We investigate the variation of the ratio of the equivalent widths of the FeII$lambda$2600 line to the MgII$lambdalambda$2796,2803 doublet as a function of redshift in a large sample of absorption lines drawn from the JHU-SDSS Absorption Line Catalog
. We find that despite large scatter, the observed ratio shows a trend where the equivalent width ratio $mathcal{R}equiv W_{rm FeII}/W_{rm MgII}$ decreases monotonically with increasing redshift $z$ over the range $0.55 le z le 1.90$. Selecting the subset of absorbers where the signal-to-noise ratio of the MgII equivalent width $W_{rm MgII}$ is $ge$3 and modeling the equivalent width ratio distribution as a gaussian, we find that the mean of the gaussian distribution varies as $mathcal{R}propto (-0.045pm0.005)z$. We discuss various possible reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a simple model where the abundances of Mg and Fe in the absorbing clouds are assumed to be the result of supernova ejecta and where the cosmic evolution in the SNIa and core-collapse supernova rates is related to the cosmic star-formation rate. If the trend in $mathcal{R}$ reflects the evolution in the abundances, then it is consistent with the predictions of the simple model.
We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance transitions with Doppler sh
ifts of -200 to -300 km/s, indicating a cool gas outflow. Emission in MgII near and redward of systemic velocity, in concert with the observed absorption, yields a P Cygni-like line profile similar to those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the MgII emission is spatially resolved, and extends significantly beyond the emission from stars and HII regions within the galaxy. Assuming the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances > ~7 kpc. We also detect several narrow FeII* fine-structure lines in emission near the systemic velocity, arising from energy levels which are radiatively excited directly from the ground state. We suggest that the MgII and FeII* emission is generated by photon scattering in the observed outflow, and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution.
We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field, has a range in
stellar mass (M_*) comparable to that of the sample at z~1.4 analyzed in a similar manner by Weiner et al. (2009; W09), but extends to lower redshifts and has specific star formation rates which are lower by ~0.6 dex. We identify outflows of cool gas from the Doppler shift of the MgII absorption lines and find that the equivalent width (EW) of absorption due to outflowing gas increases on average with M_* and star formation rate (SFR). We attribute the large EWs measured in spectra of the more massive, higher-SFR galaxies to optically thick absorbing clouds having large velocity widths. The outflows have hydrogen column densities N(H) > 10^19.3 cm^-2, and extend to velocities of ~500 km/s. While galaxies with SFR > 10 Msun/yr host strong outflows in both this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log M_*/Msun < 10.5) galaxies at lower redshifts. Using a simple galaxy evolution model which assumes exponentially declining SFRs, we infer that strong outflows persist in galaxies with log M_*/Msun > 10.5 as they age between z=1.4 and z~1, presumably because of their high absolute SFRs. Finally, using high resolution HST/ACS imaging in tandem with our spectral analysis, we find evidence for a weak trend (at 1 sigma significance) of increasing outflow absorption strength with increasing galaxy SFR surface density.
We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5/h_70 kpc. The background galaxy spectrum reveals strong FeII, MgII, MgI, and CaII
absorption at the redshift of the foreground galaxy, with a MgII 2796 rest equivalent width of 3.93 +/- 0.08 Angstroms, indicative of a velocity width exceeding 400 km/s. Because the background galaxy is large (> 4/h_70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M_*/M_sun = 11.15 +/- 0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak AGN. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude the absorbing gas was most likely ejected or tidally stripped from the interstellar medium of the host galaxy or its progenitors during the past starburst event. Adopting the latter interpretation, these results place one of only a few constraints on the radial extent of cool gas driven or stripped from a galaxy in the distant Universe. Future studies with integral field unit spectroscopy of spatially extended background galaxies will provide multiple sightlines through foreground absorbers and permit analysis of the morphology and kinematics of the gas surrounding galaxies with a diverse set of properties and environments.
We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the ~225 Myr old (log tau_cl = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV
imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. We find an effective temperature (T_eff) and surface gravity (log g) for each DA WD by fitting Balmer-line profiles from model atmospheres to the observed spectra. WD evolutionary models are then invoked to derive masses and cooling times for each DA WD. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population. Eight of the 17 DA WDs show significant CaII K absorption; comparison of the absorption strength with the WD distances suggests that the absorption is interstellar, though this cannot be confirmed with the current data.
