نتایج جستجو برای: quasar
تعداد نتایج: 5239 فیلتر نتایج به سال:
We present a sample of 218 new quasar pairs with proper transverse separations Rprop < 1 h −1 Mpc over the redshift range 0.5 < z < 3.0, discovered from an extensive follow up campaign to find companions around the Sloan Digital Sky Survey and 2dF Quasar Redshift Survey quasars. This sample includes 26 new binary quasars with separations Rprop < 50 h −1 kpc (θ < 10), more than doubling the numb...
Recently, a very large clustering length has been measured for quasars at a redshift of z ∼ 4. In combination with the observed quasar luminosity function we assess the implications of this clustering for the relationship between quasar luminosity and dark matter halo mass. Our analysis allows for non-linearity and finite scatter in the relation between quasar luminosity and halo mass, as well ...
We present a new method to measure the episodic lifetime of quasars with current and future large-scale sky surveys. Future photometric observations of large samples of confirmed quasars can provide a direct measurement (or interesting lower limit) to the lifetime of an individual episode of quasar activity (tQ) and potentially enable the study of post-quasar host galaxies. Photometric observat...
The associations of the angular positions of background quasars with foreground galaxies, clusters of galaxies and quasars are often attributed to the statistical lensing by gravitational potentials of the matter along the lines of sight, although it has been known that none of the individual objects (galaxies, clusters or quasars) are able to fully explain the reported amplitudes of the quasar...
We present spectroscopic observations of the damped Lyα absorber at redshift z = 1.9342 seen in the spectrum of the quasar Q0151+048A. The redshift of the absorber is greater than the redshift of the quasar, so the system resembles the zabs ≈ zem damped absorber at z = 2.81 towards the quasar PKS0528-250. We have previously reported the detection of Lyα emission from the latter absorber, one of...
UNJ1025−0040 is a quasar at z = 0.6344 that shows an extremely bright post starburst population of age ∼ 400 Myr (Brotherton et al. 1999). Images of UNJ1025−0040 show a nearly stellar object 4. 2 SSW of the quasar. We present imaging and spectroscopy that confirm that this object is a companion galaxy at redshift z = 0.6341. We estimate an age of ∼ 800 Myr for the dominant stellar population in...
A BeppoSAX observation of the z=2.34 quasar PKS2149−306 produced a strong signal in the high energy PDS instrument up to a maximum observed energy of nearly 50 keV, 150 keV in the quasar frame. The Beppo-SAX spectrum spans almost 3 decades (0.3−150 keV, quasar frame) and shows an extremely hard (α=0.4±0.05) X-ray spectrum above 3 keV (comparable to XJB the X-ray background slope), and either a ...
We compute the expected number of quasars multiply imaged by cluster size dark halos for current wide field quasar surveys by carrying out a large ensemble of ray tracing simulations through clusters from a cosmological N-body simulation of the ΛCDM cosmology. Our calculation predicts ∼ 4 quasar lenses with splittings θ > 10 in the SDSS spectroscopic quasar sample, consistent with the recent di...
We present models representing the scattering of quasar radiation off free electrons and dust grains in geometries that approximate the structure of quasar host galaxies. We show that, for reasonable assumptions, scattering alone can easily produce ratios of nuclear (point source) to extended fluxes comparable to those determined in studies of quasar hosts. This result suggests that scattered q...
نمودار تعداد نتایج جستجو در هر سال
با کلیک روی نمودار نتایج را به سال انتشار فیلتر کنید