Skip to main content

Research Repository

Advanced Search

Color gradients reflect an inside-out growth in early-type galaxies of the cluster MACS

Marian, V.; Ziegler, B.; Kuchner, U.; Verdugo, M.


V. Marian

B. Ziegler

M. Verdugo


Aims. Color gradients of galaxies are a powerful tool to resolve the variations of stellar populations within galaxies. We use this approach to explore the evolution of early-type galaxies in the core of the massive galaxy cluster MACS J1206.2-0847 at z = 0.44. Methods. For this study, we use imaging data in 12 filters (covering a wavelength range from 400 − 1600nm) from the Hubble Space Telescope provided by the CLASH survey, as well as additional spectral information from its follow-up program, CLASH-VLT. We perform multi-wavelength optimized model fitting using Galapagos-2 from the MegaMorph project to measure their photometric parameters (total integrated magnitudes, effective radii r e and Sérsic indices n). We use them to derive color gradients for the colors g 475 − I 814 , r 625 − Y 105 , I 814 − H 160 and Y 105 − H 160 at radii ranging between 0.1-2 r e for 79 early-type cluster galaxies. From synthetic spectral models that use simple star formation recipes, we infer ages and metallicities of the stellar population at different locations within each galaxy and characterize their influence on the radial color trends. Results. Early-type galaxies show a substantial decrease in effective radii r e with wavelength. We measure that galaxy sizes are ∼25 % smaller in the blue H 160 filter than in the red r 625 filter while maintaining constant (within 3σ) Sérsic index n with wavelength. We find negative color gradients in all colors with slopes ranging between-0.07 and-0.17 mag dex −1 and with no obvious dependence on total magnitude, stellar mass or location inside the cluster core. We explain the observed radial trends of color gradients as a result of both, the ages and metallicities of the respective stellar populations. Red galaxy cores are typically ∼3 Gyr older and metal-enriched, in comparison to galaxy outskirts of solar metallicity. Current adress: Article number, page 1 of 24 V. Marian et al.: Color-gradients reflect an inside-out growth in early-type cluster galaxies Conclusions. Our results support the predictions from hydrodynamical cosmological simulations that describe a passive evolution combined with an 'inside-out-growth' of early-type galaxies. In this scenario, galaxies assemble their stellar mass primarily onto the outskirts through the accretion of mass-poor satellites and thus manifest their observed trends of color-, metallicity-and age gradients.


Marian, V., Ziegler, B., Kuchner, U., & Verdugo, M. (2018). Color gradients reflect an inside-out growth in early-type galaxies of the cluster MACS. Astronomy and Astrophysics, 617, Article A34.

Journal Article Type Article
Acceptance Date Jun 1, 2018
Online Publication Date Sep 19, 2018
Publication Date Nov 22, 2018
Deposit Date Dec 20, 2022
Publicly Available Date Dec 22, 2022
Print ISSN 2329-1273
Electronic ISSN 1432-0746
Publisher Hans Publishers
Peer Reviewed Peer Reviewed
Volume 617
Article Number A34
Keywords galaxies: Sérsic profile; color; color gradient -galaxies: clusters: individual: MACS J12062-0847 -galaxies: evolution -galaxies: stellar content
Public URL
Publisher URL


You might also like

Downloadable Citations