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About 35 years ago a class of galaxies with unusually strong Balmer absorption lines and weak emission lines was discovered in distant galaxy clusters. These objects, alternatively referred to as post-starburst, E+A or k+a galaxies, are now known to occur in all environments and at all redshifts, with many exhibiting compact morphologies and low-surface brightness features indicative of past galaxy mergers. They are commonly thought to represent galaxies that are transitioning from blue to red sequence, making them critical to our understanding of the origins of galaxy bimodality. However, recent observational studies have questioned this simple interpretation. From observations alone, it is challenging to disentangle the different mechanisms that lead to the quenching of star formation in galaxies. Here we present examples of three different evolutionary pathways that lead to galaxies with strong Balmer absorption lines in the EAGLE simulation: classical blue-to-red quenching, blue-to-blue cycle and red-to-red rejuvenation. The first two are found in both post-starburst galaxies and galaxies with truncated star formation. Each pathway is consistent with scenarios hypothesised for observational samples. The fact that 'post-starburst' signatures can be attained via various evolutionary channels explains the diversity of observed properties, and lends support to the idea that slower quenching channels are important at low redshift., Comment: Published in Nature Astronomy, 25th March 2019 (submitted version available on arxiv only). The final accepted version is available for all to read here https://rdcu.be/bsQIC. Corresponding author: V. Wild. 11 pages, 4 figures

In the past few years, cosmic-rays beyond the GZK cut-off ($E > 5 \times 10^{19}$ eV) have been detected by leading collaborations such as Pierre Auger Observatory. Such observations raise many questions as to how such energies can be reached and what source can possibly produce them. Although at lower energies, mechanisms such as Fermi acceleration in supernovae front shocks seem to be favored, top-down scenarios have been proposed to explain the existence of ultra-high energy cosmic-rays: the decay of super-massive long-lived particles produced in the early Universe may yield to a flux of ultra-high energy photons. Such photons might be presently generating so called super-preshowers, an extended cosmic-ray shower with a spatial distribution that can be as wide as the Earth diameter. The Cosmic Ray Extremely Distributed Observatory (CREDO) mission is to find such events by means of a network of detectors spread around the globe. CREDO's strategy is to connect existing detectors and create a worldwide network of cosmic-ray observatories. Moreover, citizen-science constitutes an important pillar of our approach. By helping our algorithms to recognize detection patterns and by using smartphones as individual cosmic-ray detectors, non-scientists can participate in scientific discoveries and help unravel some of the deepest mysteries in physics., Comment: excited QCD Conference, CREDO Collaboration, 7 pages, 3 figures

Galaxy interactions are thought to be one of the main triggers of Active Galactic Nuclei (AGN), especially at high luminosities, where the accreted gas mass during the AGN lifetime is substantial. Evidence for a connection between mergers and AGN, however, remains mixed. Possible triggering mechanisms remain particularly poorly understood for luminous AGN, which are thought to require triggering by major mergers, rather than secular processes. We analyse the host galaxies of a sample of 20 optically and X-ray selected luminous AGN (log($L_{bol}$ [erg/s]) $>$ 45) at z $\sim$ 0.6 using HST WFC3 data in the F160W/H band. 15/20 sources have resolved host galaxies. We create a control sample of mock AGN by matching the AGN host galaxies to a control sample of non-AGN galaxies. Visual signs of disturbances are found in about 25% of sources in both the AGN hosts and control galaxies. Using both visual classification and quantitative morphology measures, we show that the levels of disturbance are not enhanced when compared to a matched control sample. We find no signs that major mergers play a dominant role in triggering AGN at high luminosities, suggesting that minor mergers and secular processes dominate AGN triggering up to the highest AGN luminosities. The upper limit on the enhanced fraction of major mergers is $\leqslant$20%. While major mergers might increase the incidence of (luminous AGN), they are not the prevalent triggering mechanism in the population of unobscured AGN., Comment: accepted for publication in MNRAS (bibtex problem fixed in v2)

We present a new morphological indicator designed for automated recognition of galaxies with faint asymmetric tidal features suggestive of an ongoing or past merger. We use this new indicator, together with preexisting diagnostics of galaxy structure to study the role of galaxy mergers in inducing (post-)starburst spectral signatures in local galaxies, and investigate whether (post-)starburst galaxies play a role in the build up of the `red sequence'. Our morphological and structural analysis of an evolutionary sample of 335 (post-)starburst galaxies in the SDSS DR7 with starburst ages 0

The complexity of the hardware and the amount of data collected during the PET imaging process require application of modern methods of efficient data organization and processing. In this article we will discuss the data structures and the flow of collected data from the novel TOF-PET medical scanner which is being developed at the Jagiellonian University. The developed data format reflects: registration process of the gamma quanta emitted from positron-electron annihilation, Front-End Electronic (FEE) structure and required input information for the image reconstruction. In addition, the system database fulfills possible demands of the evolving J-PET project., Comment: 6 p, 3 figs, based on talk given at Symposium on Positron Emission Tomography, Sept. 19-22, 2013, Jagiellonian University, Krak\'ow PL, submitted to Bio-Algorithms and Med-Systems

