Broad Raman-scattered wings of hydrogen lines can be used to map neutral gas illuminated by high-mass stars in star forming regions. Raman scattering transforms far-ultraviolet starlight from the wings of the Lyman beta line (1022 Angstrom to 1029 Angstrom) to red visual light in the wings of the H alpha line (6400 Angstrom to 6700 Angstrom). Analysis of spatially resolved spectra of the Orion Bar and other regions in the Orion Nebula shows that this process occurs in the neutral photo-dissociation region between the ionization front and dissociation front. The inner Raman wings are optically thick and allow the neutral hydrogen density to be determined, implying n(H0) ~= 100,000 per cubic cm for the Orion Bar. Far-ultraviolet resonance lines of neutral oxygen imprint their absorption onto the stellar continuum as it passes through the ionization front, producing characteristic absorption lines at 6633 Angstrom and 6664 Angstrom with widths of order 2 Angstrom. This is a unique signature of Raman scattering, which allows it to be easily distinguished from other processes that might produce broad H alpha wings, such as electron scattering or high-velocity outflows.
The mid-infrared (MIR) spectra of dense photodissociation regions (PDRs) are typically dominated by emission from polycyclic aromatic hydrocarbons (PAHs) and the lowest pure rotational states of molecular hydrogen (H2); two species which are probes of the physical properties of gas and dust in intense UV radiation fields. We utilize the high angular resolution of the Infrared Spectrograph on the Spitzer Space Telescope to construct spectral maps of the PAH and H2 features for three of the best studied PDRs in the galaxy, NGC 7023, NGC 2023 and IC 63. We present spatially resolved maps of the p…
Photodissociation regions (PDRs) are parts of the ISM consisting of predominantly neutral gas, located at the interface between H II regions and molecular clouds. The physical conditions within these regions show variations on very short spatial scales, and therefore PDRs constitute ideal laboratories for investigating the properties and evolution of dust grains. We have mapped IC 63 at high resolution from the UV to the NIR (275 nm to 1.6 $μ$m), using the Hubble Space Telescope WFC3. Using a Bayesian SED fitting tool, we simultaneously derive a set of stellar ($T_\text{eff}$, $\log(g)$, dista…
The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix Nebula as seen in the submillimeter range with Herschel. We use 5 SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyze the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiat…
A previous analysis of methanol and formaldehyde towards the Orion Bar concluded that the two molecular species may trace different physical components, methanol the clumpy material, and formaldehyde the interclump medium. To verify this hypothesis, we performed multi-line mapping observations of the two molecules to study their spatial distributions. The observations were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular resolution of ~11''. Additional data for H2CO from the Plateau de Bure array are also discussed. The data were analysed using an LVG approach. Both mo…
We have obtained maps of the molecular emission within the central five arcminutes (12 pc) of the Galactic center (GC) in selected molecular tracers: SiO(2-1), HNCO(5_{0,5}-4_{0,4}), and the J=1-->0 transition of H^{13}CO+, HN^{13}C, and C^{18}O at an angular resolution of 30" (1.2 pc). The mapped region includes the circumnuclear disk (CND) and the two surrounding giant molecular clouds (GMCs) of the Sgr A complex, known as the 20 and 50 km s^{-1} molecular clouds.Additionally, we simultaneously observed the J=2-1 and 3-2 transitions of SiO toward selected positions to estimate the physical c…
We observationally investigate the relation between the photoelectric heating efficiency in PDRs and the charge of PAHs, which are considered to play a key role in photoelectric heating. Using PACS onboard Herschel, we observed six PDRs spanning a wide range of FUV radiation fields (G_0=100-10^5). To measure the photoelectric heating efficiency, we obtained the intensities of the main cooling lines, i.e., the [OI]63um, 145um, and [CII]158um, as well as the FIR continuum intensity. We used Spitzer/IRS spectroscopic mapping observations to investigate the MIR PAH features in the same regions. We…
Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde VI. The photodissociation region M17SW
State Key Laboratory of Radio Astronomy and Technology, Xinjiang Astronomical Observatory, CAS（中国科学院新疆天文台射电天文与技术国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Xinjiang Key Laboratory of Radio Astrophysics（新疆射电天体物理重点实验室）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）
We present a novel approach to estimating the intensity mapping signal of any CO rotational line emitted during the Epoch of Reionization (EoR). Our approach is based on large velocity gradient (LVG) modeling, a radiative transfer modeling technique that generates the full CO spectral line energy distribution (SLED) for a specified gas kinetic temperature, volume density, velocity gradient, molecular abundance, and column density. These parameters, which drive the physics of CO transitions and ultimately dictate the shape and amplitude of the CO SLED, can be linked to the global properties of …
