NGC 185

NGC 185 (also known as Caldwell 18) is a dwarf spheroidal galaxy located 2.08 million light-years from Earth, appearing in the constellation Cassiopeia. It is a member of the Local Group, and is a satellite of the Andromeda Galaxy (M31).[6] NGC 185 was discovered by William Herschel on November 30, 1787, and he cataloged it "H II.707".[6] John Herschel observed the object again in 1833 when he cataloged it as "h 35", and then in 1864 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters.[6] NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory.[6] Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus (AGN) and is usually classified as a type 2 Seyfert galaxy,[7] though its status as a Seyfert is questioned.[8] It is possibly the closest Seyfert galaxy to Earth, and is the only known Seyfert in the Local Group.

NGC 185
Ngc185 rgb combined
Dwarf Spheroidal Galaxy NGC 185
Observation data (J2000.0[1] epoch)
ConstellationCassiopeia
Right ascension 00h 38m 57.970s[1]
Declination+48° 20′ 14.56″[1]
Redshift-202 ± 3 km/s[2]
Distance2.05 ± 0.13 Mly (630 ± 40 kpc)[3][4][5][a]
Apparent magnitude (V)10.1[2]
Characteristics
TypedSph/dE3,[2] Sy2 [1]
Apparent size (V)11′.7 × 10′.0[2]
Notable featuressatellite galaxy of the
Andromeda Galaxy
Other designations
UGC 396,[2] PGC 2329,[2] LEDA 2329,[1] Caldwell 18

Distance measurements

At least two techniques have been used to measure distances to NGC 185. The surface brightness fluctuations distance measurement technique estimates distances to galaxies based on the graininess of their appearance. The distance measured to NGC 185 using this technique is 2.08 ± 0.15 Mly (640 ± 50 kpc).[3] However, NGC 185 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 185 using this technique is 2.02 ± 0.2 Mly (620 ± 60 kpc).[4][5]

Star formation

Martínez-Delgado, Aparicio, & Gallart (1999) looked into the star formation history of NGC 185 and found that the majority of star formation in NGC 185 happened at early times.[8] In the last ~1 Gyr, stars have formed only near the center of this galaxy. Walter Baade discovered young blue objects within this galaxy in 1951, but these have turned out to be star clusters and not individual stars. A supernova remnant near the center was also discovered by Martínez-Delgado et al.[9]

NGC 185 HST
The galaxy observed by the Hubble Space Telescope.
NGC 0185 2MASS
The galaxy observed by the 2MASS.

See also

References

  1. ^ a b c d e "NGC 185". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2014-05-05.
  2. ^ a b c d e f "NASA/IPAC Extragalactic Database". Results for NGC 185. Retrieved 2006-11-29.
  3. ^ 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.
  4. ^ a b I. D. Karachentsev; V. E. Karachentseva; W. K. Huchtmeier; D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  5. ^ a b Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6.
  6. ^ a b c d "SEDS — NGC 185".
  7. ^ Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for 'Dwarf' Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". The Astrophysical Journal Supplement Series. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041.
  8. ^ a b Martins, Lucimara P.; Lanfranchi, Gustavo; Goncalves, Denise R.; Magrini, Laura; Teodorescu, Ana M.; Quireza, Cintia (February 2012). "The ionization mechanism of NGC 185: How to fake a Seyfert galaxy?". Monthly Notices of the Royal Astronomical Society. 419 (4): 3159–3166. arXiv:1110.5891. Bibcode:2012MNRAS.419.3159M. doi:10.1111/j.1365-2966.2011.19954.x.
  9. ^ van den Bergh, Sidney (April 2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific. 112 (770): 529–536. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548.

External links

Coordinates: Sky map 00h 38m 58.0s, +48° 20′ 15″

185 (number)

185 (one hundred [and] eighty-five) is the natural number following 184 and preceding 186.

