Extreme Galaxies

The take home idea is that thesebright galaxies are bright because they are passing through an era of starformation.  That works rather well as ahypothesis.  Why such behavior should becyclical is hardly answered and needs more ideas and data.

Thus we have evidence thatgalaxies exhibit cyclical behavior, or alternately our distance model is inerror which appears unlikely or an as yet unknown factor is involved.  I like the cyclic explanation but see noobvious mechanism unless we are seeing the remnant of a super nova triggeringstar formation and this is the after glow.

It would be worthwhile todetermine the brightness of each galaxy to detect the distribution ofbrightness generally.  That may link itall to the phenomenon of super novae.

February 22, 2011

Arp 220 is the closest galaxy to the Milly Way with an extremeluminosity, defined as being more than about 300 times that of our own galaxy.Some dramatic galaxies have values of luminosity ten times brighter still.Astronomers are still piecing together the reasons for these huge energyoutputs, while sorting out why our own galaxy is so modest.

The two primary suspects for the energetics are bursts of star formation thatproduce many hot young stars, and processes associated with accretion ofmaterial onto a supermassive black hole at a galaxy's nucleus. Arp 220 is theclosest example, and one of the best places to probe these scenarios.

A team of astronomers have used the Submillimeter Array (SMA) to obtainthe first unbiased galaxy survey of molecular and atomic lines using atelescope array. They covered a complete, large wavelength interval in themillimeter regime that is accessible through Earth's atmosphere. 

The team reports finding seventy-three spectral features from fifteen molecularspecies in this survey band. A remarkable 28% of the total flux from thisgalaxy in this band is emitted by these molecules. The SMA also obtains imagesof the galaxy at each of the many wavelengths.

The results are consistent with Arp 220's luminosity being driven primarily bystar-formation. The chemistry of the galaxy derived from the observations alsoleads to this conclusion, with species normally enhanced by star formationclearly detected. Moreover, it appears one such burst of activity is currentlyunderway. 

The team estimates, for this extreme galaxy, that several million regions ofactivity are localized within a relatively small volume (a few thousand light-years)around the nucleus. The new results are an important improvement in ourunderstanding of what powers extreme galaxies, and how they differ from theMilky Way.

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