NGC 5238

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NGC 5238
NGC 5238 Hubble WikiSky.jpg
Hubble Space Telescope image of NGC 5238
Observation data (J2000 epoch)
Constellation Canes Venatici
Right ascension 13h 34m 43.8s [1]
Declination +51° 36 33 [1]
Redshift 0.0015 [2]
Helio radial velocity 229 km/s [3]
Distance 4.51 Mpc [4]
Characteristics
Type Irr [5] [ failed verification ]
Mass 1.17×106 [6]   M
Mass/Light ratio 0.6 [7]   M/L
Apparent size  (V)64.4" [8]
Other designations
UGC 8565, VV 828, Mrk 1479, SBS 1332+518, I Zw 64, KPG 384

NGC 5238 is an irregular galaxy [5] in the constellation Canes Venatici. Located at a comoving distance of 4.51 Mpc, [4] it is 64.4 arcseconds in diameter. [8] It has sometimes been classified as a blue compact dwarf galaxy. [9] Although some authors have hypothesized it to be a member of the M101 Group of galaxies, it is currently believed to be an isolated galaxy. [10]

Contents

At an inclination of 39° with respect to Earth, [3] NGC 5238 has a total mass of 117 million solar masses, [6] with a star formation rate of 0.01 solar masses per year. [11] Of the total mass, HI gas appears to account for 26 million solar masses. [3]

Classification

In 1977, NGC 5238 was hypothesized to not be a single galaxy, but rather a pair of interacting galaxies. [12] It was not until ten years later that a dedicated study of the galaxy's rotation curve was undertaken, showing that the galaxy is indeed a single galaxy. One of the two regions that was thought to be the nucleus of a galaxy was instead shown to be simply a large HII region around 100 pc in diameter. [13]

The morphological type of NGC 5238 has been the subject of some controversy. In 1979, the galaxy was classified as a barred spiral galaxy. [14] Soon after, in 1984, the galaxy was included in a study of blue compact dwarf galaxies, incompatible with the classification of a barred spiral. [15] However, the barred spiral classification was considered the correct classification for years. It was not until the mid 1990s that the galaxy was first recognized as a dwarf irregular galaxy. [16] [17] Even after this, the majority of studies recognized the galaxy as a spiral galaxy until 2015, when the classification of irregular finally became widely accepted [5] [9]

Appearance

As it appears to us, NGC 5238 is tilted at an inclination of 39°. [3] This 2013 estimate follows previous estimates of 30° in 1987, [13] 37 ± 5° in 1992, [18] and 47° in 1999 [19] In the Spitzer 3.6 µm band, the semimajor axis of its angular size is 64.4", with an ellipticity of 0.201. [8]

Distance

The distance estimate to NGC 5238 has been brought down considerably since first calculated. The first published distance estimate was 7 Mpc, derived using redshift. [14] This remained the predominant estimate until 1996, when the distance was found to be much less, estimated at 5.18 Mpc. [20] Subsequently, using spectral data from the HI 21cm line, the distance was calculated to be 4.7 Mpc in 1999, [21] although an updated HI study found a slightly higher value at 5.20 Mpc in 2002. [22] Five years later, in 2007, the distance estimate was lowered even further to 4.50 Mpc, extremely close to today's accepted value. [23]

One way to determine distance unambiguously is by standard candles. The tip of the red giant branch is such a method; every galaxy's brightest red giant stars must have exactly the same known luminosity. When combined with corrections for interstellar reddening, this allows for accurate determination of a galaxy's distance. By 2009, a Hubble Space Telescope image of NGC 5238 had become available, resolving the individual stars within the galaxy. Using this method, the distance modulus was calculated at 28.27 magnitudes, corresponding to a distance of 4.51 Mpc, today's accepted value. [4]

