Using Protostellar Outflow Chemistry to Probe Extraterrestrial Ice Abundances: A study in the chemical morphology of L1551 IRS5

Understanding the chemistry that occurs during solar system formation can give insight to how life on earth developed. Most of this chemistry develops on the icy mantles of interstellar grains. To study it we can either observe the species directly in other star systems (in the gas or ice phase) or use models to simulate the process. To detect molecules in space, we can observe emission spectra when a molecule emits a photon or absorption spectra as a molecule absorbs a photon. While the most complex chemistry in space occurs on icy dust grains, it is difficult to detect molecules in the ice phase due to observational limitations. Specifically, the absorption features of ice chemistry are harder to detect than gas phase spectra. While we see complex molecules in the icy interstellar medium and comets, the most complex molecule we can confidently identify in the ice phase using vibrational spectroscopy is methanol (CH3OH). Thus to observe more complex molecules than methanol, we look to find alternative methods of constraining interstellar ice abundances. We present one such alternative approach, using protostellar outflows as a proxy for ice chemistry. These outflows can sputter and sublimate ice into the gas phase without inducing thermal chemical changes. We can thus observe this gas as a measurement of the material that has left the solid phase. Recent studies suggest that L1551 IRS5 shows evidence of chemically rich outflows. Here we use an interferometric survey at radio wavelengths that spans 50 GHz of bandwidth from around 290-365 GHz to examine the chemical morphology of the outflow regions. Specifically, we analyze the spectra of L1551 IRS5 to determine molecular abundances throughout the outflow of the protostar, and image the emission locations to compare the chemistry and morphology of different molecules in the region. We then compare abundances of different regions to other protostellar systems and comets. We compare these outflows to the chemical complexity in comets to test the validity of using shocks to probe the ice cloud of L1551 IRS5. We find a rich chemical profile of many species in the outflow of L1551 IRS5 consistent with previous structural studies of the region. Our analysis shows significant variation in chemical richness and column densities along the outflow as a function of radial distance from the center protostar. Additionally, six of the nine most abundant species present in the outflow are also present in comet 67P/C-G. We conclude that this similarity may suggest that by probing the outflow in L1551 IRS5, we are indeed able to proxy the ice chemistry of the surrounding molecular cloud to better understand the overall chemistry of stellar evolution.Astro 9