Context. The C ii 158 μm fine structure line is one of the dominant cooling lines in the interstellar medium (ISM) and is an important tracer of star formation. Recent velocity-resolved studies with ...Herschel/HIFI and SOFIA/GREAT showed that the C ii line can constrain the properties of the ISM phases in star-forming regions. The C ii line as a tracer of star formation is particularly important in low-metallicity environments where CO emission is weak because of the presence of large amounts of CO-dark gas. Aims. The nearby irregular dwarf galaxy NGC 4214 offers an excellent opportunity to study an actively star-forming ISM at low metallicity. We analyzed the spectrally resolved C ii line profiles in three distinct regions at different evolutionary stages of NGC 4214 with respect to ancillary H i and CO data in order to study the origin of the C ii line. Methods. We used SOFIA/GREAT C ii 158 μm observations, H i data from THINGS, and CO(2 → 1) data from HERACLES to decompose the spectrally resolved C ii line profiles into components associated with neutral atomic and molecular gas. We use this decomposition to infer gas masses traced by C ii under different ISM conditions. Results. Averaged over all regions, we associate about 46% of the C ii emission with the H i emission. However, we can assign only ~9% of the total C ii emission to the cold neutral medium (CNM). We found that about 79% of the total molecular hydrogen mass is not traced by CO emission. Conclusions. On average, the fraction of CO-dark gas dominates the molecular gas mass budget. The fraction seems to depend on the evolutionary stage of the regions: it is highest in the region covering a super star cluster in NGC 4214, while it is lower in a more compact, more metal-rich region.
The Fifth Neurocritical Care Research Network (NCRN) Conference held in Boca Raton, Florida, in September of 2018 was devoted to challenging the current status quo and examining the role of the ...Neurocritical Care Society (NCS) in driving the science and research of neurocritical care. The aim of this in-person meeting was to set the agenda for the NCS’s Neurocritical Care Research Central, which is the overall research arm of the society. Prior to the meeting, all 103 participants received educational content (book and seminar) on the ‘Blue Ocean Strategy
®
,’ a concept from the business world which aims to identify undiscovered and uncontested market space, and to brainstorm innovative ideas and methods with which to address current challenges in neurocritical care research. Three five-member working groups met at least four times by teleconference prior to the in-person meeting to prepare answers to a set of questions using the Blue Ocean Strategy concept as a platform. At the Fifth NCRN Conference, these groups presented to a five-member jury and all attendees for open discussion. The jury then developed a set of recommendations for NCS to consider in order to move neurocritical care research forward. We have summarized the topics discussed at the conference and put forward recommendations for the future direction of the NCRN and neurocritical care research in general.
Context. Understanding the star-forming processes is key to understanding the evolution of galaxies. Investigating star formation requires precise knowledge of the properties of the dense molecular ...gas complexes where stars form and a quantification of how they are affected by the physical conditions to which they are exposed. The proximity, low metallicity, and wide range of star formation activity of the Large and Small Magellanic Clouds (LMC and SMC) make them prime laboratories to study how local physical conditions impact the dense gas reservoirs and their star formation efficiency. Aims. The aim of the Dense Gas Survey for the Magellanic Clouds (DeGaS-MC) project is to expand our knowledge of the relation between dense gas properties and star formation activity by targeting the LMC and SMC observed in the HCO+(2−1) and HCN(2−1) transitions. Methods. We carried out a pointing survey targeting two lines toward ∼30 LMC and SMC molecular clouds using the SEPIA180 instrument installed on the Atacama Pathfinder EXperiment (APEX) telescope. We performed a follow-up mapping campaign of the emission in the same transition in 13 star-forming regions. This first paper provides line characteristic catalogs and integrated line-intensity maps of the sources. Results. HCO+(2−1) is detected in 20 and HCN(2−1) in 8 of the 29 pointings observed. The dense gas velocity pattern follows the line-of-sight velocity field derived from the stellar population. The three SMC sources targeted during the mapping campaign were unfortunately not detected in our mapping campaign but both lines are detected toward the LMC 30Dor, N44, N105, N113, N159W, N159E, and N214 regions. The HCN emission is less extended than the HCO+ emission and is restricted to the densest regions. The HCO+(2−1)/HCN(2−1) brightness temperature ratios range from 1 to 7, which is consistent with the large ratios commonly observed in low-metallicity environments. A larger number of young stellar objects are found at high HCO+ intensities and lower HCO+/HCN flux ratios, and thus toward denser lines of sight. The dense gas luminosities correlate with the star formation rate traced by the total infrared luminosity over the two orders of magnitude covered by our observations, although substantial region-to-region variations are observed.
We present the detection and analysis of molecular hydrogen emission towards ten interstellar regions in the Large Magellanic Cloud. We examined low-resolution infrared spectral maps of 12 regions ...obtained with the Spitzer infrared spectrograph (IRS). The pure rotational 0-0 transitions of H... at 28.2 and 17.1 mu m are detected in the IRS spectra for 10 regions. The higher level transitions are mostly upper limit measurements except for three regions, where a 3... detection threshold is achieved for lines at 12.2 and 8.6 mu m. The excitation diagrams of the detected H... transitions are used to determine the warm H... gas column density and temperature. The single-temperature fits through the lower transition lines give temperatures in the range 86-137 K. The bulk of the excited H... gas is found at these temperatures and contributes ~5-17 per cent to the total gas mass. We find a tight correlation of the H... surface brightness with polycyclic aromatic hydrocarbon and total infrared emission, which is a clear indication of photoelectric heating in photodissociation regions. We find the excitation of H... by this process is equally efficient in both atomic- and molecular-dominated regions. We also present the correlation of the warm H... physical conditions with dust properties. The warm H... mass fraction and excitation temperature show positive correlations with the average starlight intensity, again supporting H... excitation in photodissociation regions. (ProQuest: ... denotes formulae/symbols omitted.)
