Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Congratulations to all the PF gurus

  1. Dec 6, 2004 #1
    Hi, and congratulations to all the PF gurus
    I have been interested for a long time in AGN unification, and I think that I know enough about it to try to devise my own model, though there's something that I've searched and I've been unable to find, and is the number of Seyfert galaxies that are actually known. I need to have that cipher
    Bye!!!!
     
  2. jcsd
  3. Dec 6, 2004 #2

    turbo

    User Avatar
    Gold Member

    Interesting question. I have found references stating that Seyferts comprise "1%" and "several%" of spirals. It may be that Seyferts are not all that special and most or all large spiral galaxies can exhibit Seyfert behaviour throughout several percent of their lifetimes, accounting for the observed population.
     
  4. Dec 6, 2004 #3
    Thanks for your interest. this page
    http://www.astro.umd.edu/education/astro/actgal/seyfert.html
    says that Seyfert galaxies comprise a 2% of all spiral galaxies, but we are not going to fight about it, right? :grumpy: :devil: :grumpy: :devil: :grumpy: :rofl:
     
  5. Dec 7, 2004 #4

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You know the reason why the number (approx 2%) can't be very well measured, right?
     
  6. Dec 7, 2004 #5
    Dear Nereid,
    if you ask me why is not possible to say exactly what's the percentage of spiral galaxies that are Seyfert galaxies, I would respond that is because the Malmquist bias, that is, you can only see the brightest objects at a given distance. But I'm not sure taht this is the answer that are you searching. So, take pity on me, i'm only an amateur...
     
  7. Dec 7, 2004 #6

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    If you are looking for all the ugly details, here is the best source I know offhand. It catalogs all known seyferts, at least as of 1988 [lots of other catalogs here too]
    http://vizier.cfa.harvard.edu/viz-bin/VizieR
     
  8. Dec 7, 2004 #7

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    meteor gets a gold star today!

    Selection effects, in general (not just Malmquist), make it difficult to get good estimates. In the words of the article you linked: "Seyfert Galaxies are spiral galaxies with unusually bright, tiny cores that fluctuate in brightness. They do not have radio lobes. Most are powerful sources of infrared radiation. In addition, some emit intensely in the radio, X ray, and gamma ray regimes. Approximately 2% of all spiral galaxies are Seyfert galaxies. This means either that about 2% of all spiral galaxies have active core or that most spiral galaxies have potentially active cores which erupt 2% of the time."

    Leave aside how cleanly one could determine whether a galaxy were spiral, and whether the core 'unusually bright, tiny' (non-trivial classifications; galaxies are not at all like members of Kingdom Animalia with nice rules, no 'transitional' and rarely any 'indeterminate'), the 'fluctuate in brightness' requires detection of variability (but non-detection doesn't rule out a spiral galaxy with a bright tiny core being a Seyfert).

    Changing the definitions to reflect the emission line characteristics of the (model) nuclei - narrow = Type II, broad = Type I - introduces its own ambiguities and selection effects.

    All these effects need to be accounted for when observations of galaxies at different distances are used to try to contrain models of the time evolution of galaxies - e.g. how do the various selection effects change as the apparent size and brightness (and colour!) of galaxies changes (distant ones will tend to be smaller, fainter, and redder than closer ones)?
     
  9. Dec 8, 2004 #8

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    But there is a way to adjust for the brightness features. Take an inventory of all nearby galaxies and compare it to large scale galactic distributions. That should result in the question... why are there so few / many galaxies at this particular distance?
     
  10. Dec 9, 2004 #9

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Chronos is of course right; if you are quite clear about what you are trying to find, and how you will use the results in your work, you will likely be able to work out a method for obtaining the data. (well, in principle anyway)

    Specifically, wrt meteor's Seyferts and AGN, if he has an idea he wishes to test, then he may be able to work backwards, to estimate the accuracy with which he needs to measure the observed incidence of Seyferts. Thinking this way too should allow him to design cutoffs for his classifications (nucleus smaller than x, brighter than y; spiral/elliptical boundary defined as z; etc) that will help rather than hinder when it comes time to do the analysis.