We use the IRS on Spitzer to observe the southern part of the reflection nebula NGC 2023, including the Southern Ridge, which is a photodissociation region par excellence excited by HD 37903. Five pure-rotational H2 emission lines are detected and mapped over and around the Southern Ridge in order to compare with predicted level column densities from theoretical PDR models. We find very good agreement between PDR model predictions and emission line intensities and ratios measured with Spitzer, leading us to conclude that grain photoelectric heating sufficiently warms the gas to produce the obs…
Quantitative understanding of the interstellar medium requires knowledge of its physical conditions. Low frequency carbon radio recombination lines (CRRLs) trace cold interstellar gas, and can be used to determine its physical conditions (e.g., electron temperature and density). In this work we present spatially resolved observations of the low frequency ($\leq390$ MHz) CRRLs centered around C$268α$, C$357α$, C$494α$ and C$539α$ towards Cassiopeia A on scales of $\leq1.2$ pc. We compare the spatial distribution of CRRLs with other ISM tracers. This comparison reveals a spatial offset between t…
Atomic carbon (CI) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of CI as the tracer, we performed [CI]$(^3P_1-^3P_0)$ (hereinafter [CI](1-0)) mapping observations of the northern part of the nearby spiral galaxy M83 with the ASTE telescope and compared the distributions of [CI](1-0) with CO lines (CO(1-0), CO(3-2), and $^{13}$CO(1-0)), HI, and infrared (IR) emission (70, 160, and 250$ μ$m). The [CI](1-0) distribution in the central region is similar to that of the CO lines, whereas [CI](1…
KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis Major star-forming region
Estimating molecular abundances ratios from the direct measurement of the emission of the molecules towards a variety of interstellar environments is indeed very useful to advance in our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio (X), is studied in detail. We selected the well-studied high-mass star-forming region G29.96-0.02, located at a distance of…
We present resolution-enhanced images of warm dust at multiple temperatures and opacity index values in the star-forming bubble/HII region, RCW 120. The image set, representing a 4D hypercube of differential column density, was obtained using our Bayesian procedure, ppmap. The cool peripheral material ($\sim16$-22 K) exhibits ragged clumpy structure as noted previously by others. However, at higher temperatures ($\stackrel{>}{_\sim}26$ K) the geometry changes dramatically, showing a bubble boundary which is accurately circular in projection, except for the previously-reported opening in the no…
We present results of the classification of cloud structures toward the Orion A Giant Molecular Cloud based on wide-field $^{12}$CO ($J$ = 1--0), $^{13}$CO ($J$ = 1-0), and C$^{18}$O ($J$ = 1-0) observations using the Nobeyama 45 m radio telescope. We identified 78 clouds toward Orion A by applying Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES) to the data cube of the column density of $^{13}$CO. Well-known subregions such as OMC-1, OMC-2/3, OMC-4, OMC-5, NGC 1977, L1641-N, and the dark lane south filament (DLSF) are naturally identified as distinct structures in…
We present a high-resolution, near-IR spectroscopic study of multiple outflows in the LkH$α$ 234 star formation region using the Immersion GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted emission of HH 167 allowed us to distinguish at least three separate, spatially overlapped, outflows in H${_2}$ and [Fe II] emission. We show that the H${_2}$ emission represents not a single jet, but complex multiple outflows driven by three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted H${_2}$ outflow at a low velocity, $\VLSR$ $<$ $+$50 {\kms}, with respe…
Large scale mapping of [CI] and the [CI]-to-CO transition in $ρ$ Ophiuchus molecular cloud
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Physics, Anhui Normal University（安徽师范大学物理学院）；Research Center for Astronomical Computing, Zhejiang Laboratory（浙江实验室天体计算研究中心）；Institute of Astronomy and Information, Dali University（大理大学天文与信息研究所）；Institut de Radioastronomie Millimetrique（毫米波射电天文学研究所）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所）；New Cornerstone Science Laboratory, Department of Astronomy, Tsinghua University（清华大学天文系新基石科学实验室）；Department of Physics, Xi’an（西安某大学物理学院）
We have measured the gas temperature in the IC 63 photodissociation region (PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen with SOFIA/EXES. We divide the PDR into three regions for analysis based on the illumination from $γ$ Cas: "sunny," "ridge" and "shady." Constructing rotation diagrams for the different regions, we obtain temperatures of T$_{ex}$=$562^{+52}_{-43}$ K towards the "ridge" and T$_{ex}$=$495^{+28}_{-25}$ K in the "shady" side. The H$_2$ emission was not detected on the "sunny" side of the ridge, likely due to the photo-dissociation of H$_2$ in this gas. …
