Chemical Models of High Mass Young Stellar Objects Great Barriers in High Mass Star Formation H. Nomura 1 and T.J. Millar 2 1.Kyoto Univ. Japan, 2. Queen’s Univ. Belfast, UK

§1 Introduction

I HC SMA1 n IRc6 Compact Ridge (Beuther et al. 2005, 2006) CH 3 OH CH 3 OCH 3 SO 2 13 CH 3 CN Orion KL, SMA Mm/sub-mm Obs. of Mol. Lines Unidentified lines (Fallscheer et al. 2009) IRDC , SMA CH 3 OH

AFGL 2591 by ISO C 2 H 2 5 HCN 2 (Knez et al. 2009) Infrared Obs. of Molecular Lines (Lahuis & van Dishoeck 2000) NGC7538IRS1 by IRTF/TEXES Orion KL by ISO (Lerate et al. 2006) Small hydrogenated, saturated molecules (Crockett et al. 2010) Orion KL by Herschel/HIFI

Origin of Abundant Molecules in HC ☆ ★ evaporation of icy mantles + subsequent gas-phase reactions abundant complex molecules prestellar star-formation protostellar &outflow(shock) freeze out & grain surface reactions evaporation of icy mantles Young Stellar Evolution X(M, hot core)~ X(M, dark cloud) M: NH 3, H 2 S, CH 3 OH, (CH 3 ) 2 O etc. O H CO S H2OH2O CH 3 OH H2SH2S

Obs. of Icy Mantle Molecules W33A by ISO (Gibb et al. 2000) Hydrogenated, saturated molecules in ice (e.g., Spitzer: Boogert+ 2008, Pontpiddan+ 2008, Oberg+ 2008, AKARI: Aikawa+ 2009) Obs. O H CO N O H 2 O CO CH 3 OH N NH 3 H (Bottinelli et al. 2010) CH 3 OH & NH 3 Dust continuum CO (Caselli+ 1999, Tafalla+ 2004, …) L1498 by IRAM SVS 4-5 by Spitzer

Grain surface chemistry (e.g., Watanabe & Kouchi 2008) (Charnley 1997, 2001, 2005) grain surface CO H... Amino acids? Surface reactions in laboratory High mass YSOs are good targets for test

Hot Core Mol. in Various Objects (Cazaux et al. 2003) ~500AU CH 3 OH C 2 H 3 CN (Kuan et al. 2004) SMA H2SH2S Starburst galaxies (Minh et al. 2007) (e.g., Martin et al. 2006, 2008) NGC253 CMZ of Galactic Center (e.g., Requena-Torres+ 2008) Nearby extragalaxies NGC253, NGC4945, M82, IC342, Marrei2, NGC6946 Grain surface chemistry seems universal IRAS IRAM

§2 Hot Core Chemistry

Hot Core Chemistry – Cold & Hot grain surface C, O, N, S, CO, … H Hydrogenated, saturated molecules CH 4, H 2 O, NH 3, H 2 S, CH 3 OH, … grain surface (Charnley+ 1992, Millar+ 1997, …) H 2 O H 3 O + destroy molecules NH 3 HCN, HC 3 N, CH 3 CN, … CH 4, C 2 H 2 ca rbon-chain mol. H 2 S SO, SO 2, … CH 3 OH CH 3 OCH 3, HCOOCH 3, … Prestellar Protostellar Grain surface T~10K Gas-phase reactions T>100K thermal evaporation from grains

Hot Core Chemistry – Warm unsaturated molecules CH 3 OCH 3, HCOOCH 3, … Thermal history & UV photons in star forming cores? (Oberg et al. 2009) CH 3, HCO, … CH 3 O grain surface (e.g., Hasegawa+ 1992, Garrod+ 2006, 2008, …) Surface reactions in laboratory Grain surface T~40K (Horn et al. 2004) UV CH 3 OH 2 + +H 2 CO HCOOCH 3 : inefficient UV

§3 Physical and Chemical Models of High Mass YSOs

Physical & Chemical Models of YSOs Line radiative transfer comparison with obs. ⇔ Chemical reaction network + radiative transfer T, hydrodynamics , v Physical structure (T dust, T gas,  gas, v gas ) gas-phase, grain surface, gas-grain interaction + constraint grain surface + + Get rid of activation barrier of reactions ★ T dust T gas v gas Transport molecules & dust grains Thermal evaporation Mobility on grains UV

Chemical Structure of YSOs Molecules are abundant at cloud center CH 3 OH H 2 CO HCN CH 3 CN HCOOCH 3 r [pc] 10 4 yr CH 3 OH H 2 CO HCN CH 3 CN HCOOCH 3 r [pc] 10 4 yr r ★ (Nomura & Millar 2004) Mantle mol. H2OH2O H 2 O, CH 3 OH NH 3, CO 2 H 2 S, O 2 H 2 O, CH 3 OH NH 3, CO 2 H2SH2S O2O2 T dust

Effect of v infall on low mass YSO chem. (Aikawa+ 2008) CH 3 OH CH 3 OCH 3 :  gas-phase chem >  infall  gas-phase chem ~ yr,  infall ~10 3 yr (~300AU/1km) Warm grain surface reactions respond to formation of unsaturated molecules? physical model radiative hydrodynamic simulation Another pathway to unsaturated molecule formation? t [yr]

Dependence on warm-up time High mass:  star 10 7 yr gas-phase reaction grain surface reaction HCOOH formation (Garrod ) HCOOH (ice) HCOOH (gas) Short (5x10 4 yr) t [yr] T [K] Abundances of unsaturated molecules in gas & ice Grain surface chemistry & Stellar evolution time ? HCOOH (ice) HCOOH (gas) Long (1x10 6 yr) t [yr] T [K]

UV,X-rays Chemical Structure of Young Disks inner disk H2OH2O CH 3 OH NH 3 dust near midplane O H CO N dust outer disk CN, C 2 H HCN, H 2 CO, etc. surface (e.g., Markwick+2002, Aikawa+ 2002, Bergin+ 2007) CO R<300AU CO R<10AU (Walsh, Millar, HN 2010, in press) Photo- dissociate Frozen- out accretion Warm grain surface reactions during accretion?

Chemical Structure of Young Disks (Heinzellar, HN, Walsh, Millar 2010, in prep.) (Okamoto+ 2009) NH 3, no motion (low mass star) NH 3, vertical motion (low mass star) Photo- evaporation? Transport of mol. from disk midplane to surface layer Diagnose high mass disk chemistry & physics by ALMA

§4 Summary Hot Core Chemistry Grain surface reactions + desorption from grains + gas-phase reactions Grain surface chemistry seems universal Physical & chemical models of high (& low) mass YSOs Certain molecules are abundant near central star Role of warm surface chemistry? Dependence on warm-up time Stellar evolution, accretion velocity in disks Diagnose physics & chemistry of YSOs by ALMA_