Browsing by Subject "galaxies: dwarf"

Now showing 1 - 6 of 6
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    Open Access
    Deep Ks -near-infrared surface photometry of 80 dwarf irregular galaxies in the local volume
    (2010) Fingerhut, Robin L; McCall, Marshall L; Argote, Mauricio; Cluver, Michelle E; Nishiyama, Shogo; Rekola, Rami T F; Richer, Michael G; Vaduvescu, Ovidiu; Woudt, Patrick A
    We present deep near-infrared (K_s) images and surface photometry for 80 dwarf irregular galaxies (dIs) within ~5 Mpc of the Milky Way. The galaxy images were obtained at five different facilities between 2004 and 2006. The image reductions and surface photometry have been performed using methods specifically designed for isolating faint galaxies from the high and varying near-infrared sky level. Fifty-four of the 80 dIs have surface brightness profiles which could be fit to a hyperbolic-secant (sech) function, while the remaining profiles could be fit to the sum of a sech and a Gaussian function. From these fits, we have measured central surface brightnesses, scale lengths, and integrated magnitudes. This survey is part of a larger study of the connection between large-scale structure and the global properties of dIs, the hypothesized building-blocks of more massive galaxies.
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    Open Access
    HI observations of two new dwarf galaxies: Pisces A and B with the SKA Pathfinder KAT-7
    (2016) Carignan, C; Libert, Y; Lucero, D M; Randriamampandry, T H; Jarrett, T H; Oosterloo, T A; Tollerud, E J
    Context. Pisces A and Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 HI clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims: We derive the HI content and kinematics of Pisces A and B. Methods. Our aperture synthesis H observations used the seven-dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results: The low rotation velocities of ∼5 km s−1 and ∼10 km s−1 in Pisces A and B, respectively, and their HI content show that they are really dwarf irregular galaxies (dIrr). Despite that small rotation component, it is more the random motions ∼9−11 km s−1 that provide most of the gravitational support, especially in the outer parts. The study of their kinematics, especially the strong gradients of random motions, suggest that those two dwarf galaxies are not yet in equilibrium. Conclusions. These HI- rich galaxies may be indicative of a large population of dwarfs at the limit of detectability. However, such gasrich dwarf galaxies will most likely never be within the virial radius of MW-type galaxies and become subhalo candidates. Systems such as Pisces A and B are more likely to be found at a few Mpc s from MW-type galaxies.
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    Open Access
    Is GBT 1355+5439 a dark galaxy?
    (2013) Oosterloo, T A; Heald, G H; de Blok, W J G
    We present H i imaging of GBT 1355+5439 performed with the Westerbork Synthesis Radio Telescope. This is a dark H i object recently discovered close to the nearby galaxy M101. We find GBT 1355+5439 to be an H i cloud 5 × 3 arcmin in size. The total H i image and the kinematics show that the cloud consists of condensations that have small (~10 km s-1) motions with respect to each other. The column densities of the H i are low; the observed peak value is 7.1 × 1019 cm-2. The velocity field shows a mild velocity gradient over the body of GBT 1355+5439, possibly due to rotation, but it may also indicate large-scale radial motions. Although our data are limited in sensitivity, at all positions the H i velocity dispersion is higher than 5 km s-1 and no narrow, cold, H i component is seen. Because its distance is not known, we considered various possibilities for the nature of GBT 1355+5439. Both the scenarios that it is a tidal remnant near M101 and that it is a dark dwarf companion of M101 meet difficulties. Neither do the data fit the properties of known compact high-velocity clouds in the Galactic halo exactly, but we cannot entirely exclude this option and deeper observations are required. We also considered the possibility that GBT 1355+5439 is a gas-rich dark minihalo in the outer regions of the Local Group. Interestingly, it would then have similar properties as the clouds of a proposed Local Group population recently found in the ALFALFA survey. In this case, the H i mass of GBT 1355+5439 would be about a few times 105M⊙, its size about 1 kpc, and the dynamical mass Mdyn > 5 × 107M⊙. However, if GBT 1355+5439 is a dark Local Group object, the internal kinematics of the H i appears to be different from that of gas-dominated, almost dark galaxies of similar size.
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    Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics
    (2012) Gentile, G; Angus, G W; Famaey, B; Oh, S-H; de Blok, W J G
    Within the framework of modified Newtonian dynamics (MOND), we investigate the kinematics of two dwarf spiral galaxies belonging to very different environments, namely KK 246 in the Local Void and Holmberg II in the M 81 group. A mass model of the rotation curve of KK 246 is presented for the first time, and we show that its observed kinematics are consistent with MOND. We re-derive the outer rotation curve of Holmberg II, by modelling its HI data cube, and find that its inclination should be closer to face-on than previously derived. This implies that Holmberg II has a higher rotation velocity in its outer parts, which, although not very precisely constrained, is consistent with the MOND prediction.
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    Stellar population and kinematics of NGC 404
    (2010) Bouchard, A; Prugniel, P; Koleva, M; Sharina, M
    Context. NGC 404 is a nearly face-on, nearby low-luminosity lenticular galaxy. Probing its characteristics provides a wealth of information on the details of the possible evolution processes of dS0 galaxies, which may not be possible in other, more distant objects.
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    The baryonic Tully-Fisher relation and its implication for dark matter halos
    (2009) Trachternach, C; de Blok, W J G; McGaugh, S S; van der Hulst, J M; Dettmar, R-J
    The baryonic Tully-Fisher relation (BTF) is a fundamental relation between baryonic mass and maximum rotation velocity. It can be used to estimate distances, as well as to constrain the properties of dark matter and its relation with the visible matter.