Figure 2.
Three of the GNIRS
galaxy spectra from
the Mason et al.
paper, showing the
wavelengths of the
calcium triplet, CO
band heads, and
numerous other
atomic and molecular
features. The blue,
black, and green
lines are observed
spectra while the red
line is a combination
of empirical stellar
spectra. The close
resemblance between
the stellar and galaxy
data shows that most
of the structure in
the galaxy spectra is
composed of real, weak
absorption lines.
to be smaller than sCaT. The so-called “sigma-discrepancy” has implications for our
understanding of galaxy evolution; masses
derived from sCaT. imply that ULIRGS could
evolve into giant elliptical galaxies, whereas
sCO would imply them to be the ancestors of
much smaller galaxies.
Members of the team wondered whether
the sigma-discrepancy would also be observed in the cores of spiral galaxies. Their
measurements show that although a statistically significant discrepancy is present, it
is much smaller than that observed in the
ULIRGS and merger remnants (Figure 1). The
lower sCO indicates that a dynamically cold
stellar population is present in the spiral galaxies. Based on the fact that small velocity
dispersions and young stellar populations
have been observed to be spatially related
in IFU spectra of a handful of galaxies, Riffel
et al. speculate that the sigma-discrepancy is
evidence of recent nuclear star formation in
these spiral galaxies.
January 2015
This work used a set of 50 new GNIRS crossdispersed spectra of nearby galaxy centers
(Figure 2). With wide wavelength coverage
and generally good signal-to-noise ratio, the
spectra are also being used to investigate
several topics related to weakly active galaxies and their stellar populations. A sizable
international collaboration is now further
examining the data to model the stellar features and emission lines and exploring the
properties of the active galactic nuclei, as
well as other areas of study.
Full results from the current work are in press
in Monthly Notices of the Royal Astronomical
Society (view here) and a preprint is available
here. The paper presenting the data and
giving access to the reduced spectra, led
by Rachel Mason (Gemini Observatory), has
been submitted to The Astrophysical Journal
Supplement Series.
GeminiFocus
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