Impact of Distance Determinations on Galactic Structure. I. Young and Intermediate-Age Tracers

Matsunaga, Noriyuki; Bono, G.; Chen, Xiaodian; Grijs, Richard de; Inno, L.; Nishiyama, Shogo

doi:10.1007/978-94-024-1631-2_5

Cited by 1 publication

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“…The zero-point uncertainty of the infrared period-luminosity relation is around 0.033 mag 9,44 . The uncertainty in the near-infrared extinction law is the main contributor to the distance error in the Galactic plane; it can be up to 15% for heavily obscured stars 45 . We adopted the infrared extinction law determined using Cepheids in the Galactic Center direction (see Table 2, first row).…”

Section: Methodsmentioning

confidence: 99%

An intuitive 3D map of the Galactic warp’s precession traced by classical Cepheids

et al. 2019

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The Milky Way's neutral hydrogen (HI) disk is warped and flared 1, 2 . However, a dearth of accurate HI-based distances has thus far prevented the development of an accurate Galactic disk model. Moreover, the extent to which our Galaxy's stellar and gas disk morphologies are mutually consistent is also unclear. Classical Cepheids, primary distance indicators with distance accuracies of 3-5% 3 , offer a unique opportunity to develop an intuitive and accurate three-dimensional picture. Here, we establish a robust Galactic disk model based on 1339 classical Cepheids. We provide strong evidence that the warp's line of nodes is not oriented in the Galactic Center-Sun direction. Instead, it subtends a mean angle of 17.5 • ± 1 • (formal) ±3 • (systematic) and exhibits a leading spiral pattern. Our Galaxy thus follows Briggs' rule for spiral galaxies 4 , which suggests that the origin of the warp is associated with torques forced by the massive inner disk 5 . The stellar disk traced by Cepheids follows the gas disk in terms of their amplitudes; the stellar disk extends to at least 20 kpc 6,7 . This morphology provides a crucial, updated map for studies of the kinematics and archaeology of the Galactic disk.We have compiled samples of classical Cepheids from the Wide-field Infrared Survey Explorer (WISE) catalogue of periodic variables 8 (our 'WISE Cepheid sample') as well as from a number of optical surveys (collectively referred to as our 'optical Cepheid sample'). We will discuss both samples separately, because the catalogues' optical and infrared passbands are characterised by significantly different photometric and extinction sensitivities. Highly accurate Cepheid distances can be estimated using their well-established wavelength-dependent period-luminosity relations. To mitigate the influence of extinction in the Galactic plane and of photometric uncertainties at infrared wavelengths, we adopted the 'infrared multi-passband optimal distance method' 9 to determine accurate Cepheid distances. Contaminants, including Type-II Cepheids, long-period eclipsing binaries and quasi-periodic variables were removed using Gaia Data Release 2 parallaxes 10 .Cepheids located in areas centered on the Magellanic Clouds were also excluded. Careful sample selection resulted in a tally of 2330 classical Cepheids for further analysis.Distances were converted to 3D XY z and spherical Rφz coordinates by adopting a reference frame centered on the Galactic Center and a solar Galactocentric distance R 0 = 8.0 kpc. Here, φ is the Galactocentric angle in the anticlockwise direction (aligned with the disk's rotation axis) with respect to the solar position (φ = 0 • ). Since Gaia parallaxes are reliable within ∼5 kpc, we only selected Cepheids within the volume R < 20, |z| < 2 kpc to avoid significant contamination by Type-II Cepheids. Our downselection included 1459 Cepheids with distances accurate to <5%, corresponding to a distance modulus standard deviation <0.108 mag. Cepheids located clearly away from the best-fitting warp model (∆ > 1 kp...

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Section: Methodsmentioning

confidence: 99%