195 research outputs found
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
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
A High-Resolution Hubble Space Telescope Study of Apparent Lyman Continuum Leakers at
We present follow-up observations of 16
candidate LyC emitters in the HS1549+1919 field. With these data, we
obtain high spatial-resolution photometric redshifts of all sub-arcsecond
components of the LyC candidates in order to eliminate foreground contamination
and identify robust candidates for leaking LyC emission. Of the 16 candidates,
we find one object with a robust LyC detection that is not due to foreground
contamination. This object (MD5) resolves into two components; we refer to the
LyC-emitting component as MD5b. MD5b has an observed 1500\AA\ to 900\AA\
flux-density ratio of , compatible with
predictions from stellar population synthesis models. Assuming minimal IGM
absorption, this ratio corresponds to a relative (absolute) escape fraction of
% (%). The stellar
population fit to MD5b indicates an age of Myr, which is in the
youngest 10% of the sample and the youngest third of typical
Lyman break galaxies, and may be a contributing factor to its LyC detection. We
obtain a revised, contamination-free estimate for the comoving specific
ionizing emissivity at , indicating (with large uncertainties) that
star-forming galaxies provide roughly the same contribution as QSOs to the
ionizing background at this redshift. Our results show that foreground
contamination prevents ground-based LyC studies from obtaining a full
understanding of LyC emission from star-forming galaxies. Future
progress in direct LyC searches is contingent upon the elimination of
foreground contaminants through high spatial-resolution observations, and upon
acquisition of sufficiently deep LyC imaging to probe ionizing radiation in
high-redshift galaxies.Comment: 31 pages, 5 tables, 19 figures. Accepted to ApJ. Version with
full-resolution figures is available at:
http://www.astro.ucla.edu/~aes/Mostardi_HST_LyC.pd
Near-Ultraviolet Sources in the Hubble Ultra Deep Field: The Catalog
The catalog from the first high-resolution U-band image of the Hubble Ultra Deep Field, taken with Hubble's Wide-Field Planetary Camera 2 through the F300W filter, is presented. We detect 96 U-band objects and compare and combine this catalog with a Great Observatories Origins Deep Survey B-selected catalog that provides B, V, i, and z photometry, spectral types, and photometric redshifts. We have also obtained far-ultraviolet (FUV, 1614 Ã…) data with Hubble's Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) and with GALEX. We detected 31 sources with ACS/SBC, 28 with GALEX/FUV, and 45 with GALEX/NUV. The methods of observations, image processing, object identification, catalog preparation, and catalog matching are presented
Constraining C iii] Emission in a Sample of Five Luminous z = 5.7 Galaxies
Recent observations have suggested that the CIII] emission
lines could be alternative diagnostic lines for galaxies in the reionization
epoch. We use the F128N narrowband filter on the Hubble Space Telescope's
() Wide Field Camera 3 (WFC3) to search for CIII] emission in a
sample of five galaxies at z = 5.7 in the Subaru Deep Field and the
Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with
the broadband imaging, we do not detect CIII] emission for the five galaxies
with ranging from 24.10 -- 27.00 in our sample. For the brightest
galaxy J132416.13+274411.6 in our sample (z = 5.70, ),
which has a significantly higher signal to noise, we report a CIII] flux of
, which places a
stringent 3- upper limit of $\mathrm{erg\
s^{-1}\ cm^{-2}}\rm\sigma\mathrm{2.55\times10^{-18}\ erg\ s^{-1}\ cm^{-2}}\rm\sigma>$ 5.70 exhibit a wide range
of distribution. Our strong limits on CIII] emission could be used as a guide
for future observations in the reionization epoch
Galaxy–galaxy lensing in the outskirts of CLASH clusters: constraints on local shear and testing mass–luminosity scaling relation
We present a selection of 24 candidate galaxy–galaxy lensing (GGL) identified from Hubble images in the outskirts of the massive galaxy clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) . These GGLs provide insights into the mass distributions at larger scales than the strong-lensing region in the cluster cores. We built parametric mass models for three of these GGLs showing simple lensing configurations, in order to assess the properties of their lens and its environment. We show that the local shear estimated from the GGLs traces the gravitational potential of the clusters at a radial distance of 1–2 arcmin, allowing us to derive their velocity dispersion. We also find a good agreement between the strength of the shear measured at the GGL positions through strong-lensing modelling and the value derived independently from a weak-lensing analysis of the background sources. Overall, we show the advantages of using single GGL events in the outskirts of clusters to robustly constrain the local shear, even when only photometric redshift estimates are known for the source. We argue that the mass–luminosity scaling relation of cluster members can be tested by modelling the GGLs found around them, and show that the mass parameters can vary up to ∼30 per cent between the cluster and GGL models assuming this scaling relation
Spectroscopic detections of CIII]1909 at z~6-7: A new probe of early star forming galaxies and cosmic reionisation
Deep spectroscopic observations of z~6.5 galaxies have revealed a marked
decline with increasing redshift in the detectability of Lyman-alpha emission.
While this may offer valuable insight into the end of the reionisation process,
it presents a fundamental challenge to the detailed spectroscopic study of the
many hundreds of photometrically-selected distant sources now being found via
deep HST imaging, and particularly those bright sources viewed through
foreground lensing clusters. In this paper we demonstrate the validity of a new
way forward via the convincing detection of an alternative diagnostic line,
CIII]1909, seen in spectroscopic exposures of two star forming galaxies at
z=6.029 and 7.213. The former detection is based on a 3.5 hour X-shooter
spectrum of a bright (J=25.2) gravitationally-lensed galaxy behind the cluster
Abell 383. The latter detection is based on a 4.2 hour MOSFIRE spectra of one
of the most distant spectroscopically confirmed galaxies, GN-108036, with
J=25.2. Both targets were chosen for their continuum brightness and
previously-known redshift (based on Lyman-alpha), ensuring that any CIII]
emission would be located in a favorable portion of the near-infrared sky
spectrum. We compare our CIII] and Lyman-alpha equivalent widths in the context
of those found at z~2 from earlier work and discuss the motivation for using
lines other than Lyman-alpha to study galaxies in the reionisation era.Comment: 10 pages, 6 figures, submitted to MNRA
Q1549-C25: A Clean Source of Lyman-Continuum Emission at
We present observations of Q1549-C25, an ~L* star-forming galaxy at z=3.15
for which Lyman-continuum (LyC) radiation is significantly detected in deep
Keck/LRIS spectroscopy. We find no evidence for contamination from a
lower-redshift interloper close to the line of sight in the high
signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25
in V_606, J_125, and H_160 Hubble Space Telescope (HST) imaging reveals that
the object consists of a single, isolated component within 1". In combination,
these data indicate Q1549-C25 as a clean spectroscopic detection of LyC
radiation, only the second such object discovered to date at z~3. We model the
spectral energy distribution (SED) of Q1549-C25, finding evidence for
negligible dust extinction, an age (assuming continuous star formation) of ~1
Gyr, and a stellar mass of M_*=7.9x10^9 M_sun. Although it is not possible to
derive strong constraints on the absolute escape fraction of LyC emission,
f_esc(LyC), from a single object, we use simulations of intergalactic and
circumgalactic absorption to infer f_esc(LyC)>=0.51 at 95% confidence. The
combination of deep Keck/LRIS spectroscopy and HST imaging is required to
assemble a larger sample of objects like Q1549-C25, and obtain robust
constraints on the average f_esc(LyC) at z~3 and beyond.Comment: 6 pages, 5 figures, accepted to ApJ Letter
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