Query : 2013A&A...555L...7O

2013A&A...555L...7O - Astronomy and Astrophysics, volume 555, L7-7 (2013/7-1)

Is GBT 1355+5439 a dark galaxy ?


Abstract (from CDS):

We present HI imaging of GBT1355+5439 performed with the Westerbork Synthesis Radio Telescope. This is a dark HI object recently discovered close to the nearby galaxy M101. We find GBT1355+5439 to be an HI cloud 5x3 arcmin in size. The total HI image and the kinematics show that the cloud consists of condensations that have small (∼10km/s) motions with respect to each other. The column densities of the HI are low; the observed peak value is 7.1x1019cm–2. The velocity field shows a mild velocity gradient over the body of GBT1355+5439, possibly due to rotation, but it may also indicate large-scale radial motions. Although our data are limited in sensitivity, at all positions the HI velocity dispersion is higher than 5km/s and no narrow, cold, HI component is seen. Because its distance is not known, we considered various possibilities for the nature of GBT1355+5439. Both the scenarios that it is a tidal remnant near M101 and that it is a dark dwarf companion of M101 meet difficulties. Neither do the data fit the properties of known compact high-velocity clouds in the Galactic halo exactly, but we cannot entirely exclude this option and deeper observations are required. We also considered the possibility that GBT1355+5439 is a gas-rich dark minihalo in the outer regions of the Local Group. Interestingly, it would then have similar properties as the clouds of a proposed Local Group population recently found in the ALFALFA survey. In this case, the HI mass of GBT1355+5439 would be about a few times 105M, its size about 1 kpc, and the dynamical mass Mdyn>5x107M. However, if GBT1355+5439 is a dark Local Group object, the internal kinematics of the HI appears to be different from that of gas-dominated, almost dark galaxies of similar size.

Abstract Copyright:

Journal keyword(s): galaxies: dwarf - radio lines: galaxies

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME Magellanic Stream HVC 00 32 -30.0           ~ 942 1
2 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6822 1
3 NAME Leo T G 09 34 53.4 +17 03 05     15.1     ~ 368 0
4 NAME Leo P BiC 10 21 45.123 +18 05 16.89           ~ 208 0
5 NAME GBT 1355+5439 G 13 54 50.6 +54 38 50           ~ 11 0
6 NAME M101 Group GrG 14 03 +54.3           ~ 98 1
7 M 101 GiP 14 03 12.583 +54 20 55.50   8.46 7.86 7.76   ~ 2833 2
8 NAME Local Group GrG ~ ~           ~ 8145 0

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