Connecting Dense Gas Tracers of Star Formation in our Galaxy to High-z Star Formation. Jingwen Wu ( The Univ. of Texas at Austin ). Collaborators: Neal Evans (Advisor, UTexas at Austin) Yu Gao (PMO); Phil Solomon, Tom Mooney (SUNY-SB); Paul Vanden Bout, Yancy Shirley (NRAO).
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Connecting Dense Gas Tracers of Star Formation
in our Galaxy to High-z Star Formation
(The Univ. of Texas at Austin)
Neal Evans (Advisor, UTexas at Austin)
Yu Gao (PMO);
Phil Solomon, Tom Mooney (SUNY-SB);
Paul Vanden Bout, Yancy Shirley (NRAO)
Solomon & Vanden Bout (2005, ARAA)
Satr Formation in galaxies empirically follows
“Schmidt Law” : SFR ~ A ρ N
Schmidt (1959) : N~2
Composite star formation law
Fit with CO, HI, Hα data on
61 normal + 36 starbursts.
∑SFR = A ∑gas1.40
CO fails to trace gas that is relevant to star formation ?
Line galaxies (EMGs)
Gao & Solomon (2004a,b):
non-linear, especially for high LIR:
CO can be misleading in starbursts
more tighter correlation than LIR-L'CO.,
for both normal spirals and starbursts
including LIRGs and ULIRGs.
normal and starburst galaxies, over
3 orders of magnitude.
A uniform star formation law (if
proper dense gas tracer is used)?
Will the correlation extend to
Star formation in the Milky Way is dominated by massive star
formation that occurs at GMC cores.
Study on massive Galactic dense cores is crucial to connect star formation from galactic to Galactic scales
We mapped HCN 1-0 and 3-2 on Galactic dense cores, to compare
with data from galaxies.
HCN 1-0 from FCRAO during 2004-2005
HCN 3-2 from CSO during
What happens with
CO traces the overall mass of molecular clouds, not the dense cores. In the
Galaxy, these dense cores occupy a negligible fraction of the mass of cloud
(~a few percent). If the fraction of the dense gas in the overall mass of cloud
Stays roughly constant, the Lir and L’co can stay linear. But for extreme
starbursts, a much large fraction of molecular gas is in the form of dense gas,
CO fails to trace the SFR in these galaxies.
L’HCN ~ Mass of dense gas
L ~ Mdense1 ???
What causes the break?
M > Mcrit
Each unit provides the same luminosity
Larger structures are only different at how many such units they contain.
Critical mass of dense gas
Luminosity depends strongly on mass available
M < Mcrit
LF of Galactic UC HII regions
Casassus et al. (2000)