Towards Precision Cosmology With Improved PNLF Distances Using VLT-MUSE I. Methodology and Tests

Abstract

The [O III] λ5007 Planetary Nebula Luminosity Function (PNLF) is an established distance indicator that has been used for more than 30 years to measure the distances of galaxies out to ∼ 15 Mpc. With the advent of the Multi-Unit Spectroscopic Explorer on the Very Large Telescope (MUSE) as an efficient wide-field integral field spectrograph, the PNLF method is due for a renaissance, as the spatial and spectral information contained in the instrument's datacubes provides many advantages over classical narrow-band imaging. Here we use archival MUSE data to explore the potential of a novel differential emission-line filter (DELF) technique to produce spectrophotometry that is more accurate and more sensitive than other methods. We show that DELF analyses are superior to classical techniques in high surface brightness regions of galaxies and we validate the method both through simulations and via the analysis of data from two early-type galaxies (NGC 1380 and NGC 474) and one late-type spiral (NGC 628). We demonstrate that with adaptive optics support or under excellent seeing conditions, the technique is capable of producing precision ( 0.05 mag) [O III] photometry out to distances of 40 Mpc while providing discrimination between planetary nebulae and other emission-line objects such as H II regions, supernova remnants, and background galaxies. These capabilities enable us to use MUSE to measure precise PNLF distances beyond the reach of Cepheids and the tip of the red giant branch method, and become an additional tool for constraining the local value of the Hubble constant.

Planetary Nebula Luminosity Function distances for 19 galaxies observed by PHANGS-MUSE

“…In Figure 2, we compare our measured fluxes. While we find good agreement for the [O ] magnitudes, with only minor offsets of Δ𝑚 [O ] = 0.03 ± 0.23 mag (Herrmann et al 2008), Δ𝑚 [O ] = 0.01 ± 0.29 mag (Kreckel et al 2017) and Δ𝑚 [O ] = 0.08 ± 0.26 mag (Roth et al 2021), the H 𝛼 fluxes are at odds. Figure 2 suggests systematically higher H 𝛼 fluxes compared to Kreckel et al (2017).…”

“…This galaxy has been studied extensively with numerous existing distance measurements from different methods (see Figure 8 for a selection). Among them are the aforementioned PNLF studies by Herrmann et al (2008), Kreckel et al (2017) and Roth et al (2021). This makes this galaxy a valuable benchmark to validate our methods.…”

“…The fitted luminosity function is shown with a black dotted line. PHANGS-MUSE data, but was limited to the three pointings that were available at the time, and Roth et al (2021) uses the same raw data but with a different data reduction. We find 139 PNe that provide a well constrained distance modulus of (𝑚 − 𝑀) = 29.89 +0.06 −0.09 mag (𝐷 = 9.52 +0.26 −0.41 Mpc).…”

“…These 'overluminous' objects are distinctly brighter than the bright end of the remaining luminosity function (see Section 4, Figure 6), and hence, cannot be described by the PNLF. They have been found in many PN studies (Longobardi et al 2013;Hartke et al 2017;Roth et al 2021), but their exact origin remains unclear (Jacoby et al 1996). Possible explanations include two PNe that accidentally fall close to each other, a misclassified H region or a background Ly-𝛼 galaxy.…”

“…In recent years, the emergence of powerful integral field unit (IFU) spectroscopy instruments has revolutionised the field (Kreckel et al 2017;Spriggs et al 2020;Roth et al 2021). Their fields of view are large enough to detect a sufficient number of PNe in order to measure the PNLF.…”