Bibcode
Sarzi, Marc; Shields, Joseph C.; Schawinski, Kevin; Jeong, Hyunjin; Shapiro, Kristen; Bacon, Roland; Bureau, Martin; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. Tim; Emsellem, Eric; Falcón-Barroso, J.; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; van den Bosch, Remco C. E.; van de Ven, Glen; Yi, Sukyoung K.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 402, Issue 4, pp. 2187-2210.
Advertised on:
3
2010
Número de citas
285
Número de citas referidas
263
Descripción
Following our study on the incidence, morphology and kinematics of the
ionized gas in early-type galaxies, we now address the question of what
is powering the observed nebular emission. To constrain the likely
sources of gas excitation, we resort to a variety of ancillary data we
draw from complementary information on the gas kinematics, stellar
populations and galactic potential from the SAURON data, and use the
SAURON-specific diagnostic diagram juxtaposing the [OIII]
λ5007/Hβ and [NI] λλ5197, 5200/Hβ line
ratios. We find a tight correlation between the stellar surface
brightness and the flux of the Hβ recombination line across our
sample, which points to a diffuse and old stellar source as the main
contributor of ionizing photons in early-type galaxies, with
post-asymptotic giant branch (pAGB) stars being still the best candidate
based on ionizing balance arguments. The role of AGN photoionization is
confined to the central 2-3arcsec of an handful of objects with radio or
X-ray cores. OB-stars are the dominant source of photoionization in 10
per cent of the SAURON sample, whereas for another 10 per cent the
intense and highly ionized emission is powered by the pAGB population
associated to a recently formed stellar subcomponent. Fast shocks are
not an important source of ionization for the diffuse nebular emission
of early-type galaxies since the required shock velocities can hardly be
attained in the potential of our sample galaxies. Finally, in the most
massive and slowly or non-rotating galaxies in our sample, which can
retain a massive X-ray halo, the finding of a spatial correlation
between the hot and warm phases of the interstellar medium (ISM)
suggests that the interaction with the hot ISM provides an additional
source of ionization besides old ultraviolet-bright stars. This is also
supported by a distinct pattern towards lower values of the
[OIII]/Hβ ratio. These results lead us to investigate the relative
role of stellar and AGN photoionization in explaining the ionized gas
emission observed in early-type galaxies by the Sloan Digital Sky Survey
(SDSS). By simulating how our sample galaxies would appear if placed at
further distance and targeted by the SDSS, we conclude that only in very
few, if any, of the SDSS galaxies which display modest values for the
equivalent width of the [OIII] line (less than ~2.4 Å) and
low-ionization nuclear emission-line region like [OIII]/Hβ values
the nebular emission is truly powered by an AGN.
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