ALMA OBSERVATIONS OF A CANDIDATE MOLECULAR OUTFLOW IN AN OBSCURED QUASAR

摘要

We present Atacama Large Millimeter/Submillimeter Array CO (1-0) and CO (3-2) observations of SDSS?J135646.10+102609.0, an obscured quasar and ultra-luminous infrared galaxy with two merging nuclei and a known 20?kpc scale ionized outflow. The total molecular gas mass is M ☉, mostly distributed in a compact rotating disk at the primary nucleus (M mol ≈ 3 × 108 M ☉) and an extended tidal arm (M mol ≈ 5 × 108 M ☉). The tidal arm is one of the most massive molecular tidal features known; we suggest that it is due to the lower chance of shock dissociation in this elliptical/disk galaxy merger. In the spatially resolved CO (3-2) data, we find a compact (r ≈ 0.3?kpc) high-velocity (v ≈ 500?km?s–1) redshifted feature in addition to the rotation at the N nucleus. We propose a molecular outflow as the most likely explanation for the high-velocity gas. The outflowing mass of M mol ≈ 7 × 107 M ☉ and the short dynamical time of t dyn ≈ 0.6?Myr yield a very high outflow rate of M ☉?yr–1 and can deplete the gas in a million years. We find a low star formation rate (16 M ☉?yr–1 from the molecular content and 21 M ☉?yr–1 from the far-infrared spectral energy distribution decomposition) that is inadequate to supply the kinetic luminosity of the outflow (?erg?s–1). Therefore, the active galactic nucleus (AGN), with a bolometric luminosity of 1046?erg?s–1, likely powers the outflow. The momentum boost rate of the outflow () is lower than typical molecular outflows associated with AGNs, which may be related to its compactness. The molecular and ionized outflows are likely two distinct bursts induced by episodic AGN activity which varies on a timescale of 107?yr.