Ultraviolet-Optical observations of the Seyfert 2 Galaxies NGC 7130, NGC 5135 and IC 3639: Implications for the Starburst-AGN Connection

摘要

We present and discuss HST (WFPC2 and FOC) images and UV GHRS spectra plusground-based near UV through to near IR spectra of three Seyfert 2 nuclei (NGC7130, NGC 5135 and IC 3639). These galaxies, together to Mrk 477, were selectedfrom a bigger sample that comprises the 20 brightest Seyfert 2 nuclei, with thegoal to study the origin of the UV-optical-near IR featureless continuum inSeyfert 2 nuclei. These four galaxies have bolometric luminosities, as computedwith the four IRAS bands, of 10^11 Lsol. They are close enough to be resolvedwith HST the nuclear zone. This makes these Seyfert 2 galaxies benchmarks tostudy the Starburst-AGN connection in more distant galaxies. The data provide direct evidence of the existence of a central nuclearstarburst that dominates the UV light, and that seem to be responsible for theorigin of the so called featureless continuum. These starbursts are dusty andcompact. They have sizes (from less than 100 pc to a few hundred pc) muchsmaller and closer to the nucleus than that seen in the prototype Seyfert 2galaxy NGC 1068. The bolometric luminosity of these starbursts is similar tothe estimated bolometric luminosities of their obscured Seyfert 1 nuclei, andthus they contribute in the same amount to the overall energetics of thesegalaxies.