The cosmic abundance of cold gas in the local Universe

ABSTRACT We determine the cosmic abundance of molecular hydrogen (H2) in the local Universe from the xCOLD GASS survey. To constrain the H2 mass function at low masses and correct for the effect of the lower stellar mass limit of $10^9 \, \mathrm{M}_{\odot }$ in the xCOLD GASS survey, we use an empirical approach based on an observed scaling relation between star formation rate and gas mass. We also constrain the H i and H i+H2 mass functions using the xGASS survey and compare them to the H i mass function from the ALFALFA survey. We find the cosmic abundance of molecular gas in the local Universe to be $\Omega _{\mathrm{H_2}} = (5.34 \pm 0.47) \times 10^{-5} h^{-1}$. Molecular gas accounts for $19.6\pm 3.9{{\ \rm per\ cent}}$ of the total abundance of cold gas, $\mathrm{\Omega _{H\,{\small I}+H_{2}}} = (4.66 \pm 0.70) \times 10^{-4}\, h_{70}^{-1}$. Galaxies with stellar masses in excess of 109$\, \mathrm{M}_{\odot }$ account for 89 per cent of the molecular gas in the local Universe, while in comparison such galaxies only contain 73 per cent of the cold atomic gas as traced by the H i 21cm line. The xCOLD GASS CO, molecular gas and cold gas mass functions, and $\Omega _{\mathrm{H_2}}$ measurements provide constraints for models of galaxy evolution and help to anchor blind molecular gas surveys attempting to determine the abundance of molecular gas at high redshifts.

Interstellar Carbon Dust

In the ranking of cosmic abundance of the elements, carbon is the second element, after oxygen, able to form multiple bonds propagating the formation of a network, thus playing an essential role in the formation of nanometer- to micrometer-sized interstellar dust grains. Astrophysical spectroscopic observations give us remote access to the composition of carbonaceous and organic interstellar grains. Their presence and abundances from spectroscopic observations and the phases of importance for the Galactic carbon budget are considered in this article.

X-ray extinction from interstellar dust

Aims. We present a study on the prospects of observing carbon, sulfur, and other lower abundance elements (namely Al, Ca, Ti, and Ni) present in the interstellar medium using future X-ray instruments. We focus in particular on the detection and characterization of interstellar dust along the lines of sight. Methods. We compared the simulated data with different sets of dust aggregates, either obtained from past literature or measured by us using the SOLEIL-LUCIA synchrotron beamline. Extinction by interstellar grains induces modulations of a given photolelectric edge, which can be in principle traced back to the chemistry of the absorbing grains. We simulated data of instruments with characteristics of resolution and sensitivity of the current Athena, XRISM, and Arcus concepts. Results. In the relatively near future, the depletion and abundances of the elements under study will be determined with confidence. In the case of carbon and sulfur, the characterization of the chemistry of the absorbing dust will be also determined, depending on the dominant compound. For aluminum and calcium, despite the large depletion in the interstellar medium and the prominent dust absorption, in many cases the edge feature may not be changing significantly with the change of chemistry in the Al- or Ca-bearing compounds. The exinction signature of large grains may be detected and modeled, allowing a test on different grain size distributions for these elements. The low cosmic abundance of Ti and Ni will not allow us a detailed study of the edge features.

Deuterated forms of H 3 + and their importance in astrochemistry

At the low temperatures (approx. 10 K) and high densities (approx. 100 000 H 2 molecules per cm −3 ) of molecular cloud cores and protostellar envelopes, a large amount of molecular species (in particular those containing C and O) freeze-out onto dust grain surfaces. It is in these regions that the deuteration of H 3 + becomes very efficient, with a sharp abundance increase of H 2 D + and D 2 H + . The multi-deuterated forms of H 3 + participate in an active chemistry: (i) their collision with neutral species produces deuterated molecules such as the commonly observed N 2 D + , DCO + and multi-deuterated NH 3 ; (ii) their dissociative electronic recombination increases the D/H atomic ratio by several orders of magnitude above the D cosmic abundance, thus allowing deuteration of molecules (e.g. CH 3 OH and H 2 O) on the surface of dust grains. Deuterated molecules are the main diagnostic tools of dense and cold interstellar clouds, where the first steps toward star and protoplanetary disc formation take place. Recent observations of deuterated molecules are reviewed and discussed in view of astrochemical models inclusive of spin-state chemistry. We present a new comparison between models based on complete scrambling (to calculate branching ratio tables for reactions between chemical species that include protons and/or deuterons) and models based on non-scrambling (proton hop) methods, showing that the latter best agree with observations of NH 3 deuterated isotopologues and their different nuclear spin symmetry states. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

K-shell photoabsorption and photoionization of trace elements

Context. This is the final report of a three-paper series on the K-shell photoabsorption and photoionization of trace elements (low cosmic abundance), namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu, and Zn. K lines and edges from such elements are observed in the X-ray spectra of supernova remnants, galaxy clusters, and accreting black holes and neutron stars, their diagnostic potential being limited by poor atomic data.Aims. We here complete the previously reported radiative datasets with new photoabsorption and photoionization cross sections for isoelectronic sequences with electron number 19 ≤N≤ 26. We also describe the access to and integrity and usability of the whole resulting atomic database.Methods. Target representations were obtained with the atomic structure code AUTOSTRUCTURE. Where possible, cross sections for ground-configuration states were computed with the Breit–PauliR-matrix method (BPRM) in either intermediate orLScoupling including damping (radiative and Auger) effects; otherwise and more generally, they were generated in the isolated-resonance approximation with AUTOSTRUCTURE.Results. Cross sections were computed with BPRM only for the K (N= 19) and Ca (N= 20) isoelectronic sequences, the latter inLScoupling. For the remaining sequences (21 ≤N≤ 26), AUTOSTRUCTURE was run inLS-coupling mode taking into account damping effects. Comparisons between these two methods for K-like ZnXIIand Ca-like ZnXIshow that to ensure reasonable accuracy, theLScalculations must be performed taking into account the non-fine-structure relativistic corrections. The original data structures of the BPRM and AUTOSTRUCTURE output files, namely photoabsorption and total and partial photoionization cross sections, are maintained but supplemented with files detailing the target (NT-electron system, whereNT=N− 1) representations and photon states (N-electron system).Conclusions. We conclude that because of the large target size, the photoionization of ions withN> 20 involving inner-shell excitations rapidly leads to untractable BPRM calculations, and is then more effectively treated in the isolated resonance approximation with AUTOSTRUCTURE. This latter approximation by no means involves small calculations as Auger damping must be explicitly specified in the intricate decay routes.