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Harry I. Teplitz,
Marc Rafelski,
Peter Kurczynski,
Nicholas A. Bond,
Norman Grogin,
Anton M. Koekemoer,
Hakim Atek,
Thomas M. Brown,
Dan Coe,
James W. Colbert, [......],
Daniel J. Hanish,
Kyoung-Soo Lee,
Duilia F. de Mello,
Swara Ravindranath,
Russell E. Ryan,
Brian D. Siana,
Claudia Scarlata,
Emmaris Soto,
Elysse N. Voyer,
Arthur M. Wolfe
[show abstract]
[hide abstract]
ABSTRACT: We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.
05/2013;
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Robin Ciardullo, Caryl Gronwall,
Joshua J. Adams,
Guillermo A. Blanc,
Karl Gebhardt,
Steven L. Finkelstein,
Shardha Jogee,
Gary J. Hill,
Niv Drory,
Ulrich Hopp,
Donald P. Schneider,
Gregory R. Zeimann,
Gavin B. Dalton
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the luminosities and equivalent widths of the 284 z
< 0.56 [O II]-emitting galaxies found in the 169 square arcmin pilot survey for
the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). By combining
emission-line fluxes obtained from the Mitchell spectrograph on the McDonald
2.7-m telescope with deep broadband photometry from archival data, we derive
each galaxy's de-reddened [O II] 3727 luminosity and calculate its total star
formation rate. We show that over the last ~5 Gyr of cosmic time there has been
substantial evolution in the [O II] emission-line luminosity function, with L*
decreasing by ~0.6 +/-0.2 dex in the observed function, and by ~0.9 +/-0.2 dex
in the de-reddened relation. Accompanying this decline is a significant shift
in the distribution of [O II] equivalent widths, with the fraction of high
equivalent-width emitters declining dramatically with time. Overall, the data
imply that the relative intensity of star formation within galaxies has
decreased over the past ~5 Gyr, and that the star formation rate density of the
universe has declined by a factor of ~2.5 between z ~ 0.5 and z ~ 0. These
observations represent the first [O II]-based star formation rate density
measurements in this redshift range, and foreshadow the advancements which will
be generated by the main HETDEX survey.
04/2013;
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James E. Rhoads,
Sangeeta Malhotra,
Daniel Stern,
Mark Dickinson,
Norbert Pirzkal,
Hyron Spinrad,
Naveen Reddy,
Nimish Hathi,
Norman Grogin,
Anton Koekemoer, [......],
Nino Panagia,
Anna Pasquali,
Kailash Sahu,
Sperello di Serego Alighieri,
Amber Straughn,
Rachel Somerville,
Jeremy Walsh,
Rogier Windhorst,
Chun Xu,
Haojing Yan
[show abstract]
[hide abstract]
ABSTRACT: We present observations of a luminous galaxy at redshift z=6.573 --- the end
of the reioinization epoch --- which has been spectroscopically confirmed
twice. The first spectroscopic confirmation comes from slitless HST ACS grism
spectra from the PEARS survey (Probing Evolution And Reionization
Spectroscopically), which show a dramatic continuum break in the spectrum at
restframe 1216 A wavelength. The second confirmation is done with Keck +
DEIMOS. The continuum is not clearly detected with ground-based spectra, but
high wavelength resolution enables the Lyman alpha emission line profile to be
determined. We compare the line profile to composite line profiles at redshift
z=4.5. The Lyman alpha line profile shows no signature of a damping wing
attenuation, confirming that the intergalactic gas is ionized at redshift
z=6.57. Spectra of Lyman breaks at yet higher redshifts will be possible using
comparably deep observations with IR-sensitive grisms, even at redshifts where
Lyman alpha is too attenuated by the neutral IGM to be detectable using
traditional spectroscopy from the ground.
02/2013;
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John Feldmeier,
Alex Hagen,
Robin Ciardullo, Caryl Gronwall,
Eric Gawiser,
Lucia Guaita,
Lea Hagen,
Nicholas Bond,
Viviana Acquaviva,
Guillermo Blanc,
Alvaro Orsi,
Peter Kurczynski
[show abstract]
[hide abstract]
ABSTRACT: We search for evidence of diffuse Ly-alpha emission from extended neutral
hydrogen surrounding Ly-alpha emitting galaxies (LAEs) using deep narrow-band
images of the Extended Chandra Deep Field South. By stacking the profiles of
187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and
carefully performing low-surface brightness photometry, we obtain mean surface
brightness maps that reach 9.9, 8.7, and 6.2 x 10^{-19} ergs cm^{-2} s^{-1}
arcsec^{-2} in the emission line. We undertake a thorough investigation of
systematic uncertainties in our surface brightness measurements, and find that
our limits are 5-10 times larger than would be expected from Poisson background
fluctuations; these uncertainties are often underestimated in the literature.
