Browsing by Author "Hau, George K. T."

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    Mapping the Kinematically Decoupled Core in NGC 1407 with MUSE
    (2018) Johnston, Evelyn J.; Hau, George K. T.; Coccato, Lodovico; Herrera, Cristian
    Studies of the kinematics of NGC 1407 have revealed complex kinematical structure, consisting of the outer galaxy, an embedded disc within a radius of similar to 60 arcsec, and a kinematically decoupled core (KDC) with a radius of less than 30 arcsec. However, the size of the KDC and the amplitude of the kinematic misalignment it induces have not yet been determined. In this paper, we explore the properties of the KDC using observations from the Multi-Unit Spectroscopic Explorer (MUSE) Integral Field Spectrograph to map out the kinematics in the central arcminute of NGC 1407. Velocity and kinemetry maps of the galaxy reveal a twist of similar to 148 degrees in the central 10 arcsec of the galaxy, and the higher order moments of the kinematics reveal that within the same region, this slowly rotating galaxy displays no net rotation. Analysis of the stellar populations across the galaxy found no evidence of younger stellar populations in the region of the KDC, instead finding uniform age and super-solar a-enhancement across the galaxy, and a smoothly decreasing metallicity gradient with radius. We therefore conclude that NGC 1407 contains a triaxial, kiloparsec-scale KDC with distinct kinematics relative to the rest of the galaxy, and that is likely to have formed through either a major merger or a series of minor mergers early in the lifetime of the galaxy. With a radius of similar to 5 arcsec or similar to 0.6 kpc, NGC 1407 contains the smallest KDC mapped by MUSE to date in terms of both its physical and angular size.
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    Spectra of globular clusters in the Sombrero galaxy: evidence for spectroscopic metallicity bimodality
    (2011) Alves-Brito, Alan; Hau, George K. T.; Forbes, Duncan A.; Spitler, Lee R.; Strader, Jay; Brodie, Jean P.; Rhode, Katherine L.
    We present a large sample of over 200 integrated-light spectra of confirmed globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with the Deep Imaging Multi-Object Spectrograph (DEIMOS) instrument on the Keck telescope. A significant fraction of the spectra have signal-to-noise ratio levels high enough to allow measurements of GC metallicities using the method of Brodie & Huchra. We find a distribution of spectroscopic metallicities in the range -2.2 < [Fe/H] < + 0.1 that is bimodal, with peaks at [Fe/H] similar to -1.4 and -0.6. Thus, the GC system of the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a bimodal spectroscopic metallicity distribution supporting the long-held belief that colour bimodality reflects two metallicity subpopulations. This further suggests that the transformation from optical colour to metallicity for old stellar populations, such as GCs, is not strongly non-linear. We also explore the radial and magnitude distribution with metallicity for GC subpopulations but small number statistics prevent any clear trends in these distributions.