241 research outputs found
The Pittsburgh Sloan Digital Sky Survey MgII Quasar Absorption-Line Survey Catalog
We present a catalog of intervening MgII quasar absorption-line systems in
the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan
Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the
catalog contains > 17,000 measured MgII doublets. We also present data on the
~44,600 quasar spectra which were searched to construct the catalog, including
redshift and magnitude information, continuum-normalized spectra, and
corresponding arrays of redshift-dependent minimum rest equivalent widths
detectable at our confidence threshold. The catalog is available on the web. A
careful second search of 500 random spectra indicated that, for every 100
spectra searched, approximately one significant MgII system was accidentally
rejected. Current plans to expand the catalog beyond DR4 quasars are discussed.
Many MgII absorbers are known to be associated with galaxies. Therefore, the
combination of large size and well understood statistics makes this catalog
ideal for precision studies of the low-ionization and neutral gas regions
associated with galaxies at low to moderate redshift. An analysis of the
statistics of MgII absorbers using this catalog will be presented in a
subsequent paper.Comment: AJ, in pres
Mg II Absorption Systems in SDSS QSO Spectra
We present the results of a MgII absorption-line survey using QSO spectra
from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than
0.3\AA and redshifts were identified and measured. We
find that the rest equivalent width ()
distribution is described very well by an exponential function , with
and \AA. Previously reported power law
fits drastically over-predict the number of strong lines. Extrapolating our
exponential fit under-predicts the number of \AA systems,
indicating a transition in near \AA. A combination of
two exponentials reproduces the observed distribution well, suggesting that
MgII absorbers are the superposition of at least two physically distinct
populations of absorbing clouds. We also derive a new redshift parameterization
for the number density of \AA lines:
and \AA. We find that the distribution steepens with decreasing redshift,
with decreasing from \AA at to \AA at
. The incidence of moderately strong MgII lines does not
show evidence for evolution with redshift. However, lines stronger than
\AA show a decrease relative to the no-evolution prediction with
decreasing redshift for . The evolution is stronger for
increasingly stronger lines. Since in saturated absorption lines is an
indicator of the velocity spread of the absorbing clouds, we interpret this as
an evolution in the kinematic properties of galaxies from moderate to low z.Comment: 50 pages, 26 figures, accepted for publication in Ap
Double-Damped Lyman Alpha Absorption: A Possible Large Neutral Hydrogen Gas Filament Near Redshift z=1
We report the discovery of two damped Ly-alpha absorption-line systems (DLAs)
near redshift z=1 along a single quasar sightline (Q1727+5302) with neutral
hydrogen column densities of N(HI) = (1.45\pm0.15)\times10^{21} and
(2.60\pm0.20)\times10^{21} atoms/cm2. Their sightline velocity difference of
13,000 km/s corresponds to a proper separation of 106h_{70}^{-1} Mpc if
interpreted as the Hubble flow (Omega_m=0.3, Omega_Lambda=0.7). The random
probability of such an occurrence is significantly less than 3%. With follow-up
spectroscopy, we find [Zn/H] = -0.58\pm0.15 (26.5% solar) and -1.32\pm0.28
(4.7% solar), respectively, and [Cr/H] = -1.26\pm0.15 (5.5% solar) and
-1.77\pm0.28 (1.7% solar), respectively, which is evidence for depletion onto
grains. Follow-up IR images show the two most likely DLA galaxy candidates to
have impact parameters of 22h_{70}^{-1} kpc and 32h_{70}^{-1} kpc if near z=1.
They are significantly underluminous relative to the galaxy population at z=1.
