arXiv subjects

Steve Maddox

Publications and source records attributed to Steve Maddox.

40 records · Page 3Linked to original sources

arXiv1999

The Local Environment of HII Galaxies

We have carried out an investigation of the environments of low redshift HII galaxies by cross-correlating their positions on the sky with those of faint field galaxies in the Automatic Plate Measuring Machine catalogues. We address the question of whether violent star formation in HII galaxies is induced by low mass companions by statistically estimating the mean space density of galaxies around them. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the APM scans. A significantly positive signal is detected for the HII galaxy-APM galaxy angular cross-correlation function, but the amplitude is poorly determined. The projected cross-correlation function has higher signal-to-noise, and suggests that the amplitude is slightly lower than for normal field galaxies. This implies that these bursting dwarf galaxies inhabit slightly lower density environments to those of normal faint field galaxies, consistent with other studies of emission line galaxies. This suggests that in these dwarf starburst galaxies, star formation is not triggered by unusually strong tidal interactions, and must have a different origin.

astro-ph↗

arXiv1998

The Local Environment of HII Galaxies

We address the question of whether violent star formation in HII galaxies is induced by low mass companions by describing statistically their local environment as estimated by the correlation function. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the Automatic Plate Measuring Machine scans. We then cross-correlate a large sample of HII galaxies with the APM faint field galaxy catalogue. The preliminary results are all consistent with HII galaxies being a randomly selected sample of normal faint field galaxy with no extra clustering. This suggests that at least in these dwarf starburst galaxies star formation is not triggered by tidal interactions and may have a different origin.

astro-ph↗

arXiv1997

The APM Galaxy Survey:- V. Catalogues of Galaxy Clusters

We describe the construction of catalogues of galaxy clusters from the APM Galaxy survey using an automated algorithm based on Abell-like selection criteria. We investigate the effects of varying several parameters in our selection algorithm, including the magnitude range, and radius from the cluster centre used to estimate the cluster richnesses. We quantify the accuracy of the photometric distance estimates by comparing with measured redshifts, and we investigate the stability and completeness of the resulting catalogues. We find that the angular correlation functions for different cluster catalogues are in good agreement with one another, and are also consistent with the observed amplitude of the spatial correlation function of rich clusters.

astro-ph↗

arXiv1997

The richness dependence of galaxy cluster correlations: Results from a redshift survey of rich APM clusters

We analyse the spatial clustering properties of a new catalogue of very rich galaxy clusters selected from the APM Galaxy Survey. These clusters are of comparable richness and space density to Abell Richness Class $\geq 1$ clusters, but selected using an objective algorithm from a catalogue demonstrably free of artificial inhomogeneities. Evaluation of the two-point correlation function $ξ_{cc}(r)$ for the full sample and for richer subsamples reveals that the correlation amplitude is consistent with that measured for lower richness APM clusters and X-ray selected clusters. We apply a maxmimum likelihood estimator to find the best fitting slope and amplitude of a power law fit to $ξ_{cc}(r)$, and to estimate the correlation length $r_{0}$ (the value of $r$ at which $ξ_{cc}(r)$ is equal to unity). For clusters with a mean space density of $1.6\times 10^{-6}\hmpccc$ (equivalent to the space density of Abell Richness $\geq 2$ clusters), we find $r_{0}=21.3^{+11.1}_{-9.3} \hmpc$ (95% confidence limits). This is consistent with the weak richness dependence of $ξ_{cc}(r)$ expected in Gaussian models of structure formation. In particular, the amplitude of $ξ_{cc}(r)$ at all richnesses matches that of $ξ_{cc}(r)$ for clusters selected in N-Body simulations of a low density Cold Dark Matter model.

astro-ph↗