Radio emission

Since a first study was published in 1986, the neutral hydrogen gas of NGC 5238 and its associated 21 cm line have been the subject of many studies. The first study calculated the total HI 21 cm flux from the galaxy to be 4.5 ± 1.0 Jy·km/s, with a full width at half maximum of 28 km/s and a maximum flux density of 0.25 ± 0.011 Jy. [24] Two years later, the 20% line width was calculated at two conflicting values from two studies: 47 km/s and 65 km/s. [7] [25] From the HI line data, the total mass to HI mass ratio was calculated to be 0.384 and the pseudo HI surface density was estimated to be 9.7 solar masses per square parsec. [7] Another two years later, another estimate for the 20% and 50% line widths was published, calculating 36 ± 4 km/s at 50% and 49 ± 4 at 20%. [26]

In 1999, the 50% line width was further refined to 32 ± 4 km/s, [21] then 36 km/s. The second study, in addition to deriving the 5.20 Mpc distance quoted above, found a total HI mass of 4.2×107 solar masses. [22] Finally, in 2013, the 50% line width estimate was further increased to 40 km/s, and the HI mass was refined to 2.6×107 solar masses, implying a total-to-HI mass ratio of 7.3. [3]

In addition to HI gas, it is thought that radio continuum emission should be present from NGC 5238 as well. The galaxy is a strong ultraviolet emitter, indicating that the galaxy is undergoing rapid star formation. Based on this, it is to be expected that there should be radio continuum emission from the galaxy, due to the acceleration of electrons in HII regions, known as bremsstrahlung. However, such emission has not been found in NGC 5238, contradicting models. To resolve this mystery, it has been hypothesized that the star formation has subsided recently enough that the UV excess from massive stars is still present, but the hydrogen has already recombined. [27]

Related Research Articles

<span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

<span class="mw-page-title-main">M81 Group</span> Galaxy group in Ursa Major and Camelopardalis

The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the 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 ×1012M. The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster.

<span class="mw-page-title-main">Triangulum Galaxy</span> Spiral galaxy in the constellation Triangulum

The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC (New General Catalogue) 598. With the D25 isophotal diameter of 18.74 kiloparsecs (61,100 light-years), the Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Andromeda Galaxy and the Milky Way.

<span class="mw-page-title-main">NGC 300</span> Galaxy in the constellation Sculptor

NGC 300 (also known as Caldwell 70) is a spiral galaxy in the constellation Sculptor. It is one of the closest galaxies to the Local Group, and probably lies between the latter and the Sculptor Group. It is the brightest of the five main spirals in the direction of the Sculptor Group. It is inclined at an angle of 42° when viewed from Earth and shares many characteristics of the Triangulum Galaxy. It is 94,000 light-years in diameter, somewhat smaller than the Milky Way, and has an estimated mass of (2.9 ± 0.2) × 1010M.

<span class="mw-page-title-main">NGC 404</span> Galaxy in the constellation Andromeda

NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes. NGC 404 lies just beyond the Local Group and does not appear gravitationally bound to it. It is located within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".

<span class="mw-page-title-main">Centaurus A/M83 Group</span> Group of galaxies in the constellations Centaurus, Hydra and Virgo

The Centaurus A/M83 Group is a complex group of galaxies in the constellations Hydra, Centaurus, and Virgo. The group may be roughly divided into two subgroups. The Cen A Subgroup, at a distance of 11.9 Mly, is centered on Centaurus A, a nearby radio galaxy. The M83 Subgroup, at a distance of 14.9 Mly, is centered on the Messier 83 (M83), a face-on spiral galaxy.

<span class="mw-page-title-main">Sculptor Galaxy</span> Intermediate spiral galaxy in the constellation Sculptor

The Sculptor Galaxy is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently undergoing a period of intense star formation.

<span class="mw-page-title-main">NGC 1569</span> Galaxy in the constellation Camelopardalis

NGC 1569 is a dwarf irregular galaxy in Camelopardalis. The galaxy is relatively nearby and consequently, the Hubble Space Telescope can easily resolve the stars within the galaxy. The distance to the galaxy was previously believed to be only 2.4 Mpc. However, in 2008 scientists studying images from Hubble calculated the galaxy's distance at nearly 11 million light-years away, about 4 million light-years farther than previously thought, meaning it is a member of the IC 342 group of galaxies.

