A revised planetary nebula luminosity function distance to NGC 628 using
  MUSE
  Distance uncertainties plague our understanding of the physical scales
relevant to the physics of star formation in extragalactic studies. The
planetary nebulae luminosity function (PNLF) is one of very few techniques that
can provide distance estimates to within ~10%, however it requires a planetary
nebula (PN) sample that is uncontaminated by other ionizing sources. We employ
optical IFU spectroscopy using MUSE on the VLT to measure [OIII] line fluxes
for sources unresolved on 50 pc scales within the central star-forming galaxy
disk of NGC 628. We use diagnostic line ratios to identify 62 PNe, 30 supernova
remnants and 87 HII regions within our fields. Using the 36 brightest PNe we
determine a new PNLF distance modulus of 29.91^{+0.08}_{-0.13} mag
(9.59^{+0.35}_{-0.57} Mpc), in good agreement with literature values but
significantly larger than the previously reported PNLF distance. We are able to
explain the discrepancy and recover the previous result when we reintroduce SNR
contaminants to our sample. This demonstrates the power of full spectral
information over narrowband imaging in isolating PNe. Given our limited spatial
coverage within the galaxy, we show that this technique can be used to refine
distance estimates even when IFU observations cover only a fraction of a galaxy
disk.
