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Post Info TOPIC: NGC 5011C
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RE: NGC 5011C
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True Identity of a Dwarf Galaxy Revealed
New data obtained on the apparent celestial couple, NGC 5011 B and C, taken with the 3.6-m ESO telescope, reveal that the two galaxies are not at the same distance, as was believed for the past 23 years. The observations show that NGC 5011C is not a giant but a dwarf galaxy, an overlooked member of a group of galaxies in the vicinity of the Milky Way.
The galaxy NGC 5011C is located towards the Centaurus constellation, in the direction of the Centaurus A group of galaxies and the Centaurus cluster of galaxies. The former is about 13 million light-years from our Milky Way, while the latter is about 12 times farther away.
The appearance of NGC 5011C, with its low density of stars and absence of distinctive features, would normally lead astronomers to classify it as a nearby dwarf elliptical galaxy. On the other hand, the galaxy's distance - as reported in the scientific literature - makes it a member of the more distant Centaurus cluster. As such, it would belong to the same cluster as its brighter, redder companion on the sky, the lenticular galaxy NGC 5011B, which is seen almost edge-on.

NGC 5011B
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Blobrana


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Title: NGC 5011C: an overlooked dwarf galaxy in the Centaurus A group
Authors: Ivo Saviane (1), Helmut Jerjen (2) ((1) ESO, (2) Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory)

We report the discovery of a previously unnoticed member of the Centaurus A Group, NGC 5011C. While the galaxy is a well known stellar system listed with a NGC number its true identity remained hidden because of coordinate confusion and wrong redshifts in the literature. NGC 5011C attracted our attention since, at a putative distance of 45.3 Mpc, it would be a peculiar object having a very low surface brightness typical of a dwarf galaxy, and at the same time having the size of an early-type spiral or S0 galaxy. To confirm or reject this peculiarity, our immediate objective was to have the first reliable measurement of its recession velocity. The observations were carried out with EFOSC2 at the 3.6m ESO telescope. We found that NGC 5011C has indeed a low redshift of v_sun=647±96 km/sec and thus is a nearby dwarf galaxy rather than a member of the distant Centaurus cluster as believed for the past 23 years. Rough distance estimates based on photometric parameters also favour this scenario. As a by-product of our study we update the redshift for NGC 5011B at v_sun=3227 ±50 km/sec. Applying population synthesis techniques, we find that NGC 5011B has a luminosity-weighted age of 4 ±1 Gyr and a solar metallicity, and that the luminosity-weighted age and metallicity of NGC 5011C are 0.9 ±0.1 Gyr and 1/5 solar. Finally we estimate a stellar mass of NGC 5011C comparable to that of dwarf spheroidal galaxies in the Local Group.

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