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Recent research relevant to quasar evolution

  1. Jan 11, 2009 #1


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    The Quasars and Cosmology thread in the Cosmology section kicks off with a reference to a late 2005 Space Telescope Science Institute (STScI) conference presentation on some recent research results on high-z quasars, from the SDSS.

    Much of the discussion in that thread, until it got distracted by non-mainstream things, was around quasar evolution, including:

    * in what ways do quasars, as individual objects, seem to change over (cosmic) time?

    * how do snapshots of quasars, as a class, at any epoch, change over time?

    * how do the inevitable selection effects skew our understanding of these changes?

    * how well do models of quasar evolution match the observations?

    * to what extent is it necessary to get a handle on galaxy evolution, in general, in order to understand quasar evolution?

    * how well can models paint a seamless picture of change from the time when radiation streamed free to the youngest quasars observed to date?

    * in particular, how confident can we be about the robustness of models of quasar formation and (very) early evolution?

    * how can the inevitable selection effects due to the Dark Ages be adequately addressed, in future studies of objects (quasars, proto-quasars) at z > 7?

    Quite early in the thread, I commented "This (quasar evolution) is, without a doubt, a fascinating area of research!", and turbo-1 and I went back and forth over the extent to which understanding quasar evolution presented real nightmares for cosmologists vs an enormous research agenda for standard astrophysics (before we could say the consensus on quasar evolution should cause those who play with LCDM models to wake at night in a cold sweat); for example here, here, here, here, and here.

    In researching my posts in that closed thread, I was struck by just how many papers there are on this topic, and just how fast the field is moving. I had intended to give readers a taste of this, but the thread is now closed; so rather than trash all my bookmarks, I thought I'd post some here.

    First, last week's arXiv.org > astro-ph preprints. It seems to have been a fairly typical week, some 250 preprints from Monday 5 to Friday 9 Jan.

    How many of these have a direct bearing on quasar evolution?

    Let's see ... (Monday first, Friday last; all quotes are from the abstracts)

    Mid-infrared imaging of 25 local AGN with VLT-VISIR ("Conclusions. Our results generally agree with the expectations from the unified scenario, while the relative weakness of the silicate feature supports clumpy torus models.")

    Radiation pressure and absorption in AGN: results from a complete unbiased sample from Swift ("We discuss briefly how the N_H - lambda_Edd plane may evolve to higher redshift, when feedback due to radiation pressure may have been strong.")

    Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines ("This results in a strongly increasing global Omega(C IV) from z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do not support widespread early IGM enrichment from e.g. Pop III stars.")

    Gas and stars in compact (young) radio sources ("we have used optical spectra and HI - in absorption - to investigate the presence of fast outflows that support the idea that compact radio sources are young radio loud AGN observed during the early stages of their evolution and currently shredding their natal cocoons through extreme circumnuclear outflows.")

    Clustering of red galaxies around the z=1.53 quasar 3C270.1 (no snappy one-liner: read the whole abstract!)

    HD and H2 formation in low-metallicity dusty gas clouds at high redshift ("Results: Grain surface reactions are crucial to the availability of H2 and HD in very metal-poor environments.")

    The mass-metallicity gradient relation of early-type galaxies ("These results suggest that galaxies above the mass threshold of ~ 3.5 x 10^10 M_sun might have formed initially by mergers of gas-rich disc galaxies and then subsequently evolved via dry merger events.")

    The Dependence of Star Formation Activity on Stellar Mass Surface Density and Sersic Index in zCOSMOS Galaxies at 0.5<z<0.9 Compared with SDSS Galaxies at 0.04<z<0.08 ("In order to try to understand the internal evolution of galaxies and relate this to the global evolution of the galaxy population, we present a comparative study of the dependence of star formation rates on the average surface mass densities (SigmaM) of galaxies at 0.5 < z < 0.9 and 0.04<z<0.08, using the zCOSMOS and SDSS surveys respectively.")

