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ISM, star formation and astrochemistry

Molecular clouds of gas and dust pervade our galaxy, and are the birthplaces of stars and planets. ALMA is revolutionizing the field of star formation thanks to a combination of unprecedented angular resolution, velocity resolution, and sensitivity.  These are important, due to the fact that: (1) physical scales of interest in studying protostellar systems and clusters span several orders of magnitude, accessible by ALMA using its interferometry and total power modes; (2) velocity structures are complex and prone to minute details, all of which affect the angular momentum transport, turbulence, rotation, and other kinematical details; and (3) sensitivity that can probe the full mass range of star formation. 

The temperature, density, and radiation conditions inside star forming clouds make them unique chemical laboratories for studying both fundamental reactions and the evolution of the molecular complexity that seeds primitive planets.  In many of these sources, the excitation conditions result in the most favorable molecular transitions falling in the millimeter and sub-millimeter regions of the spectrum observable with ALMA.  

The extreme conditions associated with star- and planet-formation (and eventually stellar death) result in substantial variations in the molecular inventories on small spatial scales, necessitating the high angular resolution provided by ALMA.  Not only is this essential for identifying and exploring chemical differentiation within, for example, a star-forming region, it can also play a role in the overall detectability of molecular species.  As these regions tend to be quite spatially compact, observations with single-dish facilities can often become heavily affected by beam dilution, whereas with ALMA we can selectively target only the areas with molecular emission.  In turn, by targeting spatially isolated regions on the sky, the observed spectral linewidths become substantially narrower, necessitating the high spectral resolution of ALMA as well. The combination of high angular resolution, high spectral resolution, and high surface brightness sensitivity of ALMA is thus providing us an unparalleled window into the evolution of molecular complexity throughout the star- and planet-forming process.  

2021 Science SP 5

Figure: Comparison of ALMA Band 10 spectrum toward the massive star forming region NGC 6334I (top; extracted toward MM1; McGuire et al. 2018, ApJL, 863, 35) to observations from the Herschel CHESS key program using the HIFI instrument covering the same data range (bottom; Zernickel et al. 2012, A&A, 546, 87) demonstrating the power of ALMA to discern complex molecular line emission .


ALMA Science Highlights

1. Possible Disk Truncation in Ophiuchus Brown Dwarfs
2. Aluminum Oxide around a High-Mass Protostar Candidate