1,721,207 research outputs found
Differential Information on the Evolution of Extragalactic Sources from Spectral Index Distributions
No full textThe dependence of the average spectral index of extragalactic sources on luminosity in complete samples selected at different frequencies is shown to vary in a manner that directly reflects their evolutionary properties. In particular, easily recognizable features are introduced by a luminosity dependent evolution and by the presence of a cutoff in the redshift distribution. The expected dependence on luminosity of the average optical to X-ray energy index αox for X-ray selected active galactic nuclei is discussed in some detail
ATMOSPHERIC EMISSION MODELS - CONFRONTATION BETWEEN OBSERVATIONAL DATA AND PREDICTIONS IN THE 2.5-300 GHZ FREQUENCY-RANGE
No full textInclination Effects and Reddening of Seyfert-1 Nuclei
No full textIt is shown through a series of calculations that the reddening law for Seyfert 1 nuclei recently proposed by Cheng et al. (1983) quantitatively accounts for the deficiency of nearly edge-on optically selected Seyferts noted in the literature. The correlation with inclination of the ratio of H-beta to hard X-ray luminosity is confirmed in the theoretical analysis. The observed distribution of values for the H-beta/hard X-ray luminosity ratio obtained by Lawrence and Elvis (1982) is compared with that predicted from the theoretical estimates
THICK TORI AROUND ACTIVE GALACTIC NUCLEI - A COMPARISON OF MODEL PREDICTIONS WITH OBSERVATIONS OF THE INFRARED CONTINUUM AND SILICATE FEATURES
No full textThe continuum expected from active galactic nuclei (AGN) surrounded by thick tori is compared to the data available for a sample of optically selected Seyfert 1 galaxies. The optical and near-IR nuclear fluxes have previously been derived for these objects, and hence the spectral energy distributions (SEDs) of their active nuclei can be analysed. We perform detailed calculations of the 0.1 to 1000 mum SEDs for AGN surrounded by dust tori with different opening angles. The dust mixture is mimicked by using three silicate and three graphite grains of different sizes. The radiative transfer equation for a cloud having azimuthal symmetry and containing a mixture of dust grains is solved by means of a numerical code that takes absorption, emission and scattering into account. We discuss the optimization of the free parameters by comparing the spectra predicted by the code to available data. The general absence of the silicate emission feature at about 10 mum in the spectra of broad-line AGN and the general presence of the 10-mum silicate absorption feature in narrow-line AGN are addressed. The ensuing constraints are discussed. We show that models of thick tori extending up to a few hundred parsecs in which physical processes such as shocks significantly reduce the silicate grain abundance within the first few tens of parsecs are fully consistent with available broad-band data and high-resolution IR spectra of Seyfert 1 and 2 nuclei
Cold or warm? Constraining dark matter with primeval galaxies and cosmic reionization after Planck
No full textDark matter constitutes the great majority of the matter content in the Universe, but its microscopic nature remains an intriguing mystery, with profound implications for particle physics, astrophysics and cosmology. Here we shed light on the longstanding issue of whether the dark matter is warm or cold by combining the measurements of the galaxy luminosity functions out to high redshifts 0z~ 1 from the Hubble Space Telescope with the recent cosmological data on the reionization history of the Universe from the Planck mission. We derive robust and tight bounds on the mass of warm dark matter particle, finding that the current data require it to be in the narrow range between 2 and 3 keV . In addition, we show that a mass not exceeding 3 keV is also concurrently indicated by astrophysical constraints related to the local number of satellites in Milky Way-sized galaxies, though it is in marginal tension with analysis of the Lyman-alpha forest. For warm dark matter masses above 3 keV as well as for cold dark matter, to satisfy the Planck constraints on the optical depth and not to run into the satellite problem would require invoking astrophysical processes that inhibit galaxy formation in halos with mass MH lesssim few × 10 8 Msolar, corresponding to a limiting UV magnitude MUV≈ -11. Anyway, we predict a downturn of the galaxy luminosity function at z~ 8 faintward of MUV≈ -12, and stress that its detailed shape is extremely informative both on particle physics and on the astrophysics of galaxy formation in small halos. These expectations will be tested via the Hubble Frontier Fields and with the advent of the James Webb Space Telescope, which will enable probing the very faint end of the galaxy luminosity function out to z ~ 8--10
- …
