Supermassive black holes in the Sbc spiral galaxies NGC 3310, NGC 4303 and NGC 4258 ,

We have undertaken an HST Space Telescope Imaging Spectrograph survey of 54 late type spiral galaxies to study the scalin g relations between black holes and their host spheroids at the low mass end. Our aim is to measure black hole masses or to set upper limits for a sizeable sample of spiral galaxies. In this paper we present new Space Telescope Imaging Spectrograph (STIS) observations of three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical emission lines Hα λ 6564A, [NII]λλ 6549, 6585A and [SII]λλ 6718, 6732A were used to study the kinematics of the ionized gas in the nuclear region of each galaxy with a∼ 0.07 ′′ spatial resolution. Our STIS data for NGC 4258 were analyzed in conjunction with archival ones to compare the gas kinematical estimate of the black hole mass with the accurate value from H20-maser observations. In NGC 3310, the observed gas kinematics is well matched by a circularly rotating disk model but we are only able to set an upper limit to the BH mass which, taking into account the allowed disk inclinations, varies in the range 5.0× 10 6 − 4.2× 10 7 M⊙ at the 95% confidence level. In NGC 4303 the kinematical data require the presence of a BH with mass MBH = (5.0) +0.87