arXiv subjects

Christian Marinoni

Publications and source records attributed to Christian Marinoni.

42 records · Page 3Linked to original sources

arXiv2001

3D Identification and Reconstruction of z~1 Clusters: Prospects for the DEEP2 Redshift Survey

We have developed a geometrical method based on 3D Voronoi polyhedra and Delaunay tessellation for identifying and reconstructing clusters of galaxies in the next generation of deep, flux-limited redshift surveys. We here describe this algorithm and tests of it using mock catalogs that simulate the DEEP2/DEIMOS redshift survey, which will begin observations in the Spring of 2002 and will provide a detailed three dimensional map of the large scale structure up to redshift 1.5.

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arXiv2001

Spectral Reduction Software for the DEEP2 Redshift Survey

The DEEP2/DEIMOS redshift survey, which will begin observing in the Spring of 2002, will gather high quality spectra on ~60000 galaxies in order to study the evolution of the properties and large scale clustering of galaxies at z~1. The data rate from DEIMOS will be in excess of 1 Gbyte/hour, and it is therefore imperative to employ completely automated data reduction techniques to manage the analysis. We here describe aspects of our data pipeline, which will make extensive use of B-splines for the sky-subtraction stage and for the combination of multiple frames.

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arXiv2001

The Optical Luminosity Function of Virialized Systems

We determine the optical luminosity function of virialized systems over the full range of density enhancements, from single galaxies to clusters of galaxies. The analysis is based on galaxy systems identified from the Nearby Optical Galaxy (NOG) sample, which is the largest, all-sky catalog of objectively- identified bound objects presently available. We find that the B-band luminosity function of systems is insensitive to the choice of the group-finding algorithms and is well described, over the absolute-magnitude range -24.5 < M < -18.5, by a Schechter function with alpha=-1.4, Mstar=-23.1 and phistar=4.8 10^{-4} Mpc^-3 The characteristic luminosity of virialized systems is ~3 times brighter than that of the luminosity function of galaxies. Our results show that half of the luminosity of the universe is generated in systems with L<2.9 Lstar and that 10% of the overall luminosity density is supplied by systems with L>30 Lstar. We find a significant environmental dependence in the luminosity function of systems, in the sense that overdense regions, as measured on scales of 5 Mpc, preferentially host brighter, and presumably more massive, virialized systems.

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arXiv2001

The Mass-To-Light Function of Virialized Systems and the Relationship Between Their Optical and X-ray Properties

We compare the B-band luminosity function of virialized halos with the mass function predicted by the Press-Schechter theory in cold dark matter cosmogonies. We find that all cosmological models fail to match our results if a constant mass-to-light ratio is assumed. In order for these models to match the faint end of the luminosity function, a mass-to-light ratio decreasing with luminosity as $L^{-0.5\pm 0.06}$ is required. For a $Λ$CDM model, the mass-to-light function has a minimum of $\sim 100 h^{-1}_{75}$ in solar units in the $B$-band, corresponding to $\sim 25%$ of the baryons in the form of stars, and this minimum occurs close to the luminosity of an $L^*$ galaxy. At the high-mass end, the $Λ$CDM model requires a mass-to-light ratio increasing with luminosity as $L^{+0.5 \pm 0.26}$. We also derive the halo occupation number, i.e. the number of galaxies brighter than $\lgal^*$ hosted in a virialized system. We find that the halo occupation number scales non-linearly with the total mass of the system, $N\sbr{gal}(>\lgal^*) \propto m^{0.55\pm0.026}$ or the $Λ$CDM model. We find a break in the power-law slope of the X-ray-to-optical luminosity relation, independent of the cosmological model. This break occurs at a scale corresponding to poor groups. In the $Λ$CDM model, the poor-group mass is also the scale at which the mass-to-light ratio of virialized systems begins to increase. This correspondence suggests a physical link between star formation and the X-ray properties of halos, possibly due to preheating by supernovae or to efficient cooling of low-entropy gas into galaxies.

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arXiv2001

Measuring the Cosmic Equation of State with Galaxy Clusters in the DEEP2 Redshift Survey

The abundances of groups and clusters of galaxies are expected to have changed substantially since high redshift, with the strength of this evolution dependent upon fundamental cosmological parameters. Upcoming large redshift surveys of distant galaxies will make it possible to measure these quantities at z~1; when combined with the results of local redshift surveys currently underway, the evolution of cluster abundances may be determined. The DEEP2 Redshift Survey, planned to begin in Spring 2002, is particularly well-suited for this work because of the high spectroscopic resolution to be used; velocity dispersions of groups will be readily measurable. In this paper, we determine the constraints on dark energy models that counts of DEEP2 clusters should provide. We find that comparing cosmological models using the simultaneous distribution of clusters in both velocity dispersion and redshift yields significantly stronger constraints than the redshift distribution alone. The method can be made more powerful by employing a value of the fluctuation amplitude sigma_8 determined with upcoming techniques (external to DEEP2) that have no Omega_m degeneracy. The equation-of-state parameter for dark energy models, w=P/rho, can then be measured to ~0.1 from observations of clusters alone.

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arXiv2001

The redshift-space two-point correlation functions of galaxies and groups in the Nearby Optical Galaxy sample

We use the two-point correlation function in redshift space, $ξ(s)$, to study the clustering of the galaxies and groups of the Nearby Optical Galaxy (NOG) sample, which is a nearly all-sky, complete, magnitude-limited sample of $\sim$7000 bright and nearby optical galaxies. The correlation function of galaxies is well described by a power law, $ξ(s)=(s/s_0)^{-γ}$, with slope $γ\sim1.5$ and $s_0\sim6.4 h^{-1}$Mpc (on scales $2.7 - 12 h^{-1}$Mpc), in agreement with previous results of several redshift surveys of optical galaxies. We confirm the existence of morphological segregation between early- and late-type galaxies and, in particular, we find a gradual decreasing of the strength of clustering from the S0 galaxies to the late-type spirals, on intermediate scales. Furthermore, luminous galaxies turn out to be more clustered than dim galaxies. The luminosity segregation, which is significant for both early- and late-type objects, starts to become appreciable only for galaxies brighter than $M_B\sim -19.5 + 5 \log h$ ($\sim 0.6 L^*$) and is independent on scale. The NOG group correlation functions are characterized by $s_0$-values ranging from $\sim 8 h^{-1}$ Mpc (for groups with at least three members) to $\sim10 h^{-1}$ Mpc (for groups with at least five members). The degree of group clustering depends on the physical properties of groups. Specifically, groups with greater velocity dispersions, sizes and masses tend to be more clustered than those with lower values of these quantities.

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