1,634 research outputs found
AAT Imaging and Microslit Spectroscopy in the Southern Hubble Deep Field
We present a deep photometric (B- and R-band) catalog and an associated
spectroscopic redshift survey conducted in the vicinity of the Hubble Deep
Field South. The spectroscopy yields 53 extragalactic redshifts in the range
0<z<1.4 substantially increasing the body of spectroscopic work in this field
to over 200 objects. The targets are selected from deep AAT prime focus images
complete to R<24 and spectroscopy is 50% complete at R=23. There is now strong
evidence for a rich cluster at z\simeq 0.58 flanking the WFPC2 field which is
consistent with a known absorber of the bright QSO in this field. We find that
photometric redshifts of z<1 galaxies in this field based on HST data are
accurate to \sigma_z/(1+z)=0.03 (albeit with small number statistics). The
observations were carried out as a community service for Hubble Deep Field
science, to demonstrate the first use of the `nod & shuffle' technique with a
classical multi-object spectrograph and to test the use of `microslits' for
ultra-high multiplex observations along with a new VPH grism and deep-depletion
CCD. The reduction of this new type of data is also described.Comment: From the better late than never department: AJ in press (2006). 16
pages, 2 tables, 6 figures, final data release + Appendix at
http://www.aao.gov.au/hdfs/Redshifts
An imaging K-band survey - I: The catalogue, star and galaxy counts
We present results from a large area (552\,\sqamin) imaging -band survey
to a 5 limit of . We have optical-infrared colours of
almost all the objects in the sample. Star-galaxy discrimination is performed
and the results used to derive the infrared star and galaxy counts. -band
``no-evolution'' galaxy-count models are constructed and compared with the
observed data. In the infrared, there is no counterpart for the large excess of
faint galaxies over the no-evolution model seen in optical counts. However, we
show that the counts can be remarkably insensitive to evolution under
certain reasonable assumptions. Finally, model predictions for -selected
redshift surveys are derived.Comment: MNRAS in press. 21 pages plain TeX; figs plus table 4 available via
anonymous ftp from /pub/kgb/paper1/sissa.uu at ftp.ast.cam.ac.u
Color bimodality: Implications for galaxy evolution
We use a sample of 69726 galaxies from the SDSS to study the variation of the
bimodal color-magnitude (CM) distribution with environment. Dividing the galaxy
population by environment (Sigma_5) and luminosity (-23<M_r<-17), the u-r color
functions are modeled using double-Gaussian functions. This enables a
deconvolution of the CM distributions into two populations: red and blue
sequences. The changes with increasing environmental density can be separated
into two effects: a large increase in the fraction of galaxies in the red
distribution, and a small color shift in the CM relations of each distribution.
The average color shifts are 0.05+-0.01 and 0.11+-0.02 for the red and blue
distributions, respectively, over a factor of 100 in projected neighbor
density. The red fraction varies between about 0% and 70% for low-luminosity
galaxies and between about 50% and 90% for high-luminosity galaxies. This
difference is also shown by the variation of the luminosity functions with
environment. We demonstrate that the effects of environment and luminosity can
be unified. A combined quantity, Sigma_mod = Sigma_5/Mpc^{-2} + L_r/L_{-20.2},
predicts the fraction of red galaxies, which may be related to the probability
of transformation events. Our results are consistent with major interactions
(mergers and/or harassment) causing galaxies to transform from the blue to the
red distribution. We discuss this and other implications for galaxy evolution
from earlier results and model the effect of slow transformations on the color
functions.Comment: 14 pages, 8 figures, in AIP Conf. Proc., The New Cosmology, eds. R.
