10,662 research outputs found
The cosmological evolution of the QSO luminosity density and of the star formation rate
We demonstrate that the evolution of the QSO luminosity density with epoch
displays a striking similarity to the cosmological evolution of the field
galaxy star formation rate, recently derived from a number of independent
surveys. The QSO luminosity density at 2800A is approximately one-fortieth that
implied by the star formation rate in galaxies throughout the past 11 Gigayears
(z<4). This similarity suggests that a substantial fraction of the QSO
luminosity may be closely linked to the star formation process and its
evolution with cosmic time.Comment: 3 pages, TeX, 1 figure, MNRAS in pres
Observations of QSO J2233-606 in the Southern Hubble Deep Field
The Hubble Deep Field South (HDF-S) HST observations are expected to begin in
October 1998. We present a composite spectrum of the QSO in the HDF-S field
covering UV/optical/near IR wavelengths, obtained by combining data from the
ANU 2.3m Telescope with STIS on the HST. This intermediate resolution spectrum
covers the range 1600-10000A and allows us to derive some basic information on
the intervening absorption systems which will be important in planning future
higher resolution studies of this QSO.Comment: 9 pages and 2 figures, submitted to ApJ
Do Quasars Lens Quasars?
If the unexpectedly high frequency of quasar pairs with very different
component redshifts is due to the lensing of a population of background quasars
by the foreground quasar, typical lens masses must be \sim10^{12}M_{\sun} and
the sum of all such quasar lenses would have to contain times the
closure density of the Universe. It then seems plausible that a very high
fraction of all \sim10^{12} M_{\sun} gravitational lenses with redshifts
contain quasars. Here I propose that these systems have evolved to
form the present population of massive galaxies with M and M
>5\times10^{11} M_{\sun}.Comment: 6 pages, aas style, ams symbols, ApJL (accepted
The environments of intermediate-redshift QSOs: 0.3 < z < 0.7
An angular correlation of low significance (2 sigma) is observed between 0.3
< z < 0.5 QSOs and V < 23 galaxies. Overall, the cross-correlation function
between 82 intermediate-redshift (0.3 < z < 0.7), X-ray selected QSOs and V <
24 galaxies is investigated, but no signal is detected for the z > 0.5 QSOs.
After converting to an excess of galaxies physically associated with the QSO,
this lack of strong correlation is shown to be consistent with the clustering
of normal galaxies at the same moderate redshifts. Combined with previous
observations, these results imply that the environments of radio-quiet QSOs do
not undergo significant evolution with respect to the galaxy population over a
wide range of redshifts (0 < z < 1.5). This is in marked contrast to the rapid
increase in the richness of the environments associated with radio-loud QSOs
over the same redshift range.Comment: 12 pages, 8 figures, MNRAS TeX macro, to appear to MNRA
Extensions around z=2 QSOs
Based on an R-band imaging survey of 6 high redshift (z~2) and high
luminosity (M<-28mag) QSOs, we report the detection of extensions in two
radio-quiet and one radio-loud QSO. The extensions are most likely due to the
host galaxies of these QSOs, with luminosities of at least 3-7 per cent of the
QSO luminosity. The most likely values for the luminosity of the host galaxies
lie in the range $6-18 per cent of the QSO luminosity.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Multicolour imaging of z= 2 QSO hosts
We present multicolour images of the hosts of three z=2 QSOs previously
detected in R-band by our group. The luminosities, colours and sizes of the
hosts overlap with those of actively star-forming galaxies in the nearby
Universe. Radial profiles over the outer resolved areas roughly follow de
Vaucouleur or exponential disk laws. These properties give support to the host
galaxy interpretation of the extended light around QSOs at high-redshift. The
rest-frame UV colours and upper limits derived for the rest-frame UV-optical
colours are inconsistent with the hypothesis of a scattered halo of light from
the active nucleus by a simple optically-thin scattering process produced by
dust or hot electrons. If the UV light is indeed stellar, star formation rates
of hundreds of solar masses per year are implied, an order of magnitude larger
than field galaxies at similar redshifts and above. This might indicate that
the QSO phenomenon (at least the high-luminosity one) is preferentially
acompanied by enhanced galactic activity at high-redshifts.Comment: Accepted to be published in MNRAS. 11 pages, Latex, uses mn macros,
also available at http://www.mpa-garching.mpg.de/~itzia
The Cambridge-Cambridge ROSAT Serendipity Survey - I. X-ray-luminous galaxies
We report on the first results obtained from a new optical identification
programme of 123 faint X-ray sources with (0.5--2ergscm serendipitously detected in {\it ROSAT}
PSPC pointed observations. We have spectroscopically identified the optical
counterparts to more than 100 sources in this survey. Although the majority of
the sample (68 objects) are QSOs, we have also identified 12 narrow emission
line galaxies which have extreme X-ray luminosities (ergs). Subsequent spectroscopy reveals them to be a
mixture of starburst galaxies and Seyfert 2 galaxies in approximately equal
numbers. Combined with potentially similar objects identified in the {\it
Einstein} Extended Medium Sensitivity Survey, these X-ray-luminous galaxies
exhibit a rate of cosmological evolution, , consistent with that derived for X-ray QSOs. This
evolution, coupled with the steep slope determined for the faint end of the
X-ray luminosity function (), implies
that such objects could comprise 15--35 per cent of the soft (1--2keV)Comment: Accepted for publication in MNRAS. 7 pages including 5 figures;
uuencoded compressed postscript; RGO-21
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