Off-nucleus IUE observations of NGC 1275.

Abstract

We have mapped the brightest parts of the two velocity systems of ionized gas in NGC 1275 with IUE. We have detected extended Lyα and an UV continuum at several positions. The Lyα emission originates from the low velocity system and, we argue, probably also the UV continuum. The UV continuum is consistent with star bursts with ages <= 2 10^7^ yr or a continuous star formation rate of 50 M_sun_ yr^-1^ during a period <= 10^8^ yr. The UV continuum constrains the formation rate of stars with masses larger than 2.5 M_sun_ to 5-15 % of the mass accretion rate inferred from X-ray observations. We find that the population of stars responsible for the UV continuum is not capable of photoionizing the low velocity gas. We speculate that the low velocity gas is associated with `H II' atmospheres around low-mass molecular clouds (inferred from CO observations). In this scenario, the gas is both evaporated from the molecular clouds and ionized by hot electrons of the X-ray emitting gas. This means an additional energy loss of the same order of magnitude as the energy lost by X-ray photons.