135 research outputs found
Lyman-alpha Imaging of a Very Luminous z=2.3 Starburst Galaxy with WFPC2
We investigate a very luminous Lyman-alpha emitting galaxy, associated with a
z=2.3 damped absorption system in the spectrum of the QSO PHL 957. The galaxy
was observed with the HST WFPC2, through a narrow filter (F410M) corresponding
to rest-frame Lyman -alpha, for 41.2 ksec, with shorter exposures in F555W and
F814W. The galaxy is resolved into a close (0.35 arcsec) pair of two
components, CFgA and CFgB. The profile of CFgA is consistent with an
exponential disk, but CFgB is closer to a bulge galaxy. Fr om the observed
colours we estimate rest-frame Lyman-alpha equivalent widths of 151 Angstroms
for CFgA and 33 for CFgB. From the F814W and F555W magnitudes we estimate
rest-frame blue-band absolute magnitudes of -23.12 for CFgA and -23.24 for
CFgB, signi ficantly brighter than local galaxies of the same size. CFgA shows
a remarkable 3.9 magnitudes of surface brightness enhancement relative to local
spirals, and we speculate that this may be the result of a very luminous
starburst, triggered by the merger of the two components. The Lyman-alpha
emission could be from a brief phase early in the starburst in which most of
these photons can escape.
We search for other z=2.3 galaxies with strong Lyman-alpha emission,
selecting these by a colour F410M-F555W<-0.2. Eight candidate sources, all
fainter than CFgA, are identified. One is a point-source and may be an AGN; the
others are irregular a nd of low surface brightness, appearing typical of Lyman
break galaxies, but with Lyman-alpha equivalent widths near 100 Angstroms.Comment: 17 pages, Latex, 17 figures. Accepted for publication in MNRA
Energetic Phenomena on the Sun: The Solar Maximum Mission Flare Workshop. Proceedings
The general objectives of the conference were as follows: (1) Synthesize flare studies after three years of Solar Maximum Mission (SSM) data analysis. Encourage a broader participation in the SMM data analysis and combine this more fully with theory and other data sources-data obtained with other spacecraft such as the HINOTORI, p78-1, and ISEE-3 spacecrafts, and with the Very Large Array (VLA) and many other ground-based instruments. Many coordinated data sets, unprecedented in their breadth of coverage and multiplicity of sources, had been obtained within the structure of the Solar Maximum Year (SMY). (2) Stimulate joint studies, and publication in the general scientific literature. The intended primary benefit was for informal collaborations to be started or broadened at the Workshops with subsequent publications. (3) Provide a special publication resulting from the Workshop
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
Ultraviolet-Bright, High-Redshift ULIRGS
We present Spitzer Space Telescope observations of the z=2.38 lya-emitter
over-density associated with galaxy cluster J2143-4423, the largest known
structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within
the filament-like structure, using the MIPS 24um band. We detected 6 of the
lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha
emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total
far-infrared luminosity using locally derived correlations suggests all the
detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG
energies. Lya blobs frequently show evidence for interaction, either in HST
imaging, or the proximity of multiple MIPS sources within the Lya cloud. This
connection suggests that interaction or even mergers may be related to the
production of Lya blobs. A connection to mergers does not in itself help
explain the origin of the Lya blobs, as most of the suggested mechanisms for
creating Lya blobs (starbursts, AGN, cooling flows) could also be associated
with galaxy interactions.Comment: 12 pages, 3 figures, accepted by ApJ 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
Polycyclic Aromatic Hydrocarbon Emission within Lyα Blobs
We present Spitzer observations of Lyα blobs (LABs) at z = 2.38-3.09. The mid-infrared ratios (4.5 μm/8 μm and 8 μm/24 μm) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGNs). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850 μm or rest-frame far-infrared) also indicates that a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with submillimeter detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of six infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^(11) M_⊙. There is a weak trend of mass upper limit with the Lyα luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs
PAH Emission Within Lyman Alpha Blobs
We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The
mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared
counterparts are cool, consistent with their infrared output being dominated by
star formation and not active galactic nuclei (AGN). The rest have a
substantial hot dust component that one would expect from an AGN or an extreme
starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest
frame far infrared) also indicates a large percentage (~2/3) of the LAB
counterparts have total bolometric energy output dominated by star formation,
although the number of sources with sub-mm detections or meaningful upper
limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of
6 infrared-bright sources associated with LABs. Four of these sources have
measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative
of significant star formation, while the remaining two show a featureless
continuum, indicative of infrared energy output completely dominated by an AGN.
Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum
ratios and PAH equivalent widths indicative of large energy contributions from
both star formation and AGN. Most of the LAB infrared counterparts have large
stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with
the Lya luminosity of the host blob, particularly after the most likely AGN
contaminants are removed. The range in likely energy sources for the LABs found
in this and previous studies suggests that there is no single source of power
that is producing all the known LABs.Comment: 34 pages, 5 figures, accepted by Ap
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
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