SPECTROSCOPIC AND PHOTOMETRIC STUDY OF STARBURST GALAXIES: OPTICAL AND NEAR INFRARED PROPERTIES OF A BLUE COMPACT DWARF GALAXY MRK 49 IN THE VIRGO CLUSTER

Abstract

We present optical and near-infrared imaging and long-slit spectroscopy for the blue compact dwarf galaxy (BCD) Mrk 49 in the Virgo Cluster. The surface brightness distribution analysis shows that Mrk 49 consists of an off-centered blue bright compact core of r = 10" and a red faint outer exponential envelope. The <TEX>$H_{\alpha}$</TEX> image and color difference suggest that these two components have different stellar populations: a high surface brightness population of massive young stars and an underlying low surface brightness population of older stars. The redder near-infrared colors of the inner most region suggest that the near-infrared flux of Mrk 49 originates from evolved massive stars associated with the current star-forming activity. The total apparent magnitude is <TEX>$B_T\;=\;14.32$</TEX> mag and the mean effective surface brightness is <TEX>${\mu}_{eff}(B)\;=\;21.56$</TEX> mag <TEX>$arcsec^{-2}$</TEX>. Long-slit spectroscopy shows that Mrk 49 rotates apparently as a solid body within r = 10" in a plane at position angle 55 degrees with an amplitude of about <TEX>$20\;km\;sec^{-1}$</TEX>. The measured radial velocity of Mrk 49 was derived as <TEX>$1,535\;km\;sec^{-1}$</TEX>; and the total mass of stars and gases is in the range of 3 to <TEX>$6\;{\times}\;10^9\;M_{\odot}$</TEX>. The mass-to-light ratios for the central region of Mrk 49 in I and B band are estimated 1.0 and 0.5, respectively. The upper limit of the dark matter to visible matter ratio seems to be < 5. The oxygen abundance is <TEX>$12\;+\;\log(O/H)\;=\;8.21\;{\pm}\; 0.1$</TEX> which is about one quarter of the solar value while the relative helium abundance appears to be similar to that of the sun.