Archival optical image (at 468 nm wavelength) of NGC 5128 taken by the UK Schmidt Telescope overlaying the locations of the two fields studied. The red cross marks the center of NGC 5128. The red circles represent the locations of selected LPVs from the ISAAC Ks band data. Credit: Aghdam et al., 2024.
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Archival optical image (at 468 nm wavelength) of NGC 5128 taken by the UK Schmidt Telescope overlaying the locations of the two fields studied. The red cross marks the center of NGC 5128. The red circles represent the locations of selected LPVs from the ISAAC Ks band data. Credit: Aghdam et al., 2024.
Using the Very Large Telescope (VLT) in Chile, astronomers observed the halo of a nearby giant elliptical galaxy known as Centaurus A. Results of the observing campaign, published June 1 on the preprint server arXivthey provide important insights into the star formation history of the investigated hall.
Discovered almost two centuries ago, Centaurus A (also known as NGC 5128 or Caldwell 77) is the nearest giant elliptical galaxy – about 12.4 million light-years away. It is also one of the closest radio galaxies to Earth, so its active galactic nucleus (AGN) has been extensively studied by researchers.
Centaurus A has an extended halo and radio lobes covering nearly 2 degrees of sky in optical maps. Its extended halo has been the subject of many studies in the past that have attempted to explore the galaxy’s formation history, given that Centaurus A is considered a post-merger galaxy.
Recently, a team of astronomers led by Sima T. Aghdam of the Institute for Basic Science Research in Tehran, Iran, conducted VLT observations of Centaur A to better understand its origin and properties. The focus of their study was two small fields in the hall of this galaxy. By examining the variables in these two fields, they wanted to gain more insight into the star formation history of Centaurus A.
“Our method is based on the identification of long-period variable (LPV) stars that follow their sibling stellar population and thus the historical star formation due to their high luminosity and strong variability,” the researchers explained.
First, the team identified 395 LPVs in the northeastern field designated as Field 1 (located about 61,300 light-years from the center of Centauri A) and 671 LPVs in Field 2 – the southern field (about 32,300 light-years from the center of the galaxy). ).
The astronomers found that although the two fields are about 91,000 light-years apart on different sides of Centauri A, they show similar star formation histories. It turns out that in Field 1 and Field 2, the rate of star formation increased significantly between 3.8 billion and 800 million years ago.
The authors of the paper hypothesize that the last enhanced star formation, which began about 800 million years ago, may have been the result of a merger that occurred about 1 billion years ago. They added that most of the stars in the Centaura A halo formed before 400 million years ago.
Based on the collected results, scientists hypothesize that Centaurus A may have formed a small, gas-rich spiral galaxy that provided fuel for continued star formation at its center. Additionally, they conclude that the intermediate-age stars either originate from this accreting galaxy or may originate from a previous merger.
More information:
Sima Taefi Aghdam et al, The Complex Star Formation History of the Halo of NGC 5128 (Prize A), arXiv (2024). DOI: 10.48550/arxiv.2406.00517
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