Caldwell catalogue

The Caldwell catalogue is an astronomical catalogue of 109 star clusters, nebulae, and galaxies for observation by amateur astronomers. The list was compiled by Patrick Moore as a complement to the Messier catalogue.While the Messier catalogue is used by amateur astronomers as a list of deep-sky objects for observation, Moore noted that Messier's list was not compiled for that purpose and excluded many of the sky's brightest deep-sky objects, such as the Hyades, the Double Cluster (NGC 869 and NGC 884), and the Sculptor Galaxy (NGC 253). The Messier catalogue was actually compiled as a list of known objects that might be confused with comets. Moore also observed that since Messier compiled his list from observations in Paris, it did not include bright deep-sky objects visible in the Southern Hemisphere, such as Omega Centauri, Centaurus A, the Jewel Box, and 47 Tucanae. Moore compiled a list of 109 objects to match the commonly accepted number of Messier objects (he excluded M110), and the list was published in Sky & Telescope in December 1995.Moore used his other surname – Caldwell – to name the list, since the initial of "Moore" is already used for the Messier catalogue. Entries in the catalogue are designated with a "C" and the catalogue number (1 to 109).

Unlike objects in the Messier catalogue, which are listed roughly in the order of discovery by Messier and his colleagues, the Caldwell catalogue is ordered by declination, with C1 being the most northerly and C109 being the most southerly, although two objects (NGC 4244 and the Hyades) are listed out of sequence. Other errors in the original list have since been corrected: it incorrectly identified the S Norma Cluster (NGC 6087) as NGC 6067 and incorrectly labelled the Lambda Centauri Cluster (IC 2944) as the Gamma Centauri Cluster.

Cassiopeia (constellation)

Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivaled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive 'W' shape, formed by five bright stars. It is opposite Ursa Major.

In northern locations above latitude 34ºN it is visible year-round and in the (sub)tropics it can be seen at its clearest from September to early November. Even in low southern latitudes below 25ºS it can be seen low in the North.

At magnitude 2.2, Alpha Cassiopeiae, or Schedar, is generally the brightest star in Cassiopeia, though is often shaded by Gamma Cassiopeiae, which has brightened to magnitude 1.6 on occasion. The constellation hosts some of the most luminous stars known, including the yellow hypergiants Rho Cassiopeiae and V509 Cassiopeiae and white hypergiant 6 Cassiopeiae. The semiregular variable PZ Cassiopeiae is one of the largest known stars. In 1572, Tycho Brahe's supernova flared brightly in Cassiopeia. Cassiopeia A is a supernova remnant and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. Fourteen star systems have been found to have exoplanets, one of which—HR 8832—is thought to host seven planets. A rich section of the Milky Way runs through Cassiopeia, containing a number of open clusters, young luminous galactic disc stars, and nebulae. IC 10 is an irregular galaxy that is the closest known starburst galaxy and the only one in the Local Group of galaxies.

Dwarf elliptical galaxy

Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are smaller than ordinary elliptical galaxies. They are quite common in galaxy groups and clusters, and are usually companions to other galaxies.

Herschel 400 Catalogue

The Herschel 400 catalogue is a subset of William Herschel's original Catalogue of Nebulae and Clusters of Stars, selected by Brenda F. Guzman (Branchett), Lydel Guzman, Paul Jones, James Morrison, Peggy Taylor and Sara Saey of the Ancient City Astronomy Club in St. Augustine, Florida, United States c. 1980. They decided to generate the list after reading a letter published in Sky & Telescope by James Mullaney of Pittsburgh, Pennsylvania, USA.In this letter Mr. Mullaney suggested that William Herschel's original catalogue of 2,500 objects would be an excellent basis for deep sky object selection for amateur astronomers looking for a challenge after completing the Messier Catalogue.

The Herschel 400 is a subset of John Herschel's General Catalogue of Nebulae and Clusters published in 1864 of 5,000 objects, and hence also of the New General Catalogue.

The catalogue forms the basis of the Astronomical League's Herschel 400 club. In 1997, another subset of 400 Herschel objects was selected by the Rose City Astronomers of Portland, Oregon as the Herschel II list, which forms the basis of the Astronomical League's Herschel II Program.

List of Andromeda's satellite galaxies

The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 14 dwarf galaxies: the brightest and largest is M32, which can be seen with a basic telescope. The second-brightest and closest one to M32 is M110. The other galaxies are fainter, and were mostly discovered only starting from the 1970s.

On January 11, 2006, it was announced that Andromeda Galaxy's faint companion galaxies lie on or close to a single plane running through the Andromeda Galaxy's center. This unexpected distribution is not obviously understood in the context of current models for galaxy formation. The plane of satellite galaxies points toward a nearby group of galaxies (M81 Group), possibly tracing the large-scale distribution of dark matter.

