Systematics in lensing reconstruction: Dark matter rings in the sky?

Non-parametric lensing methods are a useful way of reconstructing the lensing mass of a cluster without making assumptions about the way the mass is distributed in the cluster. These methods are particularly powerful in the case of galaxy clusters with a large number of constraints. The advantage of not assuming implicitly that the luminous matter follows the dark matter is particularly interesting in those cases where the cluster is in a non-relaxed dynamical state. On the other hand, non-parametric methods have several limitations that should be taken into account carefully. We explore some of these limitations and focus on their implications for the possible ring of dark matter around the galaxy cluster CL0024+17. We project three background galaxies through a mock cluster of known radial profile density and obtain a map for the arcs ($\theta$ map). We also calculate the shear field associated with the mock cluster across the whole field of view (3.3 arcmin). Combining the positions of the arcs and the two-direction shear, we perform an inversion of the lens equation using two separate methods, the biconjugate gradient, and the quadratic programming (QADP) to reconstruct the convergence map of the mock cluster. We explore the space of the solutions of the convergence map and compare the radial density profiles to the density profile of the mock cluster. When the inversion matrix algorithms are forced to find the exact solution, we encounter systematic effects resembling ring structures, that clearly depart from the original convergence map. Overfitting lensing data with a non-parametric method can produce ring-like structures similar to the alleged one in CL0024.Comment: 12 pages, 8 image

Enhanced recording paradigms and advanced analyses of peripheral nerve fibers SPiike software

[eng] The aim of this work is to investigate the human nociceptive system at the peripheral level. Researchers are still debating how the pain perception arises from this very intricate network. The human perception is the most elusive part of our knowledge since different subsystems are involved. The external information such as noxious stimuli must be processed at the peripheral level and through signal cascades and transduction this signal must reach the brain. At the brain level the information is processed and some decisions are taken, such as the well-known fight-or-flight response. In the introduction, the author describes how the human nociceptive system works and in which way the noxious stimulus is converted into a signal understandable by the brain. Several cortical and subcortical areas are involved in this signal processing and going deeper in this assembly line the information becomes more abstracted. The whole pathway is fundamental for pain perception, however some diseases start at the peripheral level. This in turn makes wrong signals reaching the brain. The brain is then processing information that are not real and the responses do not suit with the needs. Therefore, the peripheral system must be investigated and understood firstly, since some central diseases may have a peripheral component as well. With this purpose in mind the microneurography technique has been used. This technique has got some complexity and a computer-aided system must be implemented. The hardware aims to filter out the noisy signal and perform recording and stimulation of the neural fibers. The software is instead used to make the stimulation and recording as automatic as possible in a way that researchers do not have to deal with a lot of parameters and steps to carry out this powerful but also time consuming technique. Some software are already available in the market however even if they work fine with slow conduction fibers such as C-fibers they cannot cope with faster neurons (e.g. Aδ fibers). The aim of this work is to create a software (i.e. SPiike) able to stimulate and record every type of fibers implementing advanced analysis technique as well. Furthermore, considering that some in vivo experiments have been pursued within the project to check the functionality of the software, more specifically in rats and mice, the comparison between human nociceptors and mouse nociceptors is depicted in this section. In the method section, the experimental approach is described step by step. This is composed by several systems that work together for the stimulation, recording and analysis of the neural fibers. The control and acquisition module is composed by the software and a data acquisition board that trigger the stimulator and record the filtered signal. The stimulation module is composed by a stimulator that can be tuned as wish through dedicated knobs. Then the stimulus is delivered to the animal model (or the human patient) and the signal is recorded though a microelectrode inserted into the sciatic nerve. The amplification module is filtering out the noisy signal and is feeding a audio monitor for helping the researcher during the insertion of the electrode inside the nerve and it provides support during the whole experiment giving insights on fiber discharges. In this section the whole setup is described in details as well as the devices needed for the recording. Furthermore, the software development that is the core of this project is described as well, with all the considerations that must be considered during coding. Indeed, the flow chart must be followed methodically in order to minimize bugs and errors that may arise in the final product. Thus a description of the compiler and the Matlab IDE is given along with system and software requirements for the making of the SPiike software. Eventually the explanation of embedded functionalities and capabilities of SPiike is depicted in the final part of this section. This software is indeed able to stimulate slow conducting fibers as well as faster ones, and enhanced analysis techniques such as supervised machine learning are implemented. In the results section, the graphical user interface of the Spiike software is reveled. It resembles the one of another software already available in the market, with a filtered signal and a raster plot embedded on it. However, this software is more user-friendly and it accounts with icons and drop-down menus that enhance the experience of the users during the use of the tool, making their interactions smooth and intuitive. The SPiike software is subdivide into two different tools, a recording module and a analysis module. The former allows the stimulation and recording of neural fibers with a stimulation frequency up to 1000Hz and some online analysis can be conducted to have insights on fibers type and behavior. The analysis module is instead a more powerful analysis environment that can retrieve the dataset recorded with the other module or with the LabChart software. Advanced analysis techniques are implemented in this module, this is meant to speed up fiber classification and analysis. Conclusion and discussion provide a overview on some results. These will be compared to those obtainable through other software available in the market. In this section, pros and cons of the new implemented software, SPiike, will be described as well

