84 research outputs found
The Distribution of Lya-Emitting Galaxies at z=2.3
We present the detection of 34 Ly-alpha emission-line galaxy candidates in a
80x80x60 co-moving Mpc region surrounding the known z=2.38 galaxy cluster
J2143-4423. The space density of Ly-alpha emitters is comparable to that found
by Steidel et al. when targeting a cluster at redshift 3.09, but is a factor of
5.8 +/- 2.5 greater than that found by field samples at similar redshifts. The
distribution of these galaxy candidates contains several 5-10 Mpc scale voids.
We compare our observations with mock catalogs derived from the VIRGO
consortium Lambda-CDM n-body simulations. Fewer than 1% of the mock catalogues
contain voids as large as we observe. Our observations thus tentatively suggest
that the galaxy distribution at redshift 2.38 contains larger voids than
predicted by current models. Three of the candidate galaxies and one previously
discovered galaxy have the large luminosities and extended morphologies of
"Ly-alpha blobs".Comment: 10 pages, 8 figures, emulateapj5, Accepted for publication in Ap
A Group of Red, Ly-alpha Emitting, High Redshift Galaxies
We have discovered two new high redshift (z=2.38) galaxies, near the
previously known z=2.38 galaxy 2139-4434 B1 (Francis et al. 1996).
All three galaxies are strong Ly-alpha emitters, and have much redder
continuum colors (I-K about 5) than other optically-selected high redshift
galaxies. We hypothesize that these three galaxies are QSO IIs; radio-quiet
counterparts of high redshift radio galaxies, containing concealed QSO nuclei.
The red colors are most easily modelled by an old (> 0.5 Gyr), massive (> 10E11
solar masses) stellar population. If true, this implies that at least one
galaxy cluster of mass much greater than 3E11 solar masses had collapsed before
redshift five.Comment: 12 pages, 2 figures, uses aaspp4 style file. Accepted for publication
in Astrophysical Journal Letter
Debris Disk Structure and Morphology as Revealed by Aggressive STIS Multi-Roll Coronagraphy: A New Look at Some Old Friends
We present new imaging results from a well-selected sample of II circumstellar debris disks, all with HST pedigree, using STIS visible-light 6-roll PSF-template subtracted coronagraphy (PSFTSC). These new observations, pushing HST to its highest levels of coronagraphic performance, simultaneously probe both the interior regions of these debris systems, with inner working distances < app 8 AU for half the stars in this sample (corresponding to the giant planet and Kuiper belt regions within our own solar system), and the exterior regions far beyond. These new images enable direct inter-comparison of the architectures of these exoplanetary debris systems in the context of our own Solar System: These observations also permit us, for the first time, to characterize material in these regions at high spatial resolution and identify disk sub-structures that are signposts of planet formation and evolution; in particular, asymmetries and non-uniform debris structures that signal the presence of co-orbiting perturbing planets, and dynamical interactions (e.g., resulting in posited small grain stripping and disk "pollution") with the ISM. We focus here on recently acquired and reduced images of he circumstellar debris systems about: AU Mic (edge-on, and @ 10 pc the closest star in our sample), HD 61005, HD 32297 and HD 15115 (all with morphologies strongly suggestive of ISM wind interactions), HD 181327 & HDI07146 (close to face-on with respectively narrow and broad debris rings), and MP Mus (a "mature" proto-planetary disk hosted by a cTTS). All of our objects were previously observed in the near-IR with inferior spatial resolution and imaging efficacy, but with NICMOS r = 0.3" inner working angle (IWA) comparable to STIS multi-roll coronagraphy. The combination of new optical and existing near-IR imaging can strongly constrain the dust properties, thus enabling an assessment of grain processing and planetesimal populations. These results will directly inform upon the posited planet formation mechanisms that occur after the approximately 10 My epoch of gas depletion, a time in our solar system when giant planets were migrating and terrestrial planets were forming, and directly test theoretical models of these processes. These observations lmiquely probe both into the interior regions of these systems and are sensitive to and spatially resolve low surface-brightness (SB) material at large stellocentric distances with spatial resolution comparable to ACS and with augmenting NICMOS near-IR disk photometry in hand
Galaxy Clusters and Large Scale Structure at High Redshifts
We present a detailed study of a rich galaxy cluster at z=2.38. We
demonstrate that this cluster contains large overdensities of damped Ly-alpha
absorption lines, of Ly-alpha emitting galaxies and of extremely red objects.
