117776477
Luminosity function of galaxies in groups in the SDSS DR7: the dependence on mass, environment and galaxy type
We perform an analysis of the luminosities of galaxies in groups in the SDSS DR7. We analyse the luminosity function (LF) as a function of group mass for different photometric bands, galaxy populations, galaxy positions within the groups, and the group surrounding large scale density. We find that M* brightens and alpha becomes steeper as a function of mass in all SDSS photometric bands, in agreement with previous results. From the analysis of different galaxy populations, we observe that different methods to split galaxy populations, based on the concentration index or the colour-magnitude diagram, produce quite different behaviours in the luminosity trends, mainly for alpha. These discrepancies and the trends with mass mentioned above are explained when analysing the LF of galaxies classified simultaneously according to their concentrations and colours. We find that only the red spheroids have a LF that strongly depends on group mass. Late type galaxies, whether blue or red, have luminosity functions that do not depend on group mass. The intrinsic change in the LF of spheroids and the varying number contributions of the different types explain all the observed trends with group mass. On the other hand, dividing the galaxy members in the inner and outer regions of the groups do not introduce a significant difference in the Schechter parameter trends, except for the characteristic absolute magnitude in the high group virial mass range (M>1x10^13 M_sun/h) which is an indication of luminosity segregation in massive groups. Finally, we also analyse the possible influence of the large scale surrounding environment on the LF. We find that galaxies inhabiting groups at low density regions experience more pronounced variations on the Schechter parameters as a function of groups mass, while galaxies in groups at high density regions show an almost constant behaviour.
16676496
Clustering and Light Profiles of Galaxies in the Environment of 20 Ultra-Steep-Spectrum Radio Sources
We have analyzed galaxy properties in the neighborhood of 20 ultra–steep-spectrum (USS) radio sources taken from the Westerbork in the Southern Hemisphere (WISH) catalog of De Breuck and coworkers. Galaxies in these USS fields were identified in deep observations that were carried out in the K' band using the OSIRIS imager at the CTIO 4 m telescope. We find a statistically significant signal of clustering around our sample of USS sources. The angular extension of the detected USS source–galaxy clustering is θc ~ 20'', corresponding to a spatial scale of ~120 h-1 kpc, assuming the sources are at z ~ 1 in an Ωm = 0.3, ΩΛ = 0.7 model universe. These results are in agreement with those obtained by Best for radio galaxy–galaxy correlation, and Best and coworkers for radio-loud AGN–galaxy correlation. We have also analyzed the light distribution of the galaxies by fitting Sersic's law profiles. Our results show no significant dependence of the galaxy shape parameters on the projected distance to the USS source.
17723357
Galaxy groups in the 2dF Galaxy Redshift Survey: luminosity and mass statistics
Several statistics are applied to groups and galaxies in groups in the Two degree Field Galaxy Redshift Survey. Firstly we estimate the luminosity functions for different subsets of galaxies in groups. The results are well fitted by a Schechter function with parameters M ∗ 5log(h) = 19.90 ± 0.03 and � = 1.13 ± 0.02 for all galaxies in groups, which is quite consistent with the results by Norberg et al. for field galaxies. When considering the four different spectral types defined by Madgwick et al. we find that the characteristic magnitude is typically brighter than in the field. We also observe a steeper value, � = 0.76± 0.03, of the faint end slope for low star-forming galaxies when compared with the corresponding field value. This steepening is more conspicuous, � = 1.10 ± 0.06, for those galaxies in more massive groups (M � 10 14 h −1 M⊙) than the obtained in the lower mass subset, � = 0.71 ± 0.04 (M < 10 14 h −1 M⊙). Secondly, we compute group total luminosities using Moore, Frenk & White prescriptions. We define a flux-limited group sample using a new statistical tool developed by Rauzy. The resulting group sample is used to determine the group luminosity function finding a good agreement with previous determinations and semianalytical models.
117908138
COMPARING GALAXY POPULATIONS IN COMPACT AND LOOSEGROUPS OF GALAXIES
Aims. We compare the properties of galaxies in compact groups, loose groups, and the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. Methods. We select samples of galaxies in compact groups, loose groups, and field galaxies from the Sloan Digital Sky Survey. We compare the properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass, and concentration. We also study the fraction of red and early-type galaxies, the luminosity function, the colourluminosity, and luminosity-size relations. Results. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of red and early-type galaxies is larger in compact groups. Galaxies in compact groups are, on average, systematically smaller in size, more concentrated, and have higher surface brightnesses than galaxies in the field and in loose groups. At a fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller in size. Conclusions. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups, owing to the typically high densities and small velocity dispersions of these environments, which could explain the large fraction of red and early-type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.
