Eugenia Díaz-Giménez

Consejo Nacional de Investigaciones Científicas y Técnicas

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Ariel Zandivarez

Consejo Nacional de Investigaciones Científicas y Técnicas

Antonela Taverna

Instituto de Astronomía Teórica y Experimental

G. A. Mamon

Institut d'Astrophysique de Paris

H. Muriel

Universidad Nacional de Córdoba

C. Mendes de Oliveira

Universidade de São Paulo

L. Raul Abramo

Universidade de São Paulo

María José Kanagusuku

Consejo Nacional de Investigaciones Científicas y Técnicas

Héctor J. Martínez

Universidad Nacional de Córdoba

M. V. Alonso

Universidad Nacional de Córdoba

Andrés N. Ruiz

Consejo Nacional de Investigaciones Científicas y Técnicas

Cooperative Institutions

Valongo Observatory

Universidade de São Paulo

Consejo Nacional de Investigaciones Científicas y Técnicas

Instituto de Astronomía Teórica y Experimental

National Observatory

Consejo Superior de Investigaciones Científicas

Universidad Nacional de Córdoba

Argentine National Observatory

Centre National de la Recherche Scientifique

Museu de Astronomia e Ciências Afins

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Fossil groups in the Millennium simulation Their environment and its evolution

Eugenia Díaz-Giménez Ariel Zandivarez Roger Proctor C. Mendes de Oliveira L. Raul Abramo

Context. Fossil systems are defined to be X-ray bright galaxy groups (or clusters) with a two-magnitude difference between their two brightest galaxies within half the projected virial radius, and represent an interesting extreme of the population of galaxy agglomerations. However, the physical conditions and processes leading to their formation are still poorly constrained. Aims. We compare the outskirts of fossil systems with that of normal groups to understand whether environmental conditions play a significant role in their formation. We study the groups of galaxies in both, numerical simulations and observations. Methods. We use a variety of statistical tools including the spatial cross-correlation function and the local density parameter Δ5 to probe differences in the density and structure of the environments of “normal” and “fossil” systems in the Millennium simulation. Results. We find that the number density of galaxies surrounding fossil systems evolves from greater than that observed around normal systems at z = 0.69, to lower than the normal systems by z = 0. Both fossil and normal systems exhibit an increment in their otherwise radially declining local density measure (Δ5) at distances of order 2.5 rvir from the system centre. We show that this increment is more noticeable for fossil systems than normal systems and demonstrate that this difference is linked to the earlier formation epoch of fossil groups. Despite the importance of the assembly time, we show that the environment is different for fossil and non-fossil systems with similar masses and formation times along their evolution. We also confirm that the physical characteristics identified in the Millennium simulation can also be detected in SDSS observations. Conclusions. Our results confirm the commonly held belief that fossil systems assembled earlier than normal systems but also show that the surroundings of fossil groups could be responsible for the formation of their large magnitude gap.

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Compact groups from semi-analytical models of galaxy formation – II. Different assembly channels

Monthly Notices of the Royal Astronomical Society (2021)

Eugenia Díaz-Giménez Ariel Zandivarez G. A. Mamon

ABSTRACT We study the formation of over 6000 compact groups (CGs) of galaxies identified in mock redshift-space galaxy catalogues built from semi-analytical models of galaxy formation (SAMs) run on the Millennium Simulations. We select CGs of four members in our mock SDSS galaxy catalogues and, for each CG, we trace back in time the real-space positions of the most massive progenitors of their four galaxies. By analysing the evolution of the distance of the galaxy members to the centre of mass of the group, we identify four channels of CG formation. The classification of these assembly channels is performed with an automatic recipe inferred from a preliminary visual inspection and based on the orbit of the galaxy with the fewest number of orbits. Most CGs show late assembly, with the last galaxy arriving on its first or second passage, while only 10–20 per cent form by the gradual contraction of their orbits by dynamical friction, and only a few per cent forming early with little subsequent contraction. However, a SAM from a higher resolution simulation leads to earlier assembly. Assembly histories of CGs also depend on cosmological parameters. At similar resolution, CGs assemble later in SAMs built on parent cosmological simulations of high density parameter. Several observed properties of mock CGs correlate with their assembly history: early-assembling CGs are smaller, with shorter crossing times, and greater magnitude gaps between their brightest two members, and their brightest galaxies have smaller spatial offsets and are more passive.

10.1093/mnras/stab535

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Fossil groups in the Millennium simulation

Astronomy and Astrophysics (2015)

María José Kanagusuku Eugenia Díaz-Giménez Ariel Zandivarez

We investigate the evolution of bright and faint galaxies in fossil and non-fossil groups. We used mock galaxies constructed based on the Millennium run simulation II. We identified fossil groups at redshift zero according to two different selection criteria, and then built reliable control samples of non-fossil groups that reproduce the fossil virial mass and assembly time distributions. The faint galaxies were defined as having r-band absolute magnitudes in the range [-16,-11]. We analysed the properties of the bright and faint galaxies in fossil and non-fossil groups during the past 8 Gyr. We observed that the brightest galaxy in fossil groups is typically brighter and more massive than their counterparts in control groups. Fossil groups developed their large magnitude gap between the brightest galaxies around 3.5 Gyr ago. The brightest galaxy stellar masses of all groups show a notorious increment at that time. By analysing the behaviour of the magnitude gap between the first and the second, third, and fourth ranked galaxies, we found that at earlier times, fossil groups comprised two large brightest galaxies with similar magnitudes surrounded by much fainter galaxies, while in control groups these magnitude gaps were never as large as in fossils. At early times, fossil groups in the faint population were denser than non-fossil groups, then this trend reversed, and finally they became similar at the present day. The mean number of faint galaxies in non-fossil systems increases in an almost constant rate towards later times, while this number in fossil groups reaches a plateau at $z\sim0.6$ that lasts $\sim 2$ Gyr, and then starts growing again more rapidly. The formation of fossil groups is defined at the very beginning of the groups according to their galaxy luminosity sampling, which could be determined by their merging rate at early times.

10.1051/0004-6361/201527269

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Systems of galaxies in the Sloan Digital Sky Survey: the fundamental plane

Monthly Notices of the Royal Astronomical Society (2005)

Eugenia Díaz-Giménez H. Muriel

We analyse a subsample of the galaxy groups recently obtained by Merchán & Zandivarez from the SDSS DR3 to study the fundamental plane and the mass-to-light ratio of galaxy groups. We find a fundamental plane given by LR∝R1.3σ0.7. We do not find differences when different dynamical states or redshift ranges are analysed. We find that the mass-to-light ratio increases with group mass as M/LR∝M0.36.

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Mass-to-light ratio

10.1111/j.1365-2966.2005.09650.x

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VizieR Online Data Catalog: Compact Groups of galaxies from 2MASX (Diaz-Gimenez+, 2012)

yCat (2013)

Eugenia Díaz-Giménez G. A. Mamon Marcela Pacheco C. Mendes de Oliveira M. V. Alonso

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