Vertical position of the Sun with $\gamma$-rays

Abstract

We illustrate a method for estimating the vertical position of the Sun above the Galactic plane by $\gamma$-ray observations. Photons of $\gamma$-ray wavelengths are particularly well suited for geometrical and kinematic studies of the Milky Way because they are not subject to extinction by interstellar gas or dust. Here, we use the radioactive decay line of ${}^{26}\mathrm{Al}$ at $1.809\mathrm{MeV}$ to perform maximum likelihood fits to data from the spectrometer SPI on board the INTEGRAL satellite as a proof-of-concept study. Our simple analytic 3D emissivity models are line-of-sight integrated, and varied as a function of the Sun's vertical position, given a known distance to the Galactic centre. We find a vertical position of the Sun of $z_0=15\pm 17\mathrm{pc}$ above the Galactic plane, consistent with previous studies, finding $z_0$ in a range between $5$ and $29\mathrm{pc}$. Even though the sensitivity of current MeV instruments is several orders of magnitude below that of telescopes for other wavelengths, this result reveals once more the disregarded capability of soft $\gamma$-ray telescopes. We further investigate possible biases in estimating the vertical extent of $\gamma$-ray emission if the Sun's position is set incorrectly, and find that the larger the true extent, the less is it affected by the observer position. In the case of ${}^{26}\mathrm{Al}$ with an exponential scale height of $150,\mathrm{pc}$ ($700\mathrm{pc}$) in the inner (full) Galaxy, this may lead to misestimates of up to $25\%$.

arXiv comment5 pages, 5 figures, accepted by A&A

References in corpus (26)

• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• A geometric distance measurement to the Galactic Center black hole with 0.3% uncertainty
• The McGill Magnetar Catalog
• Radioactive 26Al and massive stars in the Galaxy
• Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole
• The all-sky distribution of 511 keV electron-positron annihilation emission
• The initial conditions of stellar protocluster formation. I. A catalogue of Spitzer dark clouds
• COBE's Galactic Bar and Disk
• Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)
• The Milky Way Project First Data Release: A Bubblier Galactic Disk
• A three-dimensional map of the Milky Way using classical Cepheid variable stars
• A radio catalog of Galactic HII regions for applications from decimeter to millimeter wavelengths
• Probing disk properties with open clusters
• Characteristics of the Galaxy according to Cepheids
• Kinematics of massive star ejecta in the Milky Way as traced by 26Al
• Spectral and intensity variations of Galactic 26^Al emission
• Revised Geometric Estimates of the North Galactic Pole and the Sun's Height Above the Galactic Midplane
• Study of open clusters within 1.8 kpc and understanding the Galactic structure
• INTEGRAL/SPI $\gamma$-ray line spectroscopy
• Properties of Star Clusters - II: Scale Height Evolution of Clusters
• The Galactic ${}^{26}$Al emission map as revealed by INTEGRAL/SPI
• Feedback by massive stars and the emergence of superbubbles II. X-ray properties
• 26Al kinematics: superbubbles following the spiral arms? Constraints from the statistics of star clusters and HI supershells
• The Compton Spectrometer and Imager
• OB Stars in the Solar Neighborhood I: Analysis of their Spatial Distribution
• Background modelling for $\gamma$-ray spectroscopy with INTEGRAL/SPI

Cited by in corpus (10)

• Local stellar formation history from the 40 pc white dwarf sample
• On the origins of extreme velocity stars as revealed by large-scale Galactic surveys
• X-Ray Constraints on Dark Photon Tridents
• Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta
• Strong Constraints on Dark Photon and Scalar Dark Matter Decay from INTEGRAL and AMS-02 data
• Detailed Mapping of the Galactic Disk Structure in the Solar Neighborhood through LAMOST K Dwarfs
• Cosmic Radioactivity and Galactic Chemical Evolution
• Multi-Wavelength characterization of VVVX open clusters
• Mapping the reddening plane in the Galactic disk through interstellar extinction of open clusters
• The Galactic population of canonical pulsars