the broad-line AGN used in this study. The top panel shows the distribution of our entire sample, while the bottom and middle panels show the distribution for sources that are and are not classified as LRDs based on the criteria of Kocevski25. The redshift distribution of the non-LRDs peaks at $z<4$, while that of the LRDs peaks at $z>5$.
  • Figure 2: Bolometric luminosity versus redshift for the broad-line AGN used in this study. The red (blue) points denote sources that are (are not) classified as LRDs based on the criteria of Kocevski25.
  • Figure 3: Examples of our broad-line fits to the NIRSpec G395M spectra of six sources in our sample from the CEERS, JADES, and RUBIES datasets. Green lines show the best-fit Gaussian for the narrow emission line component, blue lines show the best-fit broad component, purple lines show our best-fit absorption components, and red lines show the best overall (narrow plus broad) fit to the observed emission line (black line and shaded area). The FWHM of the broad component, corrected for instrument broadening, is shown in the upper left of each panel.
  • Figure 4: Examples of our two-dimensional surface brightness profile fitting. From left to right, the columns show F200W images of several broad-line AGN, residual images after subtracting off our best-fit point source only model, our full, best-fit GALFIT model, and residual images after subtracting our full, best-fit model. Images are $1.5^{\prime\prime}\times~1.5^{\prime\prime}$ in size. Sources RUBIES-UDS 40579, RUBIES-EGS 42046, and RUBIES-EGS 28812 are LRDs. RUBIES-UDS 40579 and RUBIES-EGS 34978 both have extended morphologies, while RUBIES-EGS 42046 and RUBIES-EGS 28812 are best-fit using a point source only model.
  • Figure 5: Examples of our SED fits with GRAHSP. The total model is shown in black, while individual galaxy and AGN components are represented by the various colored lines (see legend for details). The posterior mean (solid line) and 2 sigma equivalent uncertainties (shaded areas) are shown for each component. Observed fluxes are shown as blue squares with $3\sigma$ error bars and predicted model fluxes are shown as red points. NIRCam images on the upper panel are $2.0^{\prime\prime}\times~2.0^{\prime\prime}$ in size. The top two sources (RUBIES-UDS 40579 and RUBIES-UDS 926125) are LRDs with their distinctive "v-shaped" SEDs.
  • ...and 4 more figures