Devasthal Fast Optical Telescope observations of Wolf-Rayet dwarf galaxy Mrk 996

Abstract

The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical telescope, recently installed at Devasthal, Nainital. We present here the first results using an \Ha filter with this telescope on a Wolf-Rayet dwarf galaxy Mrk 996. The instrumental response and the \Ha sensitivity obtained with the telescope are $(3.3 \pm 0.3)\times 10^{-15} (erg s^{-1} cm^{-2})/(counts s^{-1})$ and $7.5\times10^{-17} erg s^{-1} cm^{-2} arcsec^{-2}$ respectively. The \Ha flux and the equivalent width for Mrk~996 are estimated as $(132 \pm 37)\times 10^{-14} erg s^{-1} cm^{-2}$ and $\sim$96 $\mathring{A}$ respectively. The star formation rate is estimated as $0.4\pm0.1 M_\odot$yr$^{-1}$. Mrk~996 deviates from the radio-FIR correlation known for normal star forming galaxies with a deficiency in its radio continuum. The ionized gas as traced by \Ha emission is found in a disk shape which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that galaxy-galaxy tidal interaction is the main cause of the WR phase in Mrk~996.