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- ItemHigh-Resolution Arrayed-Waveguide-Gratings in Astronomy: Design and Fabrication Challenges(Basel : MDPI, 2017) Stoll, Andreas; Zhang, Ziyang; Haynes, Roger; Roth, MartinA comprehensive design of a folded-architecture arrayed-waveguide-grating (AWG)-device, targeted at applications as integrated photonic spectrographs (IPS) in near-infrared astronomy, is presented. The AWG structure is designed for the astronomical H-band (1500 nm-1800 nm) with a theoretical maximum resolving power R = 60,000 at 1630 nm. The geometry of the device is optimized for a compact structure with a footprint of 5.5 cm × 3.93 cm on SiO2 platform. To evaluate the fabrication challenges of such high-resolution AWGs, effects of random perturbations of the effective refractive index (RI) distribution in the free propagation region (FPR), as well as small variations of the array waveguide optical lengths are numerically investigated. The results of the investigation show a dramatic degradation of the point spread function (PSF) for a random effective RI distribution with variance values above ~10-4 for both the FPR and the waveguide array. Based on the results, requirements on the fabrication technology for high-resolution AWG-based spectrographs are given in the end.
- ItemDecoding Galactic Merger Histories(Basel : MDPI, 2017) Bell, Eric; Monachesi, Antonela; D’Souza, Richard; Harmsen, Benjamin; de Jong, Roelof; Radburn-Smith, David; Bailin, Jeremy; Holwerda, BenneGalaxy mergers are expected to influence galaxy properties, yet measurements of individual merger histories are lacking. Models predict that merger histories can be measured using stellar halos and that these halos can be quantified using observations of resolved stars along their minor axis. Such observations reveal that Milky Way-mass galaxies have a wide range of stellar halo properties and show a correlation between their stellar halo masses and metallicities. This correlation agrees with merger-driven models where stellar halos are formed by satellite galaxy disruption. In these models, the largest accreted satellite dominates the stellar halo properties. Consequently, the observed diversity in the stellar halos of MilkyWay-mass galaxies implies a large range in the masses of their largest merger partners. In particular, the Milky Way's low mass halo implies an unusually quiet merger history. We used these measurements to seek predicted correlations between the bulge and central black hole (BH) mass and the mass of the largest merger partner. We found no significant correlations: while some galaxies with large bulges and BHs have large stellar halos and thus experienced a major or minor merger, half have small stellar halos and never experienced a significant merger event. These results indicate that bulge and BH growth is not solely driven by merger-related processes.
- ItemThe “Building Blocks” of Stellar Halos(Basel : MDPI, 2017) Oman, Kyle; Starkenburg, Else; Navarro, JulioThe stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the APOSTLE project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ~0.2-0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.
- ItemA Multiwavelength Dynamical State Analysis of ACT-CL J0019.6+0336(Basel : MDPI, 2021) Pillay, Denisha S.; Turner, David J.; Hilton, Matt; Knowles, Kenda; Kesebonye, Kabelo C.; Moodley, Kavilan; Mroczkowski, Tony; Oozeer, Nadeem; Pfrommer, Christoph; Sikhosana, Sinenhlanhla P.; Wollack, Edward J.In our study, we show a multiwavelength view of ACT-CL J0019.6+0336 (which hosts a radio halo), to investigate the cluster dynamics, morphology, and ICM. We use a combination of XMM-Newton images, Dark Energy Survey (DES) imaging and photometry, SDSS spectroscopic information, and 1.16 GHz MeerKAT data to study the cluster properties. Various X-ray and optical morphology parameters are calculated to investigate the level of disturbance. We find disturbances in two X-ray parameters and the optical density map shows elongated and axisymmetric structures with the main cluster component southeast of the cluster centre and another component northwest of the cluster centre. We also find a BCG offset of ~950 km/s from the mean velocity of the cluster, and a discrepancy between the SZ mass, X-ray mass, and dynamical mass (MX,500 and MSZ,500 lies > 3σ away from Mdyn,500), showing that J0019 is a merging cluster and probably in a post-merging phase.
