Nancy A. Levenson
Science Highlights
This month’s Science Highlights reveal how Gemini’s evolving suite
of state-of-the-art instruments are providing astronomers with the
tools needed to explore the origins of lenticular galaxies, energetic
outflows from active galactic nuclei, and star-forming clumps in
high-redshift galaxies.
The Origin of Lenticular Galaxies
Lenticular (S0) galaxies are more common now than they were in the past, implying that
they represent the late stages or endpoints of galactic evolution. Their precursors are likely
spiral galaxies that have lost their disks. New work led by Evelyn Johnston (University of
Nottingham) specifically traces the properties of their component stellar populations to
provide evidence for this transformation.
The research team found that, unlike spiral galaxies (such as the Milky Way), lenticular galaxies have bulges that are younger and more metal-rich than their disks. The team describes
an evolutionary process whereby enriched gas in the spiral disk moves to the bulge, providing the material for the last episode of star formation in the new lenticular galaxy.
The researchers concentrate on a sample of 21 S0 galaxies located in the Virgo Cluster. They
employ a novel analysis technique, which uses the spatial light profile to decompose the
separate bulge and disk spectra for each galaxy. This simple spatial model consists of only
the bulge and disk components, so complicated morphologies, such as dust lanes and rings,
are problematic.
In all cases, the team needs high signal-to-noise ratios to extract the distinct spectra, which
is possible in the relatively nearby Virgo Cluster and using the Gemini Multi-Object Spectrographs (GMOS) at both Gemini North and South. Absorption lines yield age and metal-
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GeminiFocus
July 2014