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Sub-mm/mm astrophysics: How to probe molecular gas Yasuo Fukui Nagoya University Summer School

Sub-mm/mm astrophysics: How to probe molecular gas Yasuo Fukui Nagoya University Summer School The Gaseous Universe Oxford, 21-23 July 2010. Lecture 3 Giant molecular clouds, GMCs. Sub-mm/mm astrophysics: How to probe molecular gas. Giant molecular clouds, GMCs. GMCs Size 100 pc

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Sub-mm/mm astrophysics: How to probe molecular gas Yasuo Fukui Nagoya University Summer School

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  1. Sub-mm/mm astrophysics: How to probe molecular gas Yasuo Fukui Nagoya University Summer School The Gaseous Universe Oxford, 21-23 July 2010

  2. Lecture 3Giant molecular clouds, GMCs Sub-mm/mm astrophysics: How to probe molecular gas

  3. Giant molecular clouds, GMCs • GMCs • Size 100 pc • Mass 105-106 Mo • Linewidth 5-15 km/s • Density 100-1000 cm-3 • Temperature 10-20 K • The disk vs. the galactic centre • Star formation • OB associations, loose clusters • less than 10% of H is converted into stars, low SF efficiency

  4. Previous observations of extragalactic GMCs; • Poor resolution • Only global averaged properties • Spiral structures seen in GMCs • Global correlation with star formation LIR vs. M(H2)

  5. Resolved GMCs; • galaxies vs. Milky Way; galaxies are too far and the MW is too much contaminated • Need spatial resolutions of 40pc or better, as compared with 100pc • Local group galaxies offer the laboratory • LMC (50kpc) in the south, M33 (700kpc) in the north see review, Fukui and Kawamura, 2010, Ann.Rev.A.A., “Molecular clouds in nearby galaxies”

  6. Key issues; • Physical properties • mass spectrum, • size, line width, • X factor, X = N(H2)/ W(12CO) uniform? • star formation • Formation and dissipation of GMCs, • Timescales of evolution • Dynamical state, • gravitationally relaxed?

  7. A survey for GMCs in the LMC; • LMC, Large Magellanic Cloud • Irr, 1/10 of the MW in mass • no central dense part • lower metallicity, active star formation (30Dor) • 4kpc x 4kpc • Low resolution 120pc observations with 1.2m telescope • NANTEN 4m telescope, 40pc resolution for the LMC

  8. NANTEN GMC survey in the LMC • Fukui et al. 1999; 2008 • 30000 points in 12CO J=1-0 • 273 GMCs discovered • first sample of GMCs complete for a single galaxy

  9. LMC HI & CO HI by ATCA : Kim et al. (1998), CO by NANTEN: Fukui et al. (2001) Total molecular mass (10% of HI)~ 7×107 M

  10. M33 Correlation with HI Deul & van der Hulst (1987)

  11. Mass Distribution Very Similar Very Similar Mass normalized by an observed area n(>M’)  M^(S+1) LMC -1.74  0.08 IC10 -1.74  0.41 M31 -1.55  0.20 M33 -2.49  0.48 Outer -1.71  0.06 Blitz et al. 2006

  12. X-factor

  13. LMC CO and H Green contour: GMCs by NANTEN Fukui et al. (2008) H by Kim et al. (1999)

  14. 3 Types of GMCs in the LMC O-Starless 44 clouds(32 %) ~ 7 Myr Type I ~ 10 Myr Only HII regions 88 clouds (51 %) Clusters and HII regions 39 clouds (23 %) Only clusters Type II ~ 5 Myr Type III ~ 5 Myr 150 pc

  15. Physical properties among three GMC types Type I Type II Type III

  16. Formation of GMCs • HII cooled down to H2? • Unlikely if see GMCs and HII regions on the LMC • HI becomes denser to H2?

