Archival optical image (at a wavelength of 468 nm) of NGC 5128, taken with the British Schmidt telescope, showing the location of the two fields studied. The red cross marks the center of NGC 5128. Red circles represent the locations of the selected LPVs from the ISAAC Ks-band data. Credit: Aghdam et al., 2024.
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Archival optical image (at a wavelength of 468 nm) of NGC 5128, taken with the British Schmidt telescope, showing the location of the two fields studied. The red cross marks the center of NGC 5128. Red circles represent the locations of the selected LPVs from the ISAAC Ks-band data. Credit: Aghdam et al., 2024.
Using the Very Large Telescope (VLT) in Chile, astronomers have observed the halo of a nearby giant elliptical galaxy known as Centaurus A. Results of the observation campaign, published June 1 on the pre-print server arXivprovide important insights into the star formation history of the investigated halo.
Discovered almost two centuries ago, Centaurus A (also known as NGC 5128 or Caldwell 77) is the closest giant elliptical galaxy – at a distance of about 12.4 million light-years. It is also one of the closest radio galaxies to Earth, so the active galactic nucleus (AGN) has been extensively studied by researchers.
Centaurus A has an extended halo and radio lobes that cover almost 2 degrees of the sky on optical maps. Its extended halo has been the subject of many studies in the past, attempting to investigate the galaxy’s genesis, as Centaurus A is believed to be a post-merger galaxy.
Recently, a team of astronomers led by Sima T. Aghdam of the Institute for Research in Fundamental Sciences in Tehran, Iran, conducted VLT observations of Centaurus A, with the aim of better understanding its origins and properties. The focus of their research was on two small fields in the halo of this galaxy. By examining variables in these two fields, they aimed to gain more insight into the star formation history of Centaurus A.
“Our method is based on identifying long-period variable (LPV) stars that track their stellar population and thus historical star formation, due to their high luminosity and strong variability,” the researchers explained.
First, the team identified 395 LPVs in the northeastern field, called Field 1 (about 61,300 light-years from the center of Centaurus A), and 671 LPVs in Field 2, the southern field (about 32,300 light-years from the center of the Milky Way). . ).
The astronomers found that although the two fields are about 91,000 light-years apart on different sides of Centaurus A, they show a similar history of star formation. It turned out that in Field 1 and Field 2, the star formation rate increased significantly between 3.8 billion and 800 million years ago.
The paper’s authors hypothesize that the last enhanced star formation, which began about 800 million years ago, could be the result of a merger that occurred about 1 billion years ago. They added that most of the stars in Centaurus A’s halo formed earlier than 400 million years ago.
Based on the results collected, the researchers believe that Centaurus A may have formed a small gas-rich spiral galaxy that provided the fuel for ongoing star formation at its center. Furthermore, they conclude that the middle-aged stars come from that accumulated galaxy or may have come from a previous merger.
More information:
Sima Taefi Aghdam et al, The complex star formation history of the Halo of NGC 5128 (Cen A), arXiv (2024). DOI: 10.48550/arxiv.2406.00517
Magazine information:
arXiv
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