Cosmic Star Formation in Infrared Galaxies: Insights and Considerations

1. What fraction of stars formed in infrared galaxies? Giavalisco et al. 2004

2. Low obscuration in normal galaxies M74 is a Sc galaxy

3. Heavy Obscuration in extreme galaxies GRB 010222 host (Frail et al. 2001) Sanders et al. (1988)

4. Ramirez-Ruiz et al. (2002) Berger et al. (1993): 4/20 GRB hosts have SFRs of about 500 Msun/yr. Others are much less. Soifer et al. (1987)

6. Field galaxy evolution Van Dokkum et al. (2004) Dickinson et al. (2003)

7. GRB host galaxy statistics Long-duration bursts appear to be linked to the deaths of massive stars and hence ongoing star formation. Berger et al. (2003) find 4/20 of their sample of well-localized GRB hosts are luminous IR galaxies. This suggests that 20-50% of cosmic star formation happened in IR galaxies. Tanvir Tanvir et al. (2004)

8. IR backgrounds + source counts Blain et al. (2002) Adelberger & Steidel (2000) AGNs not major contributor to IR background or would overproduce local MDO density.

9. IMF considerations 30 Doradus Selman et al. (1999) cB58 (z=2.7) Pettini et al.(2000) Status of IMFs in starbursts reviewed 6/9. Can it be top-heavy in IR galaxies?

10. Densities in IR galaxies • Either • Much lower than ULIGs like Arp 220, which have above 100 Msun/pc3 • Or • 2) Very active redistribution of stars (constraint on SSC sizes) Lamers et al. (2004)

11. Summary • Considerations from optical Madau-Lilly plot and W(z) relation do not leave much room for IR galaxies. Possible disagreement from IR background considerations. • My best guesses are: fopt= 0.2, fIR,low= 0.6, fIR, high = 0.2 • f(SFR) is probably bimodal. The IMF might be top heavy in IR galaxies but is not in UV luminous ones. • 4. Strongest constraints will come from many measurements combined.