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Star formation and black hole growth at z=4.8
Hagai Netzer, Rivay Mor, Benny Trakhtenbrot, Ohad Shemmer, Paulina Lira
Description
We report Herschel/SPIRE Spitzer and Wise observations of 44 z=4.8 optically selected active
galactic nuclei (AGNs). This flux limited sample contains the highest mass black holes (BHs) at this
redshift. Ten of the objects were detected by Herschel with star formation (SF) luminosity (LSF,
integrated over 8-1000 mic) in the range 10^(46.70)-10^(47.21) erg/s corresponding to SF rates of
1310-4240 Msun/yr. Stacking analysis of 29 undetected sources gives a significant signal
corresponding to LSF=10^(46.23) erg/s. The remaining 5 sources show emission that is not clearly
associated with the AGNs. The mean BH mass (mbh) and associated AGN luminosity (LAGN) of
the detected sources are significantly higher than those of the undetected sources. The luminosity
differences are seen from rest-frame 900A all the way to the far infrared. The mean optical-UV
spectra of the two groups are similar to the spectrum of standard accretion disks around BHs with
the measured masses and accretion rates. The Herschel data are consistent with the idea 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. 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 about 3/4 of the sources. We discuss the LSF-LAGN correlation
in comparison to lower redshift samples and show a new correlation between LSF and mbh. We
also follow the build-up of stellar and BH mass from z=4.8 to z=2.4 and derive accretion and SF
duty cycles under various conditions.
Cite as:
arXiv:1308.0012 [astro-ph.CO]
(or arXiv:1308.0012v2 [astro-ph.CO] for this version)
Read full version at : Paper
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