Abstract by Ka-Hei Law
In star forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAH), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region - the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the infrared emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.
Relevant Papers
"Young, UV-bright Stars Dominate Dust Heating in Star Forming Galaxies"
Law et al. 2011
Talk Slides
pdf
Would the SFR measured from the TIR be different for disk galaxies of same mass and different orientation?
ReplyDeleteFrom Claus:
ReplyDeleteWhat type of stars are included in the "old" stellar component? Are these UV bright, low-luminosity stars, like white dwarfs, host post-AGB stars, etc?
To Aida:
ReplyDeleteI do not know the answer, but I'd guess that SFR measured from TIR is higher at lower inclination (e.g. when seen face-on). Compare to UV-photons, IR-photons has a less forward-biased scattering phase function. As IR-photons travel across the disk, some of them gets scattered out of plane, and so these photons are more likely seen at lower inclination.
To Claus:
The "old" stellar component includes stars in different stages of evolution (including thermally pulsing-AGB and post-AGB), as well as white dwarfs and neutron stars. The mass in white dwarfs is about 10% at 13 Gyr. I haven't been able to find out the fraction of luminosity due to white dwarfs/post-AGB stars because the Fortran 77 code of PEGASE (the stellar model) isn't easy to modify, but I may do it when I've time.