- ItemThe Optical Variability of the BL Lac AO 0235+164(Basel : MDPI, 2016) Fan, Junhui; Kurtanidze, Omar; Liu, Yi; Liu, Xiang; Richter, Gotthard; Nikolashvili, Maria; Kurtanidze, Sophia; Chanishvili, Revaz; Wang, Hongtao; Sasada, Mahito; Zhou, Aiying; Lin, Chao; Yuan, YuhaiIn this work, we present optical R band observations of AO 0235+164 carried out during the period of November 2006 to December 2012 using the Ap6E CCD camera attached to the primary focus of the 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of ΔR = 4.88 mag (14.19–19.07 mag) and a short time scale of ΔTv = 73.5 min during our monitoring period. When periodicity analysis methods are applied to the R-band data from both historic and our observations, periods P1 = 8.26 yr and P2 = 0.54 yr are found.
- ItemPhase-Space Correlations among Systems of Satellite Galaxies(Basel : MDPI, 2021) Pawlowski, Marcel S.Driven by the increasingly complete observational knowledge of systems of satellite galaxies, mutual spatial alignments and relations in velocities among satellites belonging to a common host have become a productive field of research. Numerous studies have investigated different types of such phase-space correlations and were met with varying degrees of attention by the community. The Planes of Satellite Galaxies issue is maybe the best-known example, with a rich field of research literature and an ongoing, controversial debate on how much of a challenge it poses to the ΛCDM model of cosmology. Another type of correlation, the apparent excess of close pairs of dwarf galaxies, has received considerably less attention despite its reported tension with ΛCDM expectations. With the fast expansion of proper motion measurements in recent years, largely driven by the Gaia mission, other peculiar phase-space correlations have been uncovered among the satellites of the Milky Way. Examples are the apparent tangential velocity excess of satellites compared to cosmological expectations, and the unexpected preference of satellites to be close to their pericenters. At the same time, other kinds of correlations have been found to be more in line with cosmological expectations—specifically, lopsided satellite galaxy systems and the accretion of groups of satellite galaxies. The latter has mostly been studied in cosmological simulations thus far, but it offers the potential to address some of the other issues by providing a way to produce correlations among the orbits of a group’s satellite galaxy members. This review is the first to provide an introduction to the highly active field of phase-space correlations among satellite galaxy systems. The emphasis is on summarizing existing, recent research and highlighting interdependencies between the different, currently almost exclusively individually considered types of correlations. Future prospects in light of upcoming observational facilities and our ever-expanding knowledge of satellite galaxy systems beyond the Local Group are also briefly discussed
- ItemThe CALIFA Survey: Exploring the Oxygen Abundance in the Local Universe(Basel : MDPI, 2015) Sánchez, Sebastian; Sánchez-Menguiano, Laura; Marino, Raffaella; Rosales-Ortega, F.; Pérez, Isabel; de Paz, Armando; Pérez, Enrique; Walcher, C.; López-Cobá, CarlosWe present here a review of the latest results on the spatially-resolved analysis of the stellar populations and ionized gas of disk-dominated galaxies based on Calar Alto Legacy Integral Field Area (CALIFA) data. CALIFA is an ongoing integral field spectroscopy (IFS) survey of galaxies in the Local Universe (0.005 < z < 0.03) that has already obtained spectroscopic information up to ∼2.5 re with a spatial resolution better than ∼1 kpc for a total number of more than 600 galaxies of different morphological types, covering the color-magnitude diagram up to MR<−18 mag. With nearly 2000 spectra obtained for each galaxy, CALIFA offers one of the best IFU datasets to study the star formation histories and chemical enrichment of galaxies. In this article, we focus on the main results from the analysis of the oxygen abundances based on the study of ionized gas in H II regions and individual spaxels and their relation to the global properties of galaxies, using an updated/revised dataset with more galaxies and ionized regions. In summary, we have confirmed previous published results indicating that: (1) the M-Z relation does not present a secondary relation to the star formation rate, when the abundance is measured at the effective radius; (2) the oxygen abundance presents a strong correlation with the stellar surface density (∑-Z relation); (3) the oxygen abundance profiles present three well-defined regimes: (i) an overall negative radial gradient between 0.5 and 2 re, with a characteristic slope of αO/H ∼−0.1 dex/re; (ii) a universal flattening beyond >2 re; and (iii) an inner drop at <0.5 re that depends on mass; (4) the presence of bending in the surface brightness profile of disk galaxies is not clearly related to either the change in the shape of the oxygen abundance profile or the properties of the underlying stellar population. All of these results indicate that disk galaxies present an overall inside-out growth, with chemical enrichment and stellar mass growth tightly correlated and dominated by local processes and limited effects of radial mixing or global outflows. However, clear deviations are shown with respect to this simple scenario, which affect the abundance profiles in both the innermost and outermost regions of galaxies
