TY - JOUR
T1 - Chemical cartography. I. A carbonicity map of the galactic halo
AU - Lee, Young Sun
AU - Beers, Timothy C.
AU - Kim, Young Kwang
AU - Placco, Vinicius
AU - Yoon, Jinmi
AU - Carollo, Daniela
AU - Masseron, Thomas
AU - Jung, Jaehun
PY - 2017/2/10
Y1 - 2017/2/10
N2 - We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H] = -1.5 and -2.2, respectively. From consideration of the absolute carbon abundances for our sample, A(C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP-s stars (those with strong overabundances of elements associated with the s-process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP-s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP-s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.
AB - We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H] = -1.5 and -2.2, respectively. From consideration of the absolute carbon abundances for our sample, A(C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP-s stars (those with strong overabundances of elements associated with the s-process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP-s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP-s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.
KW - galaxy: halo
KW - methods: data analysis
KW - stars: abundances
KW - stars: carbon
KW - techniques: imaging spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85014227476&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/836/1/91
DO - 10.3847/1538-4357/836/1/91
M3 - Article
AN - SCOPUS:85014227476
SN - 0004-637X
VL - 836
SP - 1
EP - 11
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 91
ER -