# Arp 21

> galaxy

**Wikidata**: [Q6043124](https://www.wikidata.org/wiki/Q6043124)  
**Source**: https://4ort.xyz/entity/arp-21


## References

1. SIMBAD
2. [Source](https://www.wis-tns.org/object/1955L)
3. The ninth data release of the Sloan Digital Sky Survey: first spectroscopic data from the SDSS-III baryon oscillation spectroscopic survey
4. The SDSS Photometric Catalog, Release 8
5. The Two Micron All Sky Survey (2MASS)