Figure: The Majestic Sombrero Galaxy, M104 (HST)

Object Names: Sombrero Galaxy, M104, NGC 4594

NASA's Hubble Space Telescope has trained its razor-sharp eye on one of the universe's most stately and photogenic galaxies, the Sombrero galaxy, Messier 104 (M104). The galaxy's hallmark is a brilliant white, bulbous core encircled by the thick dust lanes comprising the spiral structure of the galaxy. As seen from Earth, the galaxy is tilted nearly edge-on. We view it from just six degrees north of its equatorial plane. This brilliant galaxy was named the Sombrero because of its resemblance to the broad rim and high-topped Mexican hat.

At a relatively bright magnitude of +8, M104 is just beyond the limit of naked-eye visibility and is easily seen through small telescopes. The Sombrero lies at the southern edge of the rich Virgo cluster of galaxies and is one of the most massive objects in that group, equivalent to 800 billion suns. The galaxy is 50,000 light-years across and is located 28 million light-years from Earth.

Hubble easily resolves M104's rich system of globular clusters, estimated to be nearly 2,000 in number - 10 times as many as orbit our Milky Way galaxy. The ages of the clusters are similar to the clusters in the Milky Way, ranging from 10-13 billion years old. Embedded in the bright core of M104 is a smaller disk, which is tilted relative to the large disk. X-ray emission suggests that there is material falling into the compact core, where a 1-billion-solar-mass black hole resides.

In the 19th century, some astronomers speculated that M104 was simply an edge-on disk of luminous gas surrounding a young star, which is prototypical of the genesis of our solar system. But in 1912, astronomer V. M. Slipher discovered that the hat-like object appeared to be rushing away from us at 700 miles per second. This enormous velocity offered some of the earliest clues that the Sombrero was really another galaxy, and that the universe was expanding in all directions.

The Hubble Heritage Team took these observations in May-June 2003 with the space telescope's Advanced Camera for Surveys. Images were taken in three filters (red, green, and blue) to yield a natural-color image. The team took six pictures of the galaxy and then stitched them together to create the final composite image. One of the largest Hubble mosaics ever assembled, this magnificent galaxy has an apparent diameter that is nearly one-fifth the diameter of the full moon.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)

http://hubblesite.org/newscenter/archive/releases/2003/28/image/a




Figure: The Sombrero Galaxy (VLT image)

This image of the Sombrero Galaxy (Messier 104) was obtained with FORS1 multi-mode instrument at VLT ANTU on January 30, 2000. It is a composite of three exposures in different wavebands, cf. the technical note below. The full-resolution version of this photo retains the orginal pixels. The detail image shows the eastern area, with the pronounced dust bands and many background galaxies. North is up and East is left.

In addition to their scientific value, many of the exposures now being obtained by visiting astronomers to ESO's Very Large Telescope (VLT) are also very beautiful. This is certainly true for this new image of the famous early-type spiral galaxy Messier 104, widely known as the "Sombrero" (the Mexican hat) because of its particular shape.

The colour image was made by a combination of three CCD images from the FORS1 multi-mode instrument on VLT ANTU, recently obtained by Peter Barthel from the Kapteyn Institute (Groningen, The Netherlands) during an observing run at the Paranal Observatory. He and Mark Neeser, also from the Kapteyn Institute, produced the composite images.

The galaxy fits perfectly into the 6.8 x 6.8 arcmin 2 field-of-view of the FORS1 camera. A great amount of fine detail is revealed, from the structures in the pronounced dust band in the equatorial plane, to many faint background galaxies that shine through the outer regions.

The "Sombrero" is located in the constellation Virgo (The Virgin), at a distance of about 50 million light-years. The overall "sharpness" of this colour image corresponds to about 0.7 arcsec which translates into a resolution of about 170 light-years at that distance.

About Messier 104

Messier 104 is the 104th object in the famous catalogue of nebulae by French astronomer Charles Messier (1730 - 1817). It was not included in the first two editions (with 45 objects in 1774; 103 in 1781), but Messier soon thereafter added it by hand in his personal copy as a "very faint nebula". The recession velocity, about 1000 km/sec, was first measured by American astronomer Vesto M. Slipher at the Lowell Observatory in 1912; he was also the first to detect the galaxy's rotation.

This galaxy is notable for its dominant nuclear bulge, composed primarily of mature stars, and its nearly edge-on disk composed of stars, gas, and intricately structured dust. The complexity of this dust, and the high resolution of this image, is most apparent directly in front of the bright nucleus, but is also very evident as dark absorbing lanes throughout the disk.

A large number of small and slightly diffuse sources can be seen as a swarm in the halo of Messier 104. Most of these are globular clusters, similar to those found in our own Galaxy.

Measurements reveal a steep increase in the mass-to-light ratio and increasing stellar speeds near the nucleus of Messier 104. This is indicative of the presence of a massive black hole at the centre, estimated at about 109 solar masses.

The radio properties of Messier 104 are unusual for a spiral galaxy - it has a variable core. The optical spectrum of the central region displays emission lines from hot gas (of the "LINER" type - Low Ionisation Nuclear Emission line Region). This points to Messier 104 harbouring a weak Active Galactic Nucleus (AGN) . Although more commonly known from the much more luminous and distant quasars and powerful radio galaxies, the weak AGN in this galaxy lies at the opposite extreme: the most likely explanation being a central black hole accreting circumnuclear matter at a slow pace.

Technical information : The two images are composites based on three exposures from the FORS1 instrument at VLT ANTU. They were obtained at about 6:20 hrs UT on January 30, 2000, through V-band (central wavelength 554 nm; 112 nm Full Width Half Maximum (FWHM); exposure time 120 sec; here rendered as blue), R-band (657 nm; 150 nm FWHM; 120 sec; green) and I-band (768 nm; 138 nm FWHM, 240 sec; red). The seeing was 0.6 - 0.7 arcsec.

Credit: ESO/VLT

http://www.eso.org/outreach/press-rel/pr-2000/phot-07-00.html