Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census

This is the fourth paper exploring the infrared properties of giant HII regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant HII regions identified by Conti & Crowther (2004), and in this paper we present the 20 and 37 micron imaging data we have obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multi-wavelength data, we derive and discuss the detailed physical properties of the individual compact sources and sub-regions as well as the large scale properties of Sgr D and W42. However, improved measurements have revealed much closer distances to both regions than previously believed, and consequently both sources are not powerful enough to be considered giant HII regions any longer. Motivated by this, we revisit the census of giant HII regions, performing a search through the last two decades of literature to update each source with the most recent and/or most accurate distance measurements. Based on these new distance estimates, we determine that 14 sources in total (25%) are at sufficiently reliable and closer distances that they are not powerful enough to be considered giant HII regions. We briefly discuss the observational and physical characteristics specific to Sgr D and W42 and show that they have properties distinct from the giant HII regions previously studied as a part of this survey.Comment: 31 pages, 8 figures, 7 tables; accepted for publication in Ap

SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines

We investigate the physical structure and conditions of photodissociation regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle Nebula using SOFIA FEEDBACK observations of the [C II] 158 micron line. These observations are velocity resolved to 0.5 km s$^{-1}$ and are analyzed alongside a collection of complimentary data with similar spatial and spectral resolution: the [O I] 63 micron line, also observed with SOFIA, and rotational lines of CO, HCN, HCO$^{+}$, CS, and N$_2$H$^{+}$. Using the superb spectral resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between the warm PDR and cool molecular gas layers in context of the Pillars' kinematic structure. We assemble a geometric picture of the Pillars and their surroundings informed by illumination patterns and kinematic relationships and derive physical conditions in the PDRs associated with the Pillars. We estimate an average molecular gas density $n_{{\rm H}_2} \sim 1.3 \times 10^5$ cm$^{-3}$ and an average atomic gas density $n_{\rm H} \sim 1.8 \times 10^4$ cm$^{-3}$ and infer that the ionized, atomic, and molecular phases are in pressure equilibrium if the atomic gas is magnetically supported. We find pillar masses of 103, 78, 103, and 18 solar masses for P1a, P1b, P2, and P3 respectively, and evaporation times of $\sim$1-2 Myr. The dense clumps at the tops of the pillars are currently supported by the magnetic field. Our analysis suggests that ambipolar diffusion is rapid and these clumps are likely to collapse within their photoevaporation timescales.Comment: 42 pages, 16 figures. Accepted for publication in The Astronomical Journa

Bringing Stellar Evolution & Feedback Together: Summary of proposals from the Lorentz Center Workshop, 2022

Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as ``feedback''. Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates, and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting `Bringing Stellar Evolution and Feedback Together' in April 2022, and identify key areas where further dialogue can bring about radical changes in how we view the relationship between stars and the universe they live in.Comment: Accepted to the Publications of the Astronomical Society of the Pacifi

La formation du gaz dense à l'origine des étoiles de faible et de haute masse

To understand how stars can form in the interstellar medium (ISM), it has to be understood how cold (~ 10 K) and dense gas (> 10^{4} cm^{-3}) can emerge during the evolution of the ISM. With the Herschel telescope it was found that most of this dense star forming gas is organised in filamentary structures.To understand how this dense filamentary gas forms, multiple CO transitions were observed towards the Musca filament, which can form low-mass stars, using the APEX telescope. These observations were complemented with [CII] and [OI] observations by the SOFIA telescope. The non-detection of [CII] demonstrates that the Musca cloud is embedded in a weak FUV field ( 50 K) CO gas around the Musca filament which cannot be explained with heating by the FUV radiation field. A comparison of the observed CO(4-3) emission with shock models shows that the emission can be the result of a low-velocity ( 1 pc) while for Musca gravity only starts to dominate locally (r 10 km/s) GMC collision can result in the formation of an OB association similar to OB2. These OB stars then form in gravitationally collapsing hubs and ridges due to the compression by the GMC collision.Pour comprendre la formation des étoiles, il faut étudier les processus physiques qui forment le gaz froid et dense dans le milieu interstellaire. Le télescope spatial Herschel a récemment démontré que la majorité du gaz froid et dense est formée de structures filamentaires (des filaments).Dans cette thèse, plusieurs raies de CO ont été observées avec le télescope APEX autour du filament de Musca. Ces observations ont été complémentées par des observations [CII] et [OI] avec le télescope SOFIA. La non-détection de [CII] démontre que le nuage de Musca est situé dans un champ de radiation UV faible (1 G0). Par contre, les observations de CO(4-3) avec APEX montrent qu'il y a du gaz CO chauffé (> 50 K) autour du filament que l'irradiation UV ne peut pas expliquer. La comparaison avec des modèles de chocs indique que l'émission CO(4-3) doit alors être le résultat d'un choc J à basse vitesse ( 1 pc) du gaz dense en contraste avec Musca pour lequel la gravité ne dominerait qu'aux plus petites échelles ( 10 km/s) qui pourrait expliquer la formation d'une association d'étoiles OB de plusieurs milliers d'étoiles. Dans ce scénario, les étoiles massives (OB) se formeraient dans les structures denses et massives (hubs et ridges) formées aux convergences dues à la collision à grande vitesse de nuages, et où la gravité à grande échelles domine la cinématique et l'évolution du gaz dense