<span class="mw-page-title-main">NGC 7793</span> Galaxy in the constellation Sculptor

NGC 7793 is a flocculent spiral galaxy in the southern constellation of Sculptor. It was discovered in 1826 by Scottish astronomer James Dunlop. The galaxy is located at a distance of 12.2 million light years and is receding with a heliocentric radial velocity of 227 km/s. NGC 7793 is one of the five brightest galaxies within the Sculptor Group.

<span class="mw-page-title-main">NGC 2683</span> Galaxy in the constellation Lynx

NGC 2683 is a field spiral galaxy in the northern constellation of Lynx. It was nicknamed the "UFO Galaxy" by the Astronaut Memorial Planetarium and Observatory. It was discovered by the astronomer William Herschel on February 5, 1788.

<span class="mw-page-title-main">NGC 2976</span> Galaxy in the constellation Ursa Major

NGC 2976 is a peculiar dwarf galaxy in the northern circumpolar constellation of Ursa Major. It was discovered by German-born astronomer William Herschel on November 8, 1801, and catalogued as H I.285. J. L. E. Dreyer described it as, "bright, very large, much extended 152°, star involved". It is a member of the M81 Group and lies 1° 20 to the southwest of Messier 81. The projected separation of this galaxy from the M81 Group is 190 kpc.

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

The Antlia Dwarf is a dwarf spheroidal/irregular galaxy. It lies about 1.3 Mpc from Earth in the constellation Antlia. It is the fourth and faintest member of the nearby Antlia-Sextans Group of galaxies. The galaxy contains stars of all ages, contains significant amounts of gas, and has experienced recent star formation. The Antlia Dwarf is believed to be tidally interacting with the small barred spiral galaxy NGC 3109.

<span class="mw-page-title-main">NGC 4449</span> Galaxy in the constellation Canes Venatici

NGC 4449, also known as Caldwell 21, is an irregular Magellanic type galaxy in the constellation Canes Venatici, being located about 13 million light-years away. It is part of the M94 Group or Canes Venatici I Group that is relatively close to the Local Group hosting our Milky Way galaxy.

<span class="mw-page-title-main">NGC 672</span> Galaxy in the constellation Triangulum

NGC 672 is a spiral galaxy in the northern constellation of Triangulum, positioned around 2° to the southwest of the star Alpha Trianguli. The original object designated NGC 672 was discovered by the German-born astronomer William Herschel on 26 October 1786, but this was later cataloged as NGC 614. The object now identified as NGC 672 was discovered by John Herschel on 11 November 1827.

<span class="mw-page-title-main">NGC 3642</span> Galaxy in the constellation Ursa Major

NGC 3642 is a spiral galaxy in the constellation Ursa Major. The galaxy has a low-ionization nuclear emission-line region. It is located at a distance of circa 30 million light years from Earth, which, given its apparent dimensions, means that NGC 3642 is about 50,000 light years across. The galaxy is characterised by an outer pseudoring, which was probably formed after the accretion of a gas rich dwarf galaxy.

<span class="mw-page-title-main">NGC 3585</span> Galaxy in the constellation Hydra

NGC 3585 is an elliptical or a lenticular galaxy located in the constellation Hydra. It is located at a distance of circa 60 million light-years from Earth, which, given its apparent dimensions, means that NGC 3585 is about 80,000 light years across. It was discovered by William Herschel on December 9, 1784.

<span class="mw-page-title-main">NGC 3729</span> Galaxy in the constellation of Ursa Major

NGC 3729 is a barred spiral galaxy located in the constellation Ursa Major. It is located at a distance of circa 65 million light years from Earth, which, given its apparent dimensions, means that NGC 3729 is about 60,000 light years across. It was discovered by William Herschel on April 12, 1789.

