Star formation and black hole growth at z=4.8

TL;DR

This study investigates star formation and black hole growth in 44 high-redshift AGNs at z=4.8, revealing high star formation rates, correlations with black hole mass, and insights into galaxy evolution during early cosmic epochs.

Contribution

It provides new measurements of star formation rates and black hole masses in z=4.8 AGNs, and explores their relationship and implications for galaxy evolution models.

Findings

Detected high star formation rates of 1090-4240 Msun/yr.

Found a correlation between star formation luminosity and black hole mass.

Observed differences in spectral properties between detected and undetected sources.

Abstract

We report Herschel Spitzer and Wise observations of 44 z=4.8 optically selected active galactic nuclei (AGNs). This sample contains the highest mass black holes (BHs) at this redshift. Ten of the objects were detected by Herschel and five show emission that is not associated with the AGNs. The star formation (SF) luminosity (LSF) obtained by fitting the spectral energy distribution (SED) with standard SF templates is in the range 10^(46.62-47.21) erg/s corresponding to SF rates of 1090-4240 Msun/yr. Fitting with luminous submillimeter galaxy SEDs gives SF rates that are smaller by 0.05 dex when using all bands and 0.1 dex when ignoring the 250-mic band. A 40K gray-body fits to only the 500-mic fluxes reduce LSF by about a factor two. Stacking analysis of 29 undetected sources give significant signals in all three bands. A SF template fit indicates LSF=10^(46.19-46.23) erg/s depending on the assume AGN contribution. A 40K fit to the stacked 500-mic flux gives LSF=10^(45.95) erg/s. The mean BH mass (mbh) and AGN luminosity (LAGN) of the detected sources are significantly higher than those of the undetected ones. The spectral differences are seen all the way from UV to far infrared wavelengths. The mean optical-UV spectra are similar to the ones predicted for thin accretion disks around BHs with the measured masses and accretion rates. We suggest two alternative explanations to the correlation of LSF, LAGN and mbh, one involving no AGN feedback and the second a moderate feedback that affects, but not totally quench SF in 3/4 of the sources. We compare our LSF and LAGN to lower redshift samples and show a new correlation between LSF and mbh. We also examine several rather speculative ideas about the host galaxy properties including the possibility that the detected sources are above the SF mass sequence (MS) at z=4.8, perhaps in mergers, and most of the undetected sources are on the MS.