Conveners
Astrophysics: Extra-galactic
- Christo Venter (North-west University, Potchefstroom Campus)
Astrophysics: Extra-galactic/Dark Matter
- Markus Bottcher (University of North West)
Astrophysics
- Anu Kundu (Centre for Space Research, North-West University)
Astrophysics
- Brian van Soelen (University of the Free State)
Astrophysics
- There are no conveners in this block
Astrophysics
- There are no conveners in this block
Astrophysics
- There are no conveners in this block
Jets in blazars are an excellent forum for studying acceleration at relativistic
MHD shocks, since this process is likely to spawn the highly-variable emission
seen across the electromagnetic spectrum from radio to gamma-rays. Our recent
work on combining time-dependent multi-wavelength leptonic emission models with
complete simulated thermal + non-thermal particle distributions from...
The spectral energy distributions (SEDs) of some blazars exhibit an ultraviolet (UV) and/or soft Xray excess, which can be modelled with different radiation mechanisms. Polarization measurements of the UV/X-ray emission from blazars may provide new and unique information about the astrophysical environment of blazar jets and could thus help to distinguish between different emission scenarios....
The radio through optical/UV/X-ray emission from blazars is dominated by highly polarised synchrotron emission from relativistic electrons in their jets. The total degree of polarisation is a composition of the polarised non-thermal synchrotron emission and thermal unpolarised emission components from the dusty torus, host galaxy, emission lines from the broad line region (BLR) and accretion...
In this talk we present an investigation into the nature of
multi-wavelength variability of blazars from a purely numerical approach.
We use a time-dependent one-zone leptonic blazar emission model to
simulate multi-wavelength variability by introducing stochastic parameter
variations in the emission region. These stochastic parameter variations
are generated by Monte...
We analyse medium resolution optical spectra of six Active Galactic Nuclei (AGN), with strong iron emission spectra and characteristics associated with the class referred to as Narrow-Line Seyfert 1 (NLS1) galaxies. These were observed using the 1.9 m telescope at the South African Astronomical Observatory in Sutherland. The objects are among the brighter sources of that description accessible...
Much of the evolution of galaxies takes place in groups that occupy the interesting intermediate-mass range, where feedback has the greatest impact on galaxy formation and evolution. By using multi-band data (FUV, Mid-IR, Radio, CO, and X-rays), and an optically selected, statistically complete sample of 53 groups (< 80 Mpc; CLoGS sample) the galaxy evolution and star-formation activity of the...
Hydra A is a type I Fanaroff-Riley radio galaxy which hosts a pair of 300-kiloparsec diameter radio lobes that are being powered by the previous powerful AGN outburst. Radio observations provide us with an excellent probe for the study of high energy particles residing in the lobes. The MeerKAT radio telescope carried out observations of Hydra A, from which we obtained radio maps at several...
The Madala model was introduced to explain several anomalies observed at the Large Hadron Collider. This model introduces a dark matter candidate through the extension of the standard model’s Higgs-sector, i.e. heavier scalar bosons are introduced, which can couple to dark matter. The cosmic ray spectra and galactic centre's gamma-ray flux excesses have been observed in the AMS-02 and...
The nature of the cold dark matter (CDM) can be understood by looking for light scalar candidates such as axion-like particles (ALPs). The coupling between ALPs and photons allows for the spontaneous decay of ALPs into pairs of photons. However, the rate of this process is believed to be small enough to be ignored on cosmological timescales. Furthermore, it has been claimed in several recent...
Generally, one expects to find accretion disks around massive objects since their gravity is able to pull in surrounding gas, dust, etc. toward themselves. Such astrophysical objects include black holes and their binaries. However, as of yet, no circumbinary disks have been found around inspiralling stellar-mass black hole binaries related to LIGO events. Our aim is to try find a mechanism to...
We present the evolutionary constraints of shear-free cosmological solutions in the presence of a dark fluid. After describing the general evolution and constraint equations for quasi-Newtonian and anti-Newtonian spacetimes, we derive, at the level of linear perturbations, the conditions for the existence and consistent evolution of such spacetimes when they are endowed with the Chaplygin...
Previous calculations of diffuse radio emissions from dark matter annihilations have made use of Green’s function approximations to solve the diffusive cosmic ray transport equation. Some notable astrophysical code packages, including GALPROP and DRAGON, take a numerical approach to this calculation that involves the use of the Crank-Nicolson finite-differencing scheme. In this work we analyse...