    The evolution of star formation in quasar host galaxies ("We find no evidence for any correlation between star formation rate and black hole mass at 0.5<z<4. Our data are consistent with feedback from black hole accretion regulating stellar mass assembly at all redshifts.")

    Luminous buried AGNs as a function of galaxy infrared luminosity revealed through Spitzer low-resolution infrared spectroscopy (" Our results may support the widely-proposed AGN-feedback scenario as the origin of galaxy downsizing phenomena, where galaxies with currently larger stellar masses previously had higher AGN energetic contributions and star-formation-originating infrared luminosities, and have finished their major star-formation more quickly, due to stronger AGN feedback.")

    Six more quasars at redshift 6 discovered by the Canada-France High-z Quasar Survey ("The new quasars have luminosities 10 to 75 times lower than the most luminous SDSS quasars at this redshift. The least luminous quasar, CFHQS J0216-0455 at z=6.01, has absolute magnitude M_1450=-22.21, well below the likely break in the luminosity function. This quasar is not detected in a deep XMM-Newton survey showing that optical selection is still a very efficient tool for finding high redshift quasars.")

    HI and Cosmology: What We Need To Know ("Each measurement presents its own set of technical, theoretical, and observational challenges, making "what we need to know" not so much an astrophysical question at this early stage as a comprehensive experimental question.")

    Early-Age Evolution of the Milky Way Related by Extremely Metal-Poor Stars ("A high-mass IMF with the typical mass~10Msun and the overwhelming contribution of low-mass members of binaries to the EMP survivors are derived from the statistics of carbon-enriched EMP stars with and without the enhancement of s-process elements (Komiya et al. 2007).")

    The Formation Rates of Population III Stars and Chemical Enrichment of Halos during the Reionization Era ("In this scenario, metal free stars contribute only to a minor fraction of the total number of photons required to re-ionize the universe. In addition, metal free star formation is primarily located in minihalos and chemically enriched halos become the dominant locus of star formation very early in the life of the Universe, at redshift z~25.")

    Evolution and Nucleosynthesis of Extremely Metal Poor & Metal-Free Low- and Intermediate-Mass Stars I: Stellar Yield Tables and the CEMPs ("Many of the models experience violent nuclear burning episodes not seen at higher metallicities.")

    The early evolution of the star cluster mass function ("This contribution considers the evolution of such a mass function due to cluster disruption, with emphasis on the part of the mass function that is observable in the first ~Gyr.")

    A top-heavy stellar initial mass function in starbursts as an explanation for the high mass-to-light ratios of ultra compact dwarf galaxies ("the model suggests the exponent of the high-mass IMF to be approximately 1.6 if the UCDs are 13 Gyr old (i.e. almost as old as the universe) or approximately 1.0 if the UCDs are 7 Gyr old, in contrast to 2.3 for the Salpeter-Massey IMF.")

    The Evolution of the Star Formation of zCOSMOS and SDSS galaxies at z<0.7 as a Function of Mass and Structural Parameters ("We present in these proceedings some preliminary results we have obtained studying the evolution of the specific star formation rate as a function of surface mass density and Sersic indices at z<0.7.")

    The metallicity of the most distant quasars (Juarez et al.) - covered in several posts in the closed thread!

    Superdense massive galaxies in the Nearby Universe ("we find only a tiny fraction of galaxies (~0.03%) with r_e<1.5 kpc and M_*>8x10^{10} Msun in the local Universe (z<0.2). Surprinsingly, they are relatively young (~2 Gyr) and metal-rich ([Z/H]~0.2). The consequences of these findings within the current two competing size evolution scenarios for the most massive galaxies ("dry" mergers vs "puffing up" due to quasar activity) are discussed.")

    Feedback from central black holes in elliptical galaxies. I: models with either radiative or mechanical feedback but not both (" In this paper we improve and extend the accretion and feedback physics explored in our previous papers to include also a physically motivated mechanical feedback.")

