151 research outputs found
The Sizes of Candidate Galaxies: confirmation of the bright CANDELS sample and relation with luminosity and mass
Recently, a small sample of six candidates was discovered in
CANDELS that are more luminous than any of the previous
galaxies identified over the HUDF/XDF and CLASH fields. We measure
the sizes of these candidates to map out the size evolution of galaxies from
the earliest observable times. Their sizes are also used to provide a valuable
constraint on whether these unusual galaxy candidates are at high redshift.
Using galfit to derive sizes from the CANDELS F160W images of these candidates,
we find a mean size of 0.130.02" (or 0.50.1 kpc at ). This
handsomely matches the 0.6 kpc size expected extrapolating lower redshift
measurements to , while being much smaller than the 0.59" mean size
for lower-redshift interlopers to photometric selections lacking
the blue IRAC color criterion. This suggests that source size may be an
effective constraint on contaminants from selections lacking IRAC
data. Assuming on the basis of the strong photometric evidence that the Oesch
et al. 2014 sample is entirely at , we can use this sample to extend
current constraints on the size-luminosity, size-mass relation, and size
evolution of galaxies to . We find that the candidate
galaxies have broadly similar sizes and luminosities as -8 counterparts
with star-formation-rate surface densities in the range of . The stellar mass-size
relation is uncertain, but shallower than those inferred for lower-redshift
galaxies. In combination with previous size measurements at z=4-7, we find a
size evolution of with for galaxies,
consistent with the evolution previously derived from galaxies.Comment: 9 figures, 5 tables, accepted by Ap
Optical Spectroscopy of Distant Red Galaxies
We present optical spectroscopic follow-up of a sample of Distant Red
Galaxies (DRGs) with K 2.3, in the Hubble Deep
Field South, the MS 1054-03 field, and the Chandra Deep Field South.
Spectroscopic redshifts were obtained for 15 DRGs. Only 2 out of 15 DRGs are
located at z < 2, suggesting a high efficiency to select high-redshift sources.
From other spectroscopic surveys in the CDFS targeting intermediate to high
redshift populations selected with different criteria, we find spectroscopic
redshifts for a further 30 DRGs. We use the sample of spectroscopically
confirmed DRGs to establish the high quality (scatter in \Delta z/(1+z) of ~
0.05) of their photometric redshifts in the considered deep fields, as derived
with EAZY (Brammer et al. 2008). Combining the spectroscopic and photometric
redshifts, we find that 74% of DRGs with K 2. The combined
spectroscopic and photometric sample is used to analyze the distinct intrinsic
and observed properties of DRGs at z 2. In our photometric sample
to K < 22.5, low-redshift DRGs are brighter in K than high-redshift DRGs by 0.7
mag, and more extincted by 1.2 mag in Av. Our analysis shows that the DRG
criterion selects galaxies with different properties at different redshifts.
Such biases can be largely avoided by selecting galaxies based on their
rest-frame properties, which requires very good multi-band photometry and high
quality photometric redshifts.Comment: Accepted for publication in the Astrophysical Journal, 13 pages, 8
figures, 5 table
FIREWORKS U38-to-24 micron photometry of the GOODS-CDFS: multi-wavelength catalog and total IR properties of distant Ks-selected galaxies
We present a Ks-selected catalog, dubbed FIREWORKS, for the Chandra Deep
Field South (CDFS) containing photometry in U_38, B_435, B, V, V_606, R, i_775,
I, z_850, J, H, Ks, [3.6 um], [4.5 um], [5.8 um], [8.0 um], and the MIPS [24
um] band. The imaging has a typical Ks limit of 24.3 mag (5 sigma, AB) and
coverage over 113 arcmin^2 in all bands and 138 arcmin^2 in all bands but H. We
cross-correlate our catalog with the 1 Ms X-ray catalog by Giacconi et al.
(2002) and with all available spectroscopic redshifts to date. We find and
explain systematic differences in a comparison with the 'z_850 + Ks'-selected
GOODS-MUSIC catalog that covers ~90% of the field. We exploit the U38-to-24
micron photometry to determine which Ks-selected galaxies at 1.5<z<2.5 have the
brightest total IR luminosities and which galaxies contribute most to the
integrated total IR emission. The answer to both questions is that red galaxies
are dominating in the IR. This is true no matter whether color is defined in
the rest-frame UV, optical, or optical-to-NIR. We do find however that among
the reddest galaxies in the rest-frame optical, there is a population of
sources with only little mid-IR emission, suggesting a quiescent nature.Comment: Accepted for publication in the Astrophysical Journal, 20 pages, 10
figures, reference to website correcte
Can dusty Lyman break galaxies produce the submillimeter counts and background? Lessons from lensed Lyman break galaxies
Can the submillimeter counts and background be produced by applying a locally
derived extinction correction to the population of Lyman break galaxies? We
investigate the submillimeter emission of two strongly lensed Lyman break
galaxies (MS1512+36-cB58 and MS1358+62-G1) and find that the procedure that is
used to predict the submillimeter emission of the Lyman break galaxy population
overpredicts the observed 850micron fluxes by up to a factor of 14. This result
calls for caution in applying local correlations to distant galaxies. It also
shows that large extinction corrections on Lyman break galaxies should be
viewed with skepticism. It is concluded that the Lyman break galaxies may
contribute to the submillimeter background at the 25 to 50% level. The brighter
submillimeter galaxies making up the rest of the background are either not
detected in optical surveys, or if they are detected, their submillimeter
