We have conducted the first blind H I survey covering 480 deg 2 and a heliocentric velocity range from 300-1900 km s −1 to investigate the H I content of the nearby spiral-rich Ursa Major region and to look for previously uncatalogued gas-rich objects. Here we present the catalog of H I sources. The H I data were obtained with the 4-beam receiver mounted on the 76.2-m Lovell telescope (FWHM 12 arcmin) at the Jodrell Bank Observatory (UK) as part of the H I Jodrell All Sky Survey (HIJASS). We use the automated source finder DUCHAMP and identify 166 H I sources in the data cubes with H I masses in the range of 10 7 -10 10.5 M . Our Ursa Major H I catalogue includes 10 first time detections in the 21-cm emission line.We identify optical counterparts for 165 H I sources (99 per cent). For 54 H I sources (∼ 33 per cent) we find numerous optical counterparts in the HIJASS beam, indicating a high density of galaxies and likely tidal interactions. Four of these H I systems are discussed in detail.We find only one H I source (1 per cent) without a visible optical counterpart out of the 166 H I detections. Green Bank Telescope (FWHM 9 arcmin) follow-up observations confirmed this H I source and its H I properties. The nature of this detection is discussed and compared to similar sources in other H I surveys.
We identify gravitationally bound structures in the Ursa Major region using positions, velocities and photometry from the Sloan Digital Sky Survey (SDSS DR7) and the Third Reference Catalogue of Bright Galaxies (RC3). A friends-of-friends algorithm is extensively tested on mock galaxy lightcones and then implemented on the real data to determine galaxy groups whose members are likely to be physically and dynamically associated with one another. We find several galaxy groups within the region that are likely bound to one another and in the process of merging. We classify 6 galaxy groups as the Ursa Major 'supergroup', which are likely to merge and form a poor cluster with a mass of ∼ 8 × 10 13 M . Furthermore, the Ursa Major supergroup as a whole is likely bound to the Virgo cluster, which will eventually form an even larger system in the context of hierarchical structure formation.To investigate the evolutionary state of the galaxy groups in the Ursa Major region, we examine the location of the brightest group galaxy (BGG) as well as galaxy properties such as colour, morphological type, luminosity and HI content. The galaxy properties are examined with respect to group/non-group membership as well as a function of their local projected surface density. We find that (i) the BGGs often show a relatively large spatial and kinematic offset from the group centres, (ii) the increase in the fraction of early-type galaxies with local projected surface density is shallow, (iii) galaxy colours tend to be redder with increasing density, (iv ) there is no trend towards brighter galaxies with increasing density and (v ) several galaxies with HI excess are found in low density environments, whereas HI deficient galaxies tend to reside in the galaxy groups. We note that several galaxy groups contain members with disturbed HI content or HI tails. Given the low velocity dispersion of the groups and the lack of X-ray emission, these disturbances are likely due to galaxy-galaxy interactions. We conclude that the galaxy groups in the Ursa Major region are in an early evolutionary state and the properties of their member galaxies are similar to those in the field.
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