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NGC 5238

Coordinates:Sky map13h37m00.9s,−29° 51′ 57″
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NGC5238
Hubble Space Telescopeimage of NGC 5238
Observation data (J2000epoch)
ConstellationCanes Venatici
Right ascension13h34m43.8s[1]
Declination+51° 36′ 33″[1]
Redshift0.0015[2]
Heliocentric radial velocity229 km/s[3]
Distance4.51Mpc[4]
Characteristics
TypeIrr[5][failed verification]
Mass1.17×106[6]M☉
Mass/Light ratio0.6[7]M☉/L☉
Apparent size(V)64.4 "[8]
Other designations
UGC8565, VV 828,Mrk1479, SBS 1332+518,I Zw64, KPG 384

NGC 5238is anirregular galaxy[5]in the constellationCanes Venatici.Located at a comoving distance of 4.51Mpc,[4]it is 64.4arcsecondsin diameter.[8]It has sometimes been classified as ablue compact dwarfgalaxy.[9]Although some authors have hypothesized it to be a member of theM101 Groupof galaxies, it is currently believed to be an isolated galaxy.[10]

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

Classification

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In 1977, NGC 5238 was hypothesized to not be a single galaxy, but rather a pair ofinteracting galaxies.[12]It was not until ten years later that a dedicated study of the galaxy'srotation curvewas undertaken, showing that the galaxy is indeed a single galaxy. One of the two regions that was thought to be thenucleusof 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 abarred spiralgalaxy.[14]Soon after, in 1984, the galaxy was included in a study ofblue compact dwarfgalaxies, 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 adwarf 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

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As it appears to us, NGC 5238 is tilted at aninclinationof 39°.[3]This 2013 estimate follows previous estimates of 30° in 1987,[13]37 ± 5° in 1992,[18]and 47° in 1999[19]In theSpitzer3.6 μm band, thesemimajor axisof itsangular sizeis 64.4",with an ellipticity of 0.201.[8]

Distance

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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 HI21cm 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 bystandard candles.Thetip of the red giant branchis such a method; every galaxy's brightestred giantstars must have exactly the same known luminosity. When combined with corrections forinterstellar reddening,this allows for accurate determination of a galaxy's distance. By 2009, aHubble Space Telescopeimage of NGC 5238 had become available, resolving the individual stars within the galaxy. Using this method, thedistance moduluswas calculated at 28.27 magnitudes, corresponding to a distance of 4.51 Mpc, today's accepted value.[4]

Radio emission

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Since a first study was published in 1986, theneutral hydrogengas 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 ± 1.0Jy·km/s, with afull width at half maximumof 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 4.2×107solar masses.[22]Finally, in 2013, the 50% line width estimate was further increased to 40 km/s, and the HI mass was refined to 2.6×107solar masses, implying a total-to-HI mass ratio of 7.3.[3]

In addition to HI gas, it is thought thatradio continuum emissionshould be present from NGC 5238 as well. The galaxy is a strongultravioletemitter, indicating that the galaxy is undergoing rapidstar formation.Based on this, it is to be expected that there should be radio continuum emission from the galaxy, due to theaccelerationofelectronsinHII regions,known asbremsstrahlung.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]

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References

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  1. ^abPaturel, 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.S2CID118938315.
  3. ^abcdeKarachentsev, 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.S2CID118585268.
  4. ^abcJacobs, 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.S2CID15727705.
  5. ^abcButa, 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.S2CID119202943.
  6. ^abCook, 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.S2CID118469122.
  7. ^abcHuchtmeier, 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. ^abcSheth, 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.S2CID13509333.
  9. ^abAnn, 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.S2CID119253507.
  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.S2CID122692981.
  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.S2CID119188439.
  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. ^abArkhipova, 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. ^abKraan-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.S2CID118985923.
  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.S2CID8834258.
  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. ^abThuan, 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. ^abSwaters, 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.S2CID14222775.
  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.S2CID118495675.
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