Ministerio de Ciencia, Innovación y Universidades Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

Astrophysics Research Projects

The Local Universe

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Galaxy Evolution in Clusters of Galaxies (P/300424)


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Jose Alfonso López Aguerri, Rafael Barrena Delgado, Casiana Muñoz Tuñón, Claudio Dalla Vecchia, Walter Boschin, Alejandro Lumbreras Calle, Lilian Domínguez Palmero

E.M. Corsini, L. Morelli, L. Costantin (Univ. Padova, Italy); J.M. Vílchez, J. Iglesias (IAA, Spain); C. del Burgo, E. Jiménez Bailon, S. Sanchez (UNAM, México); N. Napolitano (Obs. Capodimonte, Italy); M. Girardi, S. Borgani (Univ. Trieste, Italy); A. Biviano (Obs. Astronómico de Trieste, Italy); V. Debattista (Univ. Central Lancashire, UK); E. D'Onghia (Univ. Wisconsin-Madison, USA); M. Moles (Centro de Estudios de Física de Aragón, Spain); M. de Santos Lleo (ESA, Spain); M. Arnaboldi (ESO, Germany); O. Gerhard (MPIA, Germany); R. Sánchez Janssen (ATC, United Kingdom); M. Huertas-Company (Obs. Paris, France); A. Diaferio (Univ. Turin, Italy), V. Wild, A. M. Weijmans (Univ. St Andrews); S. Zarattini (Osservatorio Astronomico di Trieste, Italy); A. Aragon-Salamanca (Univ. Nottingha, R. Peletier (Kapteyn Institute, Netherlands); S. Trager (Kapteyn Institute, Netherlands); G. Dalton (Oxford University)


Galaxies in the universe can be located in different environments, some of them are isolated or in low density regions, they are usually called field galaxies. The others can be located in galaxy associations, going from loose groups to clusters or superclusters of galaxies. One of the foremost challenges of the modern Astrophysics is to achieve a complete theory about galaxy evolution. This theory should explain the relation between the environment and the galaxy evolution. Galaxy clusters are high density environments where galaxies interact one to each other and with the intracluster material (ICM). In addition, the cluster dynamics is drove by the high density and quantity of dark matter present in them. Therefore, galaxy clusters are complex systems with multiple components (galaxies, ICM, dark matter) which are tightly bounded. The mix of all these components, as well as their interactions, makes galaxy clusters ideal laboratories to study the different mechanisms which cause the different evolution of galaxies in this high density environments with respect to field galaxies.

The objective of this project is to study the formation and evolution of galaxies in these dense environments. We intend to understand in what environment each of the mechanisms proposed by numerical simulations to transform the galaxies dominates and how the evolution of the different types of galaxies (both bright and dwarf) occurs in the clusters. Quantifying observationally the efficiency of these mechanisms is not an easy task since many of them act at the same time, they do it in very different time scales, and in diverse regions of the cluster. However, there is a series of observational evidences that can be directly contrasted: i) morphological and structural distribution of the galaxies of the clusters; ii) luminosity function of galaxies in clusters; iii) diffuse light (quantity and distribution); iv) presence of galactic substructures within the clusters; v) spectro-photometric properties of dwarf and bright galaxies; vi) ICM properties. All these observables provide us with the necessary information to understand the relationship between environment and galactic evolution. These are the quantities we aim at measuring in this project for large samples of galaxy clusters.


The orbital structure of Abell 85

Galaxies in clusters are strongly affected by their environment. They evolve according to several physical mechanisms that are active in clusters. Their efficiency can strongly depend on the orbital configuration of the galaxies. Our aim is to analyse the orbits of the galaxies in the cluster Abell 85, based on the study of the galaxy velocity anisotropy parameter. We have solved the Jeans equation under the assumption that the galaxies in A 85 are collisionless objects, within the spherically symmetric gravitational potential of the virialized cluster. The mass of the cluster was estimated with X-ray and caustic analyses. We find that the anisotropy profile of the full galaxy population in A 85 is an increasing monotonic function of the distance from the cluster centre: on average, galaxies in the central region (r/r200 < 0.3) are on isotropic orbits, while galaxies in the outer regions are on radial orbits. We also find that the orbital properties of the galaxies strongly depend on their stellar colour. In particular, blue galaxies are on less radial orbits than red galaxies. The different families of cluster galaxies considered here have the pseudo phase-space density profiles Q(r) and Qr(r) consistent with the profiles expected in virialized dark matter haloes in N-body simulations. This result suggests that the galaxies in A 85 have reached dynamical equilibrium within the cluster potential. Our results indicate that the origin of the blue and red colours of the different galaxy populations is the different orbital shape rather than the accretion time.


