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  • 1
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society Vol. 510, No. 1 ( 2021-12-21), p. 373-382
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 510, No. 1 ( 2021-12-21), p. 373-382
    Abstract: We re-examine the extremely metal-poor dwarf galaxy AGC 198691 using a high quality spectrum obtained by the LBT’s MODS instrument. Previous spectral observations obtained from KOSMOS on the Mayall 4-m and the Blue channel spectrograph on the MMT 6.5-m telescope did not allow for the determination of sulfur, argon, or helium abundances. We report an updated and full chemical abundance analysis for AGC 198691, including confirmation of the extremely low “direct” oxygen abundance with a value of 12 + log (O/H) = 7.06 ± 0.03. AGC 198691’s low metallicity potentially makes it a high value target for helping determine the primordial helium abundance (Yp). Though complicated by a Na i night sky line partially overlaying the He i λ5876 emission line, the LBT/MODS spectrum proved adequate for determining AGC 198691’s helium abundance. We employ the recently expanded and improved model of Aver et al., incorporating higher Balmer and Paschen lines, augmented by the observation of the infrared helium emission line He i λ10830 obtained by Hsyu et al. Applying our full model produced a reliable helium abundance determination, consistent with the expectation for its metallicity. Although this is the lowest metallicity object with a detailed helium abundance, unfortunately, due to its faintness [EW(Hβ) & lt; 100 Å] and the compromised He i λ5876, the resultant uncertainty on the helium abundance is too large to allow a significant improvement on the measurement of Yp.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 2
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 940, No. 1 ( 2022-11-01), p. L23-
    Abstract: We analyze the rest-frame near-UV and optical nebular spectra of three z 〉 7 galaxies from the Early Release Observations taken with the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). These three high- z galaxies show the detection of several strong emission nebular lines, including the temperature-sensitive [O iii ] λ 4363 line, allowing us to directly determine the nebular conditions and abundances for O/H, C/O, and Ne/O. We derive O/H abundances and ionization parameters that are generally consistent with other recent analyses. We analyze the mass–metallicity relationship (i.e., slope) and its redshift evolution by comparing between the three z 〉 7 galaxies and local star-forming galaxies. We also detect the C iii ] λλ 1907, 1909 emission in a z 〉 8 galaxy from which we determine the most distant C/O abundance to date. This valuable detection of log(C/O) = −0.83 ± 0.38 provides the first test of C/O redshift evolution out to high redshift. For neon, we use the high-ionization [Ne iii ] λ 3869 line to measure the first Ne/O abundances at z 〉 7, finding no evolution in this α -element ratio. We explore the tentative detection of [Fe ii ] and [Fe iii ] lines in a z 〉 8 galaxy, which would indicate a rapid buildup of metals. Importantly, we demonstrate that properly flux-calibrated and higher-S/N spectra are crucial to robustly determine the abundance pattern in z 〉 7 galaxies with NIRSpec/JWST.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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  • 3
    Online Resource
    Online Resource
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Vol. 894, No. 2 ( 2020-05-15), p. 138-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 894, No. 2 ( 2020-05-15), p. 138-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
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  • 4
    Online Resource
    Online Resource
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Vol. 893, No. 2 ( 2020-04-20), p. 96-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 893, No. 2 ( 2020-04-20), p. 96-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
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  • 5
    Online Resource
    Online Resource
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Vol. 915, No. 1 ( 2021-07-01), p. 21-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 915, No. 1 ( 2021-07-01), p. 21-
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 6
    Online Resource
    Online Resource
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 955, No. 2 ( 2023-10-01), p. 112-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 955, No. 2 ( 2023-10-01), p. 112-
