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

Stars are forming in giant molecular clouds (GMCs)

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

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

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

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

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

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

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

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

Gao, Carilli, Solomon & Vanden Bout 2007 ApJ, 660, L93

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

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

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

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

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

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

SFR vs. M_dense(H2): linear correlation

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

Liu & Gao 2010 RC-HCN corr.

Liu & Gao 2010 ApJ submitted

Gao & Solomon 2004b Liu & Gao 2010

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

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