166 research outputs found
Tracing Galaxy Assembly: Tadpole Galaxies in the Hubble Ultra Deep Field
In the Hubble Ultra Deep Field (HUDF) an abundance of galaxies is seen with a
knot at one end plus an extended tail, resembling a tadpole. These "tadpole
galaxies" appear dynamically unrelaxed--presumably in an early merging
state--where tidal interactions likely created the distorted knot-plus-tail
morphology. Here we systematically select tadpole galaxies from the HUDF and
study their properties as a function of their photometric redshifts. In a
companion HUDF variability study, Cohen et al. (2005) revealed a total of 45
variable objects believed to be Active Galactic Nuclei (AGN). Here we show that
this faint AGN sample has no overlap with the tadpole galaxy sample, as
predicted by theoretical work. The tadpole morphology--combined with the lack
of overlap with the variable objects--supports the idea that these galaxies are
in the process of an early-stage merger event, i.e., at a stage that likely
precedes the "turn-on" of any AGN component and the onset of any point-source
variability.Comment: 7 pages, 4 figures. Accepted for publication by Astrophysical Journa
Emission-Line Galaxies from the HST PEARS Grism Survey I: The South Fields
We present results of a search for emission-line galaxies in the Southern
Fields of the Hubble Space Telescope PEARS (Probing Evolution And Reionization
Spectroscopically) grism survey. The PEARS South Fields consist of five ACS
pointings (including the Hubble Ultra Deep Field) with the G800L grism for a
total of 120 orbits, revealing thousands of faint object spectra in the
GOODS-South region of the sky. Emission-line galaxies (ELGs) are one subset of
objects that are prevalent among the grism spectra. Using a 2-dimensional
detection and extraction procedure, we find 320 emission lines orginating from
226 galaxy "knots'' within 192 individual galaxies. Line identification results
in 118 new grism-spectroscopic redshifts for galaxies in the GOODS-South Field.
We measure emission line fluxes using standard Gaussian fitting techniques. At
the resolution of the grism data, the H-beta and [OIII] doublet are blended.
However, by fitting two Gaussian components to the H-beta and [OIII] features,
we find that many of the PEARS ELGs have high [OIII]/H-beta ratios compared to
other galaxy samples of comparable luminosities. The star-formation rates
(SFRs) of the ELGs are presented, as well as a sample of distinct giant
star-forming regions at z~0.1-0.5 across individual galaxies. We find that the
radial distances of these HII regions in general reside near the galaxies'
optical continuum half-light radii, similar to those of giant HII regions in
local galaxies.Comment: 15 pages, 13 figures; Accepted for publication in A
Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at z>1
We identify an abundant population of extreme emission line galaxies (EELGs)
at redshift z~1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy
Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3
(HST/WFC3). 69 EELG candidates are selected by the large contribution of
exceptionally bright emission lines to their near-infrared broad-band
magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission
lines -- with rest-frame equivalent widths ~1000\AA -- in the four candidates
that have HST/WFC3 grism observations, we conclude that these objects are
galaxies with 10^8 Msol in stellar mass, undergoing an enormous starburst phase
with M_*/(dM_*/dt) of only ~15 Myr. These bursts may cause outflows that are
strong enough to produce cored dark matter profiles in low-mass galaxies. The
individual star formation rates and the co-moving number density (3.7x10^-4
Mpc^-3) can produce in ~4 Gyr much of the stellar mass density that is
presently contained in 10^8-10^9 Msol dwarf galaxies. Therefore, our
observations provide a strong indication that many or even most of the stars in
present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z>1.Comment: accepted for publication in ApJ; 10 pages; 6 figures; 1 tabl
Emission-Line Galaxies from the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) Grism Survey. II: The Complete Sample
We present a full analysis of the Probing Evolution And Reionization
Spectroscopically (PEARS) slitess grism spectroscopic data obtained with the
Advanced Camera for Surveys on HST. PEARS covers fields within both the Great
Observatories Origins Deep Survey (GOODS) North and South fields, making it
ideal as a random survey of galaxies, as well as the availability of a wide
variety of ancillary observations to support the spectroscopic results. Using
the PEARS data we are able to identify star forming galaxies within the
redshift volume 0< z<1.5. Star forming regions in the PEARS survey are
pinpointed independently of the host galaxy. This method allows us to detect
the presence of multiple emission line regions (ELRs) within a single galaxy.
