301 research outputs found
Ultraviolet Luminosity Density of the Universe During the Epoch of Reionization
The spatial fluctuations of the extragalactic background light trace the
total emission from all stars and galaxies in the Universe. A multi-wavelength
study can be used to measure the integrated emission from first galaxies during
reionization when the Universe was about 500 million years old. Here we report
arcminute-scale spatial fluctuations in one of the deepest sky surveys with the
Hubble Space Telescope in five wavebands between 0.6 and 1.6 m. We
model-fit the angular power spectra of intensity fluctuation measurements to
find the ultraviolet luminosity density of galaxies at > 8 to be erg s Hz Mpc
. This level of integrated light emission allows for a significant
surface density of fainter primeval galaxies that are below the point source
detection level in current surveys.Comment: The official typeset version is available from the Nature
Communications website at
http://www.nature.com/ncomms/2015/150907/ncomms8945/full/ncomms8945.html The
data used in this work can be found at http://herschel.uci.edu/CANDELS
An Increasing Stellar Baryon Fraction in Bright Galaxies at High Redshift
Recent observations have shown that the characteristic luminosity of the
rest-frame ultraviolet (UV) luminosity function does not significantly evolve
at 4 < z < 7 and is approximately M*_UV ~ -21. We investigate this apparent
non-evolution by examining a sample of 178 bright, M_UV < -21 galaxies at z=4
to 7, analyzing their stellar populations and host halo masses. Including deep
Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that
M*_UV galaxies at z=4-7 have similar stellar masses of log(M/Msol)=9.6-9.9 and
are thus relatively massive for these high redshifts. However, bright galaxies
at z=4-7 are less massive and have younger inferred ages than similarly bright
galaxies at z=2-3, even though the two populations have similar star formation
rates and levels of dust attenuation. We match the abundances of these bright
z=4-7 galaxies to halo mass functions from the Bolshoi Lambda-CDM simulation to
estimate the halo masses. We find that the typical halo masses in ~M*_UV
galaxies decrease from log(M_h/Msol)=11.9 at z=4 to log(M_h/Msol)=11.4 at z=7.
Thus, although we are studying galaxies at a similar mass across multiple
redshifts, these galaxies live in lower mass halos at higher redshift. The
stellar baryon fraction in units of the cosmic mean Omega_b/Omega_m rises from
5.1% at z=4 to 11.7% at z=7; this evolution is significant at the ~3-sigma
level. This rise does not agree with simple expectations of how galaxies grow,
and implies that some effect, perhaps a diminishing efficiency of feedback, is
allowing a higher fraction of available baryons to be converted into stars at
high redshifts.Comment: Accepted to ApJ. 15 pages, 5 figures, 6 table
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
Expanding the search for galaxies at z ~7-10 with new NICMOS Parallel Fields
We have carried out a search for galaxies at z ~ 7-10 in ~14.4 sq. arcmin of
new NICMOS parallel imaging taken in the Great Observatories Origins Deep
Survey (GOODS, 5.9 sq. arcmin), the Cosmic Origins Survey (COSMOS, 7.2 sq.
arcmin), and SSA22 (1.3 sq. arcmin). These images reach 5 sigma sensitivities
of J110 = 26.0-27.5 (AB), and combined they increase the amount of deep
near-infrared data by more than 60% in fields where the investment in deep
optical data has already been made. We find no z>7 candidates in our survey
area, consistent with the Bouwens et al. (2008) measurements at z~7 and 9 (over
23 sq. arcmin), which predict 0.7 galaxies at z~7 and <0.03 galaxies at z~9. We
estimate that 10-20% of z>7 galaxies are missed by this survey, due to
incompleteness from foreground contamination by faint sources. For the case of
luminosity evolution, assuming a Schecter parameterization with a typical phi*
= 10^-3 Mpc^-3, we find M* > -20.0 for z~7 and M* > -20.7 for z~9 (68%
confidence). This suggests that the downward luminosity evolution of LBGs
continues to z~7, although our result is marginally consistent with the z~6 LF
of Bouwens et al.(2006, 2007). In addition we present newly-acquired deep
MMT/Megacam imaging of the z~9 candidate JD2325+1433, first presented in Henry
et al. (2008). The resulting weak but significant detection at i' indicates
that this galaxy is most likely an interloper at z~2.7.Comment: Accepted to ApJ. Replacement includes updated discussion of
incompleteness from foreground contaminatio
The mass evolution of the first galaxies: stellar mass functions and star formation rates at in the CANDELS GOODS-South field
We measure new estimates for the galaxy stellar mass function and star
formation rates for samples of galaxies at using data in
the CANDELS GOODS South field. The deep near-infrared observations allow us to
construct the stellar mass function at directly for the first time.
