Mathematics – Logic
Scientific paper
Oct 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aps..tsf..be09b&link_type=abstract
American Physical Society, Texas Section Fall Meeting, October 10-11, 1997, abstract #BE.09
Mathematics
Logic
Scientific paper
Early in extragalactic astronomy it was noticed that nearly every spiral galaxy had almost precisely the same central optical surface brightness, the amount of light measured per unit area. Freeman (1970) quantified this property of spirals and measured the average surface brighness value to be 21.65 mag/arcsec^2, with a remarkably small scatter of 0.3 mag/arcsec^2. The reason for this ``universal'' surface brightness value is difficult to explain physically, given that Hubble morphological sequence represents galaxies with different kinematic, structural and starforming properties. The motivation behind our study is to see whether or not the constant surface brightness trend holds for Freeman galaxies at infrared wavelengths, where a different (older) component of the stellar population is being traced, and also the effects of internal dust within the galaxies are much less pronounced. Our use of data from the galaxy infrared catalogue by Longo et al (1988) shows a clear correlation between infrared surface brightness and morphological type. Bulge-dominated (early type) spiral galaxies have brighter surface brightnesses than disk-dominated (late type) spirals. Specifically, Sa galaxies have the brightest surface brightess, Sb galaxies are less bright, Sc's are even dimmer, and Sd's are the dimmest. The fact that such a trend is seen at infrared wavelengths, but not at optical (B-band) wavelengths, may provide insight into the history of the disks themselves.
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