scholarly journals Cosmic Distribution of Optically Selected Quasars

1987 ◽  
Vol 124 ◽  
pp. 619-625
Author(s):  
Maarten Schmidt
Keyword(s):  
Luminosity Function ◽  
Birth Rate ◽  
Emission Lines ◽  
Short Life ◽  
Large Redshift ◽  
X Ray ◽  
Wide Range ◽  
X Ray Background ◽  
Spectral Survey ◽  
Luminosity Evolution

Counts of optically selected quasars as a function of magnitude and redshift show the effects of strong evolution. If quasars have relatively short life times, then the observed numbers at a given redshift are mostly determined by their birth rate and mean luminosity over their lifetime. In this case the evolution of the luminosity function can be described by density evolution, where the rate of evolution may depend on luminosity and other properties. On the other hand, if all quasars were formed at large redshift and have been decaying in luminosity since that time, then the evolution of the luminosity function is best described in terms of luminosity evolution. We discuss some of the consequences of luminosity evolution for the mass of quasars and for the X-ray background.We explore the observational aspects of the redshift cutoff of quasars. The situation is complicated by the unavoidable bias in slitless surveys against weak-line objects. Since quasar emission lines show a wide range of equivalent widths, a spectral survey will be characterized by a distribution of limiting continuum magnitudes rather than by a single value. The decline in the space density of quasars at large redshift may depend on luminosity, and may also have structure, such as a steep drop, but not a total cutoff, in density at a redshift near 3.

AGN1 vs AGN2 dichotomy as seen from the point of view of ionized outflows

2019 ◽  
Vol 15 (S356) ◽  
pp. 96-96
Author(s):  
Eleonora Sani
Keyword(s):  
Accretion Rate ◽  
Point Of View ◽  
Emission Lines ◽  
Black Hole Mass ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Wide Range ◽  
Strong Contrast

AbstractI present a detailed study of ionized outflows in a large sample of 650 hard X-ray detected AGN. Taking advantage of the legacy value of the BAT AGN Spectroscopic Survey (BASS, DR1), we are able to reveal the faintest wings of the [OIII] emission lines associated with outflows. The sample allows us to derive the incidence of outflows covering a wide range of AGN bolometric luminosity and test how the outflow parameters are related with various AGN power tracers, such as black hole mass, Eddington ratio, luminosity. I’ll show how ionized outflows are more frequently found in type 1.9 and type 1 AGN (50% and 40%) with respect to the low fraction in type 2 AGN (20%). Within such a framework, I’ll demonstrate how type 2 AGN outflows are almost evenly balanced between blue- and red-shifted winds. This, in strong contrast with type 1 and type 1.9 AGN outflows which are almost exclusively blue-shifted. Finally, I’ll prove how the outflow occurrence is driven by the accretion rate, whereas the dependence of outflow properties with respect to the other AGN power tracers happens to be quite mild.

scholarly journals Evolution and State of the Local ISM

1996 ◽  
Vol 171 ◽  
pp. 442-442
Author(s):  
T. Schmutzler ◽  
D. Breitschwerdt
Keyword(s):  
Basic Feature ◽  
Emission Lines ◽  
Continuum Emission ◽  
Ionization Equilibrium ◽  
X Ray ◽  
Self Consistent ◽  
X Ray Background ◽  
Collisional Ionization ◽  
Consistent Approach ◽  
The Continuum

The most puzzling observations concerning the LISM (distance < 100 pc) can be explained by a fast adiabatically cooled gas in the cavity of an old superbubble. The ultrasoft X-ray background and contributions to the C- and M-bands are due to the continuum emission of delayed recombination [1]. In contrast to collisional ionization equilibrium (CIE) models, but consistent with recent observations [2], our model predicts a lack of emission lines and a low emissivity in the EUV range. In the figure below we compare the emissivities resulting from CIE at T = 106 K and those from our model at T = 4.2 × 104 K. The basic feature of our model is a thermally self-consistent approach of the time-dependent evolution.

scholarly journals UHURU Results on Extragalactic X-Ray Sources

1973 ◽  
Vol 55 ◽  
pp. 171-183 ◽  
Author(s):  
Edwin M. Kellogg
Keyword(s):  
High Latitude ◽  
Luminosity Function ◽  
Optical Data ◽  
Clusters Of Galaxies ◽  
X Rays ◽  
Total Contribution ◽  
X Ray ◽  
Normal Galaxies ◽  
X Ray Background ◽  
Individual Galaxies

Data from the UHURU satellite have provided a list of more than forty high latitude sources (|b| > 20°). X-rays have been detected from among the nearest normal galaxies, giant radio galaxies, Seyferts, QSOs and clusters of galaxies. The cluster sources appear to be extended by several hundred kiloparsecs as well as being very luminous. These cluster sources have systematic differences in their X-ray spectra from individual galaxies.About twenty sources are not reliably identified so far. A few of these are located near undistinguished 3C or MSH radio sources. The rest are either located near distant clusters or undistinguished bright galaxies, or are too far south, so that we have not sufficient optical data to allow a thorough search for possible association with clusters or unusual individual galaxies.The luminosity function for weak, high latitude X-ray sources is determined, and the contribution of sources just below the UHURU threshold of detectability to observed fluctuations in the diffuse X-ray background is evaluated. The total contribution of all observed types of extragalactic sources to the X-ray background is estimated.

