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The https://www.physicsforums.com/showthread.php?t=282116" 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?
https://www.physicsforums.com/showpost.php?p=2017734&postcount=12".
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)
http://arxiv.org/abs/0901.0106" ("Conclusions. Our results generally agree with the expectations from the unified scenario, while the relative weakness of the silicate feature supports clumpy torus models.")
http://arxiv.org/abs/0901.0250" ("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.")
http://arxiv.org/abs/0901.0286" ("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.")
http://arxiv.org/abs/0901.0433" ("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.")
http://arxiv.org/abs/0901.0452" (no snappy one-liner: read the whole abstract!)
http://arxiv.org/abs/0901.0514" ("Results: Grain surface reactions are crucial to the availability of H2 and HD in very metal-poor environments.")
http://arxiv.org/abs/0901.0548" ("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.")
http://arxiv.org/abs/0901.0550" ("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.")
http://arxiv.org/abs/0901.0552" ("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.")
http://arxiv.org/abs/0901.0558" (" 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.")
http://arxiv.org/abs/0901.0565" ("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.")
http://arxiv.org/abs/0901.0569" ("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.")
http://arxiv.org/abs/0901.0617" ("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).")
http://arxiv.org/abs/0901.0711" ("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.")
http://arxiv.org/abs/0901.0799" ("Many of the models experience violent nuclear burning episodes not seen at higher metallicities.")
http://arxiv.org/abs/0901.0830" ("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.")
http://arxiv.org/abs/0901.0915" ("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.")
http://arxiv.org/abs/0901.0921" ("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.")
http://arxiv.org/abs/0901.0974" (Juarez et al.) - covered in several posts in the closed thread!
http://arxiv.org/abs/0901.1032" ("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.")
http://arxiv.org/abs/0901.1089" (" 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.")
http://arxiv.org/abs/0901.1090" ("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.")
http://arxiv.org/abs/0901.1109" ("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.")
http://arxiv.org/abs/0901.1110" ("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).
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?
https://www.physicsforums.com/showpost.php?p=2017734&postcount=12".
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)
http://arxiv.org/abs/0901.0106" ("Conclusions. Our results generally agree with the expectations from the unified scenario, while the relative weakness of the silicate feature supports clumpy torus models.")
http://arxiv.org/abs/0901.0250" ("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.")
http://arxiv.org/abs/0901.0286" ("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.")
http://arxiv.org/abs/0901.0433" ("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.")
http://arxiv.org/abs/0901.0452" (no snappy one-liner: read the whole abstract!)
http://arxiv.org/abs/0901.0514" ("Results: Grain surface reactions are crucial to the availability of H2 and HD in very metal-poor environments.")
http://arxiv.org/abs/0901.0548" ("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.")
http://arxiv.org/abs/0901.0550" ("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.")
http://arxiv.org/abs/0901.0552" ("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.")
http://arxiv.org/abs/0901.0558" (" 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.")
http://arxiv.org/abs/0901.0565" ("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.")
http://arxiv.org/abs/0901.0569" ("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.")
http://arxiv.org/abs/0901.0617" ("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).")
http://arxiv.org/abs/0901.0711" ("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.")
http://arxiv.org/abs/0901.0799" ("Many of the models experience violent nuclear burning episodes not seen at higher metallicities.")
http://arxiv.org/abs/0901.0830" ("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.")
http://arxiv.org/abs/0901.0915" ("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.")
http://arxiv.org/abs/0901.0921" ("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.")
http://arxiv.org/abs/0901.0974" (Juarez et al.) - covered in several posts in the closed thread!
http://arxiv.org/abs/0901.1032" ("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.")
http://arxiv.org/abs/0901.1089" (" 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.")
http://arxiv.org/abs/0901.1090" ("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.")
http://arxiv.org/abs/0901.1109" ("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.")
http://arxiv.org/abs/0901.1110" ("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).
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