The Interstellar Medium of Dwarf Galaxies

Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs that are known to host significant amounts of gas and dust. The neutral and ionized gas components and the impact of the dust will be discussed, as well as first indications for the existence of active nuclei in these sources. Cosmological implications are also addressed, considering the primordial helium abundance and the similarity of local Green Pea galaxies with young, sometimes protogalactic sources in the early Universe.

Synthetic Approaches to Complex Organic Molecules in the Cold Interstellar Medium

The observation and synthesis of organic molecules in interstellar space is one of the most exciting and rapidly growing topics in astrochemistry. Spectroscopic observations especially with millimeter and submillimeter waves have resulted in the detection of more than 250 molecules in the interstellar clouds from which stars and planets are ultimately formed. In this review, we focus on the diverse suggestions made to explain the formation of Complex Organic Molecules (COMs) in the low-temperature interstellar medium. The dominant mechanisms at such low temperatures are still a matter of dispute, with both gas-phase and granular processes, occurring on and in ice mantles, thought to play a role. Granular mechanisms include both diffusive and nondiffusive processes. A granular explanation is strengthened by experiments at 10 K that indicate that the synthesis of large molecules on granular ice mantles under space-like conditions is exceedingly efficient, with and without external radiation. In addition, the bombardment of carbon-containing ice mantles in the laboratory by cosmic rays, which are mainly high-energy protons, can lead to organic species even at low temperatures. For processes on dust grains to be competitive at low temperatures, however, non-thermal desorption mechanisms must be invoked to explain why the organic molecules are detected in the gas phase. Although much remains to be learned, a better understanding of low-temperature organic syntheses in space will add both to our understanding of unusual chemical processes and the role of molecules in stellar evolution.

The Minimal Astration Hypothesis—a Necessity for Solving the Dust Budget Crisis?

Assuming that gas and dust separate in the interstellar medium (ISM) so that high-density regions, where stars can form, are almost devoid of dust, the amount of metals being removed from the ISM can be significantly reduced (minimized astration). Here, it is shown by simple analytical models that this may increase the total metal budget of a galaxy considerably. It is suggested that these extra metals may increase the mass of dust such that the “dust budget crisis”, i.e., the fact that there seems to be more dust at high redshifts than can be accounted for, can be ameliorated. Reducing the amount of astration, the metal budget can be more than doubled, in particular for systems that evolve under continuous gas accretion.

C2H5NO Isomers: from Acetamide to1,2-Oxazetidine and Beyond

This work documents the properties of a number of isomers of molecular formula C2H5NO from the most stable, acetamide, through 1,2-oxazetidine and including even higher energy species largely of a dipolar nature. Only two of the isomers have been detected in emissions from the interstellar medium (ISM); possible further candidates are identifi�ed and the likelihood of their being detectable are considered. In general hardly any of these compounds have featured in the existing chemical literature so this work represents an important contribution extending the canon of chemical bonding which can contribute to machine-learning | providing a more exacting test of AI applications. The presence of acetamide, CH3C(O)NH2, is the subject of current debate with no clear and obvious paths to its formation; it is shown that a 1,3[H]-transfer from (E,Z ) ethanimidic acid, CH3C(OH){{NH, is feasible in spite of an energy barrier of 130 kJ/mol. It is speculated that the imidic acid can itself be formed from abundant precursors, H2O and CH3C{{{N, in an acid-induced, water addition, auto-catalytic reaction on water-ice grains.

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol−1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol−1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.

C2H5NO Isomers: from Acetamide to1,2-Oxazetidine and Beyond

This work documents the properties of a number of isomers of molecular formula C2H5NO from the most stable, acetamide, through 1,2-oxazetidine and including even higher energy species largely of a dipolar nature. Only two of the isomers have been detected in emissions from the interstellar medium (ISM); possible further candidates are identifi�ed and the likelihood of their being detectable are considered. In general hardly any of these compounds have featured in the existing chemical literature so this work represents an important contribution extending the canon of chemical bonding which can contribute to machine-learning | providing a more exacting test of AI applications. The presence of acetamide, CH3C(O)NH2, is the subject of current debate with no clear and obvious paths to its formation; it is shown that a 1,3[H]-transfer from (E,Z ) ethanimidic acid, CH3C(OH){{NH, is feasible in spite of an energy barrier of 130 kJ/mol. It is speculated that the imidic acid can itself be formed from abundant precursors, H2O and CH3C{{{N, in an acid-induced, water addition, auto-catalytic reaction on water-ice grains.

Systems Astrochemistry: A New Doctrine for Experimental Studies

Laboratory experiments play a key role in deciphering the chemistry of the interstellar medium (ISM) and the formation of complex organic molecules (COMs) relevant to life. To date, however, most studies in experimental astrochemistry have made use of a reductionist approach to experimental design in which chemical responses to variations in a single parameter are investigated while all other parameters are held constant. Although such work does afford insight into the chemistry of the ISM, it is likely that several important points (e.g., the possible influence of experimental parameter interaction) remain ambiguous. In light of this, we propose the adoption of a new “systems astrochemistry” approach for experimental studies and present the basic tenants and advantages of this approach in this perspective article. Such an approach has already been used for some time now and to great effect in the field of prebiotic chemistry, and so we anticipate that its application to experimental astrochemistry will uncover new data hitherto unknown which could aid in better linking laboratory work to observations and models.