2024/02/28 by Chisholm, J., Berg, D. A., Endsley, R. +16 · 4 citations
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2402.18643
Here we present high spectral resolution JWST NIRSpec observations of GN42437, a low-mass (log(M_∗/M_\odot)=7.9), compact (re < 500pc), extreme starburst galaxy at z=5.59 with 13 emission line detections. GN42437 has a low-metallicity (5-10% Z_\odot) and its rest-frame Hα equivalent width suggests nearly all of the observed stellar mass formed within the last 3 Myr. GN42437 has an extraordinary 7σ significant [Ne V] 3427 \mathring\rm A detection. The [Ne V] line has a rest-frame equivalent width of 11±2\mathring\rm A, [Ne V]/Hα=0.04±0.007, [Ne V]/[Ne III] 3870\mathring\rm A = 0.26±0.04, and [Ne V]/He II 4687 \mathring\rm A = 1.2±0.5. Ionization from massive stars, shocks, or high-mass X-ray binaries cannot simultaneously produce these [Ne V] and low-ionization line ratios. Reproducing the complete nebular structure requires both massive stars and accretion onto a black hole. We do not detect broad lines nor do the traditional diagnostics indicate that GN42437 has an accreting black hole. Thus, the very-high-ionization emission lines powerfully diagnose faint narrow-line black holes at high-redshift. We approximate the black hole mass in a variety of ways as log(M\rm BH/M_\odot) ∼ 5-7. This black hole mass is consistent with local relations between the black hole mass and the observed velocity dispersion, but significantly more massive than the stellar mass would predict. Very-high-ionization emission lines may reveal samples to probe the formation and growth of the first black holes in the universe.