tag:blogger.com,1999:blog-6453356098257713185.post3627219821577039358..comments2023-11-02T13:19:04.779+01:00Comments on Leiden's Galaxies Journal Club: The mid-IR luminosities of normal galaxiesOlivera Rakichttp://www.blogger.com/profile/00805004998323584773noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-6453356098257713185.post-34117687175470101672010-03-13T04:31:20.365+01:002010-03-13T04:31:20.365+01:00Ryan, perhaps I can help clarify the issue with th...Ryan, perhaps I can help clarify the issue with the Chary & Elbaz (2001) correlation. It is that for a constant star-forming system, one need not look back 1.5 Gyr to derive an average rate of SF that agrees with CE2001. But if a system has a non-constant SFH, then, essentially, the on-going instantaneous rate of SF is simply out of sync with the number of intermediate mass TPAGB stars present because those are produced over such a long timescale.<br /><br />Now, you raise a subtle question: how CE2001 was derived in the first place. If you recall, CE2001 is all about the correlation between L_12um (and L_15um, etc) with L_TIR, and then L_TIR vs SFR is simply from Kennicutt (1998). Setting aside any implications for where L_TIR arises (!), this calibration is derived for galaxies selected to be star forming. Odds are that something forming stars today probably was forming stars 1 Gyr ago. What the correlation is between the ongoing rate of today and the rates in the previous 1 Gyr is not obvious but one can evoke the central limit theorem to suppose that things probably average out fairly well. But if one were to select a bunch of galaxies, say, by their stellar continuum and make plots of L_12 vs H_alpha star-formation rate, it might look a little different than CE2001 (see, e.g., Calzetti et al, Kennicutt et al, etc) but the lore is that the difference is all "obscured star formation".<br /><br />Or is it?Anonymoushttps://www.blogger.com/profile/18119946993699816006noreply@blogger.com