Local Tadpole Galaxies
  Tadpole galaxies have a giant star-forming region at the end of an elongated
intensity distribution. Here we use SDSS data to determine the ages, masses,
and surface densities of the heads and tails in 14 local tadpoles selected from
the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to
tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar
mass in the head scales linearly with restframe galaxy luminosity, ranging from
~10^5 M_solar at galaxy absolute magnitude U=-13 mag to 10^9 M_solar at U=-20
mag. The corresponding head surface density increases from several M_solar
pc^{-2} locally to 10-100 M_solar pc^{-2} at high redshift, and the star
formation rate per unit area in the head increases from ~0.01 M_solar yr^{-1}
kpc^{-2} locally to ~1 M_solar yr^{-1} kpc^{-2} at high z. These local values
are normal for star-forming regions, and the increases with redshift are
consistent with other cosmological star formation rates, most likely reflecting
an increase in gas abundance. The tails in the local sample look like
bulge-free galaxy disks. Their photometric ages decrease from several Gyr to
several hundred Myr with increasing z, and their surface densities are more
constant than the surface densities of the heads. The far outer intensity
profiles in the local sample are symmetric and exponential. We suggest that
most local tadpoles are bulge-free galaxy disks with lopsided star formation,
perhaps from environmental effects such as ram pressure or disk impacts, or
from a Jeans length comparable to half the disk size.
