Low Surface Brightness galaxy

A low-surface-brightness galaxy, or LSB galaxy, is a diffuse galaxy with a surface brightness that, when viewed from Earth, is at least one magnitude lower than the ambient night sky.

Most LSBs are dwarf galaxies, and most of their baryonic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95% of their mass as non-baryonic dark matter. There appears to be no supernova activity in these galaxies.

Rotation curve measurements indicate an extremely high mass-to-light ratio, meaning that stars and luminous gas contribute only very little to the overall mass balance of an LSB. The centers of LSBs show no large overdensities in stars, unlike e.g. the bulges of normal spiral galaxies. Therefore, they seem to be dark-matter-dominated even in their centers, which makes them excellent laboratories for the study of dark matter.

In comparison to the high-surface-brightness galaxies, LSBs are mainly isolated field galaxies, found in regions devoid of other galaxies. In their past, they had fewer tidal interactions or mergers with other galaxies, which could have triggered enhanced star formation. This is an explanation for the small stellar content.

LSB galaxies were theorized to exist in 1976 by Mike Disney.

NGC 45 GALEX WikiSky
An image of NGC 45 , a low surface brightness spiral galaxy, by GALEX.
Hiding in the night sky
UGC 477 is located over 110 million light-years away in the constellation of Pisces.[1]

Giant low-surface-brightness galaxies

Giant low surface brightness (GLSB) galaxies are among the most massive known spiral galaxies in the Universe.[2] They have very faint stellar disks that are very rich in neutral hydrogen but low in star formation and thus low in surface brightness.[2] Such galaxies often have bright bulges that can host low luminosity active galactic nuclei.[2] GLSB galaxies are usually isolated systems that rarely interact with other galaxies.[2] The first LSB galaxy verified to exist was Malin 1, discovered in 1986. As such, it was also the first giant LSB galaxy identified. At the time of its discovery, it was the largest spiral galaxy known (by scale-length measurement).[3][4]

UGC 1382 was previous thought to be an elliptical galaxy, but low-brightness spiral arms were later detected. UGC 1382 is much closer to Earth than Malin 1.[5]

Examples

See also

References

  1. ^ "Hiding in the night sky". Retrieved 4 April 2016.
  2. ^ a b c d Mousumi Das (March 2013). "Giant Low Surface Brightness Galaxies: Evolution in Isolation". Journal of Astrophysics and Astronomy. arXiv:1310.6495. Bibcode:2013JApA...34...19D. doi:10.1007/s12036-013-9166-8.
  3. ^ a b c Scientific American, "The Ghostliest Galaxies", GD Bothun, Vol. 276, No. 2, February 1997, pp.40-45, Bibcode1997SciAm.276b..40B
  4. ^ Ken Crosswell, "Malin 1: A Bizarre Galaxy Gets Slightly Less So", 22 January 2007
  5. ^ "Surprise: Small elliptical galaxy actually a giant disk". 11 July 2016. Retrieved 12 July 2016.
Andromeda XXI

Andromeda XXI (And 21, And XXI) is a moderately bright dwarf spheroidal galaxy about 859 ± 51 kiloparsecs (2.80 ± 0.17 Mly) away from the Sun in the constellation Andromeda. It is the fourth largest Local Group dwarf spheroidal galaxy.

This large satellite of the Andromeda Galaxy (M31) has a half-light radius of nearly 1 kpc.The discovery arose from the first year data of a photometric survey of the M31/M33 subgroupings of the Local Group by the Pan-Andromeda Archaeological Survey (PAndAS). This survey was conducted with the Megaprime/MegaCam wide-field camera mounted on the Canada-France-Hawaii Telescope.

Andromeda XXI appears as a spatial overdensity of stars. It has red giant branches at the distance of M31/M33, and follows metal-poor, [Fe/H]=-1.8 when plotted in a color-magnitude diagram.

Although moderately bright (MV=-9.9 ± 0.6), it has low surface brightness. This indicates that numerous relatively luminous M31 satellites remain undiscovered.

Andromeda XXII

Andromeda XXII (Pisces VI, Triangulum I) is a low surface brightness dwarf spheroidal galaxy about 940–1,033 kiloparsecs (3.07×10^6–3.37×10^6 ly) away from the Sun in the constellation Pisces, of the Local Group.

