Extragalactic Star Formation into the ALMA Era (Beyond CO)* Yu GAO 高 煜 Purple Mountain Observatory, Nanjing Chinese Academy of Sciences *Dedicated to the Memorial of Phil Solomon

Talk Outline 1) Introduction: Massive Star Formation GMC Dense Cores, Probes of Complex Molecules 2) Beyond CO ( Extragalactic SF=CO until 90’s) ALMA; Importance of Dense Molecular Gas in Gals. 3) HCN in Galaxies Near and Far a) Observations of HCN in 65 local Galaxies b) FIR--HCN Correlation c) High-z HCN Observations 4) FIR-HCN (Global SF Law) Dense Cores to Hyper/Ultraluminous Galaxies (High-z)

HI, Atomic Gas, PDRs

Many additional molecular lines are detected by single-dish mm telescopes M82 A G

Nearby Galaxies (thanks to Jean Turner)

(from Jean Turner’s Apr’08 China-US Workshop)

Gao, Lo & Lee^2 2001, SFE contours 2.(Cont.) Importance of Dense Gas

Gao 2008

SCUBA: Zhu, Gao, Seaquist & Dunne 2007 CO: Gao, Zhu, Seaquist um contours on 8um image 850um contours on CO image

CO Contours overlaid on the optical images (false-color) Molecular gas density increases as merging advances Gao, Gruendl, Hwang, Lo 1999

2. Summary on Dense Gas Dense molecular gas is the ultimate material to make stars in star-forming regions in galaxies (dense GMC cores to ultraluminous starbursts) Interaction drives gas into inner disks, overlap starburst regions, and nuclear regions (& becomes much denser) initiating the ultraluminous starbursts Dense gas (traced by HCN, CS etc.), not the total gas (H2+HI), is the key to star formation. Beyond CO: a wide variety of molecular lines in mm/sub-mm regime

3. 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

3. (Cont.) HCN Obs. in Local Gals. Baan et al. (2007) arXiv: Kohno 2007, et al. (2003) Imanishi et al. 2006, 2007 Aalto et al Solomon et al Nguyen et al Henkel et al (NGC4945) Henkel, Baan, Mauersberger 1991

SFR Dense Molecular Gas

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

Baan, Henkel, Loenen et al. (2008, arXiv: )

3. High-z HCN Obs.(+Literature) Complications: lens, L IR (SFR vs AGN), CO(1-0) Source Lfir Lhcn Lco hcn/co mag.f a H F J A B J < < J < < J < < J c B < < J < < J < < M < < J < <

Gao, Carilli, Solomon & Vanden Bout 2007 ApJ, 660, L93 (astro-ph/ )

(13 HCN at high-z)HCN at high-z

4. FIR-HCN (Global SF Law) Dense Cores to Hyper/Ultraluminous Galaxies (High-z) Kennicutt (1998): global n=1.4 ? Total gas (HI + H2) vs. Molecular gas Sample dependent !! (e.g., Wong & Blitz 2002; Heyer et al. 2004; etc.) Kennicutt et al. (2007): local n= vs. Dense molecular gas !? Linear !? Better SF law in dense molecular gas!

SFR vs. M(H2): No Unique Slope:1, 1.4, 1.7? HI-dominated HI ~ H2 H2-dominated

SFR vs. M_dense(H2): linear correlation

Wu, Evans, Gao et al ApJL Krumholz & Thompson arXiv: !!! Papadopoulos et al.

VLA  EVLA! GBT