The Distribution, Excitation, and Abundance of C +, CH +, and CH in Orion KL Harshal Gupta, 1 Patrick W. Morris, 1 Zsofia Nagy, 2 John C. Pearson, 3 Volker Ossenkopf, 4 and the HEXOS Team 1 IPAC-Caltech, USA; 2 U. Toledo, Toledo, OH; 3 JPL-Caltech, USA; 4 Universität Zu Köln, DE Herschel-HIFI observations of EXtraordinary sources: the Orion and Sagittarius B2 star-forming regions (PI: E. A. Bergin)

Fundamental Molecule, Fundamental Problem C+C+ C CH + CH 2 + CH 3 + CH CH 2 h /H + H2H2 H3+H3+ e-e- H2H2 H2H2 e-e- e-e- CH 3 H3+H3+ H3+H3+ e - /H H2H2 H2H2 H2H2 C + + H 2 CH + + H 4640 K  [CH + ] 10 2 – 10 3 x predicted by steady-state chemistry!  Simplest C-bearing molecule  ID’d 70+ y ago in diffuse clouds (Douglas & Herzberg 1941)

What drives CH + formation in space? C + + H 2 CH + + H 4640 K  Shocks?  Elitzur & Watson (1978); Draine & Katz (1986)  Dissipation of turbulence?  Diffuse ISM (e.g. Godard et al. 2009)  Vibrationally excited H 2 (v = 1; E/k = 5986 K)? Dense PDRs: e.g., Orion Bar ☞ All may need to be examined in Orion KL … Nagy et al. 2013, A&A 550 A96

Orion KL Environment Bar Trapezium  1 Ori C BN IRc 2 12 .227 .3 Zapata et al A&A Boonman et al. 2003

HIFI C +, CH +, and CH Maps of Orion CH + J = 1 – 0 C + 2 P 3/2 – 2 P 1/2 CH + J = 2 – 1 CH ( 2  1/2 ; 2  3/2 ) Contours: CH + J = Fields: OTF: position-switched/ load-chopped/ DBS raster

C+C+ = 1.3; and 2.1 at pk A [For 12 C/ 13 C = 67 and obs. I( 12 C + )/I( 13 C + )] N( 12 C + ) = (2 – 11) x cm -2 (T ex = 200 K) ~ to Orion Bar PDR (Ossenkopf et al 2012). A B C D E F Highly structured emission Up to 5 components > 3σ = 9.3 km/s Δv = 4.6 km/s Outflow 13 C +

Excitation LTE analysis: T rot = 25 – 35 K N(CH + ) ≅ few cm -2 Statistical equilibrium incl. PACS lines through J = 5 – 4: N(CH + ) = (1 – 3) x cm -2 CH + Velocity Structure Δv = 4 – 7 km/s; V LSR = 7 – 10 km/s A B C D E F

CH Velocity Structure Δv and V LSR ~ CH + Excitation LTE at T rot = 35 K N(CH) ≅ 2 x cm -2 From [CH]/[H 2 ] = 3.5 x (Sheffer et al. 2008), N(H 2 )~(5-12) x cm -2 Distribution Peaks closest to BN/KL; E – W: C + - CH + - CH

2-sided illumn.  front  10 3  back  =2x s -1 Isobaric PDR models of CH + Orion Bar (Nagy et al. 2013, A&A, 550, A96) Similar parameters to Orion Bar:  2 P/k    N(CH + ) ~ 2 x cm -2 Orion KL (Morris et al. in prep.) Includes key CH + reactions [ Meudon PDR code v (Le Petit et al. 2006) ]

RADEX models of CH+ Orion Bar: n(H 2 ) = 10 5 cm -3 ; T = 500 K; n(e - ) = 10 cm -3 ; N(CH + ) = 9 x cm -2 (Nagy et al. 2013, A&A 550 A96) Orion KL: n(H 2 ) = 5 x 10 5 cm -3 ; T = 500 K; n(e - ) = 10 cm -3 ; N(CH + ) = x cm -2 (Morris et al. in prep.) N(CH + ) consistent with PDR model T bg raises I of lowest 3 transitions 10 – 50 %

PDR model abundances Orion Bar (Nagy et al. 2013, A&A, 550, A96) Orion KL (Morris et al. in prep.) [CH + ] rises and[H 2 (v=1)] falls at PDR surface

CH + shows little overlap with shock-excited H 2 ! Red = CH + (J = 1 – 0) Green = H 2 [v = 1 – 0; S(1)] 2.12  m (Bally et al. 2011; APO 3.5m) CH + and H 2 (v = 1 )

CH + Production What supplies H 2 (v ≥ 1)?  Shocks? But CH + unassociated with H 2 outflow  UV field sets r 21 =I v=1–0 /I v=2–1 of S(1) H 2 emission lines (Sternberg & Dalgarno 1989) Timescale:  Net [CH + ] ~ 0.02 cm -3 in 50 y << 500 – 1000 y outflow Radiative; n ≤ 10 4 cm -3 Collisional; n > 10 4 cm -3 Thermal; n > 10 4 cm -3 Weak χ Strong χ r 21 ~ 3: “interclump medium” of Orion Bar PDR (van der Werf et al. 1996) r 21 ~ 8: T ~ 2000 K, n ≥ 10 5 cm -3 in Orion Bar r 21 ~ 10 in Orion KL (Beckwith et al. 1978)

Summary & Conclusions  High-resolution maps of C +, CH +, and CH in Orion KL  UV rather than shocks probably yields CH +  Little overlap between CH + and shocked H 2  PDR and RADEX models agree well with observations  Production timescale (50 y) << outflow age (500 – 1000 y)  Future work:  Shock + UV models  Other molecules with highly endothermic formation, e.g., SH + requires K; H 2 (v = 2; K )  Orion Bar with HIFI (Nagy et al. 2013) and APEX (Müller et al. 2014); Orion KL with APEX (Gupta et al. in progress)

Hydride Thermochemistry: IP and D 0 Neufeld & Wolfire (2009) IP > IP(H) D 0 (HX) < D 0 (H 2 ) D 0 (HX + ) > D 0 (H 2 ) IP < IP(H) D 0 (HX) < D 0 (H 2 ) D 0 (HX + ) < D 0 (H 2 ) IP > IP(H) D 0 (HX) > D 0 (H 2 ) IP < IP(H) D 0 (HX) < D 0 (H 2 ) D 0 (HX + ) > D 0 (H 2 ) Neutral CR-driven High T Ionized UV-driven High T Neutral Exothermic Ionized UV-driven Exothermic IP(X) > IP(H) IP(X) < IP(H) D 0 (H 2 )