136 research outputs found
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
A Search for H-alpha Absorption in the Exosphere of the Transiting Extrasolar Planet HD 209458b
There is evidence that the transiting planet HD 209458b has a large exosphere
of neutral hydrogen, based on a 15% decrement in Lyman-alpha flux that was
observed by Vidal-Madjar et al. during transits. Here we report upper limits on
H-alpha absorption by the exosphere. The results are based on optical spectra
of the parent star obtained with the Subaru High Dispersion Spectrograph.
Comparison of the spectra taken inside and outside of transit reveals no
exospheric H-alpha signal greater than 0.1% within a 5.1A band (chosen to have
the same Delta_lambda/lambda as the 15% Ly-alpha absorption). The corresponding
limit on the column density of n=2 neutral hydrogen is N_2 <~ 10^9 cm^{-2}.
This limit constrains proposed models involving a hot (~10^4 K) and
hydrodynamically escaping exosphere.Comment: To appear in PASJ [9 pages, 5 figures]. Minor corrections to match
published versio
Observations of the Gas Reservoir around a Star Forming Galaxy in the Early Universe
We present a high signal-to-noise spectrum of a bright galaxy at z = 4.9 in
14 h of integration on VLT FORS2. This galaxy is extremely bright, i_850 =
23.10 +/- 0.01, and is strongly-lensed by the foreground massive galaxy cluster
Abell 1689 (z=0.18). Stellar continuum is seen longward of the Ly-alpha
emission line at ~7100 \AA, while intergalactic H I produces strong absorption
shortward of Ly-alpha. Two transmission spikes at ~6800 Angstroms (A) and ~7040
A are also visible, along with other structures at shorter wavelengths.
Although fainter than a QSO, the absence of a strong central ultraviolet flux
source in this star forming galaxy enables a measurement of the H I flux
transmission in the intergalactic medium (IGM) in the vicinity of a high
redshift object. We find that the effective H I optical depth of the IGM is
remarkably high within a large 14 Mpc (physical) region surrounding the galaxy
compared to that seen towards QSOs at similar redshifts. Evidently, this
high-redshift galaxy is located in a region of space where the amount of H I is
much larger than that seen at similar epochs in the diffuse IGM. We argue that
observations of high-redshift galaxies like this one provide unique insights on
the nascent stages of baryonic large-scale structures that evolve into the
filamentary cosmic web of galaxies and clusters of galaxies observed in the
present universe.Comment: Accepted for publication in ApJL (corrected typos
Spectral Evidence for Widespread Galaxy Outflows at z>4
We present discovery spectra of a sample of eight lensed galaxies at high
redshift, 3.7<z<5.2, selected by their red colors in the fields of four massive
clusters: A1689, A2219, A2390, and AC114. Metal absorption lines are detected
and observed to be blueshifted by 300-800 km/s with respect to the centroid of
Ly-alpha emission. A correlation is found between this blueshift and the
equivalent width of the metal lines, which we interpret as a broadening of
saturated absorption lines caused by a dispersion in the outflow velocity of
interstellar gas. Local starburst galaxies show similar behavior, associated
with obvious gas outflows. We also find a trend of increasing equivalent width
of Ly-alpha emission with redshift, which may be a genuine evolutionary effect
towards younger stellar populations at high redshift with less developed
stellar continua. No obvious emission is detected below the Lyman limit in any
of our spectra, nor in deep U or B-band images. The UV continua are reproduced
well by early B-stars, although some dust absorption would allow a fit to
hotter stars. After correcting for the lensing, we derive small physical sizes
for our objects, ~0.5-5 kpc/h for a flat cosmology with Omega_m=0.3,
Omega_Lambda=0.7. The lensed images are only marginally resolved in good seeing
despite their close proximity to the critical curve, where large arcs are
visible and hence high magnifications of up to ~20x are inferred. Two objects
show a clear spatial extension of the Ly-alpha emission relative to the
continuum starlight, indicating a ``breakout'' of the gas. The sizes of our
galaxies together with their large gas motion suggests that outflows of gas are
common at high redshift and associated with galaxy formation.Comment: 48 pages, 16 figures, ApJ, in press. Manuscript with full resolution
color images available at (http://astro.princeton.edu/~bfrye
High Metallicity, Photoionised Gas in Intergalactic Large-Scale Filaments
We present high-resolution UV spectra of absorption-line systems toward the
low-z QSO HS0624+6907 (z=0.3700). Coupled with spectroscopic galaxy redshifts,
we find that many of these absorbers are integalactic gas clouds distributed
within large-scale structures. The gas is cool (T<10^5 K) and has relatively
high metallicity (Z/Z_sol>0.9). STIS data reveal a cluster of 13 HI Lyman alpha
lines within a 1000 km/s interval at z=0.0635. We find 10 galaxies at this
redshift with impact parameters ranging from 135 h^-1 kpc to 1.37 h^-1 Mpc. We
attribute the HI Lya absorptions to intragroup medium gas, possibly from a
large-scale filament viewed along its long axis. Remarkably, the metallicity is
near-solar, [M/H] = -0.05 +/- 0.4 (2 sigma uncertainty), yet the nearest galaxy
which might pollute the IGM is at least 135 h_70^-1 kpc away. Tidal stripping
from nearby galaxies appears to be the most likely origin of this highly
enriched, cool gas. More than six Abell galaxy clusters are found within 4
degree of the sight line suggesting that the QSO line of sight passes near a
node in the cosmic web. At z~0.077, we find absorption systems as well as
galaxies at the redshift of the nearby clusters Abell 564 and Abell 559. We
conclude that the sight line pierces a filament of gas and galaxies feeding
into these clusters. The absorber at z_abs = 0.07573 associated with Abell
564/559 also has a high metallicity with [C/H] > -0.6, but again the closest
galaxy is relatively far from the sight line (293 h^-1 kpc).Comment: 18 pages, 16 figures, delete from table 3 some uncorrect HI
