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Using ESA's XMM-Newton satellite, astronomers have conducted deep observations of a massive galaxy known as NGC 5746. As a result, they detected a hot gaseous outflow in the galaxy. The , presented Oct. 1 on the arXiv pre-print server, could shed more light on the nature of NGC 5746.

NGC 5746 is a massive barred spiral galaxy located some 94.5 million light years away. The galaxy is seen almost edge-on, has a stellar mass of about 110–130 billion solar masses, and a modest star-formation rate (SFR), which is estimated to be 0.8–1.0 solar masses per year. It forms a very wide galaxy pair with NGC 5740 and is the largest member of the NGC 5746 Group of galaxies.

Previous observations of NGC 5746 have detected a hot X-ray halo extending out to at least 65,000 light years from the center of the galaxy. However, later research has found that this halo does not exist. The doubtful presence of the X-ray halo and the low level of SFR in NGC 5746 raise questions regarding the evolution of this galaxy.

A team of German astronomers led by Roman Laktionov of the Dr. Karl Remeis Observatory in Bamberg, Germany, decided to address these questions with the help of XMM-Newton's European Photon Imaging Camera (EPIC). They employed EPIC to search for the potential X-ray halo of NGC 5746 and to investigate its gas content.

"Due to the larger effective area and better low-energy response of EPIC compared to the Chandra ACIS, XMM-Newton is more sensitive at energies below ∼1 keV compared to Chandra and thus better suited for the search of faint, diffuse emission in the halo of galaxies," the researchers explained.

The observations provided strong evidence for a diffuse X-ray halo out to, on average, 100,000 light years, and even more than 130,000 light years to the east and west of the disk of NGC 5746. The halo has a plasma temperature of about 0.56 keV, which is higher when compared to halos in other spiral galaxies.

Within the halo, the observations identified two hot bubbles above and below the galactic plane. The biconical structure of the bubbles is reminiscent of a stellar outflow. However, this structure appears to be less clumpy and more extended than in other spiral galaxies.

According to the authors of the paper, these results suggest that the outflow is not currently active, but has happened in the past. It allowed the heated gas to extend and relax in a larger volume.

The astronomers noted that the signs of a recent stellar outflow in NGC 5746 indicate that the star-forming activity in this galaxy is higher than previously thought. They estimate it to be at a level of approximately 2.9 solar masses per year.

The study also found that the disk of NGC 5746 has a plasma temperature of about 0.7 keV and it turned out that the diffuse X-ray emission from the disk is strongly dominated by unresolved X-ray binaries.