At z ~ 3.1, we find marginal evidence for extended halos with scale lengths of
5-8 kpc, and demonstrate that sub-samples of galaxies with low equivalent
widths and brighter continuum magnitudes are more likely to possess such halos.
At z ~ 2.1, we find no evidence of extended Ly-alpha emission down to our
detection limits. We compare these findings to other measurements in the
literature, and discuss possible instrumental and astrophysical reasons for the
discrepancies, including possible evolution of Ly-alpha halo properties from z
~ 3.1 to z ~ 2.1.
01/2013;
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Tyler D. Desjardins,
Sarah C. Gallagher,
Panayiotis Tzanavaris,
John S. Mulchaey,
William N. Brandt,
Jane C. Charlton,
Gordon P. Garmire, Caryl Gronwall,
Ann E. Hornschemeier,
Kelsey E. Johnson,
Iraklis S. Konstantopoulos,
Ann I. Zabludoff
[show abstract]
[hide abstract]
ABSTRACT: Isolated compact groups of galaxies (CGs) present a range of dynamical
states, group velocity dispersions, and galaxy morphologies with which to study
galaxy evolution, particularly the properties of gas both within the galaxies
and in the intragroup medium. As part of a large, multiwavelength examination
of CGs, we present an archival study of diffuse X-ray emission in a subset of
nine Hickson compact groups observed with the Chandra X-ray Observatory. We
find that seven of the groups in our sample exhibit detectable diffuse
emission. However, unlike large-scale emission in galaxy clusters, the diffuse
features in the majority of the detected groups are linked to the individual
galaxies, in the form of both plumes and halos likely as a result of star
formation or AGN activity, as well as in emission from tidal features. Unlike
previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found
to be consistent with the Lx-T relationship from clusters within the errors,
while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though
this is likely coincidental given that the hot gas in these two systems is
largely due to star formation. We find that Lx increases with decreasing group
HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray
luminosity on HI morphology whereby systems with intragroup HI indicative of
strong interactions are considerably more X-ray luminous than passively
evolving groups. We also find a gap in the Lx of groups as a function of the
total group specific star formation rate. Our findings suggest that the hot gas
in these groups is not in hydrostatic equilibrium and these systems are not
low-mass analogs of rich groups or clusters, with the possible exception of HCG
62.
12/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present optical HST/STIS spectroscopy of RZ 2109, a globular cluster in
the elliptical galaxy NGC 4472. This globular cluster is notable for hosting an
ultraluminous X-ray source as well as associated strong and broad [OIII] 4959,
5007 emission. We show that the HST/STIS spectroscopy spatially resolves the
[OIII] emission in RZ 2109. While we are unable to make a precise determination
of the morphology of the emission line nebula, the best fitting models all
require that the [OIII] 5007 emission has a half light radius in the range 3-7
pc. The extended nature of the [OIII] 5007 emission is inconsistent with
published models that invoke an intermediate mass black hole origin. It is also
inconsistent with the ionization of ejecta from a nova in the cluster. The
spatial scale of the nebula could be produced via the photoionization of a
strong wind driven from a stellar mass black hole accreting at roughly its
Eddington rate.
09/2012;
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[show abstract]
[hide abstract]
ABSTRACT: A large number of high-redshift galaxies have been discovered through
narrow-band Lya line or broad-band continuum in recent years. The escaping
process of photons from these early galaxies is crucial to understanding galaxy
evolution and the cosmic reionization. Here, we investigate the escape of Lya,
non-ionizing UV-continuum (l = 1300 - 1600 angs in rest frame), and ionizing
photons (l < 912 angs) from galaxies by combining cosmological hydrodynamic
simulations with three-dimensional multi-wavelength radiative transfer
calculations. We find that the escape fraction (fesc) of these different
photons shows a complex dependance on redshift and galaxy properties: fesc(Lya)
and fesc(UV) appear to evolve with redshift, and they show similar, weak
correlations with galaxy properties such as mass, star formation, metallicity,
and dust content, while fesc(Ion) remains roughly constant at ~ 0.2 from z ~ 0
- 10, and it does not show clear dependence on the properties of the galaxy.
