Size and Shape of Galaxies as seen with 2MASS, IRAC and WISE
An ellipsoid model (representing an exponential-disk galaxy) is convolved with a symmetric gaussian that is matched to the beams of 2MASS, IRAC and WISE. The shape and size of the resulting ellipsoid is measured and compared between beams.

Example: Relatively small, inclined disk galaxy

Ellipsoid:
alpha = 2.0 arcsec;
axis ratio = 0.500;
R95 = 9.50 arcsec
w/ 2MASS
FWHM = 2.5 arcsec;
axis ratio = 0.562;
R95 = 9.60 arcsec
w/ IRAC
FWHM = 2.2 arcsec;
axis ratio = 0.549;
R95 = 9.55 arcsec
w/ WISE W1, W2, W3
FWHM = 6 arcsec;
axis ratio = 0.717;
R95 = 10.85 arcsec
w/ WISE W4
FWHM = 12 arcsec;
axis ratio = 0.874;
R95 = 17.00 arcsec

Table notes:


Semi-major axis of the disk galaxy compared to the actual radius due to the beam resolution.

Axis ratio departure from 0.5 due to the beam resolution.


Last update - [3 May 2009]
T.H. Jarrett (IPAC/SSC)