Euclid

Abstract:

Context: X-ray surveys of Active Galactic Nuclei (AGN) indicate `cosmic downsizing', with the comoving number density of high-luminosity objects peaking at higher redshifts (z about 2) than low-luminosity AGN (z<1). Aims: We test whether downsizing is caused by activity shifting towards low-mass black holes accreting at near-Eddington rates, or by a change in the average rate of accretion onto supermassive black holes. We estimate the black hole masses and Eddington ratios of an X-ray selected sample of AGN in the Chandra Deep Field South at z<1, probing the epoch where AGN cosmic downsizing has been reported. Methods: Black hole masses are estimated both from host galaxy stellar masses, which are estimated from fitting to published optical and near-infrared photometry, and from near-infrared luminosities, applying established correlations between black hole mass and host galaxy properties. Both methods give consistent results. Comparison and calibration of possible redshift-dependent effects is also made using published faint host galaxy velocity dispersion measurements. Results: The Eddington ratios in our sample span the range 10^{-5} to 1, with median log(L_bol/L_Edd)=-2.87, and with typical black hole masses about 10^{8} solar masses. The broad distribution of Eddington ratios is consistent with that expected for AGN samples at low and moderate luminosity. We find no evidence that the CDF-S AGN population is dominated by low-mass black holes accreting at near-Eddington ratios and the results suggest that diminishing accretion rates onto average-sized black holes are responsible for the reported AGN downsizing at redshifts below unity.

Abstract:

Aims. The radio-quiet quasar PG 1416-129 (z = 0.129) exhibits atypical optical and X-ray properties. Between 1990 and 2000, in response to its optical continuum decrease, the "classical" broad component of Hβ almost completely disappeared, with a factor of 10 decrease in the line flux. In addition, the width of the broad component of the Hβ line decreased significantly from 4000 km s-1 to 1450 km s-1. In the X-ray band, this object was observed by Ginga in 1988 to have the hardest quasar photon index, with Γ = 1.1 ± 0.1. We present an XMM-Newton/EPIC observation of PG 1416-129 performed in July 2004. Methods. We analyze the time-averaged pn spectrum of this quasar, as well as perform time-resolved spectroscopy. Results. We find that during the present XMM-Newton observation, PG 1416-129 still has a rather hard photon index, both in the soft (0.2-2 keV) and hard (2-12 keV) energy ranges, compared to radio-quiet quasars (BLS1 and NLS1) but compatible with the photon index value found for radio-loud quasars. This object also shows long-term luminosity variability over 16 years by a factor of three with a variation of photon index from ∼ 1.2 to ∼ 1.8. In the soft energy band (0.2-2 keV), we found a very weak soft X-ray excess compared to other RQ quasars. The whole time averaged spectrum is fit very well either by X-ray ionized reflection from the accretion disk surface, by a warm absorber-emitter plus power-law, or by a smeared absorption/emission from a relativistic outflow. While no constant narrow Fe K line at 6.4 keV is observed, we find the possible presence of two non-simultaneous transient iron lines: a redshifted narrow iron line at about 5.5 keV (96.4% confidence level according to multi-trial Monte-Carlo simulations) at the beginning of this observation and the appearance of a line at 6.3-6.4 keV (99.1% c.l.) at the end of the observation. These variable lines could be generated by discrete hot-spots on the accretion disk surface. © ESO 2007.

Abstract:

We present the energy-dependent power spectral density (PSD) and cross spectral properties of Mrk 766, obtained from combining data obtained during an XMM-Newton observation spanning six revolutions in 2005 with data obtained from an XMM-Newton long look in 2001. The PSD shapes and rms-flux relations are found to be consistent between the 2001 and 2005 observations, suggesting that the 2005 observation is simply a low-flux extension of the 2001 observation and permitting us to combine the two data sets. The resulting PSD has the highest temporal frequency resolution for any AGN PSD measured to date. Applying a broken power-law model yields break frequencies that increase in temporal frequency with photon energy. Obtaining a good fit when assuming energy-independent break frequencies requires the presence of a Lorentzian at (4.6 ± 0.4) × 10-4 Hz whose strength increases with photon energy, a behavior seen in black hole X-ray binaries. The cross spectral properties are measured; temporal frequency-dependent soft-to-hard time lags are detected in this object for the first time. Cross spectral results are consistent with those for other accreting black hole systems. The results are discussed in the context of several variability models, including those based on inwardly propagating viscosity variations in the accretion disk. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

Aims. We analyse a long XMM-Newton observation of the narrow-line Seyfert 1 galaxy Mrk 766, using the marked spectral variability on timescales >20 ks to separate components in the X-ray spectrum. Methods. Principal components analysis is used to identify distinct emission components in the X-ray spectrum, possible alternative physical models for those components are then compared statistically. Results. The source spectral variability is well-explained by additive variations, with smaller extra contributions most likely arising from variable absorption. The principal varying component, eigenvector one, is found to have a steep (photon index 2.4) power-law shape, affected by a low column of ionised absorption that leads to the appearance of a soft excess. Eigenvector one varies by a factor 10 in amplitude on time-scales of days and appears to have broad ionised Fe Kα emission associated with it: the width of the ionised line is consistent with an origin at ∼100 gravitational radii. There is also a strong component of near-constant emission that dominates in the low state, whose spectrum is extremely hard above 1 keV, with a soft excess at lower energies, and with a strong edge at Fe K but remarkably little Fe Kα emission. Although this component may be explained as relativistically-blurred reflection from the inner accretion disc, we suggest that its spectrum and lack of variability may alternatively be explained as either (i) ionised reflection from an extended region, possibly a disc wind, or (ii) a signature of absorption by a disc wind with a variable covering fraction. Absorption features in the low state may indicate the presence of an outflow. © ESO 2007.

Abstract:

The principles of measuring the shapes of galaxies by a model-fitting approach are discussed in the context of shape measurement for surveys of weak gravitational lensing. It is argued that such an approach should be optimal, allowing measurement with maximal signal-to-noise ratio, coupled with estimation of measurement errors. The distinction between likelihood-based and Bayesian methods is discussed. Systematic biases in the Bayesian method may be evaluated as part of the fitting process, and overall such an approach should yield unbiased shear estimation without requiring external calibration from simulations. The principal disadvantage of model fitting for large surveys is the computational time required, but here an algorithm is presented that enables large surveys to be analysed in feasible computation times. The method and algorithm is tested on simulated galaxies from the Shear TEsting Programme (STEP). © 2007 The Authors.