Low-ionization nuclear emission-line region

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The Sombrero Galaxy (M104) as observed by the Hubble Space Telescope (HST). The Sombrero Galaxy is an example of a LINER galaxy. Credit: HST/NASA/ESA. M104 ngc4594 sombrero galaxy hi-res.jpg
The Sombrero Galaxy (M104) as observed by the Hubble Space Telescope (HST). The Sombrero Galaxy is an example of a LINER galaxy. Credit: HST/NASA/ESA.

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. [2] 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. [2]

Contents

Demographics of LINER galaxies

Galaxies that contain LINERs are often referred to as LINER galaxies. LINER galaxies are very common; approximately one-third of all nearby galaxies (galaxies within approximately 20-40 Mpc) may be classified as LINER galaxies. [2] [3] Approximately 75% of LINER galaxies are either elliptical galaxies, lenticular galaxies, or S0/a-Sab galaxies (spiral galaxies with large bulges and tightly wound spiral arms). LINERs are found less frequently in Sb-Scd galaxies (spiral galaxies with small bulges and loosely wound spiral arms), and they are very rare in nearby irregular galaxies. [3] LINERs also may be commonly found in luminous infrared galaxies (LIRGs), a class of galaxies defined by their infrared luminosities that are frequently formed when two galaxies collide with each other. Approximately one-quarter of LIRGs may contain LINERs. [4]

Scientific debates: energy sources and ionization mechanisms

LINERs have been at the center of two major debates. First, astronomers have debated the source of energy that excites the ionized gas in the centers of these galaxies. Some astronomers have proposed that active galactic nuclei (AGN) with supermassive black holes are responsible for the LINER spectral emission. [2] [5] Other astronomers have asserted that the emission is powered by star formation regions. [6] [7] The other major issue is related to how the ions are excited. Some astronomers have suggested that shock waves propagating through the gas may ionize the gas, [2] while others have suggested that photoionization (ionization by ultraviolet light) may be responsible. [5] [6] [7]

These debates are complicated by the fact that LINERs are found in a wide variety of objects with different brightnesses and morphologies. Moreover, the debate over the energy sources for LINERs is entangled with a similar debate over whether the light from star formation regions or the light from AGN produce the high infrared luminosities seen in LIRGs. [4]

Although both the energy sources and the excitation mechanisms for LINER emission are still being studied, many LINERs are frequently referred to as AGN. [1]

Star formation in LINERs

A number of surveys have been performed to explore the connection between star formation and LINER activity. If a connection can be found between star formation activity and LINER activity, then this strengthens the possibility that LINERs are powered by the hot gas found in star formation regions. However, if star formation cannot be found in LINERs, then this definitively excludes star formation as powering LINER emission.

Star formation in LIRGs with LINERs

Recent observations with the Spitzer Space Telescope show a clear connection between LINER emission in luminous infrared galaxies (LIRGs) and star formation activity. The mid-infrared spectra of LIRGs with LINERs have been shown to look similar to the mid-infrared spectra of starburst galaxies, which suggest that infrared-bright LINERs are powered by star formation activity. However, some mid-infrared spectral line emission from AGN have also been detected in these galaxies, indicating that star formation may not be the only energy sources in these galaxies. [8]

Star formation in normal galaxies with LINERs

Normal nearby galaxies with LINERs, however, appear to be different. A few near-infrared spectroscopic surveys have identified some LINERs in normal galaxies that may be powered by star formation. [9] However, most LINERs in nearby galaxies have low levels of star formation activity. [9] [10] [11] Moreover, the stellar populations of many LINERs appear to be very old, [12] [13] [11] and the mid-infrared spectra, as observed by the Spitzer Space Telescope, do not appear similar to the spectra expected from star formation. [8] These results demonstrate that most LINER in nearby normal galaxies may not be powered by star formation, although a few exceptions clearly exist.

Notable LINER galaxies

See also

Related Research Articles

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.

<span class="mw-page-title-main">Seyfert galaxy</span> Class of active galaxies with very bright nuclei

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

<span class="mw-page-title-main">Sombrero Galaxy</span> Galaxy in the constellation Virgo

The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It has an isophotal diameter of approximately 29.09 to 32.32 kiloparsecs, making it slightly bigger in size than the Milky Way.

<span class="mw-page-title-main">NGC 3227</span> Galaxy in the constellation Leo

NGC 3227 is an intermediate spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies. Both galaxies may be found in the constellation Leo. It is a member of the NGC 3227 Group of galaxies, which is a member of the Leo II Groups, a series of galaxies and galaxy clusters strung out from the right edge of the Virgo Supercluster.

<span class="mw-page-title-main">NGC 3226</span> Dwarf elliptical galaxy in the constellation Leo

NGC 3226 is a dwarf elliptical galaxy that is interacting with the spiral galaxy NGC 3227. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies. Both galaxies may be found in the constellation Leo. It is a member of the NGC 3227 Group of galaxies, which is a member of the Leo II Groups, a series of galaxies and galaxy clusters strung out from the right edge of the Virgo Supercluster.

