arXiv subjects

M. Makler

Publications and source records attributed to M. Makler.

46 records · Page 3Linked to original sources

arXiv2011

The Dark Energy Survey: Prospects for Resolved Stellar Populations

Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2x10^8 stars will be sampled in DES grizY filters. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from 3 to 8 times larger than SDSS. The faint end of the main-sequence will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar IMF will be constrained to within a few hundredth dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog ϕ(m) / dlog m ~ 0.1$. About 3x10^4 brown dwarf and at least 7.6x10^5 white dwarf candidates will be selected, the latter embedded into the thick disk and halo. The stellar halo flattening will also be constrained to within a few percent. DES will probe the main sequence of new Milky Way satellites and halo clusters for distances out to ~ 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality.

astro-ph.GA↗

arXiv2007

A Systematic Search for High Surface Brightness Giant Arcs in a Sloan Digital Sky Survey Cluster Sample

We present the results of a search for gravitationally-lensed giant arcs conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of the images and an automated search were performed and no arcs were found. This result is used to set an upper limit on the arc probability per cluster. We present selection functions for our survey, in the form of arc detection efficiency curves plotted as functions of arc parameters, both for the visual inspection and the automated search. The selection function is such that we are sensitive only to long, high surface brightness arcs with g-band surface brightness mu_g < 24.8 and length-to-width ratio l/w > 10. Our upper limits on the arc probability are compatible with previous arc searches. Lastly, we report on a serendipitous discovery of a giant arc in the SDSS data, known inside the SDSS Collaboration as Hall's arc.

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arXiv2006

Is it possible to observationally distinguish adiabatic Quartessence from LambdaCDM?

The equation of state (EOS) in quartessence models interpolates between two stages: $p\simeq 0$ at high energy densities and $p\approx -ρ$ at small ones. In the quartessence models analyzed up to now, the EOS is convex, implying increasing adiabatic sound speed ($c_{s}^{2}$) as the energy density decreases in an expanding Universe. A non-negligible $c_{s}^{2}$ at recent times is the source of the matter power spectrum problem that plagued all convex (non-silent) quartessence models. Viability for these cosmologies is only possible in the limit of almost perfect mimicry to $Λ$CDM. In this work we investigate if similarity to $Λ$CDM is also required in the class of quartessence models whose EOS changes concavity as the Universe evolves. We focus our analysis in the simple case in which the EOS has a step-like shape, such that at very early times $p\simeq0$, and at late times $p\simeq const<0$. For this class of models a non-negligible $c_{s}^{2}$ is a transient phenomenon, and could be relevant only at a more early epoch. We show that agreement with a large set of cosmological data requires that the transition between these two asymptotic states would have occurred at high redshift ($z_t\gtrsim38$). This leads us to conjecture that the cosmic expansion history of any successful non-silent quartessence is (practically) identical to the $Λ$CDM one.

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arXiv2006

Supernovae observations and cosmic topology

Two fundamental questions regarding our description of the Universe concern the geometry and topology of its 3-dimensional space. While geometry is a local characteristic that gives the intrinsic curvature, topology is a global feature that characterizes the shape and size of the 3-space. The geometry constrains, but does not dictate the the spatial topology. We show that, besides determining the spatial geometry, the knowledge of the spatial topology allows to place tight constraints on the density parameters associated with dark matter ($Ω_m$) and dark energy ($Ω_Λ$). By using the Poincaré dodecahedral space as the observable spatial topology, we reanalyze the current type Ia supenovae (SNe Ia) constraints on the density parametric space $Ω_{m} - Ω_Λ$. From this SNe Ia plus cosmic topology analysis, we found best fit values for the density parameters, which are in agreement with a number of independent cosmological observations.

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arXiv2005

Constraints from the Detection of Cosmic Topology on the Generalized Chaplygin Gas

Despite our present-day inability to predict the topology of the universe one may expect that we should be able to detect it in the near future, given the increasing accuracy in the astro-cosmological observations. Motivated by this, we examine to what extent a possible detection of a non-trivial topology of a low curvature (Omega_0 ~ 1) universe, suggested by a diverse set of current observations, may be used to place constraints on the matter content of the universe, focusing our attention on the generalized Chaplgygin gas (GCG) model, which unifies dark matter and dark energy in a single matter component. We show that besides constraining the GCG free parameters, the detection of a nontrivial topology also allows to set bounds on the total density parameter Omega_0. We also study the combination of the bounds from the topology detection with the limits that arise from current data on 194 SNIa, and show that the determination of a given nontrivial topology sets complementary bounds on the GCG parameters (and on Omega_0) to those obtained from the SNIa data.

