M81 Group
Encyclopedia
The M81 Group is a group of galaxies in the constellation
Ursa Major
that includes the well-known galaxies Messier 81
and Messier 82
, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is located at a distance of 3.6 Mpc
, making it one of the nearest groups to the Local Group
. The group is estimated to have a total mass of (1.03 ± 0.17)M☉
.
The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster
(i.e. the Local Supercluster).
Note that the object names used in the above table differ from the names used by Karachentsev. NGC
, IC
, UGC
, and PGC
numbers have been used in many cases to allow for easier referencing.
with each other. The gravitational interactions have stripped some hydrogen
gas away from all three galaxies, leading to the formation of filamentary gas structures within the group. Moreover, the interactions have also caused some interstellar gas
to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity
(or the formation of many stars) within the centers of these two galaxies.
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Ursa Major
Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
that includes the well-known galaxies Messier 81
Messier 81
Messier 81 is a spiral galaxy about 12 million light-years away in the constellation Ursa Major. Due to its proximity to Earth, large size and active galactic nucleus Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a spiral galaxy about 12 million light-years away in the constellation Ursa...
and Messier 82
Messier 82
Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major...
, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is located at a distance of 3.6 Mpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
, making it one of the nearest groups to the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
. The group is estimated to have a total mass of (1.03 ± 0.17)M☉
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
.
The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster
Virgo Supercluster
The Virgo Supercluster or Local Supercluster is the irregular supercluster that contains the Virgo Cluster in addition to the Local Group, which in turn contains the Milky Way and Andromeda galaxies. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs...
(i.e. the Local Supercluster).
Members
The table below lists galaxies that have been identified as associated with the M81 Group by I. D. Karachentsev.| Name | Type | R.A. Right ascension Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:... (J2000) |
Dec. Declination In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and... (J2000) |
Redshift Redshift In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum... (km/s Second The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock.... ) |
Apparent Magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere... |
|---|---|---|---|---|---|
| Arp's Loop | 99 | 16.1 | |||
| DDO 78 | Im | 55 ± 10 | 15.8 | ||
| F8D1 | dE | 13.9 | |||
| FM1 | dSph | 17.5 | |||
| HIJASS J1021+6842 | 46 | 20 | |||
| HS 117 | I | -37 | 16.5 | ||
| Holmberg I | IAB(s)m | 139 ± 0 | 13.0 | ||
| Holmberg II | Im | 142 ± 1 | 11.1 | ||
| Holmberg IX Holmberg IX Holmberg IX is a dwarf irregular galaxy and a satellite galaxy of M81. The galaxy is named after Erik Holmberg who first described it. Based on the observed age distribution of stars it contains it is thought to have formed within the last 200 Myr making it the youngest nearby galaxy... |
Im | 46 ± 6 | 14.3 | ||
| IC 2574 | SAB(s)m | 57 ± 2 | 13.2 | ||
| IKN | 17.0 | ||||
| KKH 57 | dSph | 18.5 | |||
| Messier 81 Messier 81 Messier 81 is a spiral galaxy about 12 million light-years away in the constellation Ursa Major. Due to its proximity to Earth, large size and active galactic nucleus Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a spiral galaxy about 12 million light-years away in the constellation Ursa... |
SA(s)ab | -34 ± 4 | 7.9 | ||
| Messier 81 Dwarf A | I | 113 ± 0 | 16.5 | ||
| Messier 82 Messier 82 Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major... |
I0 | 203 ± 4 | 9.3 | ||
| NGC 2366 NGC 2366 NGC 2366 is an irregular galaxy located in the constellation Camelopardalis. NGC 2363 is a star forming region within the NGC 2366.-External links:*... |
IB(s)m | 80 ± 1 | 11.4 | ||
| NGC 2403 NGC 2403 NGC 2403 is an intermediate spiral galaxy in the constellation Camelopardalis. NGC 2403 is an outlying member of the M81 Group, and is approximately 8 million light-years distant... |
SAB(s)cd | 131 ± 3 | 8.9 | ||
| NGC 2976 NGC 2976 Part of the M81 group, NGC 2976, located 1° 20′ southwest of M81, is an unbarred spiral galaxy. The inner structure contains many dark lanes and stellar condensations in its disk. The galaxy is sometimes classified as Sdp because its spiral arms are difficult to be traced. The bright inner... |
SAc pec | 3 ± 5 | 10.8 | ||
| NGC 3077 NGC 3077 NGC 3077 is a smaller member of the M81 Group. It looks much like an elliptical galaxy. However, it is peculiar for two reasons. First, it shows wispy edges and scattered dust clouds that are probably a result of gravitational interaction with its larger neighbors, similar to the galaxy M82.... |
I0 pec | 14 ± 4 | 10.6 | ||
| NGC 4236 NGC 4236 NGC 4236 is a barred spiral galaxy located in the constellation Draco.-Galaxy group information:NGC 4236 is a member of the M81 Group, a group of galaxies located at a distance of approximately 11.7 Mly from Earth. The group also contains the well-known spiral galaxy Messier 81 and the... |
SB(s)dm | 0 ± 4 | 10.1 | ||
| PGC 28529 | Im | -40 | 17.1 | ||
| PGC 28731 | dE | -135 ± 30 | 15.6 | ||
| PGC 29231 | dE | 16.7 | |||
| PGC 31286 | dSph | 16.7 | |||
| PGC 32667 | Im | 116 ± 1 | 14.9 | ||
| UGC 4459 | Im | 20 ± 0 | 14.5 | ||
| UGC 4483 | 156 ± 0 | 15.1 | |||
| UGC 5428 | Im | -129 ± 0 | 18 | ||
| UGC 5442 | Im | -18 ± 14 | 18 | ||
| UGC 5692 | 13.5 | 56 ± 3 | 13.5 | ||
| UGC 6456 | Pec | -103 ± 0 | 14.5 | ||
| UGC 7242 | Scd | 68 ± 2 | 14.6 | ||
| UGC 8201 | Im | 31 ± 0 | 12.8 | ||
| UGCA 133 | Im | 15.6 | |||
Note that the object names used in the above table differ from the names used by Karachentsev. NGC
New General Catalogue
The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
, IC
Index Catalogue
The Index Catalogue —also known as the Index Catalogue of Nebulae, the Index Catalogue of Nebulae and Clusters of Stars, IC I, or IC II— is a catalogue of galaxies, nebulae and star clusters that serves as a supplement to the New General Catalogue...
, UGC
Uppsala General Catalogue
The Uppsala General Catalogue of Galaxies is a catalogue of 12921 galaxies visible from the northern hemisphere. It was published the first time in 1973....
, and PGC
Principal Galaxies Catalogue
The Catalogue of Principal Galaxies is an astronomical catalogue published in 1989 that lists B1950 and J2000 equatorial coordinates and cross-identifications for 73,197 galaxies. 40,932 coordinates have standard deviations smaller than 10″. A total of 131,601 names from the 38 most...
numbers have been used in many cases to allow for easier referencing.
Interactions within the group
Messier 81, Messier 82, and NGC 3077 are all strongly interactingInteracting galaxy
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.-Satellite interaction:A giant...
with each other. The gravitational interactions have stripped some hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas away from all three galaxies, leading to the formation of filamentary gas structures within the group. Moreover, the interactions have also caused some interstellar gas
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity
Starburst galaxy
A starburst galaxy is a galaxy in the process of an exceptionally high rate of star formation, compared to the usual star formation rate seen in most galaxies. Galaxies are often observed to have a burst of star formation after a collision or close encounter between two galaxies...
(or the formation of many stars) within the centers of these two galaxies.