Constraining physical conditions for the PDR of Trumpler 14 in the Carina Nebula

Abstract

We investigate the physical conditions of the CO gas, based on the submillimeter imaging spectroscopy from a 2 × 7 (1.5 × 5 pc 2 ) area near the young star cluster, Trumpler 14 of the Carina Nebula. The observations presented in this work are taken with the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [Ci] 370 µm, [Ci] 609 µm, and CO transitions from J = 4 − 3 to J = 13 − 12. Our field of view covers the edge of a cavity carved by Trumpler 14 about 1 Myr ago and marks the transition from Hii regions to photodissociation regions. The observed CO intensities are the most prominent at the northwest region, Car I-E. With the state-of-the-art Meudon PDR code, we successfully derive the physical conditions, which include the thermal pressure (P) and the scaling factor of radiation fields (G UV ), from the observed CO spectral line energy distributions (SLEDs) in the observed region. The derived G UV values generally show an excellent agreement with the UV radiation fields created by nearby OB-stars and thus confirm that the main excitation source of the observed CO emission are the UV-photons provided by the massive stars. The derived thermal pressure is between 0.5 − 3 × 10 8 K cm −3 with the highest values found along the ionization front in Car I-E region facing Trumpler 14, hinting that the cloud structure is similar to the recent observations of the Orion Bar. We also note a discrepancy at a local position (< 0.17 × 0.17 pc 2 ) between the PDR modeling result and the UV radiation fields estimated from nearby massive stars, which requires further investigation on nearby objects that could contribute to local heating, including outflow. Comparing the derived thermal pressure with the radiation fields, we report the first observationally-derived and spatially-resolved P ∼ 2 × 10 4 G UV relationship. As direct comparisons of the modeling results to the observed 13 CO, [Oi] 63 µm, and [Cii] 158 µm intensities are not straightforward, we urge the readers to be cautious when constraining the physical conditions of PDRs with combinations of 12 CO, 13 CO, [Ci], [Oi] 63 µm, and [Cii] 158 µm observations.

The water line emission and ortho-to-para ratio in the Orion Bar photon-dominated region

“…However, the clumpy model is challenged by the very high resolution observations provided by the Atacama Large Millimeter/submillimeter Array (ALMA) radiotelescope (Goicoechea et al 2016, which show that, to the first order, the structure of the PDR is a compressed layer at high-pressure where a warm chemistry takes place, leading to the presence of molecules such as SH + and high-J excited CO (Joblin et al 2018). This structure is also observed in other PDRs, such as Trumpler 14 in the Carina nebula (Wu et al 2018). High-density structures exist inside the PDR, as seen in OH (Goicoechea et al 2011;Parikka et al 2017) and H 13 CN maps (Lis & Schilke 2003), as well as in ALMA maps (Goicoechea et al 2016).…”

“…The incoming UV radiation field is based on the interstellar radiation field (ISRF) (Mathis et al 1983), scaled by a multiplicative factor G 0 . Mathis UV radiation field is about 1.3 factor as high as Habing one (Habing 1968) in the spectral range of 91.2 to 111 nm (Wu et al 2018).…”

Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

“…The diagnostic power of CO rotational transitions has been explored to a greater extent since the advent of the ESA Herschel Space Observatory (Pilbratt et al 2010). The three detectors on board Herschel, PACS (Photodetector Array Camera and Spectrometer; Poglitsch et al 2010), SPIRE (Spectral and Photometric Imaging Receiver; Griffin et al 2010), and HIFI (Heterodyne Instrument for the Far Infrared; de Graauw et al 2010), provide access to a wavelength window of ∼50-670 µm and enable the study of CO spectral line energy distributions (SLEDs) up to the upper energy level J u = 50 for Galactic and extragalactic sources including photodissociation regions (PDRs; e.g., Habart et al 2010;Köhler et al 2014;Stock et al 2015;Joblin et al 2018;Wu et al 2018), protostars (e.g., Larson et al 2015), infrared (IR) dark clouds (e.g., Pon et al 2016), IR bright galaxies (e.g., Rangwala et al 2011;Kamenetzky et al 2012;Meijerink et al 2013;Pellegrini et al 2013;Papadopoulos et al 2014; A113, page 1 of 25 A&A 628, A113 (2019) Fig. 1.…”

The nature of molecular cloud boundary layers from SOFIA [O I] observations

“…By comparison, H II regions have much larger thermal pressures and values of G o . For example, in H II regions, the CO spectral line energy distribution (CO SLEDs) (along with other tracers) along with PDR models (cf., Bron et al 2018) have been used to derive P th and G o (Stock et al 2015;Joblin et al 2018;Wu et al 2018). Among several sources studied, P th and G o range from 10 6 to a few × 10 8 (K cm −3 ) and 10 2 to 10 8 , respectively (Stock et al 2015;Joblin et al 2018;Wu et al 2018), much larger than the values derived for our sources.…”

“…They have been the focus of a considerable modeling effort (see Tielens & Hollenbach 1985;Sternberg & Dalgarno 1989;Kaufman et al 1999;Abel et al 2005;Le Petit et al 2006;Bron et al 2018, and references therein). The observational analysis of PDRs, H II regions, and IBLs has improved considerably since the availability of far-infrared spectroscopic data from the Herschel Space Observatory (see Ossenkopf et al 2013;Köhler et al 2014;Stock et al 2015;Joblin et al 2018;Wu et al 2018, and references therein) and the Stratospheric Observatory for Infrared Astronomy (SOFIA; e.g., Schneider et al 2012;Pérez-Beaupuits et al 2015;Pabst et al 2017;Mookerjea et al 2018) . Most of these studies of the ionized and PDR layers have focused on very bright H II regions where high UV flux, density, and temperature produce strong far-infrared emission, making such regions easily observable in key gas tracers such as the fine-structure lines of C + , N + , and O.…”