To investigate the possibility of additional high-N(HI) absorbers we have
searched the SDSS database for z>1 quasars within 30 arcmin of the original
sightline. Five were found, and two show strong MgII-FeII absorption near z=1,
consistent with classical DLA absorption approx 37% of the time, but almost
always N(HI) > 10^{19} atoms/cm2. Consequently, this rare configuration of four
high-N(HI) absorbers with a total sightline velocity extent of 30,600 km/s may
represent a large filament-like structure stretching over a proper distance of
241h_{70}^{-1} Mpc along our sightline, and a region in space capable of
harboring excessive amounts of neutral gas. Future studies of this region of
the sky are encouraged.Comment: ApJL, accepte
A Refined Estimate of the Ionizing Emissivity from Galaxies at z ≃ 3: Spectroscopic Follow-up in the SSA22a Field
We investigate the contribution of star-forming galaxies to the ionizing background at z ~ 3, building on previous work based on narrowband (NB3640) imaging in the SSA22a field. We use new Keck/LRIS spectra of Lyman break galaxies (LBGs) and narrowband-selected Lyα emitters (LAEs) to measure redshifts for 16 LBGs and 87 LAEs at z > 3.055, such that our NB3640 imaging probes the Lyman-continuum (LyC) region. When we include the existing set of spectroscopically confirmed LBGs, our total sample with z > 3.055 consists of 41 LBGs and 91 LAEs, of which 9 LBGs and 20 LAEs are detected in our NB3640 image. With our combined imaging and spectroscopic data sets, we critically investigate the origin of NB3640 emission for detected LBGs and LAEs. We remove from our samples three LBGs and three LAEs with spectroscopic evidence of contamination of their NB3640 flux by foreground galaxies and statistically model the effects of additional, unidentified foreground contaminants. The resulting contamination and LyC-detection rates, respectively, are 62% ± 13% and 8% ± 3% for our LBG sample, and 47% ± 10% and 12% ± 2% for our LAE sample. The corresponding ratios of non-ionizing UV to LyC flux density, corrected for intergalactic medium (IGM) attenuation, are 18.0^(+34.8)_(–7.4) for LBGs and 3.7^(+2.5)_(–1.1) for LAEs. We use these ratios to estimate the total contribution of star-forming galaxies to the ionizing background and the hydrogen photoionization rate in the IGM, finding values larger than, but consistent with, those measured in the Lyα forest. Finally, the measured UV to LyC flux-density ratios imply model-dependent LyC escape fractions of f^(LyC)_(esc) ~ 5%-7% for our LBG sample and f^(LyC)_(esc) ~ 10%-30% for our fainter LAE sample
Large scale outflows from z ~ 0.7 starburst galaxies identified via ultra-strong MgII quasar absorption lines
(Abridged) Star formation-driven outflows are a critical phenomenon in
theoretical treatments of galaxy evolution, despite the limited ability of
observations to trace them across cosmological timescales. If the strongest
MgII absorption-line systems detected in the spectra of background quasars
arise in such outflows, "ultra-strong" MgII (USMgII) absorbers would identify
significant numbers of galactic winds over a huge baseline in cosmic time, in a
manner independent of the luminous properties of the galaxy. To this end, we
present the first detailed imaging and spectroscopic study of the fields of two
USMgII absorber systems culled from a statistical absorber catalog, with the
goal of understanding the physical processes leading to the large velocity
spreads that define such systems. Each field contains two bright emission-line
galaxies at similar redshift (dv < 300 km/s) to that of the absorption.
Lower-limits on their instantaneous star formation rates (SFR) from the
observed OII and Hb line fluxes, and stellar masses from spectral template
fitting indicate specific SFRs among the highest for their masses at z~0.7.
Additionally, their 4000A break and Balmer absorption strengths imply they have
undergone recent (~0.01 - 1 Gyr) starbursts. The concomitant presence of two
rare phenomena - starbursts and USMgII absorbers - strongly implies a causal
connection. We consider these data and USMgII absorbers in general in the
context of various popular models, and conclude that galactic outflows are
generally necessary to account for the velocity extent of the absorption. We
favour starburst driven outflows over tidally-stripped gas from a major
interaction which triggered the starburst as the energy source for the majority
of systems. Finally, we discuss the implications of these results and speculate
on the overall contribution of such systems to the global SFR density at z~0.7.Comment: 15 pages, 6 figure, accepted for publication by MNRA
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