Browsing by Author "Ran Wang"

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    AGN Feedback and Star Formation of Quasar Host Galaxies: Insights from the Molecular Gas
    (2020) Jinyi Shangguan; Luis C. Ho; Franz E. Bauer; Ran Wang; Ezequiel Treister
    Molecular gas serves as a key probe of the complex interplay between black hole accretion and star formation in the host galaxies of active galactic nuclei (AGNs). We use CO(2-1) observations from a new Atacama Large Millimeter/submillimeter Array survey, in conjunction with literature measurements, to investigate the molecular gas properties of a representative sample of 40z < 0.3 Palomar-Green quasars, the largest and most sensitive study of molecular gas emission to date for nearby quasars. We find that the AGN luminosity correlates with both the CO luminosity and black hole mass, suggesting that AGN activity is loosely coupled to the cold gas reservoir of the host. The observed strong correlation between host galaxy total infrared luminosity and AGN luminosity arises from their common dependence on the molecular gas. We argue that the total infrared luminosity, at least for low-redshift quasars, can be used to derive reliable star formation rates for the host galaxy. The host galaxies of low-redshift quasars have a molecular gas content similar to that of star-forming galaxies of comparable stellar mass. Moreover, they share similar gas kinematics, as evidenced by their CO Tully-Fisher relation and the absence of detectable molecular outflows down to sensitive limits. There is no sign that AGN feedback quenches star formation for the quasars in our sample. On the contrary, the abundant gas supply forms stars prodigiously, at a rate that places most of them above the star-forming main sequence and with an efficiency that rivals that of starburst systems.
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    Compact Molecular Gas Distribution in Quasar Host Galaxies
    (2021) Juan Molina; Ran Wang; Jinyi Shangguan; Luis C. Ho; Franz E. Bauer; Ezequiel Treister; Yali Shao
    We use Atacama Large Millimeter/submillimeter Array CO (2-1) observations of six low-redshift Palomar-Green quasars to study the distribution and kinematics of the molecular gas of their host galaxies at kiloparsec-scale resolution. While the molecular gas content, molecular gas fraction, and star formation rates are similar to those of nearby massive, star-forming galaxies, the quasar host galaxies possess exceptionally compact, disky molecular gas distributions with a median half-light radius of 1.8 kpc and molecular gas mass surface densities greater than or similar to 22 M pc(-2). While the overall velocity field of the molecular gas is dominated by regular rotation out to large radii, with ratio of rotation velocity to velocity dispersion greater than or similar to 9, the nuclear region displays substantial kinematic complexity associated with small-scale substructure in the gas distribution. A tilted-ring analysis reveals that the kinematic and photometric position angles are misaligned on average by similar to 34 degrees 26 degrees and provides evidence of kinematic twisting. These observations provide tantalizing clues to the detailed physical conditions of the circumnuclear environments of actively accreting supermassive black holes.