# Resolving the Discrepancy of Distance to M60, a Giant Elliptical Galaxy in Virgo

## TL;DR

This study uses Hubble Space Telescope data to measure the distance to M60 via the tip of the red giant branch, resolving discrepancies between previous planetary nebula luminosity function and surface brightness fluctuation distance estimates.

## Contribution

It provides a new TRGB-based distance measurement to M60, clarifying the uncertainties in prior PNLF and SBF distance estimates for this galaxy.

## Key findings

- TRGB distance to M60 is 16.23 Mpc
- PNLF distances are overestimated compared to TRGB
- SBF distances are slightly underestimated compared to TRGB

## Abstract

There is a well-known discrepancy in the distance estimation for M60, a giant elliptical galaxy in Virgo: the planetary nebula luminosity function (PNLF) distance moduli for this galaxy are, on average, $~0.4$ mag smaller than the values based on the surface brightness fluctuation (SBF) in the literature. We present photometry of the resolved stars in an outer field of M60 based on deep F775W and F850LP images in the Hubble Space Telescope obtained as part of the Pure Parallel Program in the archive. Detected stars are mostly old red giants in the halo of M60. With this photometry we determine a distance to M60 using the tip of the red giant branch (TRGB). A TRGB is detected at $F850LP_{\rm TRGB}=26.70\pm0.06$ mag, in the luminosity function of the red giants. This value corresponds to $F814W_{0,\rm TRGB}=27.13\pm0.06$ mag and $QT_{\rm TRGB}=27.04\pm0.07$ mag, where $QT$ is a color-corrected F814W magnitude. From this we derive a distance modulus, $(m-M)_0=31.05\pm0.07{\rm(ran)}\pm0.06{\rm (sys)}$ ($d=16.23\pm0.50{\rm (ran)}\pm0.42{\rm (sys)}$ Mpc). This value is $0.3$ mag larger than the PNLF distances and $0.1$ mag smaller than the SBF distances in the previous studies, indicating that the PNLF distances to M60 in the literature have larger uncertainties than the suggested values.