1,722 research outputs found
The Evolution of Early-type Field Galaxies Selected from a NICMOS Map of the Hubble Deep Field North
The redshift distribution of well-defined samples of distant early-type
galaxies offers a means to test the predictions of monolithic and hierarchical
galaxy formation scenarios. NICMOS maps of the entire Hubble Deep Field North
in the F110W and F160W filters, when combined with the available WFPC2 data,
allow us to calculate photometric redshifts and determine the morphological
appearance of galaxies at rest-frame optical wavelengths out to z ~ 2.5. Here
we report results for two subsamples of early-type galaxies, defined primarily
by their morphologies in the F160W band, which were selected from the NICMOS
data down to H160_{AB} < 24.0. The observed redshift distributions of our two
early-type samples do not match that predicted by a monolithic collapse model,
which shows an overabundance at z > 1.5. A hierarchical formation model better
matches the redshift distribution of the HDF-N early-types at z > 1.5, but
still does not adequately describe the observed early-types. The hierarchical
model predicts significantly bluer colors on average than the observed
early-type colors, and underpredicts the observed number of early-types at z <
1. [abridged]Comment: Accepted for publication in the Astronomical Journal; 54 pages, 21
figures. Figures 10 and 11 are included separately in JPEG forma
Secular values and the location of religion: a spatial analysis of an English medical centre
What do contemporary controversies in healthcare reveal about secular values and the location of religion within an English medical centre? Using a socio-spatial methodology designed to break open ideological perspectives and normative values, we analyse the doctor-patient relationship, complementary and alternative medicine, and an issue that bridges the two, evidence-based medicine. In the physical, social and mental spaces of the medical centre we uncover the traces of religious activity and roles and of alternative therapeutic regimes often informed by spiritual or religious systems. Furthermore we disclose the heterogeneity of values that comprise the secular worldview of one group of contemporary general practitioners
The Hubble Ultra Deep Field
This paper presents the Hubble Ultra Deep Field (HUDF), a one million second
exposure of an 11 square minute-of-arc region in the southern sky with the
Hubble Space Telescope. The exposure time was divided among four filters, F435W
(B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately
uniform limiting magnitudes mAB~29 for point sources. The image contains at
least 10,000 objects presented here as a catalog. Few if any galaxies at
redshifts greater than ~4 resemble present day spiral or elliptical galaxies.
Using the Lyman break dropout method, we find 504 B-dropouts, 204 V-dropouts,
and 54 i-dropouts. Using these samples that are at different redshifts but
derived from the same data, we find no evidence for a change in the
characteristic luminosity of galaxies but some evidence for a decrease in their
number densities between redshifts of 4 and 7. The ultraviolet luminosity
density of these samples is dominated by galaxies fainter than the
characteristic luminosity, and the HUDF reveals considerably more luminosity
than shallower surveys. The apparent ultraviolet luminosity density of galaxies
appears to decrease from redshifts of a few to redshifts greater than 6. The
highest redshift samples show that star formation was already vigorous at the
earliest epochs that galaxies have been observed, less than one billion years
after the Big Bang.Comment: 44 pages, 18 figures, to appear in the Astronomical Journal October
200
Morphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field
Using U'- through Ks-band imaging data in the GOODS-South field, we construct
a large, complete sample of 275 ``extremely red objects'' (EROs; K_s<22.0,
R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and
z_850, and well-calibrated photometric redshifts. Quantitative concentration
and asymmetry measurements fail to separate EROs into distinct morphological
classes. We therefore visually classify the morphologies of all EROs into four
broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies),
``Irregular'' and ``Other'' (chain galaxies and low surface brightness
galaxies), and calculate their relative fractions and comoving space densities.
