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New Discovery Provides a Clearer Picture of How Galaxies Form and Grow in the Early Universe



Astronomers have drawn a detailed temperature map of an ancient galaxy’s dust, revealing variations between the heat from a central supermassive black hole and the cooler regions heated by star formation. This study, leveraging the ALMA telescope’s capabilities, elucidates how galaxies and their central black holes grow in the early Universe.

Precise mapping of temperature changes provides insights into its evolution.

A multinational team of astronomers has developed a temperature map for the cosmic dust swirling within one of the universe’s oldest spiral galaxies, offering fresh insights into the galaxy’s rate of growth. Prior to this, scientists have only been able to measure the temperature of most distant galaxies in broad terms, without showing how temperatures vary in individual areas.

This research, described in a paper recently published in Monthly Notices of the Royal Astronomical Society (MNRAS) reveals clear evidence of temperature variation within the far-flung galaxy. This suggests the existence of two unique heat sources – a gigantic black hole at the galaxy’s core and the heat generated by newly-formed stars in the surrounding rotating disk.

“The temperature of a galaxy’s dust can vary greatly according to which region it is in,” says Dr. Takafumi Tsukui of the Australian National University (ANU) in Canberra, lead author of the paper. “But most of the measurements of dust temperature for distant galaxies in the past have been for the galaxy as a whole, due to limited instrument resolution.

“We were able to measure the temperature by region to region so that we could determine how much heat is coming from individual sources. Previously, such mapping has mostly been limited to nearby galaxies.”

The research reveals a clear distinction between warm dust in the central region – where the heat is derived from the galaxy’s supermassive black hole – and colder dust in the outer region, which is likely being heated by star formation.

Most galaxies have a supermassive black hole in the center, which is thought to grow in mass with the galaxy. When the gas accretes to the black hole, it is heated up by collisions of the fast-moving particles in the vicinity of the black hole and sometimes shines brighter than the stellar body of the galaxy itself.

“The heating energy from the black hole reflects the amount of the gas being fed into it and so the black hole growth rate, while the heating energy from star formation reflects the number of stars newly forming in the galaxy – the galaxy growth rate,” Dr. Tsukui says.

“This discovery provides a clearer picture of how galaxies and central massive black hole form and grow in the early Universe.”

The current research was made possible thanks to the Atacama Large Millimeter/submillimeter Array (ALMA) telescope operated by the European Southern Observatory (ESO) in Chile.

“This study demonstrates the detailed mapping ability of the ALMA telescope, operated by ESO,” Astro3D Director Professor Emma Ryan-Weber said. “ALMA is the most powerful array for measuring millimeter and submillimetre radiation. It’s incredible that ALMA can look at a 12-billion-year-old galaxy and separate the image into two components – one of dust heated from the central supermassive hole, and the other from the dust in the underlying host galaxy.”

Reference: “Spatially resolved dust properties and quasar-galaxy decomposition of a hyper-luminous infrared galaxy at z = 4.4” by Takafumi Tsukui, Emily Wisnioski, Mark R Krumholz and Andrew Battisti, 22 June 2023, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stad1464

ALMA is a global collaboration and comprises 66 high-precision antennas, spread over distances of up to 16 kilometers making it the world’s largest ground-based astronomical project. It is designed to detect faint light from some of the coldest objects in the Universe which have wavelengths of around a millimeter, somewhere between infrared light and radio waves.

The $40 million ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) is funded by the Australian Research Council (ARC) and six collaborating Australian universities: The Australian National University, The University of Sydney, The University of Melbourne, Swinburne University of Technology, The University of Western Australia, and Curtin University.

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