The extended H i disk and star formation in the dwarf spiral galaxy NGC 4701

Abstract

We present H i, optical, and near-infrared observations of the nearby bulgeless, dwarf spiral galaxy NGC 4701. The galaxy lies on the Virgo filament and is one of the most gas-rich dwarfs in our local environment. Our aim is to understand the gas-disk morphology of the galaxy and see how it relates to the star formation in its disk. Our Hα observations reveal a small star-forming disk associated with the old stellar disk of radius ~50''. However, the B-band and near-UV GALEX emission extend out to a radius of R b25 = 108'', revealing an extended star-forming disk lying in the halo-dominated region of the galaxy. The H i disk extends out to a radius of ~200'', which is close to four times the size of the old stellar disk. The rotation curve has a flat rotation velocity of ~125 km s−1 and starts falling after a radius of 160'', indicating that the dark matter mass is at least ~76% of the galaxy mass. The environment and H i rich nature suggest that cold gas accretion could be driving the star formation in the outer blue disk. The disk morphology and star formation in NGC 4701 are very similar to those of late-type spirals that have extended UV disks. Thus, our observations lead us to conclude that NGC 4701 is a classic example of a late-type dwarf spiral galaxy and its nature supports the idea that dwarfs also follow a morphological sequence similar to spirals on the Hubble Sequence