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

Paper 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 {\rm H\alpha} emitters (BHAEs) at z~ 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 ~ 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 {\rm H\alpha}-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 {\rm H\alpha} luminosity function indicates an increasing AGN fraction towards the higher {\rm H\alpha} 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 {\rm H\alpha} 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 {\rm H\alpha} sample provides a good database for future studies of faint AGN populations at high redshift.