The fesc(Lya) correlates more strongly with fesc(UV) than with fesc(Ion). In
addition, we estimate the ionizing photon emissivity of Lyman Alpha Emitters
(LAEs) and their contribution to the ionization of intergalactic medium (IGM),
by combining our simulations with the observed luminosity functions of LAEs at
different redshift. Our result suggests that ionizing photons from LAEs alone
are not sufficient to ionize IGM at z > 6, but they can maintain the ionization
of IGM at z ~ 0 - 5.
09/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We have compiled a catalog of optically-selected quasars with simultaneous
observations in UV/optical and X-ray bands by the Swift Gamma Ray Burst
Explorer. Objects in this catalog are identified by matching the Swift
pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The
final catalog contains 843 objects, among which 637 have both UVOT and XRT
observations and 354 of which are detected by both instruments. The overall
X-ray detection rate is ~60% which rises to ~85% among sources with at least 10
ks of XRT exposure time. We construct the time-averaged spectral energy
distribution for each of the 354 quasars using UVOT photometric measurements
and XRT spectra. From model fits to these SEDs, we find that the big blue bump
contributes about 0.3 dex to the quasar luminosity. We re-visit the
alpha_ox-L_uv relation by selecting a clean sample with only type 1 radio-quiet
quasars; the dispersion of this relation is reduced by at least 15% compared to
studies that use non-simultaneous UV/optical and X-ray data. We only found a
weak correlation between L/L_Edd and alpha_uv. We do not find significant
correlations between alpha_x and alpha_ox, alpha_ox and alpha_uv, and alpha_x
and Log L(0.3-10 keV). The correlations between alpha_uv and alpha_x, alpha_ox
and alpha_x, alpha_ox and alpha_uv, L/L_Edd and alpha_x, and L/L_Edd and
alpha_ox are stronger amongst low-redshift quasars, indicating that these
correlations are likely driven by the changes of SED shape with accretion
state.
03/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present properties of individual and composite rest-UV spectra of
continuum- and narrowband-selected star-forming galaxies (SFGs) at a redshift
of 2<z<3.5 discovered by the MUSYC collaboration in the ECDF-S. Among our
sample of 81 UV-bright SFGs, 59 have R<25.5, of which 32 have rest-frame
equivalent widths W_{Ly{\alpha}}>20 {\AA}, the canonical limit to be classified
as a LAE. We divide our dataset into subsamples based on properties we are able
to measure for each individual galaxy: Ly{\alpha} equivalent width, rest-frame
UV colors, and redshift. Among our subsample of galaxies with R<25.5, those
with rest-frame W_{Ly{\alpha}}>20 {\AA} have bluer UV continua, weaker
low-ionization interstellar absorption lines, weaker C IV absorption, and
stronger Si II* nebular emission than those with W_{Ly{\alpha}}<20 {\AA}. We
measure a typical velocity offset of {\Delta}v~600 km s$^{-1}$ between
Ly{\alpha} emission and low-ionization absorption among our subsamples. We find
that the interstellar component, as opposed to the stellar component, dominates
the high-ionization absorption line profiles. We find the low- and
high-ionization Si ionization states have similar kinematic properties, yet the
low-ionization absorption is correlated with Ly$\alpha$ emission and the
high-ionization absorption is not. These trends are consistent with outflowing
neutral gas being in the form of neutral clouds embedded in ionized gas as
previously suggested by \cite{Steidel2010}. Moreover, our galaxies with bluer
UV colors have stronger Ly{\alpha} emission, weaker low-ionization absorption
and more prominent nebular emission line profiles. Among our dataset, UV-bright
galaxies with W_{Ly{\alpha}}>20 {\AA} exhibit weaker Ly{\alpha} emission at
lower redshifts, although we caution that this could be caused by spectroscopic
confirmation of low Ly{\alpha} equivalent width galaxies being harder at z~3
than z~2.
