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High red shift black holes

  1. Jun 3, 2005 #1

    wolram

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    http://arxiv.org/PS_cache/astro-ph/pdf/0506/0506040.pdf

    Title: Rapid growth of high redshift black holes
    Authors: Marta Volonteri, Martin J. Rees
    Comments: Submitted to ApJ letters. AASTeX format. 11 pages, 1 colour figure

    We discuss a model for the early assembly of supermassive black holes (SMBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo `merger tree'. Motivated by the observations of luminous quasars around redshift z=6 with SMBH masses of billion solar masses, we assess the possibility of an early phase of stable super-critical quasi-spherical accretion in the BHs hosted by metal free halos with virial temperature larger than 10000 K. We assume that the first `seed' black holes formed with intermediate masses following the collapse of the first generation of stars, in mini-halos collapsing at z=20-30 from high peaks of density fluctuations. In high redshift halos with virial temperature larger than 10000 K, conditions exist for the formation of a fat disc of gas at T_gas=5000-10000 K. Cooling via hydrogen atomic lines is in fact effective in these comparatively massive halos. The cooling and collapse of an initially spherical configuration of gas leads to a rotationally supported disc at the center of the halo if baryons preserve their specific angular momentum during collapse. The conditions for the formation of the gas disc and accretion onto a central black holes out of this supply of gas are investigated, as well as the feedback of the emission onto the host and onto the intergalactic medium. We find that even a short phase of supercritical accretion eases the requirements set by the z=6 quasars.
     
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  3. Jun 3, 2005 #2

    SpaceTiger

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    This is an interesting paper and, far as I can tell, completely reasonable. I dunno whether or not it's right, but I wouldn't be overly hesitant to jump explanation such as "super-accretion". Why?

    Whenever one is considering things such as the "highest redshift quasars" and the limits they present, one should always keep in mind the extreme selection effects involved in the observations. In other words, the quasars wouldn't be observed if they weren't so bright, so if even a small fraction of "baby" quasars grew to large masses by z~6, they might be seen by our telescopes. Because we're selecting outliers to begin with, it's not unreasonable that their formation history might have been special as well.

    Honestly, I think this theoretical bandwagon, much like the low quadrupole in the CMB, is fairly premature. We should wait until we are more completely and precisely sampling the high-z population of quasars before we conclude any kind of theoretical crisis.
     
  4. Jun 3, 2005 #3

    turbo

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    The paper presumes that mass can accrete at super-Eddington rates as long as the metallicity is low.

    However, the distant z~6-6.5 quasars in the SDSS exhibit solar and super-solar metallicities, and no evolution of metallicity with redshift has been observed.

    http://cosmos.as.arizona.edu/~thompson/pubdb/docs/barth03a.pdf
    http://citebase.eprints.org/cgi-bin...pdf&identifier=oai:arXiv.org:astro-ph/0112075
    http://cosmos.as.arizona.edu/~thompson/pubdb/docs/freudling03a.pdf

    It is reasonable to ask why we see no evolution in metallicity z=1~6.5.

    This sounds reasonable, but again, at what redshift will quasars exhibit sub-solar metallicities? At some redshift, we should see quasars that are feeding on a mix of highly metallized stars and gases AND poorly metallized stars and gases, and one would expect a continuum in the metallicity curve, not an abrupt discontinuity somewhere in 6<z<10. The LBT and Webb will allow us to probe these redshifts soon.
     
    Last edited: Jun 3, 2005
  5. Jun 4, 2005 #4

    Chronos

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    And that is just plain wrong. There is plenty of evidence of metallicity evolution. But you won't see it when you are blinded by selection effects in your sources. How many dozens of references will it take to dispell that mythology? BTW, Wolram, nice find and very credible. Rees is top drawer in my book. I read that paper earlier today. You saved me the trouble by starting this thread.
     
    Last edited: Jun 4, 2005
  6. Jun 4, 2005 #5

    wolram

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    Last edited: Jun 4, 2005
  7. Jun 4, 2005 #6

    turbo

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    I have cited these papers before, Chronos, but I will trot them out again with short quotes from their abstracts. The sample sizes are small in these studies, but you simply cannot dismiss every discordant observation as a selection effect.

    http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0112075

    http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0303424

    http://citebase.eprints.org/cgi-bin...pdf&identifier=oai:arXiv.org:astro-ph/0311043

     
    Last edited: Jun 4, 2005
  8. Jun 5, 2005 #7

    Chronos

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