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Two Red Clumps and the X-Shaped Milky Way Bulge
Astrophysics of Galaxies · Submitted 3 Aug 2010
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim The distance between the two RCs decreases towards the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extra-galactic bulges and the results of N-body simulations.
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The abstract, sentence by sentence
From 2MASS infra-red photometry we find two red clump (RC) populations co-existing in the same fields toward the Galactic bulge at latitudes |b|>5.5 deg., ranging over ~13 degrees in longitude and 20 degrees in latitude. We can only understand the data if these RC peaks simply reflect 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, which is also inconsistent with a tilted bar, although an underlying bar may be present. The stellar densities in the two RCs changes 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 deg., similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases towards the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extra-galactic 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 ends of a Galactic bar, each side shaped like a funnel or horn. Alternatively, the X, or double funnel shape, may continue to the Galactic center. This would appear peanut/box shaped from the Solar direction, but X-shaped when viewed tangentially.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | From 2MASS infra-red photometry we find two red clump (RC) populations co-existing in the same fields toward the Galactic bulge at latitudes |b|>5.5 deg., ranging over ~13 degrees in longitude and 20 degrees in latitude. | result 0.94 | 0.97 | 0.07 | asserted 1.00 |
| s1 | We can only understand the data if these RC peaks simply reflect 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. | interpretation 0.60 | 0.87 | 0.27 | asserted 0.92 |
| s2 | The double-peaked RC is inconsistent with a tilted bar morphology. | interpretation 0.81 | 0.78 | 0.15 | asserted 0.99 |
| s3 | Most of our fields show the two RCs at roughly constant distance with longitude, which is also inconsistent with a tilted bar, although an underlying bar may be present. | result 0.76 | 0.92 | 0.10 | asserted 0.76 |
| s4 | The stellar densities in the two RCs changes dramatically with longitude: on the positive longitude side the foreground RC is dominant, while the background RC dominates negative longitudes. | result 1.00 | 0.93 | 0.08 | asserted 1.00 |
| s5 | A line connecting the maxima of the foreground and background populations is tilted to the line of sight by ~20 +/-4 deg., similar to claims for the tilt of a Galactic bar. | result 0.91 | 0.89 | 0.12 | asserted 0.99 |
| s6 | The distance between the two RCs decreases towards the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extra-galactic bulges and the results of N-body simulations. | result 0.87 | 0.89 | 0.47 | asserted 0.99 |
| s7 | 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. | result 0.57 | 0.74 | 0.08 | hedged possibility 0.97 |
| s8 | Our observations may be understood if the two RC populations emanate, nearly tangentially, from the ends of a Galactic bar, each side shaped like a funnel or horn. | interpretation 1.00 | 0.47 | 0.47 | hedged possibility 1.00 |
| s9 | Alternatively, the X, or double funnel shape, may continue to the Galactic center. | interpretation 1.00 | 0.24 | 0.09 | hedged possibility 0.98 |
| s10 | This would appear peanut/box shaped from the Solar direction, but X-shaped when viewed tangentially. | interpretation 0.99 | 0.29 | 0.14 | asserted 0.73 |
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Original abstract
From 2MASS infra-red photometry we find two red clump (RC) populations co-existing in the same fields toward the Galactic bulge at latitudes |b|>5.5 deg., ranging over ~13 degrees in longitude and 20 degrees in latitude. We can only understand the data if these RC peaks simply reflect 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, which is also inconsistent with a tilted bar, although an underlying bar may be present. The stellar densities in the two RCs changes 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 deg., similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases towards the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extra-galactic 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 ends of a Galactic bar, each side shaped like a funnel or horn. Alternatively, the X, or double funnel shape, may continue to the Galactic center. This would appear peanut/box shaped from the Solar direction, but X-shaped when viewed tangentially.
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5 arXiv papers cite this in 6 sentences
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Evidence has been emerging that each of these is subdivided into thin/thick disks of various metallicities [ref] , inner/outer halos displaying abundance gradients [ref] , and a complicated bulge plus bar structure [ref] .
Chemodynamical evidence of the HR 1614 moving group as a bar resonance · Introduction · 0.86
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