<span class="mw-page-title-main">NGC 4299</span> Spiral galaxy in the constellation Virgo

NGC 4299 is a featureless spiral galaxy located about 55 million light-years away in the constellation Virgo. It was discovered by astronomer William Herschel on March 15, 1784 and is a member of the Virgo Cluster.

<span class="mw-page-title-main">NGC 4324</span> Galaxy in the constellation of Virgo

NGC 4324 is a lenticular galaxy located about 85 million light-years away in the constellation Virgo. It was discovered by astronomer Heinrich d'Arrest on March 4, 1862. NGC 4324 has a stellar mass of 5.62 × 1010M, and a baryonic mass of 5.88 × 1010M. The galaxy's total mass is around 5.25 × 1011M. NGC 4324 is notable for having a ring of star formation surrounding its nucleus. It was considered a member of the Virgo II Groups until 1999, when its distance was recalculated and it was placed in the Virgo W Group.

References

  1. 1 2 Paturel, G.; Petit, C.; Prugniel, Ph.; Theureau, G.; Rousseau, J.; Brouty, M.; Dubois, P.; Cambrésy, L. (2003). "HYPERLEDA. I. Identification and designation of galaxies". Astronomy and Astrophysics. 412: 45–55. Bibcode:2003A&A...412...45P. doi: 10.1051/0004-6361:20031411 .
  2. Gyulzadyan, M. V.; Stepanian, J. A.; Petrosian, A. R.; Kunth, D.; McLean, B.; Comte, G. (2003). "Spectroscopic Study of a Large Sample of Galaxies Discovered in the Second Byurakan Survey Fields". Astrophysics (English Translation of Astrofizika). 46 (2): 131. Bibcode:2003Ap.....46..131G. doi:10.1023/A:1024011318696. S2CID   118938315.
  3. 1 2 3 4 5 Karachentsev, Igor D.; Makarov, Dmitry I.; Kaisina, Elena I. (2013). "Updated Nearby Galaxy Catalog". The Astronomical Journal. 145 (4): 101. arXiv: 1303.5328 . Bibcode:2013AJ....145..101K. doi:10.1088/0004-6256/145/4/101. S2CID   118585268.
  4. 1 2 3 Jacobs, Bradley A.; Rizzi, Luca; Tully, R. Brent; Shaya, Edward J.; Makarov, Dmitry I.; Makarova, Lidia (2009). "The Extragalactic Distance Database: Color-Magnitude Diagrams". The Astronomical Journal. 138 (2): 332. arXiv: 0902.3675 . Bibcode:2009AJ....138..332J. doi:10.1088/0004-6256/138/2/332. S2CID   15727705.
  5. 1 2 3 Buta, Ronald J.; Sheth, Kartik; Athanassoula, E.; Bosma, A.; Knapen, Johan H.; Laurikainen, Eija; Salo, Heikki; Elmegreen, Debra; Ho, Luis C.; Zaritsky, Dennis; Courtois, Helene; Hinz, Joannah L.; Muñoz-Mateos, Juan-Carlos; Kim, Taehyun; Regan, Michael W.; Gadotti, Dimitri A.; Gil De Paz, Armando; Laine, Jarkko; Menéndez-Delmestre, Karín; Comerón, Sébastien; Erroz Ferrer, Santiago; Seibert, Mark; Mizusawa, Trisha; Holwerda, Benne; Madore, Barry F. (2015). "A Classical Morphological Analysis of Galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G)". The Astrophysical Journal Supplement Series. 217 (2): 32. arXiv: 1501.00454 . Bibcode:2015ApJS..217...32B. doi:10.1088/0067-0049/217/2/32. S2CID   119202943.
