Doron Chelouche

Lensing, reddening and extinction effects of Mg ii absorbers from z= 0.4 to 2

Using a sample of almost 7000 strong Mg II absorbers with W 0 > 1 A and 0.4 < z < 2.2 detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W 0 . We find the amount of dust to increase with cosmic time as τ(z) α(1 I + z)- 1.1± 0.4, following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E(B - V) and we find that r α (W 0 ) 1.9+0.1 , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg II systems. We measure the upper limit μ < 1.10 and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range 1 < W 0 < 6 A. We parametrize this effect and provide a correction for recovering the intrinsic ∂N/bw 0 distribution.

Dynamical and Spectral Modeling of the Ionized Gas and Nuclear Environment in NGC 3783

We present a new approach for calculating the physical properties of highly ionized X-ray flows in active galactic nuclei. Our method relies on a detailed treatment of the structure, dynamics, and spectrum of the gas. A quantitative comparison of our model predictions with the 900 ks Chandra HETG X-ray spectrum of NGC 3783 shows the following: (1) The highly ionized outflow is driven by thermal pressure gradients, and radiation pressure force is less important. (2) A full-featured dynamical model that provides a very good fit to the high-resolution X-ray spectrum requires a multiphased flow with a density power spectrum reminiscent of the interstellar medium. (3) Adiabatic cooling is an important factor, and so is an additional heating source that may be related to the apparent multiphase and turbulent nature of the flow. (4) The base of the flow is ~1 pc from the central object, in agreement with some, but not all, previous estimates. (5) The mass-loss rate is in the range 0.01-0.1 M☉ yr-1, which is smaller than previous estimates and is on the same order as the mass accretion rate in this object.

QSO Absorption Lines from QSOS

We present the results of a search for metal absorption lines in the spectra of background QSOs whose sight lines pass close to foreground QSOs. We detect Mg II λλ2796, 2803 absorption in Sloan Digital Sky Survey (SDSS) spectra of four z > 1.5 QSOs whose lines of sight pass within 26-98 h kpc of lower redshift (z 0.5-1.5) QSOs. The 100% detection rate (four out of four pairs) of Mg II in the background QSOs is clearly at odds with the incidence of associated zabs zem systems—absorbers that exist toward only a few percent of QSOs. Although the quality of our foreground QSO spectra is not as high as the SDSS data, absorption seen toward one of the background QSOs clearly does not show up at the same strength in the spectrum of the corresponding foreground QSO. This implies that the absorbing gas is distributed inhomogeneously around the QSO, presumably as a direct consequence of the anisotropic emission from the central active galactic nucleus. We discuss possible origins for the Mg II lines, including absorption by gas from the foreground QSO host galaxy, companion galaxies fueling the QSO through gravitational interactions, and tidal debris left by galaxy mergers or interactions that initiated the QSO activity. No single explanation is entirely satisfactory, and we may well be seeing a mixture of phenomena.

XMM-Newton Spectroscopy of the Starburst-Dominated Ultraluminous Infrared Galaxy NGC 6240

We present a new XMM-Newton observation of the ultraluminous infrared galaxy (ULIRG) NGC 6240. We analyze the reflecting grating spectrometer (RGS) data, as well as data from the other instruments, and find a starburst-dominated 0.5-3 keV spectrum with global properties resembling those observed in M82 but with a much higher luminosity. We show that the starburst region can be divided into an outer zone, beyond a radius of about 2.1 kpc, with a gas temperature of about 107 K, and a central region with temperatures in the range (2-6) × 107 K. The gas in the outer region emits most of the observed O VIII Lyα line, and the gas in the inner region the emission lines of higher ionization ions, including a strong Fe XXV line. We also identify a small inner part, very close to the active nuclei, with typical Seyfert 2 properties, including a large amount of photoionized gas producing a strong Fe Kα 6.4 keV line. The combined abundance, temperature, and emission measure analysis indicates supersolar Ne/O, Mg/O, Si/O, S/O, and possibly also Fe/O. The analysis suggests densities in the range of (0.07-0.28)-1/2 cm-3 and a total thermal gas mass of ~4 × 1081/2 M☉, where is the volume filling factor. We used a simple model to argue that a massive starburst with an age of 2 × 107 yr can explain most of the observed properties of the source. NGC 6240 is perhaps the clearest case of an X-ray-bright luminous AGN that is in a merger and whose soft X-ray spectrum is dominated by a powerful starburst.

Spectral Signatures of Photon-Particle Oscillations from Celestial Objects

We give detailed predictions for the spectral signatures arising from photon-particle oscillations in astrophysical objects. The calculations include quantum electrodynamic effects and effects due to active relativistic plasma. We show that, by studying the spectra of compact sources, it may be possible to directly detect (pseudo-)scalar particles, such as the axion, with much greater sensitivity, by up to three orders of magnitude, than is currently achievable by other methods. In particular, if such particles exist with masses ma 10?13 GeV?1, then their oscillation signatures are likely to be lurking in the spectra of magnetars, pulsars, and quasars.

Gravitational Microlensing and the Structure of Quasar Outflows

We show that invaluable information on the structure quasar outflows can be obtained by considering microlensing (ML)-induced variability of absorption-line troughs in lensed quasars. Depending on the structure and geometry of the outflowing gas, such extrinsic line variability is manifested as changes to the equivalent width of the trough as well as line profile distortions. Here we consider several physically distinct outflow models having very similar spectral predictions, and show how ML-induced absorption-line variability can be used to distinguish between them. Possible merits from future systematic studies of these effects are exemplified.