Fonoquilla: Diseño de un mapa sonoro de los sitios representativos de la ciudad de Barranquilla

Proyecto del Semillero de Investigación de la Universidad Autónoma del Caribe.La persona que habita en Barranquilla identifica unos sitios representativos para él, y estos sitios hacen parte de su identidad como barranquillero. Sin embargo se dificulta tal actividad para aquellos que no están radicados en ella, llámense visitantes, extranjeros o simplemente los que emigraron de la ciudad y tienen nostalgia del terruño, sin detrimento de todas las personas que desean conocer sobre esta ciudad enmarcada entre el mar Caribe y el río Magdalena, de la cual se han tejido historias en el pasado y está nuevamente en la mirada de muchos, gracias a la apertura económica, académica y tecnológica actual. Esta propuesta de investigación tiene como finalidad identificar los sonidos característicos de los sitios que según personas propias o conocedoras del territorio barranquillero denominan representativos de esta ciudad, para luego trasladarlos a una guía audio – grafica denominada Mapa Sonoro, disponible en un portal digital emitido por la web, donde pueda ser de fácil acceso para cualquier usuario virtual que desee visitar espacial y acústicamente la ciudad de Barranquilla. Apoyándose en diversas bases teóricas relacionadas con imaginarios, geolocalización y fonografía, este trabajo exploratorio pretende en primera instancia ubicarnos en la espacialidad del territorio y representarlo mediante el sonido y la connotación visual de éste, para ellos será necesario el trabajo de campo y herramientas diversas iluminadas desde la comunicación, la producción mediática e informática.Universidad Autónoma del Carib

Diseño de una campaña de comunicación audiovisual que fortalezca la convivencia ciudadana en la Ciudad de Barranquilla: Proyecto VIVE EMPAZ

Proyecto del Semillero de Investigación de la Universidad Autónoma del Caribe.En la actualidad la dinámica de la sociedad y del ser humano mismo, se traduce el uso efectivo de los canales de comunicación y de las formas de interacción dentro del contexto social. En esa medida, desde el Proyecto VIVE EMPAZ del Programa de Dirección y Producción de Radio y Televisión de la Universidad Autónoma del Caribe se propone el diseño y producción de una estrategia de comunicación audiovisual apoyada en recursos de audio y video que faciliten o propicien la convivencia pacifica en la ciudad de Barranquilla. En ese sentido, el proyecto de se apoya en Tucho (2006), ya que establece interrogantes como: ¿qué tipo de ciudadanía queremos promover?, ¿qué objetivos nos mueven al formar a los nuevos ciudadanos?, ¿hablamos de un ciudadano con ciertos valores ético-cívicos que asuma e integre el sistema en el que vivimos o de uno que además de convivir con sus iguales reflexione críticamente sobre la sociedad en la que vivimos y se mueva para su transformación? A partir de esto, la intención de la campaña como estrategia, es llegar a los ciudadanos de forma amable, entretenida y cordial (lograr una verdadera mediación para con la sociedad) a fin de intervenir o lograr un cambio, frente a la problemática que se esté abordandoUniversidad Autónoma del Carib

