Determining distances to individual galaxies using a
variety of methods is a fundamental part of mapping out
the distribution of galaxies in the Universe. Research
work at Tuorla
Observatory, part of a PhD thesis by Rami Rekola
has recently focussed on the issue of distances to nearby
galaxies. Three very different techniques with which to
measure distances: the first based on the brightness of
small, ionized spheres of gas in the galaxies, called
planetary nebula; the second, a classical technique, of
using the brightness of pulsating, luminous stars called
cepheids; and the third, a method based on the variations
in brightness from place to place within a high quality
image of a galaxy.
Part of the
giant spiral galaxy IC 342. It lies just beyond our own Local Group of
Galaxies in another group called Maffei Group or IC342/Maffei Group.
The image above is a combination of images taken with BVRI filters
(roughly blue, visual = green, red, and infrared) by Rami Rekola and
Kari Nilsson at the Nordic Optical Telescope. |
Distances have been obtained for dwarf elliptical and irregular
galaxies of the extended local group using the NOT, in collaboration with Helmut
Jerjen at Mount Stromlo
Observatory. A Cepheid based distance has been obtained for IC
342, a large, starburst spiral galaxy, for which few (and
contradictory) distance estimates exist in the literature, using
observations with the NOT over a
long baseline (5 years). Planetary nebulae have been used to make a
distance determination to NGC 253 (using imaging data from the ESO 3.6
metre).
Rami Rekola's work is part of a longer term programme to assemble
reliable masses and distances for the extended local group galaxies
with a view to simulating their dynamics. Many of these galaxies are
at distances where the effects of "dark
energy" on the Hubble flow are first noticable; accurate distances
to the galaxies are therefore of particular interest. The surface
brightness fluctuation method has been shown to be a particularly
efficient means of determining good distances, especially for dwarf
galaxies for which other methods cannot be easily applied. We are
planning to use the method to measure distances for large numbers of
nearby dwarfs in an ongoing effort to understand better the local
Hubble flow.
Posted 14th September 2005.
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