arXiv subjects

Bianca Garilli

Publications and source records attributed to Bianca Garilli.

24 records · Page 2Linked to original sources

arXiv2010

Designing a space-based galaxy redshift survey to probe dark energy

A space-based galaxy redshift survey would have enormous power in constraining dark energy and testing general relativity, provided that its parameters are suitably optimized. We study viable space-based galaxy redshift surveys, exploring the dependence of the Dark Energy Task Force (DETF) figure-of-merit (FoM) on redshift accuracy, redshift range, survey area, target selection, and forecast method. Fitting formulae are provided for convenience. We also consider the dependence on the information used: the full galaxy power spectrum P(k, P(k) marginalized over its shape, or just the Baryon Acoustic Oscillations (BAO). We find that the inclusion of growth rate information (extracted using redshift space distortion and galaxy clustering amplitude measurements) leads to a factor of ~ 3 improvement in the FoM, assuming general relativity is not modified. This inclusion partially compensates for the loss of information when only the BAO are used to give geometrical constraints, rather than using the full P(k) as a standard ruler. We find that a space-based galaxy redshift survey covering ~20,000 deg^2 over 0.5< z < 2 with σ_z/(1+z)<= 0.001 exploits a redshift range that is only easily accessible from space, extends to sufficiently low redshifts to allow both a vast 3-D map of the universe using a single tracer population, and overlaps with ground-based surveys to enable robust modeling of systematic effects. We argue that these parameters are close to their optimal values given current instrumental and practical constraints.

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arXiv2007

Visualization, Exploration and Data Analysis of Complex Astrophysical Data

In this paper we show how advanced visualization tools can help the researcher in investigating and extracting information from data. The focus is on VisIVO, a novel open source graphics application, which blends high performance multidimensional visualization techniques and up-to-date technologies to cooperate with other applications and to access remote, distributed data archives. VisIVO supports the standards defined by the International Virtual Observatory Alliance in order to make it interoperable with VO data repositories. The paper describes the basic technical details and features of the software and it dedicates a large section to show how VisIVO can be used in several scientific cases.

astro-ph↗

arXiv2001

The VIMOS Mask Preparation Software

The main scientific characteristic of VIMOS (VIsible Multi Object Spectrograph, to be placed on ESO Very Large Telescope) is its high multiplexing capability, allowing astronomers to obtain up to 800 spectra per exposure. To fully exploit such a potential a dedicated tool, the VIMOS Mask Preparation Software (MPS), has been designed. The MPS provides the astronomer with tools for the selection of the objects to be spectroscopically observed, including interactive object selection, handling of curved slits, and an algorithm for automatic slit positioning that derives the most effective solution in terms of number of object selected per field. The slit positioning algorithm must take into account both the initial list of user's preferred objects, and the constraints imposed either by the instrument characteristics or by the requirement of having easily reduceable data. The number of possible slit combinations in a field is in any case very high (10^73), and the task of slits maximization cannot be solved through a purely combinational approach. We have introduced an innovative approach, based on the analysis of the function (Number of slits)/(slit length) vs. (slit length). The algorithm has been fully tested with good results, and it will be distributed to the astronomical community for the observation preparation phase.

astro-ph↗

arXiv1998

Composite luminosity function of cluster galaxies

We constructed the composite Luminosity Function (LF) of cluster galaxies in the g,r and i bands from the photometry of a mixed (Abell and X-ray selected) sample of the cores of 65 clusters, ranging in redshift from 0.05 to 0.25. The composite LF has been obtained from complete samples of ~2200 galaxies in the magnitude range -23<M<-17.5 (-18 in i). Cluster membership has been determined on the basis of color-color plots for each cluster and the resulting outlier counts have been checked against field counts in the same bands. We find that the galaxy density of the environment determines the shape of the LF, in the sense that bright galaxies are more abundant in dense clusters.

astro-ph↗

arXiv1997

Two-Color Surface Photometry of Brightest Cluster Members

The Gunn g, r and i CCD images of a representative sample of 17 Brightest Cluster Galaxies (BCM) have been analyzed in order to derive surface brightness and color profiles, together with geometrical parameters like eccentricity and position angle. The sample includes both X-ray and optically selected clusters, ranging in redshift from z=0.049 to z=0.191. We find that BCMs are substantially well described by de Vaucouleurs' law out to radii of $\sim 60-80$ kpc, and that color gradients are generally absent. Only in two cases we find a surface brightness excess with respect to the $r^{1/4}$ law, which for A150 is coupled with a change in the $g-r$ color. The rest frame colors of BCMs do not show any intrinsic dispersion. By parametrizing the environment with the local galaxy number density, we find that it is correlated with the BCM extension, i.e. BCMs with larger effective radii are found in denser environments.

astro-ph↗

arXiv1996

Photometric properties of clusters of galaxies

We report the first results of a long term program aimed at investigating the photometric properties of the cores of Abell and X-ray selected (EMSS, \cite{emss}) clusters of galaxies. We observed 77 clusters of galaxies in the redshift range $0.05\leq z \leq 0.25$ in the Gunn $g$, $r$ and $i$ filters: in this paper we present the data on 59 clusters with good absolute photometry and on another group of 8 clusters with acceptable relative photometry. For all these clusters we show color--magnitude diagrams in the two colors: when, as in most cases, the early type galaxy sequence is identifiable, we compare it with the expectation from the Virgo c--m relation (\cite{vs}) and find that the Virgo relation holds to $z\sim0.2$. We do not find any sign of active evolution in cluster galaxies since that epoch, nor in the percentage of blue galaxies or in the early type galaxy colors, if we accept that the scatter is of the order of 0.2--0.3 mag with respect to the expectations on the basis of standard k--corrections. We point out the presence of a certain number of anomalously red galaxies in the $r-i$ color, which are too red with respect to their $g-r$ color to be normal field galaxies at a redshift higher than the cluster one. Finally we briefly compare a few properties of the two subsamples of optically selected and X--ray selected clusters.

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