AND HIGH H2 IONIZATION RATE CENTRAL 300 PC OF THE GALAXY PROBED BY THE INFRARED SPECTRA OF H3+ AND CO I. PREDOMINANCE OF WARM AND DIFFUSE GAS AND HIGH H2 IONIZATION RATE Takeshi Oka, Department of Astronomy and Astrophysics and Department of Chemistry, University of Chicago, Chicago, IL Tom Geballe, Gemini Observatory, Hilo, HI Miwa Goto, Centre for Astrochemical Studies, Max Planck Institute of Extraterrestrial Physics, Garching, Germany Tomonori Usuda, National Astronomical Observatory of Japan Nick Indriolo, Department of Astronomy, University of Michigan, Ann Arbor, MI 71st International Symposium on Molecular Spectroscopy University of Illinois Urbana, Champaign, June 22, 2016

The Central Molecular Zone (CMZ) The treasure house of H3+ Geballe, Phil. Trans. Roy. Soc. Lond. (2000) D CMZ ~ 10-2DGalaxy VCMZ ≤ 10-5 VGalaxy NCMZ ~ 10-1NGalaxy CMZ 300 pc Mezger, Duschl, Zylka, A&AR 7, 289 (1996)

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

H3+ probes deep into the Central Molecular Zone Depth meter

CMZ is not as opaque as previously thought Morris & Serabyn, ARA&A 1996 N = n f R ≥ (104 cm-3)(0.1)(150 pc) = 4.6 × 1023 cm-2 ~ N(H2) 5 × 1019 cm-2 ~ N(CO) Sgr E Sgr C Star N(CO) % α 0.22 0.04 β 0.01 γ 0.08 0.02 δ 0.13 0.03 IRS21 0.05 IRS3 0.25 IRS16NE 0.15 IRS1W 0.28 0.06 NHS21 NHS22 NHS42 0.07 NHS25 η GCS3-2 GCS4 FMM362 0.11 θ ι 2.7 0.54 Sgr A Sgr B

Warm (T ~ 250 K) and Diffuse (n < 100 K) Gas H3+ Thermometer Densitometer

High cosmic ray ionization rate H3+ production: H2 → H2+ + e̶ H2+ + H2 → H + H3+ 𝑓 H 2 = 2𝑛( H 2 ) 𝑛(H) + 2𝑛( H 2 ) dilution: H2+ + H → H2 + H+　　　　 H3+ destruction: H3+ + e̶ → H + H + H, H2 + H 1.6×10-4 8×10-8 cm3 s-1 3 H3+ Dosimeter (2‒6) ×1015 cm-2 < (2/3)2 > (4 ‒ 12) ×105 cm s-1 For L = 150 pc ζ > (1 ‒ 3) × 10-15 s-1 ζ = (1 ‒ 11) × 10-14 s-1 Le Petit, Ruaud, Bron, Godard, Roueff, Languignon, Le Bourlot, A&A, 585 (2016)

High L ‒ high volume filling factor High velocity dispersion Saturation with ζ Le Petit, Ruaud, Bron, Godard, Roueff, Languignon, Le Bourlot, A&A, 585 (2016)

Conclusions Corollary Low volume filling factor of dense clouds f ≥ 0.1 → f < 0.01 Agrees with AV ~ 20 ‒ 40 Cotera et al. (2000), Schultheis et al. (2009) Predominance of warm (T ~ 250 K) diffuse (n < 100 cm-3) gas f ≥ 0.5 High cosmic ray ionization rate of H2 ζ ~ 5 × 10-15 s-1 Corollary Molecular mass in dense clouds ~ diffuse clouds ~ 107 M X-ray emitting ultrahot (T ~ 108 K) does not exist

High Ionization Rate: ζ ~ 5 × 10=15 s-1 1.6×10-4 8×10-8 cm3 s-1 3 (2‒6) ×1015 cm-2 < (2/3)2 > (4 ‒ 12) ×105 cm s-1 For L = 150 pc ζ > (1 ‒ 3) × 10-15 s-1 From X-rays and γ-rays ζ ~ 5 × 10-13 s-1 Yusef-Zadeh, Muno, Wardle, Lis, ApJ 656, 847 (2007) ζ ~ 1 × 10-13 s-1 Tatischeff, Decourschelle, Maurin, A&A 546, 88 (2012) ζ ~ 5 × 10-15 s-1 Yusef-Zadeh, Hewitt, Wardle, Tatischeff, Robert, Cotton, Uchiyama, Nobukawa, Tsuru, Heinke, Royster, ApJ