7,056 research outputs found
A catalogue of the Chandra Deep Field South with multi-colour classification and photometric redshifts from COMBO-17
We present the COMBO-17 object catalogue of the Chandra Deep Field South for
public use, covering a field which is 31.5' x 30' in size. This catalogue lists
astrometry, photometry in 17 passbands from 350 to 930 nm, and ground-based
morphological data for 63,501 objects. The catalogue also contains multi-colour
classification into the categories 'Star', 'Galaxy' and 'Quasar' as well as
photometric redshifts. We include restframe luminosities in Johnson, SDSS and
Bessell passbands and estimated errors. The redshifts are most reliable at
R<24, where the sample contains approximately 100 quasars, 1000 stars and 10000
galaxies. We use nearly 1000 spectroscopically identified objects in
conjunction with detailed simulations to characterize the performance of
COMBO-17. We show that the selection of quasars, more generally type-1 AGN, is
nearly complete and minimally contaminated at z=[0.5,5] for luminosities above
M_B=-21.7. Their photometric redshifts are accurate to roughly 5000 km/sec.
Galaxy redshifts are accurate to 1% in dz/(1+z) at R<21. They degrade in
quality for progressively fainter galaxies, reaching accuracies of 2% for
galaxies with R~222 and of 10% for galaxies with R>24. The selection of stars
is complete to R~23, and deeper for M stars. We also present an updated
discussion of our classification technique with maps of survey completeness,
and discuss possible failures of the statistical classification in the faint
regime at R>24.Comment: submitted to Astronomy & Astrophysics, public data set available at
http://www.mpia.de/COMBO/combo_index.htm
The evolution of faint AGN between z~1 and z~5 from the COMBO-17 survey
We present a determination of the optical/UV AGN luminosity function and its
evolution, based on a large sample of faint (R<24) QSOs identified in the
COMBO-17 survey. Using multi-band photometry in 17 filters within 350nm <
lambda_obs < 930nm, we could simultaneously determine photometric redshifts
with an accuracy of sigma_z<0.03 and obtain spectral energy distributions. The
redshift range covered by the sample is 1.2<z<4.8, which implies that even at
z~3, the sample reaches below luminosities corresponding to M_B = -23,
conventionally employed to distinguish between Seyfert galaxies and quasars. We
clearly detect a broad plateau-like maximum of quasar activity around z~2 and
map out the smooth turnover between z~1 and z~4. The shape of the LF is
characterised by some mild curvature, but no sharp `break' is present within
the range of luminosities covered. Using only the COMBO-17 data, the evolving
LF can be adequately described by either a pure density evolution (PDE) or a
pure luminosity evolution (PLE) model. However, the absence of a strong L*-like
feature in the shape of the LF inhibits a robust distinction between these
modes. We present a robust estimate for the integrated UV luminosity generation
by AGN as a function of redshift. We find that the LF continues to rise even at
the lowest luminosities probed by our survey, but that the slope is
sufficiently shallow that the contribution of low-luminosity AGN to the UV
luminosity density is negligible. Although our sample reaches much fainter flux
levels than previous data sets, our results on space densities and LF slopes
are completely consistent with extrapolations from recent major surveys such as
SDSS and 2QZ.Comment: 17 pages, 14 figures, Astronomy & Astrophysics, in print, revised
versio
Strategies for prompt searches for GRB afterglows: the discovery of the GRB 001011 optical/near-infrared counterpart using colour-colour selection
We report the discovery of the optical and near-infrared counterparts to GRB
001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously
imaged in the near-infrared by the 3.58-m New Technology Telescope and in the
optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we
implement the colour-colour discrimination technique proposed by Rhoads (2001)
and extend it using near-IR data as well. We present the results provided by an
automatic colour-colour discrimination pipe-line developed to discern the
different populations of objects present in the GRB 001011 error box. Our
software revealed three candidates based on single-epoch images. Second-epoch
observations carried out ~3.2 days after the burst revealed that the most
likely candidate had faded, thus identifying it with the counterpart to the
GRB. In deep R-band images obtained 7 months after the burst a faint
(R=25.38+/-0.25) elongated object, presumably the host galaxy of GRB 001011,
was detected at the position of the afterglow. The GRB 001011 afterglow is the
