Using new images from the NASA/ESA/CSA James Webb Space Telescope as well as archival data from the NASA/ESA Hubble Space Telescope, astronomers have studied the nuclear star cluster of Messier 74, a grand-design spiral galaxy located in the constellation of Pisces.
This Webb image shows central 950 x 950 parsecs of Messier 74. Image credit: NASA / ESA / CSA / Webb / Hoyer et al., arXiv: 2211.13997.
Messier 74 resides approximately 32 million light-years away from Earth in the equatorial constellation of Pisces.
The galaxy was discovered by the French astronomer Pierre Méchain in September 1780.
Also known as the Phantom Galaxy, M74, NGC 628, LEDA 5974 and HIPASS J0136+15, Messier 74 has a diameter of 95,000 light-years.
It belongs to a particular class of spiral galaxy known as a grand design spiral, meaning that its spiral arms are prominent and well-defined, unlike the patchy and ragged structure seen in some spiral galaxies.
Messier 74 is the brightest member of the M74 Group, a group of several spiral and irregular galaxies.
“This grand-design spiral galaxy is located at a distance of 9.84 megaparsecs (32 million light-years) at the edge of the Local Volume,” said Donostia International Physics Center astronomer Nils Hoyer and his colleagues.
“Both its relatively isolated position and nearly face-on orientation make the galaxy an optimal test-case for detailed studies of galactic disks, and star- and cluster-formation in massive late-types.”
Messier 74 shines at its brightest in this combined optical/mid-infrared image, featuring Webb and Hubble data. Image credit: NASA / ESA / CSA / Webb / Hubble / J. Lee / PHANGS-JWST Team / R. Chandar / J. Schmidt.
In their new work, the astronomers combined archival Hubble and newly obtained Webb imaging data to study the structural and photometric properties of Messier 74’s nuclear star cluster in great detail
“Nuclear star clusters are massive and compact stellar systems in galactic nuclei,” they explained.
“Their effective radii range from a few to tens of parsecs. Such radii are typical of globular clusters and ultra-compact dwarfs.”
“Stellar masses may reach up to 109 solar masses, which, in combination with the small effective radii, lead to core densities that can approach 108 solar masses per cubic parsec, effectively making nuclear star clusters the densest stellar systems known.”
“The nuclear star cluster of Messier 74 was analyzed previously by astronomers using Hubble/WFPC2 imaging data, but no in-depth analysis of all available high-resolution data has been performed yet.”
“With the advent of Webb earlier this year, we aimed to study the nuclear star clusters of Messier 74 across the optical and infrared regimes, analyzing both its structural and photometric properties.”
This Webb image shows the heart of Messier 74. Image credit: NASA / ESA / CSA / Webb / J. Lee / PHANGS-JWST Team.
The authors found that Messier 74’s nuclear star cluster is between 10 parsecs (33 light-years) across and is located in a cavity 200 parsecs by 400 parsecs (652 by 1,304 light-years), lacking both dust and gas.
The cluster hosts a stellar population that is 8 billion years old with no indication of any significant star formation over the last few billion years.
“The color, age, and metallicity of the main stellar population of Messier 74’s nuclear star cluster indicate that no star formation has taken place in the previous few billion years in its center,” the researchers said.
“This is caused either by a dynamical mechanism preventing gas and dust inflow, or by feedback from the center.”
“The lack of a young stellar population hints that the central cavity, which lacks both gas and dust and has a size of approximately 200 parsecs by 400 parsecs around the nuclear star cluster, has existed for the last few billion years as well.”
“The reason for the lack of recent in-situ star formation and origin of the central cavity remains unknown.”
“The nature of the emission in the mid-infrared bands remains a mystery as well.”
The team’s results will be published in the Astrophysical Journal Letters.
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Nils Hoyer et al. 2022. PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628. ApJL, in press; arXiv: 2211.13997
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