  6. 1 2 Cook, David O.; Dale, Daniel A.; Johnson, Benjamin D.; Van Zee, Liese; Lee, Janice C.; Kennicutt, Robert C.; Calzetti, Daniela; Staudaher, Shawn M.; Engelbracht, Charles W. (2014). "Spitzer Local Volume Legacy (LVL) SEDs and physical properties". Monthly Notices of the Royal Astronomical Society. 445 (1): 899–912. arXiv: 1409.0847 . Bibcode:2014MNRAS.445..899C. doi:10.1093/mnras/stu1787. S2CID   118469122.
  7. 1 2 3 Huchtmeier, W. K.; Richter, O.-G. (1988). "H I observations of galaxies in the Kraan-Korteweg-Tammann catalogue of nearby galaxies. III - Global parameters of the galaxies". Astronomy and Astrophysics. 203: 237. Bibcode:1988A&A...203..237H.
  8. 1 2 3 Sheth, Kartik; Regan, Michael; Hinz, Joannah L.; Gil De Paz, Armando; Menéndez-Delmestre, Karín; Muñoz-Mateos, Juan-Carlos; Seibert, Mark; Kim, Taehyun; Laurikainen, Eija; Salo, Heikki; Gadotti, Dimitri A.; Laine, Jarkko; Mizusawa, Trisha; Armus, Lee; Athanassoula, E.; Bosma, Albert; Buta, Ronald J.; Capak, Peter; Jarrett, Thomas H.; Elmegreen, Debra M.; Elmegreen, Bruce G.; Knapen, Johan H.; Koda, Jin; Helou, George; Ho, Luis C.; Madore, Barry F.; Masters, Karen L.; Mobasher, Bahram; Ogle, Patrick; et al. (2010). "The Spitzer Survey of Stellar Structure in Galaxies (S4G)". Publications of the Astronomical Society of the Pacific. 122 (898): 1397. arXiv: 1010.1592 . Bibcode:2010PASP..122.1397S. doi:10.1086/657638. S2CID   13509333.
  9. 1 2 Ann, H. B.; Seo, Mira; Ha, D. K. (2015). "A Catalog of Visually Classified Galaxies in the Local (z ∼ 0.01) Universe". The Astrophysical Journal Supplement Series. 217 (2): 27. arXiv: 1502.03545 . Bibcode:2015ApJS..217...27A. doi:10.1088/0067-0049/217/2/27. S2CID   119253507.
  10. Tikhonov, N. A.; Lebedev, V. S.; Galazutdinova, O. A. (2015). "M 101 group galaxies". Astronomy Letters. 41 (6): 239. Bibcode:2015AstL...41..239T. doi:10.1134/S1063773715060080. S2CID   122692981.
  11. Karachentsev, Igor D.; Kaisina, Elena I. (2013). "Star Formation Properties in the Local Volume Galaxies via Hα and Far-ultraviolet Fluxes". The Astronomical Journal. 146 (3): 46. arXiv: 1305.4791 . Bibcode:2013AJ....146...46K. doi:10.1088/0004-6256/146/3/46. S2CID   119188439.
  12. Vorontsov-Velyaminov, B. A. (1977). "Atlas of interacting galaxies, part II and the concept of fragmentation of galaxies". Astronomy and Astrophysics. 28: 1. Bibcode:1977A&AS...28....1V.
  13. 1 2 Arkhipova, V. P.; Noskova, R. I.; Sil'Chenko, O. K.; Zasov, A. V. (1987). "The internal motions in three dwarf irregular galaxies". Pis'ma v Astronomicheskii Zhurnal. 13: 575. Bibcode:1987PAZh...13..575A.
  14. 1 2 Kraan-Korteweg, R. C.; Tammann, G. A. (1979). "A catalogue of galaxies within 10 MPC". Astronomische Nachrichten. 300 (4): 181. Bibcode:1979AN....300..181K. doi:10.1002/asna.19793000403.
  15. Klein, U.; Wielebinski, R.; Thuan, T. X. (1984). "Radio continuum observations of blue compact dwarf galaxies". Astronomy and Astrophysics. 141: 241. Bibcode:1984A&A...141..241K.
