4,405 research outputs found

    The Impact of Galaxy Formation on the Diffuse Background Radiation

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    The far infrared background is a sink for the hidden aspects of galaxy formation. At optical wavelengths, ellipticals and spheroids are old, even at z∌1.z \sim 1. Neither the luminous formation phase nor their early evolution is seen in the visible. We infer that ellipticals and, more generally, most spheroids must have formed in dust-shrouded starbursts. In this article, we show how separate tracking of disk and spheroid star formation enables us to infer that disks dominate near the peak in the cosmic star formation rate at z \lapproxeq 2 and in the diffuse ultraviolet/optical/infrared background, whereas spheroid formation dominates the submillimetre background.Comment: 12 pages, 5 figures, to appear in proceedings of IAU symp.204, "The Extragalactic Infrared Background and its Cosmological Implications", Martin Harwit and Michael G. Hauser, ed

    Ultraviolet absorption lines in cosmic ray heated H I regions

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    Ultraviolet absorption lines in cosmic ray heated H I region

    Star Formation-Regulated Growth of Black Holes in Protogalactic Spheroids

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    The observed relation between central black hole mass and spheroid velocity dispersion is interpreted in terms of a self-regulation model that incorporates a viscous Keplerian accretion disk to feed the black hole, embedded in a massive, self-gravitating star forming disk that eventually populates the spheroid. The model leads to a constant ratio between black hole mass and spheroid mass which is equal to the inverse of the critical Reynolds number for the onset of turbulence in the accretion disk surrounding the central black hole. Applying the fundamental plane correlation for spheroids, we find that the black hole mass has a power-law dependence on the spheroid velocity dispersion with a slope in the range of 4-5. We explain the larger scatter in the Magorrian relation with respect to the black hole mass-spheroid velocity dispersion relationship as a result of secular evolution of the spheroid that primarily affects its luminosity and to a much lesser extent its velocity dispersion.Comment: 12 pages, no figures, submitted to ApJ Letter

    On breaking the age-metallicity degeneracy in early-type galaxies: Outflows versus Star Formation Efficiency

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    A simple model of chemical enrichment in cluster early-type galaxies is presented where the main parameters driving the formation of the stellar component are reduced to four: infall timescale (tf), formation epoch (zF), star formation efficiency (Ceff) and fraction of gas ejected in outflows (Bout). We find that only variations in Bout or Ceff can account for the colour-magnitude relation, so that the most luminous galaxies had low values of ejected gas and high efficiencies. The combination of chemical enrichment tracks with population synthesis models is used to explore the correlation between mass-to-light ratios and masses. A significant slope mismatch is found between stellar and total M/L ratios, which cannot be explained by an age spread and implies a non-linear correlation between total and stellar mass. The sequences driven by star formation efficiency and outflows are shown to predict different trends at high redshift. Measurement of the dependence of the tilt of the fundamental plane on redshift will break the degeneracy between outflows and star formation efficiency, which will enable us to determine whether the colour-magnitude relation is controlled by age or metallicity.Comment: 8 pages, 5 figures. To be published in MNRA

    On the Fueling of Massive Black Holes and the Properties of their Host Spheroids

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    We study the relation between nuclear massive black holes and their host spheroid gravitational potential. Using simple models, we analyze how gas is expected to be transported in the nuclear regions of galaxies. When we couple it with the expected gas lifetime given by the Kennicutt-Schmidt Law, this naturally leads to the `M_BH - M_virial' and `M_BH - sigma' relations. We also numerically test, using AMR simulations, our simple models for the mass transport with satisfactory results.Comment: Reduced version that fit the 4-page limit. In press ApJ Letter