Radio footprints of a minor merger in the Shapley Supercluster:: from supercluster down to galactic scales

Large scale structure and cosmolog

Radio footprints of a minor merger in the Shapley Supercluster:: from supercluster down to galactic scales

Large scale structure and cosmolog

An ultra-wide bandwidth (704 to 4 032 MHz) receiver for the Parkes radio telescope

We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ${∼}60$ ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability

Dynamics of coastal cod populations: intra- and intercohort density dependence and stochastic processes

Skagerrak populations of Atlantic cod (Gadus morhua L.) have been surveyed at several fixed stations since 1919. These coastal populations consist of local stocks with a low age of maturity and a short life span. We investigated 60 time-series of 0-group juveniles (i.e. young of the year) sampled annually from 1945 to 1994. An age-structured model was developed which incorporates asymmetrical interactions between the juvenile cohorts (0-group and 1-group; i.e. one-year-old juveniles) and stochastic reproduction. The model was expressed in delay coordinates in order to estimate model parameters directly from the time-series and thereby test the model predictions. The autocovariance structure of the time-series was consistent with the delay coordinates model superimposed upon a long-term trend. The model illustrates how both regulatory (density-dependent) and disruptive (stochastic) forces are crucial in shaping the dynamics of the coastal cod populations. The age-structured life cycle acts to resonance the stochasticity inherent in the recruitment process

Radio footprints of a minor merger in the Shapley Supercluster: from supercluster down to galactic scales

Context. The Shapley Supercluster (äzaa 0.048) contains several tens of gravitationally bound clusters and groups, making it an ideal subject for radio studies of cluster mergers. Aims. We used new high sensitivity radio observations to investigate the less energetic events of mass assembly in the Shapley Supercluster from supercluster down to galactic scales. Methods. We created total intensity images of the full region between A3558 and A3562, from a 14;230 to a 14;1650 MHz, using ASKAP, MeerKAT and the GMRT, with sensitivities ranging from a 14;6 to a 14;100 μJy beama 1. We performed a detailed morphological and spectral study of the extended emission features, complemented with ESO-VST optical imaging and X-ray data from XMM-Newton. Results. We report the first GHz frequency detection of extremely low brightness intercluster diffuse emission on a a 14;1 Mpc scale connecting a cluster and a group, namely: A3562 and the group SC 1329a 313. It is morphologically similar to the X-ray emission in the region. We also found (1) a radio tail generated by ram pressure stripping in the galaxy SOS 61086 in SC 1329a 313; (2) a head-tail radio galaxy, whose tail is broken and culminates in a misaligned bar; (3) ultrasteep diffuse emission at the centre of A3558. Finally (4), we confirm the ultra-steep spectrum nature of the radio halo in A3562. Conclusions. Our study strongly supports the scenario of a flyby of SC 1329a 313 north of A3562 into the supercluster core. This event perturbed the centre of A3562, leaving traces of this interaction in the form of turbulence between A3562 and SC 1329a 313, at the origin of the radio bridge and eventually affecting the evolution of individual supercluster galaxies by triggering ram pressure stripping. Our work shows that minor mergers can be spectacular and have the potential to generate diffuse radio emission that carries important information on the formation of large-scale structures in the Universe