Kavli Affiliate: Luis C. Ho
| First 5 Authors: John D. Silverman, John D. Silverman, , ,
| Summary:
Contamination-free assessments of the interstellar medium and star formation
in quasar host galaxies, particularly based on the far-infrared, offer insights
into the role of supermassive black holes in galaxy evolution. Motivated by
predictions of quasar heating of dust on both nuclear and galaxy-wide scales,
we perform two-component (host galaxy + point source) modeling of
high-resolution (~0.1") ALMA observations of the FIR continuum in Band 5
(lambda_rest~500 um) of three highly luminous quasars (L_bol~10^47 erg/s),
powered by supermassive black holes having M_BH~10^9 M_sun, at z=2. We include
Band 9 (lambda_rest~154 um; 0.06" and 0.3") data at high S/N which places
further constraints on the unresolved nuclear component in two cases. To break
the degeneracy between quasar and stellar heating, we use CO (J=5-4), observed
in Band 5, to gauge the expected contribution of star formation to the infrared
luminosity. We find very good agreement between the strength and spatial
distribution of the extended continuum component and its prediction based on CO
(J=5-4). This is supported by the location of our three quasars along the L_(CO
5-4)-L_(IR, SFR) luminosity relation for inactive star-forming galaxies. As a
consequence, there is no evidence for additional continuum emission on extended
scales which could be attributed to quasar-heated dust. As expected, the
nuclear (i.e., torus) contribution is present and subdominant (12% in Band 9
for one quasar with a typical star-forming host) or non-existent (<8% in Band 9
for the starbursting host). Based on the continuum and CO, the presence of
substantial levels of ongoing star formation agrees with previous estimates
from unresolved ALMA continuum observations which finds SFRs consistent with
star-forming main-sequence galaxies. Therefore, our results do not provide
evidence for a quasar-mode feedback, even for the most luminous cases at z=2.
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