Aperture Synthesis CO(J=1—0) Observations and Near-Infrared Photometry of the Non-Barred Seyfert Galaxy NGC 5033

Abstract

Abstract Aperture synthesis observations of CO($J = 1 \hbox{-} 0$) emission and near-infrared broad-band photometry of the non-barred Seyfert galaxy NGC 5033 ($D = 18.7 \,\mathrm{Mpc}$) were performed. Our ${3\rlap {.}{}^{\mathrm {\prime \prime }}9} \times {3\rlap {.}{}^{\mathrm {\prime \prime }}6}$ resolution CO observations reveal a perturbed distribution and the kinematics of molecular gas in the center of NGC 5033; we find the characteristic gaseous features that are widely observed in barred spiral galaxies, such as two bright CO peaks near the center (separated by $\sim 3^{\prime\prime}$ or 270 pc from the nucleus), two offset ridges of CO emission emanating from the CO peaks, and a CO ring (with a radius of $\sim 14^{\prime\prime}$ or 1.3 kpc). Double-peaked velocity profiles are also evident near the two CO peaks, implying that these CO peaks are orbit crowding zones in a barred/oval potential. Although NIR data only give an upper limit of the possible bar lengths due to a large inclination of the NGC 5033 disk ($i = 68^{\circ}$), our CO data clearly suggests the presence of a small (the semi-major axis of about $12^{\prime\prime} \hbox{-} 15^{\prime\prime}$ or 1.1–1.4 kpc) nuclear bar (or oval structure) in the center of the “non-barred” galaxy NGC 5033. Our results demonstrate that high-resolution CO imaging-spectroscopy is useful to search for nuclear bars, even in highly inclined systems where isophoto fitting techniques are not applicable. We find that the gas mass-to-dynamical mass ratio, $M_\mathrm{gas}/M_\mathrm{dyn}$, is small ($\leq 1\%$) within a radius of $2^{\prime\prime}$ or 180 pc, in contrast to starburst nuclei. This implies that the starburst does not cohabitate in the type-1.5 Seyfert nucleus of NGC 5033.