The formation of dense gas in low- and high-mass star forming regions

Pour comprendre la formation des étoiles, il faut étudier les processus physiques qui forment le gaz froid et dense dans le milieu interstellaire. Le télescope spatial Herschel a récemment démontré que la majorité du gaz froid et dense est formée de structures filamentaires (des filaments).Dans cette thèse, plusieurs raies de CO ont été observées avec le télescope APEX autour du filament de Musca. Ces observations ont été complémentées par des observations [CII] et [OI] avec le télescope SOFIA. La non-détection de [CII] démontre que le nuage de Musca est situé dans un champ de radiation UV faible (1 G0). Par contre, les observations de CO(4-3) avec APEX montrent qu'il y a du gaz CO chauffé (> 50 K) autour du filament que l'irradiation UV ne peut pas expliquer. La comparaison avec des modèles de chocs indique que l'émission CO(4-3) doit alors être le résultat d'un choc J à basse vitesse ( 1 pc) du gaz dense en contraste avec Musca pour lequel la gravité ne dominerait qu'aux plus petites échelles ( 10 km/s) qui pourrait expliquer la formation d'une association d'étoiles OB de plusieurs milliers d'étoiles. Dans ce scénario, les étoiles massives (OB) se formeraient dans les structures denses et massives (hubs et ridges) formées aux convergences dues à la collision à grande vitesse de nuages, et où la gravité à grande échelles domine la cinématique et l'évolution du gaz dense.To understand how stars can form in the interstellar medium (ISM), it has to be understood how cold (~ 10 K) and dense gas (> 10^{4} cm^{-3}) can emerge during the evolution of the ISM. With the Herschel telescope it was found that most of this dense star forming gas is organised in filamentary structures.To understand how this dense filamentary gas forms, multiple CO transitions were observed towards the Musca filament, which can form low-mass stars, using the APEX telescope. These observations were complemented with [CII] and [OI] observations by the SOFIA telescope. The non-detection of [CII] demonstrates that the Musca cloud is embedded in a weak FUV field ( 50 K) CO gas around the Musca filament which cannot be explained with heating by the FUV radiation field. A comparison of the observed CO(4-3) emission with shock models shows that the emission can be the result of a low-velocity ( 1 pc) while for Musca gravity only starts to dominate locally (r 10 km/s) GMC collision can result in the formation of an OB association similar to OB2. These OB stars then form in gravitationally collapsing hubs and ridges due to the compression by the GMC collision

On the 3D Curvature and Dynamics of the Musca Filament

Filaments are ubiquitous in the interstellar medium, yet their formation and evolution remain the topic of intense debate. In order to obtain a more comprehensive view of the 3D morphology and evolution of the Musca filament, we model the C ^18 O(2-1) emission along the filament crest with several large-scale velocity field structures. This indicates that Musca is well described by a 3D curved cylindrical filament with longitudinal mass inflow to its center unless the filament is a transient structure with a lifetime ≲0.1 Myr. Gravitational longitudinal collapse models of filaments appear unable to explain the observed velocity field. To better understand these kinematics, we further analyze a map of the C ^18 O(2-1) velocity field at the location of SOFIA HAWC+ dust polarization observations that trace the magnetic field in the filament. This unveils an organized magnetic field that is oriented roughly perpendicular to the filament crest. Although the velocity field is also organized, it progressively changes its orientation by more than 90° when laterally crossing the filament crest and thus appears disconnected from the magnetic field in the filament. This strong lateral change of the velocity field over the filament remains unexplained and might be associated with important longitudinal motion that can be associated to the large-scale kinematics along the filament

The GENESIS project

The formation of stars is intimately linked to the structure and evolution of molecular clouds in the interstellar medium. The French-German (ANR/DFG) collaborative project GENESIS (GENeration and Evolution of Structures in the ISm, http://www.astro.uni-koeln.de/GENESIS), explores this link with a new approach: by combining far-infrared data of dust (Herschel), observations of major cooling lines in the interstellar medium (CII, CI, CO, OI with the Stratospheric Observatory for FIR astronomy SOFIA), and molecular line maps from ground-based telescopes. It is also supported by the German Government funded MOBS (Modelling SOFIA data). We here present results of two workpackages, one showing SOFIA OI observations in the massive star-forming regions S106, and one investigating molecular cloud formation in the diffuse Draco cloud

The GENESIS project

International audienceThe formation of stars is intimately linked to the structure and evolution of molecular clouds in the interstellar medium. The French-German (ANR/DFG) collaborative project GENESIS (GENeration and Evolution of Structures in the ISm, http://www.astro.uni-koeln.de/GENESIS), explores this link with a new approach: by combining far-infrared data of dust (Herschel), observations of major cooling lines in the interstellar medium (CII, CI, CO, OI with the Stratospheric Observatory for FIR astronomy SOFIA), and molecular line maps from ground-based telescopes. It is also supported by the German Government funded MOBS (Modelling SOFIA data). We here present results of two workpackages, one showing SOFIA OI observations in the massive star-forming regions S106, and one investigating molecular cloud formation in the diffuse Draco cloud