A New Cepheid Distance Measurement and Method for NGC 6822

Abstract

We present a revised distance to the nearby galaxy NGC 6822 using a new multi-band fit to both previously published and new optical, near-and mid-infrared data for Cepheid variables. The new data presented in this study include multi-epoch observations obtained in 3.6 µm and 4.5 µm with the Spitzer Space Telescope taken for the Carnegie Hubble Program. We also present new observations in J, H and K s with FourStar on the Magellan Baade telescope at Las Campanas Observatory. We determine mean magnitudes and present new period-luminosity relations in V, I, J, H, K s , IRAC 3.6 µm and 4.5 µm . In addition to using the multiband distance moduli to calculate extinction and a true distance, we present a new method for determining an extinction-corrected distance modulus from multi-band data with varying sample sizes. We combine the distance moduli and extinction for individual stars to determine E(B − V ) = 0.35 ± 0.04 and a true distance modulus µ o = 23.38 ± 0.02 stat ± 0.04 sys . * This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

On a New Method to Estimate the Distance, Reddening, and Metallicity of RR Lyrae Stars Using Optical/Near-infrared (B, V, I, J, H, K) Mean Magnitudes: ω Centauri as a First Test Case

“…The slope of the nonlinear fit, and in turn, the reddening is mainly constrained by shorter wavelength B-, V-and I-band mean magnitudes. This "star-by-star" multi-wavelength, reddening and true distance modulus plot was first introduced by Rich et al (2014) in their parallel study of Cepheids in NGC 6822 (see their Figures 5 and 6). The difference in the dispersion when moving from optical to NIR measurements is due to intrinsic and extrinsic effects.…”

Physical Properties of Molecular Clouds at 2 pc Resolution in the Low-metallicity Dwarf Galaxy NGC 6822 and the Milky Way

“…In many ways NGC 6822 resembles a two times less massive version of the SMC (e.g., Jameson et al 2016), except that the SMC is currently undergoing a strong interaction with the LMC and the Milky Way. The proximity ( =  D 474 13 kpc; Rich et al 2014) makes NGC 6822 an ideal target to study cloud structure and star formation at high resolution; at this distance,  » 1 2.3 pc, so that ALMA easily resolves cloud substructure. Like other comparatively isolated dwarf irregular galaxies, NGC 6822 is rich in gas with an atomic gas mass 11 of »Ḿ 1.3 10 atom 8  M (Weldrake et al 2003;de Blok & Walter 2006b).…”

AT 2017fvz: a nova in the dwarf irregular galaxy NGC 6822

“…McAlary et al (1983) found E B−V = 0.36 mag, Gieren et al (2006) reported a similar average reddening of E B−V = 0.36 ± 0.01 mag. Rich et al (2014) used optical and infrared data for Cepheids to determine that the foreground reddening along the line of sight to NGC 6822 is E B−V = 0.35 ± 0.04 mag.…”

“…NGC 6822 is a dark matter dominated (Weldrake et al 2003) dwarf irregular galaxy in the Local Group at a distance 476 ± 44 kpc (Rich et al 2014). It provides a low-metallicity environment compared to the majority of Local Group novae: [Fe/H] ≈ −0.5 (see, e.g., Larsen et al 2018).…”