103 research outputs found
A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1^HXMMâNewton/Chandra survey field
We present the results of a deep 610-MHz survey of the 1^HXMMâNewton/Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ~7 arcsec and an rms noise limit of 60 ÎŒJy. To a 5Ï detection limit of 300 ÎŒJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ~2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of â0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. 'Q'= 2.45^(+0.3)_(â0.4))
2dF QSO Redshift Survey
With approximately 6000 QSO redshifts,the 2dF QSO redshift survey is already
the biggest complete QSO survey. The aim for the survey is to have 25000 QSO
redshifts, providing an order of magnitude increase in QSO clustering
statistics. We first describe the observational parameters of the 2dF QSO
survey. We then describe several highlights of the survey so far, including new
estimates of the QSO luminosity function and its evolution. We also review the
current status of QSO clustering analyses from the 2dF data. Finally, we
discuss how the complete QSO survey will be able to constrain the value of
Omega_o by measuring the evolution of QSO clustering, place limits on the
cosmological constant via a direct geometrical test and determine the form of
the fluctuation power-spectrum out to the approximately 1000 Mpc scales only
previously probed by COBE.Comment: 6 pages; to be published in Clustering at High Redshift, Marseille,
June 1999, eds. A. Mazure, O. LeFevre, V. Lebru
The 2dF QSO Redshift Survey
We present preliminary results from the 2-degree Field (2dF) QSO Redshift
Survey currently under way at the Anglo-Australian Telescope. This survey aims
to determine the redshifts of >25000 QSOs over a redshift range of 0.3<z<3.0
with the primary goal of investigating large-scale structure in the Universe to
high redshift and at very large scales (~1000h-1Mpc).
We describe the photometric procedure used to select QSO candidates for
spectroscopic observation. We then describe results from our first 2dF
observations, which have so far measured the redshifts for over 1000 QSOs. We
already find a significant detection of clustering and have also found one
close pair of QSOs (separation 17'') which are gravitational lens candidates.
To keep up to date with the current progress of the survey see:
http://msowww.anu.edu.au/~rsmith/QSO_Survey/qso_surv.htmlComment: 5 pages Latex including 6 figures, To appear in the proceedings of
"Evolution of Large Scale Structure: From Recombination to Garching", held
August 199
The polar ring galaxy AM1934-563 revisited
We report long-slit spectroscopic observations of the dust-lane polar-ring
galaxy AM1934-563 obtained with the Southern African Large Telescope (SALT)
during its performance-verification phase. The observations target the spectral
region of the Ha, [NII] and [SII] emission-lines, but show also deep NaI
stellar absorption lines that we interpret as produced by stars in the galaxy.
We derive rotation curves along the major axis of the galaxy that extend out to
about 8 kpc from the center for both the gaseous and the stellar components,
using the emission and absorption lines. We derive similar rotation curves
along the major axis of the polar ring and point out differences between these
and the ones of the main galaxy. We identify a small diffuse object visible
only in Ha emission and with a low velocity dispersion as a dwarf HII galaxy
and argue that it is probably metal-poor. Its velocity indicates that it is a
fourth member of the galaxy group in which AM1934-563 belongs. We discuss the
observations in the context of the proposal that the object is the result of a
major merger and point out some observational discrepancies from this
explanation. We argue that an alternative scenario that could better fit the
observations may be the slow accretion of cold intergalactic gas, focused by a
dense filament of galaxies in which this object is embedded (abridged).Comment: 19 pages, 13 figures, submitted to MNRAS. Some figures were bitmapped
to reduce the size. Full resolution version is available from
http://www.saao.ac.za/~akniazev/pub/AM1934_563.pd
Clustering in the 2dF QSO Redshift Survey
We present clustering results from the 2dF QSO Redshift Survey (2QZ) which
currently contains over 20,000 QSOs at z<3. The two-point correlation function
of QSOs averaged over the entire survey (~1.5) is found to be similar to
that of local galaxies. When sub-dividing the sample as a function of redshift,
we find that for an Einstein-de Sitter universe QSO clustering is constant (in
comoving coordinates) over the entire redshift range probed by the 2QZ, while
in a universe with Omega_0=0.3 and Lambda_0=0.7 there is a marginal increase in
clustering with redshift. Sub-dividing the 2QZ on the basis of apparent
magnitude we find only a slight difference between the clustering of QSOs of
different apparent brightness, with the brightest QSOs having marginally
stronger clustering. We have made a first measurement of the redshift space
distortion of QSO clustering, with the goal of determining the value of
cosmological parameters (in partcular Lambda_0) from geometric distortions. The
current data do not allow us to discriminate between models, however, in
combination with constraints from the evolution of mass clustering we find
Omega_0=1-Lambda_0=0.23 +0.44-0.13 and beta(z~1.4)=0.39 +0.18-0.17. The full
2QZ data set will provide further cosmological constraints.Comment: 5 pages, 7 figures. Contributed to the 'Where's the Matter'
conference in Marseille 25-29 June 200
The 2dF QSO Redshift Survey - 10K@2K!
