Mastodawn

Hamburg Observatory Oct 13, 2023

The 2nd: Simulations of galaxy cluster mergers with velocity-dependent, rare and frequent self-interactions led by V. Sabarish.We find that effects of velocity-dep X-sections appear when comparing early-time and late-time oscillation amplitude of the BCG
https://arxiv.org/abs/2310.07769

Simulations of galaxy cluster mergers with velocity-dependent, rare and frequent self-interactions

Self-interacting dark matter (SIDM) has been proposed to solve small-scale problems in $Λ$CDM cosmology. In previous work, constraints on the self-interaction cross-section of dark matter have been derived assuming that the self-interaction cross-section is independent of velocity. However, a velocity-dependent cross-section is more natural in most theories of SIDM. Using idealized $N$-body simulations, we study merging clusters, with velocity-dependent SIDM. In addition to the usual rare scattering in the isotropic limit, we also simulate these systems with anisotropic, small-angle (frequent) scatterings. We study the qualitative features of the mergers and we find that the effects of velocity-dependent cross-sections are observed when comparing early-time and late-time oscillation amplitude of the brightest cluster galaxy (BCG). Finally, we also extend the existing upper bounds on the velocity-independent, isotropic self-interaction cross-section to the parameter space of rare and frequent velocity-dependent self-interactions by studying the central densities of dark matter only isolated haloes. For these upper-bound parameters, we find that the offsets just after the first pericentre to be $\leq$ 10 kpc. On the other hand, because of BCG oscillations, we speculate that the distribution of BCG offsets in relaxed cluster to be a statistically viable probe. Therefore, this motivates further studies of BCG off-centering in cosmological simulations.

arXiv.org

Hamburg Observatory Oct 13, 2023

Today a double feature on astro-ph: Two studies using simulations of velocity-dependent and self-interacting Dark Matter.
First up: Cosmological & idealised simulations of DM haloes with velocity-dependent, rare and frequent self-interactions, led by M. Fischer. We find that a strongly velocity-dependent cross-section can significantly amplify the diversity of rotation curves https://arxiv.org/abs/2310.07750

Cosmological and idealized simulations of dark matter haloes with velocity-dependent, rare and frequent self-interactions

Dark matter self-interactions may have the capability to solve or at least mitigate small-scale problems of the cosmological standard model, Lambda Cold Dark Matter. There are a variety of self-interacting dark matter models that lead to distinguishable astrophysical predictions and hence varying success in explaining observations. Studies of dark matter (DM) density cores on various mass scales suggest a velocity-dependent scattering cross-section. In this work, we investigate how a velocity dependence alters the evolution of the DM distribution for frequent DM scatterings and compare to the velocity-independent case. We demonstrate that these cases are qualitatively different using a test problem. Moreover, we study the evolution of the density profile of idealized DM haloes and find that a velocity dependence can lead to larger core sizes and different time-scales of core formation and core collapse. In cosmological simulations, we investigate the effect of velocity-dependent self-interaction on haloes and satellites in the mass range of $\approx 10^{11} - 10^{14}$ M$_\odot$. We study the abundance of satellites, density, and shape profiles and try to infer qualitative differences between velocity-dependent and velocity-independent scatterings as well as between frequent and rare self-interactions. We find that a strongly velocity-dependent cross-section can significantly amplify the diversity of rotation curves, independent of the angular dependence of the differential cross-section. We further find that the abundance of satellites in general depends on both the velocity dependence and the scattering angle, although the latter is less important for strongly velocity-dependent cross-sections.

arXiv.org

Hamburg Observatory Oct 13, 2023

Thomas Kupfer Sep 1, 2023

What better first post, than to share that today is my first day at the University of Hamburg. I'm excited to get to work. You can find me at the observatory in Bergedorf @HambObs
https://www.uni-hamburg.de/newsroom/presse/2023/pm50.html

1,7 Millionen Euro für astrophysikalische Forschung zu Doppelsternen

Hamburg Observatory Oct 13, 2023

franco_vazza Oct 10, 2023

#paperday

“A multishock scenario for the formation of radio relics”

by D. Smolinksi, D. Wittor, M. Bruggen of @HambObs and myself.
in press on MNRAS

https://arxiv.org/abs/2310.04504

in this work, we explored the importance of the multiple re-acceleration by shocks in the intracluster medium, as a general mechanism to explain why many clusters of galaxies light up with radio emission in spite of the fact that the shocks
they contain are weak.

#astrodon #astronomy #simulation

A multishock scenario for the formation of radio relics

Radio relics are giant sources of diffuse synchrotron radio emission in the outskirts of galaxy clusters that are associated with shocks in the intracluster medium. Still, the origin of relativistic particles that make up relics is not fully understood. For most relics, diffusive shock acceleration (DSA) of thermal electrons is not efficient enough to explain observed radio fluxes. In this paper, we use a magneto-hydrodynamic simulation of galaxy clusters in combination with Lagrangian tracers to simulate the formation of radio relics. Using a Fokker-Planck solver to compute the energy spectra of relativistic electrons, we determine the synchrotron emission of the relic. We find that re-acceleration of fossil electrons plays a major role in explaining the synchrotron emission of radio relics. Particles that pass through multiple shocks contribute significantly to the overall luminosity of a radio relic and greatly boosts the effective acceleration efficiency. Furthermore, we find that the assumption that the luminosity of a radio relic can be explained with DSA of thermal electrons leads to an overestimate of the acceleration efficiency by a factor of more than $10^3$.

arXiv.org

Hamburg Observatory Oct 13, 2023

Show thread

franco_vazza Oct 10, 2023

In this new work led by D. Smolinksi (master student at @HambObs) we started instead with the blind selection of a simulated cluster with a large shock crossing its periphery at the end of the run. This shock is wide by weak, M~1.6. Can it become a radio relic too?

