New Perspective on Galaxy Outflows From the First Detection of Both Intrinsic and Traverse Metal-Line Absorption

Glenn G. Kacprzak; Crystal L. Martin; Nicolas Bouché; Christopher W. Churchill; Jeff Cooke; Audrey LeReun; Ilane Schroetter; Stephanie H. Ho; Elizabeth Klimek

doi:10.1088/2041-8205/792/1/L12

paper

New Perspective on Galaxy Outflows From the First Detection of Both Intrinsic and Traverse Metal-Line Absorption

arXiv:1407.4126 · doi:10.1088/2041-8205/792/1/L12

Abstract

We present the first observation of a galaxy (z=0.2) that exhibits metal-line absorption back-illuminated by the galaxy ("down-the-barrel") and transversely by a background quasar at a projected distance of 58 kpc. Both absorption systems, traced by MgII, are blueshifted relative to the galaxy systemic velocity. The quasar sight-line, which resides almost directly along the projected minor axis of the galaxy, probes MgI and MgII absorption obtained from Keck/LRIS and Lya, SiII and SiIII absorption obtained from HST/COS. For the first time, we combine two independent models used to quantify the outflow properties for down-the-barrel and transverse absorption. We find that the modeled down-the-barrel deprojected outflow velocities range between $V_{d t b} = 45 - 255$ km/s. The transverse bi-conical outflow model, assuming constant-velocity flows perpendicular to the disk, requires wind velocities $V_{o u t f l o w} = 40 - 80$ km/s to reproduce the transverse MgII absorption kinematics, which is consistent with the range of $V_{d t b}$ . The galaxy has a metallicity, derived from H $α$ and NII, of $[O/H] = - 0.21 \pm 0.08$ , whereas the transverse absorption has $[X/H] = - 1.12 \pm 0.02$ . The galaxy star-formation rate is constrained between $4.6 - 15$ M $_{⊙}$ /yr while the estimated outflow rate ranges between $1.6 - 4.2$ M $_{⊙}$ /yr and yields a wind loading factor ranging between $0.1 - 0.9$ . The galaxy and gas metallicities, the galaxy-quasar sight-line geometry, and the down-the-barrel and transverse modeled outflow velocities collectively suggest that the transverse gas originates from ongoing outflowing material from the galaxy. The $\sim$ 1 dex decrease in metallicity from the base of the outflow to the outer halo suggests metal dilution of the gas by the time it reached 58 kpc.

arXiv comment6 pages, 4 figures. Accepted for publication in ApJL

New Perspective on Galaxy Outflows From the First Detection of Both Intrinsic and Traverse Metal-Line Absorption

Abstract

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