Chandra Observations of Circumnuclear Star Formation in NGC 3351

The nearby SB(r)b galaxy NGC 3351 (M95) displays an ~600 pc diameter star-forming circumnuclear ring fueled by gas accreted through a stellar bar. The X-ray emission from this region is composed of numerous pointlike sources embedded in hot (kT=0.5+/-0.1 keV), nonuniform diffuse gas. Most of the pointlike sources are likely themselves concentrated regions of hot gas. The morphology of the X-ray emission is similar to, but not identical with, UV and Hα hot spots in the circumnuclear ring. The emission morphology can be understood if star formation is occurring through a series of instantaneous starbursts at various locations around the ring and the UV, Hα, and X-ray emission trace successively later stages in the evolution of the underlying stellar populations. X-ray emission extends at least 500 pc beyond the circumnuclear ring. This emission is interpreted as the result of gas outflow from the star-forming ring into the disk and halo of NGC 3351. There is evidence that the outflow is confined by cold ambient gas near the plane of the galaxy but that flow out of the plane is not restricted. The nucleus of the galaxy lacks both large amounts of hot gas and any pointlike source above an estimated X-ray luminosity of 10³⁷ ergs s^-1 in the 0.5-8.0 keV band. This luminosity is orders of magnitude too low to account for the observed nuclear Hα luminosity, 3.5×10³⁸ ergs s^-1, by X-ray photoionization.