The (Neutral) ISM in Local Group Galaxies

Jonathan Braine

Laboratoire d'Astrophysique de Bordeaux

with the help of many others

Pierre Gratier, Erwan Gardan, Karl Schuster, Nathalie Brouillet, Carsten Kramer ...

abstract:

Within the Local Group, a wide variety of objects are available: big spirals, small spirals, Irr with and without gas, DwSph... with a broad range in metallicities.

The physical resolution is excellent: 1" < 5 pc throughout and in the Magellanic Clouds, 1" = 0.25 pc. Stars can be resolved.

I will try and discuss what we know about the Local Group galaxies in relation to the following questions:

In the cycle HI --> H2 --> stars

-- what provokes the formation of H2 ? Collisions, pressure, patience ...

-- is there a threshold surface or volume density for star formation ?

How does the state of the ISM (particularly Z, pressure, B field) influence:

-- the clump Mass Function (CMF)

-- the stellar IMF

-- the Star Formation Efficiency (rapidity of converting H2 into stars)

-- reason for high SFE at z~1 ?

Where is the gas (in the Local Group) and how did it get there ?

-- Do galaxies need refuelling ?

-- If so, where does the gas come from ?

What links exist between the current distribution of gas and that of stars

far out in galaxies ?