TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE

By A. McWilliam, M. Zoccali. 2010

209 citations recorded by the source corpus.

From Two Micron All Sky Survey infrared photometry, we find two red clump (RC) populations coexisting in fields toward the Galactic bulge at latitudes |b|>5.°5, ranging over ∼13° in longitude and 20° in latitude. These RC peaks indicate two stellar populations separated by ∼2.3 kpc; at (l, b) = (+1, − 8) the two RCs are located at 6.5 and 8.8 ± 0.2 kpc. The double-peaked RC is inconsistent with a tilted bar morphology. Most of our fields show the two RCs at roughly constant distance with longitude, also inconsistent with a tilted bar; however, an underlying bar may be present. Stellar densities in the two RCs change dramatically with longitude: on the positive longitude side the foreground RC is dominant, while the background RC dominates negative longitudes. A line connecting the maxima of the foreground and background populations is tilted to the line of sight by ∼20°±4°, similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases toward the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extragalactic bulges and the results of N-body simulations. The center of this X is consistent with the distance to the Galactic center, although better agreement would occur if the bulge is 2–3 Gyr younger than 47 Tuc. Our observations may be understood if the two RC populations emanate, nearly tangentially, from the Galactic bar ends, in a funnel shape. Alternatively, the X, or double funnel, may continue to the Galactic center. From the Sun, this would appear peanut/box shaped, but X-shaped when viewed tangentially.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d77e952391bbcaba25dbedf93ea83e9653887d09

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Citations in the corpus

REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S RV ∼ 2.5 EXTINCTION CURVE (2012, background): “…2008), deviations from the classical picture of the triaxial ellipsoid at large separations from the minor axis (Benjamin et al. 2005; Cabrera-Lavers et al. 2008), and both large (Nataf et al. 2010; McWilliam & Zoccali 2010) and small (Alard 2001; Nishiyama et al. 2005) separations from the plane.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, unknown): “…that the bulk of the bulge stars are part of a so-called box/peanut or b/p bulge structure representing the inner, 3D part of the Galactic bar (McWilliam & Zoccali 2010, Nataf et al. 2010, Wegg & Gerhard 2013), consistent with the observed cylindrical rotation (Kunder et al. 2012, Ness et al.…”
The structure of the Milky Way's bar outside the bulge (2015, methodology): “Recent interest was stimulated by the discovery that close to the bulge minor axis at |b|& 5◦ the RCGs have two distinct magnitudes (McWilliam & Zoccali 2010; Nataf et al. 2010).”
Mapping the three-dimensional density of the galactic bulge with VVV red clump stars (2013, methodology): “More recently Nataf et al. (2010) using OGLE-III data, and McWilliam & Zoccali (2010) using 2MASS, demonstrated that at high latitudes the RC splits into two as a result of the X-shaped structure characteristic for boxy/peanut bulges in barred galaxies (e.g. Martinez-Valpuesta et al. 2006 from…”
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Galactic bulge studies (2012, background): “…as follows: i) the GB structure is dominated by the bar (Stanek et al. 1994), which appears to have a peanut or X-shape in the outer regions (McWilliam & Zoccali 2010; Nataf et al. 2010; Saito et al. 2011); ii) there is a radial stellar metallicity gradient (Zoccali et al. 2008; Johnson et…”
THE APOGEE RED-CLUMP CATALOG: PRECISE DISTANCES, VELOCITIES, AND HIGH-RESOLUTION ELEMENTAL ABUNDANCES OVER A LARGE AREA OF THE MILKY WAY'S DISK (2014, methodology): “…using local data from Hipparcos (ESA 1997), precise distances to the Galactic center (Paczynski & Stanek 1998), various parts of the Galactic bulge (McWilliam & Zoccali 2010; Nataf et al. 2010), the Large Magellanic Cloud (Stanek et al. 1998; Udalski 1998), M31 (Stanek & Garnavich 1998), and many…”
Made-to-measure models of the Galactic box/peanut bulge: stellar and total mass in the bulge region (2015, methodology): “This was first reported from the 2MASS catalogue by McWilliam & Zoccali (2010) and from the OGLE-III survey by Nataf et al. (2010).”
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “The double clump is clearly visible in several color magnitude diagrams available in the literature (e.g. Zoccali et al. 2003; Rattenbury et al. 2007; McWilliam & Zoccali 2010; Nataf et al. 2010).”
The mass distribution and gravitational potential of the Milky Way (2016, background): “It is increasingly clear that it is a boxy (or ‘peanut shaped’) bulge (McWilliam & Zoccali 2010; Nataf et al. 2010; Ness et al. 2012, and others).”
Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data (2011, methodology): “In figure 14 we show the star counts around the clump in various fields at latitude b=-8◦ in order to compare with figure 3 of McWilliam & Zoccali (2010).”
Target Selection for the SDSS-IV APOGEE-2 Survey (2017, background): “…have been known for this past century, surprises do continue to this day, for example, with the discoveries of the X-shaped bulge in the center (McWilliam & Zoccali 2010; Nataf et al. 2010; Ness & Lang 2016) and the presence of multiple stellar populations in globular clusters (e.g., Piotto…”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “At high metallicity ([Fe/H] >∼ – 0.5), the bulge appears to be dominated by a boxy/peanutshaped structure, associated with a bar (Blitz & Spergel 1991), which in projection has been found to assume an X shape in 2MASS maps (McWilliam & Zoccali 2010; Ness et al. 2012).”
Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution (2016, background): “The discovery of the so-called split red clump in the galactic bulge (Nataf et al. 2010; McWilliam & Zoccali 2010) and the later 3D mapping of the bulge density by Wegg & Gerhard (2013) showed that the galactic bulge has a boxy/peanut (B/P) shape, similarly to bulges formed in N-body models by…”
ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way (2012, background): “Although the bulge region can no longer be described as a single stellar population, it appears to be a mostly old, α-enhanced system whose stars formed over a short period of time early in the life of the Galaxy (Zoccali et al. 2003; Meléndez et al. 2008; McWilliam & Zoccali 2010; Lecureur etal.”