Galaxy Cluster Formation from the Large-scale Structure: A Case Study of the Abell 2125 Complex at z=0.247

The structure of the universe is believed to have formed by clustering hierarchically from small to large scales. Much of this evolution occurs very slowly but at a few special times more, rapid, violent activity may occur as major subunits collide at high velocities. The Abell 2125 complex (z=0.247) appears to be undergoing such an event as shown by modeling of the optical velocity field and by the detection with the VLA of an unusually large number of associated radio active galaxies. We present an 80 ksec Chandra imaging of Abell 2125, together with extensive complementary multi-wavelength data. We show direct evidence for galaxy transformation and destruction during the cluster formation. The Chandra data unambiguously separate the X-ray contributions from discrete sources and large-scale diffuse gas in the Abell 2125 complex, which consists of various merging clusters/groups of galaxies and low-surface brightness emission. This enables us to study processes affecting galaxy evolution during this special time from scales of Mpc down to a few kpc. The overall level of activity plus the special time for the cluster-cluster merger suggests that an important phase of galaxy evolution can take place during such events.Comment: 4 pages plus 4 figures. To appear in proceedings of IAU CColloquium No. 195: Outskirts of Galaxy Clusters: Intense Life in the Suburbs. A high resolution version may be found at http://www.astro.umass.edu/~wqd/papers/iau195.ps.g

The behaviour of side weirs in prismatic rectangular channels

Abstract Not Provided

Interview with William Frazer

An interview in March 1992 with Dr. William Frazer, professor of physics at UC Berkeley (emeritus since 1996). As UC’s senior vice president for academic affairs (1983-1991), he oversaw the planning for Keck I, the first of the W. M. Keck 10-meter telescopes on Mauna Kea. He discusses the offer of funding from the Hoffman Foundation and its eventual withdrawal and replacement with Keck Foundation money. He recalls his interactions with UC president David Gardner, Caltech president Marvin L. (Murph) Goldberger, and Caltech provost Rochus E. (Robbie) Vogt, as the UC/Caltech partnership was put together; plans to have a Keck telescope and a Hoffman telescope; the uneasiness of the UC astronomers at the prospect of an equal partnership with Caltech; and the disagreement over the siting of the telescope’s headquarters in Hawaii

The Dynamics of Abell 2125

We present 371 galaxy velocities in the field of the very rich cluster Abell 2125 (z~0.25). These were determined using optical spectroscopy collected over several years from both the WIYN 3.5m telescope and NOAO Mayall 4m telescope. Prior studies at a variety of wavelengths (radio, optical, and X-ray) have indicated that A2125 is a likely cluster-cluster merger, a scenario which we are able to test using our large velocity database. We identified 224 cluster galaxies, which were subjected to a broad range of statistical tests using both positional and velocity information to evaluate the cluster dynamics and substructure. The tests confirmed the presence of substructures within the Abell 2125 system at high significance, demonstrating that A2125 is a complex dynamical system. Comparison of the test results with existing simulations strengthens the merger hypothesis, and provides clues about the merger geometry and stage. The merger model for the system can reconcile A2125's low X-ray temperature and luminosity with its apparently high richness, and might also explain A2125's high fraction of active galaxies identified in prior radio and optical studies.Comment: 34 pages, including tables and 3 color figures; to appear in Ap

Subtle changes in chromatin loop contact propensity are associated with differential gene regulation and expression.

While genetic variation at chromatin loops is relevant for human disease, the relationships between contact propensity (the probability that loci at loops physically interact), genetics, and gene regulation are unclear. We quantitatively interrogate these relationships by comparing Hi-C and molecular phenotype data across cell types and haplotypes. While chromatin loops consistently form across different cell types, they have subtle quantitative differences in contact frequency that are associated with larger changes in gene expression and H3K27ac. For the vast majority of loci with quantitative differences in contact frequency across haplotypes, the changes in magnitude are smaller than those across cell types; however, the proportional relationships between contact propensity, gene expression, and H3K27ac are consistent. These findings suggest that subtle changes in contact propensity have a biologically meaningful role in gene regulation and could be a mechanism by which regulatory genetic variants in loop anchors mediate effects on expression

Inferring late-Holocene climate in the Ecuadorian Andes using a chironomid-based temperature inference model

Presented here is the first chironomid calibration data set for tropical South America. Surface sediments were collected from 59 lakes across Bolivia (15 lakes), Peru (32 lakes), and Ecuador (12 lakes) between 2004 and 2013 over an altitudinal gradient from 150 m above sea level (a.s.l) to 4655 m a.s.l, between 0–17◦ S and 64–78◦ W. The study sites cover a mean annual temperature (MAT) gradient of 25 ◦ C. In total, 55 chironomid taxa were identified in the 59 calibration data set lakes. When used as a single explanatory variable, MAT explains 12.9% of the variance (λ1/λ2 =1.431). Two inference models were developed using weighted averaging (WA) and Bayesian methods. The best performing model using conventional statistical methods was a WA (inverse) model (R2jack= 0.890; RMSEPjack= 2.404 ◦C, RMSEP – root mean jack squared error of prediction; mean biasjack = −0.017 ◦C; max biasjack = 4.665 ◦C). The Bayesian method produced a model with R2jack = 0.909, RMSEPjack = 2.373 ◦C, mean jack biasjack = 0.598 ◦C, and max biasjack = 3.158 ◦C. Both models were used to infer past temperatures from a ca. 3000-year record from the tropical Andes of Ecuador, Laguna Pindo. Inferred temperatures fluctuated around modern-day conditions but showed significant departures at certain intervals (ca. 1600 cal yr BP; ca. 3000–2500 cal yr BP). Both methods (WA and Bayesian) showed similar patterns of temperature variability; however, the magnitude of fluctuations differed. In general the WA method was more variable and often underestimated Holocene temperatures (by ca. −7 ± 2.5 ◦C relative to the modern period). The Bayesian method provided temperature anomaly estimates for cool periods that lay within the expected range of the Holocene (ca. −3 ± 3.4 ◦C). The error associated with both reconstructions is consistent with a constant temperature of 20 ◦C for the past 3000 years. We would caution, however, against an over-interpretation at this stage. The reconstruction can only currently be deemed qualitative and requires more research before quantitative estimates can be generated with confidence. Increasing the number, and spread, of lakes in the calibration data set would enable the detection of smaller climate signals

Southern Cross Soloists 2017 Concert Season

Ensemble in Residence at the Queensland Performing Arts Centre, the Southern Cross Soloists present three concerts with guest performers Damien Beaumont (presenter) and Alexandra Flood (soprano). Featuring music of all periods from the history of Western art music up to today, with new works by Australian composers Elena Kats-Chernin and John Rotar