Ram Pressure Stripping in the Low-Luminosity Virgo Cluster Elliptical Galaxy NGC 4476

We present a deep VLA search for HI emission from the low-luminosity VirgoCluster elliptical galaxy NGC 4476, which contains 1.1 x 10^8 M_sun ofmolecular gas in an undisturbed disk in regular rotation. No HI was detected.The rms noise in the final image corresponds to a 3 sigma column densitysensitivity of 1.2 x 10^20 cm^{-2} at the position of NGC 4476, averaged overthe 4 kpc beam. The total HI mass is less than 1.5 x 10^7 M_sun. If we compareour HI upper limit to the H_2 content, we find that NGC 4476 is extremelydeficient in HI compared to other galaxies detected in these two species. TheH_2/HI mass ratio for NGC 4476 is > 7, whereas typical H_2/HI ratios forelliptical galaxies detected in both HI and H_2 are <~2. Based on this extremeHI deficiency and the intra-cluster medium (ICM) density at the projecteddistance from M87 we argue that either NGC 4476 has undergone ram-pressurestripping while traveling through the Virgo cluster core or its averagemolecular gas density is larger and its interstellar UV field is smaller thanin typical spiral galaxies. NGC 4476 is located 12' in projection from M87,which causes extreme continuum confusion problems. We also discuss in detailthe techniques used for continuum subtraction. The spectral dynamic range ofour final image is 50,000 to 1.Comment: accepted by A