01/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We have co-added the X-ray flux of all known Lyα emitters (LAEs) in the 4 Ms Chandra Deep Field South (CDF-S) region, achieving the tightest upper limits yet on the X-ray to Lyα ratio. We use the X-ray data to place sensitive upper limits on the average unobscured star formation rate (SFR X ) in these galaxies. A very small fraction of Lyα galaxies in the field are individually detected in the X-rays, implying a low fraction of active galactic nucleus activity. After excluding the few X-ray-detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S data and 250 ks Extended CDF-S (ECDF-S) data, and compute a 1σ upper limit on SFR X < 1.6, 14, 28, 28, 140, 440, 880 M ☉ yr–1 for LAEs located at z ~ 0.3 and z = 2.1, 3.1, 3.2, 4.5, 5.7, and 6.5, respectively. The upper limit of SFR X in LAEs can be then compared to SFRLyα derived from Lyα line and thus can constrain on the Lyα escape fraction (f Esc Lyα). The f Esc Lyα from X-ray at z ~ 0.3 is substantially larger than that from UV or Hα. Three X-ray-detected LAE galaxies at z ~ 0.3 show f Esc Lyα ~ 3%-22%, and the average Lyα escape fraction from stacking the X-ray-undetected LAEs show f Esc Lyα > 28% at 3σ significance level at the same redshift. We derive a lower limit on f Esc Lyα > 14% (84% confidence level, 1σ lower limit) for LAEs at redshift z ~ 2.1 and z ~ 3.1-3.2. At z > 4, the current LAE samples are not of sufficient size to constrain SFR X well. By averaging all the LAEs at z > 2, the X-ray non-detection constrains f Esc Lyα > 17% (84% confidence level, 1σ lower limit), and rejects f Esc Lyα < 5.7% at the 99.87% confidence level from 2.1 < z < 6.5.
The Astrophysical Journal 01/2012; 746(1):28. · 6.02 Impact Factor
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Robin Ciardullo, Caryl Gronwall,
Christopher Wolf,
Emily McCathran,
Nicholas A. Bond,
Eric Gawiser,
Lucia Guaita,
John J. Feldmeier,
Ezequiel Treister,
Nelson Padilla,
Harold Francke,
Ana Matković,
Martin Altmann,
and David Herrera
[show abstract]
[hide abstract]
ABSTRACT: We describe the results of a new, wide-field survey for z = 3.1 Lyα emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010 Å filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141 objects with monochromatic fluxes brighter than 2.4 × 10–17 erg cm–2 s–1 and observers-frame equivalent widths (EWs) greater than ~80 Å (i.e., 20 Å in the rest frame of Lyα). The bright end of this data set is dominated by X-ray sources and foreground objects with Galaxy Evolution Explorer detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filter's redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z = 3.1 LAE emission-line luminosity function and show that an apparent anticorrelation between EW and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic data set. Finally, we compare the properties of z = 3.1 LAEs to LAEs found at z = 2.1. We show that in the ~1 Gyr after z ~ 3, the LAE luminosity function evolved significantly, with L* fading by ~0.4 mag, the number density of sources with L > 1.5 × 1042 erg s–1 declining by ~50%, and the EW scale length contracting from 70+7 – 5 Å to 50+9 – 6 Å. When combined with literature results, our observations demonstrate that over the redshift range z ~ 0 to z ~ 4, LAEs contain less than ~10% of the star formation rate density of the universe.
The Astrophysical Journal 12/2011; 744(2):110. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The Lya emission has been observed from galaxies over a redshift span z ~ 0 -
8.6. However, the evolution of high-redshift Lya emitters (LAEs), and the link
between these populations and local galaxies, remain poorly understood. Here,
we investigate the Lya properties of progenitors of a local L* galaxy by
combining cosmological hydrodynamic simulations with three-dimensional
radiative transfer calculations using the new ART^2 code. We find that the main
progenitor (the most massive one) of a Milky Way-like galaxy has a number of
Lya properties close to those of observed LAEs at z ~ 2 - 6, but most of the
fainter ones appear to fall below the detection limits of current surveys. The
Lya photon escape fraction depends sensitively on a number of physical
properties of the galaxy, such as mass, star formation rate, and metallicity,
as well as galaxy morphology and orientation. Moreover, we find that
high-redshift LAEs show blue-shifted Lya line profiles characteristic of gas
inflow, and that the Lya emission by excitation cooling increases with
redshift, and becomes dominant at z > 6. Our results suggest that some observed
LAEs at z ~ 2-6 with luminosity of L_Lya ~ 10^{42-43} ergs/s may be similar to
the main progenitor of the Milky Way at high redshift, and that they may evolve
into present-day L* galaxies.
