High redshift ellipticals: prospects for the VLT

The results and the present limits of the observations of high-z ellipticals are discussed in the framework of VLT imminent and future instruments.Comment: 6 pages, 3 figures, to appear in the proceedings of the ESO workshop 'Scientific Drivers for ESO Future VLT/VLTI Instrumentation', Garching, June 200

Conformant Planning via Symbolic Model Checking

We tackle the problem of planning in nondeterministic domains, by presenting a new approach to conformant planning. Conformant planning is the problem of finding a sequence of actions that is guaranteed to achieve the goal despite the nondeterminism of the domain. Our approach is based on the representation of the planning domain as a finite state automaton. We use Symbolic Model Checking techniques, in particular Binary Decision Diagrams, to compactly represent and efficiently search the automaton. In this paper we make the following contributions. First, we present a general planning algorithm for conformant planning, which applies to fully nondeterministic domains, with uncertainty in the initial condition and in action effects. The algorithm is based on a breadth-first, backward search, and returns conformant plans of minimal length, if a solution to the planning problem exists, otherwise it terminates concluding that the problem admits no conformant solution. Second, we provide a symbolic representation of the search space based on Binary Decision Diagrams (BDDs), which is the basis for search techniques derived from symbolic model checking. The symbolic representation makes it possible to analyze potentially large sets of states and transitions in a single computation step, thus providing for an efficient implementation. Third, we present CMBP (Conformant Model Based Planner), an efficient implementation of the data structures and algorithm described above, directly based on BDD manipulations, which allows for a compact representation of the search layers and an efficient implementation of the search steps. Finally, we present an experimental comparison of our approach with the state-of-the-art conformant planners CGP, QBFPLAN and GPT. Our analysis includes all the planning problems from the distribution packages of these systems, plus other problems defined to stress a number of specific factors. Our approach appears to be the most effective: CMBP is strictly more expressive than QBFPLAN and CGP and, in all the problems where a comparison is possible, CMBP outperforms its competitors, sometimes by orders of magnitude

Formal Design of Asynchronous Fault Detection and Identification Components using Temporal Epistemic Logic

Autonomous critical systems, such as satellites and space rovers, must be able to detect the occurrence of faults in order to ensure correct operation. This task is carried out by Fault Detection and Identification (FDI) components, that are embedded in those systems and are in charge of detecting faults in an automated and timely manner by reading data from sensors and triggering predefined alarms. The design of effective FDI components is an extremely hard problem, also due to the lack of a complete theoretical foundation, and of precise specification and validation techniques. In this paper, we present the first formal approach to the design of FDI components for discrete event systems, both in a synchronous and asynchronous setting. We propose a logical language for the specification of FDI requirements that accounts for a wide class of practical cases, and includes novel aspects such as maximality and trace-diagnosability. The language is equipped with a clear semantics based on temporal epistemic logic, and is proved to enjoy suitable properties. We discuss how to validate the requirements and how to verify that a given FDI component satisfies them. We propose an algorithm for the synthesis of correct-by-construction FDI components, and report on the applicability of the design approach on an industrial case-study coming from aerospace.Comment: 33 pages, 20 figure

On the robustness of the Hβ\beta Lick index as a cosmic clock in passive early-type galaxies

We examine the H$\beta$ Lick index in a sample of $\sim 24000$ massive ($\rm log(M/M_{\odot})>10.75$) and passive early-type galaxies extracted from SDSS at z<0.3, in order to assess the reliability of this index to constrain the epoch of formation and age evolution of these systems. We further investigate the possibility of exploiting this index as "cosmic chronometer", i.e. to derive the Hubble parameter from its differential evolution with redshift, hence constraining cosmological models independently of other probes. We find that the H$\beta$ strength increases with redshift as expected in passive evolution models, and shows at each redshift weaker values in more massive galaxies. However, a detailed comparison of the observed index with the predictions of stellar population synthesis models highlights a significant tension, with the observed index being systematically lower than expected. By analyzing the stacked spectra, we find a weak [NII]$\lambda6584$ emission line (not detectable in the single spectra) which anti-correlates with the mass, that can be interpreted as a hint of the presence of ionized gas. We estimated the correction of the H$\beta$ index by the residual emission component exploiting different approaches, but find it very uncertain and model-dependent. We conclude that, while the qualitative trends of the observed H$\beta$-z relations are consistent with the expected passive and downsizing scenario, the possible presence of ionized gas even in the most massive and passive galaxies prevents to use this index for a quantitative estimate of the age evolution and for cosmological applications.Comment: 20 pages, 11 figures, 1 table. Accepted for publication in MNRAS Main Journa

Satisfiability Modulo Transcendental Functions via Incremental Linearization

In this paper we present an abstraction-refinement approach to Satisfiability Modulo the theory of transcendental functions, such as exponentiation and trigonometric functions. The transcendental functions are represented as uninterpreted in the abstract space, which is described in terms of the combined theory of linear arithmetic on the rationals with uninterpreted functions, and are incrementally axiomatized by means of upper- and lower-bounding piecewise-linear functions. Suitable numerical techniques are used to ensure that the abstractions of the transcendental functions are sound even in presence of irrationals. Our experimental evaluation on benchmarks from verification and mathematics demonstrates the potential of our approach, showing that it compares favorably with delta-satisfiability /interval propagation and methods based on theorem proving

An improved measurement of baryon acoustic oscillations from the correlation function of galaxy clusters at z∼0.3z \sim 0.3

We detect the peak of baryon acoustic oscillations (BAO) in the two-point correlation function of a spectroscopic sample of $25226$ clusters selected from the Sloan Digital Sky Survey. Galaxy clusters, as tracers of massive dark matter haloes, are highly biased structures. The linear bias $b$ of the sample considered in this work, that we estimate from the projected correlation function, is $b \sigma_8 = 1.72 \pm 0.03$. Thanks to the high signal in the cluster correlation function and to the accurate spectroscopic redshift measurements, we can clearly detect the BAO peak and determine its position, $s_p$, with high accuracy, despite the relative paucity of the sample. Our measurement, $s_p = 104 \pm 7 \, \mathrm{Mpc} \, h^{-1}$, is in good agreement with previous estimates from large galaxy surveys, and has a similar uncertainty. The BAO measurement presented in this work thus provides a new strong confirmation of the concordance cosmological model and demonstrates the power and promise of galaxy clusters as key probes for cosmological applications based on large scale structures.Comment: 10 pages, 7 figure, accepted for publication in MNRA

Exploring the formation and evolution of massive ellipticals with Extremely Red Objects

Extremely Red Objects (EROs) provide the important possibility to shed light on the formation and evolution of the present-day massive ellipticals. On one hand, they allow to select z>1 old passively evolving spheroidals and to compare their abundance with the predictions of galaxy formation scenarios. On the other hand, they provide the possibility to find dust obscured starbursts, a fraction of which may trace the formation of proto-ellipticals at z>2. In this paper, the most recent results on EROs are reviewed and the main implications discussed.Comment: 5 pages, 1 figure, invited contribution, to appear in the proceedings of the Deep Fields Workshop, Garching, October 200