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Published August 1, 2017 | Published
Journal Article Open

The Circumgalactic Medium of Submillimeter Galaxies. II. Unobscured QSOs within Dusty Starbursts and QSO Sightlines with Impact Parameters below 100 kpc


We present Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm observations of 29 bright Herschel sources near high-redshift QSOs. The observations confirm that 20 of the Herschel sources are submillimeter-bright galaxies (SMGs) and identify 16 new SMG−QSO pairs that are useful to studies of the circumgalactic medium (CGM) of SMGs. Eight out of the 20 SMGs are blends of multiple 870 μm sources. The angular separations for six of the Herschel-QSO pairs are less than 10", comparable to the sizes of the Herschel beam and the ALMA primary beam. We find that four of these six "pairs" are actually QSOs hosted by SMGs. No additional submillimeter companions are detected around these QSOs, and the rest-frame ultraviolet spectra of the QSOs show no evidence of significant reddening. Black hole accretion and star formation contribute almost equally in bolometric luminosity in these galaxies. The SMGs hosting QSOs show similar source sizes, dust surface densities, and star formation rate surface densities to those of other SMGs in the sample. We find that the black holes are growing ~3× faster than the galaxies when compared to the present-day black hole/galaxy mass ratio, suggesting a QSO duty cycle of ≾ 30% in SMGs at z ~ 3. The remaining two Herschel-detected QSOs are undetected at 870 μm, but each has an SMG "companion" only 9" and 12" away (71 and 95 kpc at z = 3). They could be either merging or projected pairs. If the former, they would represent a rare class of "wet−dry" mergers. If the latter, the QSOs would, for the first time, probe the CGM of SMGs at impact parameters below 100 kpc.

Additional Information

© 2017 American Astronomical Society. Received 2017 April 14. Accepted 2017 June 26. Published 2017 July 31. We thank K. Gayley, J. Hennawi, C. Liang, R. Mutel, and D. Riechers for useful discussions. We also thank the anonymous referee for detailed comments that helped improve the presentation of the paper. The National Radio Astronomy Observatory is a facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc. Support for this work was provided by the NSF through award GSSP SOSPA3-016 from the NRAO. H.F. acknowledges support from NASA JPL award RSA#1568087, NSF grant AST-1614326, and funds from the University of Iowa. J.X.P. acknowledges support from the NSF grants AST-1010004, AST-1109452, AST-1109447, and AST-1412981. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00131.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The Herschel-ATLAS is a project with Herschel, which is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. The H-ATLAS Web site is http://www.h-atlas.org/. The U.S. participants acknowledge support from the NASA Herschel Science Center/JPL. Facilities: ALMA, Herschel, Sloan, WISE.

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