Cepheid-based Distances to NGC 4303 and NGC 1068

TL;DR

This study uses Hubble Space Telescope observations of Cepheid variables to accurately measure the distances to NGC 4303 and NGC 1068, refining the cosmic distance scale for these key galaxies.

Contribution

First precise Cepheid-based distance measurements to NGC 4303 and NGC 1068 using HST data and updated calibration methods.

Findings

Distances: 16.47 Mpc for NGC 4303 and 10.72 Mpc for NGC 1068.

Identified 33,694 Cepheid candidates across both galaxies.

Calibrated period-luminosity relation with recent LMC distance measurements.

Abstract

We present Cepheid-based distances to two canonical AGN: NGC 4303 (M 61) and NGC 1068. Data were obtained using the Hubble Space Telescope with nonredundant time spacing over 12 visits for each target, and observations were made with the F555W and F814W filters. We found 32,694 point sources in NGC 4303, and 130 of these were determined to be strong Cepheid candidates with periods ranging ~$13-93$ days. In NGC 1068, we found 20,207 point sources, where 51 of these were strong Cepheid candidates with periods ~$14-92$ days. We fit the period$-$luminosity relationship, calibrated based on a geometric distance to the LMC by Riess et al. (2019), to our Cepheid candidates in each galaxy and correct for potential effects of metallicity. Using a distance constraint for the LMC given by Pietrzy\'nski et al. (2019), this yields a distance modulus of $\mu = 31.083 \pm 0.035$ mag for NGC 4303 and $\mu = 30.150 \pm 0.106$ mag for NGC 1068. Thus, we measure distances of $D = 16.47 \pm 0.27$ Mpc to NGC 4303 and $D = 10.72 \pm 0.52$ Mpc to NGC 1068.