Near-Infrared Wide-Field Surface Photometry of M82

Details Near-Infrared Wide-Field Surface Photometry of M82 Near-Infrared Wide-Field Surface Photometry of M82

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109.2038i&link_type=abstract

Astronomical Journal v.109, p.2038

Astronomy and Astrophysics

Astronomy

18

Galaxies: Individual: M82, Galaxies: Starburst, Galaxies: Stellar Content

Scientific paper

We present near-infrared surface photometry of the starburst galaxy M82, based on wide-field (~12'X 12' on average) imaging in the IJHK' bands, to determine the properties of the stellar system hidden behind the prominent dust clouds. In contrast to the amorphous features seen at optical wavelengths, the near-infrared images disclose the smooth structure of the M82 stellar system, which is that of an early-type barred spiral galaxy seen nearly edge on. To determine the components of the stellar system, we performed a bulge/disk decomposition. The bulge light distribution along the minor axis in the J, H, and K' bands is well fitted by the de Vaucouleurs R^1/4^ law. Its effective radius and axial ratio are r_e_ ~21" (K' band)-29" (H band) (340-460 pc at a distance of 3.3 Mpc) and b/a ~ 0.80 (H band), respectively. The disk follows an exponential law with a scale length of ~40" (640 pc) along the major axis, virtually independent of wavelength in the B to K' bands. Its axial ratio is b/a = 0.34, implying an inclination of 73^deg^ for M82. Thus, we derive a disk-to-bulge luminosity ratio of 0.39 and 0.48 in the H and K' bands, respectively; the bulge is a substantially more important component of M82 than would be expected from optical surface photometry. This ratio also supports the classification of M82 as an early-type spiral galaxy. It should be noted that the decomposition also reveals a thick disk component, whose luminosity distribution follows an exponential law with a scale length of 140" (2.2 kpc) at z = +/-2' (19 kpc) and a thickness of 58" (0.9 kpc) at r = +/-100", about four times thicker than the primary disk. No dust lane can be seen in the fundamental disk plane. On the contrary, heavily reddened regions are distributed over the bar and the bulge, as well as over the disk at high galactic latitudes. The near-infrared color-color relation suggests that the reddening is caused by foreground dust clouds, and the color excess corresponds to an extinction A_v_ ~2-6 mag. The dense dust clouds, which bisect the galactic center, extend to |z|~1 kpc in the bulge above and below the fundamental plane, and out to ~3 kpc projected distance parallel to the major axis. The gradual change of the position angle of the major axis ({DELTA}PA~5^deg^) and the S shape of the disk major axis indicate a warping of the disk. The SW edge of the disk is bent toward the companion galaxy, M81. The disk rises by 0.6 kpc from the fundamental plane at a distance of 5 kpc from the galactic center. The opposite NE edge is warped by 1 kpc. The strong similar warp of the stellar and H I gas disks provides direct evidence for a recent gravitational interaction of M82 with M81.

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