emission cannot be reliably estimated from their rest-frame ultraviolet
properties.Comment: 4 pages, 1 embedded postscript figure; to appear in proceedings of
the UMass/INAOE conference on Deep Millimeter Surveys, eds. J. Lowenthal and
D. Hughes; revised version corrects small numerical error
Discovery of a dark, massive, ALMA-only galaxy at z~5-6 in a tiny 3-millimeter survey
We report the serendipitous detection of two 3 mm continuum sources found in
deep ALMA Band 3 observations to study intermediate redshift galaxies in the
COSMOS field. One is near a foreground galaxy at 1.3", but is a previously
unknown dust-obscured star-forming galaxy (DSFG) at probable ,
illustrating the risk of misidentifying shorter wavelength counterparts. The
optical-to-mm spectral energy distribution (SED) favors a grey
attenuation curve and results in significantly larger stellar mass and SFR
compared to a Calzetti starburst law, suggesting caution when relating
progenitors and descendants based on these quantities. The other source is
missing from all previous optical/near-infrared/sub-mm/radio catalogs
("ALMA-only"), and remains undetected even in stacked ultradeep optical
( AB) and near-infrared ( AB) images. Using the ALMA position as
a prior reveals faint measurements in stacked IRAC 3.6+4.5,
ultradeep SCUBA2 850m, and VLA 3GHz, indicating the source is real. The
SED is robustly reproduced by a massive M and
M, highly obscured , star forming
Myr galaxy at redshift 1.1. The
ultrasmall 8 arcmin survey area implies a large yet uncertain
contribution to the cosmic star formation rate density CSFRD(z=5)
M yr Mpc, comparable to all
ultraviolet-selected galaxies combined. These results indicate the existence of
a prominent population of DSFGs at , below the typical detection limit of
bright galaxies found in single-dish sub-mm surveys, but with larger space
densities Mpc, higher duty cycles ,
contributing more to the CSFRD, and potentially dominating the high-mass galaxy
stellar mass function.Comment: Accepted for publication in ApJ. 2 galaxies, too many pages, 8
figures, 2 table
Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization
We report the discovery of Lyman-alpha emission (Ly) in the bright
galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at
the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was
selected for spectroscopic observations because of its photometric redshift
(), apparent brightness (H)
and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong
oxygen emission in the [4.5] band. With a total integration of 4.3 hours,
our data reveal an emission line at 11776 {\AA} which we argue is
likely Ly at a redshift , in good
agreement with the photometric estimate. The line was detected independently on
two nights using different slit orientations and its detection significance is
. An overlapping skyline contributes significantly to the
uncertainty on the total line flux although the significance of the detected
line is robust to a variety of skyline-masking procedures. By direct addition
and a Gaussian fit, we estimate a 95\% confidence range of
1.0--2.5 erg s cm, corresponding to a rest-frame
equivalent width of 17--42 {\AA}. EGSY8p7 is the most distant galaxy confirmed
spectroscopically to date, and the third luminous source in the EGS field
beyond with detectable Ly emission viewed at a
time when the intergalactic medium is believed to be fairly neutral. Although
the reionization process was probably patchy, we discuss whether luminous
sources with prominent IRAC color excesses may harbor harder ionizing spectra
than the dominant fainter population thereby creating earlier ionized bubbles.
Further spectroscopic follow-up of such bright sources promises important
insight into the early formation of galaxies.Comment: V3: ApJL accepted; 7 pages, 4 figures, 1 tabl
A Public Ks-selected Catalog in the COSMOS/UltraVISTA Field: Photometry, Photometric Redshifts and Stellar Population Parameters
We present a catalog covering 1.62 deg^2 of the COSMOS/UltraVISTA field with
PSF-matched photometry in 30 photometric bands. The catalog covers the
wavelength range 0.15um - 24um including the available GALEX, Subaru, CFHT,
VISTA and Spitzer data. Catalog sources have been selected from the DR1
UltraVISTA Ks band imaging that reaches a depth of K_{s,tot} = 23.4 AB (90%
completeness). The PSF-matched catalog is generated using position-dependent
PSFs ensuring accurate colors across the entire field. Also included is a
catalog of photometric redshifts (z_phot) for all galaxies computed with the
EAZY code. Comparison with spectroscopy from the zCOSMOS 10k bright sample
shows that up to z ~ 1.5 the z_phot are accurate to dz/(1 + z) = 0.013, with a
catastrophic outlier fraction of only 1.6%. The z_phot also show good agreement
with the z_phot from the NEWFIRM Medium Band Survey (NMBS) out to z ~ 3. A
catalog of stellar masses and stellar population parameters for galaxies
determined using the FAST spectral energy distribution fitting code is provided
for all galaxies. Also included are rest-frame U-V and V-J colors, L_2800 and
L_IR. The UVJ color-color diagram confirms that the galaxy bi-modality is
well-established out to z ~ 2. Star-forming galaxies also obey a star forming
"main sequence" out to z ~ 2.5, and this sequence evolves in a manner
consistent with previous measurements. The COSMOS/UltraVISTA Ks-selected
catalog covers a unique parameter space in both depth, area, and
multi-wavelength coverage and promises to be a useful tool for studying the
growth of the galaxy population out to z ~ 3 - 4.Comment: 20 pages, 14 figures. Accepted to the ApJSS. Catalog data products
available for download here:
http://www.strw.leidenuniv.nl/galaxyevolution/ULTRAVISTA
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