The ortho-to-para ratio (OPR) of H$_2$O is thought to be sensitive to the temperature of water formation. The OPR of H$_2$O is thus useful to study the formation mechanism of water. We investigate the OPR of water in the Orion PDR (Photon-dominated region), at the Orion Bar and Orion S positions, using data from {\it Herschel}/HIFI. We detect the ground-state lines of ortho- and para-H$_2$$^{18}$O in the Orion Bar and Orion S and we estimate the column densities using LTE and non-LTE methods. Based on our calculations, the ortho-to-para ratio (OPR) in the Orion Bar is 0.1 $-$ 0.5, which is unexpectedly low given the gas temperature of $\sim$ 85 K, and also lower than the values measured for other interstellar clouds and protoplanetary disks. Toward Orion S, our OPR estimate is below 2. This low OPR at 2 positions in the Orion PDR is inconsistent with gas phase formation and with thermal evaporation from dust grains, but it may be explained by photodesorption.
Water Abundance and Ortho-Para Ratio in the S140 Photon Dominated Region
Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Columbia University（哥伦比亚大学）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学）；Instituto de Física Fundamental (CSIC)（基础物理研究所（西班牙高等科学研究委员会））
JWST observations of photodissociation regions: II. Warm molecular Hydrogen spectroscopy in the Horsehead nebula
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale（巴黎萨克雷大学）；Sorbonne Université, CNRS, Institut d’Astrophysique de Paris（索邦大学）；Space Telescope Science Institute（太空望远镜科学研究所）；LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS（巴黎天文台）；Université Paris-Cité（巴黎西岱大学）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Department of Physics & Astronomy, The University of Western Ontario（韦仕敦大学物理与天文学系）；Ritter Astrophysical Research Center, University of Toledo（托莱多大学里特天体物理研究中心）
We present 5--14~$μ$m spectra at two different positions across the Orion Bar photodissociation region (PDR) obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and 3.3~$μ$m PAH observations obtained with the Stratospheric Observatory for Infrared Astronomy (SOFIA). We aim to characterize emission from Polycyclic Aromatic Hydrocarbon (PAH), dust, atomic and molecular hydrogen, argon, sulfur, and neon as a function of distance from the primary illuminating source. We find that all the major PAH bands peak between the ionization front and the PDR front, as traced by H$_{2…
We present our new ALMA observations targeting [OIII]88um, [CII]158um, [NII]122um, and dust continuum emission for three Lyman break galaxies at z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels, and identify multi-band dust continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z>6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[C…
We analyze $^{12}$CO($J$=2-1), $^{13}$CO($J$=2-1), C$^{18}$O ($J$=2-1), and 1.3 mm continuum maps of the $ρ$ Ophiuchi A photo-dissociation region (PDR) obtained with ALMA. Layered structures of the three CO isotopologues with an angular separation of 10 arcsec = 6.6$\times$10$^{-3}$ pc = 1400 au are clearly detected around the Be star, S1 (i.e., each front of emission shifts from the near to far side in order of $^{12}$CO, $^{13}$CO, and C$^{18}$O). We estimate the spatial variations of $X$($^{13}$CO)/$X$(C$^{18}$O) abundance ratios, and find that the abundance ratio is as high as 40 near the …
PDRs4All XVII: Formation and excitation of HD in photodissociation regions. Application to the Orion Bar
Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS（空间天体物理研究所，巴黎萨克雷大学，法国国家科学研究中心）；LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS（LUX，巴黎天文台，巴黎文理研究大学，索邦大学，法国国家科学研究中心）；Université Paris-Cité（巴黎西岱大学）；Department of Physics, College of Science, United Arab Emirates University (UAEU)（阿拉伯联合酋长国大学理学院物理学系）；Instituto de Física Fundamental (CSIC)（基础物理研究所（西班牙国家研究委员会））；Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory（查尔姆斯理工大学空间、地球与环境系，翁萨拉空间观测站）
Context. The combined use of carbon radio recombination lines (CRRLs) and the 158 $μ$m-[CII] line is a powerful tool for the study of the energetics and physical conditions (e.g., temperature and density) of photodissociation regions (PDRs). However, there are few observational studies that exploit this synergy. Aims. Here we explore the relation between CRRLs and the 158 $μ$m-[CII] line in light of new observations and models. Methods. We present new and existing observations of CRRLs in the frequency range 0.15--230 GHz with ALMA, VLA, the GBT, Effelsberg 100m, and LOFAR towards Orion~A (M42…
Weak, extended water vapor emission in the Horsehead nebula
Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；LUX, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université（巴黎天文台卢克瑟姆宇宙学与天体物理实验室，巴黎文理研究大学，法国国家科学研究中心，索邦大学）；Instituto de Física Fundamental (CSIC)（基础物理研究所（西班牙国家科学研究委员会））；European Space Agency (ESA), European Space Astronomy Centre (ESAC)（欧洲空间局欧洲空间天文中心）
A very low ortho-to-para ratio (OPR) of 0.1-0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin $\mathrm{H_2^{18}O}$ lines which were analyzed by using a single-slab large velocity gradient model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. A more complete set of water observations in the Orion B…
PDRs4All: XVIII. The evolution of the PAH ionisation and PAH size distribution across the Orion Bar
NASA Ames Research Center（NASA 艾姆斯研究中心）；Department of Physics & Astronomy, The University of Western Ontario（韦仕敦大学物理与天文系）；Institute for Earth and Space Exploration, The University of Western Ontario（韦仕敦大学地球与太空探索研究所）；Carl Sagan Center, SETI Institute（SETI 研究所卡尔·萨根中心）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III - Paul Sabatier, CNRS, CNES（图卢兹第三大学-保罗·萨巴蒂尔大学、法国国家科学研究中心、法国国家空间研究中心天体物理学和行星学研究所在）；School of Physics, University of Hyderabad（海得拉巴大学物理学院）；Department of Astronomy, The Ohio State University（俄亥俄州立大学天文学系）；Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS（巴黎南天体物理研究所）
Aims: We study the spatial distribution and kinematics of water emission in a ~64 pc$^2$ region of the Galactic Center (GC) around Sgr A*. We also analyze the water excitation to derive the physical conditions and water abundances in the CND and the `quiescent clouds'. Methods: We presented the integrated intensity maps of the ortho 1$_{10}-1_{01}$, and para 2$_{02}-1_{11}$ and 1$_{11}-0_{00}$ water transitions observed with the HIFI instrument on board Herschel. To study the water excitation we used ground state ortho and para H$_2^{18}$O transitions. In our study, we also used SPIRE continuu…
