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The Two T ightest 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 - PowerPoint PPT Presentation
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The Two Tightest Correlations: FIR-RC and FIR-HCN
Yu GAO
Purple Mountain Observatory, NanjingChinese Academy of Sciences
Stars are forming in giant molecular clouds (GMCs)
Diffuse atomic gas( HI) , the gas reservoir for the molecular clouds,and the supply of future star formation. PDRs
Zhang, Gao & Wang arXiv: 0911.4815
Break-down of corr.: one example
Zhang, Gao & Wang arXiv: 0911.481570um and 160um overlaid with CO(1-0)
Zhang, Gao & Wang arXiv: 0911.4815HI 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
Wu, Evans, Gao et al. 2005 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 & comparedto HCN measurements
Work in progress!
Still far from the size scale of SSCs(by more than twoorders of magnitude)
Baan, Henkel,Loenen et al. 2008
• 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
HCN,CS,HNC etc. in SF Gals.
Big
iel’s
talk
@S
FR50
SF thresholds maysimply reflect the change of the dominant cold gas phase in galaxiesfrom 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-dominatedLSB galaxies
HI ~ H2
H2-dom
inated
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