    Star formation histories of resolved galaxies ("It is shown that all the galaxies studied so far were already forming stars at the lookback time reached by the observational data, independently of morphological type and metallicity.")

    The Cosmic Evolution of AGN in galaxy clusters ("We thus confirm the existence of a Butcher-Oemler type effect for AGN in galaxy clusters, with the number of AGN in clusters increasing with redshift.")

    Self-Consistent Solution of Cosmological Radiation-Hydrodynamics and Chemical Ionization ("We consider a PDE system comprising compressible hydrodynamics, flux-limited diffusion radiation transport and chemical ionization kinetics in a cosmologically-expanding universe.")

    Whew! That's ~10% (24) of the week's preprints of at least considerable relevance to quasar evolution!! (YMMV, of course).
  2. jcsd
  3. Jan 12, 2009 #2

    I enjoyed this thread very much until it got polarised, off-topic and was closed. The links you provide here, Nereid, will provide a useful resource for those who would like to closely follow the astrophysics of quasar heavy-element enrichment as this hot research topic evolves.

    I think a little background to this topic might also be useful.

    The question of how all elements heavier than say Lithium were created seemed to me until recently to have been fully answered, after a long history of struggle and debate. The story of this struggle and debate, and how such elements can, over long periods, be cooked in stars or (beyond iron) be flash-synthesized in supernova explosions is set out clearly in Penzias's Nobel lecture. Good background reading.

    This fascinating story has also become part of popular astronomy, where it is often claimed that we ourselves are made of just such metal-rich "stardust" - a humbling thought indeed.

    But now --- with the observation of metal-rich quasars in even the distant too-early? universe --- it seems that this until-now-fully-accepted conventional astronomical wisdom may turn out to be only part of the story.

    At the very least this tells us to be more sceptical of conventional wisdom, whether it be about element synthesis or the LCDM itself. My own opinion is that not nearly enough is understood about the physics of structure formation in the ultradense, ultrahot celestial kitchen of the early universe (if such an element-cooking facility indeed existed) --- to decide which ideas, if any, should be discarded or modified. It's a fence-sitting situation.
    Last edited: Jan 12, 2009
  4. Jan 12, 2009 #3


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    Glad to read that you have found the (now closed) thread interesting, and this new one potentially so.

    I find myself in a bit of a quandary, and hope that you can help me out ...

    The relative abundances of the light nuclides - H, D, 3He, 4He, and Li - has been intensively studied for decades now, and the derived estimates of their primordial abundances consistent with LCDM models (see Spergel et al. 2007, for example (link is to the preprint)). The only anomaly is Li ... and that is particularly difficult to measure, as well as particularly difficult to model (it's the only element created in primordial nucleosynthesis AND in stars AND in the ISM AND destroyed in stars AND destroyed in the ISM!).

    The origins of stable nuclides other than the isotopes of H, He, and Li (one anyway) is also well understood, in the sense that the observed abundances - both relative and absolute - in the local universe can be fairly well-modelled using a combination of stellar (evolution) models, galaxy models (esp transport of gas and dust in the ISM), and cosmic ray spallation models.

    However, when it comes to modelling the early universe - between when radiation streamed free and z ~ 5 (say) - the models that are so successful in explaining locally observed abundances become increasingly wobbly.

    Not that the nuclear physics is not understood (though this may play a minor role), but that the assumptions on which the models are built, for the local universe, either may not apply or do not apply ... and several of the ~20 preprints in my OP seek to address at least some small parts of those weaknesses.

    And that's assuming - as marcus did - that the very recent papers reporting estimated abundances will a) be confirmed by independent work, and b) can be put into a proper context (by getting a good handle on all the selection effects, for example). Even a cursory read of any theme in modern astrophysics suggests that later work will very likely change our understanding of these early papers in both subtle and substantial ways. Pentericci et al. 2005 may be quite instructive in this regard!

