Deep XMM-Newton observation reveals extraplanar emission in NGC 5746

Dr. Karl Remeis-Observatory, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany

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Received: 1 October 2025
Accepted: 16 March 2026

Abstract

Context. We present a deep XMM-Newton observation of the massive edge-on galaxy NGC 5746. The total exposure time of ∼250 ks provides unprecedented sensitivity to study the diffuse hot gas in the halo, significantly surpassing the depth of previous observations.

Aims. While the presence of hot, circumgalactic gas has been thoroughly tested in starburst galaxies, detections in normal galaxies remain scarce. By studying the diffuse X-ray emission in NGC 5746, we aim to constrain the extent and physical properties of its halo.

Methods. We created X-ray images and surface-brightness profiles to quantify the distribution of extraplanar gas in NGC 5746. In addition, we isolated the diffuse emission from point-source and background contamination and studied its spectral characteristics.

Results. We detected diffuse extraplanar emission in the azimuthally averaged surface-brightness profile out to a projected radius of ∼30 kpc with an integrated significance of 3σ. The emission is anisotropic: The western quadrant shows a significant excess at ∼1.5 − 3.5′ (integrated 3.7σ), while the eastern quadrant exhibits a marginal enhancement in a single radial bin. The northern and southern quadrants are consistent with the background within uncertainties. The X-ray luminosity of the hot halo is ∼8.8 ⋅ 10³⁹ erg s⁻¹ in 0.3–2.0 keV. Spectral modeling yielded a plasma temperature of ∼0.6 keV, while the disk emission is dominated by nonthermal emission from unresolved X-ray sources.

Conclusions. Our results provide evidence of the presence of diffuse hot gas in the halo of NGC 5746 and suggest that earlier nondetections may be attributed to sensitivity limits. The asymmetric morphology highlights the complexity of the halo emission. Distinguishing between the possible origin scenarios for the extraplanar gas requires future observations with improved sensitivity and spectral resolution.