| Title | Quantified H I morphology - IV. The merger fraction and rate in WHISP |
| Authors | Holwerda, B. W.; Pirzkal, N.; de Blok, W. J. G.; Bouchard, A.; Blyth, S. -L.; van der Heyden, K. J. |
| Bibcode | 2011MNRAS.416.2437H Search ADS ↗ |
| Abstract | The morphology of the atomic hydrogen (H I) disc of a spiral galaxy is the first component to be disturbed by a gravitational interaction such as a merger between two galaxies. We use a simple parametrization of the morphology of H I column density maps of the Westerbork observations of neutral Hydrogen in Irregular and SPiral galaxies (WHISP) project to select those galaxies that are likely undergoing a significant interaction. Merging galaxies occupy a particular part of parameter space defined by Asymmetry (A), the relative contribution of the 20 per cent brightest pixels to the second-order moment of the column density map (M20) and the distribution of the second-order moment over all the pixels (GM). Based on their H I morphology, we find that 13 per cent of the WHISP galaxies are in an interaction (Concentration-M20) and only 7 per cent are based on close companions in the data cube. This apparent discrepancy can be attributed to the difference in visibility time-scales: mergers are identifiable as close pairs for 0.5 Gyr but are identifiable for ̃1 Gyr by their disturbed H I morphology. Expressed as volume merger rates, the two estimates agree very well: 7 and 6.8 × 10-3 mergers Gyr-1 Mpc-3 for paired and morphologically disturbed H I discs, respectively. The consistency of our merger fractions with those published for bigger surveys such as the Sloan Digital Sky Survey shows that H I morphology can be a very viable way to identify mergers in large H I surveys. The relatively high value for the volume merger rate may be a bias in the selection or WHISP volume. The expected abundance in high-resolution H I data by the planned South African Karoo Array Telescope (MeerKAT), Australian SKA Pathfinder (ASKAP) and Westerbork Synthesis Radio Telescope/APERture Tile In Focus instrument (WSRT/APERTIF) radio observatories will reveal the importance of mergers in the local Universe and, with the advent of the Square Kilometer Array (SKA), over cosmic times. |
| Objects | 340 Objects Search NED ↙ |