Luminous infrared galaxies or LIRGs are galaxies with luminosities, the measurement of brightness, above 1011 L☉. They are also referred to as submillimeter galaxies (SMGs) through their normal method of detection. LIRGs are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. A LIRG's luminosity is 100 billion times that of the Sun.

<span class="mw-page-title-main">NGC 5005</span> Galaxy in the constellation Canes Venatici

NGC 5005, also known as Caldwell 29, is an inclined spiral galaxy in the constellation Canes Venatici. The galaxy has a relatively bright nucleus and a bright disk that contains multiple dust lanes. The galaxy's high surface brightness makes it an object that is visible to amateur astronomers using large amateur telescopes.

<span class="mw-page-title-main">NGC 1672</span> Galaxy in the constellation Dorado

NGC 1672 is a barred spiral galaxy located in the constellation Dorado. It was discovered by the astronomer James Dunlop on November 5, 1826. It was originally unclear whether it was a member of the Dorado Group, with some sources finding it to be a member and other sources rejecting its membership. However, recent tip of the red-giant branch (TRGB) measurements indicate that NGC 1672 is located at the same distance as other members, suggesting it is indeed a member of the Dorado Group.

<span class="mw-page-title-main">Ionization cone</span> Astronomical phenomenon

Ionization cones are cones of ionized material extending from active galactic nuclei, predominantly observed in type II Seyfert galaxies. They are detected through their emission of electromagnetic radiation in the visible and infrared parts of the spectrum. The main method of observation is through spectroscopy, using spectral line analysis to measure the shape of the ionized region and the condition of the material such as temperature, density, composition, and degree of ionization.

<span class="mw-page-title-main">NGC 7469</span> Galaxy located in the constellation Pegasus

NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus. NGC 7469 is located about 200 million light-years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 90,000 light-years across. It was discovered by William Herschel on November 12, 1784.

<span class="mw-page-title-main">NGC 3367</span> Spiral galaxy in the constellation Leo

NGC 3367 is a barred spiral galaxy located in the constellation Leo. It is located at a distance of about 120 million light years from Earth, which, given its apparent dimensions, means that NGC 3367 is about 85,000 light years across. It was discovered by William Herschel on March 19, 1784.

<span class="mw-page-title-main">NGC 7130</span> Galaxy in the constellation Piscis Austrinus

NGC 7130 is a spiral galaxy located in the constellation Piscis Austrinus. It is located at a distance of about 220 million light years from Earth, which, given its apparent dimensions, means that NGC 7130 is about 100,000 light years across. It was discovered by John Herschel on September 25, 1834, and discovered independently by Lewis Swift on September 17, 1897. The location of the galaxy given in the New General Catalogue was off by 30 arcminutes in declination from the location of the galaxy.

<span class="mw-page-title-main">NGC 4636</span> Galaxy in the constellation Virgo

NGC 4636 is an elliptical galaxy located in the constellation Virgo. It is a member of the NGC 4753 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of about 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4636 is about 105,000 light years across.

<span class="mw-page-title-main">NGC 1386</span> Galaxy in the constellation Eridanus

NGC 1386 is a spiral galaxy located in the constellation Eridanus. It is located at a distance of circa 53 million light years from Earth, which, given its apparent dimensions, means that NGC 1386 is about 50,000 light years across. It is a Seyfert galaxy, the only one in Fornax Cluster.

<span class="mw-page-title-main">NGC 2273</span> Galaxy in the constellation Lynx

NGC 2273 is a barred spiral galaxy located in the constellation Lynx. It is located at a distance of circa 95 million light years from Earth, which, given its apparent dimensions, means that NGC 2273 is about 100,000 light years across. It was discovered by Nils Dunér on September 15, 1867.

<span class="mw-page-title-main">NGC 1142</span> Interacting and distorted spiral galaxy in the constellation Cetus

NGC 1142 is a distorted spiral galaxy in the constellation of Cetus. It is located about 370 million light years away from Earth, which means, given its apparent dimensions, that NGC 1142 is approximately 170,000 light years across. It is a type 2 Seyfert galaxy. It interacts with the elliptical galaxy NGC 1141.

<span class="mw-page-title-main">NGC 7592</span> Interacting galaxy system in the constellation Aquarius

NGC 7592 is an interacting galaxy system located 300 million light years away in the constellation Aquarius. It was discovered by William Herschel on September 20, 1784. The total infrared luminosity is 1011.33 L☉, and thus it is categorised as a luminous infrared galaxy. One of the galaxies hosts a type 2 Seyfert nucleus.

<span class="mw-page-title-main">NGC 3516</span> Galaxy in the constellation of Ursa Major

NGC 3516 is a barred lenticular galaxy in the constellation of Ursa Major. NGC 3516 is located about 150 million light years away from Earth, which means, given its apparent dimensions, that NGC 3516 is approximately 100,000 light years across. It was discovered by William Herschel on April 3, 1785.

