180 research outputs found
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 (WFC3) 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. The high sensitivity of these grism observations, with >1σ detections of emission lines to f > 2.5 × 10^(–18) erg s^(–1) cm^(–2), means that the galaxies in the sample are typically ~7 times less massive (median M_* = 10^(9.5) M_☉) than previously studied z ~ 2 emission-line galaxies. Despite their lower mass, the galaxies have [O III]/Hβ 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 [O III] emission line is more spatially concentrated than the Hβ emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L_([O III])/L_(0.5-10keV) ratio is intermediate between typical z ~ 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O III] 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
Rest Frame Optical Spectra of Lyman Break Galaxies: Other Lensing Arcs around MS1512-cB58
We have obtained near-infrared spectra of two images of the galaxy at z=2.72 which is gravitationally lensed by the foreground cluster MS1512+36. The brighter arc, cB58, is an image of only the nucleus and the southern half of the background galaxy, while the fainter image, A2, encompasses the entire background galaxy. Thus the gravitational lensing provides spatial resolution on a smaller scale than is routinely available by other methods.
Our observations indicate no evidence for any systematic rotational velocity gradient across the face of this galaxy. The nucleus and outer regions of the galaxy do not differ in their gas reddening or excitation level, based on the identical Hα/5007 ratios. cB58 (which is more dominated by the nucleus) has relatively stronger continuum emission, perhaps because of a higher ratio of old to young stars, compared to the outer parts of the galaxy.
A second emission line source, denoted as K1, at a slightly lower redshift was serendipitously detected in the slit. It appears to be the gravitationally lensed image of another background galaxy in the same group as cB58
Near-Infrared Observations of the Environments of Radio Quiet QSOs at z >~ 1
We present the results of an infrared survey of QSO fields at z=0.95, 0.995
and 1.5. Each z<1 field was imaged to typical continuum limits of J=20.5,
Kprime=19 (5 sigma), and line fluxes of 1.3E10{-16}ergs/cm^2/s (1 sigma)in a 1%
interference filter. 16 fields were chosen with z~0.95 targets, 14 with z~0.995
and 6 with z~1.5. A total area of 0.05 square degrees was surveyed, and two
emission-line objects were found. We present the infrared and optical
photometry of these objects. Optical spectroscopy has confirmed the redshift of
one object (at z=0.989) and is consistent with the other object having a
similar redshift. We discuss the density of such objects across a range of
redshifts from this survey and others in the literature. We also present
number-magnitude counts for galaxies in the fields of radio quiet QSOs,
supporting the interpretation that they exist in lower density environments
than their radio loud counterparts. The J-band number counts are among the
first to be published in the J=16--20.Comment: 34 pages, including 12 figures; accepted for publication in the Ap
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
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8-1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z > 1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10^9 M_☉ to z ≈ 2, reaching the knee of the ultraviolet luminosity function of galaxies to z ≈ 8. The survey covers approximately 800 arcmin^2 and is divided into two parts. The CANDELS/Deep survey (5σ point-source limit H = 27.7 mag) covers ~125 arcmin^2 within Great Observatories Origins Deep Survey (GOODS)-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (Extended Groth Strip, COSMOS, and Ultra-deep Survey) and covers the full area to a 5σ point-source limit of H ≳ 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding-cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper
The Counter Arc to MS1512-cB58 and a Companion Galaxy
We present near-infrared spectra of ``A2'', the primary counter arc to the
gravitationally lensed galaxy MS1512-cB58. The spectra showredshifted H-alpha,
[NII], [OIII], and H-beta at z=2.728 +/- 0.001. We observe the same
H-alpha/[OIII] ratio as cB58, which together with the redshift confirms that A2
is indeed another image of a single background galaxy. Published lensing
reconstruction reports that A2 is a magnification of the entire source, while
cB58 is an image of only a part. At marginal significance, A2 shows higher line
to continuum ratios than cB58 (by a factor of about 2), suggesting a
non-uniform ratio of young to old stars across the galaxy. We observe a second
emission line source in the slit. This object, ``W5'', is predicted to be a
lensed image of another galaxy at a redshift similar to cB58. W5 is blueshifted
