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The Question
(Submitted July 11, 1997)
I recently read a book which gave reference to the
Loh and Spillars test which can be used to find a
value of the Hubble Constant. Unfortunately, the
book did not give many details of this method
nor give any findings for this test.
Do you happen to know anything about the Loh &
Spillar test? Also do you know of any results this
test has provided?
The Answer
The method of Loh and Spillar uses the photometric
redshifts of nearly 1000 galaxies to determine cosmological
parameters. A photometric redshift is measured by observing
the flux of a galaxy through different filters, and combining
this information to determine the Spectral Energy Distribution
(SED) of the galaxy. This is different than the typical method
of determining redshifts, which uses the shift of narrow spectral
features. The photometric method concentrates on the broad
features and overall shape of the spectrum. It is easier to
obtain the photometric data than the spectroscopic data for
dim galaxies. Using imaging detectors helps even more when
multiple galaxies can be measured simultaneously.
The results of their test indicate that the Universe
is "flat", one of three possible overall geometries, and the
one that results in the Universe decelerating to zero expansion
rate as time approaches infinity.
You will find a lot of details about the method at the
web page:
http://astrowww.phys.uvic.ca/grads/gwyn/pz/index.html
Regards,
Padi Boyd
for the Ask a High-Energy Astronomer Team
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