MODIFICATIONS OF THE RELATION BETWEEN COSMIC RAY IONIZATION RATE ζ AND H3+ DENSITY TAKESHI OKA, Department of Astronomy & Astrophysics and Department of Chemistry, The Enrico Fermi Institute, University of Chicago, Chicago, IL, USA June 20, 2017, 72nd ISMS, UIUC

ne= nC In-situ chemical measurement of ionization rate ζ → cosmic ray flux Simple H3+ chemistry p C.R. H2 → H2+ + e̶ H2+ + H2 → H + H3+ H3+ + e̶ → H + H + H ζ ~ 10-17 s-1 kLn(H2) ~ 10-7 s-1 kene~ 10-9 s-1 3 × 109 years 4 months 30 years ζn(H2) = ken(H3+)ne ne= nC ζLn(H2) = keN(H3+)ne ζL= keN(H3+)[ne /n(H2)]

Ups and downs of ζ ups 10-17 s-1 H3+ 10-16 s-1 10-15 s-1 10-14 s-1 1961 Hayakawa et al. ζH = 4 × 10-16 s-1 1968 Spitzer & Tomasko ζH= 6.8 × 10-18 s-1 1.2 × 10-15 s-1 1978 Hartquist, Black, Dalgarno ζH= 1.5 × 10-17 s-1 (ζ Oph) 2.2 × 10-17 s-1 (ζ Per) 10-17 s-1 1986 van Dishoeck & Black, ζH= 7 × 10-17 s-1 H3+ 1998 Webber ζH = (3 – 4) × 10-17 s-1 2000 van der Tak & van Dishoeck ζ = 2.6 × 10-17 s-1 10-16 s-1 2003 McCall et al. ζL 40 times higher ζ = 5.55 × 10-16 s-1 (ζ Per) 10-15 s-1 2005 Oka et al. ζ ~ 3 × 10-15 s-1 (Galactic center) 2008 NSF panel “The panel was skeptical about some of the ideas in the proposal. For instance, his estimates of the cosmic ray ionization rates in the Galactic center are unusually high compared to elsewhere in the ISM” 2011 Amo-Baladrón et al. “our values do not support the high ionization rate derived by Oka et al. (2005)” 2007 Yusef-Zadeh et al. ζ ~ 2 × 10-14 s-1 (Sgr B) ζ ~ 5 × 10-13 s-1 (Sgr C) 2013 Yusef-Zadeh et al. ζ ~ (1 – 10) × 10-15 s-1 (Central 300 pc) 2011 Becker, Black et al. ζ ~ 4.5 × 10-12 s-1 10-14 s-1 2016 Le Petit et al. ζ ~ (1 – 11) × 10-14 s-1 (Galactic center)

Two new effects 1) Decrease of H3+ production by H2+ + H → H2 + H+ H2 → H2+ + e̶ H2+ + H2 → H + H3+ H3+ + e̶ → H + H + H e̶ H2+ + H → H2 + H+ + 1.83 eV Indriolo, McCall 2012 ζn(H2) = ζnHf(H2)/2 → ζnH[f(H2)]2/2 f(H2) = 0.6 Increase of H3+ destruction by ionization of H2 and H ken(H3+)ne ne = (nC/nH)SVRnH + ne C H2 H

Self-consistent solution of ζ ζL = 2keN(H3+)(nC/nH)SVR/f(H2) N(H3+)/L = n(H3+) N(H3+) = 3 × 1015 cm-2 ke = 7.67 × 10-8 cm3 s-1, kr = 5.0 × 10-12 cm3 s-1 (nC/nH)SVR = 4.8 × 10-4, f(H2) = 0.6

Estimating ζ and L

Summary ζ ~ 2 × 10-14 s-1 Cosmic ray flux in the CMZ 1000 times higher than that in S.V. *If the equipartition is assumed magnetic field ~ 100 μG L ~ 100 pc, f = 2/3 The warm (T ~ 250 K) and diffuse (n ~ 50 cm-3) dominates the CMZ *CMZ not as opaque as thought. n ≥ 104 cm-3, f ≥ 0.1 → AV ≥ 500 *The ultra-hot (108 K) X-ray emitting plasma does not exist. Chemistry nH = n(H) + 2n(H2) ~ 70 cm-3, n = n(H) + n(H2) ~ 50 cm-3, n(H2) ~ 20 cm-3, n(H) ~ 30 cm-3, n(H3+) ~ 1 × 10-5 cm-3, n(H+) ~ ne ~ 0.30 cm-3, ne ~ 0.33 cm-3. Morphology and dynamics Part II Stay tuned Oka, Geballe, Goto, Usuda, McCall, Indriolo Part I

Bright dust-embedded stars with smooth continuum c GCS3-2 Oka et al. (2005) 8 stars Goto et al. (2008) Geballe Oka (2010)