Abstract
Abstract The well-known cluster of galaxies ZwCl0024+1652 at z ∼ 0.4 lacks an in-depth morphological classification of its central region. While previous studies provide a visual classification of a patched area, we used the public code called galaxy Support Vector Machine (galsvm) and HST/ACS data as well as the WFP2 master catalogue to automatically classify all cluster members up to 1 Mpc. galsvm analyses galaxy morphologies through support vector machine (SVM). From the 231 cluster galaxies, we classified 97 as early types (ETs) and 83 as late types (LTs). The remaining 51 stayed unclassified (or undecided). By cross-matching our results with the existing visual classification, we found an agreement of 81 per cent. In addition to previous Zwcl0024 morphological classifications, 121 of our galaxies were classified for the first time in this work. In addition, we tested the location of classified galaxies on the standard morphological diagrams, colour–colour and colour–magnitude diagrams. Out of all cluster members, ∼20 per cent are emission-line galaxies, taking into account previous GLACE results. We have verified that the ET fraction is slightly higher near the cluster core and decreases with the clustercentric distance, while the opposite trend has been observed for LT galaxies. We found a higher fraction of ETs (54 per cent) than LTs (46 per cent) throughout the analysed central region, as expected. In addition, we analysed the correlation between the five morphological parameters (Abraham concentration, Bershady–Concelice concentration, asymmetry, Gini, and M20 moment of light) and the clustercentric distance, without finding a clear trend. Finally, as a result of our work, the morphological catalogue of 231 galaxies containing all the measured parameters and the final classification is available in the electronic form of this paper.
Highlights
A consolidated observational fact is the outstanding difference in the properties of galaxies located in the cores and in the external parts of low- and intermediate-redshift clusters: The former regions are dominated by red, massive, and passive early-type galaxies (ET galaxies, comprising ellipticals and S0 galaxies), while a substantial increase of the fraction of late-type galaxies (LTs, comprising spiral and irregular objects) is observed in the latter galaxies
These studies show that the proportion of late types (LTs) at z ∼ 0.4 accounts for about ∼35–40 per cent
In this work the fraction of LT galaxies is ∼36 per cent, which is in agreement with previous results
Summary
A consolidated observational fact is the outstanding difference in the properties of galaxies located in the cores (or regions of high local galaxy density) and in the external parts (or low-density ones) of low- and intermediate-redshift clusters: The former regions are dominated by red, massive, and passive early-type galaxies (ET galaxies, comprising ellipticals and S0 galaxies), while a substantial increase of the fraction of late-type galaxies (LTs, comprising spiral and irregular objects) is observed in the latter galaxies. A decrease of the fraction of star-forming (SF) galaxies is observed with increasing local galaxy density [the star formation–density relation; see for instance Pintos-Castro et al 2013, and references therein] These relations evolve with cosmic time, as was realized by Butcher & Oemler (1978), who found that cluster galaxy populations evolve as the redshift changes in such a way that rich clusters at higher redshifts (z > 0.2) are populated with a higher fraction of blue galaxies than lowredshift clusters. An increase of the cluster SF and active galactic nucleus (AGN) activity is observed (see for instance Haines et al 2009; Martini et al 2013)
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