33 research outputs found
Deep Extragalactic X-ray Surveys
Deep surveys of the cosmic X-ray background are reviewed in the context of
observational progress enabled by the Chandra X-ray Observatory and the X-ray
Multi-Mirror Mission-Newton. The sources found by deep surveys are described
along with their redshift and luminosity distributions, and the effectiveness
of such surveys at selecting active galactic nuclei (AGN) is assessed. Some key
results from deep surveys are highlighted including (1) measurements of AGN
evolution and the growth of supermassive black holes, (2) constraints on the
demography and physics of high-redshift AGN, (3) the X-ray AGN content of
infrared and submillimeter galaxies, and (4) X-ray emission from distant
starburst and normal galaxies. We also describe some outstanding problems and
future prospects for deep extragalactic X-ray surveys.Comment: 32 pages; Annu. Rev. Astron. Astrophys., Volume 43 (2005); updated to
match accepted versio
Spectral Classification; Old and Contemporary
Beginning with a historical account of the spectral classification, its
refinement through additional criteria is presented. The line strengths and
ratios used in two dimensional classifications of each spectral class are
described. A parallel classification scheme for metal-poor stars and the
standards used for classification are presented. The extension of spectral
classification beyond M to L and T and spectroscopic classification criteria
relevant to these classes are described. Contemporary methods of
classifications based upon different automated approaches are introduced.Comment: To be published in "Principles and Perspectives in Cosmochemistry"
Lecture Notes on Kodai School on Synthesis of Elements in Stars: Ed Aruna
Goswami & Eswar Reddy, Springer Verlag, 2009, 17 pages, 10 figure
Shedding Light on the Galaxy Luminosity Function
From as early as the 1930s, astronomers have tried to quantify the
statistical nature of the evolution and large-scale structure of galaxies by
studying their luminosity distribution as a function of redshift - known as the
galaxy luminosity function (LF). Accurately constructing the LF remains a
popular and yet tricky pursuit in modern observational cosmology where the
presence of observational selection effects due to e.g. detection thresholds in
apparent magnitude, colour, surface brightness or some combination thereof can
render any given galaxy survey incomplete and thus introduce bias into the LF.
Over the last seventy years there have been numerous sophisticated
statistical approaches devised to tackle these issues; all have advantages --
but not one is perfect. This review takes a broad historical look at the key
statistical tools that have been developed over this period, discussing their
relative merits and highlighting any significant extensions and modifications.
In addition, the more generalised methods that have emerged within the last few
years are examined. These methods propose a more rigorous statistical framework
within which to determine the LF compared to some of the more traditional
methods. I also look at how photometric redshift estimations are being
incorporated into the LF methodology as well as considering the construction of
bivariate LFs. Finally, I review the ongoing development of completeness
estimators which test some of the fundamental assumptions going into LF
estimators and can be powerful probes of any residual systematic effects
inherent magnitude-redshift data.Comment: 95 pages, 23 figures, 3 tables. Now published in The Astronomy &
Astrophysics Review. This version: bring in line with A&AR format
requirements, also minor typo corrections made, additional citations and
higher rez images adde
Evolution of the Luminosity Function of Quasars
The luminosity function of quasars shows a strong dependence on redshift. We discuss alternate descriptions of this evolution. Density evolution is assumption-free if the density variation with red-shift is also allowed to be a function of absolute magnitude. Luminosity evolution and, in particular, pure luminosity evolution make a priori assumptions about the shape of the luminosity function. We illustrate the derivation of density evolution and its strong dependence on optical luminosity. We discuss work by Schmidt and Green (1985) on X-ray counts of quasars and the need for negative X-ray luminosity evolution to explain the counts and the low average redshift of X-ray quasars. As a consequence the quasar contribution to the 2 keV X-ray background is only around 8–13%. The evolution of active galactic nuclei of lower optical luminosity is tightly constrained by the observed X-ray background
The BTC40 Survey for Quasars at 4.8 < z < 6
The BTC40 Survey for high-redshift quasars is a multicolor search using images obtained with the Big Throughput Camera (BTC) on the CTIO 4-m telescope in V, I, and z filters to search for quasars at redshifts of 4.8 < z < 6. The survey covers 40 sq. deg. in B, V, and I and 36 sq. deg. in z. Limiting magnitudes (3 sigma) reach to V = 24.6, I = 22.9 and z = 22.9. We used the (V-I) vs. (I-z) two-color diagram to select high-redshift quasar candidates from the objects classified as point sources in the imaging data. Follow-up spectroscopy with the AAT and CTIO 4-m telescopes of candidates having I < 21.5 has yielded two quasars with redshifts of z = 4.6 and z = 4.8 as well as four emission line galaxies with z = 0.6. Fainter candidates have been identified down to I = 22 for future spectroscopy on 8-m class telescopes