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Oxygen Abundance Measurements of SHIELD Galaxies
Astrophysics of Galaxies · Submitted 21 Jan 2015
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim This indicates a different mass-to-light ratio for the galaxies in this sample and we suggest this may be indicative of differing star-formation histories in the lowest luminosity and surface brightness dwarf irregulars.
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We have derived oxygen abundances for 8 galaxies from the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). The SHIELD survey is an ongoing study of very low-mass galaxies, with M$_{\rm HI}$ between 10$^{6.5}$ and 10$^{7.5}$ M$_{\odot}$, that were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. H$\alpha$ images from the WIYN 3.5m telescope show that these 8 SHIELD galaxies each possess one or two active star-forming regions which were targeted with long-slit spectral observations using the Mayall 4m telescope at KPNO. We obtained a direct measurement of the electron temperature by detection of the weak [O III] $\lambda$4363 line in 2 of the HII regions. Oxygen abundances for the other HII regions were estimated using a strong-line method. When the SHIELD galaxies are plotted on a B-band luminosity-metallicity diagram they appear to suggest a slightly shallower slope to the relationship than normally seen. However, that offset is systematically reduced when the near-infrared luminosity is used instead. This indicates a different mass-to-light ratio for the galaxies in this sample and we suggest this may be indicative of differing star-formation histories in the lowest luminosity and surface brightness dwarf irregulars.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We have derived oxygen abundances for 8 galaxies from the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). | contribution 0.51 | 0.98 | 0.05 | asserted 1.00 |
| s1 | The SHIELD survey is an ongoing study of very low-mass galaxies, with M$_{\rm HI}$ between 10$^{6.5}$ and 10$^{7.5}$ M$_{\odot}$, that were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. | background 0.94 | 0.11 | 0.02 | asserted 1.00 |
| s2 | H$\alpha$ images from the WIYN 3.5m telescope show that these 8 SHIELD galaxies each possess one or two active star-forming regions which were targeted with long-slit spectral observations using the Mayall 4m telescope at KPNO. | method 0.99 | 0.87 | 0.02 | asserted 1.00 |
| s3 | We obtained a direct measurement of the electron temperature by detection of the weak [O III] $\lambda$4363 line in 2 of the HII regions. | method 0.78 | 0.97 | 0.03 | asserted 1.00 |
| s4 | Oxygen abundances for the other HII regions were estimated using a strong-line method. | method 0.99 | 0.89 | 0.03 | asserted 1.00 |
| s5 | When the SHIELD galaxies are plotted on a B-band luminosity-metallicity diagram they appear to suggest a slightly shallower slope to the relationship than normally seen. | result 0.99 | 0.88 | 0.18 | hedged possibility 0.99 |
| s6 | However, that offset is systematically reduced when the near-infrared luminosity is used instead. | result 0.98 | 0.85 | 0.13 | asserted 1.00 |
| s7 | This indicates a different mass-to-light ratio for the galaxies in this sample and we suggest this may be indicative of differing star-formation histories in the lowest luminosity and surface brightness dwarf irregulars. | interpretation 1.00 | 0.74 | 0.64 | hedged possibility 0.98 |
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Original abstract
We have derived oxygen abundances for 8 galaxies from the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). The SHIELD survey is an ongoing study of very low-mass galaxies, with M$_{\rm HI}$ between 10$^{6.5}$ and 10$^{7.5}$ M$_{\odot}$, that were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. H$\alpha$ images from the WIYN 3.5m telescope show that these 8 SHIELD galaxies each possess one or two active star-forming regions which were targeted with long-slit spectral observations using the Mayall 4m telescope at KPNO. We obtained a direct measurement of the electron temperature by detection of the weak [O III] $\lambda$4363 line in 2 of the HII regions. Oxygen abundances for the other HII regions were estimated using a strong-line method. When the SHIELD galaxies are plotted on a B-band luminosity-metallicity diagram they appear to suggest a slightly shallower slope to the relationship than normally seen. However, that offset is systematically reduced when the near-infrared luminosity is used instead. This indicates a different mass-to-light ratio for the galaxies in this sample and we suggest this may be indicative of differing star-formation histories in the lowest luminosity and surface brightness dwarf irregulars.
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As a check we used a straight-forward conversion of 3.6$$ luminosity into mass assuming a mass-to-light ratio of 0.5 [ref] and $M_⊙, 3.6 = 3.24$ [ref] .
The Stellar Masses of Disk Galaxies and the Calibration of Color-Mass to Light Ratio Relations · ANALYSIS · 0.80
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