1 / 32

The G lobal S tar F ormation L aw in Dense M olecular G as

The G lobal S tar F ormation L aw in Dense M olecular G as. Yu Gao Purple Mountain Observatory Chinese Academy of Sciences . Sept. 7 , 2011 @SED2011 ( IAUS 284). Outline of this talk.

apria
Download Presentation

The G lobal S tar F ormation L aw in Dense M olecular G as

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Global Star Formation Law in Dense Molecular Gas Yu Gao Purple Mountain Observatory Chinese Academy of Sciences Sept. 7, 2011@SED2011 (IAUS 284)

  2. Outline of this talk • What are the star formation (SF) recipes? SFR-gas (HI, CO) scaling laws: Schmidt law, SF laws in other forms • 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 • Major Issues and debates • Conclusion+Solutions?!

  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, Georges Lemaître& H0analogy)

  4. Kennicutt 1998 n=1.4

  5. IR circumnuclear starbursts Normal disk spirals

  6. 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

  7. 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!

  8. 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) DenseCoresin nuclear regions of LSB spirals?

  9. 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

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

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

  12. 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 dipolemoment molecules HCN, HNC, HCO+, CS (mu ~ 30x > CO), etc.. * X factor ? CO-to-H2, HCN-to-DenseH2 conversions

  13. 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

  14. SFR Dense Molecular Gas

  15. 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)

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

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

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

  19. 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.

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

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

  22. M31GMCs (Rosolowsky, Pineda & Gao 2011 MN) Chen & Gao in prep.

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

  24. Poster by Liu+

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

  26. Poster by Liu+

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

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

  29. FIR – CS(5-4): linear! (SMT 10m, still limited data; Wang, Zhang & Shi 2011 MN) FIR – CS(3-2): linear! (IRAM 30m)

  30. Poster by Z. Zhang fresh results from the APEX telescope

  31. 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

More Related