1162 Ha, [OIII] and/or [OII] emission lines have been identified in the PEARS
sample of ~906 galaxies down to a limiting flux of ~1e-18 erg/s/cm^2. The ELRs
have also been compared to the properties of the host galaxy, including
morphology, luminosity, and mass. From this analysis we find three key results:
1) The computed line luminosities show evidence of a flattening in the
luminosity function with increasing redshift; 2) The star forming systems show
evidence of disturbed morphologies, with star formation occurring predominantly
within one effective (half-light) radius. However, the morphologies show no
correlation with host stellar mass; and 3) The number density of star forming
galaxies with M_* > 1e9} M_sun decreases by an order of magnitude at z<0.5
relative to the number at 0.5<z<0.9 in support of the argument for galaxy
downsizing.Comment: Submitted. 48 pages. 19 figures. Accepted to Ap
Clues to AGN Growth from Optically Variable Objects in the Hubble Ultra Deep Field
We present a photometric search for objects with point-source components that
are optically variable on timescales of weeks--months in the Hubble Ultra Deep
Field (HUDF) to i'(AB)=28.0 mag. The data are split into four sub-stacks of
approximately equal exposure times. Objects exhibiting the signature of optical
variability are selected by studying the photometric error distribution between
the four different epochs, and selecting 622 candidates as 3.0 sigma outliers
from the original catalog of 4644 objects. Of these, 45 are visually confirmed
as free of contamination from close neighbors or various types of image
defects. Four lie within the positional error boxes of Chandra X-ray sources,
and two of these are spectroscopically confirmed AGN. The photometric redshift
distribution of the selected variable sample is compared to that of field
galaxies, and we find that a constant fraction of ~1% of all field objects show
variability over the range of 0.1<z<4.5. Combined with other recent HUDF
results, as well as those of recent state-of-the-art numerical simulations, we
discuss a potential link between the hierarchical merging of galaxies and the
growth of AGN.Comment: 9 pages, 6 figures, accepted for publication in Astrophysical
Journal, minor changes to reference
First results from Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyman-alpha emission and Lyman break from a galaxy at z=7.51
Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and
therefore it is crucial to reliably identify these galaxies. Here, we present
an unambiguous and first simultaneous detection of both the Lyman-alpha
emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the
Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on
Hubble Space Telescope (HST), show a significant emission line detection (6
sigma) in multiple observational position angles (PA), with total integrated
Ly{\alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly
a factor of four higher than the previous MOSFIRE spectroscopic observations of
faint Ly{\alpha} emission at {\lambda} = 1.0347{\mu}m, yielding z = 7.5078+/-
0.0004. This is consistent with other recent observations implying that
ground-based near-infrared spectroscopy underestimates total emission line
fluxes, and if confirmed, can have strong implications for reionization studies
that are based on ground-based Lyman-{\alpha} measurements. A 4-{\sigma}
detection of the NV line in one PA also suggests a weak Active Galactic Nucleus
(AGN), potentially making this source the highest-redshift AGN yet found. Thus,
this observation from the Hubble Space Telescope clearly demonstrates the
sensitivity of the FIGS survey, and the capability of grism spectroscopy to
study the epoch of reionization.Comment: Published in ApJL; matches published versio
The Hubble Legacy Archive ACS Grism Data
A public release of slitless spectra, obtained with ACS/WFC and the G800L
grism, is presented. Spectra were automatically extracted in a uniform way from
153 archival fields (or "associations") distributed across the two Galactic
caps, covering all observations to 2008. The ACS G800L grism provides a
wavelength range of 0.55-1.00 \mu40 \ \AA / pixel\sim 80\ \AA32,149i_{\rm