12/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present a morphological analysis of the rest-frame ultraviolet emission of 78 resolved, high signal-to-noise z ~ 3.1 Lyα emitters (LAEs) in the Extended Chandra Deep Field-South. Using Hubble Space Telescope/Advanced Camera for Surveys V-band images taken as part of the Galaxy Evolution from Morphology and SEDs, Great Observatories Origins Deep Survey, and Hubble Ultra Deep Field surveys, we investigate both single-component and multi-component LAEs, and derive concentration indices, Sérsic indices, ellipticities, and half-light radii for all resolved components and systems with a signal-to-noise >30. We show that, although the LAE population is heterogeneous in nature, most LAEs are highly concentrated, with a distribution of C values similar to that measured for field stars; this suggests that the diagnostic is a poor discriminator near the resolution limit. The LAEs also display a wide range of Sérsic indices (0 < n < 12), similar to that seen for galaxies in the local neighborhood. However, the majority of LAEs have n < 2, and a visual inspection of the images suggests that the small-n objects have extended or multimodal luminosity profiles, while the LAEs with n > 2 have compact components surrounded by diffuse emission. Moreover, unlike nearby spiral galaxies, whose distribution of ellipticities is flat, the LAE ellipticity distribution peaks near 1 – b/a ~ 0.55. Thus, the population has more in common with z ~ 3 Lyman-break galaxies than local star-forming objects.
The Astrophysical Journal 11/2011; 743(1):9. · 6.02 Impact Factor
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Peter J. Brown,
Kyle S. Dawson,
Massimiliano de Pasquale, Caryl Gronwall,
Stephen Holland,
Stefan Immler,
Paul Kuin,
Paolo Mazzali,
Peter Milne,
Samantha Oates,
Michael Siegel
[show abstract]
[hide abstract]
ABSTRACT: We present the earliest ultraviolet (UV) observations of the bright Type Ia
supernova SN 2011fe/PTF11kly in the nearby galaxy M101 at a distance of only
6.4 Mpc. It was discovered shortly after explosion by the Palomar Transient
Factory and first observed by Swift/UVOT about a day after explosion. The early
UV light is well-defined, with ~20 data points per filter in the five days
after explosion. These early and well-sampled UV observations form new template
light curves for comparison with observations of other SNe Ia at low and high
redshift. We report fits from semi-empirical models of the explosion and find
the time evolution of the early UV flux to be well fit by the superposition of
two parabolic curves. Finally, we use the early UV flux measurements to examine
a possible shock interaction with a non-degenerate companion. From models
predicting the measurable shock emission, we find that even a solar mass
companion at a distance of a few solar radii is unlikely at more than 95%
confidence.
10/2011;
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Robin Ciardullo, Caryl Gronwall,
Christopher Wolf,
Emily McCathran,
Nicholas A. Bond,
Eric Gawiser,
Lucia Guaita,
John J. Feldmeier,
Ezequiel Treister,
Nelson Padilla,
Harold Francke,
Ana Matkovic,
Martin Altmann,
David Herrera
[show abstract]
[hide abstract]
ABSTRACT: We describe the results of a new, wide-field survey for z=3.1 Ly-alpha
emission-line galaxies (LAEs) in the Extended Chandra Deep Field South
(ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary
broadband photometry from the MUSYC survey, we identify a complete sample of
141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and
observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20
Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is
dominated by x-ray sources and foreground objects with GALEX detections, but
when these interlopers are removed, we are still left with a sample of 130 LAE
candidates, 39 of which have spectroscopic confirmations. This sample overlaps
the set of objects found in an earlier ECDF-S survey, but due to our filter's
redder bandpass, it also includes 68 previously uncataloged sources. We confirm
earlier measurements of the z=3.1 LAE emission-line luminosity function, and
show that an apparent anti-correlation between equivalent width and continuum
brightness is likely due to the effect of correlated errors in our
heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to
LAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity
function evolved significantly, with L* fading by ~0.4 mag, the number density
of sources with L > 1.5E42 ergs/s declining by ~50%, and the equivalent width
scale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms.
When combined with literature results, our observations demonstrate that over
the redshift range z~0 to z~4, LAEs contain less than ~10% of the
star-formation rate density of the universe.