    {aside: should I claim that this didactic lesson was what I had in mind from the very beginning? :approve: or be honest and admit that it only occurred to me when I woke up this morning? o:) }
     
  11. Dec 10, 2004 #10

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Were I doing the study, I would start by comparing Seyfert distributions to quasar distributions as both are obscenely luminous. Assuming distributions are isotropic and powered by uncorrelated mechanisms, a gaussian distribution would be expected.
     
    Last edited: Dec 10, 2004
  12. Dec 11, 2004 #11
    Nereid and Chronos, Tx for the feedback
    I will pose here some questions. If they're answered it will help me in my effort for an unification scheme:

    1)what's the difference between a high energy peaked BL Lac object and a low energy peaked BL Lac object? What's the divisory line between these 2 classes of objects?
    2)What's understood by blazar unification?
    3) What's an X-Ray selected BL object? (It seems a BL object emiting very much X-Ray radiation, but how much?)
    4)what are the characteristics of a highly polarized quasar?
    5)What exactly is a miniquasar?

    I have a lot more questions, but I will try to look myself for them
     
    Last edited: Dec 11, 2004
  13. Dec 11, 2004 #12

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Generally speaking, it has to do with the location of EM spectral peaks.
    Finding a common mechanism for radio loud objects, which include BL Lac objects and quasars
    Same as question 1
    There is a correlation with Ks band luminosity
    An object within the milky way that exhibits properties similar to extragalactic quasars.

    Here are some informative sources:

    Research Highlights on Active Galactic Nuclei
    http://www.phy.ohiou.edu/~mboett/agn.html

    MICRO-QUASAR WITHIN OUR GALAXY !
    http://home.achilles.net/~ypvsj/news/GRS1915n105.html

    A Physical Classification Scheme for Blazars
    http://arxiv.org/abs/astro-ph/0402494

    The Optical Polarization of Near-Infrared Selected QSOs
    http://arxiv.org/abs/astro-ph/0112334
     
  14. Dec 14, 2004 #13

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    meteor, this may be gratuitous advice, but it may also be a little bit helpful ....

    Whatever your research programme, it might be a good idea to do a 'reality check' or three along the way. For example, if you have a working model that predicts certain observable energy distribution across the EM spectrum, check your prediction against the actual data from observations, not (for example) against broad descriptions of classes of objects (this may mean going to 'cleaned' data products from surveys, or observatories, or extracted from published papers - i.e. 'photons from above the atmosphere, with instrumental effects removed'). This applies both to objects that you expect would fall into your model's classes, and to other objects ... e.g. 'Seyfert type X' objects were selected by some observers according their own 'filters'; you need to be sure about any objects that didn't pass their 'filters' but may be in the domain of your model. Again, the publicly available surveys may be very helpful here.
     
  15. Dec 14, 2004 #14
    Advice taken! Actually I'm interested in a model of AGN evolution of this kind
    http://www.physics.gmu.edu/~rms/astro113/myimages/agn-evolution-scheme.jpg
    that is because the great quantity of quasars observed at great distances. They should evolve to Seyfert galaxies and BL Lac/radiogalaxies, that are found at intermediate distances. In fact the BL Lac object with higher redshift that I've found is PKS 0215+015, with z=1.71 (if somebody find some with higher redshift, I'd like to know...)
     
  16. Dec 14, 2004 #15

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    According to the VII/235/table2 "Confirmed, probable or possible BL Lac objects", these are confirmed mag 1.7+ BL's

    DES.....................z
    Q J02340-3015...1.710
    B3 1222+438.....1.872
    Q J14092-0000...2.128
    Q J23031-3127...2.440

    Here are 2 candidate BL objects

    PKS 0913+003....3.074
    PKS 0933-333....2.906

    Here is a link to the catalog. It includes data on 876 BL objects [table 2] and about 15,000 AGNs [table 1]. Should be enough to get you started.
    http://cdsweb.u-strasbg.fr/cgi-bin/VizieR-2?-source=VII/235
     
    Last edited: Dec 14, 2004
  17. Apr 21, 2008 #16
    AGNs catalog

    can any body tell me how to download the whole catalog from the link below:

    webviz.u-strasbg.fr/viz-bin/VizieR?-source=VII/248

    I need the absolute magnitude of all AGNs and normal galaxies...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Congratulations to all the PF gurus
  1. Congratulations, Jen! (Replies: 17)

  2. Congrats to the Gurus! (Replies: 2)

  3. Is this all worth it? (Replies: 3)

Loading...