With ~10000 QSO redshifts, the 2dF QSO Redshift Survey (2QZ) is already the
biggest individual QSO survey. The aim for the survey is to have ~25000 QSO
redshifts, providing an order of magnitude increase in QSO clustering
statistics. We first describe the observational parameters of the 2dF QSO
survey. We then describe several highlights of the survey so far; we present
new estimates of the QSO luminosity function and the QSO correlation function.
We also present the first estimate of the QSO power spectrum from the 2QZ
catalogue, probing the form of the fluctuation power-spectrum out to the
\~1000h-1Mpc scales only previously probed by COBE. We find a power spectrum
which is steeper than the prediction of standard CDM and more consistent with
the prediction of Lambda-CDM. The best-fit value for the power spectrum shape
parameter for a range of cosmologies is Gamma=0.1+-0.1. Finally, we discuss how
the complete QSO survey will be able to constrain the value of Omega_Lambda by
combining results from the evolution of QSO clustering and from a geometric
test of clustering isotropy.Comment: 11 pages, 6 figures, latex, eso and springer sty files included. To
appear in the proceedings of the MPA/ESO/MPA conference "Mining the Sky",
Garching, July 31 - August 4 2000, eds. A.J. Banday et a
First Results from the 2dF QSO redshift survey
We present some initial results from the 2dF QSO redshift survey. The aim of
the survey is to produce an optically-selected catalogue of 25000 QSOs over the
redshift range 0<z<3 using the 2-degree field at the Anglo-Australian
Telescope.Comment: 7 pages, 6 figures, submitted to proceedings of ESO Deep Fields
conferenc
The Star-formation History of the Universe as Revealed from Deep Radio Observations of the 13^H XMM-Newton/Chandra Deep Field
Discerning the exact nature of the faint (sub-mJy) radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep observations from Chandra/XMM-Newton/Spitzer and ground based follow up we are able to disentangle the AGN and star-
forming populations for the first time in a deep multi-frequency GMRT/VLA/MERLIN Survey. The many diagnostics include radio luminosity, morphology, radio to mid-IR flux density ratios, radio to optical flux density ratios and
radio spectral indices. Further diagnostics, e.g. optical spectra, X-ray spectra/hardness ratios, IR colours indicate the presence of the AGN independent of whether the radio emission is powered by AGN or star-formation. We are able to
examine the star-formation history of the universe up to z = 2.5 in a unique way based on an unbiased star-formation rate indicator, radio luminosity. This work provides an alternative perspective on the distribution of star-formation by mass, âdownsizingâ and allows us to examine the prevalence of AGN in star-bursts
Constraints on the distribution of absorption in the X-ray selected AGN population found in the 13H XMM-Newton/Chandra deep field
We present an analysis of the X-ray properties of sources detected in the 13H
XMM-Newton deep (200ks) field. In order to constrain the absorbed AGN
population, we use extensive Monte Carlo simulations to directly compare the
X-ray colours of observed sources with those predicted by several model
distributions. We have tested the simplest form of the AGN unified scheme,
whereby the intrinsic XLF of absorbed AGN is set to be the same as that of
their unabsorbed brethren, coupled with various model distributions of
absorption. The best fitting of these models sets the fraction of AGN with
absorbing column NH, proportional to (logNH)^8. We have also tested two
extensions to the unified scheme: an evolving absorption scenario, and a
luminosity dependent model distribution. Both of these provide poorer matches
to the observed X-ray colour distributions than the best fitting simple unified
model. We find that a luminosity dependent density evolution XLF reproduces
poorly the 0.5-2 keV source counts seen in the 13H field. Field to field
variations could be the cause of this disparity. Computing the simulated X-ray
colours with a simple absorbed power-law + reflection spectral model is found
to over-predict, by a factor of two, the fraction of hard sources that are
completely absorbed below 0.5 keV, implying that an additional source of
soft-band flux must be present for a number of the absorbed sources. Finally,
we show that around 40% of the 13H sample are expected to be AGN with NH>10^22
cm^-2.Comment: 13 pages, 9 figures, Accepted for publication in MNRA
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