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Hole Growth (hole + growth)

Distribution by Scientific Domains
Physics and Astronomy100%

Kinds of Hole Growth

  • black hole growth
    		•

    Selected Abstracts

    Enhanced star formation in narrow-line Seyfert 1 active galactic nuclei revealed by Spitzer

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010
    E. Sani
    ABSTRACT We present new low-resolution Spitzer mid-infrared spectroscopy of a sample of 20 ROSAT -selected local narrow-line Seyfert 1 galaxies (NLS1s). We detect strong active galactic nucleus (AGN) continuum in all and clear polycyclic aromatic hydrocarbon (PAH) emission in 70 per cent of the sources. The 6.2 ,m PAH luminosity spans three orders of magnitude, from ,1039 to ,1042 erg s,1, providing strong evidence for intense ongoing star formation in the circumnuclear regions of these sources. Using the Infrared Spectrograph/Spitzer archive, we gathered a large number of additional NLS1s and their broad-line counterparts (BLS1s) and constructed NLS1 and BLS1 subsamples to compare them in various ways. The comparison shows a clear separation according to full width at half-maximum (H,) [FWHM(H,)] such that objects with narrower broad H, lines are the strongest PAH emitters. We test this division in various ways trying to remove biases due to luminosity and aperture size. Specifically, we find that star formation activity around NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above result seems to hold over the entire range of distance and luminosity. Moreover, the star formation rate is higher in low black hole mass and high L/LEdd systems indicating that black hole growth and star formation are occurring simultaneously. [source]

    Black hole growth in hierarchical galaxy formation

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
    Rowena K. Malbon
    ABSTRACT We incorporate a model for black hole growth during galaxy mergers into the semi-analytical galaxy formation model based on ,CDM proposed by Baugh et al. Our black hole model has one free parameter, which we set by matching the observed zero-point of the local correlation between black hole mass and bulge luminosity. We present predictions for the evolution with redshift of the relationships between black hole mass and bulge properties. Our simulations reproduce the evolution of the optical luminosity function of quasars. We study the demographics of the black hole population and address the issue of how black holes acquire their mass. We find that the direct accretion of cold gas during starbursts is an important growth mechanism for lower mass black holes and at high redshift. On the other hand, the re-assembly of pre-existing black hole mass into larger units via merging dominates the growth of more massive black holes at low redshift. This prediction could be tested by future gravitational wave experiments. As redshift decreases, progressively less massive black holes have the highest fractional growth rates, in line with recent claims of ,downsizing' in quasar activity. [source]

    The merger-driven evolution of warm infrared luminous galaxies

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009
    Joshua D. Younger
    ABSTRACT We present a merger-driven evolutionary model for the production of luminous (LIRGs) and ultraluminous infrared galaxies (ULIRGs) with warm infrared (IR) colours. Our results show that simulations of gas-rich major mergers including star formation, black hole growth and feedback can produce warm (U)LIRGs. We also find that while the warm evolutionary phase is associated with increased active galactic nucleus (AGN) activity, star formation alone may be sufficient to produce warm IR colours. However, the transition can be suppressed entirely , even when there is a significant AGN contribution , when we assume a single-phase interstellar medium, which maximizes the attenuation. Finally, our evolutionary models are consistent with the 25-to-60 flux density ratio versus LHX/LIR relation for local LIRGs and ULIRGs, and predict the observed scatter in IR colour at fixed LHX/LIR. Therefore, our models suggest a cautionary note in the interpretation of warm IR colours: while associated with periods of active black hole growth, they are probably produced by a complex mix of star formation and AGN activity intermediate between the cold star formation dominated phase and the birth of a bright, unobscured quasar. [source]

    Most supermassive black hole growth is obscured by dust

    ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006
    A. Martínez-Sansigre
    Abstract We present an alternative method to X-ray surveys for hunting down the high-redshift type-2 quasar population, using Spitzer and VLA data on the Spitzer First Look Survey. By demanding objects to be bright at 24 µm but faint at 3.6 µm, and combining this with a radio criterion, we find 21 type-2 radio-quiet quasar candidates at the epoch at which the quasar activity peaked. Optical spectroscopy with the WHT confirmed 10 of these objects to be type-2s with 1.4 , z , 4.2 while the rest are blank. There is no evidence for contamination in our sample, and we postulate that our 11 blank-spectrum candidates are obscured by kpc-scale dust as opposed to dust from a torus around the accretion disk. By carefully modelling our selection criteria, we conclude that, at high redshift, 50,80% of the supermassive black hole growth is obscured by dust. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]