Tip of the red giant branch distances to galaxies .3. The dwarf galaxy Sextans A

We present color-magnitude diagrams and luminosity functions for 4486 stars in the nearby dwarf galaxy Sextans A, based on VI photometry obtained with the COSMIC CCD prime-focus camera on the Palomar 5 m telescope. We discuss the previous disagreement in the literature over published zero points for multicolor photometry of the resolved stars in Sex A. The new data presented here shed light on and offer a means of resolving these differences. The discontinuity of the I-band red giant branch luminosity function has been measured at I = 21.73 +/- 0.09 mag. Identification of this feature with the tip of the first-ascent red giant branch at M(I) = -4.01 mag yields an independent (Population II) distance-modulus estimate of 25.74 +/- 0.13 mag (1.42 Mpc) to this galaxy. BVRI CCD observations are presented and combined with published data to derive period-luminosity relations for the six previously known Cepheids in Sex A that have periods ranging from 10 to 25 days. A reddening-corrected true (Population I) distance modulus of 25.85 +/- 0.15 mag is derived, which corresponds to a linear distance of 1.48 Mpc. The agreement of these two independent distance determinations is extremely encouraging; together with similar intercomparisons for other nearby galaxies, it would appear that the zero points of the Cepheid and TRGB distance scales agree at the 0.1 mag level (or 5% in distance). The TRGB method appears to be a distance indicator that is of comparable precision and accuracy as Cepheids, which for so long have been unique in this respect.