19 research outputs found
Element Abundances at High-redshift: Magellan MIKE Observations of sub-Damped Lyman-alpha Absorbers at 1.7 < z <2.4
We present chemical abundance measurements from high-resolution observations
of 5 sub-damped Lyman-alpha absorbers at 1.7 < z < 2.4 observed with the
Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II
Clay telescope. Lines of Zn II, Mg I, Mg II, Al II, Al III, S II, Si II, Si IV,
C II, C II*, C IV, Ni II, Mn II and Fe II were detected and column densities
were determined. The metallicity of the absorbing gas, inferred from the nearly
undepleted element Zn, is in the range of < -0.95 to +0.25 dex for the five
absorbers in our sample, with three of the systems being near-solar or
super-solar. We also investigate the effect of ionisation on the observed
abundances using photoionisation modelling. Combining our data with other
sub-DLA and DLA data from the literature, we report the most complete existing
determination of the metallicity vs. redshift relation for sub-DLAs and DLAs.
We confirm the suggestion from previous investigations that sub-DLAs are, on
average, more metal-rich than DLAs and evolve faster. We also discuss relative
abundances and abundance ratios in these absorbers. The more metal-rich systems
show significant dust depletion levels, as suggested by the ratios [Zn/Cr] and
[Zn/Fe]. For the majority of the systems in our sample, the [Mn/Fe] vs. [Zn/H]
trend is consistent with that seen previously for lower-redshift sub-DLAs. We
also measure the velocity width values for the sub-DLAs in our sample from
unsaturated absorption lines of Fe II 2344, 2374, 2600 A, and examine where
these systems lie in a plot of metallicity vs. velocity dispersion. Finally, we
examine cooling rate vs. H I column density in these sub-DLAs, and compare this
with the data from DLAs and the Milky Way ISM. We find that most of the systems
in our sample show higher cooling rate values compared to those seen in the
DLAs.Comment: Accepted for publication in the Monthly Notices of The Royal
Astronomical Societ
Hubble Space Telescope Observations of Sub-Damped Lyman-alpha Absorbers at z < 0.5, and Implications for Galaxy Chemical Evolution
We report observations of four sub-damped Lyman-alpha (sub-DLA) quasar
absorbers at z<0.5 obtained with the Hubble Space Telescope Cosmic Origins
Spectrograph. We measure the available neutrals or ions of C, N, O, Si, P, S,
Ar, Mn, Fe, and/or Ni. Our data have doubled the sub-DLA metallicity samples at
z<0.5 and improved constraints on sub-DLA chemical evolution. All four of our
sub-DLAs are consistent with near-solar or super-solar metallicities and
relatively modest ionization corrections; observations of more lines and
detailed modeling will help to verify this. Combining our data with
measurements from the literature, we confirm previous suggestions that the
N(HI)-weighted mean metallicity of sub-DLAs exceeds that of DLAs at all
redshifts studied, even after making ionization corrections for sub-DLAs. The
absorber toward PHL 1598 shows significant dust depletion. The absorbers toward
PHL 1226 and PKS 0439-433 show the S/P ratio consistent with solar, i.e., they
lack a profound odd-even effect. The absorber toward Q0439-433 shows
super-solar Mn/Fe. For several sub-DLAs at z<0.5, [N/S] is below the level
expected for secondary N production, suggesting a delay in the release of the
secondary N or a tertiary N production mechanism. We constrain the electron
density using Si II* and C II* absorption. We also report different metallicity
vs. Delta V_90 relations for sub-DLAs and DLAs. For two sub-DLAs with
detections of emission lines from the underlying galaxies, our measurements of
the absorption-line metallicities are consistent with the emission-line
metallicities, suggesting that metallicity gradients are not significant in
these galaxies.Comment: 77 pages, 13 figures; accepted for publication in the Astrophysical
Journal. Submitted (in the original form) May 26, 2014; accepted Apr. 15,
201
New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA
We present chemical abundance measurements from high resolution observations
of 7 sub-damped Lyman-alpha absorbers and 1 damped Lyman-alpha system at z<1.5.
Three of these objects have high metallicity, with near or super-solar Zn
abundance. Grids of Cloudy models for each system were constructed to look for
possible ionization effects in these systems. For the systems in which we could
constrain the ionization parameter, we find that the ionization corrections as
predicted by the Cloudy models are generally small and within the typical error
bars (~0.15 dex), in general agreement with previous studies. The Al III to Al
II ratio for these and other absorbers from the literature are compared, and we
find that while the sub-DLAs have a larger scatter in the Al III to Al II
ratios than the DLAs, there appears to be little correlation between the ratio
and N(H I). The relationship between the metallicity and the velocity width of
the profile for these systems is investigated. We show that the sub-DLAs that
have been observed to date follow a similar trend as DLA absorbers, with the
more metal rich systems exhibiting large velocity widths. We also find that the
systems at the upper edge of this relationship with high metallicities and
large velocity widths are more likely to be sub-DLAs than DLA absorbers,
perhaps implying that the sub-DLA absorbers are more representative of massive
galaxies.Comment: 15 pages, 15 Figures, Accepted by MNRAS, updated references and
author
Do Damped and Sub-damped Lyman-alpha Absorbers Arise in Galaxies of Different Masses?