The contribution of star-forming galaxies to the cosmic radio background

Recent measurements of the temperature of the sky in the radio band, combined with literature data, have convincingly shown the existence of a cosmic radio background with an amplitude of $\sim 1$ K at 1 GHz and a spectral energy distribution that is well described by a power law with index $\alpha \simeq -0.6$. The origin of this signal remains elusive, and it has been speculated that it could be dominated by the contribution of star-forming galaxies at high redshift \change{if the far infrared-radio correlation $q(z)$ evolved} in time. \change{We fit observational data from several different experiments by the relation $q(z) \simeq q_0 - \beta \log(1+z)$ with $q_0 = 2.783 \pm 0.024$ and $\beta = 0.705 \pm 0.081$ and estimate the total radio emission of the whole galaxy population at any given redshift from the cosmic star formation rate density at that redshift. It is found that} star-forming galaxies can only account for $\sim$13 percent of the observed intensity of the cosmic radio background.Comment: 5 pages, 3 figure

The cosmological free-free signal from galaxy groups and clusters

Using analytical models and cosmological N-body simulations, we study the free-free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the mass function and scaling relations. Earlier works based on analytical models have shown that the average free-free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the CMB spectrum at low frequencies ($\nu <$ 5 GHz). We focus on the period after the reionization time (from redshift $z=0$ up to $z=7$) and on haloes that are more massive than in previous works (groups and clusters). We show how the average signal from haloes with $M > 10^{13} h^{-1} M_{\odot}$ is less than 10% the signal from the more abundant and colder smaller mass haloes. However, the individual signal from the massive haloes could be detected with future experiments opening the door for a new window to study the intracluster medium.Comment: 11 pages, 7 figure

The Universal Einstein Radius Distribution from 10,000 SDSS Clusters

We present results from strong-lens modelling of 10,000 SDSS clusters, to establish the universal distribution of Einstein radii. Detailed lensing analyses have shown that the inner mass distribution of clusters can be accurately modelled by assuming light traces mass, successfully uncovering large numbers of multiple-images. Approximate critical curves and the effective Einstein radius of each cluster can therefore be readily calculated, from the distribution of member galaxies and scaled by their luminosities. We use a subsample of 10 well-studied clusters covered by both SDSS and HST to calibrate and test this method, and show that an accurate determination of the Einstein radius and mass can be achieved by this approach "blindly", in an automated way, and without requiring multiple images as input. We present the results of the first 10,000 clusters analysed in the range $0.1<z<0.55$, and compare them to theoretical expectations. We find that for this all-sky representative sample the Einstein radius distribution is log-normal in shape, with < Log(\theta_{e}\arcsec)>=0.73^{+0.02}_{-0.03}, $\sigma=0.316^{+0.004}_{-0.002}$, and with higher abundance of large $\theta_{e}$ clusters than predicted by $\Lambda$CDM. We visually inspect each of the clusters with \theta_{e}>40 \arcsec ($z_{s}=2$) and find that $\sim20$ are boosted by various projection effects detailed here, remaining with $\sim40$ real giant-lens candidates, with a maximum of \theta_{e}=69\pm12 \arcsec ($z_{s}=2$) for the most massive candidate, in agreement with semi-analytic calculations. The results of this work should be verified further when an extended calibration sample is available.Comment: 18 pages, 15 figures, 1 table; V2 accepted to MNRAS, includes a significant revision, in particular a new discussion of the result

Enabling non-parametric strong lensing models to derive reliable cluster mass distributions – WSLAP+

In the strong lensing regime, non-parametric models struggle to achieve sufficient angular resolution for a meaningful derivation of the central cluster mass distribution. Cluster members perturb lensed images and generate additional images, requiring high-resolution modelling. In practice, the required resolution for a fully non-parametric mass map is not achievable because the separation between lensed images is several times larger than the deflection angles by member galaxies. Here we bypass this limitation by incorporating a simple physical prior for member galaxies, using their observed positions and their luminosity scaled masses. This high-frequency contribution is added to a relatively coarse Gaussian pixel grid used to model the more smoothly varying cluster mass distribution, extending our established wslap code (Diego et al.). We test this new code (wslap+) with an empirical simulation based on A1689, using all the pixels belonging to multiply lensed images and the observed member galaxies. Dealing with the cluster members this way leads to stable convergent solutions, without resorting to regularization, reproducing well smooth input cluster distributions and substructures. We highlight the ability of this method to recover ‘dark’ subcomponents and other differences between the distributions of cluster mass and member galaxies. Such anomalies can provide clues to the nature of invisible dark matter, but are difficult to discover using parametrized models where substructures are modelled on the basis of the visible data. With our increased resolution and stability, we show that non-parametric models can be made sufficiently precise to locate multiply lensed systems, thereby achieving fully self-consistent solutions without reliance on input systems from less objective means