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Post Info TOPIC: VV124 (UGC4879)
Blobrana


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RE: VV124 (UGC4879)
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Title: The Dynamics and Metallicity Distribution of the Distant Dwarf Galaxy VV124
Authors: Evan N. Kirby (Caltech), Judith G. Cohen (Caltech), Michele Bellazzini (INAF)

VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial velocities for different components of the galaxy, and photometry hinted at the presence of a stellar disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/DEIMOS spectrograph. We validated members based on their positions in the colour-magnitude diagram, radial velocities, and spectral features. Our sample contains 67 members. The average radial velocity is = -29.1 ± 1.3 km/s, in agreement with the previous radio measurements of HI gas. The velocity distribution is Gaussian, indicating that VV124 is supported primarily by velocity dispersion inside a radius of 1.5 kpc. Outside that radius, our measurements provide only an upper limit of 8.6 km/s on any rotation in the photometric disk-like feature. The velocity dispersion is sigma_v = 9.4 ± 1.0 km/s, from which we inferred a mass of M_½ = (2.1 ± 0.2) x 10^7 M_sun and a mass-to-light ratio of (M/L_V)_½ = 5.2 ± 1.1 M_sun/L_sun, both measured within the half-light radius. Thus, VV124 contains dark matter. We also measured the metallicity distribution from neutral iron lines. The average metallicity, = -1.14 ± 0.06, is consistent with the mass-metallicity relation defined by dwarf spheroidal galaxies. The dynamics and metallicity distribution of VV124 appear similar to dSphs of similar stellar mass.

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Blobrana


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Posts: 131433
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VV124=UGC4879
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Title: HST-ACS photometry of the isolated dwarf galaxy VV124=UGC4879. Detection of the Blue Horizontal Branch and identification of two young star clusters
Authors: M. Bellazzini (INAF-OABO), S. Perina (INAF-OABO), S. Galleti (INAF-OABO), T. OOsterloo (ASTRON / Kapteyn Inst.)

We present deep V and I photometry of the isolated dwarf galaxy VV124=UGC4879, obtained from archival images taken with the Hubble Space Telescope - Advanced Camera for Surveys. In the colour-magnitude diagrams of stars at distances larger than 40" from the center of the galaxy, we clearly identify for the first time a well-populated old Horizontal Branch (HB). We show that the distribution of these stars is more extended than that of Red Clump stars. This implies that very old and metal poor populations becomes more and more dominant in the outskirts of VV124. We also identify a massive (M~1.2 x 10^4 M_sun) young (age ~250 Myr) star cluster (C1), as well as another of younger age (C2, <= 30 Myr) with a mass similar to classical open clusters (M<= 3.3 x 10^3 M_sun). Both clusters lie at projected distances smaller than 100 pc from the center of the galaxy.

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igorek7


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RE: VV124 (UGC4879)
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Despite five decades since its original discovery, only recently VV124 (UGC4879) was found to be in the outskirts of the Local Group. It is kind of ironic that such a bright nearby object remained unnoticed for such a long time. We should expect more nearby objects to be found, particularly in the less-studied areas of the sky.

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Blobrana


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Title: VV124 (UGC4879): A new transitional dwarf galaxy in the periphery of the Local Group
Authors: Alexander I. Kopylov (1), Nikolay A. Tikhonov (1), Sergey Fabrika (1), Igor Drozdovsky (2), Azamat F. Valeev (1) ((1) Special Astrophysical Observatory, (2) Instituto de Astrofisica de Canarias)
(Version v2)

We present the first resolved-star photometry of VV124 (UGC4879) and find that this is the most isolated dwarf galaxy in the periphery of the Local Group. Based on imaging and spectroscopic follow up observations with the 6m BTA telescope, we resolve VV124 into 1560 stars down to the limiting magnitude levels of V~25.6 and I~23.9. The young blue stellar populations and emission gas are found near the core, but noticeably displaced from the centre of the galaxy as traced by dominant evolved red stars. The mean radial velocity derived from the spectra of two Blue Supergiant stars, an HII region and unresolved continuum sources is -80±10 km/s. The evolved "red tangle" stellar populations, which contains the red giant branch (RGB), are identified at large galactocentric radii. We use the I-band luminosity function to determine the distance based on the Tip of RGB method, 1.1±0.1 Mpc. This is ~10 times closer than the values usually assumed in the literature, and we provide revised distance dependent parameters. From the mean (V-I) colour of the RGB, we estimate the mean metallicity as [Fe/H]~-1.37 dex. Despite of its isolated location, the properties of VV124 are clearly not those of a galaxy in formation, but rather similar to a transitional dIrr/dSph type.

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