Browsing by Author "Mieske, S"

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    Distance to the Centaurus cluster and its subcomponents from surface brightness fluctuations
    (2003) Mieske, S; Hilker, M
    We present I-band Surface Brightness Fluctuations (SBF) measurements for 15 early type galaxies ( 3 giants, 12 dwarfs) in the central region of the Centaurus cluster, based on deep photometric data in 7 fields obtained with VLT FORS1 and with very good seeing. From the SBF-distances to our sample galaxies we determine the distance of the Centaurus cluster to be 41.3 +/- 2.1 Mpc (33.08 +/- 0.11 mag). This places the Centaurus cluster at about the same distance as the "Great Attractor". We find a distance difference of 0.27 +/- 0.34 mag between the two subcomponents Cen 30 and Cen 45, ruling out that both components are separated by their Hubble flow distance. A distance difference of 0.48 +/- 0.21 mag is found between the central galaxies NGC 4696 (Cen 30) and NGC 4709 (Cen 45) of both components, supported by the different turn-over magnitudes of their respective globular cluster systems. This suggests that Cen 45 is falling into but has not yet reached Cen 30, supporting the idea of a large scale filament along the line of sight towards Centaurus (Churazov et al. 1999). H-0 = 83.0 +/- 8.3 km s(-1) Mpc(-1) is obtained for our Cen 30 sample taking into account the peculiar motion of the Local Group into the direction of the Centaurus cluster. This value of H0 corresponds to a much smaller Hubble flow distortion in the direction of Centaurus than determined by Tonry et al. ( 2000), implying that the GA mass estimate by Tonry et al. may be too high and/or that the Centaurus cluster falls into the GA almost perpendicularly to the line of sight. As our mean single measurement error is very close to the measured distance scatter of the investigated galaxies, we can only derive an upper limit of +/- 10 Mpc radial extension for the Centaurus cluster, corresponding to a five times larger radial than tangential extension. No evidence for an infall pattern into the Great Attractor is found within the uncertainties for the 11 galaxies with measured redshifts.
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    Faint dwarf spheroidals in the Fornax Cluster - A flat luminosity function
    (2003) Hilker, M; Mieske, S; Infante, L
    We have discovered similar or equal to70 very faint dwarf galaxies in the Fornax Cluster. These dSphs candidates follow the same magnitude-surface brightness relation as their counterparts in the Local Group, and even extend it to fainter limits. The faintest dSph candidate in our sample has an absolute magnitude of M-V similar or equal to -8.8 mag and a central surface brightness of mu(V) similar or equal to 27 mag/arcsec(2). There exists a tight color-magnitude relation for the early-type galaxies in Fornax that extends from the giant to the dwarf regime. The faint-end slope of the luminosity function of the early-type dwarfs is flat (alpha similar or equal to -1.1 +/- 0.1), contrary to the results obtained by Kambas et al. (2000).
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    Ultracompact dwarf galaxies in Abell 1689
    (2004) Mieske, S; Infante, L; Benítez, N; Coe, D; Blakeslee, JP; Zekser, K; Ford, HC; Broadhurst, TJ; Illingworth, GD; Hartig, GF; Clampin, M; Ardila, DR; Bartko, F; Bouwens, RJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Homeier, N; Kimble, RA; Krist, JE; Lesser, MP; Martel, AR; Menanteau, F; Meurer, GR; Miley, GK; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    The properties of ultracompact dwarf (UCD) galaxy candidates in Abell 1689 (z = 0.183) are investigated, based on deep high-resolution images from the Hubble Space Telescope Advanced Camera for Surveys. A UCD candidate has to be unresolved, have i < 28 mag (M-V < -11.5 mag), and satisfy color limits derived from Bayesian photometric redshifts. We find 160 UCD candidates with 22 mag < i < 28 mag. We estimate that about 100 of these are cluster members, based on their spatial distribution and photometric redshifts. For i greater than or similar to 26.8 mag, the radial and luminosity distribution of the UCD candidates can be explained well by Abell 1689's globular cluster ( GC) system. For i less than or similar to 26.8 mag, there is an overpopulation of 15 +/- 5 UCD candidates with respect to the GC luminosity function. For i less than or similar to 26 mag, the radial distribution of UCD candidates is more consistent with the dwarf galaxy population than with the GC system of Abell 1689. The UCD candidates follow a color-magnitude trend with a slope similar to that of Abell 1689's genuine dwarf galaxy population, but shifted fainter by about 2-3 mag. Two of the three brightest UCD candidates (M-V similar or equal to -17 mag) are slightly resolved. At the distance of Abell 1689, these two objects would have King profile core radii of similar or equal to35 pc and r(eff) similar or equal to 300 pc, implying luminosities and sizes 2-3 times those of M32's bulge. Additional photometric redshifts obtained with late-type stellar and elliptical galaxy templates support the assignment of these two resolved sources to Abell 1689 but also allow for up to four foreground stars among the six brightest UCD candidates. Our findings imply that in Abell 1689 there are greater than or equal to10 UCDs with M-V < -12.7 mag, probably created by stripping "normal" dwarf or spiral galaxies. Compared with the UCDs in the Fornax Cluster - the location of their original discovery - they are brighter, larger, and have colors closer to normal dwarf galaxies. This suggests that they may be in an intermediate stage of the stripping process. Checking the photometric redshifts of the brightest UCD candidates with spectroscopy would be the next step to definitely confirm the existence of UCDs in Abell 1689.