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

Abstract

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 massmore » 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.« less

Authors:
;  [1]; ; ;  [2];  [3];  [4];  [5]
  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)
Publication Date:
OSTI Identifier:
22663828
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; DATA ANALYSIS; DISTRIBUTION FUNCTIONS; MASS; MASS DISTRIBUTION; METALS; MILKY WAY; NEUTRON REACTIONS; S PROCESS; SKY; SPECTROSCOPY; SUN

Citation Formats

Lee, Young Sun, Kim, Young Kwang, Beers, Timothy C., Placco, Vinicius, Yoon, Jinmi, Carollo, Daniela, Masseron, Thomas, and Jung, Jaehun, E-mail: youngsun@cnu.ac.kr. Chemical Cartography. I. A Carbonicity Map of the Galactic Halo. United States: N. p., 2017. Web. doi:10.3847/1538-4357/836/1/91.
Lee, Young Sun, Kim, Young Kwang, Beers, Timothy C., Placco, Vinicius, Yoon, Jinmi, Carollo, Daniela, Masseron, Thomas, & Jung, Jaehun, E-mail: youngsun@cnu.ac.kr. Chemical Cartography. I. A Carbonicity Map of the Galactic Halo. United States. doi:10.3847/1538-4357/836/1/91.
Lee, Young Sun, Kim, Young Kwang, Beers, Timothy C., Placco, Vinicius, Yoon, Jinmi, Carollo, Daniela, Masseron, Thomas, and Jung, Jaehun, E-mail: youngsun@cnu.ac.kr. Fri . "Chemical Cartography. I. A Carbonicity Map of the Galactic Halo". United States. doi:10.3847/1538-4357/836/1/91.
@article{osti_22663828,
title = {Chemical Cartography. I. A Carbonicity Map of the Galactic Halo},
author = {Lee, Young Sun and Kim, Young Kwang and Beers, Timothy C. and Placco, Vinicius and Yoon, Jinmi and Carollo, Daniela and Masseron, Thomas and Jung, Jaehun, E-mail: youngsun@cnu.ac.kr},
abstractNote = {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.},
doi = {10.3847/1538-4357/836/1/91},
journal = {Astrophysical Journal},
number = 1,
volume = 836,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2017},
month = {Fri Feb 10 00:00:00 EST 2017}
}
  • We have detected over 400 H I clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18 deg. in longitude, 40 deg. in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6 K, a median velocity width of 12.8 km s{sup -1}, and angular sizes {approx}<1deg . The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18 km s{sup -1}. A sample of clouds likely tomore » be near tangent points was analyzed in detail. These clouds have radii on the order of 30 pc and a median H I mass of 630 M{sub sun}. The population has a vertical scale height of 400 pc and is concentrated in Galactocentric radius, peaking at R = 3.8 kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.« less
  • Cited by 5
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  • A new solution to the observed Galactic globular cluster metallicity distribution is proposed by considering inhomogeneous collapse of a centrally condensed proto-Galaxy. In contrast to the standard one-zone model, it is shown that, for inhomogeneous models, the metallicity distribution can be reproduced without the need to decrease the nucleosynthetic yield for metal-poor stars. Chemical evolution in free fall is calculated analytically. A hybrid hydroparticle code is developed to study the effect of supernova induced pressure. 62 refs.
  • Recent determinations of (Fe/H) for individual stars in globular clusters are used to obtain the frequency in (Fe/H) among 60 halo globular clusters. The shape of this distribution is unlike its counterpart in the solar vicinity in that there are relatively more very metal-poor stars in the halo. The halo distribution is compared with that predicted by Larson's hydrodynamical models for elliptical galaxies, and it is found that star formation is less efficient in the galactic halo than in the outer regions of the models. A satisfactory fit to the observations is obtained by making either of two modifications tomore » a simple one-zone model. The first assumes a decrease in the heavy-element yield by a factor of 13 and results in a model with a very large halo mass/disk mass ratio. Alternatively, if gas is temporarily removed from the halo star-forming region and eventually forms a disk, the resulting ratio of halo mass to disk mass becomes approx.8 percent, and the G-dwarf problem in the solar neighborhood is slightly alleviated. (AIP)« less