Connecting Dense Gas Tracers of Star Formation
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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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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)


Molecules seen to z 6

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)


Connecting dense gas tracers of star formation in our galaxy to high z star formation

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


But sfr mass l fir l co increases with sfr

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)


Connecting dense gas tracers of star formation in our galaxy to high z star formation

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?


Connecting dense gas tracers of star formation in our galaxy to high z star formation

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


Connecting dense gas tracers of star formation in our galaxy to high z star formation

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.


Questions for the plot

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?


Propose a model of basic unit

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


What is why how is the realistic of the basic unit

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 ?

    ……


Connecting dense gas tracers of star formation in our galaxy to high z star formation

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


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