Observations of OH+ and H2O+ Across the Galaxy with Herschel

Nick Indriolo1, David Neufeld1, Maryvonne Gerin2,

& PRISMAS consortium1 – Johns Hopkins University2 – LERMA, CNRS, Observatoire de Paris & ENS

June 20, 201267th International Symposium on

Molecular SpectroscopyWH05

What is PRISMAS?

• PRobing InterStellar Molecules with Absorption line Studies

• Herschel guaranteed time key program headed by Maryvonne Gerin

• Uses H II regions as background THz sources to probe intervening clouds for rotational transitions of small moleclues

PRISMAS sight lines

Oxygen Chemistry

• CR + H H+ + e- + CR'• H+ + O O+ + H• O+ + H2 OH+ + H

• OH+ + H2 H2O+ + H

• H2O+ + H2 H3O+ + H

• OH+ + e- products• H2O+ + e- products

• H3O+ + e- products

• O+ + H H+ + O• H+ + e- H + hν

OH+H2

H2O+

H2H3O+

CRH H

+

OO+

H2

H e- e-e-e-

H2 Fraction & Ionization Rate

OH+ + H2 H2O+ + H2 H2O+ + e-

CR + H OH+ + H2 OH+ + e-

OH+ Transitions

N=0

N=1

J=1

J=1

J=2

J=0

F=3/2F=1/2

F=3/2

F=1/2

F=1/2

F=3/2

F=5/2

909

GH

z

971

GH

z

103

3 G

Hz

OH+ Observations

H2O+ Transitions

Schilke et al. 2010 A&A, 521, L11 Bruderer et al 2010 A&A, 521, L44

ortho-H2O+ Observations

para-H2O+ toward W51

W49N Profile Fitting

Neufeld et al. 2010 A&A, 521, L10

Determining Column Densities

W49N Results

vLSR Δv N(OH+) N(H2O+)

(km/s)

(km/s)

(1013 cm-

2)(1013 cm-2)

6.6 5.1 2.9 0.42

13.4 4.6 2.2 0.69

21.2 7.0 8.2 0.56

34.7 9.0 26.1 2.68

43.5 8.4 7.5 0.72

62.5 13.3 18.9 1.67

fH2

0.049

0.126

0.021

0.033

0.031

0.028

N(H)

(1021 cm-

2)

...

...

...

6.95

7.23

εζH

(10-17 s-

1)

...

...

...

4.28

2.19Neufeld et al. 2010 A&A, 521, L10

Assume ε=0.1

Preliminary Ionization Rates

Δv ζH σ(ζH)

(km/s) (10-16 s-1) (10-16 s-1)

30—50 4.28 2.14

50—80 2.19 1.10

-2.5—7 3.36 1.68

7—20 1.64 0.82

20—34 0.19 0.10

0—11 2.10 1.05

11—17 1.48 0.74

42—55 1.31 0.66

55—75 0.47 0.24

W49N

G34.3+0.1

W51

Distribution of Ionization Rates

Probability Density Function

Cumulative Distribution Function

Indriolo & McCall 2012 ApJ, 745, 91

Future Work

• Continue analyzing OH+, o-H2O+, p-H2O+, and H3O+ spectra from PRISMAS

• Add OH+ and o-H2O+ observations from the WISH program to our sample

• Utilize new JVLA observations of H I in inferring ionization rates

• Map ζH as a function of position in the Galaxy