For a broad range of limiting magnitudes and color thresholds, the relative
number of early-type EROs is approximately constant at 33-44%, and the comoving
space densities of Early- and Late-type EROs are comparable. Mean rest-frame
spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are
constructed for all EROs. The SEDs are extremely similar in their range of
shapes, independent of morphological type. The implication is that any
differences between the broad-band SEDs of Early-type EROs and the other types
are relatively subtle, and there is no robust way of photometrically
distinguishing between different morphological types with usual
optical/near-infrared photometry.Comment: Submitted to the ApJL. A version with full-resolution figures, all
GOODS data and all GOODS collaboration papers may be found at
http://www.stsci.edu/science/goods
A Disk-Wind Model for the Near-Infrared Excess Emission in Protostars
Protostellar systems, ranging from low-luminosity T Tauri and Herbig Ae stars
to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in
their spectra that is dominated by a bump in the monochromatic luminosity with
a peak near 3 microns. The bump can be approximated by a thermal emission
component of temperature 1500 K that is of the order of the sublimation
temperature of interstellar dust grains. In the currently popular "puffed up
rim" scenario, the bump represents stellar radiation that propagates through
the optically thin inner region of the surrounding accretion disk and is
absorbed and reemitted by the dust that resides just beyond the dust
sublimation radius, Rsub. However, this model cannot account for the strongest
bumps measured in these sources, and it predicts a large secondary bounce in
the interferometric visibility curve that is not observed. In this paper we
present an alternative interpretation, which attributes the bump to reemission
of stellar radiation by dust that is uplifted from the disk by a centrifugally
driven wind. Winds of this type are a leading candidate for the origin of the
strong outflows associated with protostars, and there is observational evidence
for disk winds originating on scales ~Rsub. Using a newly constructed Monte
Carlo radiative transfer code, we show that this model can account for the NIR
excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275,
and that it successfully reproduces the basic features of the visibilities
measured in these protostars. We argue that a robust dusty outflow in these
sources could be self-limiting to a relatively narrow launching region between
Rsub and 2Rsub. Finally, we suggest that our model could also naturally account
for the NIR and scattered-light variability exhibited by a source like MWC 275,
which may be triggered by the uplifting of dust clouds from the disk.Comment: 19 pages, 8 figures. Updated submitted version to refereed and
accepted one (accepted 8/29/2012 for publication in The Astrophysical
Journal
Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
Although giant clumps of stars are crucial to galaxy formation and evolution,
the most basic demographics of clumps are still uncertain, mainly because the
definition of clumps has not been thoroughly discussed. In this paper, we study
the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3,
using our proposed physical definition that UV-bright clumps are discrete
star-forming regions that individually contribute more than 8% of the
rest-frame UV light of their galaxies. Clumps defined this way are
significantly brighter than the HII regions of nearby large spiral galaxies,
either individually or blended, when physical spatial resolution and
cosmological dimming are considered. Under this definition, we measure the
fraction of SFGs that contain at least one off-center clump (Fclumpy) and the
contributions of clumps to the rest-frame UV light and star formation rate of
SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample
consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of
Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass
(log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from
z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from
55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend
of disk stabilization predicted by violent disk instability matches the Fclumpy
trend of massive galaxies; (2) minor mergers are a viable explanation of the
Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic
observability timescale; and (3) major mergers are unlikely responsible for the
Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame
UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at
all redshifts, possibly linked to the molecular gas fraction of the galaxies.
(Abridged)Comment: 22 pages, 15 figures. Appeared in ApJ (2015, 800, 39). A few typos
correcte
2-Amino-4-methoxy-6-methylpyrimidin-1-ium picrate
In the title salt, C6H10N3O+·C6H2N3O7
−, the dihedral angle between the mean planes of the benzene and pyridine rings is 3.1 (1)°. In the cation, the methoxy group is almost coplanar with the pyridine ring [C—O—C—N = −0.6 (2)°]. The p-nitro [C—C—N—O = −1.17 (19)°] and one o-nitro [C—C—N—O = 1.83 (19)°] group in the anion are essentially coplanar with the benzene ring. The other disordered o-nitro group containing the major occupancy [0.868 (6)] O atom is twisted −29.0 (2)° from the mean plane of the benzene ring. A bifurcated N—H⋯(O.O) hydrogen bond and weak C—H⋯O intermolecular interaction between the cation and anion produce a network of infinite O—H⋯O—H⋯O—H chains along the c axis in the [101] plane which helps to establish crystal packing. Comparison to a DFT computational calculation indicates that significant conformational changes occur in the free state
