Ñjlmkl{

Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA
Jes K. Jørgensen1,2 , C´ cile Favre3 , Suzanne E. Bisschop2,1 , Tyler L. Bourke4 , Ewine F. van Dishoeck5,6 , e and Markus Schmalzl5

arXiv:1208.5498v1 [astro-ph.SR] 27 Aug 2012

ABSTRACT Glycolaldehyde (HCOCH2 OH) is the simplest sugar and an important intermediate in the path toward forming more complexbiologically relevant molecules. In this paper we present the first detection of 13 transitions of glycolaldehyde around a solar-type young star, through Atacama Large Millimeter Array (ALMA) observations of the Class 0 protostellar binary IRAS 16293-2422 at 220 GHz (6 transitions) and 690 GHz (7 transitions). The glycolaldehyde lines have their origin in warm (200–300 K) gas close to the individualcomponents of the binary. Glycolaldehyde co-exists with its isomer, methyl formate (HCOOCH3 ), which is a factor 10–15 more abundant toward the two sources. The data also show a tentative detection of ethylene glycol, the reduced alcohol of glycolaldehyde. In the 690 GHz data, the seven transitions predicted to have the highest optical depths based on modeling of the 220 GHz lines all showred-shifted absorption profiles toward one of the components in the binary (IRAS16293B) indicative of infall and emission at the systemic velocity offset from this by about 0.2′′ (25 AU). We discuss the constraints on the chemical formation of glycolaldehyde and other organic species – in particular, in the context of laboratory experiments of photochemistry of methanolcontaining ices. The relativeabundances appear to be consistent with UV photochemistry of a CH3 OH–CO mixed ice that has undergone mild heating. The order of magnitude increase in line density in these early ALMA data illustrate its huge potential to reveal the full chemical complexity associated with the formation of solar system analogs. Subject headings: astrochemistry — astrobiology — stars: formation — ISM: abundances — ISM:molecules — ISM: individual (IRAS 16293-2422)

1 Centre for Star and Planet Formation and Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø., Denmark, jeskj@nbi.dk

Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K., Denmark, suzanne@snm.ku.dk
3 4 5

2Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000, Aarhus C., Denmark, favre@phys.au.dk Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA, tbourke@cfa.harvard.edu

Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands, ewine@strw.leidenuniv.nl, schmalzl@strw.leidenuniv.nl
6

Max-Planck Institut f¨ rextraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany u

–2– 1. Introduction

One of the most intriguing questions in studies of the chemistry of the early solar system is whether, how, when and where complex organic and potentially prebiotic molecules are formed. One of the key species in this context is glycolaldehyde (HCOCH2 OH). It is the simplest sugar and the firstintermediate product in the formose reaction that begins with formaldehyde (H2 CO) and leads to the (catalyzed) formation of sugars and ultimately ribose, the backbone of RNA, under early Earth conditions (e.g., Larralde et al. 1995). The presence of glycolaldehyde is therefore an important indication that the processes leading to biologically relevant molecules are taking place. However, themechanism responsible for its formation in space is still unclear (see, e.g., Woods et al. 2012). Glycolaldehyde has so-far been detected in two places in space – toward the Galactic center source SgrB2(N) (Hollis et al. 2000; see also Hollis et al. 2001; Hollis et al. 2004; Halfen et al. 2006; Requena-Torres et al. 2008) and the high-mass hot molecular core G31.41+0.31 (Beltr´ n et al. 2009). Another...