H I and mass distribution of GR8

The dwarf irregular galaxy GR8, which is at the extreme faint end of the luminosity and mass functions, is studied using optical photometry and 21 cm H I line observations. It is shown that rotation is only important to the gravitational support of the system in the inner parts (r less than 250 pc). GR8 is one of the very few non-elliptical systems known (with M81dwA) where the random motions provide essentially all the support in the outer parts (4 greater than or equal to 500 pc). The Gaussian nature of the H I distribution and the isothermal distribution of the H I velocity dispersion implies M is directly proportional to R(exp 3) in the outer regions of GR8 (i.e., the stellar disk and the H I lie in the approximately uniform density core of the dark halo)

H I studies of the sculptor group galaxies

Results from large-scale mapping of the H I gas in the Sculptor group are presented. From this kinematic analysis, a mean global (M/L sub B) approx. equals 9 solar maximum/solar luminosity (at the last observed velocity point) is found for the individual galaxies. This is only a factor approx. 10 smaller than the (M/L sub B) dyn approx. equals 90 solar maximum/solar luminosity derived from a dynamical study of the whole group. The parameters derived from the mass models suggest that most of the unseen matter has to be concentrated around the luminous galaxies. Under the assumption that the Sculptor group is a virialized system and that all the mass is associated with the galaxies, an upper limit of approx. 40 kpc is derived for the size of the dark halos present in the five late-type spirals of the group

Deep wide field HI imaging of Messier 31

We report on preliminary results from a new deep 21-cm survey of the Andromeda galaxy, based on observations performed with the Synthesis Telescope and the 26-m antenna at DRAO. The HI distribution and kinematics of the disc are analyzed and basic dynamical properties are derived. New HI structures are discovered, like thin HI spur-like structures and an external arm in the disc outskirts. The HI spurs are related to perturbed stellar clumps outside the main disc of M31. The external arm lies on the far, receding side of the galaxy and has no obvious counterpart in the opposite side. These HI perturbations probably result from tidal interactions with companions. It is found a dynamical mass of 4.7 +/- 0.5 x10^11 Msol enclosed within a radius R = 38 kpc and a total mass of ~1 x10^12 Msol inside the virial radius.Comment: 4 pages, 1 figure, proceeding of the conference "Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution", June 02 - 05 2009, Groninge

Dark matter in low mass surface density galaxies

Low mass surface density spiral and irregular galaxies like low surface brightness (LSB) and dwarf galaxies are unique laboratories to study the dynamical properties of Dark Matter halos because their mass is generally dominated by dark matter at all galactocentric radii. We present results from the largest sample ever assembled of high resolution Halpha velocity fields of LSB and dwarf galaxies in order to study their mass distributions.Comment: 2 pages, 1 figure, proceedings of the conference "Pathways Through an Eclectic Universe", Johan Knapen, Terry Mahoney, and Alexandre Vazdekis ed

Faint flux performance of an EMCCD

Thorough numerical simulations were run to test the performance of three processing methods of the data coming out from an electron multiplying charge coupled device (EMCCD), or low light level charge coupled device (L3CCD), operated at high gain, under real operating conditions. The effect of read-out noise and spurious charges is tested under various low flux conditions (0.001 event/pixel/frame < f < 20 events/pixel/frame). Moreover, a method for finding the value of the gain applied by the EMCCD amplification register is also developed. It allows one to determine the gain value to an accuracy of a fraction of a percent from dark frames alone.Comment: 9 pages, 6 figures, to appear in SPIE conference proceedings vol 6276, "High Energy, Optical & Infrared Detectors for Astronomy II" Orlando FL USA, 24-31 May 2006. Code is available at http://www.astro.umontreal.ca/~odaigle/emcc