WFPC2 Observations of the Hubble Deep Field-South
The Hubble Deep Field-South observations targeted a high-galactic-latitude
field near QSO J2233-606. We present WFPC2 observations of the field in four
wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations,
data reduction procedures, and noise properties of the final images are
discussed in detail. A catalog of sources is presented, and the number counts
and color distributions of the galaxies are compared to a new catalog of the
HDF-N that has been constructed in an identical manner. The two fields are
qualitatively similar, with the galaxy number counts for the two fields
agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z
> 2 than the HDF-N. The star-formation rate per unit volume computed from the
HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of
1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.Comment: 93 pages, 25 figures; contains very long table
Demography and Viability of a Hunted Population of Polar Bears
We estimated demographic parameters and harvest risks for a population of polar bears (Ursus maritimus) inhabiting Baffin Bay, Canada and Greenland, from 1974 to 1997. Our demographic analysis included a detailed assessment of age- and sex-specific survival and recruitment from 1221 marked polar bears, which used information contained within the standing age distribution of captures and mark-recapture analysis performed with Program MARK. Unharvested (natural) survival rates for females (± 1 SE) from mark-recapture analysis were 0.620 ± 0.095 (cubs), 0.938 ± 0.042 (ages 1–4), 0.953 ± 0.020 (ages 5–20), and 0.919 ± 0.046 (ages 21+). Total (harvested) survival rates for females were reduced to 0.600 ± 0.096 (cubs), 0.901 ± 0.045 (ages 1–4), 0.940 ± 0.021 (ages 5–20), and 0.913 ± 0.047 (ages 21+). Mean litter size was 1.59 ± 0.07 cubs, with a mean reproductive interval of 2.5 ± 0.01 years. By age 5, on average 0.88 ± 0.40 of females were producing litters. We estimated the geometric means (± bootstrapped SDs) for population growth rates at stable age distribution as 1.055 ± 0.011 (unharvested) and 1.019 ± 0.015 (harvested). The model-averaged, mark-recapture estimate of mean abundance (± 1 SE) for years 1994–97 was 2074 ± 266 bears, which included 1017 ± 192 females and 1057 ± 124 males. We incorporated demographic parameters and their error terms into a harvest risk analysis designed to consider demographic, process, and sampling uncertainty in generating likelihoods of persistence (i.e., a stochastic, harvest-explicit population viability analysis). Using our estimated harvest of polar bears in Baffin Bay (88 bears/yr), the probability that the population would decline no more than could be recovered in five years was 0.95, suggesting that the current hunt is sustainable.De 1974 à 1997, on a évalué les paramètres démographiques d’une population d’ours polaires (Ursus maritimus) habitant la baie de Baffin (Canada et Groenland), ainsi que les risques associés à leur prélèvement. Notre analyse démographique comprenait un bilan détaillé de la survie et du recrutement par âge et par sexe, bilan mené sur 1221 ours polaires étiquetés et qui faisait appel à l’information contenue dans les limites de la structure d’âge des captures à un moment précis, ainsi que des analyses de marquage-recapture réalisées avec le logiciel MARK. Les taux de survie sans prélèvements (c’est-à-dire naturels) des femelles (± 1 erreur-type) tirés de l’analyse de marquage-recapture étaient les suivants: 0,620 ± 0,095 (oursons), 0,938 ± 0,042 (1–4 ans), 0,953 ± 0,020 (5–20 ans) et 0,919 ± 0,046 (21 ans et plus). Les taux de survie globaux (avec prélèvements) des femelles diminuaient à: 0,600 ± 0,096 (oursons), 0,901 ± 0,045 (1–4 ans), 0,940 ± 0,021 (5–20 ans) et 0,913 ± 0,047 (21 ans et plus). La taille moyenne des portées était de 1,59 ± 0,07 ourson avec des intervalles moyens de reproduction de 2,5 ± 0,01 ans. Arrivées à l’âge de cinq ans, en moyenne 0,88 ± 0,40 des femelles avaient eu des petits. On a évalué que les moyennes géométriques (± écart-type bootstrappé) pour les taux de croissance de la population à la structure d’âge stable étaient de 1,055 ± 0,011 (sans prélèvements) et de 1,019 ± 0,015 (avec prélèvements). La valeur estimée à partir du marquage-recapture, moyennée par le modèle, de l’abondance moyenne (± 1 erreur-type), pour les années allant de 1994 à 1997 était de 2074 ± 266 ours, dont 1017 Å} 192 femelles et 1057 ± 124 mâles. On a intégré les paramètres démographiques et leurs termes d’erreur dans une analyse des risques de prélèvements conçue pour tenir compte des incertitudes démographiques, de processus et d’échantillonnage lors du calcul des probabilités de persistance (c.-à-d. une analyse stochastique de la viabilité de la population qui tient compte des prélèvements). En se basant sur nos prélèvements estimés de l’ours polaire dans la baie de Baffin (88 ours/an), la probabilité que la population ne décline pas plus que ce qu’elle pourrait récupérer en 5 ans était de 0,95, ce qui suggère que la chasse actuelle est durable
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