456 research outputs found
The nature of proximate damped Lyman alpha systems
We present high resolution echelle spectra of 7 proximate damped Lyman alpha
(PDLA) systems whose relative velocity separation from the background quasar is
Delta V < 3000 km/s. Combining our sample with a further 9 PDLAs from the
literature we compare the chemical properties of the proximate systems with a
control sample of intervening DLAs. Taken at face value, the sample of 16 PDLAs
exhibits a wide range of metallicities, ranging from Z ~ 1/3 Z_sun down to Z ~
1/1000 Z_sun, including the DLA with the lowest N(SiII)/N(HI) yet reported in
the literature. We find several pieces of evidence that indicate enhanced
ionization and the presence of a hard ionizing spectrum in PDLAs which lead to
properties that contrast with the intervening DLAs, particularly when the N(HI)
is low. The abundances of Zn, Si and S in PDLAs with log N(HI) > 21, where
ionization corrections are minimized, are systematically higher than the
intervening population by a factor of around 3. We also find possible evidence
for a higher fraction of NV absorbers amongst the PDLAs, although the
statistics are still modest. 6/7 of our echelle sample show high ionization
species (SiIV, CIV, OVI or NV) offset by >100 km/s from the main low ion
absorption. We analyse fine-structure transitions of CII* and SiII* to
constrain the PDLA distance from the QSO. Lower limits range from tens of kpc
up to >160 kpc for the most stringent limit. We conclude that (at least some)
PDLAs do exhibit different characteristics relative to the intervening
population out to 3000 km/s (and possibly beyond). Nonetheless, the PDLAs
appear distinct from lower column density associated systems and the inferred
QSO-absorber separations mean they are unlikely to be associated with the QSO
host. We speculate that the PDLAs preferentially sample more massive galaxies
in more highly clustered regions of the high redshift universe.Comment: Accepted for publication in MNRAS. Abstract abridged
Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
We study the kinematically narrow, low-ionization line emission from a
bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with
Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance
transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas
outflow. Emission in MgII near and redward of systemic velocity, in concert
with the observed absorption, yields a P Cygni-like line profile similar to
those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the
MgII emission is spatially resolved, and extends significantly beyond the
emission from stars and HII regions within the galaxy. Assuming the emission
has a simple, symmetric surface brightness profile, we find that the gas
extends to distances > ~7 kpc. We also detect several narrow FeII*
fine-structure lines in emission near the systemic velocity, arising from
energy levels which are radiatively excited directly from the ground state. We
suggest that the MgII and FeII* emission is generated by photon scattering in
the observed outflow, and emphasize that this emission is a generic prediction
of outflows. These observations provide the first direct constraints on the
minimum spatial extent and morphology of the wind from a distant galaxy.
Estimates of these parameters are crucial for understanding the impact of
outflows in driving galaxy evolution.Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj forma
Resolving The ISM Surrounding GRBs with Afterglow Spectroscopy
We review current research related to spectroscopy of gamma-ray burst (GRB)
afterglows with particular emphasis on the interstellar medium (ISM) of the
galaxies hosting these high redshift events. These studies reveal the physical
conditions of star-forming galaxies and yield clues to the nature of the GRB
progenitor. We offer a pedagogical review of the experimental design and review
current results. The majority of sightlines are characterized by large HI
column densities, negligible molecular fraction, the ubiquitous detection of UV
pumped fine-structure transitions, and metallicities ranging from 1/100 to
nearly solar abundance.Comment: Conference procedings for Gamma Ray Bursts 2007 November 5-9, 2007
Santa Fe, New Mexico (8 pages, 4 figures
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
emulateapj forma
A Budget and Accounting of Metals at z~0: Results from the COS-Halos Survey
We present a budget and accounting of metals in and around star-forming
galaxies at . We combine empirically derived star formation histories
with updated supernova and AGB yields and rates to estimate the total mass of
metals produced by galaxies with present-day stellar mass of
--. On the accounting side of the ledger, we
show that a surprisingly constant 20--25% mass fraction of produced metals
remain in galaxies' stars, interstellar gas and interstellar dust, with little
dependence of this fraction on the galaxy stellar mass (omitting those metals
immediately locked up in remnants). Thus, the bulk of metals are outside of
galaxies, produced in the progenitors of today's galaxies. The COS-Halos
survey is uniquely able to measure the mass of metals in the circumgalactic
medium (to impact parameters of kpc) of low-redshift
