1. 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) Tracing molecular gas mass in extreme environments

2. Introduction CO(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

13. CO10 and CO32

14. NGC3310

15. NGC157

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

17. R31 on Antenne

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

19. 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

20. Excitation analysis: r31 ratio

21. LVG model fitting

23. 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 N33102-3 ( excitation effect offset by metallicity eff) N157C4-8 N157S1-2 (the uncertainty could be a factor of 2 or 3)

24. Non-viralized clouds LVG model results 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

25. 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

26. 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?

27. Scuba 850 on Ant

28. NGC3310: 850 on HI

29. NGC157: SCUBA 850 on HI

30. NGC4038/39

31. SED of NGC3310

32. SED of NGC1569

33. NGC3310 radiation field

34. NGC157 radiation field

35. NGC3310 –enhanced VSG

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

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

38. Gas-to-dust ratio in Taffy galaxies

39. N157 and N3310

40. 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.

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

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

43. 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

44. Nearby Galaxy Survey Goals: 1.Physical properties of dust in Galaxies 2.Molecular gas mass and gas-to-dust ratio 3.Effect of galaxy morphology 4.Luminosity and dust mass function

47. 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

48. 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).