15285334
On the luminosity function of galaxies in groups in the Sloan Digital Sky Survey
Using galaxy groups identified in the fourth data release of the Sloan Digital Sky Survey (SDSS), we compute the luminosity function for several subsamples of galaxies in groups. In all cases, the luminosity functions are well described by Schechter functions, down to the faintest magnitudes we probe, M0.1r - 5 log(h) ~ -16. For the general luminosity function of galaxies in groups in the five SDSS bands, we observe that the characteristic magnitude is brighter at ~0.5 mag than those obtained for field galaxies by Blanton et al. Even when the observed faint-end slope is steeper in galaxy groups, it is statistically comparable with the field value. We analyze the dependence of the galaxy luminosity function with system masses, finding two clear trends: a continuous brightening of the characteristic magnitude and a steepening of the faint-end slope as mass increases. The results in 0.1g, 0.1r, 0.1i, and 0.1z bands show the same behavior. Using the u - r color to split the galaxy sample into red and blue galaxies, we show that the changes observed as a function of the system mass are mainly seen in the red, passively evolving galaxy population, while the luminosities of blue galaxies remain almost unchanged with mass. Finally, we observe that groups having an important luminosity difference between the two brightest galaxies of a system show a steeper faint-end slope than the other groups. Our results can be interpreted in terms of galaxy mergers as the main driving force behind galaxy evolution in groups.
119183957
The environmental dependence of the red galaxy sequence
The dependence of the sequence of red galaxies (RS) with the environment is investigated using volume-limited samples of field, group and cluster galaxies drawn from the Sloan Digital Sky Survey. Our work focuses on studying the mean colour (μ R ) and the scatter (σ R ) of the RS as a function of 0.1 r-band absolute magnitude in different environments characterized either by the mass of the system in which the galaxies are located or by the distance to the system's centre. These results are compared with the RS of field galaxies. The same analysis is carried out using subsamples of red galaxies classified as early types according to their concentration parameter. For a given luminosity, μ R of field galaxies is bluer and σ R is larger than their group and cluster counterparts irrespective of mass and position within the systems. Among systems of galaxies, high-mass groups and clusters have the reddest μ R and the smallest σ R . These differences almost disappear when red early-type galaxies alone are considered. Galaxies in the core and in the outskirts of groups have similar μ R , whereas galaxies in clusters show a strong dependence on cluster-centric distance, the inner galaxies being the reddest objects. Red early-type galaxies in the outskirts of clusters have σ R values as large as those of field galaxies, while galaxies in the inner regions of clusters have lower values, comparable to those of group galaxies. We find that bright red early-type galaxies have reached nearly the same evolutionary stage in all environments. Our results suggest that, although effective in drifting galaxies of intermediate luminosities towards redder colours, the cluster environment is not necessary to populate the RS. We propose a scenario in which the RS in massive systems is populated by two different star formation history galaxies: red early-type galaxies that formed the bulk of their stars during the early stages of massive halo assembly and red galaxies that passed most of their lives inhabiting poor groups or the field and fell into massive systems at lower redshifts.
56302496
Design, analysis, and fabrication of the APT cavities
The design for the superconducting cavities of the high-energy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.
122910167
Implications of Yukawa textures in the neutral Higgs decays within the 2HDM–III
We discuss the implications of assuming a four–zero Yukawa ansatz for the neutral Higgs decays, within the context of the general 2–Higgs Doublet Model of type III. We begin by presenting a detailed analysis of the neutral Higgs boson couplings with fermions and gauge bosons and the resulting effects on its decays. In particular, we are interested on the possibility of the neutral Higgs boson production in current colliders.
54807942
Self-similarity in a Kantowski-Sachs universe with a string cloud
We study a cosmological model with very simple solutions characterized by string clouds. Assuming self-similar symmetry for a Kantowski- Sachs spacetime we study the gravitational effects of the cosmic strings. It is also assumed that the primitive universe enters in a false vacuum-dominated era, accelerating the expansion in a time period of the order of 10 -35 sec (a phase transition), satisfying all the energy conditions. Finally, we examine the possibility that in the last stages of this evolution, the geometry of the universe could be flat.