2,398 research outputs found
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data
We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization.Comment: 21 pages, 13 figures, 6 tables; submitted to Ap
A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE
We present a spectroscopic redshift measurement of a very bright Lyman break
galaxy at z=7.7302+-0.0006 using Keck/MOSFIRE. The source was pre-selected
photometrically in the EGS field as a robust z~8 candidate with H=25.0 mag
based on optical non-detections and a very red Spitzer/IRAC [3.6]-[4.5]
broad-band color driven by high equivalent width [OIII]+Hbeta line emission.
The Lyalpha line is reliably detected at 6.1 sigma and shows an asymmetric
profile as expected for a galaxy embedded in a relatively neutral
inter-galactic medium near the Planck peak of cosmic reionization. The line has
a rest-frame equivalent width of EW0=21+-4 A and is extended with
V_FWHM=360+90-70 km/s. The source is perhaps the brightest and most massive z~8
Lyman break galaxy in the full CANDELS and BoRG/HIPPIES surveys, having
assembled already 10^(9.9+-0.2) M_sol of stars at only 650 Myr after the Big
Bang. The spectroscopic redshift measurement sets a new redshift record for
galaxies. This enables reliable constraints on the stellar mass, star-formation
rate, formation epoch, as well as combined [OIII]+Hbeta line equivalent widths.
The redshift confirms that the IRAC [4.5] photometry is very likely dominated
by line emission with EW0(OIII+Hbeta)= 720-150+180 A. This detection thus adds
to the evidence that extreme rest-frame optical emission lines are a ubiquitous
feature of early galaxies promising very efficient spectroscopic follow-up in
the future with infrared spectroscopy using JWST and, later, ELTs.Comment: 6 pages, 4 figures, small updates to match ApJL accepted versio
A Rest-frame Optical View on z~4 Galaxies I: Color and Age Distributions from Deep IRAC Photometry of the IUDF10 and GOODS Surveys
We present a study of rest-frame UV-to-optical color distributions for z~4
galaxies based on the combination of deep HST/ACS+WFC3/IR data with
Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC
Ultradeep Field program (IUDF10). Our sample contains a total of ~2600 galaxies
selected as B-dropout Lyman Break Galaxies (LBGs) in the HUDF and one of its
deep parallel fields, the HUDF09-2, as well as GOODS-North and South. This
sample is used to investigate the UV continuum slopes beta and Balmer break
colors (J_125-[4.5]) as a function of rest-frame optical luminosity. The [4.5]
filter is chosen to avoid potential contamination by strong rest-frame optical
emission lines. We find that galaxies at M_z<-21.5 (roughly corresponding to
L*[z~4]) are significantly redder than their lower luminosity counterparts. The
UV continuum slopes and the J_125-[4.5] colors are well correlated. The most
simple explanation for this correlation is that the dust reddening at these
redshifts is better described by an SMC-like extinction curve, rather than the
typically assumed Calzetti reddening. After correcting for dust, we find that
the galaxy population shows mean stellar population ages in the range 10^8.5 to
10^9 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of
luminosity. In contrast to some results from the literature, we find that only
a small fraction of galaxies shows Balmer break colors which are consistent
with extremely young ages, younger than 100 Myr. Under the assumption of smooth
star-formation histories, this fraction is only 12-19% for galaxies at
M_z<-19.75. Our results are consistent with a gradual build-up of stars and
dust in galaxies at z>4, with only a small fraction of stars being formed in
short, intense bursts of star-formation.Comment: 11 pages, 10 figures; submitted to Ap
Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0
We examined the morphology-density relations for galaxy samples selected by
luminosity and by mass in each of five massive X-ray clusters from z=0.023 to
0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and
visual morphologies were obtained primarily from Hubble Space Telescope images.
Morphology-density relations (MDR) are derived in each cluster from a complete,
luminosity-selected sample of 452 galaxies with a magnitude limit M_V <
M^{*}_{V} + 1. The change in the early-type fraction with redshift matches
previous work for massive clusters of galaxies. We performed a similar
analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies
with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects,
the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and
encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the
mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar
to those in the luminosity-selected sample but show larger early-type
fractions. However, the trend with redshift in the fraction of elliptical and
S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the
mass- and luminosity-selected samples. The clear trend seen in the early-type
fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The
early-type galaxy fraction changes much less, and is consistent with being
constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 <
\Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than
> 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type
fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to
ApJ. Version updated to reflect published version, includes new references
and a correction to table
Surviving Supergentrification in Inner City Sydney: Adaptive Spaces and Makeshift Economies of Cultural Production
Artists and creative workers have long been recognized as playing an important role in gentrification, being often portrayed as forerunners of urban change and displacement in former industrial and working-class suburbs of ‘post-Fordist’ cities. However, as is well represented by recent research, the relationship between the arts, gentrification and displacement has been called into question. The purpose of this article, which draws on 30 case studies of creative spaces in Sydney's inner suburbs, is to chart some of the strategies of spatial adaptation and makeshift economies of solidarity that cultural workers adopt in order to keep living and working in areas of ‘supergentrification’. We document how cultural infrastructure is transformed by the gentrification process and argue that these alterations are critical to the survival of arts and culture in the city. Such makeshift economies contribute, in a practical way, to preserving the diversity that gentrification is sometimes deemed to destroy or displace. While the survival of creative spaces is a much less researched phenomenon than other forms of resistance or displacement, we suggest that it has important consequences for both research and policy decisions around gentrification, infrastructural development and urban cultural economies
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