from cB58 by about 400 km/s and has a significantly lower H-alpha/[OIII] ratio,
confirming that it is an image of a different background galaxy in a group with
cB58. The H-alpha emission line in W5 implies a star formation rate of 6
Msun/yr (H_0 = 70 km/s/Mpc, Omega_M=0.3, Omega_L=0.7), after correcting for
lensing magnification.Comment: Accepted by ApJ. 18 pages including 5 figure
Far-Ultraviolet Number Counts on Field Galaxies
The far-ultraviolet (FUV) number counts of galaxies constrain the evolution of the star formation rate density of the universe. We report the FUV number counts computed from FUV imaging of several fields including the Hubble Ultra Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North and South fields. These data were obtained with the Hubble Space Telescope (HST) Solar Blind Channel of the Advance Camera for Surveys. The number counts sample an FUV AB magnitude range from 21 to 29 and cover a total area of 15.9 arcmin^2, ~4 times larger than the most recent HST FUV study. Our FUV counts intersect bright FUV Galaxy Evolution Explorer counts at 22.5 mag and they show good agreement with recent semi-analytic models based on dark matter "merger trees" by R. S. Somerville et al. We show that the number counts are ~35% lower than in previous HST studies that use smaller areas. The differences between these studies are likely the result of cosmic variance; our new data cover more lines of sight and more area than previous HST FUV studies. The integrated light from field galaxies is found to contribute between 65.9^(+8)_(–8) and 82.6^(+12)_(–)12 photons s^(–1) cm^(–2) sr^(–1) Å^(–1) to the FUV extragalactic background. These measurements set a lower limit for the total FUV background light
Far-Ultraviolet Number Counts of Field Galaxies
The far-ultraviolet (FUV) number counts of galaxies constrain the evolution
of the star-formation rate density of the universe. We report the FUV number
counts computed from FUV imaging of several fields including the Hubble Ultra
Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North
and -South fields. These data were obtained with the Hubble Space Telescope
Solar Blind Channel of the Advance Camera for Surveys. The number counts sample
a FUV AB magnitude range from 21-29 and cover a total area of 15.9 arcmin^2, ~4
times larger than the most recent HST FUV study. Our FUV counts intersect
bright FUV GALEX counts at 22.5 mag and they show good agreement with recent
semi-analytic models based on dark matter "merger trees" by Somerville et al.
(2011). We show that the number counts are ~35% lower than in previous HST
studies that use smaller areas. The differences between these studies are
likely the result of cosmic variance; our new data cover more lines of sight
and more area than previous HST FUV studies. The integrated light from field
galaxies is found to contribute between 65.9 +/-8 - 82.6 +/-12
photons/s/cm^2/sr/angstrom to the FUV extragalactic background. These
measurements set a lower limit for the total FUV background light.Comment: Accepted for publication in ApJ, including 34 pages, 6 figures, and 2
table
Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density
We present the luminosity function of [OII]-emitting galaxies at a median
redshift of z=0.9, as measured in the deep spectroscopic data in the STIS
Parallel Survey (SPS). The luminosity function shows strong evolution from the
local value, as expected. By using random lines of sight, the SPS measurement
complements previous deep single field studies. We calculate the density of
inferred star formation at this redshift by converting from [OII] to H-alpha
line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014
Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 =
70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a
(1+z)^4 evolution in global star formation since z~1. To reconcile the density
with similar measurements made by surveys targeting H-alpha may require
substantial extinction correction.Comment: 16 preprint pages including 5 figures; accepted for publication in
Ap
Galaxy Morphology from NICMOS Parallel Imaging
We present high resolution NICMOS images of random fields obtained in
parallel to other HST observations. We present galaxy number counts reaching
H=24. The H-band galaxy counts show good agreement with the deepest I- and
K-band counts obtained from ground-based data. We present the distribution of
galaxies with morphological type to H<23. We find relatively fewer irregular
galaxies compared to an I-band sample from the Hubble Deep Field, which we
attribute to their blue color, rather than to morphological K-corrections. We
conclude that the irregulars are intrinsically faint blue galaxies at z<1.Comment: 13 pages, including 4 figures. Accepted for publication in ApJ
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