So we tracked the Lagrangan history of 10 million gas tracer particles ending up there, thanks to the magic allowed by simulations, which allow us to analyse any past moments in time of a system’s evolution.

Hamburg Observatory Jun 13, 2023

Big code paper dropped by our S. Rosswog introducing the Lagrangian Numerical Relativity code SPHINCS_BSSN. https://arxiv.org/pdf/2306.06226.pdf

Hamburg Observatory Jun 9, 2023

Today on astro-ph: Evidence of Extended Dust and Feedback around z≈1 Quiescent Galaxies via Millimeter Observations
with our student K. Böckmann
https://arxiv.org/abs/2306.04760

Evidence of Extended Dust and Feedback around z$\approx$1 Quiescent Galaxies via Millimeter Observations

We use public data from the South Pole Telescope (SPT) and Atacama Cosmology Telescope (ACT) to measure radial profiles of the thermal Sunyaev-Zel'dovich (tSZ) effect and dust emission around massive quiescent galaxies at $z\approx1.$ Using survey data from the Dark Energy Survey (DES) and Wide-Field infrared Survey Explorer (WISE), we selected $387,627$ quiescent galaxies within the ACT field, with a mean stellar $\log_{10}(M_{\star}/\rm{M_{\odot}})$ of $11.40$. A subset of $94,452$ galaxies, with a mean stellar $\log_{10}(M_{\star}/\rm{M_{\odot}})$ of $11.36,$ are also covered by SPT. In $0.5$ arcminute radial bins around these galaxies, we detect the tSZ profile at levels up to $11σ$, and dust profile up to $20σ.$ Both profiles are extended, and the dust profile slope at large radii is consistent with galaxy clustering. We analyze the thermal energy and dust mass versus stellar mass via integration within $R=2.0$ arcminute circular apertures and fit them with a forward-modeled power-law to correct for our photometric stellar mass uncertainty. At the mean log stellar mass of our overlap and wide-area samples, respectively, we extract thermal energies from the tSZ of $E_{\rm{pk}}=6.45_{-1.52}^{+1.67}\times10^{60}{\rm{ erg}}$ and $8.20_{-0.52}^{+0.52}\times10^{60}{\rm{ erg}},$ most consistent with moderate to high levels of active galactic nuclei feedback acting upon the circumgalactic medium. Dust masses at the mean log stellar mass are $M_{\rm{d,pk}}=6.23_{-0.67}^{+0.67}\times10^{8}\rm{ M_{\odot}}$ and $6.76_{-0.56}^{+0.56}\times10^{8}\rm{ M_{\odot}},$ and we find a greater than linear dust-to-stellar mass relation, which indicates that the more massive galaxies in our study retain more dust. Our work highlights current capabilities of stacking millimeter data around individual galaxies and potential for future use.

arXiv.org

Hamburg Observatory Jun 7, 2023

Today on astro-ph: A search for inter-cluster filaments with LOFAR and eROSITA led by D. Hoang et al. We did not find any emission from filaments but could find important constraints on B-fields.
Discovery should be within reach.

https://arxiv.org/abs/2306.03904

A search for inter-cluster filaments with LOFAR and eROSITA

Cosmological simulations predict the presence of warm hot thermal gas in the cosmic filaments that connect galaxy clusters. This gas is thought to constitute an important part of the missing baryons in the Universe. In addition to the thermal gas, cosmic filaments could contain a population of relativistic particles and magnetic fields. A detection of magnetic fields in filaments can constrain early magnetogenesis in the cosmos. So far, the resulting diffuse synchrotron emission has only been indirectly detected. We present our search for thermal and non-thermal diffuse emission from inter-cluster regions of 106 paired galaxy clusters by stacking the $0.6-2.3$~keV X-ray and 144~MHz radio data obtained with the eROSITA telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory and LOw Frequency ARray (LOFAR), respectively. The stacked data do not show the presence of X-ray and radio diffuse emission in the inter-cluster regions. This could be due to the sensitivity of the data sets and/or the limited number of cluster pairs used in this study. Assuming a constant radio emissivity in the filaments, we find that the mean radio emissivity is not higher than $1.2\times10^{-44}\,{\rm erg \, s^{-1} \, cm^{-3} \, Hz^{-1}}$. Under equipartition conditions, our upper limit on the mean emissivity translates to an upper limit of $\sim75\,{\rm nG}$ for the mean magnetic field strength in the filaments, depending on the spectral index and the minimum energy cutoff. We discuss the constraint for the magnetic field strength in the context of the models for the formation of magnetic fields in cosmic filaments.

arXiv.org

Hamburg Observatory Jun 6, 2023

Start of our bike trip to the Norderstedt LOFAR Station.

Hamburg Observatory May 22, 2023

Scientific American May 22, 2023

Referenced link: https://www.scientificamerican.com/article/six-gravitational-wave-breakthroughs-scientists-cant-wait-to-see/
Discuss on https://discu.eu/q/https://www.scientificamerican.com/article/six-gravitational-wave-breakthroughs-scientists-cant-wait-to-see/

Originally posted by Scientific American / @sciam: http://nitter.platypush.tech/sciam/status/1660685509281103878#m

After years of downtime for upgrades, the world's premier gravitational-wave observatories are coming back online with big hopes for transformative discoveries https://www.scientificamerican.com/article/six-gravitational-wave-breakthroughs-scientists-cant-wait-to-see/

Six Gravitational-Wave Breakthroughs Scientists Can’t Wait to See

After years of downtime for upgrades, the world’s premier gravitational-wave observatories are coming back online with big hopes for transformative discoveries

Scientific American