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A recent observational study found that the projected spatial distributions of the satellites of bright, isolated host galaxies tend to be lopsided with respect to the locations of the hosts. Here, we examine the spatial distributions of the satellites of a large number of bright, isolated host galaxies that were obtained from mock redshift surveys of a Λ-cold dark matter (ΛCDM) simulation. Host galaxies and their satellites were identified using selection criteria that are identical to those used in the observational study, allowing for a direct comparison of the results for the simulated and observed systems. To characterize the spatial distribution of the satellites, we adopt two statistics: (1) the pairwise clustering of the satellites and (2) the mean resultant length. In agreement with the observational study, we find a strong tendency for satellites in the simulation to be located on the same side of their host, and the signal is most pronounced for the satellites of blue hosts. These lopsided satellite distributions are not solely attributable to incompleteness of the observed satellite catalog or the presence of objects that have been falsely identified as satellites. In addition, satellites that joined their hosts' halos in the distant past (≳8 Gyr) show a pronounced lopsidedness in their spatial distributions and, therefore, the lopsidedness is not solely attributable to the late-time accretion of satellites. [ABSTRACT FROM AUTHOR]

Central Asia is a key migratory route for the peopling of Asia during the Palaeolithic. Unfortunately, chronological information is limited, leaving a geographical and temporal gap in our knowledge of human migrations. One of the aims of the transdisciplinary project THOCA ("Timing and Ecology of the Human Occupation in Central Asia") is to determine the chronology of the first settlements in Central Asia over time through the study of three major archaeological sites (Khonako, Obi Mazar and Kuldara) located in the Khovaling Loess Plateau of Tajikistan [1]. Luminescence dating is being used to date the upper part of the sections, providing a chronological framework for palaeoenvironmental, palaeoecological, and palaeoclimatic studies over the past ~250 ka. Here we present the first detailed luminescence chronology of the Khonako sites. These sections consist of an alternation of thick loess units and up to 16 well-developed pedocomplexes (PC), providing a sedimentary record presumably back to MIS 31. Lithic assemblages excavated in the upper PC 1 and PC 2 are among the best representatives of the regional Middle Palaeolithic industries. About 320 samples were taken to establish a chronological model down to at least PC 2. Because of the high dose rates (~ 3 Gy/ka), the OSL signal from quartz can only be used to date the last ~30 ka, and so only the upper part of the section (~ top of L1). Quartz OSL and feldspar pIRIR200,290 ages are compared to evaluate the completeness of bleaching of the pIRIR200,290 signal and evaluate the size of the presumed residual dose that was present at deposition. First IR stimulation temperature tests are used to confirm the suitability of our pIRIR protocol. Because of the fine-grained nature of the sediment, only very small amounts of 63-90 µm K-rich feldspar grains could be extracted. Therefore, measurements using a pIRIR200,290 protocol were also carried out on the polymineral 63-90 µm fractions (i.e. no HF treatment or heavy liquid separation). All these measurements were made using a test dose approximately equal to the measured De. Dose recovery ratios (of between 0.91 ± 0.09 and 1.07 ± 0.02) are satisfactory for 6 samples ranging from ~ 20 ka (given dose of ~ 90 Gy) to ~ 250 ka (given dose of ~ 770 Gy) after the subtraction of residual doses (from 16 Gy to 54 Gy). Our preliminary test results also show that the polymineral 63-90 µm fraction yields the same De values as purified K-rich feldspar extracts. The new chronology for the Khonako sites confirms that PC 2 and PC 1 can be associated with MIS 7 and 5, respectively. The sedimentary record appears to be almost continuous through the last 250 ka, although there may be a hiatus in sedimentation at the bottom of PC 1 (end of MIS 6/beginning MIS 5). [ABSTRACT FROM AUTHOR]