Interstellar Extinction toward the Galactic Bulge from OGLE-III data

We present a paper by David M. Nataf et al., entitled Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way’s RV∼2.5 Extinction Curve, ApJ,2013,769,88, available also from arXiv archive as arXiv:1208.1263

In this paper we combine V I photometry from OGLE-III with VVV and 2MASS measurements of E(J−Ks) (predominantly measurements with VVV data from Gonzalez et al. 2012, A&A...543A..13G) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well-fit by the relation AI = 0.7465×E(V−I) + 1.3700×E(J−Ks), or, equivalently, AI = 1.217×E(V−I)(1 + 1.126×(E(J−Ks )/E(V−I) − 0.3433)). The optical and near-IR reddening law toward the inner Galaxy approximately follows an RV ≈ 2.5 extinction curve with a dispersion σRV≈0.2, consistent with extragalactic investigations of the hosts of type Ia SNe. Differential reddening is shown to be significant on scales as small as as our mean field size of 6′, with the 1σ dispersion in reddening averaging 9% of total reddening for our fields. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (MI,RC, σI,RC,0, (V−I)RC,0, σ(V−I)RC, (J−Ks)RC,0) = (−0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc, resolving previous discrepancies in distance determinations to the bulge based on I-band observations. We measure an upper bound on the tilt α≈40° between the bar’s major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at α=25°. The number of RC stars suggests a total stellar mass for the Galactic bulge of 2.0×1010 M, if one assumes a Salpeter IMF.

Reddening map

Color-coded reddening map of the Galactic bulge as observed by the OGLE-III VI photometric survey.

Mean distance to GB stars

Mean distance to Galactic bulge stars as a function of direction projected onto a face-on view of the central region of the Milky Way. Black points show the projected location of each measured centroid, and green points show 50 binned values.

We provide the reddening and extinction data in Tables 3 and 4 of this paper, available from the OGLE Internet archive. See the README file there for the detailed description of the data.

We also provide an extinction calculator allowing to extract the reddening and extiction values at any point of the sky covered by this analysis.

Any comments about the paper and data presented here are welcome and should be sent to this address.