Are starburst galaxies proton calorimeters?

Xilu Wang, Brian D. Fields

Research output: Contribution to journalConference article

Abstract

In star-forming galaxies, gamma rays are mainly produced through the collision of high-energy protons in cosmic rays and protons in the interstellar medium (i.e., cosmic-ray induced p0 g- radiation). For a 'normal' star-forming galaxy like the Milky Way, most cosmic rays escape the galaxy before such collisions, but in starburst galaxies with dense gas and huge star formation rate, it is thought that most cosmic rays 'die' in these interactions. To test this, we construct a 'thicktarget' model for the starburst galaxies, in which cosmic rays are accelerated by supernovae, and escape is neglected. This model gives an upper limit to a galaxy's gamma-ray emission, and tests the calorimetric relation between gamma rays and cosmic rays for starbursts. Only two free parameters are involved in the model: the cosmic-ray proton acceleration energy per supernova ecr, and the proton injection spectral index s. We apply our model to five observed starburst galaxies: M82, NGC 253, NGC 1068, NGC 4945 and the Circinus galaxy, and find most of these starbursts are consistent with being proton calorimeters, with ecr (0:1-0:25)1051erg and s -2:1-2:4. But we confirm that for Circinus, other gamma-ray sources are needed to explain its GeV luminosity.

Original languageEnglish (US)
Article number905
JournalProceedings of Science
Volume30-July-2015
StatePublished - Jan 1 2015
Event34th International Cosmic Ray Conference, ICRC 2015 - The Hague, Netherlands
Duration: Jul 30 2015Aug 6 2015

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starburst galaxies
calorimeters
cosmic rays
protons
galaxies
gamma rays
escape
supernovae
stars
collisions
star formation rate
proton energy
rays
luminosity
injection
radiation
gases

ASJC Scopus subject areas

  • General

Cite this

Are starburst galaxies proton calorimeters? / Wang, Xilu; Fields, Brian D.

In: Proceedings of Science, Vol. 30-July-2015, 905, 01.01.2015.

Research output: Contribution to journalConference article

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