  Recent far-UV (FUV) and near-UV (NUV) observations of the nearby galaxy
NGC4625 made by the Galaxy Evolution Explorer (GALEX) show the presence of an
extended UV disk reaching 4 times the optical radius of the galaxy. The
UV-to-optical colors suggest that the bulk of the stars in the disk of NGC4625
are currently being formed, providing a unique opportunity to study today the
physics of star formation under conditions similar to those when the normal
disks of spiral galaxies like the Milky Way first formed. In the case of
NGC4625, the star formation in the extended disk is likely to be triggered by
interaction with NGC4618 and possibly also with the newly discovered galaxy
NGC4625A. The positions of the FUV complexes in the extended disk coincide with
peaks in the H I distribution. The masses of these complexes are in the range
10^3-10^4 Msun with their Halpha emission (when present) being dominated by
ionization from single stars.

Astrophysics