Chemical tracers of high-metallicity environments

Abstract

We present for the first time a detailed study of the properties of molecular gas in metal-rich environments such as early-type galaxies (ETGs). We have explored Photon-Dominated Region (PDR) chemistry for a wide range of physical conditions likely to be appropriate for these sources. We derive fractional abundances of the 20 most chemically reactive species as a function of the metallicity, as a function of the optical depth and for various volume number gas densities, Far-Ultra Violet (FUV) radiation fields and cosmic ray ionisation rates. We also investigate the response of the chemistry to the changes in $\alpha -$element enhancement as seen in ETGs. We find that the fractional abundances of CS, H${}_2$S, H${}_2$CS, H${}_2$O, H${}_3$O${}^{+}$, HCO${}^{+}$ and H${}_2$CN seem invariant to an increase of metallicity whereas C${}^{+}$, CO, C${}_2$H, CN, HCN, HNC and OCS appear to be the species most sensitive to this change. The most sensitive species to the change in the fractional abundance of $\alpha -$elements are C${}^{+}$, C, CN, HCN, HNC, SO, SO${}_2$, H${}_2$O and CS. Finally, we provide line brightness ratios for the most abundant species, especially in the range observable with ALMA. Discussion of favorable line ratios to use for the estimation of super-solar metallicities and $\alpha$-elements are also provided.

15 pages, 6 figures, 4 tables, Accepted for publication into MNRAS

References in corpus (5)

• Molecular Gas and Star Formation in the SAURON Early-type Galaxies
• Molecular line intensities as measures of cloud masses - I. Sensitivity of CO emissions to physical parameter variations
• The Cool ISM in Elliptical Galaxies. I. A Survey of Molecular Gas
• A survey of submillimeter C and CO lines in nearby galaxies
• Models for extremely metal-poor halo stars

Cited by in corpus (10)

• Submillimeter-HCN Diagram for an Energy Diagnostics in the Centers of Galaxies
• The MALATANG Survey: the L_gas-L_IR correlation on sub-kiloparsec scale in six nearby star-forming galaxies as traced by HCN J=4-3 and HCO^+ J=4-3
• ALMA imaging of C2H emission in the disk of NGC1068
• ALMA Observations of Circumnuclear Disks in Early Type Galaxies: 12CO(2-1) and Continuum Properties
• The ATLAS 3D project - XVI. Physical parameters and spectral line energy distributions of the molecular gas in gas-rich early-type galaxies
• ISM chemistry in metal rich environments: molecular tracers of metallicity
• DeGaS-MC: Dense Gas Survey in the Magellanic Clouds I -- An APEX survey of HCO+ and HCN(2-1) toward the LMC and SMC
• The Evolution of NGC 7465 as Revealed by its Molecular Gas Properties
• The molecular ISM in luminous infrared galaxies: a 3mm line survey of Arp 157
• The Recent Evolution of Early-Type Galaxies as Seen in their Cold Gas