Messier 94

Messier 94 (also known as NGC 4736) is a spiral galaxy in the constellation Canes Venatici. It was discovered by Pierre Méchain in 1781,[6] and catalogued by Charles Messier two days later. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped.[7] The galaxy has two ring structures.[5]

Messier 94[1][2][3]
Messier 94
M94 Galaxy
Observation data
Epoch J2000
Constellation Canes Venatici[4]
Right ascension  12h 50m 53.1s[5]
Declination +41° 07′ 14″[5]
Apparent dimension (V) 11.2 × 9.1 moa[5]
Apparent magnitude (V)8.99[5]
Characteristics
Type(R)SA(r)ab,[5] LINER[5]
Astrometry
Heliocentric radial velocity 308 ± 1[5] km/s
Redshift 0.001027 ± 0.000005[5]
Galactocentric velocity 360 ± 3[5] km/s
Distance 16.0 ± 1.3 Mly (4.91 ± 0.40 Mpc)
Other designations
NGC 4736, UGC 7996, PGC 43495[5]

Structure

Starburst galaxy Messier 94
Detail of the central area of M94.

M94 is classified as having a low ionization nuclear emission region (LINER) nucleus.[8] LINERs in general are characterized by optical spectra that reveal that ionized gas is present but the gas is only weakly ionized (i.e. the atoms are missing relatively few electrons).

M94 contains both an inner ring with a diameter of 70 arcseconds and an outer ring with a diameter of 600 arcseconds. These rings appear to form at resonance locations within the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas that is dynamically driven into the ring by the inner oval-shaped bar-like structure.[9]

A 2009 study[10] conducted by an international team of astrophysicists revealed that the outer ring of M94 is not a closed stellar ring, as historically attributed in the literature, but a complex structure of spiral arms when viewed in mid-IR and UV. The study found that the outer disk of this galaxy is active. It contains approximately 23% of the galaxy's total stellar mass and contributes about 10% of the galaxy's new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk because it is more efficient per unit of stellar mass.

There are several possible external events that could have led to the origin of M94's outer disk including the accretion of a satellite galaxy or the gravitational interaction with a nearby star system. However, further research found problems with each of these scenarios. Therefore, the report concludes that the inner disk of M94 is an oval distortion which led to the creation of this galaxy's peripheral disk.

In a paper published in 2004, John Kormendy and Robert Kennicutt argued that M94 contains a prototypical pseudobulge.[7] A classical spiral galaxy consists of a disk of gas and young stars that intersects a large sphere (or bulge) of older stars. In contrast, a galaxy with a pseudobulge does not have a large bulge of old stars but instead contain a bright central structure with intense star formation that looks like a bulge when the galaxy is viewed face-on. In the case of M94, this pseudobulge takes the form of a ring around a central oval-shaped region.

In 2008 a study was published[11] showing that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models do not indicate how a galaxy could form without a dark matter halo or how a galaxy could lose its dark matter. Other explanations for galactic rotation curves, such as MOND, also have difficulty explaining this galaxy.[12] This result has yet to be confirmed or accepted by other research groups, however, and has not actually been tested against the predictions of standard galaxy formation models.

Location

Small new m94 announcement
M94 as seen in at various wavelengths of light

At least two techniques have been used to measure distances to M94. The surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to M94 using this technique is 17.0 ± 1.4 Mly (5.2 ± 0.4 Mpc).[1] However, M94 is close enough that the Hubble Space Telescope can be used to resolve and measure the fluxes of the brightest individual stars within the galaxy. These measured fluxes can then be compared to the measured fluxes of similar stars within the Milky Way to measure the distance. The estimated distance to M94 using this technique is 15 ± 2 Mly (4.7 ± 0.6 Mpc).[2] Averaged together, these distance measurements give a distance estimate of 16.0 ± 1.3 Mly (4.9 ± 0.4 Mpc).

M94 is one of the brightest galaxies within the M94 Group, a group of galaxies that contains between 16 and 24 galaxies.[13][14][15] This group is one of many that lie within the Virgo Supercluster (i.e. the Local Supercluster).[16] Although a large number of galaxies may be associated with M94, only a few galaxies near M94 appear to form a gravitationally bound system. Most of the other nearby galaxies appear to be moving with the expansion of the universe.[2][17]

See also

  • NGC 1512, a galaxy with a similar inner ring.

