A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Broad-line AGN at $z=4-5$ revealed by JWST/NIRCam WFSS

Abstract

Low-luminosity AGNs with low-mass black holes (BHs) in the early universe are fundamental to understanding the BH growth and their co-evolution with the host galaxies. Utilizing JWST NIRCam Wide Field Slitless Spectroscopy (WFSS), we perform a systematic search for broad-line $\mathrm{H}\hat{\mathrm{I}}\pm$ emitters (BHAEs) at $z\approx 4-5$ in 25 fields of the ASPIRE (A SPectroscopic survey of biased halos In the Reionization Era) project, covering a total area of 275 arcmin${}^2$. We identify 16 BHAEs with FWHM of the broad components spanning from $\sim$ 1000 km s${}^{-1}$ to 3000 km s${}^{-1}$. Assuming the broad linewidths arise due to Doppler broadening around BHs, the implied BH masses range from $10^7$ to $10^8{M}_{\odot }$, with broad $\mathrm{H}\hat{\mathrm{I}}\pm$-converted bolometric luminosity of $10^{44.5}-10^{45.5}$ erg s${}^{-1}$ and Eddington ratios of $0.07-0.47$. The spatially extended structure of the F200W stacked image may trace the stellar light from the host galaxies. The $\mathrm{H}\hat{\mathrm{I}}\pm$ luminosity function indicates an increasing AGN fraction towards the higher $\mathrm{H}\hat{\mathrm{I}}\pm$ luminosities. We find possible evidence for clustering of BHAEs: two sources are at the same redshift with a projected separation of 519 kpc; one BHAE appears as a composite system residing in an overdense region with three close companion $\mathrm{H}\hat{\mathrm{I}}\pm$ emitters. Three BHAEs exhibit blueshifted absorption troughs indicative of the presence of high-column-density gas. We find the broad-line and photometrically selected BHAE samples exhibit different distributions in the optical continuum slopes, which can be attributed to their different selection methods. The ASPIRE broad-line $\mathrm{H}\hat{\mathrm{I}}\pm$ sample provides a good database for future studies of faint AGN populations at high redshift.

19 pages, 13 figures, 4 tables. Accepted by the ApJ