Testing large scale cosmology with MeerKAT

Promotionskolloquium
Jonah Wagenveld
SCHEDULED
MPIfR

The cosmic radio dipole is an anisotropy in the number counts of radio sources, analogous to the dipole seen in the cosmic microwave background (CMB). Measurements of the radio dipole with large radio surveys have shown that though the radio dipole is aligned in direction with the CMB dipole, the amplitudes are in tension. These observations present an intriguing puzzle as to the cause of this discrepancy, with a true anisotropy having large repercussions for cosmology as a whole. Measurements of the cosmic radio dipole with large radio surveys have often suffered from systematics in the data, hampering sensitivity and reliability of these measurements. In this thesis, I aim to measure the cosmic radio dipole with the MeerKAT Absorption Line Survey (MALS). Though sky coverage of MALS is low, with 391 pointings observed in total, the sensitivity and field of view of MeerKAT yields thousands of sources observed in each pointing. We perform a deep analysis of the complete set of processing steps, from observations to cataloguing, of ten MALS pointings, to characterise and quantify potential systematic effects which could hamper a dipole measurement. Using the noise characteristics of these pointings, we find that we can homogenise the catalogues to a deep enough level for a dipole measurement. We furthermore define Bayesian estimators that are able to perform a dipole measurement with the sparse sky coverage of MALS. Testing these estimators out on other radio surveys, we perform the most significant measurement of the cosmic radio dipole yet. Finally, we perform a measurement of the dipole using all MALS pointings, but find an effect in the data which causes a systematic variation in source density with declination, hampering a dipole measurement. Though we can account for the effect by extending our estimators, it comes at the cost of further uncertainties, which can only be remedied by reprocessing the data. However, combined with other measurements performed in this thesis and in the literature, there is a little doubt anymore as to the legitimacy of the radio dipole measurement, and we may look forward to further measurements which aim to uncover the cause of the dipole tension.

It takes two to Tango - Stellar Physics in the Era of Stellar, Transient, and Gravitational Wave Surveys

Main Colloquium
Prof. Dr. Selma de Mink
SCHEDULED
MPA

The majority of stars form in binary and multiple systems. To understand the lives and final fates of stars we need to understand how the presence of companions can affect their lives. This is especially true for massive stars we think that the majority interact with its binary companion and more than a fifth can even interact with the third star. These questions are especially timely now in the era of gravitational wave detections which are starting to reveal the properties binary black holes and neutron stars. At the same time large stellar surveys, in particular Gaia, are probing these multiple systems, Tess and soon PLATO are uncovering stellar oscillations that allow us go probe the interior of these stars, time domain surveys catch the more dramatic events involving mergers, disruptions and explosions. I like to discuss a few fun and possibly important new insights in massive (binary) stars that we have been pursuing at the new stellar department at the Max Planck Institute for Astrophysics in Garching near Munichm Germany. This will include a discussion of the claims that the Red Supergiant Betelgeuse is rotating, why the widest binaries are not boring at all, the elusive stripped stars that were missing and have now been found and if time permits a discussion about Blue Supergiants.

TBD

Main Colloquium
Dr. Roberto Neri
SCHEDULED
IRAM Grenoble (France)

TBD

TBD

Main Colloquium
Prof. Dr. Felix Aharonian
CANCELED
DIAS/Dublin and MPIK/Heidelberg

TBD

TBD

Main Colloquium
Prof. Dr. Felix Aharonian
SCHEDULED
DIAS/Dublin and MPIK/Heidelberg

TBD

MIGHTEE-COSMOS: The Radio Spectral Energy Distribution and Star Formation Rate Calibration of Galaxies at z<5

Special Colloquium
Prof. Dr. Fatemeh Tabatabaei
CANCELED
MPIA

Studying the radio spectral energy distribution (SED) of distant galaxies is essential for understanding their assembly and evolution over cosmic time. We present rest-frame SEDs of a sample of star-forming galaxies at z< 5 in the COSMOS field as part of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) project. MeerKAT observations combined with archival VLA and GMRT data allow us to estimate the equipartition magnetic field and calibrate star formation rate (SFR) up to z=5. We also measure the total energy budget of high-z galaxies emitting in the mid-radio continuum (MRC bolometric luminosities) at 1.5

TBD

Main Colloquium
Dr. Nadine Neumayer
SCHEDULED
Max-Planck-Institut für Astronomie, Heidelberg

TBD