scholarly journals Problems of Clustering of Radiogalaxies

2012 ◽  
Vol 8 (S290) ◽  
pp. 215-216
Author(s):  
Włodzimierz Godłowski ◽  
Agnieszka Pollo ◽  
Jacek Golbiak
Keyword(s):  
Correlation Function ◽  
Active Galactic Nuclei ◽  
Autocorrelation Function ◽  
Correlation Length ◽  
Power Law ◽  
Preliminary Analysis ◽  
Control Sample ◽  
Galactic Nuclei

AbstractWe present the preliminary analysis of clustering of a sample of 1157 radio-identified galaxies from Machalski & Condon (1999). We found that for separations 2–15 h−1 Mpc their redshift space autocorrelation function ξ(s) can be approximated by the power law with the correlation length ~3.75h−1 Mpc and slope γ ~ 1.8. The correlation length for radiogalaxies is found to be lower and the slope steeper than the corresponding parameters of the control sample of optically observed galaxies. Analysis the projected correlation function Ξ(r) displays possible differences in the clustering properties between active galactic nuclei (AGN) and starburst (SB) galaxies.

On the origin of power-law X-ray spectra of active galactic nuclei

1984 ◽  
Vol 287 ◽  
pp. 534 ◽  
Author(s):  
I. Schlosman ◽  
J. Shaham ◽  
G. Shaviv
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals Statistical characterization of gas-patch distributions in partially saturated rocks

Geophysics ◽  
2009 ◽  
Vol 74 (2) ◽  
pp. WA51-WA64 ◽  
Author(s):  
Julianna Toms-Stewart ◽  
Tobias M. Müller ◽  
Boris Gurevich ◽  
Lincoln Paterson
Keyword(s):  
Correlation Function ◽  
Autocorrelation Function ◽  
Correlation Length ◽  
Wave Attenuation ◽  
Length Scales ◽  
Gas Saturation ◽  
Partially Saturated ◽  
Statistical Measures ◽  
Fluid Saturation ◽  
Limestone Sample

Reservoir rocks are often saturated by two or more fluid phases forming complex patterns on all length scales. The objective of this work is to quantify the geometry of fluid phase distribution in partially saturated porous rocks using statistical methods and to model the associated acoustic signatures. Based on X-ray tomographic images at submillimeter resolution obtained during a gas-injection experiment, the spatial distribution of the gas phase in initially water-saturated limestone samples are constructed. Maps of the continuous variation of the percentage of gas saturation are computed and associated binary maps obtained through a global thresholding technique. The autocorrelation function is derived via the two-point probability function computed from the binary gas-distribution maps using Monte Carlo simulations.The autocorrelation function can be approximated well by a single Debye correlation function or a superposition of two such functions. The characteristic length scales and show sensitivity (and hence significance) with respect to the percentage of gas saturation. An almost linear decrease of the Debye correlation length occurs with increasing gas saturation. It is concluded that correlation function and correlation length provide useful statistical information to quantify fluid-saturation patterns and changes in these patterns at the mesoscale. These spatial statistical measures are linked to a model that predicts compressional wave attenuation and dispersion from local, wave-induced fluid flow in randomly heterogeneous poroelastic solids. In particular, for a limestone sample, with flow permeability of 5 darcies and an average gas saturation of [Formula: see text], significant [Formula: see text]-wave attenuation is predicted at ultrasonic frequencies.

Infrared Power‐Law Galaxies in the Chandra Deep Field–South: Active Galactic Nuclei and Ultraluminous Infrared Galaxies

2006 ◽  
Vol 640 (1) ◽  
pp. 167-184 ◽  
Author(s):  
A. Alonso‐Herrero ◽  
P. G. Perez‐Gonzalez ◽  
D. M. Alexander ◽  
G. H. Rieke ◽  
D. Rigopoulou ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Infrared Galaxies ◽  
Ultraluminous Infrared Galaxies

scholarly journals X-ray variability of 104 active galactic nuclei

2012 ◽  
Vol 8 (S290) ◽  
pp. 37-40
Author(s):  
O. González-Martín ◽  
S. Vaughan
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Power Law Model ◽  
Black Hole Mass ◽  
Periodic Oscillations ◽  
Fundamental Plane ◽  
X Ray ◽  
Single Power

