SWAS and Arecibo observations of H2O and OH in a diffuse cloud along the line-of-sight to W51

Observations of W51 with the Submillimeter Wave Astronomy Satellite (SWAS) have yielded the first detection of water vapor in a diffuse molecular cloud. The water vapor lies in a foreground cloud that gives rise to an absorption feature at an LSR velocity of 6 km/s. The inferred H2O column density is 2.5E+13 cm-2. Observations with the Arecibo radio telescope of hydroxyl molecules at ten positions in W51 imply an OH column density of 8E+13 cm-2 in the same diffuse cloud. The observed H2O/OH ratio of ~ 0.3 is significantly larger than an upper limit derived previously from ultraviolet observations of the similar diffuse molecular cloud lying in front of HD 154368. The observed variation in H2O/OH likely points to the presence in one or both of these clouds of a warm (T > 400) gas component in which neutral-neutral reactions are important sources of OH and/or H2O.Comment: 15 pages (AASTeX) including 4 (eps) figures. To appear in the Astrophysical Journa

Herschel Search for O_2 toward the Orion Bar

We report the results of a search for molecular oxygen (O_2) toward the Orion Bar, a prominent photodissociation region at the southern edge of the H II region created by the luminous Trapezium stars. We observed the spectral region around the frequency of the O_2 NJ = 33-12 transition at 487 GHz and the 5_(4)-3_(4) transition at 774 GHz using the Heterodyne Instrument for the Far-Infrared on the Herschel Space Observatory. Neither line was detected, but the 3σ upper limits established here translate to a total line-of-sight O2 column density <1.5 × 10^(16) cm^(–2) for an emitting region whose temperature is between 30 K and 250 K, or <1 × 10^(16) cm^(–2) if the O_2 emitting region is primarily at a temperature of ≲100 K. Because the Orion Bar is oriented nearly edge-on relative to our line of sight, the observed column density is enhanced by a factor estimated to be between 4 and 20 relative to the face-on value. Our upper limits imply that the face-on O_2 column density is less than 4 × 10^(15) cm^(–2), a value that is below, and possibly well below, model predictions for gas with a density of 10^(4)-10^(5) cm^(–3) exposed to a far-ultraviolet flux 10^4 times the local value, conditions inferred from previous observations of the Orion Bar. The discrepancy might be resolved if (1) the adsorption energy of O atoms to ice is greater than 800 K; (2) the total face-on A V of the Bar is less than required for O_2 to reach peak abundance; (3) the O_2 emission arises within dense clumps with a small beam filling factor; or (4) the face-on depth into the Bar where O_2 reaches its peak abundance, which is density dependent, corresponds to a sky position different from that sampled by our Herschel beams

Herschel HIFI observations of O2_2 toward Orion: special conditions for shock enhanced emission

We report observations of molecular oxygen (O$_2$) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O$_2$ emission is 9" (6e16 cm) in size, and is located close to the H2 Peak 1position (where vibrationally-excited H$_2$ emission peaks), and not at Peak A, 23" away. The peak O2 column density is 1.1e18/cm2. The line velocity is close to that of 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line-of-sight. The enhanced O$_2$ abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C-shock through a clump with preshock density 2e4/cm3, if a reasonable flux of UV radiation is present. The postshock O$_2$ can explain the emission from the source if its line of sight dimension is ~10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O$_2$ emission has not been detected in the cores of other massive star-forming molecular clouds.Comment: 28 pages, 13 figure

Probing ISM Structure in Trumpler 14 & Carina I Using The Stratospheric Terahertz Observatory 2

We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I region is in the west part of the Carina Nebula Complex, which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 158 $\mu$m transition of [C\,{\sc ii}] with a spatial resolution of 48$''$ and a velocity resolution of 0.17 km s$^{-1}$. The observations cover a 0.25$^\circ$ by 0.28$^\circ$ area with central position {\it l} = 297.34$^\circ$, {\it b} = -0.60$^\circ$. The kinematics show that bright [C\,{\sc ii}] structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region and ionization front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into the dark ridge to the southwest, we find that the [C\,{\sc ii}] luminosity from the HII region is 3.7 times that from the PDR. In same los we find in the PDRs an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular gas traced by CO. Comparing multiple gas tracers including HI 21cm, [C\,{\sc ii}], CO, and radio recombination lines, we find that the HII regions of the Carina Nebula Complex are well-described as HII regions with one-side freely expanding towards us, consistent with the champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.Comment: ApJ accepte

Submillimeter Wave Astronomy Satellite mapping observations of water vapor around Sagittarius B2

Observations of the 1(10)-1(01) 556.936 GHz transition of ortho-water with the Submillimeter Wave Astronomy Satellite (SWAS) have revealed the presence of widespread emission and absorption by water vapor around the strong submillimeter continuum source Sagittarius B2. An incompletely-sampled spectral line map of a region of size 26 x 19 arcmin around Sgr B2 reveals three noteworthy features. First, absorption by foreground water vapor is detectable at local standard-of-rest (LSR) velocities in the range -100 to 0 km/s at almost every observed position. Second, spatially-extended emission by water is detectable at LSR velocities in the range 80 to 120 km/s at almost every observed position. This emission is attributable to the 180-pc molecular ring identified from previous observations of CO. The typical peak antenna temperature of 0.075 K for this component implies a typical water abundance of 1.2E-6 to 8E-6 relative to H2. Third, strong absorption by water is observed within 5 arcmin of Sgr B2 at LSR velocities in the range 60 to 82 km/s. An analysis of this absorption yields a H2O abundance ~ 2E-7 to 4E-7 relative to H2 if the absorbing water vapor is located within the core of Sgr B2 itself; or, alternatively, a water column density ~ 2.5E+16 to 4E+16 per cm2 if the water absorption originates in the warm, foreground layer of gas proposed previously as the origin of ammonia absorption observed toward Sgr B2.Comment: 29 pages (AASTeX), including 9 postscript figures, to appear in the Astrophysical Journa

