These two galaxies are of special interest to infrared astronomers.
They are the largest ever to be discovered in infrared, rather
than visible, light. They were first noted as anomalous sources on
infrared photographic plates in 1968 by the astronomer Paolo Maffei,
but within several years were confirmed to be galaxies.
Both galaxies are several arcminutes across in diameter, making them among
the largest in the sky. Most other galaxies of their size had been cataloged
over a century ago! The reason for their late discovery is that
they both lie deep within the dusty plane of our Milky Way Galaxy. This
foreground dust (spread out hundreds to thousands of parsecs away)
blocks our visible light view of these more distant objects
(several million parsecs away).
In the infrared this obscuring dust becomes increasingly transparent,
allowing us to see these hidden galaxies. Their yellowish infrared
colors are caused by the same effect that reddens the sun at sunset:
the bluer, shorter wavelengths of light are blocked more effectively by
the dust allowing only the redder, longer wavelengths through.
Maffei 1 is a classic elliptical galaxy while Maffei 2 has a strong bar
and obvious, if somewhat asymmetric spiral arms. A strong burst of
massive star formation is ongoing in the core of Maffei 2, deduced from
strong far infrared and radio emissions, that is possibly driven by an
ongoing merger with a small satellite companion galaxy.