The overdensity of extremely red objects in this field demonstrates that many
are high z galaxies.
The huge overdensities we measure for these three classes of object are much
larger than the mass overdensities of typical clusters at this redshift, as
predicted by CDM and related models. We suggest therefore that the distribution
of damped Ly-alpha absorption line systems, of Ly-alpha emitting galaxies and
of extremely red objects are all very strongly biassed, and that somehow a
small overdensity of mass has increased the fraction of baryons in collapsed
objects, in the volume occupied by the cluster, to close to unity (a factor of
~10 increase).
We speculate that some unknown physical process, acting on the volume
occupied by our cluster, caused the normally diffuse ionised inter-galactic
medium to coalesce into small (< 10^8 Solar masses) blobs of neutral hydrogen,
which produce the Ly-alpha absorption-lines. Star formation occurred within
these blobs at z>5, enriching them with metals and producing stars, which after
several mergers and ~ 0.5 Gyr of passive evolution form the extremely red
objects. The Ly-alpha emitting galaxies are probably AGN, triggered perhaps by
mergers of the small blobs.Comment: Invited talk to appear in "The Young Universe", proceedings of Rome
conference, ed. D'Odorico, Fontana and Giallongo. 8 pages, uses paspconf.st
Cool Customers in the Stellar Graveyard I: Limits to Extrasolar Planets Around the White Dwarf G29-38
We present high contrast images of the hydrogen white dwarf G 29-38 taken in
the near infrared with the Hubble Space Telescope and the Gemini North
Telescope as part of a high contrast imaging search for substellar objects in
orbit around nearby white dwarfs.
We review the current limits on planetary companions for G29-38, the only
nearby white dwarf with an infrared excess due to a dust disk. We add our
recent observations to these limits to produce extremely tight constraints on
the types of possible companions that could be present. No objects 6
M are detected in our data at projected separations 12 AU, and no
objects 16 M are detected for separations from 3 to 12 AU, assuming
a total system age of 1 Gyr. Limits for companions at separations 3 AU come
from a combination of 2MASS photometry and previous studies of G29-38's
pulsations. Our imaging with Gemini cannot confirm a tentative claim for the
presence of a low mass brown dwarf. These observations demonstrate that a
careful combination of several techniques can probe nearby white dwarfs for
large planets and low mass brown dwarfs.Comment: 20 pages, 4 figures, Accepted to Ap
On the Gas Surrounding High Redshift Galaxy Clusters
Francis & Hewett (1993) identified two 10-Mpc scale regions of the high
redshift universe that were seemingly very overdense in neutral hydrogen.
Subsequent observations showed that at least one of these gas-rich regions
enveloped a cluster of galaxies at redshift 2.38. We present improved
observations of the three background QSOs with sightlines passing within a few
Mpc of this cluster of galaxies. All three QSOs show strong neutral hydrogen
absorption at the cluster redshift, suggesting that this cluster (and perhaps
all high redshift clusters) may be surrounded by a ~5 Mpc scale region
containing ~ 10^12 solar masses of neutral gas.
If most high redshift clusters are surrounded by such regions, we show that
the gas must be in the form of many small ( 0.03 cm^-3)
clouds, each of mass < 10^6 solar masses. These clouds are themselves probably
gathered into > 20 kpc sized clumps, which may be galaxy halos or
protogalaxies.
