Invited review article for the international symposium "Penetrating Bars Through Masks of Cosmic Dust" (Johannesburg, South Africa, 6-12 June 2004), edited by D.L. Block & K. Freeman, Kluwer Academic Publisher, pp. 535-559

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THE WARM, COLD AND VERY COLD DUSTY UNIVERSE

Aigen Li


Theoretical Astrophysics Program, University of Arizona, Tucson, AZ 85721


Abstract. We are living in a dusty universe: dust is ubiquitously seen in a wide variety of astrophysical environments, ranging from circumstellar envelopes around cool red giants to supernova ejecta, from diffuse and dense interstellar clouds and star-forming regions to debris disks around main-sequence stars, from comets to interplanetary space to distant galaxies and quasars.

These grains, spanning a wide range of sizes from a few angstroms to a few micrometers, play a vital role in the evolution of galaxies as an absorber, scatterer, and emitter of electromagnetic radiation, as a driver for the mass loss of evolved stars, as an essential participant in the star and planet formation process, as an efficient catalyst for the formation of H2 and other simple molecules as well as complex organic molecchapules which may lead to the origins of life, as a photoelectric heating agent for the interstellar gas, and as an agent shaping the spectral appearance of dusty systems such as protostars, young stellar objects, evolved stars and galaxies.

In this review I focus on the dust grains in the space between stars (interstellar dust), with particular emphasis on the extinction (absorption plus scattering) and emission properties of cold submicron-sized "classical" grains which, in thermal equilibrium with the ambient interstellar radiation field, obtain a steady-state temperature of ~ 15-25 K, warm nano-sized (or smaller) "ultrasmall" grains which are, upon absorption of an energetic photon, transiently heated to temperatures as high as a few hundred to over 1000 K, and the possible existence of a population of very cold (< 10 K) dust. Whether dust grains can really get down to "Temperature" less than the 2.7 K cosmic microwave background radiation temperature will also be discussed. The robustness of the silicate-graphite-PAHs interstellar dust model is demonstrated by showing that the infrared emission predicted from this model closely matches that observed for the Milky Way, the Small Magellanic Cloud, and the ringed Sb galaxy NGC7331.


keywords Interstellar dust - extinction - absorption - infrared emission


Table of Contents

INTRODUCTION

OBSERVATIONAL CONSTRAINTS ON INTERSTELLAR DUST

WARM AND COLD DUST IN THE ISM

THE SILICATE-GRAPHITE-PAHS INTERSTELLAR DUST MODEL

VERY COLD DUST OR HOW COLD COULD GALAXIES BE?

CAN DUST GET DOWN TO 2.7 K AND APPEAR IN ABSORPTION AGAINST THE CMB?

NOTES

REFERENCES

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