Far-UV Emission Properties of FR1 Radio Galaxies
  The power mechanism and accretion geometry for low-power FR1 radio galaxies
is poorly understood in comparison to Seyfert galaxies and QSOs. In this paper
we use the diagnostic power of the Lya recombination line observed using the
Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST) to
investigate the accretion flows in three well-known, nearby FR1s: M87, NGC4696,
and HydraA. The Ly$\alpha$ emission line's luminosity, velocity structure and
the limited knowledge of its spatial extent provided by COS are used to assess
conditions within a few parsecs of the super-massive black hole (SMBH) in these
radio-mode AGN. We observe strong Ly$\alpha$ emission in all three objects with
similar total luminosity to that seen in BL Lacertae objects. M87 shows a
complicated emission line profile in Lya which varies spatially across the COS
aperture and possibly temporally over several epochs of observation. In both
NGC 4696 and M87, the Ly$\alpha$ luminosities $\sim 10^{40}$ ergs/s are closely
consistent with the observed strength of the ionizing continuum in Case B
recombination theory and with the assumption of near unity covering factor. It
is possible that the Ly$\alpha$ emitting clouds are ionized largely by beamed
radiation associated with the jets. Long-slit UV spectroscopy can be used to
test this hypothesis. Hydra A and the several BL Lac objects studied in this
and previous papers have Lya luminosities larger than M87 but their
extrapolated, non-thermal continua are so luminous that they over-predict the
observed strength of Ly$\alpha$, a clear indicator of relativistic beaming in
our direction. Given their substantial space density ($\sim 4\times10^{-3}
Mpc^{-3}$) the unbeamed Lyman continuum radiation of FR1s may make a
substantial minority contribution (~10%) to the local UV background if all FR1s
are similar to M87 in ionizing flux level.
