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IMF and First Stars

  1. Oct 25, 2005 #1

    wolram

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    http://arxiv.org/abs/astro-ph/0510685

    Authors: R. Schneider, R. Salvaterra, A. Ferrara, B. Ciardi
    Comments: 11 pages, 8 figures, submitted to MNRAS

    Motivated by theoretical predictions that first stars were predominantly very massive, we investigate the physics of the transition from an early epoch dominated by massive Pop III stars to a later epoch dominated by familiar low-mass Pop II/I stars by means of a numerically-generated catalogue of dark matter halos coupled with a self-consistent treatment of chemical and radiative feedback. Depending on the strength of the chemical feedback, Pop III stars can contribute a substantial fraction (several percent) of the cosmic star formation activity even at moderate redshifts, z = 5. We find that the three z = 10 sources tentatively detected in NICMOS UDFs should be powered by Pop III stars, if these are massive; however, this scenario fails to reproduce the derived WMAP electron scattering optical depth. Instead, both the UDFs and WMAP constraints can be fulfilled if stars at any time form with a more standard, slightly top-heavy, Larson IMF in the range 1 Msun < M < 100 Msun.
     
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  3. Oct 25, 2005 #2

    Garth

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    Thank you wolram, a paper I have been looking out for...

    However:
    The only problem is how to explain how such stars could form in the metal free environment, several possibilities are referred to....
    And if so then
    What would such relics be? Although not as supermassive as originally thought they would still be very massive compared to the Sun and consequently would now be supernova relics - IMBHs possibly?? (Now with a mass range of ~10 - 100 M.)

    Garth
     
  4. Oct 25, 2005 #3

    turbo

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    I envision the relics in our MW for such processes would appear as regions dominated by metal-poor stars - not Pop III by any stretch but poorly enriched. Is this observed?
     
    Last edited: Oct 25, 2005
  5. Oct 25, 2005 #4

    Garth

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    Although metal poor stars are observed they can be explained by the H/He rising to the photosphere and the metals lost in the stellar interiors OR they may be very early stars (Pop III) that have not synthesised much metallicity.

    The question is still how would Pop III stars in this mass range form with zero metallicity in the first place? And how many - i.e. what baryon density - is needed to explain the observations of IGM metallicity and re-ionisation?

    Garth
     
  6. Oct 25, 2005 #5

    SpaceTiger

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    The "relics" he refers to are low-mass stars, not remnants of high-mass stars. He's saying that the Pop III IMF ought to extend to low masses (if their observations are to be fit) and, since low-mass stars are long-lived, there should still be some alive and kicking in our galaxy.

    The observations are pretty sketchy, though, so I would be cautious in interpreting the results.
     
  7. Oct 25, 2005 #6

    Garth

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    Thank you ST. I agree that any results from that epoch are going to be tentative, however when they said
    presumably the number of low mass - and still active stars - should be quite small? Would not what is left of the mass of the majority of the relics originally have been in the higher end of that scale?

    Garth
     
  8. Oct 25, 2005 #7

    SpaceTiger

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    Yes, but the point is that they should exist. Some other theories suggest that there shouldn't be any Pop III stars still around.


    I think you're just using different (though not incorrect) terminology. From the context given in their paper, "relic" is only referring to stars still on the main sequence. If IMBHs exist, then it seems perfectly reasonable to think they might be Pop III remnants.
     
  9. Oct 25, 2005 #8

    turbo

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    It seems pretty speculative to propose that low-mass Pop IIIs stars might still be around in our galaxy, without first establishing the physics by which primeval stars follow their own "main sequence" and relating that to the observed main sequence of highly metallized stars. Are there any observations that support the notion that Sol-mass stars of low metallicity can live for 10-13 Gy? Most BB papers seem to ascribe the "live fast - die young" philosophy to Pop III stars, so they can supply both the observed metalicity and the reionization radiation required prior to z~6. It seems that the Pop III stars are being asked to do quite a lot in this model.
     
    Last edited: Oct 25, 2005
  10. Oct 26, 2005 #9

    Garth

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    That depends on the IMF - this paper is saying that in fact observations suggest the range of Pop III masses are lower than theory predicts.

    Garth
     
  11. Oct 27, 2005 #10

    Chronos

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    I think [albeit it with great effort], that pop III stars were bit players in a much larger theatre in the early universe. The CMB was still fiercely hot, IMBH's were forming and merging furiously, and GRB's were popping off like fire crackers... from IMBH mergers [long bursters] and Pop III hypernovas [short bursters]. Add a dense cloud of primordial hydrogen, and no telling what might arise from that mess. There are probably some other collateral collision events that could arise from large scale effects.
     
  12. Oct 27, 2005 #11

    Garth

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    While I agree with the general idea - that the early environment was complex and we should keep an open mind as we have very little idea what really went on - nevertheless, should that not be the other way round? i.e. IMBH mergers [short bursters] and Pop III hypernovas [long bursters].

    Garth
     
  13. Oct 27, 2005 #12

    turbo

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    Pop III as bit player? I see a problem here that maybe you can clear up. IMBHs had to originate from something else through the processes of merger or accretion. Without massive stars (Pop III) playing that crucial role at progenitors, how do you form IMBHs?

    In a reasonable heirarchical model, Pop III stars form before IMBHs, and since only a fraction of the Pop III stars will end up as IMBHs, they would have to far outnumber IMBHs.

    http://arxiv.org/PS_cache/astro-ph/pdf/0410/0410526.pdf

     
  14. Oct 27, 2005 #13

    Garth

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    Perhaps locally in our Milky Way's galactic ring? As here:Outer Disk Ring?
    (Thank you hellfire for the link)

    Garth
     
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