first discovered with the assistance of colour-colour diagram techniques. We
discuss the advantages of using this method and its application to error boxes
determined by future missions.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 16
figure
The COMBO-17 Survey: Evolution of the Galaxy Luminosity Function from 25,000 Galaxies with 0.2<z<1.2
We present a detailed empirical assessment of how the galaxy luminosity
function and stellar luminosity density evolves over the last half of the
universe's age (0.2<z<1.2) for galaxies of different spectral energy
distributions (SED). The results are based on ~25,000 galaxies (R<24) with
redshift measurements (sigma_z~0.03) and SEDs across 350..930 nm, derived from
medium-band photometry in 17 filters, observed as part of the COMBO-17 survey
(``Classifying Objects by Medium-Band Observations in 17 Filters'') over three
disjoint fields with a total area of 0.78 square degrees. Luminosity functions
(LF), binned in redshift and SED-type, are presented in the restframe passbands
of the SDSS r-band, the Johnson B-band and a synthetic UV continuum band at 280
nm. We find that the luminosity function depends strongly on SED-type at all
redshifts covered. The shape of the LF, i.e. the faint-end power-law slope,
does depend on SED type, but not on redshift. However, the redshift evolution
of the characteristic luminosity M* and density phi* depends strongly on
SED-type: (1) Early-type galaxies, defined as redder than a present-day
reference Sa spectrum, become drastically more abundant towards low redshift,
by a factor of 10 in the number density phi* from z=1.1 to now, and by a factor
of 4 in their contribution to the co-moving r-band luminosity density, j_r. (2)
Galaxies resembling present-day Sa- to Sbc-colours show a co-moving number
density and contribution to j_r that does not vary much with redshift. (3)
Galaxies with blue spectra reflecting strong star formation decrease towards
low redshift both in luminosity and density, and by a factor of 4 in their j_r
contribution. (abridged)Comment: 35 pages, 32 figures, submitted to Astronomy & Astrophysic
Susceptibility to tuberculosis is associated with variants in the ASAP1 gene encoding a regulator of dendritic cell migration
Human genetic factors predispose to tuberculosis (TB). We studied 7.6 million genetic variants in 5,530 people with pulmonary TB and in 5,607 healthy controls. In the combined analysis of these subjects and the follow-up cohort (15,087 TB patients and controls altogether), we found an association between TB and variants located in introns of the ASAP1 gene on chromosome 8q24 (P = 2.6 Ă 10â11 for rs4733781; P = 1.0 Ă 10â10 for rs10956514). Dendritic cells (DCs) showed high ASAP1 expression that was reduced after Mycobacterium tuberculosis infection, and rs10956514 was associated with the level of reduction of ASAP1 expression. The ASAP1 protein is involved in actin and membrane remodeling and has been associated with podosomes. The ASAP1-depleted DCs showed impaired matrix degradation and migration. Therefore, genetically determined excessive reduction of ASAP1 expression in M. tuberculosisâinfected DCs may lead to their impaired migration, suggesting a potential mechanism of predisposition to TB
Bilingualism alters childrenâs frontal lobe functioning for attentional control
Bilingualism is a typical linguistic experience, yet relatively little is known about its impact on childrenâs cognitive and brain development. Theories of bilingualism suggest that early dualĂą language acquisition can improve childrenâs cognitive abilities, specifically those relying on frontal lobe functioning. While behavioral findings present much conflicting evidence, little is known about its effects on childrenâs frontal lobe development. Using functional nearĂą infrared spectroscopy (fNIRS), the findings suggest that SpanishĂą English bilingual children (nĂÂ =ĂÂ 13, ages 7Ăą 13) had greater activation in left prefrontal cortex during a nonĂą verbal attentional control task relative to ageĂą matched English monolinguals. In contrast, monolinguals (nĂÂ =ĂÂ 14) showed greater right prefrontal activation than bilinguals. The present findings suggest that early bilingualism yields significant changes to the functional organization of childrenâs prefrontal cortex for attentional control and carry implications for understanding how early life experiences impact cognition and brain development.This fNIRS study investigated the impact of bilingual exposure on childrenâs brain organization for attentional control (N = 27, ages 7Ăą 13). During a nonĂą verbal attention task, bilinguals showed greater left frontal lobe activation than monolinguals. Monolinguals showed greater right frontal lobe activation than bilinguals. The findings suggest that bilingualism affects the functionality of childrenâs left prefrontal cortex for attentional control.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136694/1/desc12377-sup-0001-FigS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136694/2/desc12377.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136694/3/desc12377_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136694/4/desc12377-sup-0003-SupInfo.pd
