1,571 research outputs found
Alien Registration- Labbe, Emilio G. (Sanford, York County)
https://digitalmaine.com/alien_docs/3227/thumbnail.jp
The Dearth of z~10 Galaxies in all HST Legacy Fields -- The Rapid Evolution of the Galaxy Population in the First 500 Myr
We present an analysis of all prime HST legacy fields spanning >800 arcmin^2
for the search of z~10 galaxy candidates and the study of their UV luminosity
function (LF). In particular, we present new z~10 candidates selected from the
full Hubble Frontier Field (HFF) dataset. Despite the addition of these new
fields, we find a low abundance of z~10 candidates with only 9 reliable sources
identified in all prime HST datasets that include the HUDF09/12, the HUDF/XDF,
all the CANDELS fields, and now the HFF survey. Based on this comprehensive
search, we find that the UV luminosity function decreases by one order of
magnitude from z~8 to z~10 at all luminosities over a four magnitude range.
This also implies a decrease of the cosmic star-formation rate density by an
order of magnitude within 170 Myr from z~8 to z~10. We show that this
accelerated evolution compared to lower redshift can entirely be explained by
the fast build-up of the dark matter halo mass function at z>8. Consequently,
the predicted UV LFs from several models of galaxy formation are in good
agreement with this observed trend, even though the measured UV LF lies at the
low end of model predictions. In particular, the number of only 9 observed
candidate galaxies is lower, by ~50%, than predicted by galaxy evolution
models. The difference is generally still consistent within the Poisson and
cosmic variance uncertainties. However, essentially all models predict larger
numbers than observed. We discuss the implications of these results in light of
the upcoming James Webb Space Telescope mission, which is poised to find much
larger samples of z~10 galaxies as well as their progenitors at less than 400
Myr after the Big Bang.Comment: 13 pages, 6 figures, minor updates to match accepted versio
Unexpected Case Assignment and Preposition Doubling in Pronoun Coordination in Spanish
The following paper is based on the observation of two related phenomena in Spanish. First, when two personal pronouns acting as prepositional objects are coordinated, they are usually constructed by repeating the preposition before each member of the coordination. Secondly, when this does not happen, the second member of the coordination does not appear in oblique case (which would be expected to happen through government), but it appears in nominative case. This can be clearly appreciated in the coordination of pronouns that display morphological case. The purpose of this paper is to explain these phenomena within the Minimalist Program. The conclusions suggest that the irregular case of the second member of the coordination can be explained by Johannessenn’s structure for coordination (1996) and default case valuation principle (2008), while the duplication of the preposition can be accounted for through reasons of economy
Newly Discovered Bright z~9-10 Galaxies and Improved Constraints on Their Prevalence Using the Full CANDELS Area
We report the results of an expanded search for z~9-10 candidates over the
~883 arcmin^2 CANDELS+ERS fields. This study adds 147 arcmin^2 to the search
area we consider over the CANDELS COSMOS, UDS, and EGS fields, while expanding
our selection to include sources with bluer J_{125}-H_{160} colors than our
previous J_{125}-H_{160}>0.5 mag selection. In searching for new z~9-10
candidates, we make full use of all available HST, Spitzer/IRAC, and
ground-based imaging data. As a result of our expanded search and use of
broader color criteria, 3 new candidate z~9-10 galaxies are identified. We also
find again the z=8.683 source previously confirmed by Zitrin+2015. This brings
our sample of probable z~9-11 galaxy candidates over the CANDELS+ERS fields to
19 sources in total, equivalent to 1 candidate per 47 arcmin^2 (1 per 10
WFC3/IR fields). To be comprehensive, we also discuss 28 mostly lower
likelihood z~9-10 candidates, including some sources that seem to be reliably
at z>8 using the HST+IRAC data alone, but which the ground-based data show are
much more likely at z<4. One case example is a bright z~9.4 candidate COS910-8
which seems instead to be at z~2. Based on this expanded sample, we obtain a
more robust LF at z~9 and improved constraints on the volume density of bright
z~9 and z~10 galaxies. Our improved z~9-10 results again reinforce previous
findings for strong evolution in the UV LF at z>8, with a factor of ~10
evolution seen in the luminosity density from z~10 to z~8.Comment: 22 pages, 12 figures, 6 tables, accepted for publication in the
Astrophysical Journa
First Frontier Field Constraints on the Cosmic Star-Formation Rate Density at z~10 - The Impact of Lensing Shear on Completeness of High-Redshift Galaxy Samples
We search the complete Hubble Frontier Field dataset of Abell 2744 and its
parallel field for z~10 sources to further refine the evolution of the cosmic
star-formation rate density (SFRD) at z>8. We independently confirm two images
of the recently discovered triply-imaged z~9.8 source by Zitrin et al. (2014)
and set an upper limit for similar z~10 galaxies with red colors of
J_125-H_160>1.2 in the parallel field of Abell 2744. We utilize extensive
simulations to derive the effective selection volume of Lyman-break galaxies at
z~10, both in the lensed cluster field and in the adjacent parallel field.