Risk-based individualisation of target haemoglobin in haemodialysis patients with renal anaemia in the post-TREAT era: theoretical attitudes versus actual practice patterns (MONITOR-CKD5 study)

Purpose: Data from an ongoing European pharmacoepidemiological study (MONITOR-CKD5) were used to examine congruence between physician-reported risk-based individualisation of target haemoglobin (Hb) and the actual Hb targets set by these physicians for their patients, as well as actual Hb levels in their patients. Methods: Physician investigators participating in the study completed a questionnaire about their anaemia practice patterns and attitudes post-TREAT at the start of the study (T1) and in summer 2013 (T2). These data were compared with the Hb targets identified at baseline for actual patients (n&nbsp;=&nbsp;1197) enrolled in the study. Risk groups included presence/absence of hypertension, diabetes, cardiovascular complications, history of stroke, history of cancer, and age/activity level (elderly/inactive or young/active). Results: At each time point, more than three quarters of physicians responded that results from the TREAT study, in patients not on dialysis, have influenced their use of erythropoiesis-stimulating agents in patients on haemodialysis. At T1, there was a clear difference in physician-reported (theoretical) target Hb levels for patients across the different risk groups, but there was no difference in patients’ actual Hb levels across the risk groups. A similar disparity was noted at T2. Conclusions: Physicians’ theoretical attitudes to anaemia management in patients on haemodialysis appear to have been influenced by the results of the TREAT study, which involved patients not on dialysis. Physicians claim to use risk-based target Hb levels to guide renal anaemia care. However, there is discrepancy between these declared risk-based target Hb levels and actual target Hb levels for patients with variable risk factors

The Dark Molecular Gas

The mass of molecular gas in an interstellar cloud is often measured using line emission from low rotational levels of CO, which are sensitive to the CO mass, and then scaling to the assumed molecular hydrogen H_2 mass. However, a significant H_2 mass may lie outside the CO region, in the outer regions of the molecular cloud where the gas phase carbon resides in C or C+. Here, H_2 self-shields or is shielded by dust from UV photodissociation, where as CO is photodissociated. This H_2 gas is "dark" in molecular transitions because of the absence of CO and other trace molecules, and because H_2 emits so weakly at temperatures 10 K < T < 100 K typical of this molecular component. This component has been indirectly observed through other tracers of mass such as gamma rays produced in cosmic ray collisions with the gas and far-infrared/submillimeter wavelength dust continuum radiation. In this paper we theoretically model this dark mass and find that the fraction of the molecular mass in this dark component is remarkably constant (~ 0.3 for average visual extinction through the cloud with mean A_V ~ 8) and insensitive to the incident ultraviolet radiation field strength, the internal density distribution, and the mass of the molecular cloud as long as mean A_V, or equivalently, the product of the average hydrogen nucleus column and the metallicity through the cloud, is constant. We also find that the dark mass fraction increases with decreasing mean A_V, since relatively more molecular H_2 material lies outside the CO region in this case.Comment: 38 page, 11 figures, Accepted for Publication in ApJ, corrected citation and typo in Appendix

[C ii] absorption and emission in the diffuse interstellar medium across the Galactic Plane

International audienceIonized carbon is the main gas-phase reservoir of carbon in the neutral diffuse interstellar medium and its 158 µm fine structure transition [C ii] is the most important cooling line of the diffuse interstellar medium (ISM). We combine [C ii] absorption and emission spectroscopy to gain an improved understanding of physical conditions in the different phases of the ISM.. We present high resolution [C ii] spectra obtained with the Herschel/HIFI instrument towards bright dust continuum sources regions in the Galactic plane, probing simultaneously the diffuse gas along the line of sight and the background high-mass star forming regions. These data are complemented by single pointings in the 492 and 809 GHz fine structure lines of atomic carbon and by medium spectral resolution spectral maps of the fine structure lines of atomic oxygen at 63 and 145 µm with Herschel/PACS. We show that the presence of foreground absorption may completely cancel the emission from the background source in medium spectral resolution PACS data and that high spectral resolution spectra are needed to interpret the [C ii] and [O i] emission and the [C ii]/FIR ratio. This phenomenon may explain part of the [C ii]/FIR deficit seen in external luminous infrared galaxies where the bright emission from the nuclear regions may be partially canceled by absorption from diffuse gas in the foreground. The C + and C excitation in the diffuse gas is consistent with a median pressure of ∼ 5900 K cm −3 for a mean kinetic temperature of ∼ 100 K. A few higher pressure regions are detected along the lines of sight, as emission features in both fine structure lines of atomic carbon. The knowledge of the gas density allows us to determine the filling factor of the absorbing gas along the selected lines of sight. The derived median value of the filling factor is 2.4 %, in good agreement with the properties of the Galactic Cold Neutral Medium. The mean excitation temperature is used to derive the average cooling due to C + in the Galactic plane : 9.5 × 10 −26 ergs −1 H −1 . Along the observed lines of sight, the gas phase carbon abundance does not exhibit a strong gradient as a function of Galacto-centric radius and has a weighted average of C/H = 1.5 ± 0.4 × 10 −4