More than half of all galaxies within the local Universe are found within group environments. Therefore, galaxy groups are excellent laboratories for studying galaxy evolution in the local Universe. The Complete Local Volume Groups Sample (CLoGS) is the first statistically complete galaxy group survey in the optical, X-ray and radio bands, consisting of 53 galaxy groups and 1427 member...
Large, state-of-the-art cosmological simulations allow us to follow the evolution of various galaxies, and since it contains detailed knowledge of e.g. the metal content of the stars in each galaxy, it can be used to compare to galaxies in the real Universe. In our work, we are improving the implementations of the stellar feedback model within the GIZMO-Mufasa cosmological simulation. This...
In 2015, the massive protostellar cluster NGC6334I-MM1 flared in various maser species detected by long term monitoring at HartRAO. Followup infrared, millimetre and centimetre observations confirmed that a massive protostar MM1B (M ~ $6.7 M_\odot$) inside the cluster underwent a period of high mass gain, an accretion burst. To probe the effects of such a transient event on the native...
Astronomical maser emission occurs in various astrophysical environments and can be used to infer the physical properties of the regions where they are excited. An import part of interpreting the presence of maser emission associated with a specific astrophysical environment is knowing what the pumping mechanism (radiative or collisional) for a particular maser is. Based on calculations using...
Hyper-runaways are stars moving at supersonic speeds through the interstellar medium; they can be thought of as a subset of runaway stars but moving with velocities that are comparable to the Galactic escape velocity $(\sim 500\,$km/s). Because of the strong stellar winds and high space velocities, we expect massive (hyper)runaway stars to produce bow shocks. We use PLUTO, a...
Capture-recapture has been identified as a possible use case for estimating the underlying size of astrophysical transient and variable populations. We present a series of exploratory analyses using capture-recapture methods from biostatistics. Several estimators were tested for their applicability. We implemented two different capture-recapture approaches: a statistically closed population...
In 2015 the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detected the first ever gravitational
event, gravitational wave event GW150914, with multiple new gravitational wave events, originating from both
binary neutron stars and binary black hole (BBH) mergers, detected in subsequent years. In light of these detections,
we simulate the dynamics of ambient test...
Neutral Hydrogen (HI) Intensity Mapping (IM) promises to open a new window for cosmology, probing Large Scales Structures (LSS) in the Universe over a wide range of redshifts. Unfortunately, HI IM is contaminated by several effects, one of these is the emission from artificial satellites. We aim to simulate the Radio Frequency Interference (RFI) emitted from the Global Navigation Satellite...
Recent detections of the Crab, Vela, Geminga pulsar as well as PSR B1706-44 by ground-based Cherenkov telescopes have created exciting prospects of many more such discoveries by the upcoming Cherenkov Telescope Array. Pulsed photons with energies in excess of 1 TeV detected from the Crab and Vela pulsars severely constrain the particle energetics, emission mechanisms, as well as spatial...
The wealth of multiwavelength pulsar data has stimulated the development of emission models that predict light curves (LCs) over multiple wavebands, most notably radio and gamma-ray. Using established statistical methods to fit these model LCs to data can prove ineffectual if the data from one waveband are substantially more precise. This waveband—typically radio—dominates the fit and biases...
The Neutron star Interior Composition Explorer (NICER) was installed aboard the International Space Station (ISS) in 2017 with the major aim of a better understanding of the extreme nature and composition of neutron stars (NSs). With its exceptional sensitivity, it hopes to constrain the equation of state for these compact objects to high precision. Modelling thermal X-ray light curves (LCs)...
Marsh et al.~(2016) detected radio/optical/UV pulsations from the binary system AR Scorpii (AR Sco) mainly at the beat period of $118$~s. This system, with an orbital period of $3.55$h, is composed of a cool, low-mass star and a white dwarf with a spin period of $117$~s. More recent observations also showed X-ray pulsations from this source (Takata et al. 2018). Buckley et al.~(2017) found...
We investigate, using dynamical system analysis, the impacts of various interaction models whereby dark energy is coupled with dark matter. Phase space analysis of each interaction is conducted where we obtain the cosmological consequence of each choice of interaction, with all components of the universe considered, namely; the radiation, matter, and dark energy dominated universes. We show...
Blazars are a class of Active Galactic Nuclei (AGN) that are radio loud and
have a small angle between the jet and the observer’s line of sight. In some
cases, flaring events in one frequency band are not accompanied by flaring in
other bands. Such events are termed orphan flares. The causes of this variabil-
ity and conditions in and location of the high energy emission region are...
