Gas mass conversion factors Axel Weiss MPIfR Bonn, Germany - - PowerPoint PPT Presentation

Gas mass conversion factors

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Axel Weiss

MPIfR Bonn, Germany Hercules team PHIBSS team

Motivation

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Daddi ea 2010 Scoville ea 2016

α=0.8 αMW Today we have much better data to reevaluate molecular gas mass conversion factors! (CO SEDs, good dust continuum coverage, information from other lines like CI in larger samples of galaxies)

L850/L’CO(1-0)

Cold H2 in action - collisions by H2 are directly observable !

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‘Hot Boltzmann tail’ Multi-component ISM versus 500-2000K 103 cm-3 105 cm-3 104 cm-3

Non-LTE line + dust radiative transfer analysis

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Parameters: Physical

• H2 density
• kinetic temperature
• turbulence δv/δr; dvturb; δv/δr ~ sqrt( n(H2) )
• size of the emission region (Ωs bff = π r0

2 )

Chemical

• [mol]/[H2]
• Gas to dust mass ratio (GDMR)

Radiation Field:

• Background CMB + Dust (Tdust β λτ=1)

Dust and gas are linked at several levels:

• dust is background for lines
• gas columns from lines linked to

dust opacity

• Tkin >= 0.5*Tdust

N(H2)/dv ~ n(H2) δv/δr -1

*[mol]/[H2] => line opacity

N(H2) = N(H2)/dv dvturb * GDMR => dust opacity M(H2) = Ωs N(H2)

(Weiss ea 2007)

Turbulent ISM

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Column density for a turbulent ISM (simulation) Density distribution is log normal Tkin ~ n(H2)-γ (hydro sim) n(H2), Tkin Tdust Ω, [CI] Numbers: dvturb κvir GDMR, [CO] Distribution: low dvturb high dvturb

e.g. Krumholz & McKee 2005, Goldbaum ea 2016

Exponential turbulent Disk

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Distribution: Σgas (r) => n(H2) (r) Tkin Tdust, Ω Numbers: dvturb κvir chemical params

Each component is the result from the turbulence model with <n(H2)> , <Tkin> and Ωsource from the exponential disk distribution

Sample and Diagnostics

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High-z QSOs and SMGs

(submm selection, above the MS)

z=2.0 – 6.3 6 SBs; 6 QSO hosts CI: 8

Hercules : local (U) LIRGs 26 galaxies CI for 21 Total 44 (U)LIRG

9 High-z MS galaxies

(z~2, NIR selection) Log M* =10.5- 11.8 CI: 4

2 comp. turb.

• turb. disk

Rosenberg ea 2015 e.g Weiss ea 2005, 07 Walter ea 2011 Daddi ea 2010/15 Tacconi ea 2013 Genzel ea 2015

CO conversion factor for the MW

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2C: αco = 4.0 +/- 1.1 Msol (K km/s pc2)-1 T: αco = 4.9 +/- 1.9 Msol (K km/s pc2)-1 TD: αco = 4.0 +/- 0.7 Msol (K km/s pc2)-1 Xco = 1.9 +/- 0.3 x 1020 cm-2 ( K km/s)-1

Calibration for inner part of the MW ( |2.5| < l < |32.5|)

Bolatto ea 2003

(Incl. He correction)

(Fixsen ea 1999) (Fixsen ea 1999) Planck, IRAS

The conversion factors:

(turbulent disk model; preliminary)

αCO αCI α850

Test case GN20

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Turbulent Disk model GN20 @ z =4.05 Limits on αco from Mdyn: αco < 3.3 Msol (K km/s pc2)-1 we find: αco : 2.2 +/ -0.8 Msol (K km/s pc2)-1 Hodge ea 2015 Radial profile model (example) vs observations 170µm rest continuum CO(2-1)

Disk sizes for different tracers

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Turbulent Disk model SMM14011 @ z =2.5 Difference compared to Σ(H2) implies that ALL conversion factors change with r!