12,740 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
Space shuttle plume simulation application. Results and math model
Pressure and gauge wind tunnel data from a transonic test of a 0.02 scale model of the space shuttle launch vehicle was analyzed to define the aerodynamic influence of the main propulsion system and solid rocket booster plumes during the transonic portion of ascent flight. Air was used as a simulant gas to develop the model exhaust plumes. A math model of the plume induced aerodynamic characteristics was developed for a range of Mach numbers to match the forebody aerodynamic math model. The base aerodynamic characteristics are presented in terms of forces and moments versus attitude. Total vehicle base and forebody aerodynamic characteristics are presented in terms of aerodynamic coefficients for Mach number from 0.6 to 1.4 Element and component base and forebody aerodynamic characteristics are presented for Mach numbers of 0.6, 1.05, 1.1, 1.25 and 1.4. The forebody data is available at Mach 1.55. Tolerances for all plume induced aerodynamic characteristics are developed in terms of a math model
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
Space shuttle plume/simulation application
An analysis of pressure and strain-gage data from space shuttle wind tunnel test IA119 and IA138 was performed to define the influence on aerodynamic characteristics resulting from the main propulsion system and solid rocket booster plumes. Aerodynamic characteristics of each of the elements, the components and total vehicle of the space shuttle vehicle during ascent flight was considered. Pressure data were obtained over the aft portions of the space shuttle wind tunnel model in addition to wing and elevon gage data
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
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