The COS CGM Compendium V: The Dichotomy of OVI Associated with Low- and High-Metallicity Cool Gas at z < 1
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2024
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| _version_ | 1866909307729084416 |
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| author | Sameer Lehner, Nicolas Howk, J. Christopher Fox, Andrew J. O'Meara, John M. Oppenheimer, Benjamin D. |
| author_facet | Sameer Lehner, Nicolas Howk, J. Christopher Fox, Andrew J. O'Meara, John M. Oppenheimer, Benjamin D. |
| contents | We analyze the \ovi\ content and kinematics for 126 {\hi}-selected absorbers at $0.14 \lesssim z \lesssim 0.73$ for which the metallicities of their cool photoionized phase have been determined. We separate the absorbers into 100 strong {\lya} forest systems (SLFSs with $15 \la$\,{\colden}\,$< 16.2$) and 26 partial Lyman Limit systems (pLLSs with $16.2\le$\,{\colden}\,$\le 17.2$). The sample is drawn from the COS CGM Compendium (CCC) and has \ovi\ coverage in $\sn \geq 8$ {\it HST}/COS G130M/G160M QSO spectra, yielding a $2σ$ completeness level of {\coldenovi}$\,\geq 13.6$. The \ovi\ detection rates differ substantially between low-metallicity (LM; {\xh} $\leq -1.4$) and high-metallicity (HM; {\xh} $> -1.4$) SLFSs, with 20\% and 60\% detection rates, respectively. The \ovi\ detection frequency for the HM and LM pLLSs is, however, similar at $\sim$60\%. The SLFSs and pLLSs without detected \ovi\ are consistent with the absorbing gas being in a single phase, while those with \ovi\ trace multiphase gas. We show that the \ovi\ velocity widths and column densities have different distributions in LM and HM gas. We find a strong correlation between \ovi\ column density and metallicity. The strongest (\coldenovi$\,\ga 14$) and broadest {\ovi} absorbers are nearly always associated with HM absorbers, while weaker \ovi\ absorbers are found in both LM and HM absorbers. From comparisons with galaxy-selected and blind \ovi\ surveys, we conclude absorbers with \coldenovi$\,\ga 14$ most likely arise in the circumgalactic medium (CGM) of star-forming galaxies. Absorbers with weak \ovi\ likely trace the extended CGM or intergalactic medium (IGM), while those without \ovi\ likely originate in the IGM. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2403_02374 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The COS CGM Compendium V: The Dichotomy of OVI Associated with Low- and High-Metallicity Cool Gas at z < 1 Sameer Lehner, Nicolas Howk, J. Christopher Fox, Andrew J. O'Meara, John M. Oppenheimer, Benjamin D. Astrophysics of Galaxies We analyze the \ovi\ content and kinematics for 126 {\hi}-selected absorbers at $0.14 \lesssim z \lesssim 0.73$ for which the metallicities of their cool photoionized phase have been determined. We separate the absorbers into 100 strong {\lya} forest systems (SLFSs with $15 \la$\,{\colden}\,$< 16.2$) and 26 partial Lyman Limit systems (pLLSs with $16.2\le$\,{\colden}\,$\le 17.2$). The sample is drawn from the COS CGM Compendium (CCC) and has \ovi\ coverage in $\sn \geq 8$ {\it HST}/COS G130M/G160M QSO spectra, yielding a $2σ$ completeness level of {\coldenovi}$\,\geq 13.6$. The \ovi\ detection rates differ substantially between low-metallicity (LM; {\xh} $\leq -1.4$) and high-metallicity (HM; {\xh} $> -1.4$) SLFSs, with 20\% and 60\% detection rates, respectively. The \ovi\ detection frequency for the HM and LM pLLSs is, however, similar at $\sim$60\%. The SLFSs and pLLSs without detected \ovi\ are consistent with the absorbing gas being in a single phase, while those with \ovi\ trace multiphase gas. We show that the \ovi\ velocity widths and column densities have different distributions in LM and HM gas. We find a strong correlation between \ovi\ column density and metallicity. The strongest (\coldenovi$\,\ga 14$) and broadest {\ovi} absorbers are nearly always associated with HM absorbers, while weaker \ovi\ absorbers are found in both LM and HM absorbers. From comparisons with galaxy-selected and blind \ovi\ surveys, we conclude absorbers with \coldenovi$\,\ga 14$ most likely arise in the circumgalactic medium (CGM) of star-forming galaxies. Absorbers with weak \ovi\ likely trace the extended CGM or intergalactic medium (IGM), while those without \ovi\ likely originate in the IGM. |
| title | The COS CGM Compendium V: The Dichotomy of OVI Associated with Low- and High-Metallicity Cool Gas at z < 1 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2403.02374 |