Andromeda XXII is located much closer in projection to M33 than M31 [42 kiloparsecs (140×10^3 ly) vs. 224 kiloparsecs (730×10^3 ly)]. This fact suggests that it might be the first Triangulum (M33) satellite ever discovered. However, it is currently catalogued as a satellite of Andromeda (M31).The discovery arose from the first year data of a photometric survey of the M31/M33 subgrouping of the Local Group by the Pan-Andromeda Archaeological Survey (PAndAS). This survey was conducted with the Megaprime/MegaCam wide-field camera mounted on the Canada-France-Hawaii Telescope.

Coma Berenices

Coma Berenices is an ancient asterism in the northern sky which has been defined as one of the 88 modern constellations. It is located in the fourth galactic quadrant, between Leo and Boötes, and is visible in both hemispheres. Its name means "Berenice's Hair" in Latin and refers to Queen Berenice II of Egypt, who sacrificed her long hair as a votive offering. It was introduced to Western astronomy during the third century BC by Conon of Samos and was further corroborated as a constellation by Gerardus Mercator and Tycho Brahe. Coma Berenices is the only modern constellation named for a historic person.

The constellation's major stars are Alpha Comae Berenices, Beta Comae Berenices and Gamma Comae Berenices. They form a 45-degree triangle, from which Berenice's imaginary tresses, formed by the Coma Star Cluster, hang. The constellation's brightest star is Beta Comae Berenices, a 4.2-magnitude main sequence star similar to the Sun. Coma Berenices contains the North Galactic Pole and one of the richest known galaxy clusters, the Coma Cluster, part of the Coma Supercluster. Galaxy Malin 1, in the constellation, is the first-known giant low-surface-brightness galaxy. Supernova SN 2005ap discovered in Coma Berenices is the second-brightest known, and SN 1940B was the first observed example of a type II supernova. The star FK Comae Berenices is the prototype of an eponymous class of variable stars. The constellation is the radiant of one meteor shower, Coma Berenicids, which has one of the fastest meteor speeds, up to 65 kilometres per second (40 mi/s).

Dark galaxy

A dark galaxy is a hypothesized galaxy with no, or very few, stars. They received their name because they have no visible stars, but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark galaxies, but there are no confirmed examples to date. Dark galaxies are distinct from intergalactic gas clouds caused by galactic tidal interactions, since these gas clouds do not contain dark matter, so they do not technically qualify as galaxies. Distinguishing between intergalactic gas clouds and galaxies is difficult; most candidate dark galaxies turn out to be tidal gas clouds. The best candidate dark galaxies to date include HI1225+01, AGC229385, and numerous gas clouds detected in studies of quasars.

On 25 August 2016, astronomers reported that Dragonfly 44, an ultra diffuse galaxy (UDG) with the mass of the Milky Way galaxy, but with nearly no discernable stars or galactic structure, may be made almost entirely of dark matter.

Dragonfly 44

Dragonfly 44 is an ultra diffuse galaxy in the Coma Cluster. Observations of the velocity dispersion suggest a mass of about one trillion solar masses, about the same as the mass of the Milky Way; the galaxy shows no evidence of rotation. This is also consistent with about 90 globular clusters observed around Dragonfly 44. However, the galaxy emits only 1% of the light emitted by the Milky Way. The galaxy was discovered with the Dragonfly Telephoto Array.To determine the amount of dark matter in this galaxy, they used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy’s mass.

The scientists then used the Gemini Multi-Object Spectrograph on the 8-m Gemini North telescope to reveal a halo of spherical clusters of stars around the galaxy’s core.In August 2016, astronomers reported that this galaxy might be made almost entirely of dark matter.

KKh 060

KKH 060 is an irregular galaxy and a low surface brightness galaxy located in the direction of the constellation Leo at a distance of 4.89 million light years from Earth. The galaxy is close to the Local Group, but is not considered to be a member of it.

LEDA 135657

LEDA 135657 is a distant low surface brightness spiral galaxy located about 570 million light-years away in the constellation Cetus. It has an estimated diameter of 97,000 light-years.

List of galaxies named after people

A small number of galaxies or galaxy groups have been named after individual people. In most cases, the named individual was the person who discovered the object, who first brought attention to it, or who first studied it scientifically.

Many of the brighter galaxies visible from the Northern Hemisphere have Messier numbers, named after Charles Messier. For instance, the Andromeda Galaxy is Messier 31 and the Whirlpool Galaxy is Messier 51. There are a few other comprehensive catalogs that assign the cataloguer's name to galaxies. For instance, Markarian galaxies, named after Benjamin Markarian, are galaxies with excess blue and ultraviolet emission; galaxies in the Atlas of Peculiar Galaxies are assigned an Arp number after Halton Arp who produced the catalog; etc. Objects in these catalogs are excluded below, except in cases where they carry the name of an additional person.

