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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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Purple Mountain Observatory
Chinese Academy of Sciences
May 15, 2012 @5th sino-french
n=1-3, mostly 2-3 in ISM of our Galaxy.
Disk-average [SFR~ density(HI+H2)^n]
n is not well constrained. ~1-3, wide spread.
Total gas (HI + H2) vs. Dense gas
(Hubble law and H0analogy)
Normal disk spirals
HI ~ H2
Extragalactic SF=CO until 90’s
Gao & Solomon 2004b ApJ
simply reflect the
change of the
dominant cold gas phase in galaxies
from HI ->H2 & from H2->denseH2
Bigiel’s talk @SFR50
~linear in H2!
and the supply for future star formation.
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
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
Dense Molecular Gas
HCN,CS,HNC etc. in SF gals.
Best case studies: Arp 220 & NGC 6240 (Greve + 2009)
13 HCN @high-z
Wu, Evans, Gao
et al. 2005 ApJL
Fit to GMCs
Fit to both
GMCs & Gals..
(a channel width dV ~7 km/s).
are overlaid on
the CO image
Chen & Gao in prep.
Liu & Gao arXiv:1106.2813
Dense H2 show the best correlation with SFR (linear Liu & Gao 2011).
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
Bi-modal SF laws in high-z gals (Daddi+2010; Genzel+2010) also exist in local gals
Juneau+2009; Narayanan+2008; Krumholz & Thompson 2007; Iono+2008; Mao+2010
SFR – CO & SFR -- HCN indexes
Gao & Solomon: Dense H2DCs/StarsClusters
(e.g. gas density >~10^5 cc), linear
Schmidt law : HI Stars
Kennicutt : HI + H2 Stars
Gao & Solomon: Dense H2 Stars
From Cores to High-z: Dense GasMassive SF