3,292 research outputs found
Interstellar Mg II and C IV absorption by 1 1/2 galaxies along the sightline to MrK 205
The first results of our HST survey designed to search for Mg 2 and C 4 absorption lines from the disks and halos of low-redshift galaxies using background QSO's and supernovae as probes are presented. Our survey utilizes the high resolution of the Goddard High Resolution Spectrograph enabling us to calculate the column densities and doppler parameters of individual components within an absorption complex, and hence determine the physical conditions of the absorbing gas. Observing the complexity of the absorption line profiles i.e., the velocity distribution and total velocity extent of the constituent components, offers an important description of the kinematics of the absorbing gas, and hence an understanding of its origin. Focus is on one sight line in particular, that towards Mrk 205, which passes 3-5 kpc from the intervening galaxy NGC 4319. Mg 2 and C 4 absorption from both local Milky Way halo gas and from NGC 4319 is detected
The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in
the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs
and AGN as probes. The foreground galaxies are intercepted between 26 and 199
h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s
of the galaxies' systemic velocities. The intervening galaxies have a wide
range of luminosities, from M_B = -17.1 to -20.0, and reside in various
environments: half the galaxies are relatively isolated, the remainder form
parts of groups or clusters of varying richness. The equivalent widths of the
Lya lines range from 0.08 - 0.68 A and, with the notable exception of
absorption from one pair, crudely correlate with sightline separation in a way
consistent with previously published data, though the column densities derived
from the lines do not. The lack of correlation between line strength and galaxy
luminosity or, in particular, the environment of the galaxy, suggests that the
absorption is not related to any individual galaxy, but arises in gas which
follows the same dark-matter structures that the galaxies inhabit.Comment: 8 pages, invited review to appear in the proceedings of the Yale
Cosmology Workshop on `The Shapes of Galaxies & their Halos", P. Natarajan,
ed. Best figures found in (17Mb) PS file at
http://astro.princeton.edu/~dvb/yale.p
Redshifts of galaxies close to bright QSO lines of sight
To expand the known number of low-redshift galaxies which lie close to bright
() QSO lines of sight, we have identified 24 galaxies within 11
arcmins of nine QSOs which have been observed with the Hubble Space Telescope
(HST). Galaxies are found between redshifts of and lie between
kpc from QSO sightlines. Knowing the redshifts of these
galaxies has already proved important in understanding results from HST
programmes designed to search for UV absorption lines from low-redshift
galaxies, and will enable future observations to probe the halos of these
galaxies in detail.Comment: MNRAS in press. 9 pages LaTeX using MNRAS sty. Postscript figures are
excluded due to large size. Paper with figures can be obtained from
http://www.roe.ac.uk/research/bowen1.ps.
A Comparison of Absorption and Emission Line Abundances in the Nearby Damped Lyman-alpha Galaxy SBS 1543+593
We have used the Space Telescope Imaging Spectrograph (STIS) aboard HST to
measure a sulfur abundance of [S/H] = -0.41 +/-0.06 in the interstellar medium
(ISM) of the nearby damped Lyman-alpha (DLA) absorbing galaxy SBS 1543+593. A
direct comparison between this QSO absorption line abundance on the one hand,
and abundances measured from HII region emission line diagnostics on the other,
yield the same result: the abundance of sulfur in the neutral ISM is in good
agreement with that of oxygen measured in an HII region 3 kpc away. Our result
contrasts with those of other recent studies which have claimed
order-of-magnitude differences between HI (absorption) and HII (emission)
region abundances. We also derive a nickel abundance of [Ni/H] < -0.81, some
three times less than that of sulfur, and suggest that the depletion is due to
dust, although we cannot rule out an over-abundance of alpha-elements as the
cause of the lower metallicity. It is possible that our measure of [S/H] is
over-estimated if some SII arises in ionized gas; adopting a plausible star
formation rate for the galaxy along the line of sight, and a measurement of the
CII* 1335.7 absorption line detected from SBS 1543+593, we determine that the
metallicity is unlikely to be smaller than we derive by more than 0.25 dex. We
estimate that the cooling rate of the cool neutral medium is log [l_c (ergs
s^{-1} H atom^{-1})] = -27.0, the same value as that seen in the high redshift
DLA population.Comment: 31 pages; accepted for publication in the Ap
21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593
We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS
1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the
spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate
measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and
derive a mass of 1.3e9 solar masses. We compare this value with limits obtained
towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have
been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible
for DLA systems at even modest redshifts without being detectable from their
21-cm emission.Comment: 4 pages, 1 figure, accepted for publication in A&
The O VI Absorbers Toward PG0953+415: High Metallicity, Cosmic-Web Gas Far From Luminous Galaxies
The spectrum of the low-redshift QSO PG0953+415 shows two strong, intervening
O VI absorption systems. To study the nature of these absorbers, we have used
the Gemini Multiobject Spectrograph to conduct a deep spectroscopic galaxy
redshift survey in the 5' x 5' field centered on the QSO. This survey is fully
complete for r' < 19.7 and is 73% complete for r' < 21.0. We find three
galaxies at the redshift of the higher-z O VI system (z = 0.14232) including a
galaxy at projected distance rho = 155 kpc. We find no galaxies in the Gemini
field at the redshift of the lower-z O VI absorber (z = 0.06807), which
indicates that the nearest galaxy is more than 195 kpc away or has L < 0.04 L*.
