Bibcode
Gomes, J. M.; Papaderos, P.; Kehrig, C.; Vílchez, J. M.; Lehnert, M. D.; Sánchez, S. F.; Ziegler, B.; Breda, I.; Dos Reis, S. N.; Iglesias-Páramo, J.; Bland-Hawthorn, J.; Galbany, L.; Bomans, D. J.; Rosales-Ortega, F. F.; Cid Fernandes, R.; Walcher, C. J.; Falcón-Barroso, J.; García-Benito, R.; Márquez, I.; Del Olmo, A.; Masegosa, J.; Mollá, M.; Marino, R. A.; González Delgado, R. M.; López-Sánchez, Á. R.; Califa Collaboration
Bibliographical reference
Astronomy and Astrophysics, Volume 588, id.A68, 58 pp.
Advertised on:
4
2016
Journal
Citations
95
Refereed citations
91
Description
Context. The morphological, spectroscopic, and kinematical properties of
the warm interstellar medium (wim) in early-type galaxies (ETGs) hold
key observational constraints to nuclear activity and the buildup
history of these massive, quiescent systems. High-quality integral field
spectroscopy (IFS) data with a wide spectral and spatial coverage, such
as those from the CALIFA survey, offer an unprecedented opportunity for
advancing our understanding of the wim in ETGs. Aims: This
article centers on a 2D investigation of the wim component in 32 nearby
(≲150 Mpc) ETGs from CALIFA, complementing a previous 1D analysis
of the same sample. Methods: The analysis presented here includes
Hα intensity and equivalent width (EW) maps and radial profiles,
diagnostic emission-line ratios, and ionized-gas and stellar kinematics.
It is supplemented by τ-ratio maps, which are a more efficient means
to quantify the role of photoionization by the post-AGB stellar
component than alternative mechanisms (e.g., AGN, low-level star
formation). Results: Confirming and strengthening our previous
conclusions, we find that ETGs span a broad continuous sequence in the
properties of their wim, exemplified by two characteristic classes. The
first (type i) comprises systems with a nearly constant EW(Hα) in
their extranuclear component, which quantitatively agrees with (but is
no proof of) the hypothesis that photoionization by the post-AGB stellar
component is the main driver of extended wim emission. The second class
(type ii) stands for virtually wim-evacuated ETGs with a very low
(≤0.5 Å), outwardly increasing EW(Hα). These two classes
appear indistinguishable from one another by their LINER-specific
emission-line ratios in their extranuclear component. Here we extend the
tentative classification we proposed previously by the type i+, which is
assigned to a subset of type i ETGs exhibiting ongoing low-level
star-forming activity in their periphery. This finding along with faint
traces of localized star formation in the extranuclear component of
several of our sample galaxies points to a non-negligible contribution
by OB stars to the global ionizing photon budget in ETGs. Additionally,
our data again highlight the diversity of ETGs in their gaseous and
stellar kinematics. While in one half of our sample, gas and stars show
similar (yet not necessarily identical) velocity patterns that are both
dominated by rotation along the major galaxy axis, our analysis also
documents several cases of kinematical decoupling between gas and stars,
or rotation along the minor galaxy axis. We point out that the generally
very low (≲1 Å) EW(Hα) of ETGs requires a careful
quantitative assessment of potential observational and analysis biases
in studies of their wim. With standard emission-line fitting tools,
Balmer emission lines become progressively difficult to detect below an
EW(Hα) ~ 3 Å, therefore our current understanding of the
presence and 2D emission patterns and kinematics of the diffuse wim ETGs
may be severely incomplete. We demonstrate that at the typical
emission-line detection threshold of ~2 Å in previous studies,
most of the extranuclear wim emission in an ETG may evade detection,
which could in turn cause ETGs to be classified as entirely gas-devoid
systems. Conclusions: This study adds further observational
evidence for a considerable heterogeneity among ETGs with regard to the
physical properties and 2D kinematics of their extended wim component,
and it clearly shows that a comprehensive understanding of these systems
requires IFS studies over their entire optical extent.