Star Counts and the Warped and Flaring Milky Way Disk

Abstract

This paper reports the star count predictions of warped and Ñaring models of the outer Milky Way disk. These have been suggested as possible locations of the lenses responsible for the microlensing events toward the Large Magellanic Cloud (LMC). Three such models are investigated in detail, and the theoretical predictions are confronted with Hubble Space T elescope star count data in seven low-latitude Ðelds (30¡ \ o b o \ 40¡). If the warped and Ñaring disk population has the same characteristics as disk stars in the solar neighborhood, then the models can be unambiguously ruled out. Metallicity gradients are well known in disk galaxies and may cause the outer disk population to di †er in colors and luminosity from the local population. This e †ect is studied using a simple Ansatz for the variation in the color-magnitude relation with position, and while it is shown to lead to better agreement with the star counts, upper limits on the contribution of the warped and Ñaring disk to the optical depth are still below the value measured toward the LMC. Only if the warp is very asymmetric or if the luminosity function changes strongly with Galactocentric radius can the models be made consistent with the star counts.

A new planetary nebula in the outer reaches of the Galaxy

“…That is a large height indeed, but we note that the well-known flaring of the outer disk (see e.g. Gyuk et al 1999) allows a high probability of thin disk objects being located even at this offset from the mid-plane. Using the Gyuk et al (1999) We will adopt for IACPN the S − r distance of 12.8 kpc.…”

“…Gyuk et al 1999) allows a high probability of thin disk objects being located even at this offset from the mid-plane. Using the Gyuk et al (1999) We will adopt for IACPN the S − r distance of 12.8 kpc. At D GC = 20.8 kpc, it would be one of the most distant planetary nebula from the Galactic centre for which a distance has been determined (cf.…”

Does the Stellar Distribution Flare? A Comparison of Stellar Scale Heights With Lab H I Data

“…For R = 2 R the flaring in H i is about a factor of two stronger compared to heights used by Gyuk et al (1999), Reylé et al (2009), andPolido et al (2013).…”

The Galactic warp as seen from 2MASS survey

“…Nearly all warp studies indicate values of this angle close to this one within an uncertainty of a few degrees. Preliminary results for the stellar warp obtained from the analysis of a part of the DE-NIS (Epchtein et al 1997) survey (Derrière & Robin 2001;Derrière 2001) indicate a best value for the starting galactocentric radius of the warp to be R warp = 8.4 kpc, close to R and a slope of (γ warp = 0.18) similar to Gyuk et al (1999).…”