IRAC Observations of M81

TL;DR

This paper presents IRAC imaging of M81 revealing its stellar, dust, and nuclear components, highlighting the distribution and properties of different constituents and their relation to star formation and extinction.

Contribution

First detailed IRAC imaging analysis of M81's morphological constituents, providing insights into stellar populations, dust distribution, and nuclear emission.

Findings

Bulge stars are M-type giants.

Dust emission traces spiral arms with extinction effects.

Nuclear emission is fainter at 8 μm than previous observations.

Abstract

IRAC images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 um than expected from ground-based 10 um observations made four years ago.