Measuring Accurate Distances with the Tip Of The Red Giant Branch

The old (>4 Gyr), metal-poor ([Fe/H] < -0.5 dex) Tip of the Red Giant Branch (TRGB) is a conceptually straightforward stellar standard candle that, when measured in nearby (<20 Mpc) galaxies under the appropriate conditions, can return distance measurements accurate to 2%. Considerable care must be taken, however, to ensure that the necessary criteria for the TRGB to remain a standard candle are satisfied. This includes controlling for the ages and metallicities of imaged TRGB stars, and the extent to which the target stars are crowded/blended, which I show is possible using only two-band point-source photometry. I explore trends observed in measured TRGB magnitudes as a function of location within host galaxies, and show that biased TRGB distance measurements can arise, particularly in star-forming environments, if important spatial information is not taken into account. From this, I will present a set of guidelines to follow in order to measure accurate TRGB distances to nearby massive galaxies.