Browsing by Subject "Telescopes"

Now showing 1 - 3 of 3
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    Open Access
    HI in group interactions: HCG 44
    (2017) Hess, Kelley M; Cluver, M E; Yahya, Sahba; Leisman, Lukas; Serra, Paolo; Lucero, Danielle M; Passmoor, Sean S; Carignan, Claude
    Extending deep observations of the neutral atomic hydrogen (H I) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example, and we have combined H I data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N _{H {I}}
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    Open Access
    H i kinematics, mass distribution and star formation threshold in NGC 6822, using the SKA pathfinder KAT-7
    (2017) Namumba, B; Carignan, C; Passmoor, S; de Blok, W J G
    We present high sensitivity H I observations of NGC 6822, obtained with the Karoo Array Telescope (KAT-7). We study the kinematics, the mass distribution and the star formation thresholds. The KAT-7 short baselines and low system temperature make it sensitive to large-scale, low surface brightness emission. The observations detected ∼ 23 per cent more flux than previous Australian Telescope Compact Array observations. We fit a tilted ring model to the H I velocity field to derive the rotation curve (RC). The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, ∼1 kpc further than existing measurements. NGC 6822 is seen to be dark matter dominated at all radii. The observationally motivated pseudo-isothermal dark matter (DM) halo model reproduces well the observed RC while the Navarro Frank-White DM model gives a poor fit to the data. We find the best-fitting mass-to-light ratio (M/L) of 0.12 ± 0.01 which is consistent with the literature. The modified Newtonian dynamics gives a poor fit to our data. We derive the star formation threshold in NGC 6822 using the H I and H α data. The critical gas densities were calculated for gravitational instabilities using the Toomre-Q criterion and the cloud-growth criterion. We found that in regions of star formation, the cloud-growth criterion explains star formation better than the Toomre-Q criterion. This shows that the local shear rate could be a key player in cloud formation for irregular galaxies such as NGC 6822.
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    Open Access
    Inhomogeneities in molecular layers of Mira atmospheres
    (2011) Wittkowski, M; Boboltz, D A; Ireland, M; Karovicova, I; Ohnaka, K; Scholz, M; van Wyk, F; Whitelock, P; Wood, P R; Zijlstra, A A
    Aims. We investigate the structure and shape of the photospheric and molecular layers of the atmospheres of four Mira variables.