1,591 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
Hybrid Lateral Transshipments in a Multi-Location Inventory System
In managing networks of stock holding locations, two approaches to the pooling of inventory have been proposed. Reactive transshipm nts respond to stockouts at a location by moving inventory from elsewhere within the network, while proactive redistribution of stock seeks to minimise the chance of future shocks. This paper is the first to propose a hybrid approach in which transshipments are viewed as an opportunity for stock redistribution. We adopt a quasi-myopic approach to the development of a strongly performing hybrid transshipment policy. Numerical studies which utilise dynamic programming and simulation testify to the benefits of using transshipments proactively. In comparison to a purely reactive approach to transshipment, service levels are improved while a reduction in safety stock levels is achieved. The aggregate costs incurred in managing the system are significantly reduced, especially so for large networks facing high levels of demand.
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
The Redshift One LDSS-3 Emission line Survey (ROLES) II: Survey method and z~1 mass-dependent star-formation rate density
Motivated by suggestions of 'cosmic downsizing', in which the dominant
contribution to the cosmic star formation rate density (SFRD) proceeds from
higher to lower mass galaxies with increasing cosmic time, we describe the
design and implementation of the Redshift One LDSS3 Emission line Survey
(ROLES). ROLES is a K-selected (22.5 < K_AB < 24.0) survey for dwarf galaxies
[8.5<log(M*/Msun)< 9.5] at 0.89 < z < 1.15 drawn from two extremely deep fields
(GOODS-S and MS1054-FIRES). Using the [OII]3727 emission line, we obtain
redshifts and star-formation rates (SFRs) for star-forming galaxies down to a
limit of ~0.3 Msun/yr. We present the [OII] luminosity function measured in
ROLES and find a faint end slope of alpha_faint ~ -1.5, similar to that
measured at z~0.1 in the SDSS. By combining ROLES with higher mass surveys, we
measure the SFRD as a function of stellar mass using [OII] (with and without
various empirical corrections), and using SED-fitting to obtain the SFR from
the rest-frame UV luminosity for galaxies with spectroscopic redshifts. Our
best estimate of the corrected [OII]-SFRD and UV SFRD both independently show
that the SFRD evolves equally for galaxies of all masses between z~1 and z~0.1.
The exact evolution in normalisation depends on the indicator used, with the
[OII]-based estimate showing a change of a factor of ~2.6 and the UV-based a
factor of ~6. We discuss possible reasons for the discrepancy in normalisation
between the indicators, but note that the magnitude of this uncertainty is
comparable to the discrepancy between indicators seen in other z~1 works. Our
result that the shape of the SFRD as a function of stellar mass (and hence the
mass range of galaxies dominating the SFRD) does not evolve between z~1 and
z~0.1 is robust to the choice of indicator. [abridged]Comment: Resubmitted to MNRAS following first referee report. 20 pages, 16
figures. High resolution version available at
http://astro.uwaterloo.ca/~dgilbank/papers/roles2.pd
A faint galaxy redshift survey to B=24
Using the multislit LDSS-2 spectrograph on the {\it William Herschel
Telescope} we have completed a redshift survey in the magnitude range which has produced 73 redshifts representing a 73\% complete sample
uniformly-selected from four deep fields at high Galactic latitude. The survey
extends out to and includes the highest redshift galaxy () yet
discovered in a field sample. The median redshift, \zmed=0.46, and form of
the redshift distribution constitute compelling evidence against simple
luminosity evolution as an explanation of the large excess of faint galaxies
(2--4 no-evolution) seen in this magnitude range. Rather we
identify the excess population as blue objects with and \,
luminosities similar to local galaxies indicating a dramatic decrease in
the density of such objects over the last Hubble time, confirming the trends
found in brighter redshift surveys. We also find a marked absence of {\it very}
low redshift galaxies (0.1) at faint limits, severely constraining any
significant steepening of the local field galaxy luminosity function at low
luminosities.Comment: uuencoded compressed postscript. The preprint are also available at
URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm
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