Browsing by Author "Hau, GKT"

Now showing 1 - 7 of 7
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    A new Local Group galaxy in Cetus
    (1999) Whiting, AB; Hau, GKT; Irwin, M
    We report the discovery of a previously uncataloged Local Group galaxy in the constellation Cetus. Faintly visible on UKST survey plates, it has a smooth, diffuse appearance and appears to be a dwarf spheroidal of type dE3.5. A color-magnitude diagram in V, V-I shows a clear giant branch but no sign of recent star formation. From the position of the tip of the giant branch, we derive a reddening-corrected distance modulus of 24.45 +/- 0.15 and a metallicity of - 1.9 +/- 0.2. With an implied heliocentric distance of 775 +/- 50 kpc, and a corresponding Local Group barycentric distance of 615 kpc, the Cetus dwarf lies well within the boundaries of the Local Group, and although it currently lacks a radial velocity measurement, it is undoubtedly a member of the Local Group. The nearest Local Group galaxies are WLM and IC 1613 at angular separations of 7 degrees.3 and 16 degrees.3 and roughly 175 and 230 kpc total distance, respectively. Although the Cetus dwarf is unlikely to be directly associated with any other Local Group galaxy, it does lie in the general direction of the extension of the Local Group toward the Sculptor Group.
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    Ages and metallicities of Hickson compact group galaxies
    (2004) Proctor, RN; Forbes, DA; Hau, GKT; Beasley, MA; De Silva, GM; Contreras, R; Terlevich, AI
    Hickson compact groups (HCGs) constitute an interesting extreme in the range of environments in which galaxies are located, as the space density of galaxies in these small groups are otherwise only found in the centres of much larger clusters. The work presented here uses Lick indices to make a comparison of ages and chemical compositions of galaxies in HCGs with those in other environments (clusters, loose groups and the field). The metallicity and relative abundance of 'alpha-elements' show strong correlations with galaxy age and central velocity dispersion, with similar trends found in all environments. However, we show that the previously reported correlation between a-element abundance ratios and velocity dispersion disappears when a full account is taken of the abundance ratio pattern in the calibration stars. This correlation is thus found to be an artefact of incomplete calibration to the Lick system.
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    Imaging of the merging galaxy NGC 3597 and its population of protoglobular clusters
    (2000) Forbes, DA; Hau, GKT
    We present wide field-of-view near-infrared imaging from the NTT and very deep optical imaging from the HST of the young merging galaxy NGC 3597. The morphology of the galaxy and the properties of the newly formed protoglobular clusters (PGCs) are examined. Our K-band data reveal the presence of a second nucleus, which provides further evidence that NGC 3597 is the result of a recent merger. Combining new K-band photometry with optical photometry, we are able for the first time to derive a unique age for the newly formed PGCs of a few Myr. This is consistent with the galaxy starburst age of less than or equal to 10 Myr. From deep HST imaging, we are able to probe the luminosity function similar to 8 magnitudes fainter than normal, old globular clusters, and confirm that the PGCs have a power-law distribution with a slope of similar to-2.
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    Kinematics, abundances and origin of brightest cluster galaxies
    (1999) Carter, D; Bridges, TJ; Hau, GKT
    We present kinematic parameters and absorption line strengths for three brightest cluster galaxies, NGC 6166, 6173 and 6086. We find that NGC 6166 has a velocity dispersion profile which rises beyond 20 arcsec from the nucleus, with a halo velocity dispersion in excess of 400 km s(-1). All three galaxies show a positive and constant h(4) Hermite moment. The rising velocity dispersion profile in NGC 6166 thus indicates an increasing mass-to-light ratio. Rotation is low in all three galaxies, and NGC 6173 and 6086 show possible kinematically decoupled cores. All three galaxies have Mg-2 gradients similar to those found in normal bright ellipticals, which are not steep enough to support simple dissipative collapse models, but these could be accompanied by dissipationless mergers which would tend to dilute the abundance gradients. The [Mg/Fe] ratios in NGC 6166 and 6086 are higher than that found in NGC 6173, and if NGC 6173 is typical of normal bright ellipticals, this suggests that cDs cannot form from late mergers of normal galaxies.
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    The dynamics of the dwarf elliptical galaxy FS 76: Bridging the kinematic dichotomy between elliptical and dwarf elliptical galaxies
    (2001) De Rijcke, S; Dejonghe, H; Zeilinger, WW; Hau, GKT
    We present major- and minor-axis kinematics out to approximate to2 half-light radii for the bright (M-B = -16.7) dwarf elliptical galaxy (dE) FS 76, a member of the NGC 5044 group. Its velocity dispersion is 46 +/- 2 km s(-1) in the center and rises to 70 +/- 10 km s(-1) at half-light radius. Beyond 1R(e), the dispersion starts to fall again. The maximum rotation velocity is 15 +/- 6 km s(-1), about the value expected for an oblate isotropic rotator with the same flattening as FS 76 (i.e., E1). Hence, FS 76 is the first dE discovered so far that is not flattened predominantly by anisotropy. There is a discontinuity in the radial velocity profile at +/- 1", corresponding to a kinematically peculiar core with a radial extent of 0.25 kpc. The reversed outward trend of the velocity dispersion is interpreted as evidence for a truncated dark halo and hence for the occurrence of tidal stripping. Using dynamical models, we estimate the total mass within a sphere of 1 kpc (approximate to1.5R(e)) to be between 1.2 and 3.4 x 10(9) M. at the 90% confidence level, corresponding to 3.2 greater than or equal to (M/L)(B)less than or equal to9.1. These values are consistent with predictions based on cold dark matter cosmological scenarios for galaxy formation.
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    The shell elliptical galaxy NGC 2865: evolutionary population synthesis of a kinematically distinct core
    (1999) Hau, GKT; Carter, D; Balcells, M
    We report on the discovery of a rapidly corotating stellar and gas component in the nucleus of the shell elliptical NGC 2865. The stellar component extends similar to 0.51 h(100)(-1) kpc along the major axis, and shows depressed velocity dispersion and absorption-line profiles skewed in the opposite sense to the mean velocity. Associated with it is a young stellar population with enhanced H beta, lowered Mg, and the same Fe indices relative to the underlying elliptical. Its recent star formation history is constrained by considering 'bulge+burst' models under four physically motivated scenarios, using evolutionary population synthesis. Scenarios in which the nuclear component is formed over a Hubble time or recently from continuous gas inflow are ruled out.
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    The southern dwarf hunt: Local Group dwarf candidates in the southern sky
    (2002) Whiting, AB; Hau, GKT; Irwin, M
    We present observations of 82 Local Group dwarf galaxy candidates, of which 62 were chosen visually from ESO-SRC survey plates of the southern sky (32 of which were not previously cataloged) and the rest suggested by various sources in the literature. Two are the Local Group galaxies Antlia and Cetus; nine are more distant galaxies, though still within a few megaparsecs; 45 are background galaxies; seven are planetary ( or other emission) nebulae; 15 are reflection or other Galactic nebulae; two are galaxy clusters; one is a Galactic star cluster; and one is a misidentified star. We conclude that there is no large population of faint Local Group dwarf galaxies of any familiar type awaiting discovery. We point out the danger of relying on a single type of data to reach conclusions about an object.