An H  survey of eight Abell clusters: the dependence of tidally induced star formation on cluster density

Abstract

We have undertaken a survey of Hα emission in a substantially complete sample of CGCG galaxies of types Sa and later within 1.5 Abell radii of the centres of eight low‐redshift Abell clusters (Abell 262, 347, 400, 426, 569, 779, 1367 and 1656). Some 320 galaxies were surveyed, of which 116 were detected in emission (39 per cent of spirals, 75 per cent of peculiars). Here we present previously unpublished data for 243 galaxies in seven clusters. Detected emission is classified as ‘compact’ or ‘diffuse’. From an analysis of the full survey sample, we confirm our previous identification of compact and diffuse emission with circumnuclear starburst and disc emission respectively. The circumnuclear emission is associated either with the presence of a bar, or with a disturbed galaxy morphology indicative of ongoing tidal interactions (whether galaxy–galaxy, galaxy–group, or galaxy–cluster). The frequency of such tidally induced (circumnuclear) starburst emission in spirals increases from regions of lower to higher local galaxy surface density, and from clusters with lower to higher central galaxy space density. The percentages of spirals classed as disturbed and of galaxies classified as peculiar show a similar trend. These results suggest that tidal interactions for spirals are more frequent in regions of higher local density and for clusters with higher central galaxy density. The prevalence of such tidal interactions in clusters is expected from recent theoretical modelling of clusters with a non‐static potential undergoing collapse and infall. Furthermore, in accord with this picture, we suggest that peculiar galaxies are predominantly ongoing mergers. We conclude that tidal interactions are likely to be the main mechanism for the transformation of spirals to S0s in clusters. This mechanism operates more efficiently in higher density environments, as is required by the morphological type–local surface density (T–Σ) relation for galaxies in clusters. For regions of comparable local density, the frequency of tidally induced starburst emission is greater in clusters with higher central galaxy density. This implies that, for a given local density, morphological transformation of disc galaxies proceeds more rapidly in clusters of higher central galaxy density. This effect is considered to be the result of subcluster merging, and could account for the previously considered anomalous absence of a significant T–Σ relation for irregular clusters at intermediate redshift.

Star-forming galaxies in low-redshift clusters: Effects of environment on the concentration of star formation

“…All apart from the field comparison sample are subsets of galaxies detected as emitters of Hα and/or [Nii] lines by the Objective Prism Survey (henceforth OPS; Moss & Whittle 2000, 2005. The OPS looked at 8 low-redshift galaxy clusters, with numbers 262, 347, 400, 426, 569, 779, 1367 and 1656 in the catalogue of Abell (1958), and characterised the line emission properties of 727 galaxies from the CGCG catalogue (Zwicky & Kowal 1968, and references therein).…”

A study of catalogued nearby galaxy clusters in the SDSS-DR4

“…Within this framework of galaxy evolution, where the environemnt plays an important role, substructure should be taken into account in seeking a global picture of the evolution of galaxies. There is thus observational evidence that a higher fraction of cluster galaxies with ongoing starburst episodes are located in substructures or in the regions of clustersubcluster interactions (Caldwell et al 1993;Biviano et al 1997;Moss & Whittle 2000;Poggianti et al 2004). Moreover, it has been observed that the presence of substructures is also directly related to the growth of the brightest cluster galaxies (BCGs).…”

OMEGA – OSIRIS Mapping of Emission-line Galaxies in A901/2 – I. Survey description, data analysis, and star formation and AGN activity in the highest density regions

“…However, the average star formation rate (SFR) in star-forming (SF) galaxies remains roughly constant with environment, and it is only the fraction of starforming galaxies that changes (Balogh et al 2004, Verdugo et al 2008, Poggianti et al 2008, Bamford et al 2008. The extent of ongoing star formation within a galaxy has also been shown to correlate with environment (Koopmann & Kenney 2004, Moss & Whittle 2000, Bamford et al 2007, implying a truncation of the star formation taking place first in the outer parts of the infalling galaxies. In fact, the last episode of star formation in cluster disc galaxies is seen to be concentrated towards the central regions (Rodríguez Del Pino et al 2014, Johnston et al 2014.…”