09/2011;
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[show abstract]
[hide abstract]
ABSTRACT: (Abridged) While the Swift satellite is primarily designed to study gamma-ray
bursts, its ultraviolet and optical imaging and spectroscopy capabilities are
also being used for a variety of scientific programs. In this study, we use the
UV/Optical Telescope (UVOT) instrument aboard Swift to discover 0.5<z<2 Lyman
break galaxies (LBGs). UVOT has covered ~266 arcmin^2 at >60ks exposure time,
achieving a limiting magnitude of u<24.5, in the Chandra Deep Field South
(CDF-S). Applying UVOT near-ultraviolet color selection, we select 50
UV-dropouts from this UVOT CDF-S data. We match the selected sources with
available multiwavelength data from GOODS-South, MUSYC, and COMBO-17 to
characterize the spectral energy distributions for these galaxies and determine
stellar masses, star formation rates (SFRs), and dust attenuations. We compare
these properties for LBGs selected in this paper versus z~3 LBGs and other
CDF-S galaxies in the same redshift range (0.5<z<2), identified using
photometric redshift techniques. The z~1 LBGs have slightly lower stellar
masses compared to z~3 LBGs and slightly higher stellar masses compared to the
z~1 CDF-S galaxies. Similarly, our sample of z~1 LBGs has SFRs (derived using
both ultraviolet and infrared data, where available) nearly an order of
magnitude lower than z~3 LBGs but slightly higher than the comparison z~1
sample of CDF-S galaxies. We find that our z~1 UV-dropouts have A_FUV higher
than z~3 LBGs, but is similar to the distribution of dust attenuations in the
other CDF-S galaxies. Using the GOODS-South multiwavelength catalog of
galaxies, we simulate a larger and fainter sample of LBGs to compare their
properties with those of the UVOT-selected LBG sample. We conclude that UVOT
can be useful for finding and studying the bright end of 0.5<z<2.0 LBGs.
07/2011;
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Guillermo A. Blanc,
Joshua J. Adams,
Karl Gebhardt,
Gary J. Hill,
Niv Drory,
Lei Hao,
Ralf Bender,
Robin Ciardullo,
Steven L. Finkelstein,
Alexander B. Fry, [......], Caryl Gronwall,
Ulrich Hopp,
Donghui Jeong,
Ralf Kelzenberg,
Eiichiro Komatsu,
Phillip MacQueen,
Jeremy D. Murphy,
Martin M. Roth,
Donald P. Schneider,
and Joseph Tufts
[show abstract]
[hide abstract]
ABSTRACT: We study the escape of Lyα photons from Lyα emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B – V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Lyα luminosity and that predicted by the dust-corrected SFR yields the Lyα escape fraction. We also measure the Lyα luminosity function and luminosity density (ρLyα) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of ρLyα. We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Lyα escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Lyα) > (3-6) × 1042 erg s–1 (0.25-0.5 L*), have a mean E(B – V) = 0.13 ± 0.01, implying an attenuation of ~70% in the UV. They show a median UV uncorrected SFR = 11 M ☉ yr–1, dust-corrected SFR = 34 M ☉ yr–1, and Lyα equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Lyα escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Lyα escape fraction in LAEs correlates with E(B – V) in a way that is expected if Lyα photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Lyα EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Lyα can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Lyα escape fraction of LAEs from z ~ 4 to 2. We see hints of a drop in the number density of LAEs from z ~ 4 to 2 in the redshift distribution and the Lyα luminosity function, although larger samples are required to confirm this. The mean Lyα escape fraction of the overall galaxy population decreases significantly from z ~ 6 to z ~ 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z ~ 6 and 2, reducing their Lyα escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Lyα photons is reached by z ~ 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.
