Near-IR TRGB Distance to Nearby Dwarf Irregular Galaxy NGC 6822

Abstract

We report the distance modulus of nearby dwarf irregular galaxy NGC 6822 estimated from the so-called Tip of Red-giant Branch (TRGB) method. To detect the apparent magnitudes of the TRGB we use the color-magnitude diagrams (CMDs) and luminosity functions (LFs) in the near-infrared JHK bands. Foreground stars, main-sequence stars, and supergiant stars have been classified on the (g - K, g) plane and removed on the near-infrared CMDs, from which only RGB and AGB stars are remained on the CMDs and LFs. By applying the Savitzky-Golay filter to the obtained LFs and detecting the peak in the second derivative of the observed LFs, we determined the apparent magnitudes of the TRGB. Theoretical absolute magnitudes of the TRGB are estimated from Yonsei-Yale isochrones with the age of 12Gyr and the metallicity range of -2.0 <[Fe/H]< -0.5. The derived values of distance modulus to NGC 6822 are (m - M) = <TEX>$23.35{\pm}0.26$</TEX>, <TEX>$23.20{\pm}0.42$</TEX>, and <TEX>$23.27{\pm}0.50$</TEX> for J, H, and K bands, respectively. Distance modulus in bolometric magnitude is also derived as (m - M) = <TEX>$23.41{\pm}0.17$</TEX>. We compare the derived values of the TRGB distance modulus to NGC 6822 in the near-infrared bands with the previous results in other bands.