14875226
Galaxy groups in the 2dF Galaxy Redshift Survey: a compactness analysis of groups
A comprehensive study on compactness has been carried out on the 2dF Galaxy Group Catalogue constructed by Merchan and Zandivarez. The compactness indices defined in this work take into account different geometrical constraints in order to explore a wide range of possibilities. Our results show that there is no clear distinction between groups with high and low levels of compactness when considering particular properties such as the radial velocity dispersion, the relative fraction of galaxies per spectral type, and the luminosity functions of their galaxy members. Studying the trend of the fraction of galaxies per spectral type as a function of the dimensionless crossing time, some signs of dynamical evolution are observed. From the comparison with previous works on compactness, we realize that special care should be taken for some compactness criteria definitions in order to avoid possible biases in the identification.
117082338
Review of the Second School on Cosmic Rays and Astrophysics
118070287
Cosmology, Relativity and Cosmic Rays
This is a short review of the evolution of ideas and concepts about the Universe. It is based on the introductory talk given on the 25 of July 2008 within the Third School on Cosmic Rays and Astrophysics held in Arequipa, Peru.
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.
18387503
Galaxy groups in the 2dF Galaxy Redshift Survey: effects of environment on star formation
We estimate the fraction of star-forming galaxies in a catalogue of groups, constructed from the 2dF Galaxy Redshift Survey by Merchan & Zandivarez. We use the η spectral type parameter of galaxies and subdivide the sample of galaxies in groups into four types depending on the values of the η parameter following Madgwick et al. We obtain a strong correlation between the relative fraction of galaxies with high star formation and the parent group virial mass. We find that even in the environment of groups with low virial mass M∼1013 M⊙ the star formation of their member galaxies is significantly suppressed. The relation between the fraction of early-type galaxies and the group virial mass obeys a simple power law spanning over three orders of magnitude in virial mass. Our results show quantitatively the way that the presence of galaxies with high star formation rates is inhibited in massive galaxy systems.
118112489
Air Shower Simulations
Air shower simulations are a vital part of the design of air shower experiments and the analysis of their data. We describe the basic features of air showers and explain why numerical simulations are the appropriate approach to model the shower simulation. The CORSIKA program, the standard simulation program in this field, is introduced and its features, performance and limitations are discussed. The basic principles of hadronic interaction models and some gerneral simulation techniques are explained. Also a brief introduction to the installation and use of CORSIKA is given.
14358536
Groups of galaxies: relationship between environment and galaxy properties
We analyse how the properties of galaxies in groups identified in the Sloan Digital Sky Survey depend on the environment. In particular, we study the relationship between galaxy properties and group mass and group-centric distance. Among the galaxy properties we have considered here, we find that the g - r colour is the most predictive parameter for group mass, while the most predictive pair of properties are g - r colour and r-band absolute magnitude. Regarding the position inside the systems, the g - r colour is the best tracer of group-centric distance and the most predictive pair of properties are g - r colour and spectral type taken together. These results remain unchanged when a subsample of high-mass groups is analysed. The same happens if the brightest group galaxies are excluded.
14588387
Galaxy groups in the 2dF Galaxy Redshift Survey: galaxy spectral type segregation in groups
The behaviour of the relative fraction of galaxies with different spectral types in groups is analysed as a function of projected local galaxy density and the group-centric distance. The group sample was taken from the 2dF Group Galaxy Calatogue constructed by Merchan & Zandivarez. Our group sample was constrained to have a homogeneous virial mass distribution with redshift. Galaxies belonging to this group sample were selected in order to minimize possible biases, such as preferential selection of high-luminosity objects. We find a clear distinction between high virial mass groups (MV≳ 1013.5 M⊙) and the less massive ones. While the massive groups show a significant dependence of the relative fraction of low star formation galaxies on local galaxy density and group-centric radius, groups with lower masses show no significant trends. We also cross-correlate our group subsample with the previously identified clusters, finding that this sample shows a very similar behaviour to that observed in the high virial mass group subsample.
118650558
Relating bars with the environment in the nearby Universe
We study the correlation between the fraction of barred spiral galaxies and environmental parameters of galaxies to understand in which environments the bars are more commonly found. For this purpose, we apply the Blanton et al. technique to a sample of spiral galaxies drawn from the Nair & Abraham catalogue. Our results agree with previous findings in which the fraction of barred galaxies is almost insensitive to environment.
17504603
Using the large scale quasar clustering to constrain flat quintessential universes
Aims. We search for the most suitable set of cosmological parameters that describes the observable universe. The search includes the possibility of quintessential flat universes, i.e., the analysis is restricted to the determination of the dimensionless matter density and the quintessential parameters, $\Omega_{\rm M}$ and w Q , respectively. Methods. Our study is focused on comparing the position of features at large scales in the density fluctuation field at different redshifts by analysing the evolution of the quasar two-point correlation function. We trace the density field fluctuations at large scales using a large and homogeneous sample of quasars (~38 000 objects with 0.3  ≲ z ≤  2.4 and a median z = 1.45) drawn from the Sloan Digital Sky Survey Data Release Six. The analysis relies on the assumption that, in the linear regime, the length scale of a particular feature should remain fixed at different times of the universe for the proper cosmological model. Our study does not assume any particular comoving length scale at which a feature should be found, but intends to perform a comparison for a wide range of scales instead. This is done by quantifying the amount of overlap among the quasar correlation functions at different times using a cross-correlation technique. Results. The most likely cosmological model is $\Omega_{\rm M}$ = 0.21 ± 0.02 and w Q = -0.93 ± 0.04, in agreement with previous studies. These constraints are the result of a good overall agreement of the correlation function at different redshifts over scales ~100–300 h -1 Mpc. Conclusions. Under the assumption of a flat cosmological model, our results indicate that we are living in a low density universe with a quintessential parameter greater than the one corresponding to a cosmological constant. This work also demonstrates that a large homogeneous quasar sample can be used to tighten the constraints upon cosmological parameters.
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.