Nancy A. Levenson and Rachel Mason
Figure 1.
The stellar velocity
dispersions measured
using CO and the
calcium triplet are
significantly different
in spiral galaxies. The
solid line is a fit to the
data; the dashed line
shows the one-to-one
relationship.
Science Highlights
Gemini’s users continued to produce great science through the
year. Among the results featured in this latest sampling are critical
measurements of stellar motions in spiral galaxies, new perspectives
on the epoch of reionization of the early universe, and a look at the
origins of massive field stars in the Milky Way’s center.
Discrepant Measurements of Stellar
Motions in Spiral Galaxies
The bulge stars and central supermassive black holes
of galaxies are fundamentally related to each other,
and, empirically, measurements of their masses are
correlated. Determination of stellar velocity dispersion (s) conveniently provides the value for stars, allowing derivation of the black hole mass, which is otherwise difficult to measure directly. Observing nearby
spiral galaxies, however, an international team reports
that the values of s they measure in the near-infrared
are systematically different from shorter wavelength
measurements.
The team, led by Rogemar A. Riffel (Universidade Federal de Santa Maria, Brazil), used the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, comparing the stellar absorption lines of the CO band heads
around 2.3 microns and the 0.85 micron calcium triplet. In elliptical galaxies, sigma values derived from the two sets of lines agree well. However, in ultraluminous infrared galaxies (ULIRGs) and merger remnant galaxies, sCO tends
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GeminiFocus
January 2015