Particular care is taken to include position-dependent lensing shear to
accurately account for the expected sizes and morphologies of highly-magnified
sources. We show that both source blending and shear reduce the completeness at
a given observed magnitude in the cluster, particularly near the critical
curves. These effects have a significant, but largely overlooked, impact on the
detectability of high-redshift sources behind clusters, and substantially
reduce the expected number of highly-magnified sources. The detections and
limits from both pointings result in a SFRD which is higher by 0.4+-0.4 dex
than previous estimates at z~10 from blank fields. Nevertheless, the
combination of these new results with all other estimates remain consistent
with a rapidly declining SFRD in the 170 Myr from z~8 to z~10 as predicted by
cosmological simulations and dark-matter halo evolution in LambdaCDM. Once
biases introduced by magnification-dependent completeness are accounted for,
the full six cluster and parallel Frontier Field program will be an extremely
powerful new dataset to probe the evolution of the galaxy population at z>8
before the advent of the JWST.Comment: 10 pages, 7 figures, changed to match accepted version to appear in
Ap
The size-star formation relation of massive galaxies at 1.5<z<2.5
We study the relation between size and star formation activity in a complete
sample of 225 massive (M > 5 x 10^10 Msun) galaxies at 1.5<z<2.5, selected from
the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis
model fits to the observed restframe UV-NIR SEDs, and independent MIPS 24
micron observations, 65% of galaxies are actively forming stars, while 35% are
quiescent. Using sizes derived from 2D surface brightness profile fits to high
resolution (FWHM_{PSF}~0.45 arcsec) groundbased ISAAC data, we confirm and
improve the significance of the relation between star formation activity and
compactness found in previous studies, using a large, complete mass-limited
sample. At z~2, massive quiescent galaxies are significantly smaller than
massive star forming galaxies, and a median factor of 0.34+/-0.02 smaller than
galaxies of similar mass in the local universe. 13% of the quiescent galaxies
are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than 5
times smaller than galaxies of similar mass locally. The quiescent galaxies
span a Kormendy relation which, compared to the relation for local early types,
is shifted to smaller sizes and brighter surface brightnesses and is
incompatible with passive evolution. The progenitors of the quiescent galaxies,
were likely dominated by highly concentrated, intense nuclear star bursts at
z~3-4, in contrast to star forming galaxies at z~2 which are extended and
dominated by distributed star formation.Comment: 6 pages, 4 figures, accepted for publication in Ap
Rest-Frame Optical Emission Lines in z~3.5 Lyman Break selected Galaxies: The Ubiquity of Unusually High [OIII]/Hbeta Ratios at 2 Gyr
We present K-band spectra of rest-frame optical emission lines for 24
star-forming galaxies at z~3.2-3.7 using MOSFIRE on the Keck 1 telescope.
Strong rest-frame optical [O III] and Hbeta emission lines were detected in 18
LBGs. The median flux ratio of [O III]5007 to Hbeta is 5.1+/-0.5, a factor of
5-10x higher than in local galaxies with similar stellar masses. The observed
Hbeta luminosities are in good agreement with expectations from the estimated
star-formation rates, and none of our sources are detected in deep X-ray
stacks, ruling out significant contamination by active galactic nuclei.
Combining our sample with a variety of LBGs from the literature, including 49
galaxies selected in a very similar manner, we find a high median ratio of
[OIII]/Hbeta = 4.8+0.8-1.7. This high ratio seems to be an ubiquitous feature
of z~3-4 LBGs, very different from typical local star-forming galaxies at
similar stellar masses. The only comparable systems at z~0 are those with
similarly high specific star-formation rates, though ~5x lower stellar masses.
High specific star-formation rates either result in a much higher ionization
parameter or other unusual conditions for the interstellar medium, which result
in a much higher [OIII]/Hbeta line ratio. This implies a strong relation
between a global property of a galaxy, the specific star-formation rate, and
the local conditions of ISM in star-forming regions.Comment: 14 pages, 8 figures, 5 color, published in ApJ, updated to reflect
published versio
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
Possible Deficiencies in Predicting Transonic Aerodynamics on the X-43A
The initial X-43A flight test, June 2, 2001, resulted in a mishap and loss of the vehicle. A mishap investigation board (MIB) report and findings, including the established root cause, were publicly released on July, 23, 2003. The X-43A Flight 1 Hyper-X Launch Vehicle (HXLV) failed because the vehicle control system design was deficient for the trajectory flown due to inaccurate analytical models (Pegasus heritage and HXLV specific), which overestimated the (control) system margin ? X-43A Mishap Investigation Report, Vol. I. ? included as Reference 1. Several specific errors were noted, 1) HXLV aerodynamics ? failure to model changes to wing, fin and rudder airfoil shapes due to addition of thermal protection system (TPS); 2) Fin actuation system (FAS) modeling ? under prediction of the control surface hinge moments and FAS compliance; and 3) Parametric uncertainties ? insufficient variation in the aerodynamic, FAS and control system models. In response to the MIB findings, the X-43A program has been working RTF through an approved Corrective Action Plan (CAP) over the last two years
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