134 research outputs found
On the Cosmic Evolution of Fe/Mg in QSO Absorption Line Systems
We investigate the variation of the ratio of the equivalent widths of the
FeII2600 line to the MgII2796,2803 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
decreases monotonically with
increasing redshift over the range . Selecting the
subset of absorbers where the signal-to-noise ratio of the MgII equivalent
width is 3 and modeling the equivalent width ratio
distribution as a gaussian, we find that the mean of the gaussian distribution
varies as . 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 reflects the
evolution in the abundances, then it is consistent with the predictions of the
simple model.Comment: 10 pages, 4 figures, final version published in MNRA
Galaxies Probing Galaxies in PRIMUS - I. Sample, Spectroscopy, and Characteristics of the z~0.5 MgII-Absorbing Circumgalactic Medium
Spectroscopy of background QSO sightlines passing close to foreground
galaxies is a potent technique for studying the circumgalactic medium (CGM).
QSOs are effectively point sources, however, limiting their potential to
constrain the size of circumgalactic gaseous structures. Here we present the
first large Keck/LRIS and VLT/FORS2 spectroscopic survey of bright (B_AB <
22.3) background galaxies whose lines of sight probe MgII 2796, 2803 absorption
from the CGM around close projected foreground galaxies at transverse distances
10 kpc < R_perp < 150 kpc. Our sample of 72 projected pairs, drawn from the
PRIsm MUlti-object Survey (PRIMUS), includes 48 background galaxies which do
not host bright AGN, and both star-forming and quiescent foreground galaxies
with stellar masses 9.0 < log M_*/M_sun < 11.2 at redshifts 0.35 < z_f/g < 0.8.
We detect MgII absorption associated with these foreground galaxies with
equivalent widths 0.25 Ang 2sigma significance in 20
individual background sightlines passing within R_perp < 50 kpc, and place
2sigma upper limits on W_2796 of <0.5 Ang in an additional 11 close sightlines.
Within R_perp < 50 kpc, W_2796 is anticorrelated with R_perp, consistent with
analyses of MgII absorption detected along background QSO sightlines.
Subsamples of these foreground hosts divided at log M_*/M_sun = 9.9 exhibit
statistically inconsistent W_2796 distributions at 30 kpc < R_perp < 50 kpc,
with the higher-M_* galaxies yielding a larger median W_2796 by 0.9 Ang.
Finally, we demonstrate that foreground galaxies with similar stellar masses
exhibit the same median W_2796 at a given R_perp to within <0.2 Ang toward both
background galaxies and toward QSO sightlines drawn from the literature.
Analysis of these datasets constraining the spatial coherence scale of
circumgalactic MgII absorption is presented in a companion paper.Comment: 36 pages, 18 figures, 5 tables. Accepted to Ap
Dissecting the Gaseous Halos of z~2 Damped Ly Systems with Close Quasar Pairs
We use spectroscopy of close pairs of quasars to study diffuse gas in the
circumgalactic medium (CGM) surrounding a sample of 40 Damped Lya systems
(DLAs). The primary sightline in each quasar pair probes an intervening DLA in
the redshift range 1.6 < z_DLA < 3.6, such that the second quasar sightline
then probes Lya, CII, SiII, and CIV absorption in the CGM transverse to the DLA
to projected distances kpc. Analysis of the Lya profiles in
these CGM sightlines constrains the covering fraction (f_C) of optically thick
HI (having column density N_HI > 10^17.2 cm^-2) to be greater than ~30% within
kpc of DLAs. Strong SiII 1526 absorption with equivalent
width W_1526 > 0.2 Ang occurs with an incidence f_C (W_1526 > 0.2 Ang) =
20(+12/-8)% within kpc, indicating that low-ionization metal
absorption associated with DLAs probes material at a physical distance R_3D <
30 kpc. However, we find that strong CIV 1548 absorption is ubiquitous in these
environments (f_C (W_1548 > 0.2 Ang) = 57(+12/-13)% within
kpc), and in addition exhibits a high degree of kinematic coherence on scales
up to ~175 kpc. We infer that this high-ionization material arises
predominantly in large, quiescent structures extending beyond the scale of the
DLA host dark matter halos rather than in ongoing galactic winds. The Lya
equivalent width in the DLA-CGM is anticorrelated with at >98%
confidence, suggesting that DLAs arise close to the centers of their host halos
rather than on their outskirts. Finally, the average Lya, CII and CIV
equivalent widths are consistent with those measured around z~2 Lyman Break
Galaxies. Assuming that DLAs trace a galaxy population with lower masses and
luminosities, this finding implies that the absorption strength of cool
circumgalactic material has a weak dependence on dark matter halo mass for M_h
< 10^12 M_sun.Comment: Submitted to ApJ. 30 pages, 13 figures, 3 tables, 1 appendix. Uses
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Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5
We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption
line profiles in individual spectra of 105 galaxies at 0.3<z<1.4. The galaxies,
drawn from redshift surveys of the GOODS fields and the Extended Groth Strip,
fully sample the range in star formation rates (SFRs) occupied by the
star-forming sequence with stellar masses log M_*/M_sun > 9.5 at 0.3<z<0.7.
Using the Doppler shifts of the MgII and FeII absorption lines as tracers of
cool gas kinematics, we detect large-scale winds in 66+/-5% of the galaxies.
HST/ACS imaging and our spectral analysis indicate that the outflow detection
rate depends primarily on galaxy orientation: winds are detected in ~89% of
galaxies having inclinations (i) <30 degrees (face-on), while the wind
detection rate is only ~45% in objects having i>50 degrees (edge-on). Combined
with the comparatively weak dependence of the wind detection rate on intrinsic
galaxy properties, this suggests that biconical outflows are ubiquitous in
normal, star-forming galaxies at z~0.5. We find that the wind velocity is
correlated with host galaxy M_* at 3.4-sigma significance, while the equivalent
width of the flow is correlated with host galaxy SFR at 3.5-sigma significance,
suggesting that hosts with higher SFR may launch more material into outflows
and/or generate a larger velocity spread for the absorbing clouds. Assuming
that the gas is launched into dark matter halos with simple, isothermal density
profiles, the wind velocities measured for the bulk of the cool material
(~200-400 km/s) are sufficient to enable escape from the halo potentials only
for the lowest-M_* systems in the sample. However, the outflows typically carry
sufficient energy to reach distances of >50 kpc, and may therefore be a viable
source of cool material for the massive circumgalactic medium observed around
bright galaxies at z~0. [abridged]Comment: Submitted to ApJ. 61 pages, 25 figures, 4 tables, 4 appendices. Uses
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