1. The Two Tightest Correlations: FIR-RC and FIR-HCN Yu GAO Purple Mountain Observatory, Nanjing Chinese Academy of Sciences

2. Stars are forming in giant molecular clouds (GMCs)

3. Diffuse a tomic gas （ HI ）, the gas reservoir for the molecular clouds, and the supply of future star formation. PDRs

4. Zhang, Gao & Wang arXiv: 0911.4815 Break-down of corr.: one example

5. Zhang, Gao & Wang arXiv: 0911.4815 70um and 160um overlaid with CO(1-0)

6. Zhang, Gao & Wang arXiv: 0911.4815 HI and RC (radio continuum) images overlaid with CO(1-0)

7. Dense gas is the essential fuel for high mass SF in Galaxies HCN Surveys in 53 Galaxies: Gao & Solomon 2004a ApJS Far-IR, HCN, CO Correlations : Gao & Solomon 2004b ApJ

8. SFR Dense Molecular Gas

9. More CO data of ULIGs (Solomon et al. 1997) that Lco > ~ 10^10 K km/s pc^2 Total Molecular Gas Mass

11. Gao, Carilli, Solomon & Vanden Bout 2007 ApJ, 660, L93 ^^^ || ~15hrs VLA, stacking 3 lens components

12. r.m.s.~19uJy/beam More than 45hrs VLA

13. 13 HCN @high-zHCN @high-z Gao, Carilli, Solomon & Vanden Bout 2007 ApJ, 660, L93

14. Wu, Evans, Gao et al. 2005 ApJL Krumholz & Thompson 2007 Fit to GMCs Fit to Galaxies Fit to All

15. SSCs in nearby galaxies could fill in the gap in FIR-HCN corr. Gap ？

17. Resovled Local (FIR-HCN) SF Law ? In Dense Gas (M51 & N6946)

18. 70um maps & compared to HCN measurements Work in progress! Still far from the size scale of SSCs (by more than two orders of magnitude)

19. Baan, Henkel, Loenen et al. 2008 Baan et al. (2008) Kohno 2007, et al. (2003) Imanishi (2006) Aalto et al. 2007, 2002, 1995 Solomon et al. 1992 Nguyen et al. 1992 Henkel et al. 1990 Henkel, Baan, Mauersberger 1991 HCN,CS,HNC etc. in SF Gals.

20. Bigiel’s talk @SFR50 SF thresholds may simply reflect the change of the dominant cold gas phase in galaxies from HI ->H2 & from H2->denseH2

21. SFR vs. M_dense(H2): linear correlation

22. SFR vs. M(H2): No Unique Slope:1, 1.4, 1.7? HI-dominated LSB galaxies HI ~ H2 H2-dominated Gao & Solomon 2004b ApJ

23. Liu & Gao 2010 RC-HCN corr.

24. Liu & Gao 2010 ApJ submitted

25. Gao & Solomon 2004b Liu & Gao 2010

26. Summary Dense Cores in Dense Molecular Gas Complexes  High Mass Stars & SSCs -> SFR (FIR-HCN Linear Correlation) SFR ~ M(DenseH2): the dense gas mass in galaxies & all star-forming systems? SF thresholds: change of the dominant cold gas phase in galaxies from HI ->H2 & from H2->denseH2 SFR: Counting Dense Cores/SSCs in Galaxies? HI (LSBs)  H2 (Spiral disks)  denseH2 (starbursts/ULIRGs)  Stars/SSCs Resolved local correlations are the key  SFR

27. FIR-radio vs. FIR-HCN correlations FIR, radio continuum (RC), HCN & CO FIR-RC > FIR/RC-HCN > FIR/RC-CO Stars Death  SN/SNRs  RC Stars Form  UV/dust  FIR CO  HCN  SF  FIR  RC FIR-RC & FIR-HCN corr. the strongest! Comparison of different SFR indicators Differ both spatially and temporally