The VIMOS VLT Deep Survey: the faint type-1 AGN sample
We present the type-1 active galactic nuclei (AGN) sample extracted from the
VIMOS VLT Deep Survey first observations of 21000 spectra in 1.75 square
degree. This sample, which is purely magnitude limited, free of morphological
or color selection biases, contains 130 broad line AGN (BLAGN) spectra with
redshift up to 5. Our data are divided into a wide (Iab < 22.5) and a deep (Iab
< 24) subsample containing 56 and 74 objects respectively. Because of its depth
and selection criteria, this sample is uniquely suited to study the population
of faint type-1 AGN. Our measured surface density (~ 472 +- 48 BLAGN per square
degree with Iab < 24) is significantly higher than that of any other optically
selected sample of BLAGN with spectroscopic confirmation. By applying a
morphological and color analysis to our AGN sample we find that: (1)~23% of the
AGN brighter than Iab=22.5 are classified as extended; this percentage
increases to ~42% for those with z < 1.6; (2) a non-negligible fraction of our
BLAGN are lying close to the color space area occupied by stars in u*-g' versus
g'-r' color-color diagram. This leads us to the conclusion that classical
optical ultraviolet preselection technique, if employed at such deep magnitudes
(Iab=22.5) in conjuction with a preselection of point-like sources, can miss
miss up to ~35% of the AGN population. Finally, we present a composite spectrum
of our sample of objects. While the continuum shape is very similar to that of
the SDSS composite at short wavelengths, it is much redder than it at lambda >
3000 A. We interpret this as due to significant contamination from emission of
the host galaxies, as expected from the faint absolute magnitudes sampled by
our survey.Comment: Accepted to A&A, 18 pages, 14 figure
Factors that impact on access to water and sanitation for older adults and people with disability in rural South Africa: An occupational justice perspective
Limited access to water and sanitation is a risk to health, dignity, and ability to engage in occupations. This article aims to: 1) discuss the current and historical factors affecting access to water and sanitation in rural South Africa, and 2) explore the occupational implications of water access, particularly for older adults and people with disability in rural South Africa. A literature review was carried out through searching JSTOR, Scopus, and MEDLINE databases and using framework analysis to interpret the retrieved documents. This paper also reports a thematic analysis of semi-structured interviews, conducted in 2012 in a rural area of South Africa. Environmental, political, social-economic and attitudinal factors were identified as impacting water access and occupation, in both the documentary analysis and the semi-structured interviews. Due to South Africaâs history, injustice has occurred in the forms of occupational apartheid and occupational deprivation. We argue that supply systems must enable people to easily access more water than is essential for survival, so that people can participate in meaningful and productive occupations. Therefore, access to water should be considered part of an occupational right. Recognising this right will be an integral step in ensuring that water supplies are improved to support better livelihoods, and to achieve economic and social empowerment, and quality of life for all, in line with many of the United Nationsâ new Sustainable Development Goals
Cytomegalovirus Infection of the Colon Presenting as a Mass-Like Lesion
Cytomegalovirus (CMV) is responsible for the most common opportunistic infections in patients with acquired immunodeficiency syndrome (AIDS). The colon is a common site for these infections in patients positive for human immunodeficiency virus. CMV rarely presents as an intraluminal inflammatory mass in the colon. Here we report the case of a CMV infection presenting as a mass-like lesion in an AIDS patient. The clinical diagnosis of CMV infection is largely based on the characteristic endoscopic appearance. Endoscopic procedures are encouraged early in the course of CMV infection in immunocompromised patients. CMV pseudotumors along with malignancy should be part of the endoscopic evaluation in patients with AIDS
- âŠ