ISM, star formation and astrochemistry
Astrochemistry and complex organic molecules
ALMA sensitivity has allowed a number of important studies related to the chemistry of the interstellar medium, especially in the areas of deuterated molecules and complex organic molecules. The ALMA detection of abundant branched form of Propyl Cyanide in the Sgr B2 region reveals that the production route of branched isomers of linear molecules may be more efficient than previously thought in the interstellar medium. This supports the idea that complex branched pre-biotic molecules, such as amminoacids, may form on interstellar ices (http://www.almaobservatory.org/en/press-room/press-releases/754-alma-finds-that-organic-molecules-are-branching-out; http://adsabs.harvard.edu/abs/2014Sci...345.1584B)
Figure 1. Dust and molecules in the central region of our Galaxy: The background image shows the dust emission in a combination of data obtained with the APEX telescope and the Planck space observatory at a wavelength around 860 micrometers. The organic molecule iso-propyl cyanide with a branched carbon backbone (i-C3H7CN, left) as well as its straight-chain isomer normal-propyl cyanide (n-C3H7CN, right) were both detected with the Atacama Large Millimeter/submillimeter Array in the star-forming region Sgr B2, about 300 light years away from the Galactic center Sgr A*. © MPIfR/A. Weiß (background image), University of Cologne/M. Koerber (molecular models), MPIfR/A. Belloche (montage).
High mass star formation and infrared dark clouds
ALMA has provided convincing evidence for the presence of disks surrounding a number of high mass protostars. These findings, thanks to ALMA angular resolution and sensitivity, support the hypothesis that stars at least up to 10-20Msun may undergo a disk accretion phase, similar to solar-type stars. The improved angular resolution now offered by ALMA will allow to extend these studies to even more massive stars, which are typically located at larger distances from the Sun. (http://adsabs.harvard.edu/abs/2013A%26A...552L..10S ).
Figure 2. Velocity pattern derived from ALMA CH3CN observations of the young massive protostar G35.20-0.74N (left), compared with a Keplerian disk model (right). Adapted from http://www.aanda.org/articles/aa/pdf/2013/04/aa21134-13.pdf
The structure of massive proto-cluster cores at the distance of the Galactic Centre can also be studied in detail with ALMA. The famous “Brick” core (G0.253+0.016, also known as the “Lima Bean”) has been mapped in detail revealing the complex internal structure, which is consistent with the object being on the verge of forming stars. The complex clumpy structure has been interpreted as induced by cloud-cloud collisions or as the result of a relatively recent passage close to the supermassive black hole in the Galactic Centre. It is expected that the detailed study of massive clouds in extreme environment in our Galaxy, as is the case for the Brick, will allow us to shed light of how star formation may progress in other similarly extreme environments in the Universe (http://adsabs.harvard.edu/abs/2014ApJ...795L..25R).
Figure 3. ALMA 3mm observations of the dust structure within the Brick (orange), overlaid on an infrared map of the region from Spitzer observations (Green/Blue). Adapted from http://iopscience.iop.org/2041-8205/795/2/L25/pdf/apjl_795_2_25.pdf
Low mass star formation
The detailed physical and chemical structure of low mass protostars in nearby star forming regions can be studied in great detail with ALMA. The interaction between disks, jets, outflow cavities, and envelopes have been investigated in several studies. The ALMA sensitivity allows to trace the coherent kinematical pattern and the transition between the different structures. As an example, in the figure we show the observations of the famous HH212 jet (http://adsabs.harvard.edu/abs/2014A&A...568L...5C).
Figure 4. ALMA maps of the various physical and kinematical components in the low mass protostellar system HH212. The disk and jet are shown in the upper panel as traced by the dust continuum and the SiO emission, repsectively; the envelope and outflow cavity are shown in the bottom panel as traced by the C17O and C34S. Adapted from http://www.aanda.org/articles/aa/pdf/2014/08/aa24103-14.pdf
ALMA sensitivity and resolution also allows to reveal and compare with models the chemical effects of accretion variability onto the protostellar envelope. As accretion bursts release energy in the envelope, the gas phase chemistry is affected by the change of temperature and the release in the gas phase of molecules that are normally locked into the icy mantles of dust grains. These effects, as well as the enhancement of carbon chain molecules and methanol in the inner regions of the envelope of the protostar IRAS 15398-3359 are consistent as being the result of a recent accretion burst (http://adsabs.harvard.edu/abs/2013ApJ...779L..22J).
Figure 5. ALMA observations of IRAS 15398–3359. Left: CH3OH (red) and H13CO+ (blue) maps; Right comparison between the observed and modeled radial intensity profiles. Adapted from http://iopscience.iop.org/2041-8205/779/2/L22/pdf/apjl_779_2_22.pdf.