We are looking at other galaxies through the dust from the disk of our own galaxy, diminishing it and making it look redder. This dust extinction is easily noticed when looking towards the plane of the galaxy, but a smaller effect exists even when looking towards the high Galactic latitudes. To get the accurate photometry of galaxies one needs to correct for the missing light using dust maps coupled with the knowledge of how extinction varies with wavelength - the so called extinction law. Although the extinction is most severe at bluer wavelengths, it does affect near-IR light as well. We know that the extinction curve varies in regions of dense dust with respect to the diffuse dust, or at least it does so for UV and optical. In the near-IR there has been a long-standing debate as to whether the extinction law varies, or is it fixed. Near-IR law is especially challenging to measure at high Galactic latitude, since there is not much dust there to begin with.
A study led by recent IU graduate Bobby Butler, titled The Near-infrared Extinction Law at High and Low Galactic Latitudes, published in the Astrophysical Journal employs the power of a large dataset of stars with SDSS spectra to overcome these limitations and determine the near-IR extinction law spanning both high and low latitudes. Study finds that the near-IR extinction law is the same irrespective of the latitude and dust column density. It also finds that it stays the same even when UV or optical portions vary. This result will be useful for upcoming near-IR surveys that aim for high photometric precision in near-IR, such as Euclid and Roman Space Telescope.
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