Starbursts: Nature and environment

Abstract

The physical mechanisms responsible for producing starbursts are outlined including interactions, mergers, bars, and sinking gas-rich satellites. The question of why a burst occurs is analysed as well as the problem of the disparate timescales of the interaction, burst and dynamical times.

It is shown that there are three principal phases of starbursts associated with dynamical processes. Most starbursts will remain in the first normal starburst phase but given sufficiently large central gas masses the second very luminous stage related to a central bar instability can be achieved. In some cases a final ultra luminous phase occurs associated with the self-gravity of a massive central gas cloud. Here an active nucleus can form associated with a dense stellar cluster formed in the burst.

This final fascinating phase has been treated in detail including the growth of a central black hole, the formation of broad emission line clouds from red-giant envelopes photoionized from the outside by the central continuum source, collisions between red giants, the evolution of the stellar population in the central star cluster, and the cosmological implications for the number density and luminosity evolution of quasars, active galactic nuclei and starbursts.

The context and relevance of starburst galaxies with respect to these important astrophysical phenomena is shown. We can learn much from concentrating on the starburst physics relevant to galaxy formation and galaxian evolution along the Hubble sequence. The intergalactic medium can be significantly enriched by the prodigious metal enhanced outflows from starburst systems driven by OB winds and supernovae. It can also be heated and ionised by the energy and momentum input from the combined active galactic nuclei and starburst galaxies. Quasar absorption lines may well arise in these huge circumgalactic flows.