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Evidence shows properties of dark matter haloes may vary with large-scale environment. By studying the halo occupation distribution in cosmic voids it is possible to obtain useful information that can shed light on the subject. The history of the formation of the haloes and galaxies residing in these regions is likely to differ from the global behaviour given their extreme environment. We use two public access simulated galaxy catalogues constructed with different methods: a semi-analytical model and a hydrodynamic simulation. In both, we identify cosmic voids and we measure the halo occupation distribution inside these regions for different absolute magnitude thresholds. We compare these determinations with the overall results and we study the dependence of different characteristics of the voids. Also, we analyze the stellar content and the formation time of the haloes inside voids and confront the general halo population results. Inside the voids, we find a significantly different halo occupation distribution with respect to the general results. This is present in all absolute magnitude ranges explored. We obtain no signs of variation related to void characteristics indicating that the effects depend only on the density of the large-scale environment. Additionally, we find that the stellar mass content also differs within voids, which host haloes with less massive central galaxies (10%) as well as satellites with significantly lower stellar mass content (30%). Finally, we find a slight difference between the formation times of the haloes which are younger in voids than the average population. These characteristics indicate that haloes populating voids have had a different formation history, inducing significant changes on the halo occupation distribution., 11 pages and 12 figures. Submitted to A&A. Comments are welcome

We perform a statistical analysis of galaxies in pairs with a Λ-CDM scenario by using the chemical GADGET-2 of Scannapieco et al. (2005, MNRAS, 364, 552) in order to study the effects of galaxy interactions on colours and metallicities. We find that galaxy-galaxy interactions can produce a bimodal colour distribution where galaxies with significant recent star formation activity contribute mainly to blue colours. In the simulations, the colours and the fractions of recently formed stars of galaxies in pairs depend on their environments more strongly than those of galaxies without close companions, suggesting that interactions play an important role in galaxy evolution. If the metallicity of the stellar populations is used as the chemical indicator, we find that the simulated galaxies determine luminosity-metallicity and stellar mass-metallicity relations that do not depend on the presence of a close companion. However, in the case of the luminosity-metallicity relation, at a given level of enrichment, we detect a systematic displacement of the relation to brighter magnitudes for active star forming systems. Regardless of relative distance and current level of star formation (SF) activity, galaxies in pairs have stellar populations with higher level of enrichment than galaxies without a close companion. In the case of the gas component, this is no longer valid for galaxies in pairs with passive star formation that only show an excess of metals for very close pair members, consequence of an important recent past star-formation activity. In agreement with observations, the signature of gas inflows driven by interactions can be also detected in the lower mean O/H abundances measured in the central regions of galaxies in pairs. Our results suggest that interactions play a significant role in the determination of colour and chemical properties of galaxies in hierarchical clustering scenarios, although SN energy feedback is needed to achieve a full agreement., Facultad de Ciencias Astronómicas y Geofísicas

We compute the galaxy luminosity function in spectroscopically selected nearby groups and clusters. Our sample comprises 728 systems extracted from the third release of the Sloan Digital Sky Survey in the redshift range $0.03 < z < 0.06$ with virial mass range $10^{11}M_\odot < M_{vir} < 2\times 10^{14}M_\odot$. In order to compute the galaxy luminosity function, we apply a statistical background subtraction method following usually adopted techniques. In the $r$ band, the composite galaxy luminosity function shows a slope $\alpha=-1.3$ in the bright--end, and an upturn of the slope in the faint--end, $M_r\ga -18+5log(h)$, to slopes $-1.9, Comment: 8 pages, 10 figures, Submitted to Astronomy and Astrophysics