Observations Indicate That The X-Ray Source AX J145732−5901 Is Likely A Galaxy Cluster

Japanese astronomers have found that the unknown X-ray source AX J145732−5901 is a galaxy cluster behind the galactic plane. The researchers outlined these findings in a paper released on April 30 on the arXiv preprint server.

Discovery and Early Observations of AX J145732−5901 with ASCA

NASA launched the ASCA satellite in 1993 to study distant active galaxies,galaxy clusters, cosmic X-ray background sources, and other high-energy phenomena. It enabled astronomers to detect faint X-ray sources, even through the dense matter of the galactic plane.

AX J145732−5901 is an unidentified X-ray source first detected in 2001 during the ASCA Galactic plane survey. Earlier observations classified it as a heavily absorbed, extended source and suggested that a galaxy cluster might lie hidden behind the Milky Way’s plane. However, researchers had not yet conducted a detailed spectral analysis to confirm this hypothesis.

Suzaku Observations Confirm the Nature of AX J145732−5901

Recently, a team of astronomers led by Shigeo Yamauchi from Nara Women’s University in Japan analyzed X-ray data from the Suzaku satellite to investigate AX J145732−5901. Their findings support the earlier assumption about its nature.

“We reanalyzed the ASCA data of AX J145732−5901 using insights from Suzaku-based studies of Galactic ridge X-ray emission and the cosmic X-ray background,” the researchers stated in their paper.

Specifically, the study revealed that AX J145732−5901 exhibits extended X-ray emission measuring 14 by 10 arcminutes, equivalent to about 5.87 by 4.24 million light-years. The emission stretches along the east-west axis and appears to contain localized structural features.

The X-ray spectrum of AX J145732−5901 shows a 5.94 keV emission line and strong absorption, with a hydrogen column density of about 100 sextillion atoms per square centimeter—much higher than the galactic average. This strong absorption supports the idea that the source lies beyond our galaxy.

Luminosity and Distance Estimates of AX J145732−5901

The paper reports that AX J145732−5901 has an X-ray luminosity of about 260 tredecillion erg/s in the 1–10 keV range. Its distance is estimated at 1.8 billion light-years, with an angular extent of around 1.43 billion light-years.

From these findings, the researchers concluded that AX J145732−5901 is a galaxy cluster located behind the galactic plane. Its X-ray morphology suggests it is an unrelaxed, or merging, cluster.

The researchers also calculated that AX J145732−5901 contains roughly 30 trillion solar masses of gas. Assuming a 15% gas fraction, they estimated the cluster’s total mass at about 200 trillion solar masses.

Read the original article on: Phys.Org

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