Distance and reddening of the Local Group dwarf irregular galaxy NGC 6822

Fusco, F.; Buonanno, R.; Bono, G.; Cassisi, S.; Monelli, M.; Pietrinferni, A.

doi:10.1051/0004-6361/201220554

Cited by 13 publications

(25 citation statements)

References 34 publications

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“…They determine a reddening using the similar CMD of the nearly extinction-free IC 1613, finding E(B − V ) = 0.30 ± 0.032 mag in their outer fields and E(B − V ) = 0.37 ± 0.02 mag in their inner field. The higher extinction in the central field calculated by Fusco et al (2012) is consistent with the average reddening we calculate using our Cepheids, which have a distance from the center consistent with the location of their central field. Fusco et al (2012) use a new theoretical calibration to determine a TRGB distance of µ o = 23.54 ± 0.05 mag, which is 0.16 mag larger than our distance, but consistent with the mean of other TRGB distance measurements.…”

Section: Trgb Distance Comparisonsupporting

confidence: 86%

“…A low galactic latitude leads to a large extinction along the line of sight to NGC 6822, extinction within the galaxy itself, and variable extinction across its face (Fusco et al 2012). It is thus of particular importance to solve for the extinction with high accuracy.…”

Section: Distance Determinations To Ngc 6822mentioning

confidence: 99%

“…The most recent study calculating a TRGB distance to NGC 6822 is Fusco et al (2012). They perform a new photometric analysis of archival HST ACS observations, obtaining color-magnitude diagrams (CMD) for three fields.…”

Section: Trgb Distance Comparisonmentioning

confidence: 99%

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A New Cepheid Distance Measurement and Method for NGC 6822

Persson

Freedman

Madore

et al. 2014

ApJ

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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.

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Section: Trgb Distance Comparisonsupporting

confidence: 86%

Section: Distance Determinations To Ngc 6822mentioning

confidence: 99%

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A New Cepheid Distance Measurement and Method for NGC 6822

Persson

Freedman

Madore

et al. 2014

ApJ

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“…The Schlegel, Finkbeiner, & Davis (1998) dust maps give a foreground extinction of EpB´V q " 0.24 based on dust column density surveys; however, the reddening map derived by Battinelli, Demers & Kunkel (2006) from these data show some hint of the NGC 6822 HI structure, indicating that at least some of the spatially variable dust emission originates in NGC 6822, where the conversion from far-infrared surface brightness to visual extinction may differ from that in the Milky Way. A recent HST study of the stellar populations by Fusco et al (2012) gives a central EpB´V qC " 0.37˘0.02 , and an exterior EpB´V qE " 0.30˘0.03 -these correspond roughly to our South and East fields, respectively.…”

Section: Reddening Correctionsupporting

confidence: 72%

Ca ii triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities

Swan

Cole

Tolstoy³

et al. 2016

Mon. Not. R. Astron. Soc.

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We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at « 8500Å was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line of sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be xv rad y "´52.8˘2.2 km s´1 with dispersion σ v " 24.1 km s´1, in agreement with other studies. Ca ii triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was x[Fe/H]y "´0.84˘0.04 with dispersion σ " 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal rich and metal poor stars; the former were found to cluster towards small radii with the metal poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal poor stars was found to be higher than that of the metal rich stars (σ vMP " 27.4 km s´1; σ vMR " 21.1 km s´1); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disklike distribution than the younger stars.. The low ratio v rot {σ v suggests that within the inner 10 1 , NGC 6822's stars are dynamically decoupled from the H I gas, and possibly distributed in a thick disc or spheroid structure.

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“…Zero-point calibrations of the TRGB in previous studies were done with theoretical models (Salaris & Cassisi 1997;Fusco et al 2012) or observational approaches (Lee et al 1993;Ferrarese et al 2000;Bellazzini et al 2001Bellazzini et al , 2004Rizzi et al 2007;Bellazzini 2008;Tammann et al 2008;Madore et al 2009). Various distance indicators (RR Lyrae stars, Cepheids, eclipsing binary stars, and horizontal branch stars) have been used for this calibration.…”

Section: Introductionmentioning

confidence: 99%

The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. Iv. Color Dependence and Zero-Point Calibration

Jang

Lee

2017

ApJ

101

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We present a revised TRGB calibration, accurate to 2.7% of distance. A modified TRGB magnitude corrected for the color dependence of the TRGB, the QT magnitude, is introduced for better measurement of the TRGB. We determine the color-magnitude relation of the TRGB from photometry of deep images of HST/ACS fields around eight nearby galaxies. The zero-point of the TRGB at the fiducial metallicity ([Fe/H]= −1.6 ((V − I) 0,T RGB = 1.5)) is obtained from photometry of two distance anchors, NGC 4258 (M106) and the LMC, to which precise geometric distances are known: M QT,T RGB = −4.023 ± 0.073 mag from NGC 4258 and M QT,T RGB = −4.004 ± 0.096 mag from the LMC. A weighted mean of the two zero-points is M QT,T RGB = −4.016 ± 0.058 mag. Quoted uncertainty is ∼ 2 times smaller than those of the previous calibrations. We compare the empirical TRGB calibration derived in this study with theoretical stellar models, finding that there are significant discrepancies, especially for red color ((F606W − F814W) 0 2.5). We provide the revised TRGB calibration in several magnitude systems for future studies. Subject headings: galaxies: distances and redshifts -galaxies: stellar content -stars : Population II 1. INTRODUCTION The Tip of the Red Giant Branch (TRGB) represents the brightest part of the Red Giant Branch (RGB) in the color-magnitude diagrams (CMDs) of old stellar systems such as globular clusters and halos in galaxies. It corresponds to the core-He flash point in the evolutionary stages of low mass stars. An implication of the TRGB as a distance indicator was suggested first by Baade (1944). In his pioneering paper introducing the concept of stellar populations I and II, he investigated the red-sensitive plates of three early type stellar systems, M32, NGC 205, and the central region (bulge) of M31, concluding that the brightest stars (RGB stars) in these three systems have similar magnitudes and colors. Sandage (1971) pointed out that photographs of the Local Group galaxies invariably show surrounding red stars, which have similar absolute magnitudes and colors. Based on the Cepheid distances to three Local Group galaxies (M31, M33 and IC 1613), he derived a mean absolute magnitude of these brightest red stars to be M V = −3.0 ± 0.2 mag.Mould et al. (1983, 1984) and Mould & Kristian (1986) carried out CCD photometry of four Local Group galaxies (M31, M33, NGC 147 and NGC 205) and determined the TRGB distances to these galaxies, which are not much different from previous distance estimates to M31 and M33 based on Cepheid variables. They adopted a bolometric magnitude of the TRGB (M bol ∼ −3.5 mag) given by Frogel et al. (1983). Freedman (1988b presented CCD photometry of two fields in IC 1613. Color-magnitude diagrams (CMDs) of these fields show a clear RGB population and the TRGB. Adopting the bolometric magnitude the TRGB (M bol ∼ −3.5 mag), she derived remarkably similar TRGB distances between the two fields, showing only 0.04 mag difference. Moreover, the TRGB distance from her photometry is in ex-

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Distance and reddening of the Local Group dwarf irregular galaxy NGC 6822

Cited by 13 publications

References 34 publications

A New Cepheid Distance Measurement and Method for NGC 6822

A New Cepheid Distance Measurement and Method for NGC 6822

Ca ii triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities

The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. Iv. Color Dependence and Zero-Point Calibration

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