Nancy A. Levenson
Science Highlights
A diverse collection of scientific results was published with Gemini
data in 2014. These highlights provide a sample of the types of
cutting-edge science our users are doing.
January 2015
Discrepant Measurements
of Stellar Motions in Spiral
Galaxies
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 oneto-one relationship.
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 nearinfrared 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
January 2015
2014 Year in Review
GeminiFocus 23