NGC 2403 explained

NGC 2403
Epoch:	J2000
Type:	SAB(s)cd^[1]
Dist Ly:	9.65 Mly (2.96 Mpc)^[2]
Z:	131 ± 3 km/s
Appmag V:	8.9
Size V:	21.9 × 12.3
Constellation Name:	Camelopardalis
Names:	UGC 3918, PGC 21396, Caldwell 7

NGC 2403 (also known as Caldwell 7) is an intermediate spiral galaxy in the constellation Camelopardalis. It is an outlying member of the M81 Group,^[3] and is approximately 8 million light-years distant. It bears a similarity to M33, being about 50,000 light years in diameter and containing numerous star-forming H II regions.^[4] The northern spiral arm connects it to the star forming region NGC 2404. NGC 2403 can be observed using 10×50 binoculars. NGC 2404 is 940 light-years in diameter, making it one of the largest known H II regions. This H II region represents striking similarity with NGC 604 in M33, both in size and location in galaxy.

Supernova and Supernova Imposters

There have been three reported astronomical transients in the galaxy:

• SN 1954J, which attained a magnitude of 16 at its brightest, was initially classified as a type V supernova. It was later determined to be a supernova imposter: a highly luminous, very massive eruptive star, surrounded by a dusty nebula, similar to the 1843 Great Eruption of η Carinae in the Milky Way.^[5]
• SN 2002kg was initially classified as a type IIn, or possibly the outburst of a luminous blue variable.^[6] In 2021, it was reclassified as a Gap transient.^[7]
• SN 2004dj was a type II-P which attained a magnitude of 11.2.^[8] At the time of its discovery, it was the nearest and brightest supernova observed in the 21st century.

History

The galaxy was discovered by William Herschel in 1788. Edwin Hubble detected Cepheid variables in NGC 2403 using the Hale Telescope, making it the first galaxy beyond the Local Group within which a Cepheid was discovered. By 1963, 59 variables had been found in NGC 2403, of which 17 were eventually confirmed as Cepheids, with periods between 20 and 87 days. As late as 1950 Hubble was using a distance of just under 2 million light years for the galaxy's distance, but by 1968 the analysis of the Cepheids increased this by almost a factor of five, to within 0.2 magnitudes of the current value.

Companions

NGC 2403 has two known companions. One is the relatively massive dwarf galaxy DDO 44. It is currently being disrupted by NGC 2403, as evidenced by a tidal stream extending on both sides of DDO 44. DDO 44 is approaching NGC 2403 at a distance much closer than typical for dwarf galaxy interactions. It currently has a V-band absolute magnitude of -12.9, but its progenitor was even more luminous.^[2]

The other known companion is officially named MADCASH J074238+652501-dw, although it is nicknamed MADCASH-1. The name refers to the MADCASH (Magellanic Analog Dwarf Companions and Stellar Halos) project. MADCASH-1 is similar to typical dwarf spheroidal galaxies in the Local Group; it is quite faint, with an absolute V-band magnitude of -7.81, and has only an ancient, metal-poor population of red giant stars.^[9]

See also

• Triangulum Galaxy-looks very similar to NGC 2403.

External links

• Spiral Galaxy NGC 2403 at the astro-photography site of Mr. Takayuki Yoshida
• NGC 2403 at ESA/Hubble
  • • SEDS – NGC 2403

Notes and References

1. Web site: NASA/IPAC Extragalactic Database. Results for NGC 2403. 2006-11-21 .
2. 1906.08260. 10.3847/1538-4357/ab4c32. Tidal Destruction in a Low-mass Galaxy Environment: The Discovery of Tidal Tails around DDO 44. 2019. Carlin. Jeffrey L.. Garling. Christopher T.. Peter. Annika H. G.. Crnojević. Denija. Forbes. Duncan A.. Hargis. Jonathan R.. Mutlu-Pakdil. Burçin. Pucha. Ragadeepika. Romanowsky. Aaron J.. Sand. David J.. Spekkens. Kristine. Kristine Spekkens. Strader. Jay. Willman. Beth. The Astrophysical Journal. 886. 2. 109. 2019ApJ...886..109C. 195218404 . free .
3. Book: Kepple , George Robert . Glen W. Sanner . The Night Sky Observer's Guide . 1 . Willmann-Bell, Inc. . 1998 . 978-0-943396-58-3 . 73.
4. Ho . Luis C. . Filippenko . Alexei V. . Sargent . Wallace L. W. . A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies . October 1997 . Astrophysical Journal Supplement . 112 . 2 . 315–390 . astro-ph/9704107 . 1997ApJS..112..315H . 10.1086/313041 . 17086638 .
5. 10.1086/430238 . Supernova 1954J (Variable 12) in NGC 2403 Unmasked . 2005 . Van Dyk . Schuyler D. . Filippenko . Alexei V. . Chornock . Ryan . Li . Weidong . Challis . Peter M. . Publications of the Astronomical Society of the Pacific . 117 . 832 . 553–562 . astro-ph/0503324 . 2005PASP..117..553V .
6. Web site: Central Bureau for Astronomical Telegrams, Circular No. 8051 . Green . Daniel W. E. . January 15, 2003 . 14 August 2024.
7. Web site: Transient Name Server . SN 2002kg . . 14 August 2024.
8. Web site: Transient Name Server . SN 2004dj . . 14 August 2024.
9. 10.3847/1538-4357/abe040. 2012.09174. 2021ApJ...909..211C. Hubble Space Telescope Observations of Two Faint Dwarf Satellites of Nearby LMC Analogs from MADCASH. 2021. Carlin. Jeffrey L.. Mutlu-Pakdil. Burçin. Crnojević. Denija. Garling. Christopher T.. Karunakaran. Ananthan. Peter. Annika H. G.. Tollerud. Erik. Forbes. Duncan A.. Hargis. Jonathan R.. Lim. Sungsoon. Romanowsky. Aaron J.. Sand. David J.. Spekkens. Kristine. Strader. Jay. The Astrophysical Journal. 909. 2. 211. 229297953 . free .