Near-infrared Detection of a Super-thin Disk in NGC 891
The Astrophysical Journal, Volume 773, Issue 1, article id. 45, 30 pp. (2013).
Published in Aug 2013
We probe the disk structure of the nearby, massive, edge-on spiral galaxy NGC 891 with subarcsecond resolution JHK s-band images covering ~ ±10 kpc in radius and ±5 kpc in height. We measure intrinsic surface brightness (SB) profiles using realistic attenuation corrections constrained from near- and mid-infrared (Spitzer) color maps and three-dimensional Monte Carlo radiative-transfer models. In addition to the well-known thin and thick disks, a super-thin disk with 60-80 pc scale-height—comparable to the star-forming disk of the Milky Way—is visibly evident and required to fit the attenuation-corrected light distribution. Asymmetries in the super-thin disk light profile are indicative of young, hot stars producing regions of excess luminosity and bluer (attenuation-corrected) near-infrared color. To fit the inner regions of NGC 891, these disks must be truncated within ~3 kpc, with almost all their luminosity redistributed in a bar-like structure 50% thicker than the thin disk. There appears to be no classical bulge but rather a nuclear continuation of the super-thin disk. The super-thin, thin, thick, and bar components contribute roughly 30%, 42%, 13%, and 15% (respectively) to the total K s-band luminosity. Disk axial ratios (length/height) decrease from 30 to 3 from super-thin to thick components. Both exponential and sech2 vertical SB profiles fit the data equally well. We find that the super-thin disk is significantly brighter in the K s-band than typically assumed in integrated spectral energy distribution models of NGC 891: it appears that in these models the excess flux, likely produced by young stars in the super-thin disk, has been mistakenly attributed to the thin disk.
galaxies: individual: NGC 891; galaxies: photometry; galaxies: spiral; galaxies: stellar content; galaxies: structure
Astrophysics - Cosmology and Extragalactic Astrophysics; Astrophysics - Galaxy Astrophysics