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A million radio sources seen by MeerKAT probes the motion of the solar system and provides a fundamental test of cosmology |
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Figure 1: A map of the sky overlaid on a portion of single MeerKAT pointing containing a few thousand radio sources. In the sky map, circles mark positions of 391 pointings containing a total of 971,980 sources. The arrow shows the direction of the cosmic dipole originally established by measurements of the cosmic microwave background radiation (CMBR). The dipole effect will make the sources appear more numerous (red portion) in the direction of the motion and less in the opposite (blue portion).
Using data from the MeerKAT radio telescope, an international team of astronomers from the MeerKAT Absorption Line Survey (MALS; https://mals.iucaa.in/) collaboration has released a million source catalog. This is the largest catalog produced by a MeerKAT survey thus far, one of only a handful of radio catalogs with a million or more sources. The MALS team has used this catalog 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 the 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 our fundamental assumptions about the structure of the Universe are correct,” explains Jonah Wagenveld, astronomer at MPIfR 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 has been set up at Inter-University Centre for Astronomy and Astrophysics (IUCAA) in India. The images and catalogs were further carefully analyzed and prepared for public release at the Max Planck Institute for Radio Astronomy (MPIfR) in Germany. “The depth and the expanse of this continuum catalog 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.” says 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 MALS images have been detected for the first time, undoubtedly influencing the dipole measurement. The mystery however is far from resolved, and future larger catalogs, 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.” notes Hans-Rainer Klöckner, researcher at MPIfR who conceptualized the usage of MALS for the dipole measurement.
The new catalog and accompanying scientific results of this study are described in Wagenveld et al. (2024), accepted for publication in Astronomy & 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 catalogs 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). The huge volume of raw survey data (1.6 petabytes) received from SARAO are hosted and processed at IUCAA using an automated pipeline built at IUCAA in collaboration with Thoughtworks Technologies India Pvt Ltd. It extensively utilizes tools and tasks from the Common Astronomy Software Applications (CASA) software built by the National Radio Astronomy Observatory (NRAO) of the USA.
To get to these deep images from the large amounts of raw data produced by MeerKAT, a sophisticated processing pipeline and data storage facility has been set up at Inter-University Centre for Astronomy and Astrophysics (IUCAA) in India. The images and catalogs were further carefully analyzed and prepared for public release at the Max Planck Institute for Radio Astronomy (MPIfR) in Germany. “The depth and the expanse of this continuum catalog 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.” says 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 MALS images have been detected for the first time, undoubtedly influencing the dipole measurement. The mystery however is far from resolved, and future larger catalogs, 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.” notes Hans-Rainer Klöckner, researcher at MPIfR who conceptualized the usage of MALS for the dipole measurement.
The new catalog and accompanying scientific results of this study are described in Wagenveld et al. (2024), accepted for publication in Astronomy & 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 catalogs 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). The huge volume of raw survey data (1.6 petabytes) received from SARAO are hosted and processed at IUCAA using an automated pipeline built at IUCAA in collaboration with Thoughtworks Technologies India Pvt Ltd. It extensively utilizes tools and tasks from the Common Astronomy Software Applications (CASA) software built by the National Radio Astronomy Observatory (NRAO) of the USA.
Reference:
Publication in Astronomy and Astrophysics: https://ui.adsabs.harvard.edu/abs/2024arXiv240816619W/abstractMeerKAT
The South African MeerKAT radio telescope, situated 90 km outside the small Northern Cape town of Carnarvon, is a precursor to the Square Kilometre Array (SKA) telescope and will be integrated into the mid-frequency component of SKA Phase 1. The MeerKAT telescope is an array of 64 interlinked receptors (a receptor is the complete antenna structure, with the main reflector, sub-reflector and all receivers, digitizers and other electronics installed).MALS
MALS is the MeerKAT Absorption Line Survey. MALS consists of 1655 hrs of MeerKAT time (anticipated raw data ~ 1.7 PB) to carry out the most sensitive search of HI and OH absorption lines at 0<z<2, the redshift range over which most of the cosmic evolution in the star formation rate density takes place. The MALS survey is described in Gupta et al. (2016).Research contacts:
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Prof. Neeraj Gupta Principal Investigator - MALS, IUCAA, India E-mail: ngupta_at_iucaa.in |
on the behalf of MALS collaboration.