James Webb Space Telescope Feed Post

Harvard ADS: A Search for z=5 H\alpha and H\beta+[O III] Dual-Line Emitting Galaxies in the JWST CEERS Field: Implications for the AGN Abundance

Paper abstract: The James Webb Space Telescope (JWST) has enabled us to uncover faint galaxies and active galactic nuclei (AGNs) in the early universe. Taking advantage of the unique filter combination used in the Cosmic Evolution Early Release Science Survey (CEERS) program, we perform an extensive photometric search of galaxies emitting strong H\beta+[O III] and H\alpha lines. The redshift range of the galaxies is limited to 5.03<= z<= 5.26 by requiring photometric excesses in NIRCam's F277W and F410M images. A total of 261 H\beta+[O III] and H\alpha dual-line emitters are found over the absolute UV magnitude -22<~ M_{\mathrm{UV}}<~ -17, with a mean rest-frame equivalent width of 1010 A for H\beta+[O III] and 1040 A for H\alpha. This population accounts for ~ 40\% of the Lyman break galaxies at this redshift range. Intriguingly, there are 58 objects (22% of the whole sample) that exhibit compact morphology at the rest-UV or optical wavelength. With an assumption that these compact dual-line emitters are dominated by AGN, their AGN bolometric luminosities are in the range of 2\times 10^{43} <~ L_{\rm bol}/({\rm erg~s}^{-1})<~ 3\times 10^{44}. Their number density is two orders of magnitude higher than the extrapolation from the UV-selected luminous quasars, which is in good agreement with previous JWST studies of broad-line AGNs, requiring a ~ 10\% of the AGN duty cycle. Moreover, our dual-line emitter sample reaches the faint end of the H\alpha and [O III] luminosity functions down to <~ 10^{42}~{\rm erg~s}^{-1}. Spectroscopic follow-up observations are planned in an approved JWST Cycle 3 program, in which we aim to confirm their nature, characterize their black hole activity, and construct their mass distribution at 10^6<~ M_{\rm BH}/M_\odot <~ 10^8.