We estimate stellar masses for our sample by fitting the observed spectral
energy distributions with synthetic stellar populations, including nebular line
and continuum emission. The observed UV luminosity functions for the samples
are consistent with previous observations, however we find that the observed
- M relation has a shallow slope more consistent with a constant
mass to light ratio and a normalisation which evolves with redshift. Our
stellar mass functions have steep low-mass slopes (),
steeper than previously observed at these redshifts and closer to that of the
UV luminosity function. Integrating our new mass functions, we find the
observed stellar mass density evolves from at to at . Finally, combining the measured UV continuum
slopes () with their rest-frame UV luminosities, we calculate dust
corrected star-formation rates (SFR) for our sample. We find the specific
star-formation rate for a fixed stellar mass increases with redshift whilst the
global SFR density falls rapidly over this period. Our new SFR density
estimates are higher than previously observed at this redshift.Comment: 28 pages, 23 figures, 2 appendices. Accepted for publication in
MNRAS, August 7 201
CANDELS/GOODS-S, CDFS, ECDFS: Photometric Redshifts For Normal and for X-Ray-Detected Galaxies
We present photometric redshifts and associated probability distributions for
all detected sources in the Extended Chandra Deep Field South (ECDFS). The work
makes use of the most up-to-date data from the Cosmic Assembly Near-IR Deep
Legacy Survey (CANDELS) and the Taiwan ECDFS Near-Infrared Survey (TENIS) in
addition to other data. We also revisit multi-wavelength counterparts for
published X-ray sources from the 4Ms-CDFS and 250ks-ECDFS surveys, finding
reliable counterparts for 1207 out of 1259 sources (). Data used for
photometric redshifts include intermediate-band photometry deblended using the
TFIT method, which is used for the first time in this work. Photometric
redshifts for X-ray source counterparts are based on a new library of
AGN/galaxy hybrid templates appropriate for the faint X-ray population in the
CDFS. Photometric redshift accuracy for normal galaxies is 0.010 and for X-ray
sources is 0.014, and outlier fractions are and respectively. The
results within the CANDELS coverage area are even better as demonstrated both
by spectroscopic comparison and by galaxy-pair statistics. Intermediate-band
photometry, even if shallow, is valuable when combined with deep broad-band
photometry. For best accuracy, templates must include emission lines.Comment: The paper has been accepted by ApJ. The materials we provide are
available under [Surveys] > [CDFS] through the portal
http://www.mpe.mpg.de/XraySurvey
A Critical Assessment of Stellar Mass Measurement Methods
In this paper we perform a comprehensive study of the main sources of random
and systematic errors in stellar mass measurement for galaxies using their
Spectral Energy Distributions (SEDs). We use mock galaxy catalogs with
simulated multi-waveband photometry (from U-band to mid-infrared) and known
redshift, stellar mass, age and extinction for individual galaxies. Given
different parameters affecting stellar mass measurement (photometric S/N
ratios, SED fitting errors, systematic effects, the inherent degeneracies and
correlated errors), we formulated different simulated galaxy catalogs to
quantify these effects individually. We studied the sensitivity of stellar mass
estimates to the codes/methods used, population synthesis models, star
formation histories, nebular emission line contributions, photometric
uncertainties, extinction and age. For each simulated galaxy, the difference
between the input stellar masses and those estimated using different simulation
catalogs, , was calculated and used to identify the most
fundamental parameters affecting stellar masses. We measured different
components of the error budget, with the results listed as follows: (1). no
significant bias was found among different codes/methods, with all having
comparable scatter; (2). A source of error is found to be due to photometric
uncertainties and low resolution in age and extinction grids; (3). The median
of stellar masses among different methods provides a stable measure of the mass
associated with any given galaxy; (4). The deviations in stellar mass strongly
correlate with those in age, with a weaker correlation with extinction; (5).
the scatter in the stellar masses due to free parameters are quantified, with
the sensitivity of the stellar mass to both the population synthesis codes and
inclusion of nebular emission lines studied.Comment: 33 pages, 20 Figures, Accepted for publication in Astrophysical
Journa
CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field
We present a UV-to-mid infrared multi-wavelength catalog in the
CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W,
F125W, and F160W data with existing public data. The catalog is based on source
detection in the WFC3 F160W band. The F160W mosaic includes the data from
CANDELS deep and wide observations as well as previous ERS and HUDF09 programs.
The mosaic reaches a 5 limiting depth (within an aperture of radius
0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF
regions, respectively. The catalog contains 34930 sources with the
representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W
band for the three regions. In addition to WFC3 bands, the catalog also
includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical
(HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M,
VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 m)
observations. The catalog is validated via stellar colors, comparison with
other published catalogs, zeropoint offsets determined from the best-fit
templates of the spectral energy distribution of spectroscopically observed
objects, and the accuracy of photometric redshifts. The catalog is able to
detect unreddened star-forming (passive) galaxies with stellar mass of
10^{10}M_\odot at a 50% completeness level to z3.4 (2.8), 4.6 (3.2), and
7.0 (4.2) in the three regions. As an example of application, the catalog is
used to select both star-forming and passive galaxies at z2--4 via the
Balmer break. It is also used to study the color--magnitude diagram of galaxies
at 0<z<4.Comment: The full resolution article is now published in ApJS (2013, 207, 24).
22 pages, 21 figures, and 5 tables. The catalogue is available on the CANDELS
website: http://candels.ucolick.org/data_access/GOODS-S.html MAST:
http://archive.stsci.edu/prepds/candels and Rainbow Database:
https://arcoiris.ucolick.org/Rainbow_navigator_public and
https://rainbowx.fis.ucm.es/Rainbow_navigator_publi
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