Aegis: the Nature of the Host Galaxies of Low-ionization Outflows

We report on a signal-to-noise–limited search for low-ionization gas outflows in the spectra of the 0.11 < z < 0.54 objects in the Extended Groth Strip (EGS) portion of the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey. Doppler shifts from the host galaxy redshifts are systematically searched for in the Na I λ 5890,96 doublet (Na I D). Although the spectral resolution and signal-to-noise limit us to study the interstellar gas kinematics from fitting a single doublet component to each observed Na I D profile, the typical outflow often seen in local luminous-infrared galaxies (LIRGs) should be detected at & 6σ in absorption equivalent width down to the survey limiting signal-to-noise (∼ 5 pixel−1) in the continuum around Na I D. The detection rate of LIRG-like outflow clearly shows an increasing trend with star-forming activity and infrared luminosity. However, by virtue of not selecting our sample on star formation, we also find a majority of outflows in galaxies on the red sequence in the rest-frame (U − B, MB) color-magnitude diagram. Most of these red-sequence outflows are of early-type morphology and show the sign of recent star formation in their UV-optical colors; some show enhanced Balmer Hβ absorption lines indicative of poststarburst as well as high dust extinction. These findings suggest that galactic-scale outflow may play an important role in quenching star formation in the host galaxies on their way to the red sequence. Furthermore, outflows well outlive starbursts and present significant columns over a relatively long timescale of ∼ Gyr, so the fate of relic winds as well as the observational constraints on the gaseous feedback models may be studied well in galaxies at their poststarburst phase. We also note the presence of inflow candidates in red, early-type galaxies, some with signs of AGN/LINERs but little evidence for star formation. Subject headings: galaxies: active — galaxies: evolution — galaxies: formation — galaxies: stellar content — ISM: jets and outflows