Resolved Near-infrared Stellar Photometry from the Magellan Telescope for 13 Nearby Galaxies: JAGB Method Distances

Kavli Affiliate: Wendy L. Freedman

| First 5 Authors: Abigail J. Lee, Andrew J. Monson, Wendy L. Freedman, Barry F. Madore, Kayla A. Owens

| Summary:

We present near-infrared JHK photometry for the resolved stellar populations
in 13 nearby galaxies: NGC 6822, IC 1613, NGC 3109, Sextans B, Sextans A, NGC
300, NGC 55, NGC 7793, NGC 247, NGC 5253, Cen A, NGC 1313, and M83, acquired
from the 6.5m Baade-Magellan telescope. We measure distances to each galaxy
using the J-region asymptotic giant branch (JAGB) method, a new standard candle
that leverages the constant luminosities of color-selected, carbon-rich AGB
stars. While only single-epoch, random-phase photometry is necessary to derive
JAGB distances, our photometry is time-averaged over multiple epochs, thereby
decreasing the contribution of the JAGB stars’ intrinsic variability to the
measured dispersions in their observed luminosity functions. To cross-validate
these distances, we also measure near-infrared tip of the red giant branch
(TRGB) distances to these galaxies. The residuals obtained from subtracting the
distance moduli from the two methods yield an RMS scatter of $sigma_{JAGB –
TRGB}= pm 0.07$ mag. Therefore, all systematics in either the JAGB method and
TRGB method (e.g., crowding, differential reddening, star formation histories)
must be contained within these $pm0.07$ mag bounds for this sample of galaxies
because the JAGB and TRGB distance indicators are drawn from entirely distinct
stellar populations, and are thus affected by these systematics independently.
Finally, the composite JAGB star luminosity function formed from this diverse
sample of galaxies is well-described by a Gaussian function with a modal value
of $M_J = -6.20 pm 0.003$ mag (stat), indicating the underlying JAGB star
luminosity function of a well-sampled full star formation history is highly
symmetric and Gaussian, based on over 6,700 JAGB stars in the composite sample.

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