Low Metallicity Gas on the Outskirts of the Local Group: the Circumgalactic Medium of Sextans B
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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866908764719808512 |
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| author | Fox, Andrew J. Mishra, Sapna Cashman, Frances H. French, David M. Richter, Philipp Bordoloi, Rongmon Lehner, Nicolas Tumlinson, Jason Borthakur, Sanchayeeta |
| author_facet | Fox, Andrew J. Mishra, Sapna Cashman, Frances H. French, David M. Richter, Philipp Bordoloi, Rongmon Lehner, Nicolas Tumlinson, Jason Borthakur, Sanchayeeta |
| contents | We present a UV absorption-line analysis of the circumgalactic medium (CGM) of Sextans B, a dwarf irregular galaxy at 1.3 Mpc distance on the outer frontier of the Local Group. Using HST/COS spectroscopy of two AGN sightlines passing through the Sextans B CGM at small impact parameters of 4 kpc and 8 kpc (0.04 and 0.08 r_vir), we detect the CGM in Si II, Si III, Si IV, and C II absorption. All four ions show a column-density profile that declines with radius. The profiles fall below the average CGM profiles of other nearby dwarfs (by 0.3-0.6 dex, depending on ion), likely due to the low halo mass and low metallicity of Sextans B. Using Cloudy photoionization models and interferometric measurements of the H I column density, we find low gas-phase silicon and carbon abundances in the Sextans B CGM, [Si/H]=-1.7+/-0.2 and [C/H]=-2.1+/-0.2, among the lowest gas-phase abundances anywhere in the Local Group. We calculate a cool CGM gas mass within 8 kpc of $\sim4\times10^7 M_\odot$, comparable to the H I mass and the stellar mass of Sextans B. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_00437 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Low Metallicity Gas on the Outskirts of the Local Group: the Circumgalactic Medium of Sextans B Fox, Andrew J. Mishra, Sapna Cashman, Frances H. French, David M. Richter, Philipp Bordoloi, Rongmon Lehner, Nicolas Tumlinson, Jason Borthakur, Sanchayeeta Astrophysics of Galaxies We present a UV absorption-line analysis of the circumgalactic medium (CGM) of Sextans B, a dwarf irregular galaxy at 1.3 Mpc distance on the outer frontier of the Local Group. Using HST/COS spectroscopy of two AGN sightlines passing through the Sextans B CGM at small impact parameters of 4 kpc and 8 kpc (0.04 and 0.08 r_vir), we detect the CGM in Si II, Si III, Si IV, and C II absorption. All four ions show a column-density profile that declines with radius. The profiles fall below the average CGM profiles of other nearby dwarfs (by 0.3-0.6 dex, depending on ion), likely due to the low halo mass and low metallicity of Sextans B. Using Cloudy photoionization models and interferometric measurements of the H I column density, we find low gas-phase silicon and carbon abundances in the Sextans B CGM, [Si/H]=-1.7+/-0.2 and [C/H]=-2.1+/-0.2, among the lowest gas-phase abundances anywhere in the Local Group. We calculate a cool CGM gas mass within 8 kpc of $\sim4\times10^7 M_\odot$, comparable to the H I mass and the stellar mass of Sextans B. |
| title | Low Metallicity Gas on the Outskirts of the Local Group: the Circumgalactic Medium of Sextans B |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2601.00437 |