GALACTIC STRUCTURE
Observing our own galaxy is a notoriously difficult and challenging problem.
We view the Galaxy from our position in the plane roughly two-thirds
of the distance from the center to the luminous edge. Interstellar
extinction limits visible studies of galactic structure to the solar
neighborhood, high latitudes and small "windows" near the
plane. Knowledge of the overall structure of the galactic disk comes
from radio and infrared measurements where the interstellar extinction is quite
low compared to the visible. To date, indirect evidence indicates
that our Galaxy is a mildly barred, possibly four-armed spiral.
UMass astronomers led the recently completed Two Micron All Sky Survey
(2MASS), which mapped the entire sky at 3 infrared wavelengths to a
sensitivity 50,000 times greater than the previous such survey, more
than 25 years ago. Surveying both the northern and southern
hemispheres, 2MASS is producing catalogs of more than 300 million
stars and 1 million galaxies. In particular, 2MASS is providing an
unprecedented view of the Milky Way. Since the extinction in the
near infrared is nearly an order of magnitude smaller than in the
visual, 2MASS provides an unbiased count of intrinsically distant
stars. Since the survey uniformly covers the entire sky, structures
on the largest scales are revealed by 2MASS, thus enabling studies
of the structure of the Galaxy, the stellar populations which make up
the Galaxy, and the distribution of interstellar dust. Analysis of
the this data will establish the galactic disk scale lengths and
heights, in-plane asymmetries such as bars and spiral arms, vertical
distortions such as warps, and a complete census of subsystems such
as star clusters. Interpretation of the more than 108
stars in the 2MASS point sources database will be a challenge for
UMass scientists.
