Jump to content

NGC 2366

From Wikipedia, the free encyclopedia
NGC 2366
GALEX image of NGC 2366
Observation data (J2000 epoch)
ConstellationCamelopardalis
Right ascension7h 28m 54.6s[1]
Declination+69° 12′ 57″[1]
Redshift80 ± 1 km/s[1]
Distance10 million light-years[2]
Apparent magnitude (V)11.4[1]
Characteristics
TypeIB(s)m [1]
Apparent size (V)8.1′ × 3.3′[1]
Notable featuresThe southern part of NGC 2366 is called Markarian 71.
Other designations
UGC 3851, PGC 21102[1]

NGC 2366 is a Magellanic barred irregular dwarf galaxy located in the constellation Camelopardalis.[3][4]

At the southern end of NGC 2366 is the large, luminous HII region known as Markarian 71 (Mrk 71).[3] To the west of Mrk 71 is another dwarf galaxy NGC 2363 which is interacting with NGC 2366.[5] There has been confusion about the various components of NGC 2366 and its neighbouring galaxy NGC 2363.[3] Corwins' notes remark that there are two galaxies with two NGC numbers clearly attached to each one: We shall just have to get used to calling the HII region "Markarian 71" (or one of its other names) since it is not N2363 as we've thought all these years.[5]

Within Mrk 71, there are two super star clusters (SSC) which are named 'A' and 'B' or 'Knot A' and 'Knot B'.[3][6]

Other names for the above components include: NGC 2366-I, NGC 2366-II, NGC 2366-III, NGC2366-A, NGC 2366-B, NGC 2366-C, NGC 2363-A, NGC 2363-B.[3] NGC 2366 is an outlying member of the M81 Group.[7]

Super star clusters within Mrk 71

[edit]
HST view of NGC 2366

NGC/Mrk71 is home to numerous young, gigantic blue stars, which in gas-rich star-forming regions, emit ultraviolet radiation that excites the hydrogen gas, making it glow. At a distance of approximately 10 million light years, it is close enough for astronomers to discern its individual stars.[2]

Within Mrk 71 there are two super star clusters which will be referred to as Mrk 71 knot A (Knot A) and Mrk 71 knot B (Knot B).

Knot A has total stellar mass of approximately (1.3–1.4)×105 solar masses.[3] The absence of Wolf–Rayet stars in its spectra might well indicate that its age is no more than 3 Myrs, while an age of less than 1 Myr is given in a study by Drissen et al. 2000.[8] Knot A hosts a massive, enshrouded SSC, in which no stellar features have been confirmed and that is still in its natal cloud.[3] Knot A might well contain 'very massive stars' (VMS), which are O-type supergiants of 150–300 solar masses. These have short lifespans of 1–3 Myr and have been suggested as a reason why there are extreme stellar temperatures.[9]

The hydrogen alpha luminosity measurement for Mrk 71, of which 90% is produced by Knot A, is given as 8.4×1039 ergs/s in a study by James et al. 2016.[9]

Knot B has a lower mass of 1.5×104 solar masses and an estimated age of 3–5 Myrs.[3] UV spectral synthesis leads to the conclusion that there are approximately 800 B and 40 O stars present.[8] Studies indicate that there might be up to 8 Wolf–Rayet stars present, which would set the age between 3–5 Myrs.[8][10]

A superbubble appears to have been generated with strong shell morphology to the east and a blow-out region to the north, with expansion velocities of approximately 20 km/s. This is consistent with the substantial mechanical feedback generated by a massive, somewhat evolved SSC.[3]

The Nearest Green Pea Analog

[edit]

In August 2017, a study was published in The Astrophysical Journal called: "Mrk 71/NGC 2366: The Nearest Green Pea Analog". This examines the links between NGC 2366 and the so-called Green Pea galaxies (GPs), some of which have recently been shown to be Lyman Continuum Emitters (LCEs). It presents a remarkable and serendipitous discovery that NGC 2366 is an excellent analog of the GPs. As NGC 2366 is located only 10 million light years away, it might provide a local example of an LCE.[3]

Finding LCEs is crucial in the study of the Big Bang, as Lyman continuum photons (LyC) emissions are thought to be a mechanism for the reionisation of the Universe.[11][12]

5 'extreme' GPs have recently been shown to be viable LCEs, with a LyC escape fraction of between 6–13%. This discovery doubled the number of low-redshift star-forming LCEs, which have been notoriously hard to detect.[3]

Table 1 in Micheva et al. compares various properties of 'average' and 'extreme' GPs with NGC 2366/Mrk 71 using the wealth of existing data.[3]

Some examples are:

i) The temperature of [OIII] (highly ionised oxygen) in extreme GPs is given as approximately 13,400–15500 K, compared with values of between 14,000 and 16,000 K for the Mrk 71 components.[10][6]
ii) An extremely high equivalent width for [OIII] is shown in Knot A of 224.3±34.5 nm, compared with values of 80–200 nm for extreme GPs.[13]
iii) The ratio of oxygen to hydrogen, which gives a value for an object's metallicity, is 7.89 in NGC 2263/MRK 71 and between 7.76 and 8.04 for extreme GPs.[13]

The study concludes that NGC2366/Mrk 71 offers an unprecedentedly detailed look at the morphology and physical conditions of a potential LyC emitter, suggesting that LCEs might be numerous and commonplace.[3]

Dense CO in Mrk 71-A

[edit]