References

  1. ^ a b J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar; et al. (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal. 546 (2): 681–693. arXiv:astro-ph/0011223. Bibcode:2001ApJ...546..681T. doi:10.1086/318301.
  2. ^ a b c I. D. Karachentsev; M. E. Sharina; A. E. Dolphin; E. K. Grebel; et al. (2003). "Galaxy flow in the Canes Venatici I cloud". Astronomy and Astrophysics. 398 (2): 467–477. arXiv:astro-ph/0210414. Bibcode:2003A&A...398..467K. doi:10.1051/0004-6361:20021598.
  3. ^ average(17.0 ± 1.4, 15 ± 2) = ((17.0 + 15) / 2) ± ((1.42 + 22)0.5 / 2) = 16.0 ± 1.3
  4. ^ R. W. Sinnott, ed. (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation / Cambridge University Press. ISBN 978-0-933346-51-2.
  5. ^ a b c d e f g h i j k "NASA/IPAC Extragalactic Database". Results for M94. Retrieved 2006-11-09.
  6. ^ Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide. Vol. 2. Willmann-Bell. p. 51. ISBN 978-0-943396-60-6.
  7. ^ a b J. Kormendy; R. C. Kennicutt Jr. (2004). "Secular Evolution and the Formation of Pseudobulges in Disk Galaxies". Annual Review of Astronomy and Astrophysics. 42 (1): 603–683. arXiv:astro-ph/0407343. Bibcode:2004ARA&A..42..603K. doi:10.1146/annurev.astro.42.053102.134024.
  8. ^ L. C. Ho; A. V. Filippenko; W. L. W. Sargent (1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041.
  9. ^ C. Muñoz-Tuñón; N. Caon; J. Aguerri; L. Alfonso (2004). "The Inner Ring of NGC 4736: Star Formation on a Resonant Pattern". Astronomical Journal. 127 (1): 58–74. Bibcode:2004AJ....127...58M. doi:10.1086/380610.
  10. ^ I. Trujillo; I. Martinez-Valpuesta; D. Martinez-Delgado; J. Penarrubia; et al. (2009). "Unveiling the Nature of M94's (NGC4736) Outer Region: A Panchromatic Perspective". Astrophysical Journal. 704 (1): 618–628. arXiv:0907.4884. Bibcode:2009ApJ...704..618T. doi:10.1088/0004-637X/704/1/618.
  11. ^ J. Jałocha; Ł. Bratek; M. Kutschera (2008). "Is Dark Matter Present in NGC 4736? An Iterative Spectral Method for Finding Mass Distribution in Spiral Galaxies". Astrophysical Journal. 679 (1): 373–378. arXiv:astro-ph/0611113. Bibcode:2008ApJ...679..373J. doi:10.1086/533511.
  12. ^ Battersby, Stephen (6 February 2008). "Galaxy without dark matter puzzles astronomers". New Scientist.
  13. ^ R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge University Press. ISBN 978-0-521-35299-4.
  14. ^ A. Garcia (1993). "General study of group membership. II – Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90. Bibcode:1993A&AS..100...47G.
  15. ^ G. Giuricin; C. Marinoni; L. Ceriani; A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543 (1): 178–194. arXiv:astro-ph/0001140. Bibcode:2000ApJ...543..178G. doi:10.1086/317070.
  16. ^ R. B. Tully (1982). "The Local Supercluster". Astrophysical Journal. 257: 389–422. Bibcode:1982ApJ...257..389T. doi:10.1086/159999.
  17. ^ I. D. Karachentsev (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal. 129 (1): 178–188. arXiv:astro-ph/0410065. Bibcode:2005AJ....129..178K. doi:10.1086/426368.

External links

Coordinates: Sky map 12h 50m 53.1s, +41° 07′ 14″

94 (number)

94 (ninety-four) is the natural number following 93 and preceding 95.

List of NGC objects (4001–5000)

This is a list of NGC objects 4001–5000 from the New General Catalogue (NGC). The astronomical catalogue is composed mainly of star clusters, nebulae, and galaxies. Other objects in the catalogue can be found in the other subpages of the list of NGC objects.

The constellation information in these tables is taken from The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer, which was accessed using the "VizieR Service". Galaxy types are identified using the NASA/IPAC Extragalactic Database. The other data of these tables are from the SIMBAD Astronomical Database unless otherwise stated.

List of novae in 2018

The following is a list of all novae that are known to have occurred in 2018. A nova is an energetic astronomical event caused by a white dwarf accreting matter from a star it is orbiting (typically a red giant, whose outer layers are more weakly attached than smaller, denser stars) Alternatively, novae can rarely be caused by a pair of stars merging with each other, however such events are vastly less common than novae caused by white dwarves.

In 2018, 15 novae were discovered in the Milky Way, 14 being classical novae, and 1 being a dwarf nova of a previously known variable star, V392 Persei, which was discovered in 1972. An additional 23 novae were discovered in the Andromeda Galaxy, 8 in Messier 81, 1 in the Triangulum Galaxy, and 1 in Messier 83.

