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- ItemMUSE crowded field 3D spectroscopy in NGC 300: III. Characterizing extremely faint HII regions and diffuse ionized gas(Les Ulis : EDP Sciences, 2022) Micheva, Genoveva; Roth, Martin M.; Weilbacher, Peter M.; Morisset, Christophe; Castro, Norberto; Monreal Ibero, Ana; Soemitro, Azlizan A.; Maseda, Michael V.; Steinmetz, Matthias; Brinchmann, JarleContext. There are known differences between the physical properties of H II and diffuse ionized gas (DIG). However, most of the studied regions in the literature are relatively bright, with log10 L(Hα)[erg s-1] ≳37. Aims. We compiled an extremely faint sample of 390 H II regions with a median Hα luminosity of 34.7 in the flocculent spiral galaxy NGC 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. Methods. We used MUSE data of nine fields in NGC 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified H II and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the H II and DIG regions. Results. The gas density in the H II and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the H II regions, which can be explained by the DIG being 1.8 kK hotter than H II gas. The DIG manifests a lower ionization parameter than H II gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the H II gas. We observe a flat metallicity profile in the central region of NGC 300, without a sign of a gradient. Conclusions. The differences between extremely faint H II and DIG regions follow the same trends and correlations as their much brighter cousins. Both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes.
- ItemResolving stellar populations with integral field spectroscopy(Berlin : Wiley-VCH Verl., 2019) Roth, Martin M.; Weilbacher, Peter M.; Castro, NorbertoHigh-performance instruments at large ground-based telescopes have made integral field spectroscopy (IFS) a powerful tool for the study of extended objects such as galaxies, nebulae, or even larger survey fields on the sky. Here, we discuss the capabilities of IFS for the study of resolved stellar populations, using the newmethod of point-spread-function-fitting crowded field IFS, analogous to the well-established technique of crowded field photometry with image sensors.We review early pioneering work with first-generation integral field spectrographs, the breakthrough achieved with the multiunit spectral explorer (MUSE) instrument at the European Organisation for Astronomical Research in the Southern Hemisphere (ESO)Very Large Telescope, the remarkable progress accomplished with MUSE in the study of globular clusters, and first results on nearby galaxies. We discuss the synergy of integral field spectrographs at 8–10 mclass telescopes with future facilities such as the extremely large telescope (ELT).
- ItemMassive stars in extremely metal-poor galaxies: a window into the past(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Garcia, Miriam; Evans, Christopher J.; Bestenlehner, Joachim M.; Bouret, Jean Claude; Castro, Norberto; Cerviño, Miguel; Fullerton, Alexander W.; Gieles, Mark; Herrero, Artemio; de Koter, Alexander; Lennon, Daniel J.; van Loon, Jacco Th.; Martins, Fabrice; de Mink, Selma E.; Najarro, Francisco; Negueruela, Ignacio; Sana, Hugues; Simón-Díaz, Sergio; Szécsi, Dorottya; Tramper, Frank; Vink, Jorick S.; Wofford, AidaCosmic history has witnessed the lives and deaths of multiple generations of massive stars, all of them invigorating their host galaxies with ionizing photons, kinetic energy, fresh material, and stellar-mass black holes. Ubiquitous engines as they are, astrophysics needs a good understanding of their formation, evolution, properties and yields throughout the history of the Universe, and with decreasing metal content mimicking the environment at the earliest epochs. Ultimately, a physical model that could be extrapolated to zero metallicity would enable tackling long-standing questions such as “What did the first, very massive stars of the Universe look like?” or “What was their role in the re-ionization of the Universe?” Yet, most of our knowledge of metal-poor massive stars is drawn from one single point in metallicity. Massive stars in the Small Magellanic Cloud (SMC, ∼1/5Z⊙ ) currently serve as templates for low-metallicity objects in the early Universe, even though significant differences with respect to massive stars with poorer metal content have been reported. This White Paper summarizes the current knowledge on extremely (sub-SMC) metal poor massive stars, highlighting the most outstanding open questions and the need to supersede the SMC as standard. A new paradigm can be built from nearby extremely metal-poor galaxies that make a new metallicity ladder, but massive stars in these galaxies are out of reach to current observational facilities. Such a task would require an L-size mission, consisting of a 10m-class space telescope operating in the optical and the ultraviolet ranges. Alternatively, we propose that ESA unites efforts with NASA to make the LUVOIR mission concept a reality, thus continuing the successful partnership that made the Hubble Space Telescope one of the greatest observatories of all time.