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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.
- ItemThe SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way(Les Ulis : EDP Sciences, 2022) Colombo, D.; Duarte-Cabral, A.; Pettitt, A.R.; Urquhart, J. S.; Wyrowski, F.; Csengeri, T.; Neralwar, K.R.; Schuller, F.; Menten, K.M.; Anderson, L.; Barnes, P.; Beuther, H.; Bronfman, L.; Eden, D.; Ginsburg, A.; Henning, T.; König, C.; Lee, M.-Y.; Mattern, M.; Medina, S.; Ragan, S.E.; Rigby, A. J.; Sánchez-Monge, Á.; Traficante, A.; Yang, A. Y.; Wienen, M.The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium) survey that observed a large area of the inner Galaxy in the 13CO (2-1) line at an angular resolution of 28′′. We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude-velocity map built from the full survey. Additionally, we examine the properties of the molecular clouds in the spiral arms compared to the properties of their counterparts in the inter-arm regions. Through flux and luminosity probability distribution functions, we find that the molecular gas emission associated with the spiral arms does not differ significantly from the emission between the arms. On average, spiral arms show masses per unit length of ~105-106 M⊙ kpc-1. This is similar to values inferred from data sets in which emission distributions were segmented into molecular clouds. By examining the cloud distribution across the Galactic plane, we infer that the molecular mass in the spiral arms is a factor of 1.5 higher than that of the inter-arm medium, similar to what is found for other spiral galaxies in the local Universe. We observe that only the distributions of cloud mass surface densities and aspect ratio in the spiral arms show significant differences compared to those of the inter-arm medium; other observed differences appear instead to be driven by a distance bias. By comparing our results with simulations and observations of nearby galaxies, we conclude that the measured quantities would classify the Milky Way as a flocculent spiral galaxy, rather than as a grand-design one.
- ItemOGHReS: Large-scale filaments in the outer Galaxy(Les Ulis : EDP Sciences, 2021) Colombo, D.; König, C.; Urquhart, J. S.; Wyrowski, F.; Mattern, M.; Menten, K. M.; Lee, M.-Y.; Brand, J.; Wienen, M.; Mazumdar, P.; Schuller, F.; Leurini, S.Filaments are a ubiquitous morphological feature of the molecular interstellar medium and are identified as sites of star formation. In recent years, more than 100 large-scale filaments (with a length > 10 pc) have been observed in the inner Milky Way. As they appear linked to Galactic dynamics, studying those structures represents an opportunity to link kiloparsec-scale phenomena to the physics of star formation, which operates on much smaller scales. In this Letter, we use newly acquired Outer Galaxy High Resolution Survey (OGHReS) 12CO(2-1) data to demonstrate that a significant number of large-scale filaments are present in the outer Galaxy as well. The 37 filaments identified appear tightly associated with inter-arm regions. In addition, their masses and linear masses are, on average, one order of magnitude lower than similar-sized molecular filaments located in the inner Galaxy, showing that Milky Way dynamics is able to create very elongated features in spite of the lower gas supply in the Galactic outskirts.
- ItemALMA and MUSE observations reveal a quiescent multi-phase circumgalactic medium around the z ≃ 3.6 radio galaxy 4C 19.71(Les Ulis : EDP Sciences, 2021) Falkendal, Theresa; Lehnert, Matthew D.; Vernet, Joël; De Breuck, Carlos; Wang, WujiWe present MUSE at VLT imaging spectroscopy of rest-frame ultraviolet emission lines and ALMA observations of the [C I] 3P1-3P0 emission line, probing both the ionized and diffuse molecular medium around the radio galaxy 4C 19.71 at z ≃ 3.6. This radio galaxy has extended Lyα emission over a region ∼100 kpc in size preferentially oriented along the axis of the radio jet. Faint Lyα emission extends beyond the radio hot spots. We also find extended C IV and He II emission over a region of ∼150 kpc in size, where the most distant emission lies ∼40 kpc beyond the north radio lobe and has narrow full width half maximum (FWHM) line widths of ∼180 km s-1 and a small relative velocity offset Δv ∼ 130 km s-1 from the systemic redshift of the radio galaxy. The [C I] is detected in the same region with FWHM ∼100 km s-1 and Δv ∼ 5 km s-1, while [C I] is not detected in the regions south of the radio galaxy. We interpret the coincidence in the northern line emission as evidence of relatively quiescent multi-phase gas residing within the halo at a projected distance of ∼75 kpc from the host galaxy. To test this hypothesis, we performed photoionization and photo-dissociated region (PDR) modeling, using the code Cloudy, of the three emission line regions: the radio galaxy proper and the northern and southern regions. We find that the [C I]/C IVλλ1548, 1551 and C IVλλ1548, 1551/He II ratios of the two halo regions are consistent with a PDR or ionization front in the circumgalactic medium likely energized by photons from the active galactic nuclei. This modeling is consistent with a relatively low metallicity, 0.03 < [Z/Z⊙] < 0.1, and diffuse ionization with an ionization parameter (proportional to the ratio of the photon number density and gas density) of log U ∼ -3 for the two circumgalactic line emission regions. Using rough mass estimates for the molecular and ionized gas, we find that the former may be tracing ≈2-4 orders of magnitude more mass. As our data are limited in signal-to-noise due to the faintness of the line, deeper [C I] observations are required to trace the full extent of this important component in the circumgalactic medium. © T. Falkendal et al. 2021.