TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE
- Observatories of the Carnegie Institute of Washington, 813 Santa Barbara Street, Pasadena, CA 91101-1292 (United States)
- Departamento Astronomia y Astrofisica, Pontifcia Universidad Catolica de Chile, Avenida Vicuna Mackenna 4860, Santiago (Chile)
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.{sup 0}5, ranging over {approx}13{sup 0} in longitude and 20{sup 0} in latitude. These RC peaks indicate two stellar populations separated by {approx}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 {approx}20{sup 0{+-}}4{sup 0}, 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.
- OSTI ID:
- 21474472
- Journal Information:
- Astrophysical Journal, Vol. 724, Issue 2; Other Information: DOI: 10.1088/0004-637X/724/2/1491; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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