50 research outputs found
Element Abundances in a Gas-rich Galaxy at z = 5: Clues to the Early Chemical Enrichment of Galaxies
Element abundances in high-redshift quasar absorbers offer excellent probes
of the chemical enrichment of distant galaxies, and can constrain models for
population III and early population II stars. Recent observations indicate that
the sub-damped Lyman-alpha (sub-DLA) absorbers are more metal-rich than DLA
absorbers at redshifts 03. It has also been suggested that the DLA
metallicity drops suddenly at 4.7. However, only 3 DLAs at 4.5 and
none at 3.5 have "dust-free" metallicity measurements of undepleted
elements. We report the first quasar sub-DLA metallicity measurement at
3.5, from detections of undepleted elements in high-resolution data for a
sub-DLA at =5.0. We obtain fairly robust abundances of C, O, Si, and Fe,
using lines outside the Lyman-alpha forest. This absorber is metal-poor, with
O/H]=-2.000.12, which is 4 below the level expected from
extrapolation of the trend for 3.5 sub-DLAs. The C/O ratio is
1.8 times lower than in the Sun. More strikingly, Si/O is
3.2 times lower than in the Sun, while Si/Fe is nearly
(1.2 times) solar. This absorber does not display a clear
alpha/Fe enhancement. Dust depletion may have removed more Si from the gas
phase than is common in the Milky Way interstellar medium, which may be
expected if high-redshift supernovae form more silicate-rich dust. C/O and Si/O
vary substantially between different velocity components, indicating spatial
variations in dust depletion and/or early stellar nucleosynethesis (e.g.,
population III star initial mass function). The higher velocity gas may trace
an outflow enriched by early stars.Comment: 42 pages including 9 figures, accepted for publication in Ap
Keck and VLT Observations of Super-damped Lyman-alpha Absorbers at z=2=2.5: Constraints on Chemical Compositions and Physical Conditions
We report Keck/ESI and VLT/UVES observations of three super-damped
Lyman-alpha quasar absorbers with H I column densities log N(HI) >= 21.7 at
redshifts z=2-2.5. All three absorbers show similar metallicities (-1.3 to -1.5
dex), and dust depletion of Fe, Ni, and Mn. Two of the absorbers show
supersolar [S/Zn] and [Si/Zn]. We combine our results with those for other DLAs
to examine trends between N(HI), metallicity, dust depletion. A larger fraction
of the super-DLAs lie close to or above the line [X/H]=20.59-log N(HI) in the
metallicity vs. N(HI) plot, compared to the less gas-rich DLAs, suggesting that
super-DLAs are more likely to be rich in molecules. Unfortunately, our data for
Q0230-0334 and Q0743+1421 do not cover H2 absorption lines. For Q1418+0718,
some H2 lines are covered, but not detected. CO is not detected in any of our
absorbers. For DLAs with log N(HI) < 21.7, we confirm strong correlation
between metallicity and Fe depletion, and find a correlation between
metallicity and Si depletion. For super-DLAs, these correlations are weaker or
absent. The absorbers toward Q0230-0334 and Q1418+0718 show potential
detections of weak Ly-alpha emission, implying star formation rates of about
1.6 and 0.7 solar masses per year, respectively (ignoring dust extinction).
Upper limits on the electron densities from C II*/C II or Si II*/Si II are low,
but are higher than the median values in less gas-rich DLAs. Finally, systems
with log N(HI) > 21.7 may have somewhat narrower velocity dispersions delta
v_90 than the less gas-rich DLAs, and may arise in cooler and/or less turbulent
gas.Comment: 57 pages, 15 figures. Accepted for publication in Ap
A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - VI. Metallicity and Geometry as Gas Flow Probes
The use of background quasars provides a powerful tool to probe the cool gas
in the circum-galactic medium of foreground galaxies. Here, we present new
observations with SINFONI and X-Shooter of absorbing-galaxy candidates at
z=0.7-1. We report the detection with both instruments of the H-alpha emission
line of one sub-DLA at z_abs=0.94187 with log N(HI)=19.38^+0.10_-0.15 towards
SDSS J002133.27+004300.9. We estimate the star formation rate: SFR=3.6+/-2.2
solar masses per year in that system. A detailed kinematic study indicates a
dynamical mass M_dyn=10^9.9+/-0.4 solar masses and a halo mass
M_halo=10^11.9+/-0.5 solar masses. In addition, we report the OII detection
with X-Shooter of another DLA at z_abs=0.7402 with log N(HI)=20.4+/-0.1 toward
Q0052+0041 and an estimated SFR of 5.3+/-0.7 solar masses per year. Three other
objects are detected in the continuum with X-Shooter but the nature and
redshift of two of these objects are unconstrained due to the absence of
emission lines, while the third object might be at the redshift of the quasar.
