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Connecting Dense Gas Tracers of Star Formation in our Galaxy to High-z Star Formation

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

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  1. 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)

  2. Molecules Seen to z>6 z= 3 | • + Local galaxies • O ULIRGS • High-z (EMGs) • Some have LARGE L(CO) • L’mol= 23.5 WS*b DL2 Imol (1+z) -3 • Can we make a connection to well known local star formation ? Solomon & Vanden Bout (2005, ARAA)

  3. Satr Formation in galaxies empirically follows “Schmidt Law” : SFR ~ A ρ N Schmidt (1959) : N~2 Kennicutt (1998): Composite star formation law Fit with CO, HI, Hα data on 61 normal + 36 starbursts. ∑SFR = A ∑gas1.40

  4. But SFR/Mass (LFIR / L‘CO) Increases with SFR • SFR----LFIR • L’co --- Luminosity of emission line • Star Formation Efficiency ---- LFIR/L’co “Efficiency” increasing or CO fails to trace gas that is relevant to star formation ? • O ULIRGS • High-z Early Universe Molecular Emission Line galaxies (EMGs) • + Local galaxies • L’mol= 23.5 WS*b DL2 Imol (1+z) -3 • Solomon & Vanden Bout (2005 ARAA)

  5. Gao & Solomon (2004a,b): • The correlation of LIR-L'CO is non-linear, especially for high LIR: CO can be misleading in starbursts • LIR and L'HCN has a linear (N=1) and more tighter correlation than LIR-L'CO., for both normal spirals and starbursts including LIRGs and ULIRGs. • The SFR/Mdense is consistent for both 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 lower/higher scales?

  6. 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 2003-2004

  7. Discussion: What happens with CO ? 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.

  8. Questions for the plot: • Why the LIR-L’HCN correlation is linear? LIR~ Luminosity L’HCN ~ Mass of dense gas L ~ Mdense1 ??? • Why there is a turn off for the slope of correlation at lower luminosity? What causes the break?

  9. Propose a Model of Basic Unit 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

  10. What is/ Why/ How is the realistic of the basic unit ? LF of Galactic UC HII regions Casassus et al. (2000) • L = 105 Lsun ? • Mdense ~ 300- 103Msun ? • M*,max ~ n X 10Msun ? ……

  11. If true, this basic unit can be the bridge to connect star formation in our Galaxy to distant star formation

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