Beyond Sérsic + exponential disc morphologies in the Coma Cluster

Jacob T. C. G. Head; John R. Lucey; Michael J. Hudson

doi:10.1093/mnras/stv1662

paper

Beyond Sérsic + exponential disc morphologies in the Coma Cluster

arXiv:1507.07930 · doi:10.1093/mnras/stv1662

Abstract

[abridged] We explore the diversity of internal galaxy structures in the Coma cluster across a wide range of luminosities ( $- 17$ \, $>$ \, $M_{g}$ \, $>$ \, $- 22$ ) and cluster-centric radii ( $0$ \, $<$ \, $r_{cluster}$ \, $<$ \,1.3 $r_{200}$ ) through analysis of deep Canada-France-Hawaii Telescope $i$ band imaging. We present 2D multi-component decomposition via GALFIT, encompassing a wide range of candidate model morphologies with up to three photometric components. Particular focus is placed on early-type galaxies with outer discs (i.e. S0s), and deviations from simple (`unbroken') exponential discs. Rigorous filtering ensures that each model component provides a statistically significant improvement to the goodness-of-fit. The majority of Coma cluster members in our sample (478 of 631) are reliably fitted by symmetric structural models. Of these, 134 ( $28%$ ) are single Sérsic objects, 143 ( $30%$ ) are well-described by 2 component structures, while 201 ( $42%$ ) require more complex models. Multi-component Sérsic galaxies resemble compact psuedobulges ( $n \sim$ \,2, $R_{e} \sim$ \, 4 kpc) surrounded by extended Gaussian-like outer structures ( $R_{e} > 10$ kpc). 11\% of galaxies ( $N = 52$ ) feature a break in their outer profiles, indicating `truncated' or `anti-truncated' discs. Beyond the break radius, truncated galaxies are structurally consistent with exponential discs, disfavouring physical truncation as their formation mechanism. Bulge luminosity in anti-truncated galaxies correlates strongly with galaxy luminosity, indicating a bulge-enhancing origin for these systems. Both types of broken disc are found overwhelmingly ( $> 70%$ ) in `barred' galaxies, despite a low measured bar fraction for Coma ( $20 \pm 2%$ ). Thus, galaxy bars play an important role in formation of broken disc structures. No strong variation in galaxy structure is detected with projected cluster-centric radius.

26 pages, 24 figures. Accepted for publication in MNRAS

Beyond Sérsic + exponential disc morphologies in the Coma Cluster

Abstract

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