AB}0.2-4.6$.Comment: Accepted for publication in Astronomy and Astrophysics; 29 pages, 16
Figures, 4 Tables in text and 3Tables in Appendi
The WFC3 Infrared Spectroscopic Parallel (WISP) Survey
We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is
obtaining slitless, near-infrared grism spectroscopy of ~ 90 independent,
high-latitude fields by observing in the pure parallel mode with Wide Field
Camera-3 on the Hubble Space Telescope for a total of ~ 250 orbits. Spectra are
obtained with the G102 (lambda=0.8-1.17 microns, R ~ 210) and G141 grisms
(lambda=1.11-1.67 microns, R ~ 130), together with direct imaging in the J- and
H-bands (F110W and F140W, respectively). In the present paper, we present the
first results from 19 WISP fields, covering approximately 63 square arc
minutes. For typical exposure times (~ 6400 sec in G102 and ~ 2700 sec in
G141), we reach 5-sigma detection limits for emission lines of 5 x 10^(-17)
ergs s^(-1) cm^(-2) for compact objects. Typical direct imaging 5sigma-limits
are 26.8 and 25.0 magnitudes (AB) in F110W and F140W, respectively. Restricting
ourselves to the lines measured with highest confidence, we present a list of
328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The
single-line emitters are likely to be a mix of Halpha and [OIII]5007,4959 A,
with Halpha predominating. The overall surface density of high-confidence
emission-line objects in our sample is approximately 4 per arcmin^(2).These
first fields show high equivalent width sources, AGN, and post starburst
galaxies. The median observed star formation rate of our Halpha selected sample
is 4 Msol/year. At intermediate redshifts, we detect emission lines in galaxies
as faint as H_140 ~ 25, or M_R < -19, and are sensitive to star formation rates
down to less than 1 Msol/year. The slitless grisms on WFC3 provide a unique
opportunity to study the spectral properties of galaxies much fainter than L*
at the peak of the galaxy assembly epoch.Comment: 15 pages, 12 figures, submitted to Ap
Hubble Space Telescope WFC3 Early Release Science: Emission-Line Galaxies from Infrared Grism Observations
We present grism spectra of emission-line galaxies (ELGs) from 0.6-1.6
microns from the Wide Field Camera 3 on the Hubble Space Telescope. These new
infrared grism data augment previous optical Advanced Camera for Surveys G800L
0.6-0.95 micron grism data in GOODS-South from the PEARS program, extending the
wavelength covereage well past the G800L red cutoff. The ERS grism field was
observed at a depth of 2 orbits per grism, yielding spectra of hundreds of
faint objects, a subset of which are presented here. ELGs are studied via the
Ha, [OIII], and [OII] emission lines detected in the redshift ranges 0.2<z<1.4,
1.2<z<2.2 and 2.0<z<3.3 respectively in the G102 (0.8-1.1 microns; R~210) and
G141 (1.1-1.6 microns; R~130) grisms. The higher spectral resolution afforded
by the WFC3 grisms also reveals emission lines not detectable with the G800L
grism (e.g., [SII] and [SIII] lines). From these relatively shallow
observations, line luminosities, star-formation rates, and grism spectroscopic
redshifts are determined for a total of 48 ELGs to m(AB)~25 mag. Seventeen
GOODS-South galaxies that previously only had photometric redshifts now have
new grism-spectroscopic redshifts, in some cases with large corrections to the
photometric redshifts (Delta(z)~0.3-0.5). Additionally, one galaxy had no
previously-measured redshift but now has a secure grism-spectroscopic redshift,
for a total of 18 new GOODS-South spectroscopic redshifts. The faintest source
in our sample has a magnitude m(AB)=26.9 mag. The ERS grism data also reflect
the expected trend of lower specific star formation rates for the highest mass
galaxies in the sample as a function of redshift, consistent with downsizing
and discovered previously from large surveys. These results demonstrate the
remarkable efficiency and capability of the WFC3 NIR grisms for measuring
galaxy properties to faint magnitudes and redshifts to z>2.Comment: Accepted for publication in AJ. Updated to include referee comments.
Updated sample using improved reduction contains 23 new galaxies (Table 1;
Figures 2 & 3
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
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