galaxies. Using these data, we map the distribution of CGM metals as traced by
both the highly ionized OVI ion and a suite of low-ionization species; combined
with constraints on circumgalactic dust and hotter X-ray emitting gas out to
similar impact parameters, we show that % of metals produced by
galaxies can be easily accounted for out to
150 kpc. With the current data, we cannot rule out a constant mass of metals
within this fixed physical radius. This census provides a crucial boundary
condition for the eventual fate of metals in galaxy evolution models.Comment: 19 pages, 12 figures, 2 tables. ApJ, in pres
Deep Learning of Sea Surface Temperature Patterns to Identify Ocean Extremes
We performed an out-of-distribution (OOD) analysis of ∼12,000,000 semi-independent 128 × 128 pixel2 sea surface temperature (SST) regions, which we define as cutouts, from all nighttime granules in the MODIS R2019 Level-2 public dataset to discover the most complex or extreme phenomena at the ocean’s surface. Our algorithm (ULMO) is a probabilistic autoencoder (PAE), which combines two deep learning modules: (1) an autoencoder, trained on ∼150,000 random cutouts from 2010, to represent any input cutout with a 512-dimensional latent vector akin to a (non-linear) Empirical Orthogonal Function (EOF) analysis; and (2) a normalizing flow, which maps the autoencoder’s latent space distribution onto an isotropic Gaussian manifold. From the latter, we calculated a log-likelihood (LL) value for each cutout and defined outlier cutouts to be those in the lowest 0.1% of the distribution. These exhibit large gradients and patterns characteristic of a highly dynamic ocean surface, and many are located within larger complexes whose unique dynamics warrant future analysis. Without guidance, ULMO consistently locates the outliers where the major western boundary currents separate from the continental margin. Prompted by these results, we began the process of exploring the fundamental patterns learned by ULMO thereby identifying several compelling examples. Future work may find that algorithms such as ULMO hold significant potential/promise to learn and derive other, not-yet-identified behaviors in the ocean from the many archives of satellite-derived SST fields. We see no impediment to applying them to other large remote-sensing datasets for ocean science (e.g., SSH and ocean color)
No evidence for feedback: Unexceptional Low-ionization winds in Host galaxies of Low Luminosity Active Galactic Nuclei at Redshift z ~1
We study winds in 12 X-ray AGN host galaxies at z ~ 1. We find, using the
low-ionization Fe II 2586 absorption in the stacked spectra, that the
probability distribution function (PDF) of the centroid velocity shift in AGN
has a median, 16th and 84th percentiles of (-87, -251, +86) km/s respectively.
The PDF of the velocity dispersion in AGN has a median, 84th and 16th
percentile of (139, 253, 52) km/s respectively. The centroid velocity and the
velocity dispersions are obtained from a two component (ISM+wind) absorption
line model. The equivalent width PDF of the outflow in AGN has median, 84th and
16th percentiles of (0.4, 0.8, 0.1) Angstrom. There is a strong ISM component
in Fe II 2586 absorption with (1.2, 1.5, 0.8) Angstrom, implying presence of
substantial amount cold gas in the host galaxies. For comparison, star-forming
and X-ray undetected galaxies at a similar redshift, matched roughly in stellar
mass and galaxy inclination, have a centroid velocity PDF with percentiles of
(-74, -258, +90) km/s, and a velocity dispersion PDF percentiles of (150, 259,
57) km/s. Thus, winds in the AGN are similar to star-formation-driven winds,
and are too weak to escape and expel substantial cool gas from galaxies. Our
sample doubles the previous sample of AGN studied at z ~ 0.5 and extends the
analysis to z ~ 1. A joint reanalysis of the z ~ 0.5 AGN sample and our sample
yields consistent results to the measurements above.Comment: 24 pages, 11 figures, accepted in Ap
GALEX Discovery of a Damped Ly-alpha System at Redshift z = 1
We report the first discovery of a QSO damped Ly-alpha (DLA) system by the
GALEX satellite. The system was initially identified as an MgII absorption-line
system (z_abs=1.028) in the spectrum of SDSS QSO J0203-0910 (z_em=1.58). The
presence of unusually strong absorption due to metal lines of ZnII, CrII, MnII,
and FeII clearly suggested that it might be a DLA system with N{HI} > 2 x 10^20
atoms cm^-2. Follow-up GALEX NUV grism spectroscopy confirms the system
exhibits a DLA absorption line, with a measured HI column density of N{HI} =
1.50+/-0.45 x 10^21 atoms cm^-2. By combining the GALEX N{HI} determination
with the SDSS spectrum measurements of unsaturated metal-line absorption due to
ZnII, which is generally not depleted onto grains, we find that the system's
neutral-gas-phase metal abundance is [Zn/H] = -0.69+/-0.22, or ~20% solar. By
way of comparison, although this system has one of the largest Zn^+ column
densities, its metal abundances are comparable to other DLAs at z~1.
Measurements of the abundances of Cr, Fe, and Mn help to further pin down the
evolutionary state of the absorber.Comment: 14 pages, 3 figures, 1 table; Submitted to The Astronomical Journa
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