Chemical Cartography. I. A Carbonicity Map of the Galactic Halo

Journal Article · Fri Feb 10 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/836/1/91· OSTI ID:22663828

Lee, Young Sun; Kim, Young Kwang ^[1]; Beers, Timothy C.; Placco, Vinicius; Yoon, Jinmi ^[2]; Carollo, Daniela ^[3]; Masseron, Thomas ^[4]; Jung, Jaehun ^[5]

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1. Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134 (Korea, Republic of)
2. Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556 (United States)
3. Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 (Australia)
4. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
5. Department of Astronomy, Space Science, and Geology, Chungnam National University, Daejeon 34134 (Korea, Republic of)

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.

• OSTI ID: 22663828
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 836; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
DATA ANALYSIS
DISTRIBUTION FUNCTIONS
MASS
MASS DISTRIBUTION
METALS
MILKY WAY
NEUTRON REACTIONS
S PROCESS
SKY
SPECTROSCOPY
SUN