FEEDBACK from the NGC 7538 H II region

Abstract

Context. The interaction of expanding H II regions with their environmental clouds is one of the central questions driving the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program FEEDBACK. Aims. We want to understand the interaction of the prototypical NGC 7538 H II region with the neighboring molecular cloud hosting several active star-forming regions. Methods. Using the SOFIA, we mapped an area of ~210′2 (~125 pc2) around NGC 7538 in the velocity-resolved ionized carbon fine-structure line [CII] at 1.9 THz (158 μm). Complementary observed atomic carbon [CI] at 492 GHz and high-J CO(8–7) data, as well as archival near- and far-infrared, cm continuum, CO(3–2), and HI data are folded into the analysis. Results. The ionized carbon [CII] data reveal rich morphological and kinematic structures. While the overall morphology follows the general ionized gas that is also visible in the radio continuum emission, the channel maps show multiple bubble-like structures with sizes on the order of ~80–100″ (~1.0–1.28 pc). While at least one of them may be an individual feedback bubble driven by the main exciting sources of the NGC 7538 H II region (the O3 and O9 stars IRS6 and IRS5), the other bubble-like morphologies may also be due to the intrinsically porous structure of the H II region. An analysis of the expansion velocities around 10 km s−1 indicates that thermal expansion is not sufficient but that wind-driving from the central O-stars is required. The region exhibits a general velocity gradient across, but we also identify several individual velocity components. The most blue-shifted [CII] component has barely any molecular or atomic counterparts. At the interface to the molecular cloud, we find a typical photon-dominated region (PDR) with a bar-shape. Ionized C+, atomic C0 and molecular carbon CO show a layered structure in this PDR. The carbon in the PDR is dominated by its ionized C+ form with atomic C0 and molecular CO masses of ~0.45 ± 0.1 M⊙ and ~1.2 ± 0.1 M⊙, respectively, compared to the ionized carbon C+ in the range of 3.6−9.7 M⊙. This bar-shaped PDR exhibits a velocity-gradient across, indicating motions along the line of sight toward the observer. Conclusions. Even if it is shown to be dominated by two nearby exciting sources (IRS6 and IRS5), the NGC 7538 H II region exhibits a diverse set of substructures that interact with each other as well as with the adjacent cloud. Compared to other recent [CII] observations of H II regions (e.g., Orion Veil, RCW120, RCW49), the bubble-shape morphologies revealed in [CII] emission that are indicative of expanding shells are recurring structures of PDRs.

SOFIA Observations of 30 Doradus. II. Magnetic Fields and Large-scale Gas Kinematics

“…These PV diagrams confirm that there are several organized VGs in the region. These gradients cover a velocity interval of 5-15 km s −1 in most PV diagrams and come in the form of curves/half-elliptical features that have been associated with expanding-shells (Pabst et al 2019(Pabst et al , 2020Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022;Bonne et al 2022a). Based on the presence of these curved features, we identify 4 expanding-shell candidates over the full map using the PV diagrams.…”

The SOFIA FEEDBACK Legacy Survey Dynamics and Mass Ejection in the Bipolar H ii Region RCW 36

“…Stellar feedback leads to the formation of H II regions, which come in the form of H II bubbles (Churchwell et al 2006;Deharveng et al 2010;Beaumont & Williams 2010;Kendrew et al 2012), bipolar H II regions (Bally & Scoville 1982;Deharveng et al 2015;Schneider et al 2018;Samal et al 2018), and more irregular features (Anderson et al 2011(Anderson et al , 2014. Recently, the kinematics of a couple of H II bubbles have been studied with the [C II] 158 μm fine-structure line (Anderson et al 2019;Pabst et al 2019Pabst et al , 2020Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022) because it traces the photodissociation regions (PDRs) at the interfaces between H II regions and molecular clouds, where mostly far-ultraviolet (FUV) photons in the energy range of 6-13.6 eV regulate the physical conditions of the ISM (Hollenbach & Tielens 1999). The [C II] kinematics in some of these regions demonstrated the presence of expanding shells with velocities up to 15 km s −1 (Pabst et al 2019(Pabst et al , 2020Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022).…”

“…Recently, the kinematics of a couple of H II bubbles have been studied with the [C II] 158 μm fine-structure line (Anderson et al 2019;Pabst et al 2019Pabst et al , 2020Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022) because it traces the photodissociation regions (PDRs) at the interfaces between H II regions and molecular clouds, where mostly far-ultraviolet (FUV) photons in the energy range of 6-13.6 eV regulate the physical conditions of the ISM (Hollenbach & Tielens 1999). The [C II] kinematics in some of these regions demonstrated the presence of expanding shells with velocities up to 15 km s −1 (Pabst et al 2019(Pabst et al , 2020Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022). However, they often show expansion in only one direction, mostly blueshifted, which suggests that the bubbles might not be fully spherical.…”

SOFIA FEEDBACK Survey: PDR Diagnostics of Stellar Feedback in Different Regions of RCW 49

“…In our previous work, we characterized the expanding shell of RCW 49 using the [C II], 12 CO, and 13 CO observations (Tiwari et al 2021). With the goal of quantifying radiative and mechanical input by massive stars into their surroundings, similar studies were performed to understand the stellar feedback mechanisms in the ISM through the FEEDBACK program (first scientific results in Luisi et al 2021;Tiwari et al 2021;Beuther et al 2022;Kabanovic et al 2022).…”