The Astrophysical Journal 06/2011; 736(1):31. · 6.02 Impact Factor
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ABSTRACT: We have coadded X-ray flux of all known Lyman Alpha Emitters (LAEs) in the 4
Msec Chandra Deep Field South (CDF-S) region, to place sensitive upper limits
on the average unobscured star-formation rate (SFR_X) in these galaxies. A very
small fraction of Lyman-Alpha galaxies in the field are individually detected
in the X-rays, implying a low fraction of AGN activity. After excluding the few
X-ray detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S
data and 250 ks Extended CDF-S (ECDFS) data, and compute a 1-\sigma upper limit
on SFR_X < 14, 28, 28, 140, 440, 880 M$_{\sun}$ yr$^{-1}$ for LAEs located at z
= 2.1, 3.1, 3.2, 4.5, 5.7 and 6.5, respectively. The upper limit of SFR_X in
LAEs can be then be compared to SFR$_{Ly\alpha}$ derived from Lyman-Alpha line
and thus can constrain on the Lyman-Alpha escape fraction
($f^{Esc}_{Ly\alpha}$). We derive a lower limit on f(Lyman-Alpha Escape) > 14%
(84 % confidence level, 1-\sigma lower limit) for LAEs at redshift z ~ 2.1 and
z ~ 3.1-3.2. At z > 4, the current LAE samples are not of sufficient size to
constrain SFR_X well. By averaging all the LAEs at z> 2, the X-ray
non-detection constrains f(Lyman-Alpha Escape) > 17% (84 % confidence level,
1-\sigma lower limit), and rejects f(Lyman-Alpha Escape) < 5.7% at the 99.87%
confidence level from 2.1 < z < 6.5.
06/2011;
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ABSTRACT: We present a rest-frame ultraviolet morphological analysis of 108 z=2.1 Lyman
Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and
compare it to a similar sample of 171 LAEs at z=3.1. Using Hubble Space
Telescope (HST) images from the Galaxy Evolution from Morphology and SEDs
survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we
measure size and photometric component distributions, where photometric
components are defined as distinct clumps of UV-continuum emission. At both
redshifts, the majority of LAEs have observed half-light radii <~ 2 kpc, but
the median half-light radius rises from 1.0 kpc at z=3.1 to 1.4 kpc at z=2.1. A
similar evolution is seen in the sizes of individual rest-UV components, but
there is no evidence for evolution in the number of multi-component systems. In
the z=2.1 sample, we see clear correlations between the size of an LAE and
other physical properties derived from its SED. LAEs are found to be larger for
galaxies with higher stellar mass, star formation rate, and dust obscuration,
but there is no evidence for a trend between equivalent width and half-light
radius at either redshift. The presence of these correlations suggests that a
wide range of objects are being selected by LAE surveys at z~2, including a
significant fraction of objects for which a massive and moderately extended
population of old stars underlies the young starburst giving rise to the Lyman
alpha emission.
04/2011;
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Steven L. Finkelstein,
Gary J. Hill,
Karl Gebhardt,
Joshua Adams,
Guillermo A. Blanc,
Casey Papovich,
Robin Ciardullo,
Niv Drory,
Eric Gawiser, Caryl Gronwall,
Donald P. Schneider,
and Kim-Vy Tran
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ABSTRACT: We present the results of Keck/NIRSPEC spectroscopic observations of three Lyα emitting galaxies (LAEs) at z~ 2.3 discovered with the HETDEX pilot survey. We detect Hα, [O III], and Hβ emission from two galaxies at z= 2.29 and 2.49, designated HPS194 and HPS256, respectively, representing the first detection of multiple rest-frame optical emission lines in galaxies at high redshift selected on the basis of their Lyα emission. We find that the redshifts of the Lyα emission from these galaxies are offset redward of the systemic redshifts (derived from the Hα and [O III] emission) by Δv = 162 ± 37 (photometric) ± 42 (systematic) km s–1 for HPS194 and Δv = 36 ± 35 ± 18 km s–1 for HPS256. An interpretation for HPS194 is that a large-scale outflow may be occurring in its interstellar medium. This outflow is likely powered by star-formation activity, as examining emission line ratios implies that neither LAE hosts an active galactic nucleus. Using the upper limits on the [N II] emission, we place meaningful constraints on the gas-phase metallicities in these two LAEs of Z< 0.17 and < 0.28 Z ☉ (1σ). Measuring the stellar masses of these objects via spectral energy distribution (SED) fitting (~1010 and 6 × 108 M ☉, respectively), we study the nature of LAEs in a mass-metallicity plane. At least one of these two LAEs appears to be more metal poor than continuum-selected star-forming galaxies at the same redshift and stellar mass, implying that objects exhibiting Lyα emission may be systematically less chemically enriched than the general galaxy population. We use the SEDs of these two galaxies to show that neglecting the contribution of the measured emission line fluxes when fitting stellar population models to the observed photometry can result in overestimates of the population age by orders of magnitude and the stellar mass by a factor of ~2. This effect is particularly important at z 7, where similarly strong emission lines may masquerade in the photometry as a 4000 Å break.
The Astrophysical Journal 02/2011; 729(2):140. · 6.02 Impact Factor