List of nearest galaxies

This is a list of known galaxies within 3.59 megaparsecs (11.7 million light-years) of the Solar System, in ascending order of distance.

This encompasses all of the about 50 Local Group galaxies, and some that are members of neighboring galaxy groups, the M81 Group and the Centaurus A/M83 Group, and some that are currently not in any defined galaxy group.

The list aims to reflect current knowledge: not all galaxies within the 3.59 Mpc radius have been discovered. Nearby dwarf galaxies are still being discovered, and galaxies located behind the central plane of the Milky Way are extremely difficult to discern. It is possible for any galaxy to mask another located beyond it.

Intergalactic distance measurements are subject to large uncertainties. Figures listed are composites of many measurements, some of which may have had their individual error bars tightened to the point of no longer overlapping with each other.

Local Group

The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a diameter of 10 Mly (3.1 Mpc) (about 1023 meters) and has a binary (dumbbell)

distribution. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster.

The three largest members of the group (in descending order) are the Andromeda Galaxy, the Milky Way and the significantly smaller Triangulum Galaxy. The larger two of these spiral galaxies each have their own system of satellite galaxies.

The Andromeda Galaxy's satellite system consists of Messier 32 (M32), Messier 110 (M110), NGC 147, NGC 185, Andromeda I (And I), And II, And III, And V, And VI (also known as Pegasus Dwarf Spheroidal Galaxy, or Pegasus DSph), And VII (also known as Cassiopeia Dwarf Galaxy), And VIII, And IX, And X, And XI, And XIX, And XXI and And XXII, plus several additional ultra-faint dwarf spheroidal galaxies.

The Milky Way's satellite galaxies system comprises Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf Galaxy (disputed, considered by some not a galaxy), Ursa Minor Dwarf Galaxy, Draco Dwarf Galaxy, Carina Dwarf Galaxy, Sextans Dwarf Galaxy, Sculptor Dwarf Galaxy, Fornax Dwarf Galaxy, Leo I (a dwarf galaxy), Leo II (a dwarf galaxy), and Ursa Major I Dwarf Galaxy and Ursa Major II Dwarf Galaxy, plus several additional ultra-faint dwarf spheroidal galaxies.

The Triangulum Galaxy may or may not be a companion to the Andromeda Galaxy. Pisces Dwarf Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.

The membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf Galaxy, is uncertain due to extreme distances from the center of the Local Group.

The other members of the group are likely gravitationally secluded from these large subgroups: IC 10, IC 1613, Phoenix Dwarf Galaxy, Leo A, Tucana Dwarf Galaxy, Cetus Dwarf Galaxy, Pegasus Dwarf Irregular Galaxy, Wolf–Lundmark–Melotte, Aquarius Dwarf Galaxy, and Sagittarius Dwarf Irregular Galaxy.

Messier 110

Messier 110 or M110, also known as NGC 205, is a dwarf elliptical galaxy that is a satellite of the Andromeda Galaxy. Although Charles Messier never included the galaxy in his list, it was depicted by him, together with M32, on a drawing of the Andromeda galaxy; a label on the drawing indicates that Messier first observed NGC 205 on August 10, 1773. The galaxy was independently discovered by Caroline Herschel on August 27, 1783; her brother William Herschel described her discovery in 1785. The suggestion to assign the galaxy a Messier number was made by Kenneth Glyn Jones in 1967.This galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical galaxy with a flattening of 50%. M110 is designated peculiar because there are patches of dust and young blue stars located near the center. This is unusual for dwarf elliptical galaxies in general, and the reason for this peculiarity is unclear. Unlike M32, NGC 205 does not (as of 2005) show evidence for a supermassive black hole at its center.The interstellar dust in M110 has a mass of (1.1–1.8)×104 M☉ with a temperature of 18–22 K, and the interstellar gas has (4–7)×106 M☉. The inner regions of M110 show a deficiency in the interstellar medium (IM) materials, which most likely were ejected by supernova explosions. Tidal interactions with M31 may have stripped away a significant fraction of the expelled gas and dust, leaving the galaxy as a whole deficient in its IM density.A few novae have been detected in this galaxy, including one discovered

in 1999 by Johnson and Modjaz, and another detected in 2002, by Nakano and Sumoto. The latter, designated EQ J004015.8+414420, had also been captured in images taken by the Sloan Digital Sky Survey (SDSS) in October, 2002.About half of the Andromeda's satellite galaxies are orbiting the host galaxy along a highly flattened plane, with 14 out of 16 following the same sense of rotation. One theory proposes that these objects once belonged to a subhalo surrounding NGC 205, then the group was broken up by tidal forces during a close encounter with Andromeda.

