Int’l collaboration of astronomers helps measure cosmic dipole effect
This is an extremely important test of cosmology, and can tell us whether or not our fundamental assumptions about the structure of the Universe are correct
An international study by astronomers including those from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Pune has recently helped measure the ‘cosmic dipole effect’ which makes sources appear brighter in one portion of the sky than the other (see details in the link below). While many other measurements in the past 10 years have disagreed with the original measurement, the (MALS) team’s findings are consistent with the prediction, a surprising result in itself.
This is an extremely important test of cosmology, and can tell us whether or not our fundamental assumptions about the structure of the Universe are correct.
Using data from the MeerKAT radio telescope, an international team of astronomers from the MeerKAT Absorption Line Survey in collaboration released a million-source catalogue. This is the largest catalogue produced by a MeerKAT survey thus far; one of only a handful of radio catalogues with a million or more sources. The MALS team used this catalogue to test the cosmic dipole effect which makes sources appear brighter in one portion of the sky than the other (details in figure). While many other measurements in the past 10 years have disagreed with the original measurement based on CMBR, the MALS team’s findings are consistent with the prediction, a surprising result in itself. “Measuring the dipole is an extremely important test of cosmology, and can tell us whether or not our fundamental assumptions about the structure of the Universe are correct,” said Jonah Wagenveld, astronomer at the Max Planck Institute for Radio Astronomy (MPIfR) in Germany and lead author of the paper.
To get to these deep images from the large amounts of raw data produced by MeerKAT, a sophisticated processing pipeline and data storage facility was set up at IUCAA Pune. The images and catalogues were further analysed and prepared for public release at the MPIfR in Germany. “The depth and expanse of this continuum catalogue holds a unique position among modern radio continuum surveys. The public release will enable the community to address a wide range of issues associated with the evolution of galaxies and the Universe.” said Neeraj Gupta, astronomer at IUCAA and lead investigator of the MALS project.
Due to its focus on depth rather than sky coverage, many sources in the MALS images have been detected for the first time, undoubtedly influencing the dipole measurement. The mystery however is far from resolved, and future larger catalogues - either from MALS using the lower frequency UHF band of MeerKAT or future observatories - will have to dissect these findings and resolve the tension. “The consistent and automated processing was essential to have a good handle on subtle effects in the data which would adversely affect the accuracy of our measurements. This new survey is the stepping stone for future large-scale radio surveys, with the Square Kilometre Array and Deep Synoptic Array,” said Hans-Rainer Klöckner, researcher at the MPIfR who conceptualised the usage of MALS for the dipole measurement.
The new catalogue and accompanying scientific results of this study are described in Wagenveld et al. (2024), accepted for publication in Astronomy and Astrophysics. This is the second of several radio continuum and spectral line data releases to come from MALS, and making this data release has been a team effort. The MALS catalogues and images are publicly available at https://mals.iucaa.in/. The MALS team is an international collaboration of researchers from around the world. The project is led by N Gupta from IUCAA, India. The MeerKAT telescope is a facility of the National Research Foundation (NRF) in South Africa and is operated by the South African Radio Astronomy Observatory (SARAO).