A Near-Infrared Period-Luminosity Relation for Miras in NGC 4258, an Anchor for a New Distance Ladder

TL;DR

This study establishes a near-infrared Period-Luminosity Relation for Miras in NGC 4258, enabling precise extragalactic distance measurements and contributing to the calibration of the cosmic distance ladder.

Contribution

It develops new criteria for classifying oxygen-rich Miras using NIR data and demonstrates their use in measuring galaxy distances with high accuracy.

Findings

Discovered 438 Mira candidates in NGC 4258.

Measured a Mira PLR with low scatter in the near-infrared.

Found consistency between Mira-based and Cepheid-based distance measurements.

Abstract

We present year-long, near-infrared Hubble Space Telescope WFC3 observations of Mira variables in the water megamaser host galaxy NGC 4258. Miras are AGB variables that can be divided into oxygen- (O-) and carbon- (C-) rich subclasses. Oxygen-rich Miras follow a tight (scatter $\sim 0.14$ mag) Period-Luminosity Relation (PLR) in the near-infrared and can be used to measure extragalactic distances. The water megamaser in NGC 4258 gives a geometric distance to the galaxy accurate to 2.6% that can serve to calibrate the Mira PLR. We develop criteria for detecting and classifying O-rich Miras with optical and NIR data as well as NIR data alone. In total, we discover 438 Mira candidates that we classify with high confidence as O-rich. Our most stringent criteria produce a sample of 139 Mira candidates that we use to measure a PLR. We use the OGLE-III sample of O-rich Miras in the LMC to obtain a relative distance modulus, $\mu_{4258} - \mu_{LMC} = 10.95 \pm 0.01 $ (statistical) $\pm 0.06 $ (systematic) mag in good agreement with the relative distance determined using Cepheids. These results demonstrate the feasibility of discovering and characterizing Miras using the near-infrared with the Hubble Space Telescope and the upcoming James Webb Space Telescope and using them to measure extragalactic distances and determine the Hubble constant.