Mid-infrared Extinction toward the Galactic Center

Abstract We determine the mid-infrared (MIR, ∼5–22 μ m) extinction toward the Galactic center using MIRI/Medium-Resolution Spectrometer (MRS) integral field unit observations of the central 3″ × 3″ region (near 5 μ m) to 7″ × 7″ region (near 22 μ m). To measure the MIR extinction, we employ two approaches: modeling the intrinsic-to-observed dust thermal spectrum and assessing the differential extinction between hydrogen recombination lines. Expanding on prior work, we directly model the dust-opacity distribution along the line of sight, and we make available a Python code that provides a flexible tool for deriving intrinsic dust emission spectra. We confirm the spatial variability of extinction across the field, demonstrating that dusty sources—such as IRS 29N—exhibit higher local extinction. Furthermore, we verify the absence of emission features from polycyclic aromatic hydrocarbons in the MIR spectra of the Galactic center. Using the two complementary methods, we derive a refined “best guess” MIR extinction law for Sgr A* and the surrounding Galactic-center region. By applying the extinction law to an MIR flare measurement discussed in a companion paper, we estimate a residual relative extinction uncertainty for the short MIRI/MRS grating of the order of 0.2 mag from ∼5 to ∼18 μ m and ∼0.3 mag from ∼18 to ∼22 μ m, consistent with our uncertainty estimate.