New distances of unresolved dwarf elliptical galaxies in the vicinity of the Local Group

We present Surface Brightness Fluctuation distances of nine early-type dwarf galaxies and the S0 galaxy NGC 4150 in the Local Volume based on deep B- and R-band CCD images obtained with the 2.56 metre Nordic Optical Telescope. Typically, six stellar fields at various galactocentric distances have been chosen for each galaxy as appropriately free of foreground stars and other contaminants, and Fourier analysed to determine the distances, which are found to lie in the range of 3 to 16 Mpc. The SBF method is thus demonstrated to efficiently measure distances from the ground with mid-aperture telescopes for galaxies for which only the tip of the red giant branch method in combination with the Hubble Space Telescope has been available until now. We obtained the following distance moduli: 28.11 +/- 0.15 mag (or 4.2 +/- 0.3 Mpc) for UGC 1703, 27.61 +/- 0.17 mag (or 3.3 +/- 0.3 Mpc) for KDG 61, 29.00 +/- 0.27 mag (or 6.3 +/- 0.8 Mpc) for UGCA 200, 27.74 +/- 0.18 mag (or 3.5 +/- 0.3 Mpc) for UGC 5442, 30.22 +/- 0.17 mag (or 11.1 +/- 0.9 Mpc) for UGC 5944, 30.79 +/- 0.11 mag (or 14.4 +/- 0.7 Mpc) for NGC 4150, 31.02 +/- 0.25 mag (or 16.0 +/- 1.9 Mpc) for BTS 128, 29.27 +/- 0.16 mag (or 7.1 +/- 0.6 Mpc) for UGC 7639, 30.19 +/- 0.23 mag (or 10.9 +/- 1.2 Mpc) for UGC 8799 with an alternative distance of 30.61 +/- 0.26 mag (or 13.2 +/- 1.7 Mpc), and 29.60 +/- 0.20 mag (or 8.3 +/- 0.8 Mpc) for UGC 8882.Comment: 14 pages, 13 figures (figures 1, 2 and 10 are of reduced quality), accepted for publication in A&

Deep Near-Infrared Surface Photometry and Properties of Local Volume Dwarf Irregular Galaxies

We present deep H-band surface photometry and analysis of 40 Local Volume galaxies, a sample primarily composed of dwarf irregulars in the Cen A group, obtained using the IRIS2 detector at the 3.9m Anglo-Australian Telescope. We probe to a surface brightness of ~25 mag arcsec$^{-2}$, reaching a 40 times lower stellar density than the Two Micron All Sky Survey (2MASS). Employing extremely careful and rigorous cleaning techniques to remove contaminating sources, we perform surface photometry on 33 detected galaxies deriving the observed total magnitude, effective surface brightness and best fitting S\'ersic parameters. We make image quality and surface photometry comparisons to 2MASS and VISTA Hemispheric Survey (VHS) demonstrating that deep targeted surveys are still the most reliable means of obtaining accurate surface photometry. We investigate the B-H colours with respect to mass for Local Volume galaxies, finding that the colours of dwarf irregulars are significantly varied, eliminating the possibility of using optical-NIR colour transformations to facilitate comparison to the more widely available optical data sets. The structure-luminosity relationships are investigated for our `clean' sample of dwarf irregulars. We demonstrate that a significant fraction of the Local Volume dwarf irregular population have underlying structural properties similar to both Local Volume and Virgo Cluster dwarf ellipticals. Linear regressions to structure-luminosity relationships for the Local Volume galaxies and Virgo Cluster dwarf ellipticals show significant differences in both slope and scatter around the established trend lines, suggesting that environment might regulate the structural scaling relationships of dwarf galaxies in comparison to their more isolated counterparts.Comment: 27 pages, 14 figures, 5 table

Photometric Properties of Six Local Volume Dwarf Galaxies from Deep Near-Infrared Observations

We have obtained deep near-infrared $J$- (1.25 $\mu$m), $H$- (1.65$\mu$m) and $K_s$-band (2.15 $\mu$m) imaging for a sample of six dwarf galaxies (M_B\ga-17 mag) in the Local Volume (LV, D\la10 Mpc). The sample consists mainly of early-type dwarf galaxies found in various environments in the LV. Two galaxies (LEDA 166099 and UGCA 200) in the sample are detected in the near-infrared for the first time. The deep near-infrared images allow for a detailed study of the photometric and structural properties of each galaxy. The surface brightness profiles of the galaxies are detected down to the ~$24 mag arcsec^{-2}$ isophote in the $J$- and $H$-bands, and $23 mag arcsec^{-2}$ in the $K_s$-band. The total magnitudes of the galaxies are derived in the three wavelength bands. For the brightest galaxies (M_B\la-15.5 mag) in the sample, we find that the Two Micron All Sky Survey (2MASS) underestimates the total magnitudes of these systems by up to \la0.5 mag. The radial surface brightness profiles of the galaxies are fitted with an exponential (for those galaxies having a stellar disk) or S\'ersic law to derive the structure of the underlying stellar component. In particular, the effective surface brightness ($\mu_e$) and effective radius ($r_e$) are determined from the analytic fits to the surface brightness profile. The $J$-$K_s$ colours for the galaxies have been measured to explore the luminosity-metallicity relation for early-type dwarfs. In addition, the $B$-$K_s$ colours of the galaxies are used to assess their evolutionary state relative to other galaxy morphologies. The total stellar masses of the dwarf galaxies are derived from the $H$-band photometric measurements. These will later be compared to the dynamical mass estimates for the galaxies to determine their dark matter content.Comment: 14 pages, 8 figures, submitted to MNRA

Discovery of a high-redshift Einstein ring

We report the discovery of a partial Einstein ring of radius 1.48arcsec produced by a massive (and seemingly isolated) elliptical galaxy. The spectroscopic follow-up at the VLT reveals a 2L* galaxy at z=0.986, which is lensing a post-starburst galaxy at z=3.773. This unique configuration yields a very precise measure of the mass of the lens within the Einstein radius, (8.3e11 +- 0.4)/h70 Msolar. The fundamental plane relation indicates an evolution rate of d [log (M/L)B] / dz = -0.57+-0.04, similar to other massive ellipticals at this redshift. The source galaxy shows strong interstellar absorption lines indicative of large gas-phase metallicities, with fading stellar populations after a burst. Higher resolution spectra and imaging will allow the detailed study of an unbiased representative of the galaxy population when the universe was just 12% of its current age.Comment: 5 pages, 3 figures, accepted in A&A Le