Thursday, May 3, 2012

Beautiful Galaxy M106

The next in my series of beautiful galaxies is inspired by today's Astronomy Picture of the Day Image.

M106 Close Up (from APOD)
Credit: Composite Image Data - Hubble Legacy ArchiveAdrian Zsilavec, Michelle Qualls, Adam Block / NOAO / AURA / NSF
Processing - Andr√© van der Hoeven

This is a composite Hubble Space Telescope and ground based (from NOAO) image. The ground based image was used to add colour to the high resolution single filter (ie. black and white) image from HST.

M106 has traditionally been classified as an unbarred Sb galaxies (although some astronomers claim a weak bar). In the 1960s it was discovered that if you look at M106 in radio and X-ray two additional "ghostly arms" appear, almost at right angles to the optical arms. These are explained as gas being shock heated by jets coming out of the central supermassive black hole (see Spitzer press release).

In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Credit: 



X-ray: NASA/CXC/Univ. of Maryland/A.S. Wilson et al.; Optical: Palomar Observatory. DSS; IR:NASA/JPL-Caltech; VLA: NRAO/AUI/NSF






Messier 106 (or NGC 4258) is an extremely important galaxy for astronomers, due to it's role in tying down the extragalactic distance scale. A search in the NASA Extragalactic Database (NED) will reveal this galaxy has 55 separate estimates of its distance, using many of the classic methods on the Cosmic distance ladder. Most importantly, M106 was the first galaxy to have an geometric distance measure using a new method which tracked the orbits of clumps of gas moving around the supermassive black hole in its centre. This remains one of the most accurate extragalactic distances ever measured with only a 4% error (7.2+/-0.3 Mpc, or 22+/-1 million light years). The error can be so low, because the number of assumptions is small (it's based on our knowledge of gravity), and as a geometrically estimated distance it leap frogs the lower rungs of the distance ladder.

This result was published in Nature in 1999: A geometric distance to the galaxy NGC4258 from orbital motions in a nuclear gas disk, Hernstein et al. 1999 (link includes an open access copy on the ArXiV). 


Because M106 has so many different distances estimated using so many different methods, and is anchored by the extremely accurate geometric distance, it helps us to calibrate the distances to many other galaxies. Almost all cosmological results, and any result looking at the masses, or physical sizes of galaxies need a distance estimate. 


So M106 is not only beautiful, it's important.  


I've cross listed this post at the Galaxy Zoo blog. 

No comments:

Post a Comment