  17. “3-D” comparison of CO and HI in the LMCFukui et al. 2009 • Previous studies: 2D projection and larger spatial averaging, 100pc ~1kpc, e.g., Schmidt law • Present study: local property of star forming GMC and HI at ~50pc scales • X-Y and Velocity: 3-D datacube of CO NANTEN and HI ATCA (Kim et al.2003) • Resolution: 40pc x 1.7 km/s HI CO

  18. HI all HI associated with CO 3-D analysis

  19. Type I Type II Type III イメージ：HI コントア：12CO (コントアレベル １２Kから3.6Kごと)

  20. 1 yx0.8 Log[<Ico> ] [K km/s] 0 +Type I+ Type II Type III -1 2.0 2.4 2.8 Log[<IHI >] [K km/s] HI and GMC relation (3-D)

  21. 3-D Results of CO-HI correlation • GMCs have “HI envelopes” of 100-200pc • HI envelope” grows from Type I to Type III GMCs Ico a IHI (HI intensity = Ts x t) By assuming spin temperature Ts = constant, the HI mass increases from Type I to III • HI filaments of ~ 500pc, birth site of GMC formed by bubbles/spiral density waves • Conversion of HI into H2 on dust grains: timescale ~10^9yrs/n(cm-3)~10Myrs for 100 cm-3

  22. GMC grows by collecting HI [106 Mo per 10 Myr] Mass flow rate; dM/dt~0.1 solar mass/yr dM/dt=4pR2 n(HI) V R~70pc n(HI)~10 cm-3 V~7 km/s HI CO

  23. SMC LMC

  24. M33 Correlation with HI Deul & van der Hulst (1987)

  25. LMC HI & CO HI by ATCA : Kim et al. (1998), CO by NANTEN: Fukui et al. (2001) Total molecular mass (10% of HI)~ 7×107 M

  26. LMC4

  27. The Galactic centre 1 • GMCs in the disk forms and evolves • Under extreme high pressure, the Galactic center, the evolution is significantly different • High velocity dispersion, High temperature, Low active star formation in the MW

  28. Binney et al. 1991 The Galactic centre 2 • Driven by stellar bar potential (Binney et al. 1991) • and/or molecular loops (Fukui et al. 2006) • - Stellar gravitational energy is converted into gas motion by he bar or by the Parker instability

  29. No reasonable definition of a GMC is possible. • GMCs are far from dynamical equilibrium, different regime from disk • Extragalactic GMCs with ALMA will resolve these clouds in galaxies, significantly different size-linewidth relation • e.g., M64, NGC253

  30. Galactic centre magnetic field

  31. Parker instability in the nuclear disk(Machida et al. 2009) left）　Blue surface：　volume rendered image of the gas density Curves：　Floating magnetic loops. Color depicts vertical velocity from minus to plus: blue – white –red. right）　Enlarged figure of the left panel. Curves are same on the left panel.

  32. Galactic magnetic flotation loops Solar loops (TRACE：191Å) Discovery in 2006 40yrs since Parker (1966) Tajima and Shibata 1997

  33. 12CO(J=3-2) observations ASTE CO(J=3-2) -180 - -40 km/s NANTEN CO J= 1-0 Torii et al. 2010b

  34. 12CO(J=3-2)/12CO(J=1-0) ratio：　R3-2/1-0 P-V diagram Color：R3-2/1-0, Contours：ASTE CO(J=3-2)　 High R3-2/1-0 inside the U shape

  35. Broad emission　Spectra LVG analysis カラー：R3-2/1-0, コントア：ASTE CO(J=3-2)　 空間分布図 Ａ • 12CO(J=1-0, 3-2, 4-3, 7-6), 13CO(J=1-0), C18O(J=1-0) • Take 10 km/s average intensities • [12CO]/[13CO] 〜 53 　 (Riquelme 2010) • [12CO]/[C18O] 〜 250 (i.e. Wilson & Matteucci 1992) • [12CO]/[H2] = 1×10-4 • dv/dr= 9.0 km/s/pc • Chi-square minimization B C

  36. LVG analysis – Results – Typically T 〜30-50 K, n〜103 /cm3 Broad emission : > 100 K Magnetic reconnection may offers a possible candidate for the hot and broad gas component.

  37. Jy/beam km/s A B Molecular Loops in Galaxies? ・NGC253 Sakamoto et al. (2006) Same size and resolution with Sakamoto et al. (2006)

  38. ALMA from 2012

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