UGC 6541
Galaxy in the constellation Ursa Major
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UGC 6541 (also known as Mrk 178) is a blue compact dwarf galaxy in the constellation of Ursa Major. Its velocity with respect to the cosmic microwave background is 455±14 km/s,[1] which is too small to use to obtain a distance using Hubble's law. However, 10 non-redshift measurements give a mean distance of 15.15 ± 2.10 Mly (4.644 ± 0.644 Mpc).[2] The first known reference to this galaxy comes from Erik Holmberg's A Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems, published in 1937, where UGC 6541 and UGC 6538 are listed together as Holm 263.[3] However, since UGC 6538 is about 10 times further away, at a distance of 158.3 ± 11.1 Mly (48.55 ± 3.41 Mpc),[4] the alignment is purely optical.
| UGC 6541 | |
|---|---|
.jpg) UGC 6541 imaged by the Hubble Space Telescope | |
| Observation data (J2000 epoch) | |
| Constellation | Ursa Major |
| Right ascension | 11h 33m 28.9488s[1] |
| Declination | +49° 14′ 13.012″[1] |
| Redshift | 0.000833±0.00000200[1] |
| Heliocentric radial velocity | 250±1 km/s[1] |
| Distance | 15.15 ± 2.10 Mly (4.644 ± 0.644 Mpc)[1] |
| Apparent magnitude (V) | 14.50[1] |
| Characteristics | |
| Type | Im[1] |
| Size | ~5,700 ly (1.76 kpc) (estimated)[1] |
| Apparent size (V) | 1.2′ × 0.7′[1] |
| Other designations | |
| HOLM 263A, MCG +08-21-053, Mrk 178, PGC 035684, CGCG 242-046[1] | |
UGC 6541 has a possible active galactic nucleus, i.e. it has a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars.[5][6] UGC 6541 is a galaxy whose nucleus shines brightly in the ultraviolet and is listed in the Markarian catalogue as Mrk 178.[7]
The stellar and gas components of UGC 6541 have been extensively studied. An integrated H I intensity map shows a broken ring-like structure.[8] Other integrated H I intensity maps show that this galaxy has a highly irregular shape to its gaseous disk.[9] A detailed study of the Wolf-Rayet population revealed a large number of Wolf-Rayet stars in its brightest stellar component.[10] The stellar population has been studied in detail, indicating that this galaxy had a higher star formation rate 500 million years ago compared to its current rate, and that this galaxy has an old underlying stellar population.[11]