- ItemPotential Role of Sequential Solid-State and Submerged-Liquid Fermentations in a Circular Bioeconomy(Basel : MDPI, 2021) López-Gómez, José Pablo; Venus, JoachimAn efficient processing of organic solid residues will be pivotal in the development of the circular bioeconomy. Due to their composition, such residues comprise a great biochemical conversion potential through fermentations. Generally, the carbohydrates and proteins present in the organic wastes cannot be directly metabolized by microorganisms. Thus, before fermentation, enzymes are used in a hydrolysis step to release digestible sugars and nitrogen. Although enzymes can be efficiently produced from organic solid residues in solid-state fermentations (SsF), challenges in the development and scale-up of SsF technologies, especially bioreactors, have hindered a wider application of such systems. Therefore, most of the commercial enzymes are produced in submerged-liquid fermentations (SmF) from expensive simple sugars. Instead of independently evaluating SsF and SmF, the review covers the option of combining them in a sequential process in which, enzymes are firstly produced in SsF and then used for hydrolysis, yielding a suitable medium for SmF. The article reviews experimental work that has demonstrated the feasibility of the process and underlines the benefits that such combination has. Finally, a discussion is included which highlights that, unlike typically perceived, SsF should not be considered a counterpart of SmF but, in contrast, the main advantages of each type of fermentation are accentuated in a synergistic sequential SsF-SmF.
- ItemTurning AGN Bubbles into Radio Relics with Sloshing: Modeling CR Transport with Realistic Physics(Basel : MDPI, 2021) ZuHone, John; Ehlert, Kristian; Weinberger, Rainer; Pfrommer, ChristophRadio relics are arc-like synchrotron sources at the periphery of galaxy clusters, produced by cosmic-ray electrons in a µG magnetic field, which are believed to have been (re-)accelerated by merger shock fronts. However, not all relics appear at the same location as shocks as seen in the X-ray. In a previous work, we suggested that the shape of some relics may result from the pre-existing spatial distribution of cosmic-ray electrons, and tested this hypothesis using simulations by launching AGN jets into a cluster atmosphere with sloshing gas motions generated by a previous merger event. We showed that these motions could transport the cosmic ray-enriched material of the AGN bubbles to large radii and stretch it in a tangential direction, producing a filamentary shape resembling a radio relic. In this work, we improve our physical description for the cosmic rays by modeling them as a separate fluid which undergoes diffusion and Alfvén losses. We find that, including this additional cosmic ray physics significantly diminishes the appearance of these filamentary features, showing that our original hypothesis is sensitive to the modeling of cosmic ray physics in the intracluster medium.
- ItemThe Abundance of S-Process Elements: Temporal and Spatial Trends from Open Cluster Observations(Basel : MDPI, 2022) Magrini, Laura; Vázquez, Carlos Viscasillas; Casali, Giada; Baratella, Martina; D’Orazi, Valentina; Spina, Lorenzo; Randich, Sofia; Cristallo, Sergio; Vescovi, DiegoSpectroscopic observations of stars belonging to open clusters, with well-determined ages and distances, are a unique tool for constraining stellar evolution, nucleosynthesis, mixing processes, and, ultimately, Galactic chemical evolution. Abundances of slow (s) process neutron capture elements in stars that retain their initial surface composition open a window into the processes that generated them. In particular, they give us information on their main site of production, i.e., the low-and intermediate-mass Asymptotic Giant Branch (AGB) stars. In the present work, we review some observational results obtained during the last decade that contributed to a better understanding of the AGB phase: the growth of s-process abundances at recent epochs, i.e., in the youngest stellar populations; the different relations between age and [s/Fe] in distinct regions of the disc; and finally the use of s-process abundances combined with those of α elements, [s/α], to estimate stellar ages. We revise some implications that these observations had both on stellar and Galactic evolution, and on our ability to infer stellar ages.