Large scale simulations of the jet-IGM interaction

In a parameter study extending to jet densities of $10^{-5}$ times the ambient one, I have recently shown that light large scale jets start their lives in a spherical bow shock phase. This allows an easy description of the sideways bow shock propagation in that phase. Here, I present new, bipolar, simulations of very light jets in 2.5D and 3D, reaching the observationally relevant scale of $>200$ jet radii. Deviations from the early bow shock propagation law are expected because of various effects. The net effect is, however, shown to remain small. I calculate the X-ray appearance of the shocked cluster gas and compare it to Cygnus A and 3C 317. Rings, bright spots and enhancements inside the radio cocoon may be explained.Comment: 8 pages, 5 figures, ApSS accepted, proceedings of the virtual jets 2003 conference in Dogliani/Italy, v3: funny and unimportant bug corrected, one reference adde

Investigating sexual strategies in a social community website

In this exploratory study we tried to corroborate existing findings of Sexual Strategies Theory (SST, Buss & Schmitt, 1993) by using data collected from an online community. A random sample of N = 460 German user profiles was drawn from Myspace, a social networking website. Sexual interests reported by the users were analyzed separately for men and women: “Dating” served as an indicator of short-term and interest in “Serious Relationship” as an indicator of long-term sexual strategy. Consistent with SST, a higher percentage of male than female users was interested in dating. However, men were also more interested in serious relationships, indicating that online partner search itself might be a short-term sexual strategy

Simulations of the interaction of cold gas with radio jets

A new scenario for the interaction of a jet with a background medium with cold clouds is investigated by means of hydrodynamic turbulence simulations with cooling. The idea is that the cold clouds are overtaken by a radio cocoon and stirred up by turbulence in this cocoon. The 2D multiphase turbulence simulations contain all the three gas phases and have a number of interesting properties. The produced power spectrum is proportional to the inverse square of the wavevector. The Mach number - density relation may explain the observed velocities in emission line gas associated with radio galaxies. The model also explains the increased optical visibility within the radio structures, the correlation between emission line and radio luminosity, and the evolution of the alignment effect with source size. I also propose this to be a useful model for the recently discovered neutral outflows in nearby radio sources.Comment: Contribution to the proceedings of "The Fate of Gas in Galaxies", Dwingeloo, July 2006, 8 pages 6 figures. To appear in New Astronomy Reviews, Vol. 51 (2007), eds. Morganti, Oosterloo, Villar-Martin & van Gorko

Observability of intermittent radio sources in galaxy groups and clusters

22 pages, 24 figures. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We have carried out numerical hydrodynamic simulations of radio jets from active galactic nuclei using the PLUTO simulation code, with the aim of investigating the effect of different environments and intermittency of energy injection on the resulting dynamics and observable properties of the jet-inflated lobes. Initially conical jets are simulated in poor group and cluster environments. We show that the environment into which a radio jet is propagating plays a large role in the resulting morphology, dynamics and observable properties of the radio source. The same jet collimates much later in a poor group compared to a cluster, which leads to pronounced differences in radio morphology. The intermittency of the jet also affects the observable properties of the radio source, and multiple hotspots are present for multiple outburst jets in the cluster environment. We quantify the detectability of active and quiescent phases, and find this to be strongly environment-dependent. We conclude that the dynamics and observational properties of jets depend strongly on the details of energy injection and environment.Peer reviewedFinal Accepted Versio

Probing gaseous halos of galaxies with radio jets

Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOContext. Gaseous halos play a key role in understanding inflow, feedback, and the overall baryon budget in galaxies. Literature models predict transitions of the state of the gaseous halo between cold and hot accretion, winds, fountains, and hydrostatic halos at certain galaxy masses. Since luminosities of radio AGN are sensitive to halo densities, any significant transition would be expected to show up in the radio luminosities of large samples of galaxies. The LOw Frequency ARray (LOFAR) Two-Metre Sky Survey (LoTSS) has identified a galaxy stellar mass scale, 10 11 M ⊙, above which the radio luminosities increase disproportionately. Aims. We investigate if radio luminosities of galaxies, especially the marked rise at galaxy masses around 10 11 M ⊙, can be explained with standard assumptions regarding jet powers, scaling between black hole mass and galaxy mass, and gaseous halos. Methods. Based on observational data and theoretical constraints, we developed models for the radio luminosity of radio AGN in halos under infall, galactic wind, and hydrostatic conditions. We compared these models to LoTSS data for a large sample of galaxies in the mass range between 10 8.5 M ⊙ and 10 12 M ⊙. Results. Under the assumption that the same characteristic upper limit to jet powers known from high galaxy masses holds at all masses, we find the maximum radio luminosities for the hydrostatic gas halos to lie close to the upper envelope of the distribution of the LOFAR data. The marked rise in radio luminosity at 10 11 M ⊙ is matched in our model and is related to a significant change in halo gas density around this galaxy mass, which is a consequence of lower cooling rates at a higher virial temperature. Wind and infall models overpredict the radio luminosities for small galaxy masses and have no particular steepening of the run of the radio luminosities predicted at any galaxy mass. Conclusions. Radio AGN could have the same characteristic Eddington-scaled upper limit to jet powers in galaxies of all masses in the sample if the galaxies have hydrostatic gas halos in phases when radio AGN are active. We find no evidence of a change of the type of galaxy halo with the galaxy mass. Galactic winds and quasi-spherical cosmological inflow phases cannot frequently occur at the same time as powerful jet episodes unless the jet properties in these phases are significantly different from what we assumed in our model.Peer reviewedFinal Accepted Versio

Regularities and Irregularities in Order Flow Data

We identify and analyze statistical regularities and irregularities in the recent order flow of different NASDAQ stocks, focusing on the positions where orders are placed in the orderbook. This includes limit orders being placed outside of the spread, inside the spread and (effective) market orders. We find that limit order placement inside the spread is strongly determined by the dynamics of the spread size. Most orders, however, arrive outside of the spread. While for some stocks order placement on or next to the quotes is dominating, deeper price levels are more important for other stocks. As market orders are usually adjusted to the quote volume, the impact of market orders depends on the orderbook structure, which we find to be quite diverse among the analyzed stocks as a result of the way limit order placement takes place.Comment: 10 pages, 9 figure