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Post Info TOPIC: NGC 4656


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Posts: 131433
Date:
PGC 42863
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Title: Interacting galaxy NGC4656 and its unusual dwarf companion
Author: Anatoly V. Zasov, Anna S. Saburova, Oleg V. Egorov, Roman I. Uklein

We studied the nearby edge-on galaxy NGC4656 and its dwarf low surface brightness companion with the enhanced UV brightness, NGC4656UV, belonging to the interacting system NGC4631/56. Regular photometric structure and relatively big size of NGC4656UV allows to consider this dwarf galaxy as a separate group member rather than a tidal dwarf. Spectral long-slit observations were used to obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us to conclude that this galaxy is the dark-matter dominated LSB dwarf or ultra diffuse galaxy. Young stellar population of NGC4656UV, as well as strong local non-circular gas motions in NGC4656 and the low oxygen gas abundance in the region of this galaxy adjacent to its dwarf companion, give evidence in favour of the accretion of metal-poor gas onto the discs of both galaxies.

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Posts: 131433
Date:
NGC 4656
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NGC 4656 (also Hockey Stick Galaxies, IRAS 12417 + 3228, MCG 5-30-66, UGC 7907 and PGC 42863) is a magnitude +10.2 irregular spiral galaxy located 25 to 30 million light-years away in the constellation Canes Venatici.
The galaxy can be found about 4.5 degrees NE of the star gamma Comae Berenices.
Telescopes of 200 mm aperture show the distorted shape of a hockey stick; the curved north-eastern part is the galaxy NGC 4657 which is located about 40 million light years away. The distortion of the disk of NGC 4656 is most likely caused by the gravitational interaction with a neighbouring galaxy NGC 4631. Another by-product of the collision may be the tidal dwarf galaxy NGC 4656UV located in the vicinity of the 'curved end' of NGC 4656 and is brightly visible in ultraviolet.
NGC 4656 is part of the poorly defined NGC 4631 Group, and also a member of the Coma I galaxies, which is approaching the Virgo Cluster, and will end up merging with it in the distant future.

The galaxy was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at Windsor Road, Slough, on the 20th March 1787.

A Luminous Blue Variable star (S Doradus-type) in "super-outburst" was discovered in NGC 4656/57 by astronomer Doug Rich on March 21, 2005.

Right ascension 12h 43m 57.7s, Declination +32 10' 05"



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