scholarly journals The X-Ray Background and the AGN Luminosity Function

1999 ◽  
Vol 183 ◽  
pp. 200-209
Author(s):  
G. Hasinger
Keyword(s):  
Black Holes ◽  
Luminosity Function ◽  
Cosmic Time ◽  
Volume Density ◽  
Energy Bands ◽  
X Ray ◽  
Normal Galaxies ◽  
X Ray Background ◽  
Acid Test

ROSAT deep and shallow surveys have provided an almost complete inventory of the constituents of the soft X-ray background which led to a population synthesis model for the whole X-ray background with interesting cosmological consequences. According to this model the X-ray background is the “echo” of mass accretion onto supermassive black holes, integrated over cosmic time. A new determination of the soft X-ray luminosity function of active galactic nuclei (AGN) is consistent with pure density evolution, and the comoving volume density of AGN at redshift 2–3 approaches that of local normal galaxies. This indicates that many larger galaxies contain black holes and it is likely that the bulk of the black holes was produced before most of the stars in the universe. However, only X-ray surveys in the harder energy bands, where the maximum of the energy density of the X-ray background resides, will provide the acid test of this picture.

The Digitized First Byurakan Survey - DFBS

2005 ◽  
Vol 216 ◽  
pp. 230-238 ◽  
Author(s):  
A. M. Mickaelian ◽  
L. A. Sargsyan ◽  
L. K. Erastova ◽  
S. K. Balayan ◽  
K. S. Gigoyan ◽  
...  
Keyword(s):  
Emission Lines ◽  
Web Page ◽  
Broad Absorption ◽  
Byurakan Survey ◽  
First Byurakan Survey ◽  
X Ray ◽  
Different Types ◽  
New Research ◽  
Spectral Survey ◽  
Flux Calibration

The First Byurakan Survey (FBS) is the largest spectral survey in the Northern sky. One can select objects by color, broad absorption and emission lines, and SED; classify and investigate them. The digitization of the FBS is aimed at making a DFBS database available for the astronomical community. Besides scanning, we are creating plate solutions, extraction software, wavelength and flux calibration, templates for different types of objects, numerical classification, a catalog of objects, a database of spectra, a user interface and a DFBS web page. New research projects based on the DFBS are possible, including a search for new QSOs and other AGN, a continuation of the second part of FBS, and identifications of radio, IR and X-ray sources. The DFBS database will be available at the end of 2004.

scholarly journals The Soft X-ray Background Spectrum from DXS

1997 ◽  
Vol 166 ◽  
pp. 83-90 ◽  
Author(s):  
W.T. Sanders ◽  
R.J. Edgar ◽  
D.A. Liedahl ◽  
J.P. Morgenthaler
Keyword(s):  
Galactic Plane ◽  
Emission Lines ◽  
Background Spectrum ◽  
Local Bubble ◽  
X Ray ◽  
Hot Plasma ◽  
Solar Abundances ◽  
Ionic Emission ◽  
X Ray Background ◽  
Ionization Balance

AbstractThe Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.

scholarly journals Discrete Source Synthesis of the X-Ray Background

1980 ◽  
Vol 92 ◽  
pp. 233-233 ◽  
Author(s):  
A. Cavaliere ◽  
L. Danese ◽  
G. De Zotti ◽  
A. Franceschini
Keyword(s):  
Power Law ◽  
Energy Content ◽  
High Energy ◽  
Discrete Source ◽  
Distribution Functions ◽  
Mean Values ◽  
X Ray ◽  
X Ray Background ◽  
Luminosity Evolution

The recent deep X-ray surveys suggest that discrete sources comprise most, if not all, of the energy content of the background (cf. Giacconi, this volume). We have shown that, if sources have flat power law spectra and relatively sharp high-energy cutoffs, their combined emission can also mimic very accurately its extended (2 - 400 keV) spectral shape. A broad distribution of cutoff energies Ec is required, in this case, to model the high-energy (E ≳ 20 - 40 keV) part: a power law envelope of distribution functions of various types of sources can be envisaged; alternatively, the well-known fact that most of the 2 − 10 keV background should be produced by low flux, low Ec sources can suggest that Ec ∝ (1 + z)−η. The quality of the fit turns out to be not very sensitive to the amount of number/luminosity evolution assumed, though the minimum χ2 test slightly favours strongly evolving sources. In the case of differential luminosity ∝ E−γ and evolution ∝ (1 + z)α with 0 ≤ α ≤ 6, the best fits to pre HEAO-1 data are obtained for mean values of the spectral index γ ≈ 0.5 − 0.9 and for dispersions Δγ ≃ 0.5 - 0.7. Rather wide ranges of values of γ and Δγ are, however, still allowed; e.g., for α = 6, the allowed intervals are 0.2 ≤ γ ≤ 1.3, 0 ≤ Δγ ≤ 0.7.

Sign in / Sign up

Export Citation Format

Share Document