IR Compendium: Background: Extragalactic Science

	X-ray Chandra observes in this regime wavelength of light ~ 2 nm temperature of emitting matter ~ 1,500,000 K By studying galaxies in this regime, we see black hole accretion disks
	Ultraviolet (UV) HST and GALEX observe in this regime wavelength of light ~ 200 nm temperature of emitting matter ~ 14,500 K By studying galaxies in this regime, we see hot young stars
	Visible HST observes in this regime wavelength of light ~ 500 nm temperature of emitting matter ~ 5800 K By studying galaxies in this regime, we see run-of-the-mill stars (all ages)
	Near-infrared (Near-IR) 2MASS, NICMOS, and Spitzer observe in this regime wavelength of light ~ 1600 nm temperature of emitting matter ~ 1800 K By studying galaxies in this regime, we see very cool stars (usually old)
	Far-infrared (Far-IR) IRAS observed (and Spitzer observes) in this regime wavelength of light ~ 100,000 nm temperature of emitting matter ~ 29 K By studying galaxies in this regime, we see cool dust, which is heated by hot stars

(To roughly translate between wavelength and temperature of the emitting matter, recall Wien's Law: max wavelength in nm = 2.9x10^6/Temperature in K. Technically this only works for thermal radiation, and x-rays in particular may be emitted via non-thermal mechanisms.)

For additional information, see these sites:

• IPAC Multiwavelength Messier Gallery
• For information specifically on these images and this galaxy, see this page on M33