If this gas exists, it will be partially photoionised by the UV background.
We predict the diffuse Ly-alpha flux from this photoionisation, and place
observational limits on its intensity.Comment: 19 pages, 5 figures. Accepted for publication in PAS
The Distribution of Ly-alpha-Emitting Galaxies at z=2.38: Paper 2, Spectroscopy
In Paper 1 of this series we identified an 80 co-moving Mpc filament of
candidate Lyman-alpha emitting galaxies at redshift 2.38. In this paper we
present spectroscopy of the 37 galaxy candidates. Our spectroscopy reached a
surface brightness limit of 5.0E-17 erg/cm^2/s/arcsec^2. Of the 14 candidates
down to this limit, 12 were confirmed to be Lyman-alpha emitting galaxies at
the filament redshift. We also obtained spectral confirmation for six of the
lower surface brightness candidates, all of which also lay at the filament
redshift. In addition, we identify a foreground cluster of QSOs at z=1.65.Comment: Accepted for publication in the Astrophysical Journa
The Evolution of Damped Lyman-alpha Absorbers: Metallicities and Star Formation Rates
The damped Lyman-alpha (DLA) and sub-DLA quasar absorption lines provide
powerful probes of the evolution of metals, gas, and stars in galaxies. One
major obstacle in trying to understand the evolution of DLAs and sub-DLAs has
been the small number of metallicity measurements at z < 1.5, an epoch spanning
\~70 % of the cosmic history. In recent surveys with the Hubble Space Telescope
and Multiple Mirror Telescope, we have doubled the DLA Zn sample at z < 1.5.
Combining our results with those at higher redshifts from the literature, we
find that the global mean metallicity of DLAs does not rise to the solar value
at low redshifts. These surprising results appear to contradict the near-solar
mean metallicity observed for nearby (z ~ 0) galaxies and the predictions of
cosmic chemical evolution models based on the global star formation history.
Finally, we discuss direct constraints on the star formation rates (SFRs) in
the absorber galaxies from our deep Fabry-Perot Ly-alpha imaging study and
other emission-line studies in the literature. A large fraction of the observed
heavy-element quasar absorbers at 0 < z < 3.4 appear to have SFRs substantially
below the global mean SFR, consistent with the low metallicities observed in
the spectroscopic studies.Comment: 6 pages,3 figures, To appear in "Probing Galaxies through Quasar
Absorption Lines", Proceedings IAU Colloquium 199, 2005, Eds. P. R. Williams,
C. Shu, and B. Menar
Cool Customers in the Stellar Graveyard II: Limits to Substellar Objects Around Nearby DAZ White Dwarfs
Results from a concerted Hubble Space Telescope (HST) survey of nearby white
dwarfs for substellar objects is presented. A total of 7 DAZ white dwarfs with
distances of 50 pc had high contrast and high spatial resolution NICMOS
coronagraphic images taken to search for candidate substellar objects at
separations \ltorder10\arcsec away. Limits to unresolved companions are
derived through analysis of 2MASS photometry of the white dwarfs compared to
expected fluxes based on the WDs effective temperature, distance, and gravity.
From our survey with HST we find several candidate companions, which have
been or will be followed up with second epoch observations. We find that for
four of the white dwarfs we are sensitive to planetary companions \gtorder10
M, and sensitive to companions 18 M for all of the targets.
The lack of significant near infrared excesses for our targets limits any kind
of unresolved companions present to be substellar. In light of these results we
make several comments on the possibility of determining the origin of white
dwarfs with metals in their atmospheres.Comment: 11 pages, 7 figures, emulateapj, revisions to figures and text, to
appear in September A
Imaging the Disk and Jet of the Classical T Tauri Star AA Tau
Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light.We measure the outer disk radius, 1 inch.15 plus-minus 0 inch.10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21 inches from the star in data from 2005. The measured outer disk inclination, 71deg plus-minus 1deg, is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature
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