We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA
absorbers in quasar spectra differ intrinsically in metallicity, and whether
they could arise in galaxies of different masses. Using the recent measurements
of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm
that sub-DLAs have higher mean metallicities than DLAs, especially at . We find that the intercept of the metallicity-redshift relation
derived from Zn and S is higher than that derived from Fe by 0.5-0.6 dex. We
also show that, while there is a correlation between the metallicity and the
rest equivalent width of Mg II or Fe II for DLAs,
no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II
selection criteria employed in the discovery of both types of systems at lower
redshifts, the difference between metallicities of DLAs and sub-DLAs appears to
be real and not an artefact of selection. This conclusion is supported by our
simulations of Mg II and Fe II lines for a wide
range of physical conditions. On examining the velocity spreads of the
absorbers, we find that sub-DLAs show somewhat higher mean and median velocity
spreads (), and an excess of systems with km
s, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for
sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and
thick disk stars, possibly suggesting different stellar populations. The
absorber data appear to be consistent with galaxy down-sizing. The data are
also consistent with the relative number densities of low-mass and high-mass
galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on
average than DLAs.Comment: 27 pages, 5 figures, 4 tables. Accepted for publication in New
Astronom
Metal line emission from galaxy haloes at z~1
We present a study of the metal-enriched halo gas, traced using MgII and
[OII] emission lines, in two large, blind galaxy surveys - the MUSE (Multi Unit
Spectroscopic Explorer) Analysis of Gas around Galaxies (MAGG) and the MUSE
Ultra Deep Field (MUDF). By stacking a sample of ~600 galaxies (stellar masses
M* ~10^{6-12} Msun), we characterize for the first time the average metal line
emission from a general population of galaxy haloes at 0.7 <= z <= 1.5. The
MgII and [OII] line emission extends farther out than the stellar continuum
emission, on average out to ~25 kpc and ~45 kpc, respectively, at a surface
brightness (SB) level of 10^{-20} erg/s/cm2/arcsec2. The radial profile of the
MgII SB is shallower than that of the [OII], suggesting that the resonant MgII
emission is affected by dust and radiative transfer effects. The [OII] to MgII
SB ratio is ~3 over ~20-40 kpc, also indicating a significant in situ origin of
the extended metal emission. The average SB profiles are intrinsically brighter
by a factor ~2-3 and more radially extended by a factor of ~1.3 at 1.0 < z <=
1.5 than at 0.7 <= z <= 1.0. The average extent of the metal emission also
increases independently with increasing stellar mass and in overdense group
environments. When considering individual detections, we find extended [OII]
emission up to ~50 kpc around ~30-40 percent of the group galaxies, and
extended (~30-40 kpc) MgII emission around two z~1 quasars in groups, which
could arise from outflows or environmental processes.Comment: 24 pages, 21 figures, 2 tables, accepted for publication in MNRA
Discovery of Super-enriched Gas 1 Gyr after the Big Bang
International audienceAbundances of chemical elements in the interstellar and circumgalactic media of high-redshift galaxies offer important constraints on the nucleosynthesis by early generations of stars. Damped Lyα absorbers (DLAs) in spectra of high-redshift background quasars are excellent sites for obtaining robust measurements of element abundances in distant galaxies. Past studies of DLAs at redshifts z > 4 have measured abundances of âČ0.01 solar. Here we report the discovery of a DLA at z = 4.7372 with an exceptionally high degree of chemical enrichment. We estimate the H I column density in this absorber to be log (N H I/cm-2) = 20.48 ± 0.15. Our analysis shows unusually high abundances of carbon and oxygen ([C/H] = 0.88 ± 0.17, [O/H] = 0.71 ± 0.16). Such a high level of enrichment a mere 1.2 Gyr after the Big Bang is surprising because of insufficient time for the required amount of star formation. To our knowledge, this is the first supersolar absorber found at z > 4.5. We find the abundances of Si and Mg to be [Si/H] = and [Mg/H] = , confirming the metal-rich nature of this absorber. By contrast, Fe shows a much lower abundance ([Fe/H] = ). We discuss implications of our results for galactic chemical evolution models. The metallicity of this absorber is higher than that of any other known DLA and is >2 orders of magnitude above predictions of chemical evolution models and the N H I-weighted mean metallicity from previous studies at z > 4.5. The relative abundances (e.g., [O/Fe] = 2.29 ± 0.05, [C/Fe] = 2.46 ± 0.08) are also highly unusual compared to predictions for enrichment by early stars
The Baryonic Content of Galaxies Mapped by MaNGA and the Gas Around Them
International audienceWe analyze the cool gas in and around 14 nearby galaxies (at z 13 to ~1020 cm-2 and decreases with impact parameter for r âł R e . Galaxies with higher stellar mass have weaker H I absorption. Comparing absorption velocities with MaNGA radial velocity maps of ionized gas line emissions in galactic disks, we find that the neutral gas seen in absorption corotates with the disk out to ~10 R e . Sight lines with lower elevation angles show lower metallicities, consistent with the metallicity gradient in the disk derived from MaNGA maps. Higher-elevation angle sight lines show higher ionization, lower H I column density, supersolar metallicity, and velocities consistent with the direction of galactic outflow. Our data offer the first detailed comparisons of circumgalactic medium (CGM) properties (kinematics and metallicity) with extrapolations of detailed galaxy maps from integral field spectroscopy; similar studies for larger samples are needed to more fully understand how galaxies interact with their CGM