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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 The Gaseous Universe Oxford, 21-23 July 2010
Lecture 3Giant molecular clouds, GMCs Sub-mm/mm astrophysics: How to probe molecular gas
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
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)
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”
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?
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
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
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
M33 Correlation with HI Deul & van der Hulst (1987)
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
LMC CO and H Green contour: GMCs by NANTEN Fukui et al. (2008) H by Kim et al. (1999)
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
Physical properties among three GMC types Type I Type II Type III
Formation of GMCs • HII cooled down to H2? • Unlikely if see GMCs and HII regions on the LMC • HI becomes denser to H2?
“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
HI all HI associated with CO 3-D analysis
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)
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)
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
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
M33 Correlation with HI Deul & van der Hulst (1987)
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
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
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
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
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.
Galactic magnetic flotation loops Solar loops (TRACE:191Å) Discovery in 2006 40yrs since Parker (1966) Tajima and Shibata 1997
12CO(J=3-2) observations ASTE CO(J=3-2) -180 - -40 km/s NANTEN CO J= 1-0 Torii et al. 2010b
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
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
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.
Jy/beam km/s A B Molecular Loops in Galaxies? ・NGC253 Sakamoto et al. (2006) Same size and resolution with Sakamoto et al. (2006)