  16. Karachentsev, I. D.; Tikhonov, N. A. (1994). "New photometric distances for dwarf galaxies in the Local Volume". Astronomy and Astrophysics. 286: 718. Bibcode:1994A&A...286..718K.
  17. Han, Cheongho; Gould, Andrew; Sackett, Penny D. (1995). "The Orientation of Spin Vectors of Galaxies in the Ursa Major Filament". The Astrophysical Journal. 445: 46. arXiv: astro-ph/9408022 . Bibcode:1995ApJ...445...46H. doi:10.1086/175671. S2CID   118985923.
  18. Schmidt, K.-H.; Boller, T. (1992). "Nearby galaxies. I - the catalogue". Astronomische Nachrichten. 313 (4): 189. Bibcode:1992AN....313..189S. doi:10.1002/asna.2113130402.
  19. Bremnes, T.; Binggeli, B.; Prugniel, P. (1999). "Structure and stellar content of dwarf galaxies. III. B and R photometry of dwarf galaxies in the M 101 group and the nearby field". Astronomy and Astrophysics Supplement. 137 (2): 337. arXiv: astro-ph/9903348 . Bibcode:1999A&AS..137..337B. doi:10.1051/aas:1999486. S2CID   8834258.
  20. Karachentsev, I. D.; Makarov, D. A. (1996). "The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field". Astronomical Journal. 111: 794. Bibcode:1996AJ....111..794K. doi: 10.1086/117825 .
  21. 1 2 Thuan, Trinh X.; Lipovetsky, V. A.; Martin, J.-M.; Pustilnik, S. A. (1999). "HI observations of blue compact galaxies from the first and second Byurakan surveys". Astronomy and Astrophysics Supplement. 139: 1–24. Bibcode:1999A&AS..139....1T. doi:10.1051/aas:1999373.
  22. 1 2 Swaters, R. A.; Balcells, M. (2002). "The Westerbork HI survey of spiral and irregular galaxies. II. R-band surface photometry of late-type dwarf galaxies". Astronomy and Astrophysics. 390 (3): 863. arXiv: astro-ph/0204526 . Bibcode:2002A&A...390..863S. doi:10.1051/0004-6361:20020449. S2CID   14222775.
  23. Lira, P.; Johnson, R. A.; Lawrence, A.; Cid Fernandes, R. (2007). "Multiwavelength study of the nuclei of a volume-limited sample of galaxies - II. Optical, infrared and radio observations" (PDF). Monthly Notices of the Royal Astronomical Society. 382 (4): 1552. Bibcode:2007MNRAS.382.1552L. doi: 10.1111/j.1365-2966.2007.12006.x .
  24. Huchtmeier, W. K.; Richter, O. G. (1986). "HI-observations of galaxies in the Kraan-Korteweg - Tammann catalogue of nearby galaxies. I - the data". Astronomy and Astrophysics Supplement Series. 63: 323. Bibcode:1986A&AS...63..323H.
  25. Tifft, W. G.; Cocke, W. J. (1988). "Uncertainties in 21 centimeter redshifts. I - Data". Astrophysical Journal Supplement Series. 67: 1. Bibcode:1988ApJS...67....1T. doi: 10.1086/191265 .
  26. Bottinelli, L.; Gouguenheim, L.; Fouque, P.; Paturel, G. (1990). "An extragalactic data base. II - the HI data". Astronomy and Astrophysics Supplement Series. 82: 391. Bibcode:1990A&AS...82..391B.
  27. Aversa, Alan G.; Johnson, Kelsey E.; Brogan, Crystal L.; Goss, W. M.; Pisano, D. J. (2011). "Very Large Array and ATCA Search for Natal Star Clusters in Nearby Star-forming Galaxies". The Astronomical Journal. 141 (4): 125. arXiv: 1102.0412 . Bibcode:2011AJ....141..125A. doi:10.1088/0004-6256/141/4/125. S2CID   118495675.