GMRT observations of NGC 2997 and radio detection of the circumnuclear ring

Abstract

We present high-resolution, high-sensitivity radio continuum observations of the nearby spiral galaxy NGC 2997 at 332, 616 and 1272 MHz using the Giant Metrewave Radio Telescope (GMRT). The integrated spectrum of this galaxy has a spectral index of -0.92 ($S_{\nu}\propto\nu^{\alpha}$) and we place an upper limit to the thermal fraction at 1272 MHz of ~ 10 per cent. Our multi-frequency study shows a relatively flat spectrum source ($\alpha$ ~ -0.6) at the centre of the galaxy. This leads to radio detection of a circumnuclear ring in the high resolution map at 1272 MHz. We detect five hotspots in the ring, with average star formation rate of ~ 0.024 $M_{\odot}\,yr^{-1}$, a median SN rate of ~ 0.001 $yr^{-1}$ and luminosity of $10^{20}$ W Hz$^{-1}$. We estimate an equipartition field in the central nuclear region of diameter ~ 750 pc to be about $30\,\mu$G. We also report several interesting features along the spiral arms. In this paper, we present the low frequency radio continuum maps, the spectral index distribution, the circumnuclear ring and the derived physical properties.