Messier 82

Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. A member of the M81 Group, it is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to Earth, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.

NGC 296

NGC 296 is a low surface brightness unbarred spiral galaxy in the constellation of Pisces. The designation NGC 295 is sometimes mistakenly used for NGC 296.

NGC 3794

NGC 3794, also cataloged in the New General Catalogue as NGC 3804, is a low-surface-brightness galaxy in the constellation Ursa Major. It is very far from Earth, with a distance of about 68,470,000 light-years (20,990,000 pc).

NGC 3883

NGC 3883 is a large low surface brightness spiral galaxy located about 330 million light-years away in the constellation Leo. NGC 3883 has a prominent bulge but does host an AGN. The galaxy also has flocculent spiral arms in its disk. It was discovered by astronomer William Herschel on April 13, 1785 and is a member of the Leo Cluster.

NGC 4571

NGC 4571 is a spiral galaxy located in the constellation of Coma Berenices that William Herschel thought was Messier 91 in Charles Messier' catalog of deep-sky objects, before nearly two centuries later that object was determined to be the nearby barred spiral galaxy NGC 4548.

NGC 5774

NGC 5774 is an intermediate spiral galaxy approximately 71 million light-years away from Earth in the constellation of Virgo. It was discovered by Irish engineer Bindon Stoney on April 26, 1851.NGC 5774 belongs to a small group of galaxies, together with nearby NGC 5775 and IC 1070.

It has been classified as a "low surface brightness" (LSB) galaxy, but its central surface brightness is 5 times brighter than the brightest LSB galaxies.

It has a multiple spiral pattern with bright blue knotty structure all along the arms.It is an extremely low star forming galaxy with five X-ray sources plus three ultraluminous X-ray source candidates.

NGC 765

NGC 765 is an intermediate spiral galaxy located in the constellation Aries. It is located at a distance of circa 220 million light years from Earth, which, given its apparent dimensions, means that NGC 765 is about 195,000 light years across. It was discovered by Albert Marth on October 8, 1864. The galaxy has an extensive hydrogen (HI) disk with low surface brightness, whose diameter is estimated to be 240 kpc (780,000 light years).

NGC 784

NGC 784 is a barred spiral galaxy about 16.0 Mly away in the constellation Triangulum. NGC 784 is located within the Virgo Supercluster.

Surface brightness

In astronomy, surface brightness quantifies the apparent brightness or flux density per unit angular area of a spatially extended object such as a galaxy or nebula, or of the night sky background. An object's surface brightness depends on its surface luminosity density, i.e., its luminosity emitted per unit surface area. In visible and infrared astronomy, surface brightness is often quoted on a magnitude scale, in magnitudes per square arcsecond in a particular filter band or photometric system.

Measurement of the surface brightnesses of celestial objects is called surface photometry.

Ultra diffuse galaxy

An ultra diffuse galaxy (UDG) is an extremely low luminosity galaxy, the first example of which was discovered in the nearby Virgo Cluster by Allan Sandage and Bruno Binggeli in 1984. Such a galaxy may have the same size and mass as the Milky Way but a visible star count of only 1%. Their lack of luminosity is due to the lack of star-forming gas in the galaxy. This results in old stellar populations.Some ultra diffuse galaxies found in the Coma Cluster, about 330 million light years from Earth, have diameters of 60 kly (18 kpc) (more than half the size of our galaxy) with 1% of the stars of the Milky Way Galaxy. The distribution of ultra diffuse galaxies in the Coma Cluster is the same as luminous galaxies; this suggests that the cluster environment strips the gas from the galaxies, while allowing them to populate the cluster the same as more luminous galaxies. The similar distribution in the higher tidal force zones suggests a larger dark matter fraction to hold the galaxies together under the higher stress.Dragonfly 44, a ultra diffuse galaxy in the Coma Cluster, is one example. Observations of the rotational speed suggest a mass of about one trillion solar masses, about the same as the mass of the Milky Way. This is also consistent with about 90 globular clusters observed around Dragonfly 44. However, the galaxy emits only 1% of the light emitted by the Milky Way. On 25 August 2016, astronomers reported that Dragonfly 44 may be made almost entirely of dark matter. In 2018 the same authors reported the discovery of a dark matter-free UDG (NGC 1052-DF2, which was already identified on photoplates by Igor Karachentsev) based on velocity measurements of ~10 globular cluster system. The authors concluded that this may rule out modified gravity theories like MOND, but other theories such as the External Field Effect are also possibilities.

Morphology
Structure
Active nuclei
Energetic galaxies
Low activity
Interaction
Lists
See also

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