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The Global Star Formation Laws in Galaxies: Recent Updates

The Global Star Formation Laws in Galaxies: Recent Updates. Yu Gao Purple Mountain Observatory Chinese Academy of Sciences . May 15, 2012 @5 th sino-french. Outline of this talk.

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The Global Star Formation Laws in Galaxies: Recent Updates

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  1. The Global Star Formation Laws in Galaxies: Recent Updates Yu Gao Purple Mountain Observatory Chinese Academy of Sciences May 15, 2012 @5th sino-french

  2. Outline of this talk • What are the star formation (SF) recipes? SFR-gas (HI, CO) scaling laws: Kennicutt - Schmidt law, SF laws in other forms • Why do we need a SFR-dense gas law • A linear FIR(SFR)--HCN (dense gas tracer) relation for all star-forming systems (GMCs-->high-z): SF law indense gas • Major issues and debates (CS surveys) • Conclusions

  3. Star formation laws • 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 and H0analogy)

  4. Hubble law

  5. Kennicutt 1998 n=1.4

  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 Schruba+2011 ~linear in H2!

  9. GMCsenbed in diffuse atomic gas（HI）, the gas reservoir for molecular clouds, and the supply for future star formation. PDRs

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

  11. High DensityTracersMerging/interactions trigger gasinfall to nuclearregionsNucleiof Galaxies shouldpossessdensergasas GMCs have to survive to tidal forces (must bedenser) Criticaldensity: the radiating molecule (eg, CO) suffers collisions at the rate: n(H2) sigma v = A (Einstein coefficient A ~ nu^3 mu^2) * High-J(>~3)levels of CO (nu ~ J) highercriticaldensity to beexcited (>105cm-3) * & High dipole moment molecules HCN, HNC, HCO+, CS (mu ~ 30x > CO), etc.. * X factor ? CO-to-H2, HCN-to-DenseH2 conversions

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

  13. SFR Dense Molecular Gas

  14. 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)

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

  16. Fit to Galaxies Wu, Evans, Gao et al. 2005 ApJL Fit to GMCs Wu+2010 Fit to both GMCs & Gals..

  17. CARMA+45m CO (Koda + 09) HST

  18. 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.

  19. HCN contours are overlaid on the CO image

  20. SFR • Correlations between 8um-HCN & 24um-HCN. The solid lines: fixed slope of 1. HCN

  21. M33GMCs (Rosolowsky, Pineda & Gao 2011) Chen & Gao in prep.

  22. ∑Mdense vs. ∑SFR Liu & Gao arXiv:1106.2813 Dense H2 show the best correlation with SFR (linear Liu & Gao 2011).

  23. K-S SF Law in high-redshift galaxies 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 for LIRGs ULIRGs & 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 for LIRGs/SMGs/QSOs

  24. Bi-modal SF laws in high-z gals (Daddi+2010; Genzel+2010) also exist in local gals

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

  26. Dense gas over a range of 10^4-8 /cm^3

  27. Concluding Remarks • SF: quiescent (few Dense Cores=DCs), normal, active/burst modes (starbursts: active formation ofDCs) • DCsin Dense Molecular Gas Complexes  High Mass Stars/Clusters (SF in different environments: SMGs/hi-zQSOs; ULIRGs/Starbursts; Spirals; LSBs;DCs) • SF thresholds: change of the dominant cold gas phase in galaxies from HI ->H2 & from H2->denseH2 • (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.)? • SFR-DenseGas: Counting DCs(=SF units) in Galaxies? Gao & Solomon: Dense H2DCs/StarsClusters

  28. New Star Formation Law • Dense Molecular Gas  High Mass Stars • SFR ~ M(DENSE) ~ density of dense gas (e.g. gas density >~10^5 cc), linear • HI  H2 DENSE H2 Stars Schmidt law : HI  Stars Kennicutt : HI + H2 Stars Gao & Solomon: Dense H2 Stars From Cores to High-z: Dense GasMassive SF

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