We have used sensitive archival data from the Infrared Space Observatory (ISO) to make maps of the edge-on low SFR galaxy, NGC 5907, in 6 different MIR bands: LW2, LW5, LW6, LW7, LW8, and LW10, ...covering the spectrum from 6.5 to 15.0 μm and including several narrow bands that isolate the infrared aromatic spectral features commonly referred to as PAHs. Most of the MIR emission is dominated by PAHs and it is likely that emission from VSGs contribute only negligibly except in the broad IRAS-equivalent band. The flux ratios are typical of galaxies with low SFRs or quiesent regions within galaxies (e.g. M 83) and a very high PAH/continuum ratio is observed. The PAH emission follows the CO distribution and also shows some correlation within the disk with the λ850 μm distribution. However, the PAH emission also reaches larger galactocentric radii than the CO and other correlations suggest that the PAHs are also more widespread. A significant new discovery is the presence of PAHs in the halo of the galaxy. In the narrow bands that isolate single PAH features, the emission shows structure similar to high latitude features seen in other galaxies in other tracers. The features extend as far as 6.5 kpc from the plane but scale heights of 3.5 kpc are more typical. The λ11.3/λ7.7 ratio also appears to increase with distance from the major axis. To our knowledge, this is the first time PAHs have been seen in the halo of an external galaxy. Just as significantly, they are seen in a low SFR galaxy, suggesting that strong SNe and winds are not necessary for these large molecules to reach high latitudes.
Context. The ambiguous origin of the C II 158μm line in the interstellar medium complicates its use for diagnostics concerning the star-formation rate and physical conditions in photodissociation ...regions. Aims. We investigate the origin of C II in order to measure the total molecular gas content, the fraction of CO-dark H2 gas, and how these parameters are impacted by environmental effects such as stellar feedback. Methods. We observed the giant H II region N 11 in the Large Magellanic Cloud with SOFIA/GREAT. The C II line is resolved in velocity and compared to H I and CO, using a Bayesian approach to decompose the line profiles. A simple model accounting for collisions in the neutral atomic and molecular gas was used in order to derive the H2 column density traced by C+. Results. The profile of C II most closely resembles that of CO, but the integrated C II line width lies between that of CO and that of H I. Using various methods, we find that C II mostly originates from the neutral gas. We show that C II mostly traces the CO-dark H2 gas but there is evidence of a weak contribution from neutral atomic gas preferentially in the faintest components (as opposed to components with low C II/CO or low CO column density). Most of the molecular gas is CO-dark. The CO-dark H2 gas, whose density is typically a few 100s cm−3 and thermal pressure in the range 103.5−5 K cm−3, is not always in pressure equilibrium with the neutral atomic gas. The fraction of CO-dark H2 gas decreases with increasing CO column density, with a slope that seems to depend on the impinging radiation field from nearby massive stars. Finally we extend previous measurements of the photoelectric-effect heating efficiency, which we find is constant across regions probed with Herschel, with C II and O I being the main coolants in faint and diffuse, and bright and compact regions, respectively, and with polycyclic aromatic hydrocarbon emission tracing the CO-dark H2 gas heating where C II and O I emit. Conclusions. We present an innovative spectral decomposition method that allows statistical trends to be derived for the molecular gas content using CO, C II, and H I profiles. Our study highlights the importance of velocity-resolved photodissociation region (PDR) diagnostics and higher spatial resolution for H I observations as future steps.
NGC 1569 has some of the most vigorous star formation among nearby galaxies. It hosts two super star clusters (SSCs) and has a higher star formation rate (SFR) per unit area than other starburst ...dwarf galaxies. Extended emission beyond the galaxy's optical body is observed in warm and hot ionized and atomic hydrogen gas; a cavity surrounds the SSCs. We aim to understand the impact of the massive star formation on the surrounding interstellar medium in NGC 1569 through a study of its stellar and dust properties. We use Herschel and ancillary multiwavelength observations, from the ultraviolet to the submillimetre regime, to construct its spectral energy distribution, which we model with magphys on ∼300 pc scales at the Spectral and Photometric Imaging Receiver (SPIRE) 250 μm resolution. The multiwavelength morphology shows low levels of dust emission in the cavity, and a concentration of several dust knots in its periphery. The extended emission seen in the ionized and neutral hydrogen observations is also present in the far-infrared emission. The dust mass is higher in the periphery of the cavity, driven by ongoing star formation and dust emission knots. The SFR is highest in the central region, while the specific SFR is more sensitive to the ongoing star formation. The region encompassing the cavity and SSCs contains only 12 per cent of the dust mass of the central starburst, in accord with other tracers of the interstellar medium. The gas-to-dust mass ratio is lower in the cavity and fluctuates to higher values in its periphery.
Aims. We present observations of the Orion Bar photodissociation region (PDR) obtained with the SPIRE instrument on-board Herschel. Methods. We obtained SPIRE Fourier-transform spectrometer (FTS) ...sparse sampled maps of the Orion bar. Results. The FTS wavelength coverage and sensitivity allow us to detect a wealth of rotational lines of CO (and its isotopologues), fine structure lines of C and N+, and emission lines from radicals and molecules such as CH+, CH, H2O or H2S. For species detected from the ground, our estimates of the column densities agree with previously published values. The comparison between 12CO and 13CO maps shows particularly the effects of optical depth and excitation in the molecular cloud. The distribution of the 12CO and 13CO lines with upper energy levels indicates the presence of warm (~100–150 K) CO. This warm CO component is a significant fraction of the total molecular gas, confirming previous ground based studies.
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