AbstractWe have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z<0.4) active galactic nuclei (AGN) using 209 XMM-Newton/pn observations, including several AGN classes. These PSDs span ≃ 3 decades in temporal frequencies, ranging from minutes to days. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. A fraction of 72% show significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of α = 2.01±0.01. In 15 sources we found that the bending power law model was preferred with a mean slope of α = 3.08±0.04 and a mean bend frequency of 〈νb〉 ≃ 2 × 10−4 Hz. Only KUG 1031+398 (RE J1034+396) shows evidence for quasi-periodic oscillations. The ‘fundamental plane’ relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature.

scholarly journals Examining the physical conditions of a warm corona in active galactic nuclei accretion discs

2019 ◽  
Vol 491 (3) ◽  
pp. 3553-3561 ◽  
Author(s):  
D R Ballantyne
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Accretion Discs ◽  
Internal Heating ◽  
One Dimensional ◽  
X Ray ◽  
Physical Conditions ◽  
Gas Layer ◽  
Hot Corona

ABSTRACT A warm corona at the surface of an accretion disc has been proposed as a potential location for producing the soft excess commonly observed in the X-ray spectra of active galactic nuclei (AGNs). In order to fit the observed data, the gas must be at temperatures of ∼1 keV and have an optical depth of τT ≈ 10–20. We present one-dimensional calculations of the physical conditions and emitted spectra of a τT = 10 or 20 gas layer subject to illumination from an X-ray power law (from above), a blackbody (from below), and a variable amount of internal heating. The models show that a warm corona with kT ∼ 1 keV can develop, producing a strong Comptonized soft excess, but only if the internal heating flux is within a relatively narrow range. Similarly, if the gas density of the layer is too large then efficient cooling will stop a warm corona from forming. The radiation from the hard X-ray power law is crucial in producing a warm corona, indicating that a warm and hot corona may coexist in AGN accretion discs, and their combined effect leads to the observed soft excess. Intense heating of a warm corona leads to steep X-ray spectra with ionized Fe K α lines, similar to those seen in some narrow-line Seyfert 1 galaxies.

scholarly journals EUV and Soft X-ray Evidence for Partially Ionized Gas in Active Galactic Nuclei

1996 ◽  
Vol 152 ◽  
pp. 45-49
Author(s):  
J.P.D. Mittaz ◽  
R. Lieu ◽  
S. Bowyer ◽  
C.-Y. Hwang ◽  
J. Lewis
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
Ionized Gas ◽  
X Ray ◽  
Partially Ionized ◽  
Best Fit

We present a synoptic study of active galactic nuclei (AGN) detected by EUVE. We also present complementary ROSAT PSPC spectra for these sources and for other AGN in directions of low galactic absorption. It is found that the best-fit power-law photon indices of the X-ray spectra at 0.1–2.4 keV are anti-correlated with their galactic hydrogen columns. The indices for the 0.9–2.4 keV range do not show such a correlation, and are considerably smaller (i.e. flatter). We discuss a number of possible interpretations of this correlation but only one of these, the presence of a partially ionized absorbing gas in the AGN, explains the observations satisfactorily. The ubiquity of this effect suggests that this component be may very common in AGN.

The relation between the environment and nuclear activity in nearby QSOs: Defining a control sample

2020 ◽  
Vol 15 (S359) ◽  
pp. 339-341
Author(s):  
Bruna L. C. Araujo ◽  
Thaisa Storchi-Bergmann ◽  
Sandro B. Rembold
Keyword(s):  
Active Galactic Nuclei ◽  
Control Sample ◽  
Galactic Nuclei ◽  
Stellar Mass ◽  
Active Galaxies ◽  
Host Galaxies ◽  
Stellar Objects ◽  
Nuclear Activity ◽  
Quasi Stellar Objects

