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Astrophysics at the UO

Small but active program
Galaxy Properties and Evolution (Bothun;
Schombert)
 Neutron Star equations of state (Imamura)
 Gravitational Waves (LIGO) (Frey)
 Theoretical Cosmology (Hsu; Kribs)
 Properties of Supernova (Bothun; Johnson)
 Alternative Gravity – MOND (Bothun; GS)

Shift in Astrophysics Research

Research now based in data mining more
so than telescope observations
The Ultraviolet Sizes of
Nearby Galaxies
A Link to Galaxy Evolution
When the Hubble Space Telescope Images the
Distant Universe (bottom image) it is detecting
the rest frame Ultraviolet Emission from these
highly redshifted galaxies. In order to better
understand these object, it is necessary to image
nearby galaxies in the Ultraviolet such as can
now be done with the GALEX telescope (right
image).
GALEX and XUV Disks
GALEX Imagery has discovered
that about 1/3 of all spiral galaxies
are significantly bigger in Ultraviolet
Light than in optical light. The
example shown to the left (NGC
4625) it typical; the bright whitish
inner part defines the optical size of
the galaxy, the bluish emission
shows the greatly extended
Ultraviolet emission (XUV).
This XUV light is remarkable for two reason: 1) it directly shows the UV sizes of
galaxies can be large relative to the optical size. This has clear implications
about the nature of high redshift galaxies as detected in deep Hubble fields, 2)
UV light comes from hot stars, which are usually newly formed. Hence these
XUV structures imply that star formation is now occurring around some galaxies
in very low density regions – this is unexpected
Space Grant Research
Supported year long ground
based imaging campaign at the
University of Oregon’s Pine
Mountain Observatory of
candidate galaxies for GALEX
mission.
New GALEX Results
NGC 5172: Confirms the XUV
phenomena – solid ellipse in the
right image shows the optical
extent of this galaxy (essentially
coincident with the inner ring in the
image below. The outer one, which
is clearly seen in the color
difference image, is a nearly
continuous ring of hot stars, again
implying the presence of significant
amounts of star formation in the
outer regions. This galaxy is
therefore clearly growing with time
and this has major implications with
respect to galaxy evolution.
New GALEX Results
When is a LSB galaxy not really a LSB
galaxy? The top image shows the optical
discovery image of this massive nearby galaxy –
most of its structure is not discernible. The
bottom image is the GALEX data. Voila – there
is really a galaxy there. There is no hint at the
LSB nature of this galaxy in the GALEX image
and the ratio of UV emission to optical emission
is unprecedented and strongly implies that this
galaxy is actually forming right now and hasn’t
had time to become more luminous in the optical
part of the spectrum. This is potentially a
major new discovery that strongly impacts
our ides about galaxy formation and
evolution and forms the basis for a larger
GAKEX campaign in the near future.
Multiwavelength Astronomy

Large Collaborations
Modified Newtonian Dynamics
• Alternative to Dark Matter – fits most all
the data well
• Whole Universe is Baryonic
• Gravity Force is a function of some scale
meaning at some scales, less force will be
required to produce a given acceleration