The structure behind the Galactic bar traced by red clump stars in the VVV survey

Abstract

Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the Vía Láctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes −10 • < l < 10 • and latitudes −1.5 • < b < 1.5 • . We use these de-reddened catalogues to construct the K s luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulge red-giant branch bump alone, as previously interpreted. Instead, this fainter clump corresponds largely to the over-density of red clump stars tracing the spiral arm structure behind the Galactic bar. This result suggests that studies aiming to characterise the bulge redgiant branch bump should avoid low galactic latitudes (|b| < 2 • ), where the background red clump population contributes significant contamination. It furthermore highlights the need to include this structural component in future modelling of the Galactic bar.

VVV WIN 1733−3349: a low extinction window to probe the far side of the Milky Way bulge

“…A multi Gaussian fit shows the presence of three peaks, interpreted as the Scutum-Centaurus arm in the foreground disk, the Galactic bar and the Sagittarius arm (that is seen wrapping around behind the Galactic centre), at the distance of d = 7.06, 9.37 and 12.92 kpc, respectively. The distance of the Galactic bar and the Sagittarius arm coincide with distances for RC stars measured by Gonzalez et al (2018) for the region within |b| < 1.5 deg. We also find a clear excess of microlensing events in this window from the sample of Navarro et al (2018Navarro et al ( , 2019, that is probably due to additional events that have lenses in the bulge and sources in the far disk.…”

“…They discovered the presence of a low extinction window right in the Galactic plane (b ∼ −0.3 deg), at just about five degrees from the Galactic centre (l ∼ −5.2 deg). This window named VVV WIN 1733−3349 inGonzalez et al (2018) is also clearly seen in the maps ofSurot et al (2019) and in the distribution of Gaia DR2 sources(Gaia Collaboration et al. 2018).…”

“…At the magnitude range of the fainter RC stars the completeness of the VVV PSF data on Galactic plane is over 80% (e.g., Saito et al 2012;Surot et al 2019). Following the discussion presented in Gonzalez et al (2018), we assume that secondary peaks in the RC distributions are not caused by the red giant branch bump (e.g., Nataf et al 2011Nataf et al , 2013. In contrast with the distances from Gaia DR2 as estimated by Bailer-Jones et al (2018), the distances to the RC giants measured from the VVV near-IR photometry clearly penetrates through the Galaxy, out to ∼ 14 kpc.…”

“…Gonzalez et al (2018) made use of VVV red clump stars detected inAlonso-García et al (2018) catalogues to create a high-resolution reddening map of the inner region of the Milky Way bulge (−10 < l < 10 deg and −1.5 < b < 1.5 deg). They discovered the presence of a low extinction window right in the Galactic plane (b ∼ −0.3 deg), at just about five degrees from the Galactic centre (l ∼ −5.2 deg).…”

Interstellar extinction law toward the Galactic center. IV. J, H, and Ks bands from VVV red clump stars

“…In contrast, we have selected a rectangle region that is supposed to be occupied only by the RC stars in each CMD, taken from each subfield, and fit the magnitude and color distributions with a Gaussian function. We made such procedures to select only the RC stars in the bulge, because other various components in the foreground and background (e.g., Alonso-García et al 2018 andGonzález et al 2018) can contaminate. Furthermore, the tile-to-tile photometry difference found here might have complicated the whole area CMDs; our average slopes for all area CMDs are different from the mean values of each tile.…”