| NGC 7531 | |
|---|---|
 NGC 7531 bylegacy surveys | |
| Observation data (J2000epoch) | |
| Constellation | Grus |
| Right ascension | 23h 14m 48.5s[1] |
| Declination | −43° 35′ 59.8″[1] |
| Redshift | 0.005324 ± 0.000010[1] |
| Heliocentric radial velocity | 1,596 ± 3 km/s[1] |
| Distance | 72.4 ± 16Mly (22.2 ± 4.9Mpc)[1] |
| Apparent magnitude (V) | 11.3 |
| Characteristics | |
| Type | SAB(r)bc[1] |
| Apparent size (V) | 4.5′ × 1.8′[1] |
| Other designations | |
| ESO 291- G010, AM 2312-435,MCG -07-47-025,PGC 70800[1] | |
NGC 7531 is anintermediate spiral galaxy located in the constellationGrus. It is located at a distance of about 70 millionlight-years from Earth, which, given its apparent dimensions, means that NGC 7531 is about 95,000 light years across.[1] It was discovered byJohn Herschel on September 2, 1836.[2]
The inner region of NGC 7531 is characterized by a high surface brightness ring. The ring is a place of activestar formation and a number ofstar clusters andH II regions have been identified in it.[3] The star formation rate of the inner ring is estimated to be 0.41 ± 0.12M☉ per year based onH-alpha emission.[4] A weakbar is observed in the nearinfrared inside the ring, along with dust lanes. Yet, the motions at the inner ring are predominately circular. The inner ring may lie at the location of the innerLindblad resonance.[3]
The galaxy has two patchyspiral arms that are relatively well defined but are of low surface brightness. H II regions have also been observed at the spiral arms of the galaxy, where there is also active star formation, which is more intense at the southwest region.[3] Asupermassive black hole is believed to lie in the centre of the galaxy whose mass is estimated to be 3–48 million (107.07±0.61)M☉, based on the spiral arm pitch angle.[5] The galaxy is seen with an inclination of 66°.[3]
Onesupernova has been observed in NGC 7531, SN 2012dj. It was atype Ib/c supernova with a peak magnitude of 15.3.[6]
In long exposure photographic plates of the galaxy, a large low surface brightness region structure was observed 2.6 arcminutes west from the nucleus of the galaxy, that has more than half the apparent diameter of NGC 7531.[3] It has been identified as a stellar cloud that may be adwarf satellite of the galaxy or a shell created by thetidal disruption of NGC 7531.[7]
NGC 7531 is a member of the NGC 7582 galaxy group.[8] Other members of the group includeNGC 7552,NGC 7582,NGC 7590, andNGC 7599, which are also known as the Grus Quartet,[9]NGC 7496,NGC 7632, andIC 5325.[8] This group, along with the group centred aroundIC 1459 form the Grus cloud, a region of elevated galaxy density. The Grus cloud, along with the nearby Pavo-Indus cloud, lies between theLocal Supercluster andPavo–Indus Supercluster.[10]
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