archive: SETI [ASTRO] Catalog Of Spiral Galaxies Shows Evidence Of Galactic

SETI [ASTRO] Catalog Of Spiral Galaxies Shows Evidence Of Galactic

Larry Klaes ( )
Mon, 03 May 1999 10:51:03 -0400

>X-Authentication-Warning: majordom set sender
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>Date: Sat, 1 May 1999 1:42:43 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Catalog Of Spiral Galaxies Shows Evidence Of Galactic
>Reply-To: Ron Baalke <>
>Ohio State University
>Jay Frogel, (614) 292-5651;
>Paul Eskridge, (614) 292-6925;
>Written by Pam Frost, (614) 292-9475;
>COLUMBUS, Ohio -- Astronomers compiling a catalog of spiral galaxies have
>discovered that collisions between such galaxies, as well as near-collisions,
>are more common than had been
>"It means there were more close encounters," said Jay Frogel, professor of
>astronomy at Ohio State. Frogel and Paul Eskridge, a postdoctoral research
>fellow, compiled pictures of more than 200 nearby spiral galaxies over the
>five years.
>When viewed through traditional optical telescopes, about 30 percent of those
>200 galaxies appear to contain a bar-shaped band of stars at the center.
>Astronomers call these galaxies "barred spirals."
>Frogel and Eskridge discovered that the fraction of strongly barred
galaxies was
>roughly twice as high when they viewed the same 200 galaxies through
infrared telescopes.
>The researchers presented their findings at a recent meeting of the American
>Astronomical Society in Austin, Texas.
>For some spiral galaxies, pinwheel-shaped arms of gas, dust, and stars extend
>directly out from the spherical nucleus of stars at the center. For barred
>spirals, the arms fan out from the ends of a bar-like structure.
>Astronomers think the bars form either when two galaxies collide or when they
>nearly miss each other as they drift through space.
>According to visual observations of the past, only about one-third of the
>galaxies near the Milky Way appeared to contain such a bar. However, computer
>simulations have predicted that many more barred spirals should exist.
>"People who model the dynamics of galactic evolution were wondering why we
>weren't seeing more of them," said Eskridge.
>Dust in the central regions of spiral galaxies can prevent a bar from
being seen
>at optical wavelengths -- the wavelengths of visible light.
>To see through the dust, the astronomers took advantage of a camera
designed and
>built at Ohio State. The Ohio State InfraRed Imager and Spectrometer (OSIRIS)
>records infrared radiation the way normal cameras record visible light.
>energy penetrates dust much more readily than visible light does.
>The astronomers' infrared observations revealed that approximately 30
percent of
>their 200-galaxy sample contains bars which are invisible at optical
>The finding indicates that galaxies in our area of the universe have
>with each other a good deal in the last 10 billion years.
>Compared to other infrared cameras, OSIRIS takes a wider picture of the
sky --
>wide enough to encompass the diameter of most galaxies visible from earth.
>Frogel and Eskridge used OSIRIS to take pictures of galaxies through
>at Lowell Observatory in Flagstaff, AZ, and American Observatory in Cerro
>Tololo, Chile.
>"Infrared observing gives us a chance to learn new things about galaxies,
>that we just couldn't figure out before," said Frogel. "We get a much clearer
>picture of what galaxies really look like."
>That's because most of the visible light from a galaxy emanates from
young, hot
>stars that represent only a fraction of the total mass. Older, cooler stars
>don't shine as bright, but radiate most of their energy at infrared
>What's more, the bars of barred spirals contain mostly old stars.
>Frogel explained that these older stars make up about 90 percent of the
mass of
>a galaxy, so infrared observations give the best view of how much matter
is in a
>galaxy and how the galaxy evolved.
>For instance, by comparing the visible, or optical, view of a galaxy to the
>infrared view, astronomers can tell whether most stars in the galaxy
formed long
>ago or more recently.
>There have been other such surveys in the past, but Ohio State's survey is
>more extensive. It also contains higher-quality images taken with long
>times in both the optical and infrared wavelengths. Each of the 200-plus
>galaxies required six hours of observation -- two at optical wavelengths and
>four at infrared -- which adds up to more than 1200 hours of observation
for the
>catalog as a whole.
>Frogel and Eskridge want to place the photos on a CD-ROM and distribute them
>through NASA, which may be able to use the infrared data to plan future
>space-based observing missions.
>This work was supported by the National Science Foundation. The funding
for the
>astronomers to build OSIRIS came from an Ohio Academic Enrichment grant that
>Frogel received when he first came to the university 11 years ago.
> # # #
>EDITOR'S NOTE: Select photographs of galaxies from the catalog are
available for
>downloading in GIF format on the World Wide Web page for the Ohio State
>University Bright Spiral Galaxy
>Survey at .