Heat spots reveal growth rate of a galaxy 12 billion years ago

ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D), Media releases

Precise mapping of temperature variation gives clue to its evolution

A team of astronomers led by ASTRO 3D has drawn a temperature map of the dust drifting within one of the oldest spiral galaxies of the Universe which provides new insights into how fast the galaxy is growing. Until now researchers 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 published today in Monthly Notices of the Royal Astronomical Society (MNRAS) shows unambiguous temperature variation within the distant galaxy indicating two distinct heat sources – a supermassive black hole at the centre of the galaxy, and the heat generated by newly-formed stars in the surrounding rotating disk.

An optical image, left, of the galaxy captured by the Hubble Space Telescope with overlaid temperature contours as detected by ALMA. The image on the right shows the dust temperature map detailed in the study.

Download figure of galaxy as pdf.

“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 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 centre, which are 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 millimetre 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 super massive hole, and the other from the dust in underlying host galaxy.”

ALMA is a global collaboration and comprises 66 high-precision antennas, spread over distances of up to 16 kilometres 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 millimetre, 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.


Bill Condie (Media Contact for ASTRO 3D)
Ph: +61 450 952 365                 E: bill@scienceinpublic.com.au


Takafumi Tsukui (ANU)
Ph: +61 0434 837 021               E. u1122744@anu.edu.au

Journal article

Full article available at: https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stad1464

Spatially resolved dust properties and quasar-galaxy decomposition of a HyLIRG at 𝑧 = 4.4

Takafumi Tsukui,1,2★ Emily Wisnioski,1,2 Mark R. Krumholz1,2 and Andrew Battisti1,2 1Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia 2ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)

Accepted 2023 May 10. Received 2023 May 8; in original form 2023 February 14


We report spatially resolved dust properties of the quasar host galaxy BRI 1335-0417 at redshift 𝑧 = 4.4 constrained by the ALMA observations. The dust temperature map, derived from a greybody fit to rest-frame 90 and 161 𝜇m continuum images, shows a steep increase towards the centre, reaching 57.1 ± 0.3 K and a flat median profile at the outer regions of ∼38 K. Image decomposition analysis reveals the presence of a point source in both dust continuum images spatially coincident with the highest temperature peak and the optical quasar position, which we attribute to warm dust heated by an active galactic nucleus (AGN). We show that a model including this warm component along with cooler dust heated by star formation describes the global SED better than a single component model, with dust temperatures of 87.1+34.1−18.3  K (warm component) and 52.6+10.3−11.0   K (cold component). The star formation rate (SFR) estimated from the cold dust component is 1700+500 −400  𝑀⊙ yr−1, a factor of three smaller than previous estimates due to a large AGN contribution (53+14 −15 %). The unresolved warm dust component also explains the steep temperature gradient, as the temperature profile derived after the point source subtraction is flat. The point source subtraction also reduces the estimated central SFR surface density ΣSFR by over a factor of three. With this correction, spatially resolved measurements of ΣSFR and the surface gas mass density Σgas form a roughly linear sequence in the Kennicutt-Schmidt diagram with a constant gas depletion time of 50-200 Myr. The demonstrated AGN-host galaxy decomposition reveals the importance of spatially resolved data for accurate measurements of quasar host galaxy properties, including dust temperature, star-formation rates, and size.