THE CONTRIBUTION OF HOST GALAXIES TO THE INFRARED ENERGY OUTPUT OF z ≳ 5.0 QUASARS

Abstract

ABSTRACT The infrared spectral energy distributions of z ≳ 5 quasars can be reproduced by combining a low-metallicity galaxy template with a standard active galactic nucleus (AGN) template. The host galaxy is represented by Haro 11, a compact, moderately low metallicity, starbursting galaxy that shares typical features of high-z galaxies. For the vast majority of z ≳ 5 quasars, the AGN contribution is well modeled by a standard empirical template with the contamination of star formation in the infrared subtracted. Together, these two templates can separate the contributions from the host galaxy and the AGN even in the case of limited data points, given that this model has only two free parameters. Using this method, we reanalyze 69 z ≳ 5 quasars with extensive Herschel observations and derive their AGN luminosities [L AGN = ( 0.78 – 27.4 ) × 10 13 L ⊙ ] , ?> infrared luminosities from star formation [ L SF,IR ≲ ( 1.5 – 25.7 ) × 10 12 L ⊙ ] , ?> and corresponding star formation rates ( SFR ≲ 290 – 2650 M ⊙ yr − 1 ?> ). The average infrared luminosity from star formation and the average total AGN luminosity of the z ≳ 5 quasar sample follow the correlation defined by quasars at z < 2.6. We assume that these quasar host galaxies maintain a constant average SFR (∼620 M ⊙ yr−1) during their mass assembly and estimate the stellar mass that could form prior to z ∼ 5−6 to be ⟨ M * ⟩ ∼ ( 3 – 5 ) × 10 11 M ⊙ . ?> Combining with the black hole (BH) mass measurements, this stellar mass is adequate to establish a BH–galaxy mass ratio M BH / M * ?> at 0.1%–1%, consistent with the local relation.