The global NIR properties of the largest galaxies are presented, including detailed analysis of the 100 largest angular-extent galaxies in the sky. Photometry and basic measurements are derived from mosaic images built from the Two Micron All Sky Survey, comprising the Large Galaxy Atlas. This Atlas will be part of the larger 2MASS Extended Source Catalog (~1.65 million sources), thus completing the bright end of the Catalog, and effectively extending the Catalog across 14 magnitudes of dynamic range in integrated flux.
The 1 arcsec pixel resolution and 2 arcsec beam resolution images reveal internal galaxy components, including spheroids and bulges, spirals, giant molecular clouds, warps and bars, spanning all Hubble types. We present size, orientation, integrated fluxes, surface brightness and imaging data for these galaxies and several hundred more large galaxies.
We show that in the near-infrared galaxies appear smooth and symmetric, exhibiting low order spiral modes (one or two spiral arm structures for disk galaxies), and morphologies that are often dramatically different from their optical counterparts (e.g., NGC 253, M51). We show that small morphological differences are seen between the extreme late and early-type spirals, as revealed in the radial profile, color and surface brightness measurements. In comparison with optical imaging, we show that large-scale bars have suggestive signatures in B-K central surface brightness. We also show that galaxies in the NIR appear much smaller and fainter in surface brightness compared to the optical, particularly for the extreme late-type, irregular and dwarf galaxies.
For disk galaxies, these results are consistent with the emerging paradigm that the stellar Population I components are (for the most part) de-coupled from the underlying stellar Population II component that constitutes the mass-"backbone" of galaxies. The 2MASS Large Galaxy Atlas will be integrated into the final all-sky 2MASS extended source catalog, and can be accessed through the NASA Extragalactic Database (for images) and the Infrared Science Archive (tabular data).