A Theoretical Model to Calculate Red-shift of Galaxies and Quasi stellar objects (QSO)‎ (original) (raw)

Calibrating photometric redshifts of luminous red galaxies

Monthly Notices of the Royal Astronomical Society, 2005

We discuss the construction of a photometric redshift catalogue of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS), emphasizing the principal steps necessary for constructing such a catalogue -(i) photometrically selecting the sample, (ii) measuring photometric redshifts and their error distributions, (iii) and estimating the true redshift distribution. We compare two photometric redshift algorithms for these data and find that they give comparable results. Calibrating against the SDSS and SDSS-2dF spectroscopic surveys, we find that the photometric redshift accuracy is σ ∼ 0.03 for redshifts less than 0.55 and worsens at higher redshift (∼ 0.06 for z < 0.7). These errors are caused by photometric scatter, as well as systematic errors in the templates, filter curves, and photometric zeropoints. We also parametrize the photometric redshift error distribution with a sum of Gaussians, and use this model to deconvolve the errors from the measured photometric redshift distribution to estimate the true redshift distribution. We pay special attention to the stability of this deconvolution, regularizing the method with a prior on the smoothness of the true redshift distribution. The methods we develop are applicable to general photometric redshift surveys. c 0000 RAS

Modelling the quasi-stellar object luminosity and spatial clustering at low redshifts

Monthly Notices of the Royal Astronomical Society, 2006

We investigate the ability of hierarchical models of quasi-stellar object (QSO) formation and evolution to match the observed luminosity, number counts and spatial clustering of quasars at redshift z < 2. These models assume that the QSO emission is triggered by galaxy mergers, that the mass of the central black hole (BH) correlates with halo properties and that quasars shine at their Eddington luminosity except, perhaps, during the very early stages of evolution. We find that models based on simple analytic approximations successfully reproduce the observed B-band QSO luminosity function (LF) at all redshifts, provided that some mechanisms is advocated to quench mass accretion within haloes larger than ∼10 13 M that host bright quasars. These models also match the observed strength of QSO clustering at z ∼ 0.8. At larger redshifts, however, they underpredict the QSO biasing which, instead, is correctly reproduced by semi-analytic models in which the halo merger history and associated BHs are followed by Monte Carlo realizations of the merger hierarchy. We show that the disagreement between the LF predicted by semi-analytic models and observations can be ascribed to the use of B-band data, which are a biased tracer of the quasar population, due to obscuration.

Photometric Redshifts for Galaxies in the GOODS Southern Field

The Astrophysical Journal, 2004

We use extensive multi-wavelength photometric data from the Great Observatories Origins Deep Survey to estimate photometric redshifts for a sample of 434 galaxies with spectroscopic redshifts in the Chandra Deep Field South. Using the Bayesian method (Benítez 2000), which incorporates redshift/magnitude priors, we estimate photometric redshifts for galaxies in the range 18 < R AB < 25.5, giving an rms scatter σ( ∆z 1+zspec ) ≤ 0.11. The outlier fraction is < 10%, with the outlier-clipped rms being 0.047. We examine the accuracy of photometric redshifts for several, special sub-classes of objects. The results for extremely red objects are more accurate than those for the sample as a whole, with σ = 0.051 and very few outliers (3%). Photometric redshifts for active galaxies, identified from their X-ray emission, have a dispersion of σ = 0.104, with 10% outlier fraction, similar to that for normal galaxies. Employing a redshift/magnitude prior in this process seems to be crucial in improving the agreement between photometric and spectroscopic redshifts.

The ESO Slice Project (ESP) galaxy redshift survey

Astronomy and Astrophysics Supplement Series, 1998

The ESO Slice Project (ESP) is a galaxy redshift survey we have recently completed as an ESO Key-Project over about 23 square degrees, in a region near the South Galactic Pole. The survey is nearly complete to the limiting magnitude b J = 19.4 and consists of 3342 galaxies with reliable redshift determination.

Redshift Distribution of Quasi-Stellar Objects and the Radio Source Counts

Symposium - International Astronomical Union, 1972

The evolution of QSOs and the reality of their apparent cutoff for z > 2.3 is determined using their large scale redshift distribution. The contributions of QSRs to radio source counts are calculated on the basis of possible evolution of QSOs having z > 2.2.

The optical redshift survey: Sample selection and the galaxy distribution

This is the first in a series of papers describing the Optical Redshift Survey (ORS), a redshift survey of optically selected galaxies covering 98% of the sky above |b| = 20 • (8.09 ster). The survey is drawn from the Uppsala Galaxy Catalogue (UGC), the European Southern Observatory Galaxy Catalogue (ESO), and the Extension to the Southern Galaxy Catalogue (ESGC), and contains two sub-catalogs, one complete to a B magnitude of 14.5, the other complete to a B major axis diameter of 1.9 ′ . The entire sample consists of 8457 objects, of which redshifts are now available for 8286; 171 objects remain without measured redshifts. Roughly 1300 of the redshifts were measured for the completion of the sample; the remainder were taken from the literature. Most of these new redshifts are concentrated at low Galactic latitudes 20 • ≤ |b| ≤ 30 • and within the strip not covered by either the UGC or ESO catalogues: −17.5 • ≤ δ ≤ −2.5 • . The ORS provides the most detailed and homogeneous sampling of the large-scale galaxy distribution to date in these areas. The density field of bright optical galaxies is well-defined to 8000 km s −1 , and is dominated by the Virgo, Hydra-Centaurus, Pisces-Perseus, Coma-A1367, and Telescopium-Pavo-Indus Superclusters. The dense sampling provided by ORS allows a detailed analysis of the galaxy density field, and will be used to test its dependence on morphology and other galaxy parameters.

Astronomy phenomenological analysis of redshift-distance power laws

Astrophysics and Space Science, 2000

The traditional astronomical literature accepts the linear redshift-distance law on the basis of its internal consistency with accepted models of the history of the universe more than on nontrivial clearly objective tests of the linear law for directly observed quantities. The reluctance to depend on such tests rested historically on the assumed large variation in the intrinsic luminosity of extragalactic objects and a distrust of curve-fitting and statistics. But such tests are eminently feasible on the basis of modern objectively specified samples and up-to-date statistical methodology. This paper compares red-shift distance relations of the form z = kr p , for real values of p. Data from the visible, infrared, radio, and X-ray bands are examined. The deviation of predicted and observed apparent magnitudes, (a), and the difference between observed and predicated slope of the magnitude-log(z) plots, (b), are used to compare values of p. In summary, the p = 1 values (corresponding to standard linear law) are more deviant than any other value of p, 1 < p <= 4 for test (a) and more deviant than any value of p, 1 < p <= 3 for test (b) except for marginal features in the smallest (radio) sample and in the lowest redshift sample. Bright subsamples and a morphologically homogeneous subsample of elliptic galaxies are also tested with similar results. In contrast, the predications for p = 2 are reasonably accurate and close to optimal among all values of p explored. The p = 2 case is predicted by the chronometric cosmology and in agreement with the independent analysis of Troitskii.