Downsizing of supermassive black holes from the SDSS quasar survey

Starting from the ∼50 000 quasars of the Sloan Digital Sky Survey for which Mg  ii line width and 3000 Å monochromatic flux are available, we aim to study the dependence of the mass of active black holes on redshift. We focus on the observed distribution in the full width at half-maximum–nuclear luminosity plane, which can be reproduced at all redshifts assuming a limiting M _BH, a maximum Eddington ratio and a minimum luminosity (due to the survey flux limit). We study the z -dependence of the best-fitting parameters of assumed distributions at increasing redshift and find that the maximum mass of the quasar population evolves as  log ( M _BH(max)/M_⊙) ∼ 0.3 z + 9  , while the maximum Eddington ratio (∼0.45) is practically independent of cosmic time. These results are unaffected by the Malmquist bias.     

The anticorrelation between the hard X-ray photon index and the Eddington ratio in low-luminosity active galactic nuclei

We find a significant anticorrelation between the hard X-ray photon index Γ and the Eddington ratio   L _bol/ L _Edd  for a sample of low-ionization nuclear emission-line regions and local Seyfert galaxies, compiled from literature with Chandra or XMM–Newton observations. This result is in contrast with the positive correlation found in luminous active galactic nuclei (AGN), while it is similar to that of X-ray binaries (XRBs) in the low/hard state. Our result is qualitatively consistent with the spectra produced from advection-dominated accretion flows (ADAFs). It implies that the X-ray emission of low-luminosity active galactic nuclei (LLAGN) may originate from the Comptonization process in ADAF, and the accretion process in LLAGN may be similar to that of XRBs in the low/hard state, which is different from that in luminous AGN.     

Impacts of aerosol chemical composition on microphysics and precipitation in deep convection

Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNC). Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The MCE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation (S_c) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Köhler curve are deactivated by the insoluble substance, S_c is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances.     

Realistic triaxial density–potential–force profiles for stellar systems and dark matter haloes

Popular models for describing the luminosity–density profiles of dynamically hot stellar systems (e.g. Jaffe, Hernquist, Dehnen) were constructed to match the deprojected form of de Vaucouleurs' R ^1/4 light-profile. However, we now know that elliptical galaxies and bulges display a mass-dependent range of structural profiles. To compensate this, the model in Terzić & Graham was designed to closely match the deprojected form of Sérsic R ^{1/ n} light-profiles, including deprojected exponential light-profiles and galaxies with partially depleted cores. It is thus applicable for describing bulges in spiral galaxies, dwarf elliptical galaxies, both 'power-law' and 'core' elliptical galaxies, also dark matter haloes formed from Λ cold dark matter cosmological simulations. In this paper, we present a new family of triaxial density–potential–force triplets, which generalizes the spherical model reported in Terzić & Graham to three dimensions. If the (optional) power-law core is present, it is a five-parameter family, while in the absence of the core it reduces to three parameters. The isodensity contours in the new family are stratified on confocal ellipsoids and the potential and forces are expressed in terms of integrals which are easy to evaluate numerically. We provide the community with a suite of numerical routines for orbit integration, which feature: optimized computations of potential and forces for this family; the ability to run simulations on parallel platforms; and modular and easily editable design.     

FG Sagittae: New observations in the R CrB photometric phase

In 1999–2002, we continued our photometric and spectroscopic observations of FG Sge. This star has been in a new R CrB photometric phase since 1992. We constructed the BV RI light curves and studied the behavior of the color indices as a function of the fading amplitude. As previously, all of the three deep minima observed during this period were found to be blue on the descent; this was interpreted as the result of strong stellar light scattering in dust clouds formed on the line of sight. We analyzed the wavelength dependence of extinction in the circumstellar shell outside fadings, which was similar to Whitford's standard reddening law. Low-resolution spectroscopic observations allowed us to study the changes in the intensities of Swan bands and the Na I D doublet during deep and shallow (up to 1^m) fadings. We confirmed the reversal of the spectrum of the extended stellar envelope on the descending branches of deep minima.     

Magnetic fields of active galactic nuclei and quasars: Redshift dependence

The observed reduction in the fraction of quasars with polarized radiation as the redshift increases is explained by an increase in the magnetic-field strength in accretion disks at high z. The emerging Faraday rotation causes the radiation to be depolarized. This mechanism allows the magnetic fields in accretion disks to be estimated at several hundred gauss. We give simple asymptotic formulas that describe the Faraday depolarization in optically thick accretion disks.     

Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds

Surface measurements of cloud condensation nuclei (CCN) number concentration (cm⁻³) are presented for unmodified marine air and for polluted air at Mace Head, for the years 1994 and 1995. The CCN number concentration active at 0.5% supersaturation is found to be approximately log-normal for marine and polluted air at the site. Values of geometric mean, median and arithmetic mean of CCN number concentration (cm⁻³) for marine air are in the range 124–135, 140–150 and 130–157 for the two years of data. Analysis of CCN number concentration for high wind speed, U, up to 20 m s⁻¹ show enhanced CCN production for U in excess of about 10–12 m s⁻¹. Approximately 7% increase in CCN per 1 m s⁻¹ increase in wind speed is found, up to 17 m s⁻¹. A relationship of the form log₁₀CCN=a+bU is obtained for the periods March 1994 and January, February 1995 for marine air yielding values a of 1.70; 1.90 and b of 0.035 for both periods.     

Isolating and identifying atmospheric ice-nucleating aerosols: a new technique

Laboratory studies examined two key aspects of the performance of a continuous-flow diffusion chamber (CFD) instrument that detects ice nuclei (IN) concentrations in air samples: separating IN from non-IN, and collecting IN aerosols to determine chemical composition. In the first study, submicron AgI IN particles were mixed in a sample stream with submicron non-IN salt particles, and the sample stream was processed in the CFD at −19°C and 23% supersaturation with respect to ice. Examination of the residual particles from crystals nucleated in the CFD confirmed that only AgI particles served as IN in the mixed stream. The second study applied this technique to separate and analyze IN and non-IN particles in a natural air sample. Energy-dispersive X-ray analyses (EDS) of the elemental composition of selected particles from the IN and non-IN fractions in ambient air showed chemical differences: Si and Ca were present in both, but S, Fe and K were also detected in the non-IN fraction.     

The Stellar Content of Active Galaxies

We present the results of a long-slit spectroscopic study of 38 active and four normal galaxies. Stellar absorption features, continuum colours and their radial variations are analysed in an effort to characterize the stellar population in these galaxies and detect the presence of a featureless continuum underlying the starlight spectral component. Spatial variations of the equivalent widths of conspicuous absorption lines and continuum colours are detected in most galaxies. Star-forming rings, in particular, leave clear fingerprints in the equivalent widths and colour profiles. We find that the stellar populations in the inner regions of active galaxies present a variety of characteristics, and cannot be represented by a single starlight template. Dilution of the stellar lines by an underlying featureless continuum is detected in most broad-lined objects, but little or no dilution is found for most of the 20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous. In particular, all but one of the observed Seyfert 2s are redder at the nucleus than in its immediate vicinity. Possible consequences of these findings are briefly outlined.