    Abstract: Studying the galaxies responsible for reionization is often conducted through local reionization-era analogs; however, many of these local analogs are too massive to be representative of the low-mass star-forming galaxies that are thought to play a dominant role in reionization. The local, low-mass dwarf starburst galaxy Pox 186 is one such system with physical conditions representative of a reionization-era starburst galaxy. We present deep ultraviolet (UV) spectroscopy of Pox 186 to study its stellar population and ionization conditions and to compare these conditions to other local starburst galaxies. The new Cosmic Origins Spectrograph data are combined with archival observations to cover ∼1150–2000 Å and allow for an assessment of Pox 186's stellar population, the relative enrichment of C and O, and the escape of ionizing photons. We detect significant Ly α and low-ionization state absorption features, indicative of previously undetected neutral gas in Pox 186. The C/O relative abundance, log(C/O) = −0.62 ± 0.02, is consistent with other low-metallicity dwarf galaxies and suggests a comparable star formation history in these systems. We compare UV line ratios in Pox 186 to those of dwarf galaxies and photoionization models, and we find excellent agreement for the ratios utilizing the intense C iii ], O iii ], and double-peaked C iv lines. However, the UV and optical He ii emission is faint and distinguishes Pox 186 from other local starburst dwarf galaxies. We explore mechanisms that could produce faint He ii , which have implications for the low-mass reionization-era galaxies that may have similar ionization conditions.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 7
    In: The Astrophysical Journal, American Astronomical Society, Vol. 935, No. 2 ( 2022-08-01), p. 74-
    Abstract: Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the Sloan Digital Sky Survey Data Release aperture, which has a 3″ diameter similar to COS, IFU, and long-slit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using IFU observations of three galaxies, we find that the E ( B − V ) values derived from the Balmer ratios decrease (by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.″5. We examine the relative contributions from the gas and stars using the H α and [O iii ] λ 5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the far-UV CLASSY spectra, even when narrow 1.″0 long-slit observations are used.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 8
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 939, No. 1 ( 2022-11-01), p. 44-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 939, No. 1 ( 2022-11-01), p. 44-
    Abstract: The dispersion in chemical abundances provides a very strong constraint on the processes that drive the chemical enrichment of galaxies. Due to its proximity, the spiral galaxy M33 has been the focus of numerous chemical abundance surveys to study the chemical enrichment and dispersion in abundances over large spatial scales. The CHemical Abundances Of Spirals project has observed ∼100 H ii regions in M33 with the Large Binocular Telescope (LBT), producing the largest homogeneous sample of electron temperatures ( T e ) and direct abundances in this galaxy. Our LBT observations produce a robust oxygen abundance gradient of −0.037 ± 0.007 dex kpc −1 and indicate a relatively small (0.043 ± 0.015 dex) intrinsic dispersion in oxygen abundance relative to this gradient. The dispersions in N/H and N/O are similarly small, and the abundances of Ne, S, Cl, and Ar relative to O are consistent with the solar ratio as expected for α -process or α -process-dependent elements. Taken together, the ISM in M33 is chemically well-mixed and homogeneously enriched from inside out, with no evidence of significant abundance variations at a given radius in the galaxy. Our results are compared to those of the numerous studies in the literature, and we discuss possible contaminating sources that can inflate abundance dispersion measurements. Importantly, if abundances are derived from a single T e measurement and T e – T e relationships are relied on for inferring the temperature in the unmeasured ionization zone, this can lead to systematic biases that increase the measured dispersion up to 0.11 dex.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 9
    In: Annals of Internal Medicine, American College of Physicians, Vol. 175, No. 10 ( 2022-10), p. 1401-1410
    Type of Medium: Online Resource
    ISSN: 0003-4819 , 1539-3704
    RVK:
    Language: English
    Publisher: American College of Physicians
    Publication Date: 2022
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  • 10
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 378, No. 6615 ( 2022-10-07)
    Abstract: Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century. Expanse of SARS-CoV-2 sequencing capacity in Africa. ( A ) African countries (shaded in gray) and institutions (red circles) with on-site sequencing facilities that are capable of producing SARS-CoV-2 whole genomes locally. ( B ) The number of SARS-CoV-2 genomes produced per country and the proportion of those genomes that were produced locally, regionally within Africa, or abroad. ( C ) Decreased turnaround time of sequencing output in Africa to an almost real-time release of genomic data.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    RVK:
    RVK:
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2022
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    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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