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arXiv2005

Detectability of Cosmic Topology in Generalized Chaplygin Gas Models

If the spatial section of the universe is multiply connected, repeated images or patterns are expected to be detected observationally. However, due to the finite distance to the last scattering surface, such pattern repetitions could be unobservable. This raises the question of whether a given cosmic topology is detectable, depending on the values of the parameters of the cosmological model. We study how detectability is affected by the choice of the model itself for the matter-energy content of the universe, focusing our attention on the generalized Chaplygin gas (GCG) model for dark matter and dark energy unification, and investigate how the detectability of cosmic topology depends on the GCG parameters. We determine to what extent a number of topologies are detectable for the current observational bounds on these parameters. It emerges from our results that the choice of GCG as an alternative to the $Λ$CDM matter-energy content model has an impact on the detectability of cosmic topology.

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arXiv2005

Extended Born-Infeld Dynamics and Cosmology

We introduce an extension of the Born-Infeld action for a scalar field and show that it can act as unifying-dark-matter, providing an explanation for both structure formation and the accelerated expansion of the universe. We investigate the cosmological dynamics of this theory in a particular case, referred as the "Milne-Born-Infeld" (MBI) Lagrangian. We show that this model, whose equation of state has effectively a single free parameter, is consistent with recent type Ia supernovae data, providing a fit as good as for the $Λ$CDM model with the same number of degrees of freedom. Furthermore, this parameter is tightly constrained by current data, making the model easily testable with other observables. Contrary to previous candidates for unifying-dark-matter, the sound velocity of the MBI model is vanishing both close to the dark matter state as well as near the cosmological constant state. This could avoid the problems on the matter power spectrum that were present in previous adiabatic dark-matter/dark-energy unification models. We also present a short discussion on the causal propagation in nonlinear scalar field theories such as the one proposed here.

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arXiv2005

Matter Power Spectrum for Convex Quartessence

The possibility of unifying dark-matter and dark-energy has recently attracted considerable interest. In this so called quartessence scenario, a single component is responsible for both the clustering of matter and the accelerated expansion of the universe. A model archetype for such scenario is provided by the Chaplygin gas. Although this model is in agreement with the data on the expansion history, problems arise in the power spectrum of density fluctuations for adiabatic perturbations. In this contribution we consider other quartessence models and confirm that instabilities and oscillations in the matter power spectrum are a characteristic of more generic quartessence models, namely those with a convex equation of state. We show that, as in the Chaplygin case, this kind of problem can be solved by considering intrinsic non-adiabatic perturbations such that, as an initial condition, the perturbed fluid is gradient pressure free. We also discuss how the problems of adiabatic quartessence can be circumvented by other types of equations of state.

astro-ph↗

arXiv2004

Skewness as a test for Quartessence

Quartessence is one of the alternatives to Lambda-CDM that has lately attracted considerable interest. According to this unifying dark matter/energy scenario, the Universe evolved from an early non-relativistic matter-dominated phase to a more recent accelerated expansion phase, driven by a single fluid component. Recently, it has been shown that some problems of the quartessence model, such as the existence of instabilities and oscillations in the matter power spectrum, can be avoided if a specific type of intrinsic entropy perturbation is considered. In the present article we explore the role of skewness in constraining this non-adiabatic scenario. We show that non-adiabatic quartessence and quintessence have different signatures for the skewness of the density distribution on large scales and suggest that this quantity might prove helpful to break possible degeneracies between them.

astro-ph↗

arXiv1998

Variational Approach to Hydrodynamics - from QGP to General Relativity

We derive the special and general relativistic hydrodynamic equations of motion for ideal fluids from a variational principle. Our approach allows to find approximate solutions, whenever physically motivated trial functions can be used. Illustrating this, a Rayleigh-Plesset type equation for the relativistic motion of a spherical (QGP) droplet is obtained. Also the corresponding general relativistic effective Lagrangian for spherically symmetric systems is presented.

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