Abstract
Context. The diffuse gamma-ray emission of 26Al at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. The morphology and dynamics of the interstellar medium are investigated in astrophysics through 3D hydrodynamic simulations in fine detail as there are few suitable astronomical probes available. Aims. We aim to compare a galactic-scale hydrodynamic simulation of the Galaxy’s interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on 26Al emission in the Milky Way, extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we performed maximum likelihood fits of both simulated sky maps and observation-based maximum entropy maps to measurements using INTEGRAL/SPI. In order to study general morphological properties, we compare the scale heights of 26Al emission produced by the simulation to INTEGRAL/SPI measurements. Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, however it differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small-scale height features and a mismatch at larger-scale heights. We attribute this to prominent foreground emission sites which are not captured by the simulation.
Highlights
26Al is an ideal tracer of ongoing nucleosynthesis in the Galaxy
We investigate a range of methodological approaches for a generalised comparison of 26Al full-sky emission maps from the simulation performed by Fujimoto et al (2018) to gamma-ray data measured with the Spectrometer on INTEGRAL (SPI) (Vedrenne et al 2003) aboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL)
In order to spatially resolve how the overall scale height is composed of certain features with different latitude extent, we investigate separate rectangular regions of interest (ROIs) of 12◦ in longitude and 180◦ in latitude each
Summary
The spatial distribution of 26Al provides information about active sites of nucleosynthesis and galactic chemical enrichment, as well as dynamics and feedback processes in the interstellar medium (ISM) throughout the Milky Way A fundamentally informative comparison of hydrodynamical simulations to actual measurements is challenging because the Milky Way is one particular realisation of a galaxy and any given hydrodynamic simulation will, even if it is intended to be similar, not necessarily match it perfectly. This is further complicated by the observational limitations of gamma-ray data due to the necessity of image reconstruction methods as compared with direct imaging.
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