Low-ionization nuclear emission-line region

A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. Conversely, the spectral line emission from strongly ionized atoms, such as O++, Ne++, and He+, is relatively weak. The class of galactic nuclei was first identified by Timothy Heckman in the third of a series of papers on the spectra of galactic nuclei that were published in 1980.

M94

M94 or M-94 may refer to:

Messier 94, a spiral galaxy in the constellation Canes Venatici

M-94 (Michigan highway), a state highway in Michigan

M-94, a cryptographic device

Messier object

The Messier objects are a set of 110 astronomical objects cataloged by the French astronomer Charles Messier in his Catalogue des Nébuleuses et des Amas d'Étoiles ("Catalogue of Nebulae and Star Clusters").

Because Messier was interested in finding only comets, he created a list of non-comet objects that frustrated his hunt for them. The compilation of this list, in collaboration with his assistant Pierre Méchain, is known as the Messier catalogue. This catalogue of objects is one of the most famous lists of astronomical objects, and many Messier objects are still referenced by their Messier number.

The catalogue includes some astronomical objects that can be observed from Earth's Northern Hemisphere such as deep-sky objects, a characteristic which makes the Messier objects extremely popular targets for amateur astronomers.A preliminary version first appeared in the Memoirs of the French Academy of Sciences in 1771,

and the last item was added in 1966 by Kenneth Glyn Jones, based on Messier's observations.

The first version of Messier's catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris. In addition to his own discoveries, this version included objects previously observed by other astronomers, with only 17 of the 45 objects being Messier's.

By 1780 the catalogue had increased to 80 objects. The final version of the catalogue containing 103 objects was published in 1781 in the Connaissance des Temps for the year 1784.

However, due to what was thought for a long time to be the incorrect addition of Messier 102, the total number remained 102. Other astronomers, using side notes in Messier's texts, eventually filled out the list up to 110 objects.The catalogue consists of a diverse range of astronomical objects, ranging from star clusters and nebulae to galaxies. For example, Messier 1 is a supernova remnant, known as the Crab Nebula, and the great spiral Andromeda Galaxy is M31. Many further inclusions followed in the next century when the first addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding Messier's side note in his 1781 edition exemplar of the catalogue. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, and M110 by Kenneth Glyn Jones in 1967.

NGC 1512

NGC 1512 is a barred spiral galaxy approximately 38 million light-years away from Earth in the constellation Horologium. The galaxy displays a double ring structure, with one ring around the galactic nucleus and another further out in the main disk. The galaxy hosts an extended UV disc with at least 200 clusters with recent star formation activity. NGC 1512 is a member of the Dorado Group.

NGC 6782

NGC 6782 is a barred spiral galaxy located in the constellation Pavo. The galaxy exhibits two distinct ring structures.

NGC 7531

NGC 7531 is an intermediate spiral galaxy located in the constellation Grus. It is located at a distance of circa 70 million light years from Earth, which, given its apparent dimensions, means that NGC 7531 is about 95,000 light years across. It was discovered by John Herschel on September 2, 1836.

Seyfert galaxy

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material.Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.

Starburst region

A starburst is an astrophysical process that involves star formation occurring at a rate that is large compared to the rate that is typically observed. This starburst activity will consume the available interstellar gas supply over a timespan that is much shorter than the lifetime of the galaxy. For example, the nebula NGC 6334 has a star formation rate estimated to be 3600 Solar Masses per million years compared the star formation rate of the entire Milky Way of about seven million solar masses per million years. Due to the high amount of star formation a starburst is usually accompanied by much higher gas pressure and a larger ratio of Hydrogen cyanide to Carbon monoxide Emission-lines than are usually observed.

Starburst can occur in entire galaxies or just regions of space. A starburst region is a region of space that is undergoing a large amount of star formation. For example, the Tarantula Nebula is a Nebula in the Large Magellanic Cloud which has one of the highest star formation rates in the Local Group. By contrast a starburst galaxy is an entire galaxy that is experiencing a very high star formation rate. One notable example being Messier 82 in which the gas pressure is 100 times greater than in the local neighborhood and it is forming stars at about the same rate as the Milky Way in a region about 600 parsecs across. At this rate M82 will consume its 200 million Solar Masses of atomic and molecular hydrogen in 100 Mega years (its Free-fall time).Starburst regions can occur in different shapes, for example in Messier 94 the inner ring is a star burst region. Messier 82 has a starburst core of about 600 parsec in diameter. Starbursts are common during galaxy mergers such as the Antennae Galaxies. In the case of mergers the starburst can either be local or galaxy wide depending on the galaxies and how they are merging.

List
See also

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