Close-up infrared image of NGC 891 taken by the Hubble Space Telescope (HST). Credit: HST/NASA/ESA.
Using the James Webb Space Telescope (JWST), an international team of astronomers has observed a nearby spiral galaxy known as NGC 891. Results of the observing campaign, published on August 15 on the preprint server arXivprovide more information about the nature of this galaxy and its circumgalactic medium.
Discovered in 1784, NGC 891 (also known as Caldwell 23 or the Silver Ribbon Galaxy) is an edge-on, unbarred spiral galaxy located about 30 million light-years away. It is about 100,000 light-years across and is classified as a normal star-forming spiral galaxy, with similarities to the Milky Way, but with a slightly higher overall star formation rate (SFR).
In an effort to shed more light on the properties of NGC 891, a group of astronomers led by Jérémy Chastenet of Ghent University in Belgium decided to study the circumgalactic medium (CGM) of this galaxy using the Mid-Infrared Instrument (MIRI) and the Near-Infrared Camera (NIRCam) of JWST.
“In this paper, we focus on the distribution of dust and stars in the disk-halo interface of the prototypical galaxy NGC 891 probed by the MIRI and NIRCam instruments on board JWST. The unprecedented resolution and sensitivity of JWST allow us to resolve and study the substructures of the CGM, which has never been possible at these wavelengths,” the researchers wrote in the study.
JWST allowed Chastenet’s team to detect dust emissions up to about 13,000 light-years from the disk of NGC 891. These emissions were identified as filaments, arcs, and superbubbles.
Some of these filaments were found to connect to the midplane, regions of high star formation in NGC 891. This finding suggests that feedback-induced galactic winds play an important role in regulating the baryon cycle.
In addition, observations have detected in NGC 891 the presence of dust in the form of small grains, and probably also polycyclic aromatic hydrocarbons (PAHs). In an attempt to explain the survival of dusty materials for several tens of millions of years after being ejected by galactic winds at the disk-halo interface, astronomers propose the two most plausible scenarios.
“These small grains could be present in pockets of dense matter and protected from ionizing radiation; this scenario is consistent with simulations and a good correspondence between emission and extinction in the literature,” the researchers explain.
They added that the emission can also come from the surface layers of clouds, where the difference in wind speed between hot and warm gases is sufficient to create a mixed layer, replenished by cooling material from the hot gas phase.
Further spectroscopic observations of the CGM in NGC 891 need to be conducted to confirm which of the hypotheses is true.
More information:
Jérémy Chastenet et al, JWST MIRI and NIRCam observations of NGC 891 and its circumgalactic medium, arXiv (2024). DOI: 10.48550/arxiv.2408.08026
Journal information:
arXiv
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Quote: Astronomers explore the nature of galaxy NGC 891 with JWST (2024, August 22) retrieved August 22, 2024 from
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