REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S<i>R_V</i>∼ 2.5 EXTINCTION CURVE

Abstract

We combine VI photometry from OGLE-III with VVV and 2MASS measurements of\nE(J-K_{s}) to resolve the longstanding problem of the non-standard optical\nextinction toward the Galactic bulge. We show that the extinction is well-fit\nby the relation A_{I} = 0.7465*E(V-I) + 1.3700*E(J-K_{s}), or, equivalently,\nA_{I} = 1.217*E(V-I)(1+1.126*(E(J-K_{s})/E(V-I)-0.3433)). The optical and\nnear-IR reddening law toward the inner Galaxy approximately follows an R_{V}\n\\approx 2.5 extinction curve with a dispersion {\\sigma}_{R_{V}} \\approx 0.2,\nconsistent with extragalactic investigations of the hosts of type Ia SNe.\nDifferential reddening is shown to be significant on scales as small as as our\nmean field size of 6', with the 1{\\sigma} dispersion in reddening averaging 9%\nof total reddening for our fields. The intrinsic luminosity parameters of the\nGalactic bulge red clump (RC) are derived to be (M_{I,RC}, \\sigma_{I,RC,0},\n(V-I)_{RC,0}, \\sigma_{(V-I)_{RC}}, (J-K_{s})_{RC,0}) = (-0.12, 0.09, 1.06,\n0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and\nnumber counts allow us to estimate several Galactic bulge structural\nparameters. We estimate a distance to the Galactic center of 8.20 kpc,\nresolving previous discrepancies in distance determinations to the bulge based\non I-band observations. We measure an upper bound on the tilt {\\alpha} \\approx\n40{\\deg}. between the bar's major axis and the Sun-Galactic center line of\nsight, though our brightness peaks are consistent with predictions of an N-body\nmodel oriented at {\\alpha} \\approx 25{\\deg}. The number of RC stars suggests a\ntotal stellar mass for the Galactic bulge of 2.0*10^{10} M_{\\odot}, if one\nassumes a Salpeter IMF.\n