E. Allen et al. (aka. The Mitchell Symposium), see
http://proceedings.aip.org/proceedings/confproceed/743.jsp ; v2: replaced
Figure 5 which was incomplete in original submissio
Optimizing baryon acoustic oscillation surveys â I. Testing the concordance ÎCDM cosmology
We optimize the design of future spectroscopic redshift surveys for
constraining the dark energy via precision measurements of the baryon acoustic
oscillations (BAO), with particular emphasis on the design of the Wide-Field
Multi-Object Spectrograph (WFMOS). We develop a model that predicts the number
density of possible target galaxies as a function of exposure time and
redshift. We use this number counts model together with fitting formulae for
the accuracy of the BAO measurements to determine the effectiveness of
different surveys and instrument designs. We search through the available
survey parameter space to find the optimal survey with respect to the dark
energy equation-of-state parameters according to the Dark Energy Task Force
Figure-of-Merit, including predictions of future measurements from the Planck
satellite. We optimize the survey to test the LambdaCDM model, assuming that
galaxies are pre-selected using photometric redshifts to have a constant number
density with redshift, and using a non-linear cut-off for the matter power
spectrum that evolves with redshift. We find that line-emission galaxies are
strongly preferred as targets over continuum emission galaxies. The optimal
survey covers a redshift range 0.8 < z < 1.4, over the widest possible area
(6000 sq. degs from 1500 hours observing time). The most efficient number of
fibres for the spectrograph is 2,000, and the survey performance continues to
improve with the addition of extra fibres until a plateau is reached at 10,000
fibres. The optimal point in the survey parameter space is not highly peaked
and is not significantly affected by including constraints from upcoming
supernovae surveys and other BAO experiments.Comment: 15 pages, 9 figure
Angular Sizes of Faint Field Disk Galaxies: Intrinsic Luminosity Evolution
In order to explain the small scale-lengths detected in the recent deep field
observations performed from large ground-based telescopes and from the Hubble
Space Telescope, we investigate the predictions at high redshifts for disk
galaxies that formed by infall. Changes with redshift in the observed
properties of field galaxies are directly related to the evolution of the disks
and of the stellar populations. We see that changes in the rest frame
luminosity of a galaxy induce smaller values of half-light radii than are
predicted assuming no evolution. Comparisons are presented with two observed
samples from Mutz et al. (1994) and Smail et al. (1995).Comment: plain tex file + 3 postscript figures. To be published in ApJ
The Star Formation History of the Hubble Sequence: Spatially Resolved Colour Distributions of Intermediate Redshift Galaxies in the Hubble Deep Field
We analyse the spatially resolved colours of distant galaxies of known
redshift in the Hubble Deep Field, using a new technique based on matching
resolved four-band internal colour data to the predictions of evolutionary
synthesis models. We quantify the relative age, dispersion in age, ongoing
star-formation rate, star-formation history, and dust content of these
galaxies. To demonstrate the potential of the method, we study the
near-complete sample of 32 I ~ 0.5 studied by
Bouwens et al (1997). The dispersion of the internal colours of a sample of
0.4<z<1 early-type field galaxies in the HDF indicates that ~40% [4/11] show
evidence of star formation which must have occurred within the past third of
their ages at the epoch of observation. For a sample of well-defined spirals,
we similarly exploit the dispersion in colour to analyse the relative histories
of bulge and disc stars, in order to resolve the current controversy regarding
the ages of galactic bulges. Dust and metallicity gradients are ruled out as
major contributors to the colour dispersions we observe in these systems. The
median ages of bulge stars are found to be signicantly older than those in
galactic discs, and exhibit markedly different star-formation histories. This
result is inconsistent with a secular growth of bulges from disc instabilities,
but consistent with gradual disc formation by accretion of gas onto bulges, as
predicted by hierarchical theories. We extend our technique in order to discuss
the star formation history of the entire Bouwens et al sample in the context of
earlier studies concerned with global star formation histories.Comment: 8 colour postscript figures plus LaTeX source; submitted to MNRAS.
Uses the mnras.sty LaTeX style fil
Mental Health of HIV Positive Adolescents in Zambia
Objectives: To assess the mental health of HIV positive Zambian adolescents by comparing with Zambian school sample and an age matched British normative sample.Design: This was a cross-sectional study of adolescents from school in the age range of 11-15 and HIV positive adolescents from clinics in Lusaka.Main outcomes: Mental health of HIV positive Zambian adolescents.Measures: Mental health was assessed using the Strengths and Difficulties Questionnaire (SDQ).Results: When compared to the school sample it is found that both the groups are almost similar in the SDQ scales. Although the HIV group seem to have more peer problems, the difference does not reach a level of significance. The HIV sample was also less likely to be in the abnormal range for conduct problems (OR = 1.8). But when compared to a British community sample the Zambian HIV positive adolescents had increased emotional symptoms (OR= 3.6) and peer problems (OR= 7.1).Conclusion: Zambian HIV positive adolescents had increased mental health problems compared to a British Community sample.Keywords: HIV, adolescents, mental health, SDQ, Za
Pair Analysis of Field Galaxies from the Red-Sequence Cluster Survey
We study the evolution of the number of close companions of similar
luminosities per galaxy (Nc) by choosing a volume-limited subset of the
photometric redshift catalog from the Red-Sequence Cluster Survey (RCS-1). The
sample contains over 157,000 objects with a moderate redshift range of 0.25 < z
< 0.8 and absolute magnitude in Rc (M_Rc) < -20. This is the largest sample
used for pair evolution analysis, providing data over 9 redshift bins with
about 17,500 galaxies in each. After applying incompleteness and projection
corrections, Nc shows a clear evolution with redshift. The Nc value for the
whole sample grows with redshift as (1+z)^m, where m = 2.83 +/- 0.33 in good
agreement with N-body simulations in a LCDM cosmology. We also separate the
sample into two different absolute magnitude bins: -25 < M_Rc < -21 and -21 <
M_Rc < -20, and find that the brighter the absolute magnitude, the smaller the
m value. Furthermore, we study the evolution of the pair fraction for different
projected separation bins and different luminosities. We find that the m value
becomes smaller for larger separation, and the pair fraction for the fainter
luminosity bin has stronger evolution. We derive the major merger remnant
fraction f_rem = 0.06, which implies that about 6% of galaxies with -25 < M_Rc
< -20 have undergone major mergers since z = 0.8.Comment: ApJ, in pres
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