X-Ray Properties of NGC 253's Starburst-driven Outflow

Abstract

We analyze image and spectral data from ≈365 ks of observations from the Chandra X-ray Observatory of the nearby, edge-on starburst galaxy NGC 253 to constrain properties of the hot phase of the outflow. We focus our analysis on the −1.1 to +0.63 kpc region of the outflow and define several regions for spectral extraction where we determine best-fit temperatures and metal abundances. We find that the temperatures and electron densities peak in the central ∼250 pc region of the outflow and decrease with distance. These temperature and density profiles are in disagreement with an adiabatic spherically expanding starburst wind model and suggest the presence of additional physics such as mass loading and nonspherical outflow geometry. Our derived temperatures and densities yield cooling times in the nuclear region of a few million years, which may imply that the hot gas can undergo bulk radiative cooling as it escapes along the minor axis. Our metal abundances of O, Ne, Mg, Si, S, and Fe all peak in the central region and decrease with distance along the outflow, with the exception of Ne, which maintains a flat distribution. The metal abundances indicate significant dilution outside of the starburst region. We also find estimates of the mass outflow rates, which are 2.8 M ⊙ yr−1 in the northern outflow and 3.2 M ⊙ yr−1 in the southern outflow. Additionally, we detect emission from charge exchange and find it makes a significant contribution (20%–42%) to the total broadband (0.5–7 keV) X-ray emission in the central and southern regions of the outflow.

The galactic bubbles of starburst galaxies

“…At the base of the wind, close to the inner boundary, we impose a high temperature of 5 × 10 7 K. This hot gas undergoes cooling due to adiabatic expansion and gradually reaches a temperature of 10 5 K at a distance of 2 kpc from the galactic center. These observations support the findings of the galactic bubble M82, as discussed in Lopez et al (2023).…”

The high energy X-ray probe: resolved X-ray populations in extragalactic environments

“…For example, a few dozen XRBs have been observed across the span of the galactic disk, probing the formation of populations of compact objects and binaries (e.g., Pietsch et al, 2001). Diffuse thermal emission (kT ≈ 0.4 keV) spans several arcminutes along the plane of the disk, with a hotter ∼1 keV gas component observed in a collimated kpc-scale outflow emanating from the nuclear starburst (e.g., Strickland and Stevens, 2000;Strickland et al, 2002;Lopez et al, 2023). Finally, NGC 253 is one of only two starburst galaxies (the other being M82) that have been detected from hundreds of MeV to TeV energies, as a result of particle accelerations (e.g., Abramowski et al, 2012;H.…”

Cosmic Ray Processes in Galactic Ecosystems

“…All three galaxies host outflows, which have substantial impacts on CR containment and feedback potential. These outflows are multi-phase [531][532][533][534][535] and are driven by the confluence of feedback winds from ongoing concentrated bursts of nuclear star-formation. M82 maintains a star formation rate of approximately 10 M yr −1 [536] within a central region of diameter 0.3 kpc [537,538].…”