OBSERVATIONS OF INTERSTELLAR HYDROGEN FLUORIDE AND HYDROGEN CHLORIDE

OBSERVATIONS OF INTERSTELLAR HYDROGEN FLUORIDE AND HYDROGEN CHLORIDE IN THE GALAXY Raquel R. Monje Darek C. Lis, Thomas Phillips, Paul F. Goldsmith Martin Emprechtinger, David Neufeld and Maryvonne Gerin

The Unique Thermochemistry of Fluorine and Chlorine • Fluorine, with IP > IP(H), D 0(HX) > D 0(H 2). Fluorine is predominantly neutral in the diffuse ISM, and can react exothermically with H 2 and HF. • Chlorine, with IP < IP(H), D 0(HX) < D 0(H 2) and D 0(HX+) > D 0(H 2). Chlorine is predominantly ionized in atomic clouds. Cl+ can react exothermically with H 2 to form HCl+

The HCl Chemistry • Once ionized Cl+ reacts with molecular hydrogen exothermically to form HCl+, a process that initiates the chemical reactions of chlorine. • In cloud interiors, atomic chlorine is mostly neutral, not ionized, so that the reaction of Cl and H 3+ drives the formation of H 2 Cl+, which then reacts with CO and H 2 O leading to the formation of HCl. • An alternative direct route to HCl in either hot gas or regions where vibrationally excited H 2 is abundant is the Cl+H 2 ->HCl+H reaction. • The destruction of HCl is dominated both by photoionization and photodissociation and by reactions with C+ and H 3+.

Source D (kpc) W 49 N 11. 5 W 31 C 4. 8 Sgr. A(+50 km/s cloud) 8. 6 W 28 A 3. 8 G 34. 3+0. 1 3. 8 W 51 7 W 33 A 4 DR 21(OH) 1. 0

HCl toward DR 21(OH) Intensity ration of 2. 7: 3: 2 (Optically thin 1: 2: 3) (Optically thick 1: 1: 1) Results from an initial LTE model: • Q= 10”, Tex =40 K, • Ntot= 3. 0 x 1014 cm-2, • DV=4 km/s, VLSR=-4 km/s • [H 35 Cl/H 37 Cl] ratio of 2. 7 (3. 1 the solar isotopic abundance)

HCl toward W 31 C Absorption by foreground in the VLSR range 15 -50 km/s self absorption feature at VLSR =-1 km/s Neufeld et al, 2010, 518, L 108

HCl toward W 31 C: The Foreground Decomposition of the Hyperfine components HFS fit + subtraction of absorption VLSR N(HCl) HCl/H 2 a 20 - 25 1. 5 x 1013 5. 42 x 10 -9 25 – 35 2. 6 x 1013 3. 52 x 10 -9 35 - 45 3. 1 x 1013 5. 64 x 10 -9 a. H column densities derived from CH observations, Gerin et al. 2010, assuming N(CH) = 3. 5 x 10 -8 N(H 2). 2 Courtesy of B. Godard’s Code

HCl toward W 49 N Self absorption from the envelope Outflows? Emission from other lines?

HCl toward Sgr. A+50 km/s cloud Hyperfine decomposition [H 35 Cl/H 37 Cl] ratio of 2. 66 Ntot= 7. 17 x 1014 cm-2

HCl toward W 33 A

HF in the ISM • Fluorine is the only atom that can react exothermically with H 2 to form a diatomic hydride: F + H 2 → HF + H +1. 4 e. V • HF is destroyed very slowly by means of cosmic ray-induced photodissociation and as a result of reactions with species of low abundances such as He+, H 3+, and C+. • HF is expected to be the dominant reservoir of gas-phase fluorine. N(HF)/N(H 2) ~ 3. 6 x 10 -8 • HF may be used as a valuable surrogate tracer for molecular hydrogen within diffuse interstellar medium, both in the Milky Way and other galaxies.

W 31 C Sgr A+50 Sgr B 2(M) W 49 W 51 Sgr B 2(N) Orion KL NGC 6334 I NGC 6634 I

Toward the Galactic center Sgr A+50 km/s Sgr B 2(M) Sonnentrucker et al. in preparation Monje et al. 2011, Apj, 734, L 23

Estimates of the HF/H 2 ratio VLSR km s-1 N(HF) x 1013 cm-2 HF/H 2 x 10 -8 Sgr B 2(M)a -115 – -60 -53 – -49 -35 – -28 -10 – -5 26 – 40 9. 9 1. 1 1. 3 1. 01 1. 7 1. 5 1. 4 1. 1 30 – 50 50 – 78 67 – 71 55 69 5. 6 1. 5 1. 1 1. 3 0 – 10 10 – 20 20 – 30 42 – 47 14. 5 1. 8 0. 8 8. 0 1. 4 1. 3 >1. 2 1. 6 3 – 13 25 – 35 45 – 50 1. 5 1. 2 2. 2 1. 6 1. 3 2. 5 W 49 N b W 51 b G 34 b a. H Sgr B 2(M) W 49 N W 51 G 34 3 N(HF)/N(H 2) x 10 -8 Object 2. 5 2 1. 5 1 0. 5 0 -200 -100 v. LSR (km s-1) column densities derived from 13 CO assuming CO abundances of 3 x 10 -5 N(H 2) (Sonnentucker 2005). b. H column densities derived from CH observations, Gerin et al. 2010, assuming N(CH) = 3. 5 x 10 -8 N(H ). 2 2 2 0 100

Conclusions • Observations of H 35 Cl and H 37 Cl, and accurate measurements of the 35 Cl/37 Cl ratio in different environments, will provide some insight into the chemical evolution of both isotopes, thus into Galactic chemical evolution. • Firs detection of HCl in diffuse medium toward the line-of-sight of W 31 C. • One key result from Herschel/HIFI is the ubiquitous nature of hydrogen fluoride within the interstellar medium of the Milky Way. • The HF abundances of 1 -2 x 10 -8 under a wide variety of interstellar conditions are consistent with the chemical models. • HF shows good promise as a tracer of H 2.

HCl in the ISM • HCl is the most abundant Cl-bearing molecule in dense clouds. • Both 35 CL and 37 CL nuclei are believed to form in the last burning stages of massive stars (>10 Msun) and by means of “explosive nucleosynthesis” during supernovae detonation. • Observations of H 35 Cl and H 37 Cl, and accurate measurements of the 35 Cl/37 Cl ratio in different environments, can provide some insight into the chemical evolution of both isotopes, thus into Galactic chemical evolution

HF in the ISM - A brief history - ISO Neufeld et al. 1997, 488, L 141 • First detection of interstellar HF J 2 -1. • Towards Sgr B 2 using LWS on ISO. • HF abundances of ~ 3 x 10 -10.

Extraordinary Source: Orion KL HF/H lower limit ~ 1. 6 x 10 -10 Phillips et al. 2010, A&A, 518, 109

Extragalactic HF Mrk 231 with SPIRE Cloverleaf: QSO at z = 2. 56 HF J = 1 -0 detection with the CSO with after ~10 hr Monje, Phillips, Peng et al. in preparation van der Werf et al. 2010, A&A, 518, L 42