"The true nature of the dark sectors of the universe (dark matter and dark energy), and its implications for cosmology has eluded physicists for decades. In this study, we will consider some cosmological models where dark matter and dark energy are coupled fluids which may interact with each other. Assuming various dark couplings, we will use the background Friedmann equations to predict how...
Gamma-ray binaries are a small subclass of high mass binary systems that display multi-wavelength emission peaking in the gamma-ray regime (≥1 MeV). All known gamma-ray binaries consist of a massive O/B type star and a compact object, either a neutron star or a black hole. There are currently less than ten known systems. The compact object has been identified for only two systems, both as a...
Blazars are a class of active galactic nuclei. These objects are bright sources of radiation throughout the entire electromagnetic spectrum. The spectral energy distributions (SEDs) of some blazars have a distinct dip feature occurring in the gamma-ray energy band of 10 - 200 GeV. We have investigated this feature in the known bright blazar 3C 279 by analysing its spectrum in earlier work....
The observational data shows that the universe is dominated by the dark sector, which is comprising of dark matter $\rho_{dust}$ and dark energy $\rho_{\Lambda}$. This is with budget allocation of $25\%$ to dark matter while dark energy is about $70\%$. Now since most of the existing work in the literature is limited to the study of background cosmological dynamics, the project aims at...
BEAMS is a spectroscopic survey of brightest cluster galaxies (BCGs) in massive clusters detected
by the Advanced Atacama Cosmology Telescope (AdvACT). The goal is to trace the evolution
of AGN feedback (both radio and quasar mode), stellar populations, and the growth of central
galaxies in clusters over a 3.4 Gyr time period (0.3 < z < 0.8). Our study is focused on analyzing
the new...
Galaxy clusters are known to harbour magnetic fields, the nature of which remains unresolved. Intra-cluster magnetic fields can be observed at the density contact discontinuity formed by cool and dense plasma running into hot ambient plasma, and the discontinuity exists near the second brightest galaxy, MRC0600-399, in the merging galaxy cluster Abell 3376 (redshift 0.0461). Elongated X-ray...
Multi-messenger observations using next generation telescopes have great potential in understanding the nature of Dark Matter. DM indirect detection through observations with CTA and LHAASO (in the gamma ray domain) and KM3NeT (in the neutrino domain) can shed light upon the non-Gravitational properties of DM. The DM models under consideration in this work were proposed to explain the DAMPE...
Blazars are a radio-loud subclass of active galactic nuclei (AGN), with relativistic jets closely aligned with the line of sight. These sources are highly variable across all timescales, often displaying flares that are observed across multiple wavelength bands. Blazars emit non-thermal emission across all wavelength regimes, which is characterised by a double-humped structure in its spectral...
The Fornax Cluster is currently experiencing active assembly of mass. It has a lower-density group surrounding the radio galaxy NGC1316 (Fornax A) currently falling into the cluster. Infalling groups are ideal environments to study the transformation in the properties of the multi-phase gas due to e.g. tidal interactions and ram pressure stripping due to the velocity change at the boundary...
This project is within a bigger project on Atomic Hydrogen in Simulated Galaxies. It is aim is to critically investigate and compare the interstellar medium scaling relations in SIMBA cosmological hydrodynamical simulations, with the interstellar medium scaling relations in the MeerKAT MHONGOOSE observed data. After post-processing, the SIMBA snapshots outputs with SKIRT parameters to produce...
Radio emission from normal galaxies and radio galaxies is due to synchrotron radiation by relativistic electrons accelerating helically in the presence of a magnetic field. At low frequencies (in the kHz to GHz frequency band), the radio emissions accumulate over cosmological time to form a diffuse background that is similar to the cosmic microwave background (CMB). This background is known as...
The problem of dark matter has been of great importance in modern physics since its inception. Many theories have been proposed about the nature of dark matter but perhaps the most studied is the WIMP (Weakly Interacting Massive Particle). This particle has been favoured because it has the properties of dark matter that have been measured experimentally, so far. In this work we present an...
Gamma-ray binaries are a rare class of high mass binary system (less than 10 sources) that emit most of their non-thermal emission in the gamma-ray regime. The gamma-ray binary PSR B1259-63/LS 2883 consists of a young pulsar in a 3.4 year orbit around a Be star. Observations around previous periastron passages have shown increased non-thermal emission associated with the pulsar crossing the Be...