Previous shallower surveys covering a larger field have shown that the z =
0.06807 O VI absorber is affiliated with a group/filament of galaxies, but the
nearest known galaxy has rho = 736 kpc. The z = 0.06807 absorber is notable for
several reasons. The absorption profiles reveal simple kinematics indicative of
quiescent material. The H I line widths and good alignment of the H I and metal
lines favor photoionization and, moreover, the column density ratios imply a
high metallicity: [M/H] = -0.3 +/- 0.12. The z = 0.14232 O VI system is more
complex and less constrained but also indicates a relatively high metallicity.
Using galaxy redshifts from SDSS, we show that both of the PG0953+415 O VI
absorbers are located in large-scale filaments of the cosmic web. Evidently,
some regions of the web filaments are highly metal enriched. We discuss the
origin of the high-metallicity gas and suggest that the enrichment might have
occurred long ago (at high z).Comment: Submitted for publication in the Astrophysical Journal Letters. Figs.
1 and 2 compressed for astro-ph. High-resolution version available at
http://www.astro.umass.edu/~tripp/astro/qualitypreps/pg0953tripp.pd
A Sub-Damped Ly Absorber with Unusual Abundances: Evidence of Gas Recycling in a Low-Redshift Galaxy Group
Using Hubble Space Telescope/Space Telescope Imaging Spectrograph G140M
spectroscopy, we investigate an absorption-line system at =0.07489 in the
spectrum of the quasi-stellar object PG 1543+489 (=0.401). The
sightline passes within kpc of an edge-on disk galaxy at a
similar redshift, but the galaxy belongs to a group with four other galaxies
within kpc. We detect H I [log (H I/) = 19.120.04]
as well as N I, Mg II, Si II, and Si III, from which we measure a gas-phase
abundance of [N/H] = . Photoionization models indicate that the
nitrogen-to-silicon relative abundance is solar, yet magnesium is underabundant
by a factor of 2. We also report spatially resolved emission-line
spectroscopy of the nearby galaxy, and we extract its rotation curve. The
galaxy's metallicity is higher than [N/H] in the absorber,
and interestingly, the absorber velocities suggest that the gas at 66
kpc is corotating with the galaxy's stellar disk, possibly with an inflow
component. These characteristics could indicate that this sub-damped Ly
absorber system arises in a "cold-accretion" flow. However, the absorber
abundance patterns are peculiar. We hypothesize that the gas was ejected from
its galaxy of origin (or perhaps is a result of tidal debris from interactions
between the group galaxies) with a solar nitrogen abundance, but that
subsequently mixed with (and was diluted by) gas in the circumgalactic medium
(CGM) or group. If the gas is bound to the nearby galaxy, this system may be an
example of the gas "recycling" predicted by theoretical galaxy simulations. Our
hypothesis is testable with future observations.Comment: 16 pages (in print): The Astrophysical Journal, vol 872, 12
The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in
the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs
and AGN as probes. The foreground galaxies are intercepted between 26 and 199
h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s
of the galaxies' systemic velocities. The intervening galaxies have a wide
range of luminosities, from M_B = -17.1 to -20.0, and reside in various
environments: half the galaxies are relatively isolated, the remainder form
parts of groups or clusters of varying richness. The equivalent widths of the
Lya lines range from 0.08 - 0.68 A and, with the notable exception of
absorption from one pair, crudely correlate with sightline separation in a way
consistent with previously published data, though the column densities derived
from the lines do not. The lack of correlation between line strength and galaxy
luminosity or, in particular, the environment of the galaxy, suggests that the
absorption is not related to any individual galaxy, but arises in gas which
follows the same dark-matter structures that the galaxies inhabit.Comment: 8 pages, invited review to appear in the proceedings of the Yale
Cosmology Workshop on `The Shapes of Galaxies & their Halos", P. Natarajan,
ed. Best figures found in (17Mb) PS file at
http://astro.princeton.edu/~dvb/yale.p
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