We use the objects detected in our whole N(HI)-selected SINFONI survey to
compute the metallicity difference between the galaxy and the absorbing gas,
delta_HI(X), where a positive (negative) value indicates infall (outflow). We
compare this quantity with the quasar line of sight alignment with the galaxy's
major (minor) axis, another tracer of infall (outflow). We find that these
quantities do not correlate as expected from simple assumptions. Additional
observations are necessary to relate these two independent probes of gas flows
around galaxies.Comment: 16 pages, 8 figures, accepted for publication in MNRA
Fireball Multi Object Spectrograph: As-built optic performances
Fireball (Faint Intergalactic Redshifted Emission Balloon) is a NASA/CNES balloon-borne experiment to study the faint diffuse circumgalactic medium from the line emissions in the ultraviolet (200 nm) above 37 km flight altitude. Fireball relies on a Multi Object Spectrograph (MOS) that takes full advantage of the new high QE, low noise 13 μm pixels UV EMCCD. The MOS is fed by a 1 meter diameter parabola with an extended field (1000 arcmin2) using a highly aspherized two mirror corrector. All the optical train is working at F/2.5 to maintain a high signal to noise ratio. The spectrograph (R~ 2200 and 1.5 arcsec FWHM) is based on two identical Schmidt systems acting as collimator and camera sharing a 2400 g/mm aspherized reflective Schmidt grating. This grating is manufactured from active optics methods by double replication technique of a metal deformable matrix whose active clear aperture is built-in to a rigid elliptical contour. The payload and gondola are presently under integration at LAM. We will present the alignment procedure and the as-built optic performances of the Fireball instrument
The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman- Metallicity Measurements and the Circum-Galactic Medium
The Circum-Galactic Medium (CGM) can be probed through the analysis of
absorbing systems in the line-of-sight to bright background quasars. We present
measurements of the metallicity of a new sample of 15 sub-damped Lyman-
absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with
redshift 0.584 < < 3.104 from the ESO Ultra-Violet Echelle
Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine
these results with other measurements from the literature to produce a
compilation of metallicity measurements for 92 sub-DLAs as well as a sample of
362 DLAs. We apply a multi-element analysis to quantify the amount of dust in
these two classes of systems. We find that either the element depletion
patterns in these systems differ from the Galactic depletion patterns or they
have a different nucleosynthetic history than our own Galaxy. We propose a new
method to derive the velocity width of absorption profiles, using the modeled
Voigt profile features. The correlation between the velocity width delta_V90 of
the absorption profile and the metallicity is found to be tighter for DLAs than
for sub-DLAs. We report hints of a bimodal distribution in the [Fe/H]
metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher
redshifts. This feature can be interpreted as a signature from the metal-poor,
accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs
at low redshifts.Comment: 64 pages, 31 figures, 27 tables. Submitted to MNRA
Noise and dark performance for FIREBall-2 EMCCD delta-doped CCD detector
The Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2) is an experiment designed to observe low density emission from HI, CIV, and OVI in the circum-galactic medium around low-redshift galaxies. To detect this diffuse emission, we use a high-efficiency photon-counting EMCCD as part of FIREBall-2's detector. The flight camera system includes a custom printed circuit board, a mechanical cryo-cooler, zeolite and charcoal getters, and a Nüvü controller, for fast read-out speeds and waveform shaping. Here we report on overall detector system performance, including pressure and temperature stability. We describe dark current and CIC measurements at several temperatures and substrate voltages, with the flight set-up
Gas Accretion via Lyman Limit Systems
In cosmological simulations, a large fraction of the partial Lyman limit
systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes
large-scale flows in and out of galaxies through their circumgalactic medium
(CGM). The overall low metallicity of the cold gaseous streams feeding galaxies
seen in these simulations is the key to differentiating them from metal rich
gas that is either outflowing or being recycled. In recent years, several
groups have empirically determined an entirely new wealth of information on the
pLLSs and LLSs over a wide range of redshifts. A major focus of the recent
research has been to empirically determine the metallicity distribution of the
gas probed by pLLSs and LLSs in sizable and representative samples at both low
(z2) redshifts. Here I discuss unambiguous evidence for
metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and
LLSs so far studied are located in the CGM of galaxies with projected distances
<100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs,
there is a significant mass of cool, dense, low-metallicity gas in the CGM that
may be available as fuel for continuing star formation in galaxies over cosmic
time. As such, the metal-poor pLLSs and LLSs are currently among the best
observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
Gas Accretion in Star-Forming Galaxies
Cold-mode gas accretion onto galaxies is a direct prediction of LCDM
simulations and provides galaxies with fuel that allows them to continue to
form stars over the lifetime of the Universe. Given its dramatic influence on a
galaxy's gas reservoir, gas accretion has to be largely responsible for how
galaxies form and evolve. Therefore, given the importance of gas accretion, it
is necessary to observe and quantify how these gas flows affect galaxy
evolution. However, observational data have yet to conclusively show that gas
accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is
a challenging endeavor and we now have obtained a significant amount of
observational evidence to support it. This chapter reviews the current
observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. This chapter includes 22 pages with 7 Figure