AbstractIn this study, we aim to investigate the relation between nuclear activity and the environment for luminous (L[O III] >7.63 × 1041 erg s–1) Active Galactic Nuclei (AGN) - that, at these luminosities are classified as quasi-stellar objects (QSOs) - using a sample of 436 type 2 QSOs. Recent studies suggest that there is an excess of interacting hosts in luminous AGN, indicating that interactions trigger the nuclear activity. In order to examine this, it is necessary to select a control sample of non-active galaxies, matched to the active ones by the properties of the host galaxies, such as distance and stellar mass. We present here the results of the search for such a control sample.

scholarly journals X-ray power law spectra in active galactic nuclei

2010 ◽  
Vol 512 ◽  
pp. A58 ◽  
Author(s):  
W. Ishibashi ◽  
T. J.-L. Courvoisier
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Galactic Nuclei ◽  
X Ray

scholarly journals Host galaxy properties and environment of obscured and unobscured X-ray selected active galactic nuclei in the COSMOS survey

2020 ◽  
Vol 494 (1) ◽  
pp. 1189-1202 ◽  
Author(s):  
C Bornancini ◽  
D García Lambas
Keyword(s):  
Active Galactic Nuclei ◽  
Formation Rate ◽  
Control Sample ◽  
Galactic Nuclei ◽  
Local Environment ◽  
Spectroscopic Properties ◽  
Stellar Mass ◽  
Host Galaxy ◽  
X Ray ◽  
Star Forming

ABSTRACT We analyse different photometric and spectroscopic properties of active galactic nuclei (AGNs) and quasars (QSOs) selected by their mid-IR power-law and X-ray emission from the COSMOS survey. We use a set of star-forming galaxies as a control sample to compare with the results. We have considered samples of obscured (HR &gt; −0.2) and unobscured (HR &lt; −0.2) sources including AGNs with LX &lt; 1044 erg s−1, as well as QSOs (LX &gt; 1044 erg s−1) with 1.4 ≤ z ≤ 2.5. We also study the typical environment of these samples, by assessing neighbouring galaxy number density and neighbour properties such as colour, stellar mass, and star formation rate. We find that the UV/optical and mid-infrared colour distribution of the different AGN types differ significantly. Also, we obtain most of AGNs and QSOs to be more compact when compared to the sample of SF galaxies. In general we find that the stellar mass distribution of the different AGN sample are similar, obtaining only a difference of $\Delta \overline{\mathrm{log}M}=0.3$ dex (M⊙) between unobscured and obscured QSOs. Obscured and unobscured AGNs and QSOs reside in different local environment at small (rp &lt; 100 kpc) scales. Our results support previous findings where AGN type correlates with environment. These differences and those found in AGN host properties cast out the simplest unified model in which obscuration is purely an orientation effect.

scholarly journals SkyMapper colours of Seyfert galaxies and Changing-Look AGN

2020 ◽  
Vol 499 (1) ◽  
pp. 1005-1022
Author(s):  
Christian Wolf ◽  
Jacob Golding ◽  
Wei Jeat Hon ◽  
Christopher A Onken
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Stellar Population ◽  
Broad Band ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Host Galaxy ◽  
Normal Galaxies ◽  
Mixing Sequences

ABSTRACT We study the utility of broad-band colours in the SkyMapper Southern Survey for selecting Seyfert galaxies at low luminosity. We find that the u − v index, built from the ultraviolet u and violet v filters, separates normal galaxies, starburst galaxies, and type-1 active galactic nuclei (AGNs). This u − v index is not sensitive to age or metallicity in a stellar population but is instead a quenching-and-bursting indicator in galaxies and detects power-law continua in type-1 AGNs. Using over 25 000 galaxies at z &lt; 0.1 from 6dFGS, we find a selection cut based on u − v and central u band brightness that identifies type-1 AGNs. By eyeballing 6dFGS spectra we classify new Seyfert galaxies of type 1 to 1.8. Our sample includes eight known Changing-Look AGNs (CLAGNs), two of which show such strong variability that they move across the selection cut during the 5 yr of SkyMapper observations in DR3, along mixing sequences of nuclear and host galaxy light. We identify 46 CLAGN candidates in our sample, one of which has been reported as a Type IIn supernova. We show that this transient persists for at least 5 yr and marks a flare in a Seyfert-1 period of a new CLAGN.

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