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

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

3. Giant molecular clouds, GMCs
Size 100 pc
Mass Mo
Linewidth 5-15 km/s
Density cm-3
Temperature 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 Formation and dissipation of GMCs,
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)
What is the hole to filament ratio?
Deul & van der Hulst (1987)

11. Mass Distribution Very Similar
Mass normalized by an observed area
n(>M’)  M^(S+1)
LMC  0.08
IC  0.41
M  0.20
M  0.48
Outer  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 ~ 7 Myr Type I ~ 10 Myr Type II ~ 5 Myr
O-Starless
44 clouds(32 %)
~ 7 Myr
Type I
Only HII regions
88 clouds (51 %)
Clusters and HII regions
39 clouds (23 %)
Only clusters
~ 10 Myr
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? HI becomes denser 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 LMC Fukui 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. 3-D analysis
HI associated with CO
HI all

20. イメージ：HI コントア：12CO (コントアレベル １２Kから3.6Kごと)
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)

22. HI and GMC relation (3-D)
Log[<Ico> ] [K km/s]
2.0
2.4
2.8 -1 1
Log[<IHI >] [K km/s]
+ Type I + Type II Type III
y x0.8

23. 3-D Results of CO-HI correlation
GMCs have “HI envelopes” of pc
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

24. 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

25. SMC　　　　　　　　　　　　　　　　　 LMC

26. M33 Correlation with HI Deul & van der Hulst (1987)
What is the hole to filament ratio?
Deul & van der Hulst (1987)

27. 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

28. LMC4

30. 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

31. Driven by stellar bar potential (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)
Binney et al. 1991
- Stellar gravitational energy is converted into gas motion by he bar or by the Parker instability

32. 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

34. Galactic centre magnetic field

35. 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.

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

37. 12CO(J=3-2) observations ASTE CO(J=3-2) -180 - -40 km/s
NANTEN CO J= 1-0
Torii et al. 2010b

38. 12CO(J=3-2)/12CO(J=1-0) ratio： R3-2/1-0
Color：R3-2/1-0, Contours：ASTE CO(J=3-2)　
P-V diagram
High R3-2/1-0 inside the U shape

39. LVG analysis 12CO(J=1-0, 3-2, 4-3, 7-6), 13CO(J=1-0), C18O(J=1-0)
Broad emission　Spectra
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] 〜 　 (Riquelme 2010)
[12CO]/[C18O] 〜 (i.e. Wilson & Matteucci 1992)
[12CO]/[H2] = 1×10-4
dv/dr= 9.0 km/s/pc
Chi-square minimization B C

40. 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.

41. Molecular Loops in Galaxies?
・NGC253 Sakamoto et al. (2006)
Jy/beam km/s A B
Same size and
resolution with
Sakamoto et al.
(2006)
Now, we have found several molecular loops magnetically floated by the parker instability in the center of the Milky Way.
Of course we have a question on this phenomenon.
If the Milky Way is a typical spiral galaxy, the molecular loops should exist in other distant galaxies.
Here I present an example of nearby nearly edge-on galaxy, NGC 253.
This is a J-Ks image of the NGC 253. Sakamoto et al. (2006) have observed a center of the NGC253 here by 2-1 line of CO and its isotopes.
This is an intensity map of the center region of NGC253 in 12CO(J=2-1).
We can see a gas condensation similar to the center of the Milky Way like this.
This is a smoothed map of the loop 1 and loop2.
If the loop 1 and 2 are located in the NGC 253, In the observation of Sakamoto et al. (2006) by using SMA these loops can be seen like this while the transition is different.
Sakamoto et al. (2006) argued that here and here there are super bubbles.
I call this A and this B.

42. ALMA from 2012