Wavelength Dependence of Classification Parameters

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Wavelength Dependence of Classification Parameters As shown in the M81 images atop the classification page , some of the quantities we've been decomposing are strong functions of wavelength, particularly bulge/disk ratio. Classically this has been done in the optical band, but sometimes (as in very dusty IR-bright galaxies, see Scoville et al. 2000 AJ 119, 991 and their data pages ), we are driven to use wavelengths where there's actually something to be seen. Elliptical galaxies generally show only the most subtle structural changes, but of course spirals become more bulge-dominated at longer wavelengths, while bulges sometimes disappear in the UV. There have been several recent surveys which should eventually put this on a quantifiable bases (for example the Ohio State survey ). Extension to the near-IR is especially important, since dust penetration and changes in stellar population
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Unformatted text preview: can make the disks look quite different. One initial attempt at a near-IR Hubble diagram was done using 2MASS images (rather shallow in surface-brightness sensitivity) by Jarrett (2000, PASP 112, 1008). Once again, note that all these exercises can in principle be done in any passband. It's common to use differences in disk scale length at various wavelengths to measure age, metallicity, or extinction gradients (depending on the passbands and one's level of understanding of the system). Ryder & Dopita (1994 ApJ 430, 142) applied it to compare the distributions of current star formation (from azimuthally averaged H-alpha images) to the integral of past star formation (from optical continuum images), to test whether gas is being depleted by star formation uniformly or from the outside inward (they come down on a remarkably uniform behavior, by the way)....
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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