The origin of star-forming rings in S0 galaxies by J. L. Tous et al. on Monday 21 November
Spatially resolved IFS maps in a sample of $532$ S0 galaxies from the MaNGA
survey have unveiled the existence of inner rings ($\langle R\rangle\sim
1\,R_\mathrm{e}$) betraying ongoing star formation in a number of these
objects. Activity gradients averaged over bins of galactocentric radius up to
$\sim 1.5\,R_\mathrm{e}$ have been measured in the subspace defined by the
first two principal components of the optical spectra of these galaxies. We
find that the gradients sign is closely related to the presence of such rings
in the spectral maps, which are specially conspicuous in the equivalent width
of the H$\alpha$ emission line, EW(H$\alpha$), with a fractional abundance
$\unicode{x2014}21\unicode{x2013}34\%\unicode{x2014}$ notably larger than that
inferred from optical images. While the numbers of S0s with positive, negative,
and flat activity gradients are comparable, star-forming rings are largely
found in objects for which quenching proceeds from the inside-out, in good
agreement with predictions from cosmological simulations studying S0 buildup.
Assessment of these ringed structures indicates that their frequency increases
with the mass of their hosts, that they have shorter lifetimes in galaxies with
ongoing star formation, that they may feed on gas from the disks, and that the
local environment does not play a relevant role in their formation. We conclude
that the presence of inner rings in the EW(H$\alpha$) is a common phenomenon in
fully formed S0s, possibly associated with annular disk resonances driven by
weakly disruptive mergers preferentially involving a relatively massive primary
galaxy and a tiny satellite strongly bound to the former.
arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.09697v1
