A NEW INTERSTELLAR MODEL FOR HIGH-TEMPERATURE TIME-DEPENDENT KINETICS Nanase Harada Eric Herbst The Ohio State University June 24, 2006 International Symposium on Molecular Spectroscopy

Motivation Accretion disk around AGNs High-temperature High-density Radiation, cosmic-rays, etc…. Active galactic nucleus (AGN) : Central region of a galaxy with very high luminosity, which is believed to be caused by a supermassive blackhole

Chemical Abundance Calculation Thermodynamic equilibrium – - High-temperature, high-density – (ex. stellar atmosphere) Kinetics – - Low-temperature, low-density (ex. cold dense cloud) – Time-dependent – Time-independent ∆ k=αexp(- Ea/kT)

High-Temperature Kinetics Model Addition and modification to the model: Reactions with high activation energy Endothermic reactions Temperature-dependence of H 2 formation on dust grains Addition of reactions with H 2 O, NH 3, etc Additional protonation reactions of ions

Hydrogenation of C, N, O, and CN More abundant H 2 O, NH 3, CH 4, and HCN O H2OH2OOH CN HCN Hydrogenation reactions with barriers: rate k = α exp(- Ea/kT) Ea = 820 K Ea = 3140 K Ea = 1040 K H2H2 H2H2 H2H2 T = 100 K T = 800 K n = 10 4 cm -3

Making Hydrocarbons Production of C 2 H 2 (diagram by Agundez et al. 2008) C 2 H 2 has been seen in protoplanetary disks (Carr and Najita 2008), and ultra-luminous infrared galaxies (ULIRGs) (Lahuis et al. 2007) Efficient production of carbon-chains by effective carbon- rich condition. ([C]/[O]>1)

Making Hydrocarbons? Production of C 2 H 2 (diagram by Agundez et al. 2008) C3HC3H C4HC4H C5HC5H C2H3C2H3 C3H2C3H2 C4H2C4H2 C5H2C5H2 C3H3C3H3 C4H3C4H3 C5H3C5H3 H2H2 C C H2H2

Making Hydrocarbons? T = 800 K n = 10 4 cm -3

Abundances of Positive Ions HCO + + H 2 O → CO + H 3 O + H 3 O + can take over the dominant form of ions 800 K 100 K n = 10 4 cm -3

Application - AGN Accretion Disk ~ 10 9 (r/pc) -3 cm -3 T ~ 1000 (r/pc) -0.5 K radio jet molecular torus / disk ~ 100s pc

Application - AGN Accretion Disk ~ 10 9 (r/pc) -3 cm -3 T ~ 1000 (r/pc) -0.5 K radio jet molecular torus / disk ~ 100s pc radiation (X-ray)

Application - AGN Accretion Disk ~ 10 9 (r/pc) -3 cm -3 T ~ 1000 (r/pc) -0.5 K radio jet molecular torus / disk ~ 100s pc radiation (X-ray) Star formation →Supernovae→ Cosmic-ray → UV-photons

Application - AGN Accretion Disk ~ 10 9 (r/pc) -3 cm -3 T ~ 1000 (r/pc) -0.5 K radio jet molecular torus / disk ~ 100s pc radiation (X-ray) Star formation →Supernovae→ Cosmic-ray → UV-photons Shock

AGN- Observation and Theoretical Models Observations I(HCN)/I(CO) ~ , I(HCN)/I(HCO + ) ≥ 2 (Kohno 2005) I(CN)/I(HCN)~0.6-2, I(HNC)/I(HCN)~ (Aalto et al. 2006) Models XDR and PDR Chemistry (Meijerink and Spaans 2005, Stäuber et al. 2005)

AGN Chemistry – preliminary result Condition for r~3pc T = 600 K, n = 4x10 7 cm -3 ζ = 1x s -1 Condition for r~30pc T = 200 K, n = 4x10 4 cm -3 ζ = 1x s -1

Summary High abundance of H 2 O in high-temperature environment will change the entire chemistry, making it effectively C-rich. The inner midplane of an AGN disk may be affected by this high-temperature chemistry, leading to C 2 H 2 and other carbon- chain abundances. In the inner AGN disk, lower CN/HCN and higher HCN/HCO+ abundance ratios, compared with the outer disk, are also expected. Advent of high resolution telescopes (ALMA, Herschel) will reveal the finer structure of the chemistry of the AGN disks.

Acknowledgement Prof. Eric Herbst Prof. Todd Thompson Dr. Valentine Wakelam Dr. Guillaume Pineau des Forêts Thank you!