Exploring Molecular Complexity with ALMA (EMoCA): High-Angular-Resolution Observations of Sagittarius B2(N) at 3 mm Holger S. P. Müller A. Belloche (PI), K. M. Menten; MPIfR R. T. Garrod; UVA 70th ISMS, Urbana-Champaign, IL, 22 – 26 June 2015, RI05

Motivation  Which level of molecular complexity in space can be detected by radio astronomical means ?  Did interstellar chemistry contribute to the formation of life on Earth or other planets ? – e.g. > 80 amino acids found in meteorites on Earth; isotopic and racemic composition suggests extraterrestrial origin – Glycine (NH 2 CH 2 COOH) in samples from comet 81P/Wild2  Newly detected molecules may evolve to tracers of specific chemical or physical conditions in space

How do complex organic molecules (COMs) form ?  Gas phase ion molecule reactions ineffective  Grain surface chemistry at low T not sufficient (hydrogenation of atoms and small molecules)  Radical radical reactions upon warm-up required  Observational results needed to test model predictions

The Star-forming Region Sagittarius B2  most massive star-forming region in our Galaxy (~ 10 7 M  )  ~100 pc from Galactic Center  very high column densities (> cm –2 ) key for detection of COMs  2 massive clumps, (M) and (N), hosting clusters of UC H II regions Sgr B2(N)  many COMs first detected there  2 hot cores: N1 (or LMH) & N2 different v lsr (10 km/s); 5" apart (0.2 pc) Sgr B2(N) at 850 µm (SMA; Qin et al., 2011) Central Molecular Zone at 870 µm ATLASGAL/LABOCA & Planck; © MPIfR/A. Weiß

Our previous IRAM 30 m survey of Sgr B2(N) 3700 lines > 4  (100 lines/GHz) 70 % identified 56 molecules 66 minor isotopologs 59 vibrationally excited states Belloche et al., A&A 559 (2013) A47 Highlights: 3 molecules newly detected aminoacetonitrile (NH 2 CH 2 CN) ethyl formate (C 2 H 5 OCHO) n-propyl cyanide (n-C 3 H 7 CN) Spectrum close to confusion limit  higher angular resolution needed

Exploring Molecular Complexity with ALMA  3 mm spectral line survey of Sgr B2(N) in Cycles 0 and 1 (84.0 – GHz)  angular resolution: 1.8" and 1.4"  sensitivity to compact emission: factor ~20 compared to our IRAM 30 m survey  status: observations completed, data reduced

Sensitivity and Resolution with ALMA N2 (secondary hot core): narrower line width  confusion limit lowered

Analysis of EMoCA survey  modeling with CLASS extension WEEDS (Maret et al., 2011) catalogs: CDMS, JPL, + private  LTE model for each identified molecule plus isotopologs and vibrational states  emission of COMs is compact (~1", 0.04 pc, 8300 AU); densities > 10 8 cm –3  LTE is a very good approximation initial focus on N2 (secondary) hot core

On propyl cyanides  gauche lower than anti by 0.48 ± 0.04 kJ/mol (PCCP 3 (2001) 766) anti 2 conformers gauche n-C 3 H 7 CN  2 isomers: normal (n) and iso (i) i-C 3 H 7 CN  rot. spectrum, HFS, dipole: H. S. P. Müller, A. Coutens, A. Walters, J.-U.Grabow, S. Schlemmer, J. Mol. Spectrosc. 267 (2011) 100

ALMA detection of iso-propyl cyanide  ~50 lines of i-C 3 H 7 CN detected and ~120 of n-C 3 H 7 CN  rotation temperature ~150 K, emission size ~1" A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, Science 345 (2014) 1584

Abundance of iso-propyl cyanide  i-C 3 H 7 CN : n-C 3 H 7 CN ~ 0.40 ± 0.06 : 1  ratio reproduced by Garrod's hot-core chemical model; formation on grain surfaces : 1 with new model dominant route to n-C 3 H 7 CN: CH 3 CH 2 + CH 2 CN (no equivalent reaction to produce i-C 3 H 7 CN) dominant route to i-C 3 H 7 CN: CH 3 CHCH 3 + CN (CH 3 CH=CH 2 + H strongly favors CH 3 CHCH 3 over CH 3 CH 2 CH 2 )

Branched molecules in the ISM  are now known to exist in the ISM !  were proposed to exist there since the 1980s  stability of tertiary radical sites over secondary ones over primary ones may favor branched molecules in even larger cases  amino acids in meteorites: branched ones dominate  our detection of i-C 3 H 7 CN bodes well for the presence of more complex molecules in the ISM, such as amino acids

"Laboratory Spectroscopy" with ALMA: Ethanol Intensities

Vibration-Rotation-Interaction and Signs of Dipole Components  (relative) signs may matter and may be determined by – Stark effect measurement, e.g. NH 2 D, Cohen & Pickett, JMSp 93 (1982) 83; HOONO 2 & CH 2 FOH, Suenram et al., JMSp 116/119 (1986) 406/446 – intensity measurements, e.g. (CH 2 OH) 2, Christen & Müller, PCCP 5 (2003) 3600; H 2 DO +, Müller et al., PCCP 12 (2010) 8362 anti gauche Initial signs: Pearson et al., JMSp 251 (2008) 394

Conclusion and Outlook  ALMA: high sensitivity, broad bandwidth, high spatial resolution  prime instrument to investigate molecular complexity can even contribute to laboratory spectroscopy  EMoCA: will provide data to test and calibrate chemical models and the means to investigate the evolutionary states of the two hot cores  branched molecules: what is the distribution of the BuCN isomers (C 4 H 9 CN) ? n-BuCN, t-BuCN studied; two more on the agenda in Köln. what about C 3 H 7 OH ?