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The star formation rate ( SFR ) and gas scaling laws

The star formation rate ( SFR ) and gas scaling laws. Yu GAO ( 高煜 ) Purple Mountain Observatory, Nanjing, China Chinese Academy of Sciences . Apr. 26, 2011@Hangzhou 70 th BD of Prof. G. Borner. Happy 70 th Birthday to Gerhard!!. Outline of this talk.

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The star formation rate ( SFR ) and gas scaling laws

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  1. The star formation rate (SFR) and gas scaling laws Yu GAO (高煜) Purple Mountain Observatory, Nanjing, China Chinese Academy of Sciences Apr. 26, 2011@Hangzhou70th BD of Prof. G. Borner

  2. Happy 70th Birthday to Gerhard!!

  3. Outline of this talk • What are the SFR-gas scaling laws: Schmidt law, K-S law, SF laws in other different forms, SF recipes • Why do we need a SFR-DenseGas law • A linear FIR(SFR)-HCN (dense gas tracer)relation for all star-forming systems: SF law in DenseGas; Work in progress • Major Issues in debates: • Solutions?!

  4. Star formation laws (& issues) • Schmidt (1959): SFR~density(HI)^n, n=1-3, mostly 2-3 in ISM of our Galaxy. • Kennicutt (1989): Disk-average [SFR~ density(HI+H2)^n] n is not well constrained. ~1-3, wide spread. • Kennicutt (1998): n=1.4 ? Total gas (HI + H2) vs. Dense gas • Better SF law in dense gas? (Hubble law, H0analogy)

  5. Kennicutt 1998

  6. IR circumnuclear starbursts Normal disk spirals

  7. SFR vs. M(H2): No Unique Slope:1, 1.4, 1.7? H2-dominated LIRGs/ULIRGs HI ~ H2 HI-dominated LSB galaxies Extragalactic SF=CO until 90’s Gao & Solomon 2004b ApJ

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

  9. CO detected in a few positions in NGC 4244 Deep CO obs. (~20 hrs on 12m) in UGC 7321 (HST/WFPC2 R+I image) First CO detections in a few edge-on LSB spirals using the 12m (Matthews & Gao 2001) DCs/SSCsin nuclear regions of LSB spirals?

  10. SFR(FIR) ~ M(H2) correlation of LSBs roughly follows that of normal spiral disks (nuclear regions, linear relation: L_FIR/M(H2)=31) Matthews, Gao, Uson & Combes 2005

  11. Shi+2011: Extended Schmidt star formation law

  12. Diffuse atomic gas（HI）, the gas reservoir for molecular clouds, and the supply for future star formation. PDRs

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

  14. Gao 2008 Zhang, Gao, Kong 2010 MNRAS

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

  16. SFR Dense Molecular Gas

  17. Baan, Henkel, Loenen + 2008 HCN,CS,HNC etc. in SF gals. • 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 Best case studies: Arp 220 & NGC 6240 (Greve + 2009)

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

  19. Fit to Galaxies Wu, Evans, Gao et al. 2005 ApJL Fit to GMCs Fit to both GMCs & Gals..

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

  21. Total useful on-source integration time >~110 hours. • HCN spectra with S/N>3 (a channel width dV ~7 km/s). • Typical rms ~1-2 mKat dV~20 km/s.

  22. Correlation between 8um-HCN. The solid line shows a fit of the fixed slope of 1.

  23. Correlation between 24um-HCN

  24. Correlation between 70um-HCN Correlation between 160um-HCN

  25. Issues: K-S SF Law in high-zgalaxies Daddi et al. 2010; Genzel+2010 Two major SF modes:1. a long-lasting mode for disks (local spirals and BzKs) 2. a rapid starburst forLIRGsULIRGs & SMGs/QSOs CO->H2 conversion factor ?? αco(Msun (K km/s pc2)-1: 4.6 for local spirals 3.6 ± 0.8 for BzKs 0.8 forLIRGs/SMGs/QSOs

  26. ∑Mdense vs. ∑SFR Dense H2 show the best correlation with SFR (linear).

  27. ∑gas vs. ∑SFR with different X-factors Similar bi-modal relations claimed in hi-z observations using different X-factors for spirals and (U)LIRGs(Daddi et al. 2010)

  28. Some more issues? Bussmann et al. 2008 FIR-HCN(3-2) sub-linear Also Juneau et al. 2009 FIR-HCN(1-0) superlinear Graciá-Carpio et al. 2008

  29. Juneau+2009; Narayanan+2008; Krumholz & Thompson 2007; Mao+2010 SFR – CO & SFR -- HCN indexes

  30. FIR – CS(2-1): linear! (IRAM 30m)

  31. FIR – CS(5-4): linear! (SMT 10m, limited data) FIR – CS(3-2): linear! (IRAM 30m)

  32. van derWerf + 2010

  33. Concluding Remarks • SF: quiescent (few Dense Cores=DCs), normal, active/burst modes (starbursts: active formation ofDCs) • DCsin Dense Molecular Gas Complexes  High Mass Stars & SSCs (SF in different environments: SMGs/hi-zQSOs; ULIRGs/Starbursts; Spirals; LSBs;DCs) • (FIR-HCN, CS Linear Correlations) SFR ~ M(DenseH2): the total mass of dense molecular gas in galaxies & all star-forming systems (spanning 10 orders of mag.)? • SF thresholds: change of the dominant cold gas phase in galaxies from HI ->H2 & from H2->denseH2 • SFR-DenseGas: Counting DCs/SSCs in Galaxies? Gao & Solomon: Dense H2DCs/Stars/SSCs

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