GMRT H i study of giant low surface brightness galaxies

Abstract

We present HI observations of four giant low surface brightness (GLSB) galaxies UGC 1378, UGC 1922, UGC 4422 and UM 163 using the Giant Meterwave Radio Telescope (GMRT). We include HI results on UGC 2936, UGC 6614 and Malin 2 from literature. HI is detected from all the galaxies and the extent is roughly twice the optical size; in UM 163, HI is detected along a broken disk encircling the optical galaxy. We combine our results with those in literature to further understand these systems. The main results are the following: (1) The peak HI surface densities in GLSB galaxies are several times 10^21 cm^{-2} . The HI mass is between 0.3 - 4 x 10^10 M_Sun/yr, dynamical mass ranges from a few times 10^11 M_Sun/yr to a few times 10^12 M_Sun/yr. (2) The rotation curves of GLSB galaxies are flat to the outermost measured point with rotation velocities of the seven GLSB galaxies being between 225 and 432 km s^{-1}. (3) Recent star formation traced by near-ultraviolet emission in five GLSB galaxies in our sample appears to be located in rings around the galaxy centre. We suggest that this could be due to a stochastic burst of star formation at one location in the galaxy being propagated along a ring over a rotation period. (4) The Hi is correlated with recent star formation in five of the seven GLSB galaxies.