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- 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