arXiv:1304.2842 OBSERVATIONS AND ANALYSIS OF EXTENDED TAIL TOWARD RED (ETR) IN THE DIFFUSE INTERSTELLAR BANDS (DIBs) OF HERSCHEL 36 arXiv:1304.2842 Takeshi Oka, Daniel E. Welty, Sean Johnson, Donald G. York, Julie Dahlstrom, and Lew Hobbs Department of Astronomy and Astrophysics, University of Chicago June 20, 2013, Columbus Meeting

Spectra toward two Stars in M8: d ~ 1.5 kpc Tr ~ 2.7 K Tr >> 2.7 K 9 Sgr Herschel 36 > 200 Ordinary Extraordinary E(B – V) = 0.33 0.87

Direct Evidence Tr=14.6 K, CH+ High radiative Temperature, Tr=14.6 K CH+ Direct Evidence Tr=14.6 K, CH+ 9 Sgr Her 36 CH+ CH 120.3 K 2 μ = 1.7 Debye A = 0.0065 s-1 τ = 150 s ncrit ~ 3 × 106 cm-3 Tex = 14.6 K = Tr 40.1 K 1

AV ~ 6 AV ~ 4 Goto, Stecklum, Linz, Feldt, Henning, Pascucci, Usuda, ApJ, 649, 299, 2006

Spectacular Effect of high Tr on DIBs 30 2 20 1 Huge difference 10 Huge Effect Many J levels are radiatively pumped Sharp contrast Polar non-polar CH+ B = 417.7 GHz μ = 1.7 D HCCCCCN B = 1.3 GHz μ = 4.33 D Spectroscopically makes sense!

Spectroscopically makes sense Extended Tail toward Red (ETR) R(J) J + 1 ← J ν = ν0 + 2B’(J + 1) + (B’ – B)J(J + 1) Q(J) J ← J ν = ν0 + (B’ – B)J(J + 1) P(J) J ˗ 1 ← J ν = ν0 – 2B’J + (B’ – B)J(J + 1) B’ < B HCCCCCN HCCCCCN

The Crucial Parameter β = (B’ – B)/B HC3N μ = 3.6 Debye HC5N μ = 4.3 Debye HC9N μ = 5.6 Debye C8H- μ = 11.9 Debye

Rotational Distribution at high Tr Collision dominated Radiation and collision , Einstein 1916 Goldreich & Kwan 1974 Principle of Detailed Balancing Boltzmann, 1872 H-theorem Wiener Berichte 66, 275

Calculated Rotational Distribution n(J)

Spectral Simulation Radiation dominated Collision dominated T = 2.73 K

Comparison of Simulated ETR with Observed Tr, Tk, B, μ, C, β, Γ DIBs CH+ CH Her 36 Her 36 SE

Other possible mechanisms Linear molecules J B’ – B μ General molecules J, Ka, Kc A’ – A, B’ – B, C’ – C μa, μb, μc Special group of molecules: Non-linear ← linear CH2 (B3Σu- - X3B1), HCO (A2Π – XA’) and NO2 (E2Σu+ - X2A1) A’ – A = A’ 100 % Vibrational excitation?

Conclusions Firm conclusions Likely conclusions λ5780.5, λ5797.1, and λ6613.6, which show strong ETR are due to polar molecules. Non-polar molecules such as carbon chains (Cn) or symmetric hydrocarbon chains (HCnH, H2CnH2, NCnN, etc.), symmetric PAHs (benzene, pyrene, coronene, ovalene etc.), or C60, C70 etc. and their cations and anions cannot be the carriers of those DIBs. Likely conclusions λ5849.8, λ 6196.0, and λ6379.3 which do not show strong ETR are Most likely due to non-polar molecules. Carriers of λ5780.5, λ5797.1, and λ6613.6, which show strong ETR are probably not very large, otherwise β is too small.

I am scared High column density 1014 cm-2 CH2CC P. Thaddeus, M. C. McCarthy, Spectrochimica Acta A, 57, 757 (2001)

Herschel 36 Trad >> 2.73 K Kinetic temperature Tk Collision Maxwell 1860 Phil. Mag. 4, 19 α2 = 2kTk/m Radiative temperature Tr Radiation Planck 1901 Ann. d. Physik 4, 564 θ = Tr Excitation temperature Tex Observed Boltzmann 1871 Wiener Berichte 63, 712 If Tk = Tr, thermal, Boltzmann Tex = Tk = Tr Tk > Tr, collision dominated thermal Tex = Tk radiation dominated thermal Tex = Tr intermediate non-thermal −∞ < Tex < ∞ CH+, CH, CN DIBs