A study named: "Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster" was published in the Astrophysical Journal Letters in November 2017.[14] One conclusion is: (quoting) "Since Mrk 71-A is a candidate Lyman continuum emitter, this implies that energy-driven superwinds may not be a necessary condition for the escape of ionizing radiation."[14]

Observations were made using the Northern Extended Millimeter Array (NOEMA) telescope, looking for carbon monoxide.[14] It revealed a compact, ~7 parsec molecular cloud.[14]

See also

[edit]

References

[edit]
  1. ^ a b c d e f g "NASA/IPAC Extragalactic Database". Results for NGC 2366. Retrieved 2007-04-08.
  2. ^ a b "Hubble Observes a Dwarf Galaxy with a Bright Nebula". ESA/Hubble Press Release. Retrieved 10 May 2012.
  3. ^ a b c d e f g h i j k l m G. Micheva; M.S. Oey; A.E. Jaskot; B.L. James (August 2017). "Mrk 71/NGC 2366: The Nearest Green Pea Analog". The Astrophysical Journal. 845 (2): 13. arXiv:1704.01678. Bibcode:2017ApJ...845..165M. doi:10.3847/1538-4357/aa830b. S2CID 119049347.
  4. ^ G. de Vaucouleurs; A. de Vaucouleurs; H.G. Corwin; R.J. Buta; G. Paturel; P. Fouque (1991). Third Reference Catalogue of Bright Galaxies. Volume I: Explanations and references. Volume II: Data for galaxies between 0h and 12h. Volume III: Data for galaxies between 12h and 24h. Springer, New York. p. 2091. Bibcode:1991rc3..book.....D. ISBN 978-0-387-97552-8.
  5. ^ a b H.G. Corwin (2006). "Historical Notes: NGC 2000 through NGC 2999". Archived from the original on 4 March 2016. Retrieved 29 October 2017.
  6. ^ a b R.M. Gonzalez-Delgado; E. Perez; G. Tenorio-Tagle; et al. (1994). "Violent star formation in NGC 2363" (PDF). The Astrophysical Journal. 437: 239–261. Bibcode:1994ApJ...437..239G. doi:10.1086/174992. hdl:10486/13452.
  7. ^ Karachentsev, I.D.; Sharina, M.E.; Dolphin, A.E.; Grebel, E.K. (2003). "Distances to nearby galaxies around IC 342". Astronomy & Astrophysics. 408 (1): 111–118. Bibcode:2003A&A...408..111K. doi:10.1051/0004-6361:20030912. ISSN 0004-6361.
  8. ^ a b c L. Drissen; J.-R. Roy; C. Robert; D. Devost; R. Doyon (2000). "The Star Formation History of the Starburst Region NGC 2363 and its Surroundings". The Astronomical Journal. 119 (22): 688–704. arXiv:astro-ph/9910476. Bibcode:2000AJ....119..688D. doi:10.1086/301204. S2CID 119372867.
  9. ^ a b B.L. James; M. Auger; A. Valois; D. Calzetti; L. Kewley (January 2016). "Resolving Ionization and Metallicity on Parsec Scales across Mrk 71 with HST-WFC3". The Astrophysical Journal. 816 (1): 40. arXiv:1510.02447. Bibcode:2016ApJ...816...40J. doi:10.3847/0004-637X/816/1/40. S2CID 118671054.
  10. ^ a b K.R. Sokal; K.E. Johnson; R. Indebetouw; P. Massey (August 2016). "The Prevalence and Impact of Wolf–Rayet Stars in Emerging Massive Star Clusters". The Astrophysical Journal. 826 (2): 194. arXiv:1605.08044. Bibcode:2016ApJ...826..194S. doi:10.3847/0004-637X/826/2/194. S2CID 118517910.
  11. ^ Y.I. Izotov; I. Orlitova; D. Schaerer; T.X. Thuan; A. Verhamme; N.G. Guseva; G. Worseck (2016). "Eight per cent leakage of Lyman continuum photons from a compact, star-forming dwarf galaxy". Nature. 529 (7585): 178–180. arXiv:1601.03068. Bibcode:2016Natur.529..178I. doi:10.1038/nature16456. PMID 26762455. S2CID 3033749.
  12. ^ Dawn Erb (2016). "Cosmology: Photons from dwarf galaxy zap hydrogen". Nature. 529 (7585): 159–160. Bibcode:2016Natur.529..159E. doi:10.1038/529159a. PMID 26762452.
  13. ^ a b Y.I. Izotov; T.X. Thuan; V.A. Lipovetsky (1997). "The Primordial Helium Abundance: Systematic Effects and a New Determination". The Astrophysical Journal Supplement Series. 108 (1): 1–39. Bibcode:1997ApJS..108....1I. doi:10.1086/312956.
  14. ^ a b c d M. S. Oey; C. N. Herrera; S. Silich; M. Reiter; B.L. James; A. E. Jaskot; G. Micheva (November 2017). "Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster". The Astrophysical Journal Letters. 849 (1): 6. arXiv:1710.03261. Bibcode:2017ApJ...849L...1O. doi:10.3847/2041-8213/aa9215. S2CID 119201873.
[edit]
  • Wikimedia Commons logo Media related to NGC 2366 at Wikimedia Commons
  • HubbleSite NewsCenter: Pictures and description
Retrieved from "https://en.wikipedia.org/w/index.php?title=NGC_2366&oldid=1352663993"