Messier 100

Spiral Galaxy M100 (NGC 4321), type Sc, in Coma Berenices

Right Ascension 12 : 22.9 (h:m)

Declination +15 : 49 (deg:m)

Distance 60000 (kly)

Visual Brightness 9.3 (mag)

Apparent Dimension 7x6 (arc min)

Right Ascension	12 : 22.9 (h:m)
Declination	+15 : 49 (deg:m)
Distance	60000 (kly)
Visual Brightness	9.3 (mag)
Apparent Dimension	7x6 (arc min)

Discovered by Pierre Méchain in 1781.

Messier 100 (M100, NGC 4321) is a beautiful example of a grand-design spiral galaxy, and one of the brightest galaxies in the Virgo Cluster, or Coma-Virgo of Galaxies. Like a number of other members of this cluster, it is situated in the southern part of constellation Coma Berenices.

On March 15, 1781, Pierre Méchain discovered this object, M100, together with its apparent neighbors, M98 and M99. His friend, Charles Messier, obtained its position on April 13, 1781, and included it in his catalog, immediately before finishing the third, final published edition.

M100 is one of the brightest member galaxies of the Virgo Cluster of galaxies.

M100 is a spiral galaxy, like our Milky Way, and tilted nearly face-on as seen from earth. It is among the first spirals that have been discovered, and listed by Lord Rosse as one of 14 "spiral nebulae" discovered to 1850. The galaxy has two prominent arms of bright blue stars and several fainter arms. The blue stars in the arms are young hot and massive stars which formed recently from density perturbations caused by interactions with neighboring galaxies which are lying just outside our image. Despite its nearly perfect symmetric outline, this galaxy appears slightly asymmetric, as on the southern (lower) side of the nucleus more (or brighter) young stars have formed.

Our photograph of this magnificient grand-design spiral was obtained by David Malin of the Anglo-Australian Observatory; interested readers may obtain more detailed informations on this image. From the same original plates by the Anglo-Australian Telescope, David Malin has provided more images of M100 showing also its dwarf neighbors.

Deep photographs of M100 have revealed that this galaxy is actually much larger than shown in conventional photographs. Therefore, a significant part of the galaxy's mass may lie in the faint outer regions and escape its discovery in conventional images.

M100 has been imaged extensively by the Hubble Space Telescope, which finally led to the discovery of over 20 Cepheids as well as one nova, and a distance determination of 56+/-6 million light years for M100, the first considerably reliable distance determination of a Virgo cluster galaxy (see H0 Key Project, paper IV, 1996). The high improvement of photographic resolution by the HST may be noticed in this comparison of HST to average quality KPNO 2.1m-photos.

Diane Dutkevitch of the Northwestern University has provided a Astronomy Web Lab on distance determination of M100 from HST Cepheid observations.

In the inner disk of M100 has been investigated by Nasa's Ultraviolet Imaging Telescope on its Astro-1 Space Shuttle mission. Intense star formation activity was found to take place in a ring of starburst activity along the periphery of the galaxy's innermost spiral arms.

M100 is located in the spring constellation Coma Berenices and can be seen through a moderate-sized amateur telescope. Amateurs can see the central regions of this galaxy as faint elliptical patch of uneven texture in small telescopes, or even in good binoculars. Under good observing conditions, suggestions of the inner spiral arms can be glimpsed in telescopes starting at 4 inch aperture (refractor or unobstructed reflector). Photos reveal the grand design spiral structure, as seen in every picture from our collection of amateur images of M100.

Five supernovae have been observed in M100 so far:

1901B, a type I, mag 15.6 in March 1901;
1914A of undetermined type, mag 15.7 in Feb/Mar 1914;
1959E of type I, mag 17.5 in Aug/Sep 1959, 58"E and 21"S of the nucleus, discovered February 21, 1960 and observed through June 17, 1960; and
1979C of type II, mag 11.6 on April 15, 1979, which however faded quickly. Supernova 1979C or its remnant was later observed at various wavelengths from radio to X-rays, notably in the X-ray light with the Rosat (Immler et.al. 1998) and XMM Newton (Immler et.al. 2005) satellites.
2006X of type Ia was found on February 7, 2006, when it was at 15.3 mag and still rising. Supernova 2006X was located 12"W and 48"S of M100's nucleus, and was discovered early before reaching its maximum.

Historical Observations and Descriptions of M100

AAT images of M100

HST images of M100, More HST images

UIT images of M100 in the Ultraviolet

More images of M100

Amateur images of M100

Multispectral Image Collection of M100, SIRTF Multiwavelength Messier Museum

SIMBAD Data of M100

NED Data of M100

Publications on M100 (NASA ADS)

Observing Reports for M100 (IAAC Netastrocatalog)

NGC Online data for M100

References:

H0 Key Project materials on M100:
- The HST Key Project Archives - M100
- Laura Ferrarese et.al., 1996. The Extragalactic Distance Scale Key Project. IV. The Discovery of Cepheids and a New Distance to M100 Using the Hubble Space Telescope. Astrophysical Journal, Vol. 464, No. 2, pp. 568-599, plates 16-32 (June 1996) [ADS: 1996ApJ...464..568F]
Other H0KP papers on M100 (earlier results, conclusions, ..):
- Wendy L. Freedman et.al., 1994. First Hubble Space Telescope observations of the brightest stars in the Virgo galaxy M100 = NGC 4321. Astrophysical Journal, Part 2 - Letters, Vol. 435, No. 1, pp. L31-L34. [ADS: 1994ApJ...435L..31F]
- Wendy L. Freedman et.al., 1994. Distance to the Virgo Cluster galaxy M100 from Hubble Space Telescope Observations of Cepheids. Nature, Vol. 371, October 27, 1994, page 757. [ADS: 1994Natur.371..757F] - Available online (H0KP)
- Robert J. Hill et.al., 1998. The Extragalactic Distance Scale Key Project. V. Photometry of the Brightest Stars in M100 and the Calibration of WFPC2. Astrophysical Journal, Vol. 496, p. 648-660. [ADS: 1998ApJ...496..648H]
- J. Mould et.al., 1995. Limits on the Hubble Constant from the HST Distance of M100. Astrophysical Journal, Vol. 449, No. 2, pp. 413-421 (August 20, 1995). [ADS: 1995ApJ...449..413M]
Stefan Immler, Wolfgang Pietsch, Bernd Aschenbach, 1998. X-ray emission from NGC 4321 (M 100): detection of supernova 1979C. Astronomy and Astrophysics, Vol. 331, pp. 601-611 (March 1998) [ADS: 1998A&A...331..601I]
Stefan Immler, Robert A. Fesen, Schuyler D. Vab Dyk, Kurt W. Weiler, Robert Petre, Walter H.G. Lewin, David Pooley, Wolfgang Pietsch, Bernd Aschenbach, Molly C. Hammell, and Gwen C. Rudie, 2005. Late-Time X-Ray, UV, and Optical Monitoring of Supernova 1979C. Astrophysical Journal, Vol. 632, No. 1, pp. 283-293 (October 2005). [ADS: 2005ApJ...632..283I] - [Preprint: astro-ph/0503678]

Hartmut Frommert
Christine Kronberg
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Last Modification: September 2, 2007