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A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe

Masafusa Onoue, Kohei Inayoshi, Xuheng Ding, Wenxiu Li, Zhengrong Li, Juan Molina, Akio K. Inoue, Linhua Jiang, Luis C. Ho

TL;DR

This study targets the origin and early growth of black holes by searching for low-luminosity AGN at $z\sim5$ in JWST CEERS imaging. It employs a parent sample of $z=2$--$9$ Lyman-break galaxies and a visual, morphology- and color-based selection to identify compact, AGN-like sources, culminating in CEERS-AGN-z5-1 as a promising $z=5$ AGN candidate. The source exhibits $M_{1450}\approx-19.5$, $L_{bol}\approx2.5\times10^{44}$ erg s$^{-1}$, and strong emission lines with $L_{\mathrm{H}\beta+ [\mathrm{OIII}]}\sim10^{43}$ erg s$^{-1}$ and $L_{\mathrm{H}\alpha}\sim10^{42.9}$ erg s$^{-1}$, along with large rest-frame EWs, suggesting a strong broad-line or super-Eddington accretion scenario; spectroscopic follow-up is needed to confirm redshift and AGN nature. If confirmed, this object helps bridge the gap between seed BH masses and the heavier quasars observed at high redshift, offering a glimpse into low-mass BH growth in the first ~1.1 Gyr of the universe.

Abstract

We report a candidate of a low-luminosity active galactic nucleus (AGN) at z=5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named CEERS-AGN-z5-1 at absolute 1450 A magnitude M1450=-19.5 +/- 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at z>4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, HST, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted Hbeta+[OIII] and Halpha are covered. The estimated line luminosity is L_Hbeta+[OIII] =10^43.0 erg s-1 and L_Halpha =10^42.9 erg s-1 with the corresponding rest-frame equivalent width EW_{Hbeta+[OIII]} =1100 A and EW_Halpha =1600 A, respectively. Our SED fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity, L_bol=2.5 +/- 0.3 \times 10^44 erg s-1, is consistent with those of z<0.35 broad-line AGNs with M_BH = 10^6 M_sun accreting at the Eddington limit. This new AGN population at the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.

A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe

TL;DR

This study targets the origin and early growth of black holes by searching for low-luminosity AGN at in JWST CEERS imaging. It employs a parent sample of -- Lyman-break galaxies and a visual, morphology- and color-based selection to identify compact, AGN-like sources, culminating in CEERS-AGN-z5-1 as a promising AGN candidate. The source exhibits , erg s, and strong emission lines with erg s and erg s, along with large rest-frame EWs, suggesting a strong broad-line or super-Eddington accretion scenario; spectroscopic follow-up is needed to confirm redshift and AGN nature. If confirmed, this object helps bridge the gap between seed BH masses and the heavier quasars observed at high redshift, offering a glimpse into low-mass BH growth in the first ~1.1 Gyr of the universe.

Abstract

We report a candidate of a low-luminosity active galactic nucleus (AGN) at z=5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named CEERS-AGN-z5-1 at absolute 1450 A magnitude M1450=-19.5 +/- 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at z>4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, HST, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted Hbeta+[OIII] and Halpha are covered. The estimated line luminosity is L_Hbeta+[OIII] =10^43.0 erg s-1 and L_Halpha =10^42.9 erg s-1 with the corresponding rest-frame equivalent width EW_{Hbeta+[OIII]} =1100 A and EW_Halpha =1600 A, respectively. Our SED fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity, L_bol=2.5 +/- 0.3 \times 10^44 erg s-1, is consistent with those of z<0.35 broad-line AGNs with M_BH = 10^6 M_sun accreting at the Eddington limit. This new AGN population at the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.
Paper Structure (7 sections, 1 figure)

This paper contains 7 sections, 1 figure.

Table of Contents

  1. Introduction
  2. Candidate Selection
  3. Sample
  4. Data Reduction
  5. Visual Selection of Point Sources
  6. Results
  7. A Candidate AGN at $z=5$

Figures (1)

  • Figure 1: The $z=5$ AGN candidate presented in this paper, CEERS-AGN-z5-1. (Top:) The snapshot images of seven NIRCam filters employed in CEERS. The image size of each panel is $1\hbox{$^{\prime\prime}$}.5 \times 1\hbox{$^{\prime\prime}$}.5$. There is a companion source to the upper left from the central source. (Bottom:) The optical-to-NIR SED of CEERS-AGN-z5-1. The NIRCam flux densities based on model magnitudes are presented in red. CEERS-AGN-z5-1 has an entry in the CANDELS catalog of Stefanon17. Here we show optical CFHT/MegaCam ($u^*$, $g'$, $r'$, $i'$, $z'$), HST/ACS (F606W, F814W) $+$ WCS3 (F105W, F125W, F140W, F160W), and Spitzer/IRAC ($3.6~\hbox{$\mu$m}$ and $4.5~\hbox{$\mu$m}$) in black. Three sigma upper-limit flux densities are shown for those with signal-to-noise ratios less than $3$. Horizontal and vertical error bars correspond to the filter bandwidths and photometric errors, respectively. The grey dashed line shows our best-fit power-law continuum model, where the continuum slope index is $\alpha_\lambda=-1.32\pm0.30$.