    Maybe it would help if we go through just one of these ~20 papers, to see how it illustrates my comments? How about "Evolution and Nucleosynthesis of Extremely Metal Poor & Metal-Free Low- and Intermediate-Mass Stars I: Stellar Yield Tables and the CEMPs"?

    ETA: BTW, there are quite a few tweaks and adjustments that need to be made to the models of primordial nucleosynthesis that Penzias refers to, to take account of various aspects that make the models more realistic ... and there's a considerable number of papers on these. However, the net is that the predicted primordial abundances differ in only minor ways from the over-simplified initial work (so it's highly unlikely you'll find any primordial iron, or even carbon, for example).
  5. Jan 14, 2009 #4


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    Hot off the (pre)press, and highly pertinent to our discussions:

    Metallicity measurements in AGNs (arXiv:0901.1323; Smita Mathur, Dale Fields; submitted on 9 Jan 2009)
  6. Jan 14, 2009 #5
    Yes, this paper does suggest that element synthesis in AGN is not the same as in the until-now-fully-accepted conventional astronomical wisdom about such processes, and that the accepted views may indeed turn out to be only part of the whole element-synthesis story, as I said.

    There's always something new to be discovered, which is what makes things so interesting!

    But when you said in your previous post that:

    I'm afraid that here you are sadly overestimating my competence to understand and judge the complexities now being unravelled by observers and modellers of happenings in of AGN. I'm just an interested spectator who has unruly ideas, which usually turn out to be wrong.

    I don't even properly understand some of the terminology. For instance "super-solar metallicity" is I think a (slightly pompous) way of describing an unexpected excess, found in AGN, of elements beyond Li, that are usually obseved only in spectra of 'ordinary' stars like the sun, whose genesis is so well-understood. Is this so?

    The (recently observed?) phenomenon of 'super-solar metallicity' in AGN will, I hope, be satisfactorily explained astrophysically, rather that becoming another unresolved puzzle in the LCDM model. Meanwhile, there's no harm in considering other options, is there?
  7. Jan 15, 2009 #6


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    Not at all, oldman. Mainstream scientists do it all the time. Super solar is merely a characterization of metallicities that exceed those of our sun. What it means is an open question. In a galaxy that is thought to be generally younger than our own sun, it suggests unconventional processes are involved [i.e. not solely the result of stellar nucleosynthesis]. No one has yet proposed and validated a mechanism that fits the body of observational evidence - albeit a number of unsupported [including some downright goofy] ideas have been proposed. The LCDM model is not yet threatened by this dichotomy. I have an abiding faith LCDM will eventually be supplanted by a broader model that overlays the LCDM solution. The conspiracy models will, IMO, continue to fall like mud in a car wash. That is the way of science. Every idea is attacked from every angle. Whatever survives is the truth - not the whole truth, but, an element thereof.
    Last edited: Jan 15, 2009
  8. Jan 16, 2009 #7


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    Let's also keep in mind that nucleosynthesis in stars may be adequate to account for the observed metal lines (in high-z AGN or galaxy spectra).

    For starters, once star formation got going in what became the highly luminous high-z quasars found to date, it may have been truly furious ... to the tune of tens of thousands of sols per year, or more! And that hectic activity may have started very early indeed.

    Then there's the fact that element production in the earliest stars may have proceeded in ways not quite the same as in new stars in our local universe; not only in the metal-free Pop III stars (where we already know it would have been considerably different), but also in the high-mass Pop II stars, which have all long since become WDs or died (the Pop II stars in the local universe are the runts of the ancient litters, and they don't necessarily tell us how their massive siblings lived and died). This could have resulted in much more rapid enrichment of the ISM in metals than current models suggest, especially in the nuclear regions of massive galaxies.

    On top of that is the twist that binaries give to stellar evolution. This was not really recognised until recently for local stars; how different would stellar evolution have been in dense clusters of Pop III stars, many of which would have been binaries?

    And so on ...
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