  Fig 1. Anisotropy radial profile of blue and red dwarf galaxies of A 85. The shaded areas correspond to the uncertainties in the values of β. The dash red and full blue lines correspond to red dwarf and blue dwarf galaxies, respectively.

Are Fossil Groups Early-forming Galaxy Systems?

Using the Illustris cosmological simulation, we investigate the origin of fossil groups in the M200 = 1013 - 1013.5 M h-1 mass regime. We examine the formation of the two primary features of fossil groups: the large magnitude gap between their two brightest galaxies and their exceptionally luminous brightest group galaxy (BGG). For fossils and nonfossils identified at z = 0, we find no difference in their halo mass assembly histories at early times, departing from previous studies. However, we do find a significant difference in the recent accretion history of fossil and nonfossil halos; in particular, fossil groups show a lack of recent accretion and have in majority assembled 80% of their M200 (z=0) mass before z ~ 0.4. For fossils, massive satellite galaxies accreted during this period have enough time to merge with the BGG by the present day, producing a more massive central galaxy. In addition, the lack of recent group accretion prevents replenishment of the bright satellite population, allowing for a large magnitude gap to develop within the past few Gyr. We thus find that the origin of the magnitude gap and overmassive BGG of fossils in Illustris depends on the recent accretion history of the groups and merger history of the BGGs after their collapse at z ~ 1. This indicates that selecting galaxy groups by their magnitude gap does not guarantee obtaining either early-forming galaxy systems or undisturbed central galaxies.


  Fig. 2. Average normalized group M200 mass assembly history of fossils and nonfossils. The 1σerrors from 1000 bootstrap resamplings are shown.

Two-dimensional multi-component photometric decomposition of CALIFA galaxies

In this work we present a two-dimensional multi-component photometric decomposition of 404 galaxies from the Calar Alto Legacy Integral Field Area data release 3 (CALIFA-DR3). They represent all possible galaxies with no clear signs of interaction and not strongly inclined in the final CALIFA data release. Galaxies were modelled in the g, r, and i Sloan Digital Sky Survey (SDSS) images including, when appropriate, a nuclear point source, bulge, bar, and an exponential or broken disc component. We use a human-supervised approach to determine the optimal number of structures to be included in the fit. The dataset, including the photometric parameters of the CALIFA sample, is publicly released together with statistical errors and a visual analysis of the quality of each fit. The combination of this catalogue with the integral field spectroscopic information from the CALIFA survey produce an unique dataset to study the spatially resolved properties of galaxies in the local Universe. The analysis of the photometric components reveals a clear segregation of the structural composition of galaxies with stellar mass (see Fig. 1). At high masses (log (M⋆/M⊙) > 11), the galaxy population is dominated by galaxies modelled with a single Sérsic or a bulge+disc with a bulge-to-total (B/T) luminosity ratio B/T > 0.2. At intermediate masses (9.5 < log (M⋆/M⊙) < 11), galaxies described with bulge+disc but B/T < 0.2 are preponderant, whereas, at the low mass end (log (M⋆/M⊙) < 9.5), the prevailing population is constituted by galaxies modelled with either purediscs or nuclear point sources+discs (I.e., no discernible bulge). 


Fig. 3. Fraction of the final models used in the photometric decomposition as a function of stellar mass. Red circles represent single Sérsic models (B). Orange stars show models composed of a bulge+disc (BD) with B/T > 0.2. Green diamonds display models composed of a bulge+disc with with B/T < 0.2. Navy blue squares show models with no bulge but pure disc (D). Blue triangles represent models with a NPS+disc (NPSD). The five different combination of structures include broken profiles and/or bars. The number of galaxies in each bin is also shown.

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