NGC 1637

NGC 1637 is an isolated, non-interacting^[7] intermediate spiral galaxy in the constellation Eridanus, about a degree to the WNW of the star Mu Eridani.^[8] It was discovered by German-British astronomer William Herschel on 1 February 1786.^[9][10] It is located at a distance of about 9.77 ± 1.82 Mpc (31.9 ± 5.9 Mly) from the Milky Way.^[3] The galaxy is inclined at an angle of 31.1° to the line of sight from the Earth and the long axis is oriented along a position angle of 16.3°.^[3]

NGC 1637
NGC 1637 imaged by the Very Large Telescope
Observation data (J2000 epoch)
Constellation	Eridanus
Right ascension	04h 41m 28.229s[1]
Declination	−02° 51′ 28.94″[1]
Redshift	0.00239[2]
Heliocentric radial velocity	717.1±1.2 km/s[2]
Distance	9.77 ± 1.82 Mpc (31.9 ± 5.9 Mly)[3] 9.18 Mpc (29.9 Mly) h−1 0.73[4]
Apparent magnitude (V)	11.5[5]
Apparent magnitude (B)	11.25[6]
Characteristics
Type	SAB(rs)c[3] or SBc(s)II.3[7]
Size	~57,000 ly (17.48 kpc) (estimated)[5]
Apparent size (V)	4.0′ × 3.2′[5]
Other designations
AGC 440323, IRAS 04389-0257, UGCA 93, MCG +00-12-068, PGC 15821, CGCG 393-066[5]

In 1991, Gérard de Vaucouleurs and associates assigned a morphological classification of SAB(rs)c to NGC 1637, indicating a spiral galaxy with a weak bar structure (SAB) across the nucleus, surrounded by a partial ring (rs) and somewhat loosely-wound arms (c).^[7] While the inner section of the galaxy shows a symmetrical two-arm structure,^[6] it has a single outer spiral arm that wraps 180° around the nucleus,^[6] giving the galaxy an overall asymmetric, lopsided appearance.^[7] The outer spiral arm has a red component that indicates a significant age.^[6] However, the existence of this structure is difficult to explain.^[7] The galaxy shows indications of recent starburst activity that may have terminated around 15 million years ago.^[6]

The active central nucleus shows weak LINER behavior, and it may be an intermediate form between a LINER and an H II region.^[7] The luminosity of the X-ray source at the nucleus is 1.2×10³⁸ ergs s⁻¹ in the 0.3–7 keV band.^[6]

Supernovae

Two supernovae have been observed in NGC 1637:

• SN 1999em (Type II-P, mag. 13.5) was discovered by the Lick Observatory Supernova Search (LOSS) on 29 October 1999, at an angular separation of 24″ to the southwest of the galaxy center.^[11][12] It was the brightest supernova discovered that year, reaching magnitude 13.1.^[13] The location corresponds to a deprojected galactocentric separation of 1.3 kpc (4.2 kly).^[3]
• SN 2025pht (Type II-P, mag. 13.3) was discovered by All Sky Automated Survey for SuperNovae on 29 June 2025.^[14]

Image and Video Gallery

• 
  NGC 1637 imaged by the Hubble Space Telescope
• Video showing the location of NGC 1637

See also

• List of NGC objects (1001–2000)