Thermalization of interstellar CO

Takeshi Oka

Department of Astronomy and Astrophysics and Department of ChemistryThe Enrico Fermi Institute, University of Chicago

Han Xiao and Phillip Lynch Department of Statistics, University of Chicago

OSU international symposium on molecular spectroscopy, June 24, 2009

Tomoharu Oka

Department of Physics, Keio University

: in diffuse clouds near the Galactic center

CO toward the Galactic center

Christian Andreas Doppler 1803-1853

(3,3) metastable

(1,1) ground

CO H3+

Oka, Geballe, Goto, Usuda, McCall, ApJ 632, 882 (2005)

CO

GC 14 % 76 %Spiral arms 86 % 24 %

H3+

IR absorption versus Radio CO emission

NHS 25

NHS 42

IRS1W

μ0 = 0.112 Debye

μ1-0 = 0.106 Debye

μ2-0 = 0.0093 Debye

150

1

Optical depth τ ∝ μ2n(CO)

GCS3-2

Critical density J = 1 → 0 700 cm-3

J = 3 → 2 3 × 104 cm-3

Radiation trapping

Wλ → N(CO)

J

7

6

5

3

4

210

Radiative processes

B = 57635.9687 MHz ≅ 2.766 K μ = 0.112 D

4 32

3

1 64

3ij ijAt hc

7.40 e-8 5.2 months

6.36 e-6 1.8 days

2.58 e-6 4.5 days

7.15 e-7 16 days

3.58 e-5 7.8 hours

2.23 e-5 12 hours

1.27 e-5 22 hours

)()( lulululu BnBAn

1

1

1

11

//

kThl

uullkThulu eg

gAn

eAn

1

1

12

32

1

11

/)1(2,1/)1(2,11

TJBJJJTJBJJJ eJ

JAn

eAn

T = 2.725 K

0.1512 J = 1 → 0 0.45360.0058 J = 2 → 1 0.0092

Collisional and radiative processes

' '

'

2 1exp( )

2 ' 1J J J J

J J

k E EJ

k J kT

Detailed balance

Steady State

1/21,/21,/)1(2,11/)1(2,1 1

1

12

12

1

11

1

1

12

32

1

11

JTBJJJJTBJJJTJBJJJTJBJJ n

eJ

JAn

eA

eJ

JAn

eA

0dt

dnJ

'

',',' 2J

HJJJJJJ nnknk

Green & Chapman, ApJS 37, 169 (1978)

D. R. Flower, J. Phys. B: At. Mol. Opt. Phys. 34, 2731 (2001)

Wernli, Valiron, Faure, Wiesenfeld, Jankowski, Swalewicz, A&A, 446, 367 (2006)

Schöier, van der Tak, van Dishoeck, Black, A&A 432, 369 (2005) LAMDA

Yang, Stancil, Balakrishnan, Forrey, J. Chem. Phys. 124, 104304 (2006)

CO J’

CO J

H2

H2

Polynomial fitting is dangerous

Cubic spline FMM

n(1)/n(0)

Some combinations are not usefuln(1)/n(0) n(2)/n(0)

Some combinations are more useful

n(1)/n(0) n(3)/n(2)

Spiral arms

Galactic C.

Radio CO, CS, HCN, CH emission

H3+ IR abs.

Understanding a monster

X-ray γ-ray

HII regionRadio recomb.Fine structure

Radio continuum

H2 FIRH2 IR emission

CO IR abs

Near IR, FIRDust emission