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 \sim 10 ^ { 5 } M _ { \odot } at galaxy absolute magnitude U = -13 mag to 10 ^ { 9 } M _ { \odot } at U = -20 mag .
The corresponding head surface density increases from several M _ { \odot } pc ^ { -2 } locally to 10 - 100 M _ { \odot } pc ^ { -2 } at high redshift , and the star formation rate per unit area in the head increases from \sim 0.01 M _ { \odot } yr ^ { -1 } kpc ^ { -2 } locally to \sim 1 M _ { \odot } 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 .