NGC 147

NGC 147 (also known as DDO3 or Caldwell 17) is a dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 147 is a member of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It forms a physical pair with the nearby galaxy NGC 185,

another remote satellite of M31. It was discovered by John Herschel in September 1829. Visually it is both fainter and slightly larger than NGC 185 (and therefore has a considerably lower surface brightness). This means that NGC 147 is more difficult to see than NGC 185, which is visible in small telescopes. In the Webb Society Deep-Sky Observer's Handbook, the visual appearance of NGC 147 is described as follows:

Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.

The membership of NGC 147 in the Local Group was confirmed by Walter Baade in 1944 when he was able to resolve the galaxy into individual stars with the 100-inch (2.5 m) telescope at Mount Wilson near Los Angeles.

Satellite galaxy

A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents are bound to their host galaxy, in the same way that planets within our own solar system are gravitationally bound to the Sun. While most satellite galaxies are dwarf galaxies, satellite galaxies of large galaxy clusters can be much more massive.Moreover, satellite galaxies are not the only astronomical objects that are gravitationally bound to larger host galaxies (see globular clusters). For this reason, astronomers have defined galaxies as gravitationally bound collections of stars that exhibit properties that cannot be explained by a combination of baryonic matter (i.e. ordinary matter) and Newton's laws of gravity. For example, measurements of the orbital speed of stars and gas within spiral galaxies result in a velocity curve that deviates significantly from the theoretical prediction. This observation has motivated various explanations such as the theory of dark matter and modifications to Newtonian dynamics. Therefore, despite also being satellites of host galaxies, globular clusters should not be mistaken for satellite galaxies. Satellite galaxies are not only more extended and diffuse compared to globular clusters, but are also enshrouded in massive dark matter halos that are thought to have been endowed to them during the formation process.Satellite galaxies generally lead tumultuous lives due to their chaotic interactions with both the larger host galaxy and other satellites. For example, the host galaxy is capable of disrupting the orbiting satellites via tidal and ram pressure stripping. These environmental effects can remove large amounts of cold gas from satellites (i.e. the fuel for star formation), and this can result in satellites becoming quiescent in the sense that they have ceased to form stars. Moreover, satellites can also collide with their host galaxy resulting in a minor merger (i.e. merger event between galaxies of significantly different masses). On the other hand, satellites can also merge with one another resulting in a major merger (i.e. merger event between galaxies of comparable masses). Galaxies are mostly composed of empty space, and therefore galaxy mergers do not necessarily involve collisions between objects from one galaxy and objects from the other, however, these events generally result in much more massive galaxies. Consequently, astronomers seek to constrain the rate at which both minor and major mergers occur to better understand the formation of gigantic structures of gravitationally bound conglomerations of galaxies such as galactic groups and clusters.

Sufi Observing Competition

Sufi Observing Competition is an international competition and like Messier marathon, but more difficult with various subjects.

Since 2006, Astronomical Society of Iran – Amateur Committee (ASIAC) holds an international observing competition in the memory of Azophi. The first competition was held in 2006 in the north of Semnan Province and the 2nd SUFI observing competition was held in summer of 2008 in Ladiz near Zahedan. More than 100 observers from Iran and Iraq participated in this event.

Third Sufi Competition was held in Pasargadae, Fars province of Iran, at the enclosure of the historical tomb of Cyrus the Great on 17–20 August 2009. More than 120 amateur astronomers participated in this competition which held in 2 class of individuals and groups. Closing ceremony of 3rd Sufi Competition was held in Persepolis historical site splendidly which is in the list of UNESCO world heritage site.

Babak Amin Tafreshi, Pouria Nazemi, Kazem Kookaram and Mohammad H. Almasi are Iranian amateur astronomers who designed and manage this competition in their country until today.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.