Turbulent magnetic field in the H II region Sh 2–27
Notice bibliographique
Résumé
Context. Magnetic fields in the turbulent interstellar medium (ISM) are a key element in understanding Galactic dynamics, but there are many observational challenges. One useful probe for studying the magnetic field component parallel to the line of sight (LoS) is Faraday rotation of linearly polarized radio synchrotron emission, combined with Hα observations. H ii regions are the perfect laboratories to probe such magnetic fields as they are localized in space, and are well-defined sources often with known distances and measurable electron densities. We chose the H ii region Sharpless 2–27 (Sh 2–27) as it is located at intermediate latitudes (b ~ 23°), meaning that it suffers from little LoS confusion from other sources. In addition, it has a large angular diameter (~10°), enabling us to study the properties of its magnetic field over a wide range of angular scales. Aims. By using a map of the magnetic field strength along the LoS (B‖)for the first time, we investigate the basic statistical properties of the turbulent magnetic field inside Sh 2–27. We study the scaling of the magnetic field fluctuations, compare it to the Kolmogorov scaling, and attempt to find an outer scale of the turbulent magnetic field fluctuations. Methods. We used the polarized radio synchrotron emission data from the S-band Polarization All-Sky Survey (S-PASS) at 2.3 GHz, which allowed us to test the impact of Sh 2–27 on diffuse Galactic synchrotron polarization. We estimated the rotation measure (RM) caused by the H ii region, using the synchrotron polarization angle. We used the Hα data from the Southern Hα Sky Survey Atlas to estimate the free electron density (ne) in the H ii region. Using an ellipsoid model for the shape of Sh 2–27, and with the observed RM and emission measure (EM), we estimated the LoS averaged B‖for each LoS within the ellipsoid. To characterize the turbulent magnetic field fluctuations, we computed a second-order structure function of B‖ We compared the structure function to Kolmogorov turbulence, and to simulations of Gaussian random fields processed in the same way as the observations. Results. We present the first continuous map of B‖ computed using the diffuse polarized radio emission in Sh 2–27. We estimate the median value of ne as 7.3 ± 0.1 cm−3, and the median value of B‖ as −4.5 ± 0.1 µG, which is comparable to the magnetic field strength in diffuse ISM. The slope of the structure function of the estimated B‖-map is found to be slightly steeper than Kolmogorov, consistent with our Gaussian-random-field B‖simulations revealing that an input Kolmogorov slope in the magnetic field results in a somewhat steeper slope in B‖.These results suggest that the lower limit to the outer scale of turbulence is 10 pc in the H ii region, which is comparable to the size of the computation domain. Conclusions. The structure functions of B‖ fluctuations in Sh 2–27 show that the magnetic field fluctuations in this H ii region are consistent with a Kolmogorov-like turbulence. Comparing the observed and simulated B‖ structure functions results in the estimation of a lower limit to the outer scale of the turbulent magnetic field fluctuations of 10 pc, which is limited by the size of the field of view under study. This may indicate that the turbulence probed here could actually be cascading from the larger scales in the ambient medium, associated with the interstellar turbulence in the general ISM, which is illuminated by the presence of Sh 2–27.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».