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Deep XMM-Newton observation reveals hot gaseous outflow in NGC 5746

Roman Laktionov, Manami Sasaki, Jörn Wilms

TL;DR

This study presents a deep XMM-Newton analysis of NGC 5746, revealing a luminous hot X-ray halo extending to tens of kiloparsecs with a halo plasma temperature around $kT\approx 0.56$ keV and a hotter disc at $kT\approx 0.70$ keV. Spectral modeling uncovers two extraplanar, biconical bubbles consistent with a past stellar outflow, while the halo’s origin is more likely tied to disc star formation feedback than to accretion of primordial gas. By applying an X-ray–SFR relation, the authors estimate a current disc SFR of about $\sim 3$ M⊙ yr$^{-1}$, higher than some previous measurements, supporting a scenario where elevated star formation drives halo heating. The results imply that massive spiral galaxies can host luminous X-ray halos and highlight the need for deeper observations of non-starburst galaxies to assess halo prevalence, metallicity, and the impact on galaxy evolution.

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 is well tested for starburst galaxies, detections in normal galaxies remain scarce. By studying the diffuse X-ray emission in NGC 5746, we aim to provide new insights into the evolution of star-forming galaxies and their surroundings. Methods. We create X-ray images and surface brightness profiles to quantify the distribution of extraplanar gas in the halo of NGC 5746. In addition, we isolate the diffuse emission component from point source- and background-contamination and study the spectral characteristics of the hot plasma. Results. We detect soft X-ray emission out to 40 kpc from the galactic disc. The gas distribution is reminiscent of a stellar outflow, with two bubbles extending perpendicular to the disc in a biconical shape. The spectral analysis of the halo emission yields a plasma temperature of 0.56 keV, higher than the typical values observed in spiral galaxies (0.2 keV). The disc has an even higher plasma temperature of 0.7 keV, and is dominated by non-thermal emission from unresolved X-ray binaries. The signs of a stellar outflow, bright X-ray emission, and high plasma temperatures indicate that the star-forming activity in NGC 5746 might be higher than previously thought. Conclusions. Our results demonstrate that massive spiral galaxies can host luminous X-ray halos, and support theoretical models that predict their existence. Earlier claims of a lack of hot gas around quiescent spirals might be attributed to the detection thresholds in shallower observations, stressing the need for more, deeper observations of non-starburst galaxies.

Deep XMM-Newton observation reveals hot gaseous outflow in NGC 5746

TL;DR

This study presents a deep XMM-Newton analysis of NGC 5746, revealing a luminous hot X-ray halo extending to tens of kiloparsecs with a halo plasma temperature around keV and a hotter disc at keV. Spectral modeling uncovers two extraplanar, biconical bubbles consistent with a past stellar outflow, while the halo’s origin is more likely tied to disc star formation feedback than to accretion of primordial gas. By applying an X-ray–SFR relation, the authors estimate a current disc SFR of about M⊙ yr, higher than some previous measurements, supporting a scenario where elevated star formation drives halo heating. The results imply that massive spiral galaxies can host luminous X-ray halos and highlight the need for deeper observations of non-starburst galaxies to assess halo prevalence, metallicity, and the impact on galaxy evolution.

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 is well tested for starburst galaxies, detections in normal galaxies remain scarce. By studying the diffuse X-ray emission in NGC 5746, we aim to provide new insights into the evolution of star-forming galaxies and their surroundings. Methods. We create X-ray images and surface brightness profiles to quantify the distribution of extraplanar gas in the halo of NGC 5746. In addition, we isolate the diffuse emission component from point source- and background-contamination and study the spectral characteristics of the hot plasma. Results. We detect soft X-ray emission out to 40 kpc from the galactic disc. The gas distribution is reminiscent of a stellar outflow, with two bubbles extending perpendicular to the disc in a biconical shape. The spectral analysis of the halo emission yields a plasma temperature of 0.56 keV, higher than the typical values observed in spiral galaxies (0.2 keV). The disc has an even higher plasma temperature of 0.7 keV, and is dominated by non-thermal emission from unresolved X-ray binaries. The signs of a stellar outflow, bright X-ray emission, and high plasma temperatures indicate that the star-forming activity in NGC 5746 might be higher than previously thought. Conclusions. Our results demonstrate that massive spiral galaxies can host luminous X-ray halos, and support theoretical models that predict their existence. Earlier claims of a lack of hot gas around quiescent spirals might be attributed to the detection thresholds in shallower observations, stressing the need for more, deeper observations of non-starburst galaxies.

Paper Structure

This paper contains 22 sections, 2 equations, 3 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Data
  3. XMM-Newton
  4. Data processing
  5. X-ray Analysis
  6. Image
  7. Surface brightness profiles
  8. Spectra
  9. Background Model
  10. Source Model
  11. Spectral Analysis
  12. Fluxes
  13. Results
  14. The disc
  15. The halo
  16. ...and 7 more sections

Figures (3)

  • Figure 1: Left: Merged three-color EPIC X-ray image of the four NGC 5746 observations. Red colors represents the soft X-ray band (0.3--0.7 keV), green colors the medium 0.7--1.2 keV band and blue colors the hard 1.2--5.0 keV band . The green ellipse displays the $D_{25}$ ellipse of NGC 5746. The cyan ellipses display the eastern and western outflow regions, the yellow circle represents the inner halo up to a distance of $5'$ from the center of the galaxy. The white annulus displays the background region with inner radius $7\farcm83$ and outer radius $9\farcm42$. Right: 16 circular regions centered on NGC 5746, separated into four quadrants: East, north, west and south (cyan circles).
  • Figure 2: Radial surface brightness profile of the halo of NGC 5746 determined for the whole annulus (left) and for the four quadrants (right) of the circular regions shown in Fig. \ref{['xmm_img']} (excluding the disc). The width of the lines represents the uncertainty interval at the center of each bin.
  • Figure 3: PN and MOS1+MOS2 spectra for the disc, the inner halo out to $r = 5\,\text{arcmin}$, and the two bubbles. The data in the plots were binned for better visibility. The colored lines represent the best fits for the different model components.