GALACTIC OUTFLOWS IN ABSORPTION AND EMISSION: NEAR-ULTRAVIOLET SPECTROSCOPY OF GALAXIES AT 1 <z< 2

Abstract

We study large-scale outflows in a sample of 96 star-forming galaxies at 1 z 2, using near-UV spectroscopy of Fe II and Mg II absorption and emission. The average blueshift of the Fe II interstellar absorption lines with respect to the systemic velocity is −85 ± 10 km s −1 at z ∼ 1.5, with standard deviation 87 km s −1 ; this is a decrease of a factor of two from the average blueshift measured for far-UV interstellar absorption lines in similarly selected galaxies at z ∼ 2. The profiles of the Mg II λλ2796, 2803 lines show much more variety than the Fe II profiles, which are always seen in absorption; Mg II ranges from strong emission to pure absorption, with emission more common in galaxies with blue UV slopes and at lower stellar masses. Outflow velocities, as traced by the centroids and maximum extent of the absorption lines, increase with increasing stellar mass with 2-3σ significance, in agreement with previous results. We study fine structure emission from Fe II*, finding several lines of evidence in support of the model in which this emission is generated by the re-emission of continuum photons absorbed in the Fe II resonance transitions in outflowing gas. In contrast, photoionization models indicate that Mg II emission arises from the resonant scattering of photons produced in H II regions, accounting for the differing profiles of the Mg II and Fe II lines. A comparison of the strengths of the Fe II absorption and Fe II* emission lines indicates that massive galaxies have more extended outflows and/or greater extinction, while two-dimensional composite spectra indicate that emission from the outflow is stronger at a radius of ∼10 kpc in high mass galaxies than in low mass galaxies.

NEAR-ULTRAVIOLET SPECTROSCOPY OF STAR-FORMING GALAXIES FROM eBOSS: SIGNATURES OF UBIQUITOUS GALACTIC-SCALE OUTFLOWS

“…Most of the space-based observations are dedicated to the far-UV (FUV) window at λ  2000 Å because of the large number of transitions available at those energies, leaving the NUV window of the SEDs of stars and galaxies as largely unexplored territory. Most of our knowledge about galaxy SEDs in the rest-frame NUV have originated from recent observations with the 8-m or larger telescopes such as the Keck and VLT telescopes (e.g., Martin & Bouché 2009;Weiner et al 2009;Rubin et al 2011;Erb et al 2012;Talia et al 2012).…”

“…In the spectra of star-forming galaxies (SFGs), these absorption lines are observed to be almost always blueshifted from the systemic velocity of the galaxy, which serves as direct evidence for ubiquitous outflows driven by star formation (Tremonti et al 2007;Martin & Bouché 2009;Weiner et al 2009;Rubin et al 2010Rubin et al , 2014Erb et al 2012;Kornei et al 2012;Martin et al 2012;Talia et al 2012).…”

The Lyman alpha reference sample

“…-From the shift between the low ionization states (LIS) and the stellar lines of the galaxy. LIS metal absorption lines are established as good tracers of neutral gas (Pettini et al 2002;Erb et al 2012;Sandberg et al 2013) and have been employed in studies of relations between neutral ISM kinematics and Lyα radiative transfer (Kunth et al 1998;Shapley et al 2003). Rivera-Thorsen et al (2015) measured the shift of four different UV SiII absorption lines in the COS spectrum of Mrk 1486.…”

The Launching of Cold Clouds by Galaxy Outflows. Ii. The Role of Thermal Conduction

“…Moreover, the observation of the multiphase ISM is difficult: the hot phases of the outflow have only been detected in a few instances (e.g., Heckman et al 1990;Veilleux et al 2014;Wang et al 2014), and the cold phases of gas are often difficult to interpret. Nevertheless, the kinematics of neutral, atomic outflows has been studied in many cases through the absorption line as well as emission line measurements of Lyα, Hα, and Hβ, as Rupke et al 2005;Weiner et al 2009;Erb et al 2012;Kornei et al 2013;Arrigoni Battaia et al 2015).…”