 '[@thornley]'
- '[@dpj]'
- '[@doherty95]'
- '[@lph320]'
- '[@shields]'
- '[@vanzi]'
- '[@vr]'
- '[@chad]'
- '[@fs-m82]'
- '[@lph328]'
- '[@seaquist]'
- '[@sb]'
- '[@chip]'
- '[@guseva]'
- '[@schmutz]'
- '[@lejeune]'
- '[@kurtz]'
- '[@hanson]'
- '[@depree]'
- '[@garcia]'
- '[@btk]'
- '[@thb]'
- '[@kj99; @vjc]'
- '[@ccm]'
title: 'Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and the IMF'
---

INTRODUCTION {#sec:intro}
============

In the very local ($D<5 h_{100}^{-1}$) Universe, the circumnuclear regions of just four galaxies (M82, NGC 253, NGC 4945, and M83) are responsible for $\sim25\%$ of the current massive star formation [@heckman97]. In these “circumnuclear starburst galaxies”, the star formation is confined to the inner $0.2$ to $2$ kpc, in a dense, gas–rich disk where star formation rates can reach $1000$   [@robhubble]. If the starburst initial mass function (IMF) includes significant numbers of low–mass stars, then each starburst is currently building up the stellar component of its host galaxy as well. A starburst enriches and heats its interstellar medium, as well as the local intergalactic medium. Starbursts can also drive large–scale winds that eject interstellar gas, presumably casting metals into the voids and heating the gas between galaxies. Starburst galaxies thus play a number of important roles in galaxy evolution.

If starbursts could be dated, then a sequence could be pieced together, charting starburst evolution from triggering to post–starburst quiescence. Starburst ages are most directly determined by understanding the population of rapidly evolving massive stars. The feedback effect of a starburst on its gas supply is transmitted through massive stellar winds and supernovae–driven superwinds. Thus, understanding the evolution of starbursts and their effects on the interstellar and intergalactic media both critically depend on understanding the populations of massive stars.

Unfortunately, since starburst galaxies are too far away to count indiv