<span class="mw-page-title-main">NGC 5135</span>

NGC 5135 is a barred spiral galaxy located in the constellation Hydra. It is located at a distance of about 200 million light years from Earth. It was discovered by John Herschel on May 8, 1834. It is a Seyfert galaxy.

<span class="mw-page-title-main">NGC 7682</span> Barred spiral galaxy in the constellation Pisces

NGC 7682 is a barred spiral galaxy in the constellation Pisces. It is located at a distance of circa 180 million light years from Earth, which, given its apparent dimensions, means that NGC 7682 is about 65,000 light years across. It was discovered by Heinrich d'Arrest on September 23, 1864.

References

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  2. 1 2 3 4 5 T. M. Heckman (1980). "An optical and radio survey of the nuclei of bright galaxies - Activity in normal galactic nuclei". Astronomy and Astrophysics . 87: 152–164. Bibcode:1980A&A....87..152H.
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  5. 1 2 L. C. Ho; A. V. Filippenko; W. L. W. Sargent (1993). "A Reevaluation of the Excitation Mechanism of LINERs". Astrophysical Journal. 417: 63–81. Bibcode:1993ApJ...417...63H. doi: 10.1086/173291 .
  6. 1 2 R. Terlevich; J. Melnick (1985). "Warmers - The missing link between Starburst and Seyfert galaxies". Monthly Notices of the Royal Astronomical Society . 213 (4): 841–856. Bibcode:1985MNRAS.213..841T. doi: 10.1093/mnras/213.4.841 .
  7. 1 2 J. C. Shields (1992). "Normal O stars in dense media generate LINERs". Astrophysical Journal Letters. 399: L27–L30. Bibcode:1992ApJ...399L..27S. doi: 10.1086/186598 .
  8. 1 2 E. Sturm; D. Rupke; A. Contursi; D.-C. Kim; D. Lutz; H. Netzer; S. Veilleux; R. Genzel; M. Lehnert; L. J. Tacconi; D. Maoz; J. Mazzarella; S. Lord; D. Sanders; A. Sternberg (2006). "Mid-Infrared Diagnostics of LINERS". Astrophysical Journal Letters. 653 (1): L13–L16. arXiv: astro-ph/0610772 . Bibcode:2006ApJ...653L..13S. doi:10.1086/510381. S2CID   51798661.
  9. 1 2 J. E. Larkin; L. Armus; R. A. Knop; B. T. Soifer; K. Matthews (1998). "A Near-Infrared Spectroscopic Survey of LINER Galaxies". Astrophysical Journal Supplement Series. 114 (1): 59–72. arXiv: astro-ph/9708097 . Bibcode:1998ApJS..114...59L. doi:10.1086/313063. S2CID   15514939.
  10. ↑ G. J. Bendo; R. D. Joseph; M. Wells; P. Gallais; M. Haas; A. M. Heras; U. Klaas; R. J. Laureijs; K. Leech; D. Lemke; L. Metcalfe; M. Rowan-Robinson; B. Schulz; C. Telesco (2002). "Star Formation in the Infrared Space Observatory Atlas of Bright Spiral Galaxies". Astronomical Journal. 124 (3): 1380–1392. arXiv: astro-ph/0206299 . Bibcode:2002AJ....124.1380B. doi:10.1086/342283. S2CID   119506664.
  11. 1 2 G. J. Bendo; R. D. Joseph (2004). "Nuclear Stellar Populations in the Infrared Space Observatory Atlas of Bright Spiral Galaxies". Astronomical Journal. 127 (6): 3338–3360. arXiv: astro-ph/0403133 . Bibcode:2004AJ....127.3338B. doi:10.1086/420712. S2CID   14169689.
  12. ↑ R. Cid Fernandes, R. M. González Delgado, H. Schmitt, T. Storchi-Bergmann, Thaisa, L. P. Martins, E. Pérez, T. Heckman, C. Leitherer, D. Schaerer (2004). "The Stellar Populations of Low-Luminosity Active Galactic Nuclei. I. Ground-based Observations". Astrophysical Journal. 605 (1): 105–126. arXiv: astro-ph/0401416 . Bibcode:2004ApJ...605..105C. doi:10.1086/382217. S2CID   119101213.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ↑ R. M. González Delgado; R. Cid Fernandes; E. Pérez; L. P. Martins; T. Storchi-Bergmann; H. Schmitt; T. Heckman; C. Leitherer (2004). "The Stellar Populations of Low-Luminosity Active Galactic Nuclei. II. Space Telescope Imaging Spectrograph Observations" (PDF). Astrophysical Journal. 605 (1): 127–143. arXiv: astro-ph/0401414 . Bibcode:2004ApJ...605..127G. doi:10.1086/382216. hdl:10183/108914. S2CID   119471662.
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