"Backbone of Night",from Sagan's Cosmos |
An
Infrared Looking Glass:
Peering Through the
|
Barred Spiral Galaxy Maffei 2 |
The disk of the Milky Way is home to a multitude of stars, born from the great clouds of gas and dust that form the beautiful "backbone of night" that is dazzling in a dark night sky. The Milky Way occupies over half of the observable sky, a magnificent veil to the outer Universe. Astronomers are not able to see through the Milky Way veil using traditional methods. What is behind the Milky Way? A great mystery .... until the dawn of infrared and radio astronomy, which provide a looking glass into and through the Milky Way.
Optical light
coming from distant objects beyond the
confines of the Milky Way is absorbed and blocked by this
gas and dust, veiling our view of the Universe over vast
swaths of our sky. Longer wavelength light, however, can
penetrate through this dusty curtain, and rain down upon
our infrared and radio telescopes.
Infrared light
provides a sharp and
transparent window through which to view the
Universe
beyond the Milky Way (see image right).
Here we see thousands of stars in a small 1 X 1 deg2 field interlaced with patches of obscuring gas and dust (image right). There is little hope of finding galaxies behind this wall of confusion. At the longer near- infrared wavelengths, we see even more stars (thus adding to the overall confusion), but we also see something quite different: background galaxies peaking through this veil. A zoomed picture of one such galaxy is shown. In the optical, this galaxy is both very faint and undistinguished from the multitude of stars that populate the same area of the sky. It is one of the primary goals of the Two Micron All Sky Survey (2MASS) to seek out and find these hidden galaxies.
The 2MASS project detects galaxies never seen before, revealing "zones" of sky traditionally avoided by astronomers due to the obscuring effects of Galactic dust and gas. The images below demonstrate the penetrating power of the infrared. We first see a composite map of the Milky Way as seen with optical telescopes. Zooming into a smaller region in the plane of the Galaxy, we see a multitude of stars densely packed onto the Galaxy plane, |glat| = 0 deg. Another phenomenon can be seen: the reddening of stars due to selective extinction from gas and dust. From the same effect, galaxies also appear much redder as their light passes through the Milky Way -- creating literally, a galaxy "sunset" (see inset images).
Galactic Coordinates: glon=55.0, glat=0.0,
The reddening effect is demonstrated below in a veritable "zoo" of 2MASS galaxies. Each small image is 90X90' in angular size. The galaxy images are ordered in decreasing (reading left to right) total integrated flux ranging from 110 mJy to 10 mJy (corresponding to a K magnitude range from 9.5 to 12.1), and in increasing stellar surface density or dust obscuration (reading top to bottom), ranging in |glat| from 20 to 0 degrees.
Read more about new galaxies discovered behind the Milky Way with 2MASS.
e-mail: Tom Jarrett
