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Tracing molecular gas mass in extreme environments

Tracing molecular gas mass in extreme environments.

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Tracing molecular gas mass in extreme environments

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  1. Tracing molecular gas mass in extreme environments Ming Zhu (JAC/NRC) P. P. Papadopoulos (Argelander Institute for Astronomy, Germany)Yu Gao (Purple Mountain Observatory, China)Ernie R. Seaquist (U. of Toronto, Canada)Manolis Xilouris (National Observatory of Athens, Greece)Nario Kuno (Nobeyama Radio Observatory, Japan)Loretta Dunne (Nottingham University, UK)Ute Lisenfeld (University of Granada, Spain)

  2. IntroductionCO(1-0) as a M(H2) tracer

  3. Introduction • Conventional way to derive molecular gas mass using the empirical relation N (H2) =X Ico or M(H2)=X Lco • X is the CO-to-H2 conversion factor • X depends on metallicity (Wilson 1995) • X is 5 times smaller in the nuclear regions of IR-luminous galaxies (Downes & Solomon 1998) • How different is the X factor in different types of galaxies? • Derive M(H2) from dust mass • Can we use the Galactic gas-to-dust ratio in external galaxies? How big is the variation?

  4. Dust mass  Gas mass • Derive M(H2) from dust mass • Our Galaxy gas/dust ~ 150 • Can we use the Galactic gas-to-dust ratio in external galaxies? Is it a constant? How much does it variate?

  5. Sample: 1. Antennae Galaxies

  6. Arp299

  7. Taffy Galaxies

  8. NGC3310

  9. NGC157

  10. Single dish data for NGC4038/39 High quality data: wavelength telescope resolution cover-region 12CO(1-0) Nobeyama 45-m 15” 60”x100” 12CO(2-1) JCMT 20” 50”x50” 12CO(3-2) JCMT 14” 60”x90” 13CO(2-1) JCMT 20” 5 points 13CO(3-2) JCMT 14” 2 points

  11. N4038: CO(1-0) on K band

  12. CO10 and CO32

  13. NGC3310

  14. NGC157

  15. Taffy: CO(3-2) profiles on CO(1-0)

  16. R31 on Antenne

  17. Excitation --CO(3-2)/(1-0) on ISO image

  18. Excitation Analysis: LVG modeling r21=Ico(2-1)/Ico(1-0) r31=Ico(3-2)/Ico(1-0) R10= I_13co(1-0)/I_12co(1-0) R21=I_12co(2-1)/I_13co(2-1) • Tk, n(H2), Nco/dV, Zco X = Nco/dV / Trad

  19. Excitation analysis: r31 ratio

  20. LVG model fitting

  21. Preliminary Results X factor (as a factor 1/f of the galactic value Xo) UGC 12915 3-6 UGC12914 2-7 Taffy Bridge 6-13 N4038C 4-6 N4039C 3-7 Overlap Region 5-10 N3310 2-3 (excitation effect offset by metallicity eff) N157C 4-8 N157S 1-2 (the uncertainty could be a factor of 2 or 3)

  22. Non-viralized clouds dV/dr = (10- 100) km/s/pc (if [12CO/H2] = 10 ^-4) but Virialized dV/dr < 3 km/s/pc Nco/dV = (1.5 -1.9) x 10^15 cm{-2} X = Nco/Ico =(5.1-6.4) x 10^19 cm^-2/(K km/s) 11- 13 times smaller than the Galactic value !! ==> True M(H2) < M(H2*) = X Lco LVG model results

  23. Summary I • The X factor can vary by a factor of 10 from galaxy to galaxy and also within one galaxy. • In starburst galaxies and interacting galaxies, the X factor is smaller than the galactic value by a factor of 5. • In the spiral arm of quiet galaxies the X factor is close to that of the Milky Way. • In extreme environment, the X factor is within 1 order of magnitude of Xo

  24. Dust mass  Gas mass • Derive M(H2) from dust mass • Our Galaxy gas/dust ~ 150 • Can we use the Galactic gas-to-dust ratio in external galaxies? Is it a constant? How much does it variate?

  25. Scuba 850 on Ant

  26. NGC3310: 850 on HI

  27. NGC157: SCUBA 850 on HI

  28. NGC4038/39

  29. SED of NGC3310

  30. SED of NGC1569

  31. NGC3310 radiation field

  32. NGC157 radiation field

  33. NGC3310 –enhanced VSG

  34. NGC3310 M(HI)/M(dust)

  35. Gas-to-dust ratio in NGC4038/39 Zhu et al. (2003)

  36. Gas-to-dust ratio in Taffy galaxies

  37. N157 and N3310

  38. Summary II • Large variation in the gas-to-dust ratio in interacting systems • NGC 3310 shows excess 850 emission which could be explained by a large fraction of very small dust grains due to a strong radiation field in this galaxy.

  39. Hubble Deep Field (Hughes et al. 1998, Nature)

  40. Next Step • JCMT local universe survey of nearby galaxies with SCUBA-2 and HARP

  41. JCMT nearby galaxy survey(Wilson et al.) • JCMT local universe survey of nearby galaxies with SCUBA-2 and HARP • 200 galaxies (HI fluxes selected) • 32 galaxies in SINGS • CO1-0 data from BIMA or NRO 45m

  42. Nearby Galaxy Survey Goals: • Physical properties of dust in Galaxies • Molecular gas mass and gas-to-dust ratio • Effect of galaxy morphology • Luminosity and dust mass function

  43. Ophiuchus • Most mass is in diffuse region • Ophiuchus, d=160pc, 4 deg^2 region • 2000 Msun from extinction • 50 Msun in submm dust core , less than 2.5% Av > 15 • So most mass in not detectable in submm • Can be observed in CO

  44. Perseus • Most mass is in diffuse region • Perseus (d=300pc) for example 3 deg^2 region • 17000 Msun from visual extinction Av=2, less than 10% from Av> 5 (Bachiller & Cernicharo 1986), • 2600 Msun in dust core , less than 20% • 6000 Msun by C18O (Hatchell et al. 2000) .

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