2024/08/16 by Kei Ito, Takumi S. Tanaka, Ito, Kei +15 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2408.08492
openalex publication_date 2024/08/16 · openalex created_date 2024/09/13 · openalex updated_date 2026/07/29
We report a characterization of an X-ray-detected quiescent galaxy at z=2.09, named COS-XQG1, using JWST/NIRCam and NIRSpec data. This galaxy is detected in Chandra imaging, suggesting the presence of an AGN with a high black hole accretion rate of M\rm BH=0.22±0.03 \rm M_\odot yr-1. Using multi-wavelength photometry from X-ray to sub-millimeter, including the latest JWST imaging, we confirm that COS-XQG1 is massive (M_⋆ = (1.6±0.2)×1011 M_\odot) and quiescent (\rm sSFR<10-10 \rm yr-1) as reported previously, even considering the contribution from AGN emission. Noticeably, COS-XQG1 displays a broad Hβ and Hα emission component with a full width at half maximum of 4365+81-81 \rm km s-1 in its NIRSpec spectrum, which is typical of Type 1 AGNs. The line width and luminosity of the broad Hα emission give a black hole mass of log(M\rm BH/M_\odot) = 8.43±0.02 (± 0.5). With a stellar velocity dispersion measurement (σ_⋆=238±32 \rm km s-1), we find that this galaxy is consistent with the local relations in the M\rm BH - σ_⋆ and M\rm BH- M_⋆ planes, which might suggest that massive quiescent galaxies at z≥2 have already been mature in terms of both stellar and black hole masses and will not evolve significantly. In addition, image 2D-decomposition analysis finds that this galaxy comprises disk and point source components. The latter is likely the composition of an AGN and a stellar bulge. Based on a comparison with numerical simulations, we expect that COS-XQG1 will evolve into a typical quiescent galaxy with lower AGN activity by redshift 0. This study shows the usefulness of X-ray-detected quiescent galaxies in investigating the co-evolution between SMBHs and galaxies in the early Universe.