identifications. Higher resolution version of the paper is available at
http://www.astro.umass.edu/~aracil/work/hs0624/hs0624_high.pd
The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation
We investigate the physical nature of blue cores in early-type galaxies
through the first multi-wavelength analysis of a serendipitously discovered
field blue-nucleated spheroid in the background of the deep ACS/WFC griz
multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and
i-z color maps reveal a prominent blue core identifying this galaxy as a
``typical'' case study, exhibiting variations of 0.5-1.0 mag in color between
the center and the outer regions, opposite to the expectations of reddened
metallicity induced gradients in passively evolved ellipticals. From a
Magellan-Clay spectrum we secure the galaxy redshift at . We find a
strong X-ray source coincident with the spheroid galaxy. Spectral features and
a high X-ray luminosity indicate the presence of an AGN in the galaxy. However,
a comparison of the X-ray luminosity to a sample derived from the Chandra Deep
Field South displays Lx to be comparable to Type I/QSO galaxies while the
optical flux is consistent with a normal star-forming galaxy. We conclude that
the galaxy's non-thermal component dominates at high-energy wavelengths while
we associate the spheroid blue light with the stellar spectrum of normal
star-forming galaxies. We argue about a probable association between the
presence of blue cores in spheroids and AGN activity.Comment: Accepted for publication in the Astrophysical Journal. 6 pages, 3
figures. Full resolution images available at
http://acs.pha.jhu.edu/~felipe/e-print
Not In Our Backyard: Spectroscopic Support for the CLASH z=11 Candidate MACS0647-JD
We report on our first set of spectroscopic Hubble Space Telescope
observations of the z~11 candidate galaxy strongly lensed by the
MACSJ0647.7+7015 galaxy cluster. The three lensed images are faint and we show
that these early slitless grism observations are of sufficient depth to
investigate whether this high-redshift candidate, identified by its strong
photometric break at ~1.5 micron, could possibly be an emission line galaxy at
a much lower redshift. While such an interloper would imply the existence of a
rather peculiar object, we show here that such strong emission lines would
clearly have been detected. Comparing realistic, two-dimensional simulations to
these new observations we would expect the necessary emission lines to be
detected at >5 sigma while we see no evidence for such lines in the dispersed
data of any of the three lensed images. We therefore exclude that this object
could be a low redshift emission line interloper, which significantly increases
the likelihood of this candidate being a bona fide z~11 galaxy.Comment: 14 Pages. 6 Figures. 2nd revised version. Accepted. To appear in ApJ.
Please contact [email protected] for comments on this pape
The Sextet Arcs: a Strongly Lensed Lyman Break Galaxy in the ACS Spectroscopic Galaxy Survey towards Abell 1689
We present results of the HST Advanced Camera for Surveys spectroscopic
ground-based redshift survey in the field of A1689. We measure 98 redshifts,
increasing the number of spectroscopically confirmed objects by sixfold. We
present two spectra from this catalog of the Sextet Arcs, images which arise
from a strongly-lensed Lyman Break Galaxy (LBG) at a redshift of z=3.038.
Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and
produces six separate images with a total r-band magnitude of r_625=21.7. The
two spectra, each of which represents emission from different regions of the
LBG, show H I and interstellar metal absorption lines at the systemic redshift.
Significant variations are seen in Ly-alpha profile across a single galaxy,
ranging from strong absorption to a combination of emission plus absorption. A
spectrum of a third image close to the brightest arc shows Ly-alpha emission at
the same redshift as the LBG, arising from either another spatially distinct
region of the galaxy, or from a companion galaxy close to the LBG. Taken as a
group, the Ly-alpha equivalent width in these three spectra decreases with
increasing equivalent width of the strongest interstellar absorption lines. We
discuss how these variations can be used to understand the physical conditions
in the LBG. Intrinsically, this LBG is faint, ~0.1L*, and forming stars at a
modest rate, ~4 solar masses per year. We also detect absorption line systems
toward the Sextet Arcs at z=2.873 and z=2.534. The latter system is seen across
two of our spectra.Comment: Accepted for publication in Ap
Efficient survey design for finding high-redshift galaxies with JWST
Several large JWST blank field observing programs have not yet discovered the
first galaxies expected to form at . This has motivated the
search for more effective survey strategies that will be able to effectively
probe this redshift range. Here, we explore the use of gravitationally lensed
cluster fields, that have historically been the most effective discovery tool
with HST. In this paper, we analyze the effectiveness of the most massive
galaxy clusters that provide the highest median magnification factor within a
single JWST NIRCam module in uncovering this population. The results of
exploiting these lensing clusters to break the barrier are compared
against the results from large area, blank field surveys such as JADES and
CEERS in order to determine the most effective survey strategy for JWST. We
report that the fields containing massive foreground galaxy clusters
specifically chosen to occupy the largest fraction of a single NIRCam module
with high magnification factors in the source plane, whilst containing all
multiple images in the image plane within a single module provide the highest
probability of both probing the regime, as well as
discovering the highest redshift galaxy possible with JWST. We also find that
using multiple massive clusters in exchange for shallower survey depths is a
more time efficient method of probing the regime.Comment: 12 pages, 5 figure
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