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Article Contents

ABSTRACT

1.GENERAL INTRODUCTION
1.1.Central role of the interstellar medium (ISM) in the physics, structure, evolution and multi-lambda emission of galaxies
1.2.Molecular gas is a major component of the ISM
1.3.Landmarks of the history of the discovery and studies of interstellar molecules in the Milky Way (MW)
1.4.Main achievements of molecular studies in external galaxies

2.COSMIC MOLECULES AND LOCAL INTERSTELLAR MEDIUM
2.1.Physics and various components of the local interstellar molecular gas
2.2.Observational techniques
2.3.Modelling (millimetre) molecular line formation, and diagnostic of physical conditions and molecular abundances in the ISM
2.4.Uniqueness of basic processes of interstellar chemistry
2.5.Relation between interstellar and other cosmic molecules

3.CO OBSERVATIONS AND GROSS STRUCTURE OF MOLECULAR GAS IN THE MILKY WAY
3.1.Introduction: atomic and molecular interstellar gas
3.2.Molecular gas in the Milky Way at galactic scale

4.CO OBSERVATIONS AND GROSS STRUCTURE OF MOLECULAR GAS IN OTHER GALAXIES
4.1.Molecular gas in spiral galaxies from CO surveys of local galaxies
4.2.Molecular gas in other types of galaxies

5.MOLECULES AS TRACERS OF STAR FORMATION AT GALACTIC SCALES
5.1.Introduction. Star formation rate
5.2.Star formation and molecular clouds in non-starburst galaxies
5.3.Molecular gas and starbursts in luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs)
5.4.OH mega-masers.

6.MOLECULAR ABUNDANCES IN VARIOUS LOCAL GALACTIC ENVIRONMENTS
6.1.Summary of standard molecular abundances in various regions of the Milky Way, and models of interstellar chemistry
6.2.Observed abundance variations in local galaxies: I. the Magellanic Clouds
6.3.Observed abundance variations in local galaxies: II. Nearby starbursts and other galaxies
6.4.Abundance ratios of isotopic varieties, and inferences for chemical evolution of galaxies

7.TRENDS IN MOLECULAR ABUNDANCES FROM ABSORPTION LINES AT HIGH REDSHIFT
7.1.H2 UV absorption lines in Damped Lyman-alpha systems of quasars
7.2.Millimetre and radio absorption lines in lensing galaxies and radio-sources

8.MOLECULES, DUST AND PAHS (LARGE AROMATIC MOLECULES)
8.1.Introduction. Interplay between dust and molecules in galaxies
8.2.Mid-infrared emission of PAHs in galaxies
8.3.Diffuse Interstellar Bands (DIBs) in galaxies
8.4.Molecular infrared spectral features in extragalactic dust

9.MILLIMETRE EMISSION OF MOLECULES AT VERY HIGH REDSHIFT
9.1.Star formation and ULIRGs at high redshift
9.2.CO studies
9.3.Molecules in the host galaxies of high-z AGN
9.4.Other species and detailed studies through strong gravitational lensing

10.INFRARED H2 EMISSION, TRACER OF WARM MOLECULAR GAS, SHOCKS AND PHOTODISSOCIATION REGIONS
10.1.Basic features and physics of H2 emission, and Milky Way observations
10.2.The 2µm H2 emission in galaxies
10.3.Mid-IR H2 pure-rotational lines in galaxies
10.4.Prospects for detecting H2 in forming galaxies

11.MOLECULES AND ACTIVE GALACTIC NUCLEI (AGN)
11.1.Interplay between super-massive black holes and their host galaxy
11.2.Molecules in the central regions and fueling the AGN
11.3.H2O mega-masers and AGN molecular disks

12.PROSPECTS
12.1.Waiting for ALMA: ongoing studies and submillimetre breakthroughs
12.2.The ALMA revolution
12.3.Accompanying- and post-ALMA: JWST, extremely large telescopes and SKA

13.GENERAL CONCLUSION

REFERENCES

List of Main Abbreviations