HI-observations of dwarf galaxies in the Local Supercluster

Abstract

We have observed 71 dwarf galaxies of low surface brightness using the 100-m radio telescope at Effelsberg in a search for new members of 27 northern galaxy groups with characteristic distances of 8 to 15 Mpc. We present radial velocities, HI-fluxes, and HI line widths for 17 detected galaxies as well as upper limits for the remaining undetected objects. Almost all detected dwarf galaxies are physical members of the corresponding group with a mean radial velocity difference of −9 ± 45 km s −1 with respect to the principal galaxy in each group. Our sample of new dwarf members of nearby groups has a median radial velocity of 700 km s −1 , a mean blue absolute magnitude of -12.7 mag, a mean linear diameter of 2.5 kpc, and a mean M HI /L B ratio of 1.1 M /L . The Ir galaxy d1217+4703 in the Canes Venatici I cloud turns out to be a very gas-rich galaxy with M HI /L B = 6.5 in solar units.

New low surface brightness dwarf galaxies detected around nearby spirals

“…The spiral structure is distorted in both galaxies, which indicates their interaction. An Im-type dwarf galaxy UGC 7751 is associated with this pair, and possibly another, fainter irregular dwarf LV J1243+4127 too [12].…”

“…The main features of the thirteen nearby spiral galaxies that we have observed with long exposures are presented in Table 1. Its columns contain: (1) the names of the galaxies, ranked by right ascension; (2) the coordinates of the galaxy for the epoch J2000.0; (3) the morphological type according to de Vaucouleurs' scale; (4) the radial velocity in km s −1 relative to the centroid of the Local Group; (5) the distance to the galaxies in Mpc and the applied method of distance determination: "cep" the Cepheid luminosity method, "rgb" by the luminosity of red giant branch stars, "sbf" by surface brightness fluctuations, "tf" by the Tully-Fisher relation between the amplitude of rotation of a galaxy and its luminosity, "bs" by the luminosity of the brightest stars; (6) the absolute magnitude of the galaxy in the B band adjusted for the Galactic [46] and internal extinction; (7) the linear Holmberg diameter of the galaxy in kpc; (8,9) the logarithm of the stellar mass and the mass of neutral hydrogen in solar mass units; (10) the logarithm of the stellar mass density within the 1 Mpc radius sphere around the galaxy, taken in relation to the average cosmic stellar mass density; (11) the number of known satellites of the galaxy within the "zero-velocity radius" sphere around it plus the number of new satellite candidates that we found and discussed above; (12) the signs of disturbances on the periphery of the galaxy if any of them can be seen in our deep images. Most of the Table 1 data are taken from the UNGC [13], which gives evaluations of the parameters used.…”

“…The two past decades witnessed the rapid formation of a new direction in extragalactic astronomy, called the cosmology of the nearby universe. This is facilitated by the ongoing wide-field surveys of the northern and southern sky in the optical, infrared, and radio ranges [1][2][3][4][5][6][7][8][9], which allowed astronomers to detect a lot of dwarf galaxies and to measure their radial velocities [10][11][12]. Accurate bulk measurements of distances to nearby galaxies carried out with the Hubble Space Telescope are also a significant advancement factor.…”

FIGGS 2: An HI survey of extremely faint irregular galaxies

“…The columns are as follows: column (1): Galaxy name, column (2) and (3): the equatorial coordinates (J2000), column (4): Distance in Mpc, column (5): the methods used to determine the distances to the galaxies, -by the tip of the red giant branch (TRGB), by the Hubble velocity-distance relation (H0 = 73 km/s/Mpc) (h), from galaxy membership (mem), column (6) the absolute blue magnitude (extinction corrected), column (7): log of HI mass, column (8) Heliocentric radial velocity, column (9): The Holmberg diameter, column (10): inclination derived from optical photometry (assuming an intrinsic thickness of 0.42 (Roychowdhury et al 2013)). The data presented in Table 1 were taken from (Karachentsev et al , 2001Makarov et al 2003;Huchtmeier et al 2000Huchtmeier et al , 2009. The first 15 galaxies in Table 1 were detected in our GMRT observations, whereas the last five galaxies (separated by an empty line) were not detected.…”

“…Two (LeG18, LVJ1217+4703) out of the five non-detections have quite large single-dish peak fluxes (> 25 mJy (Huchtmeier et al 2009)). However their GMRT observations were affected by strong RFI and a significant fraction of the data had to be flagged, resulting in higher noise levels in the data cube.…”