The ALHAMBRA survey: 2D analysis of the stellar populations in massive early-type galaxies at z < 0.3^⋆

¹ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Unidad Asociada al CSIC, Plaza San Juan 1, 44001 Teruel, Spain
e-mail: isanroman@cefca.es
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18080 Granada, Spain
³ Departamento de Física Teórica, Universidad Autonoma de Madrid (UAM-CSIC), 28049 Cantoblanco, Madrid, Spain
⁴ AstroParticule et Cosmologie (APC), Université Paris Diderot, CNRS/IN2P3, CEA/lrfu, Observatoire de Paris, Sorbonne Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
⁵ Instituto de Astrofísica de Canarias (IAC), vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁶ Institut de Ciències de l’Espai (IEEC-CSIC), Facultat de Ciències, Campus UAB, 08193 Bellaterra, Barcelona, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
⁸ Instituto de Física de Cantabria (CSIC-UC), 39005 Santander, Spain
⁹ Unidad Asociada Observatorio Astronómico (IFCA-UV), 46980 Paterna, Valencia, Spain
¹⁰ Ethiopian Space Science and Technology Institute (ESSTI), Entoto Observatory and Research Center (EORC), Astronomy and Astrophysics Research Division, PO Box 33679, Addis Ababa, Ethiopia
¹¹ Observatori Astronòmic, Universitat de València, C/ Catedràtic José Beltrán 2, 46980 Paterna, Spain
¹² Departament d’Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, Spain
¹³ Department of Theoretical Physics, University of the Basque Country UPV/EHU, 48080 Bilbao, Spain
¹⁴ IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
¹⁵ Departamento de Física Atómica, Molecular y Nuclear, Facultad de Física, Universidad de Sevilla, 41012 Sevilla, Spain
¹⁶ Instituto de Astrofísica, Universidad Católica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁷ Centro de Astro-Ingeniería, Universidad Católica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁸ Campus of International Excellence UAM+CSIC, Cantoblanco, 28049 Madrid, Spain

Received: 21 December 2016
Accepted: 25 July 2017

Abstract

We present a technique that permits the analysis of stellar population gradients in a relatively low-cost way compared to integral field unit (IFU) surveys. We developed a technique to analyze unresolved stellar populations of spatially resolved galaxies based on photometric multi-filter surveys. This technique allows the analysis of vastly larger samples and out to larger galactic radii. We derived spatially resolved stellar population properties and radial gradients by applying a centroidal Voronoi tessellation and performing a multicolor photometry spectral energy distribution fitting. This technique has been successfully applied to a sample of 29 massive (M_⋆ > 10^10.5M_⊙) early-type galaxies at z < 0.3 from the ALHAMBRA survey. We produced detailed 2D maps of stellar population properties (age, metallicity, and extinction), which allow us to identify galactic features. Radial structures were studied, and luminosity-weighted and mass-weighted gradients were derived out to 2–3.5 R_eff. We find that the spatially resolved stellar population mass, age, and metallicity are well represented by their integrated values. We find the gradients of early-type galaxies to be on average flat in age (∇log Age_L = 0.02 ± 0.06 dex/R_eff) and negative in metallicity (∇[Fe/H]_L = −0.09 ± 0.06 dex/R_eff). Overall,the extinction gradients are flat (∇A_v = −0.03 ± 0.09 mag/R_eff ) with a wide spread. These results are in agreement with previous studies that used standard long-slit spectroscopy, and with the most recent IFU studies. According to recent simulations, these results are consistent with a scenario where early-type galaxies were formed through major mergers and where their final gradients are driven by the older ages and higher metallicity of the accreted systems. We demonstrate the scientific potential of multi-filter photometry to explore the spatially resolved stellar populations of local galaxies and confirm previous spectroscopic trends from a complementary technique.