We discuss computing issues for data analysis and image reconstruction of PET-TOF medical scanner or other medical scanning devices producing large volumes of data. Service architecture based on the grid and cloud concepts for distributed processing is proposed and critically discussed., Comment: 9 p, 3 figs, based on talk given at Symposium on Positron Emission Tomography, Sept. 19-22, 2013, Jagiellonian University, Krak\'ow, Pl

Photomultipliers are commonly used in commercial PET scanner as devices which convert light produced in scintillator by gamma quanta from positron-electron annihilation into electrical signal. For proper analysis of obtained electrical signal, a photomultiplier gain curve must be known, since gain can be significantly different even between photomultipliers of the same model. In this article we describe single photoelectron method used for photomultipliers calibration applied for J-PET scanner, a novel PET detector being developed at the Jagiellonian University. Description of calibration method, an example of calibration curve and gain of few R4998 Hamamatsu photomultipliers are presented., Comment: Submitted to Bio-Algorithms and Med-Systems (12 pages, 6 figures)

This article describes simulations of scattering of annihilation gamma quanta in a strip of plastic scintillator. Such strips constitute basic detection modules in a newly proposed Positron Emission Tomography which utilizes plastic scintillators instead of inorganic crystals. An algorithm simulating chain of Compton scatterings was elaborated and series of simulations have been conducted for the scintillator strip with the cross section of 5 mm x 19 mm. Obtained results indicate that secondary interactions occur only in the case of about 8% of events and out of them only 25$\%$ take place in the distance larger than 0.5 cm from the primary interaction. It was also established that light signals produced at primary and secondary interactions overlap with the delay which distribution is characterized by FWHM of about 40 ps., Comment: Submitted to Bio-Algorithms and Med-Systems (14 pages, 9 figures)

Novel TOF-PET scanner solutions demand, apart from the state of the art detectors, software for fast processing of the gathered data, monitoring of the whole scanner and reconstruction of the PET image. In this article we present an analysis framework for the novel STRIP-PET scanner developed by the J-PET collaboration in the Institute of Physics of the Jagiellonian University. This software is based on the ROOT package used in many particle physics experiments., Comment: 4 pages, 2 figures

All of the present methods for calibration and monitoring of TOF-PET scanner detectors utilize radioactive isotopes such as e.g. $^{22}$Na or $^{68}$Ge, which are placed or rotate inside the scanner. In this article we describe a novel method based on the cosmic rays application to the PET calibration and monitoring methods. The concept allows to overcome many of the drawbacks of the present methods and it is well suited for newly developed TOF-PET scanners with a large longitudinal field of view. The method enables also monitoring of the quality of the scintillator materials and in general allows for the continuous quality assurance of the PET detector performance., Comment: 10 pages, 7 figures

A method of determination of a gamma quantum absorption point in a plastic scintillator block using a matrix of wavelength-shifting (WLS) strips is proposed. Application of this method for improvement of position resolution in newly proposed PET detectors based on plastic scintillators is presented. The method enables to reduce parallax errors in reconstruction of images which occurs in the presently used Positron Emission Tomography scanners., Comment: Submitted to Bio-Algorithms and Med-Systems (6 pages, 4 figures)

This article presents a novel technique for precise measurement of time and charge based solely on FPGA (Field Programmable Gate Array) device and few satellite discrete electronic components used in Positron Emission Tomography (PET). Described approach simplifies electronic circuits, reduces the power consumption, lowers costs, merges front-end electronics with digital electronics and also makes more compact final design. Furthermore, it allows to measure time when analog signals cross a reference voltage at different threshold levels with a very high precision of $\sim$ 10ps (rms) and thus enables sampling of signals in a voltage domain., Comment: Submitted to Bio-Algorithms and Med.-Systems (6 pages, 6 figures)

Reconstruction of the image in Positron Emission Tomographs (PET) requires the knowledge of the system response kernel which describes the contribution of each pixel (voxel) to each tube of response (TOR). This is especially important in list-mode reconstruction systems, where an efficient analytical approximation of such function is required. In this contribution, we present a derivation of the system response kernel for a novel 2D strip PET., Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear physics and innovative technologies, Cracow, 03-06 June 2013

Compressive Sensing theory says that it is possible to reconstruct a measured signal if an enough sparse representation of this signal exists in comparison to the number of random measurements. This theory was applied to reconstruct signals from measurements of plastic scintillators. Sparse representation of obtained signals was found using SVD transform., Comment: 7 pages, 3 figures; Presented at Symposium on applied nuclear physics and innovative technologies, Cracow, 03-06 June 2013