Detection of vibrational emissions from the helium hydride ion (HeH+^+) in the planetary nebula NGC 7027

We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) rovibrational lines of the helium hydride cation (HeH+) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J=1-0 transition at 149.137 micron. The flux measured for the HeH+ v=1-0 P(1) line is in good agreement with our model for the formation, destruction and excitation of HeH+ in NGC 7027. The measured strength of the J=1-0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v=1-0 P(2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26 - 3.93 micron spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH+. The latter are detected for the first time in an astronomical source.Comment: 49 pages, including 17 figures. Accepted for publication in Ap

Velocity resolved [CII], [CI], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities

The [CII]158um line is one of the dominant cooling lines in star-forming active regions. The commonly assumed clumpy UV-penetrated cloud models predict a [CII] line profile similar to that of CO. However, recent spectral-resolved observations show that they are often very different, indicating a more complex origin of the line emission including the dynamics of the source region. The aim of our study is to investigate the physical properties of the star-forming ISM in the Large Magellanic Cloud (LMC) by separating the origin of the emission lines spatially and spectrally. In this paper, we focus on the spectral characteristics and the origin of the emission lines, and the phases of carbon-bearing species in the N159 star-forming region in the LMC. We mapped a 4'x(3-4)' region in N159 in [CII]158um and [NII]205um with the GREAT on board SOFIA, and in CO(3-2), (4-3), (6-5), 13CO(3-2), and [CI]3P1-3P0 and 3P2-3P1 with APEX. The emission of all transitions observed shows a large variation in the line profiles across the map and between the different species. At most positions the [CII] emission line profile is substantially wider than that of CO and [CI]. We estimated the fraction of the [CII] integrated line emission that cannot be fitted by the CO line profile to be 20%-50%. We derived the relative contribution from C+, C, and CO to the column density in each velocity bin. The contribution from C+ dominates the velocity range far from the velocities traced by the dense molecular gas, and the region located between the CO cores of N159 W and E. We estimate the contribution of the ionized gas to the [CII] emission using the ratio to the [NII] emission to be < 19% to the [CII] emission at its peak position, and <15% over the whole observed region. Using the integrated line intensities, we present the spatial distribution of I([CII])/I(FIR). (abridged for arXiv)Comment: 16 pages with 14 figures, accepted for publication in A&

Submillimeter Polarimetry with PolKa, a reflection-type modulator for the APEX telescope

Imaging polarimetry is an important tool for the study of cosmic magnetic fields. In our Galaxy, polarization levels of a few up to $\sim$10\% are measured in the submillimeter dust emission from molecular clouds and in the synchrotron emission from supernova remnants. Only few techniques exist to image the distribution of polarization angles, as a means of tracing the plane-of-sky projection of the magnetic field orientation. At submillimeter wavelengths, polarization is either measured as the differential total power of polarization-sensitive bolometer elements, or by modulating the polarization of the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to observe the continuum emission from fields as large as \sim0\fdg2 in diameter. %Here we present the results from the commissioning of PolKa, a polarimeter for Here we present PolKa, a polarimeter for LABOCA with a reflection-type waveplate of at least 90\% efficiency. The modulation efficiency depends mainly on the sampling and on the angular velocity of the waveplate. For the data analysis the concept of generalized synchronous demodulation is introduced. The instrumental polarization towards a point source is at the level of $\sim0.1$\%, increasing to a few percent at the $-10$db contour of the main beam. A method to correct for its effect in observations of extended sources is presented. Our map of the polarized synchrotron emission from the Crab nebula is in agreement with structures observed at radio and optical wavelengths. The linear polarization measured in OMC1 agrees with results from previous studies, while the high sensitivity of LABOCA enables us to also map the polarized emission of the Orion Bar, a prototypical photon-dominated region

GREAT/SOFIA atmospheric calibration

The GREAT observations need frequency-selective calibration across the passband for the residual atmospheric opacity at flight altitude. At these altitudes the atmospheric opacity has both narrow and broad spectral features. To determine the atmospheric transmission at high spectral resolution, GREAT compares the observed atmospheric emission with atmospheric model predictions, and therefore depends on the validity of the atmospheric models. We discusse the problems identified in this comparison with respect to the observed data and the models, and describe the strategy used to calibrate the science data from GREAT/SOFIA during the first observing periods.Comment: 14 pages, 4 figure

The fine structure line deficit in S 140

We try to understand the gas heating and cooling in the S 140 star forming region by spatially and spectrally resolving the distribution of the main cooling lines with GREAT/SOFIA. We mapped the fine structure lines of [OI] (63 {\mu}m) and [CII] (158 {\mu}m) and the rotational transitions of CO 13-12 and 16-15 with GREAT/SOFIA and analyzed the spatial and velocity structure to assign the emission to individual heating sources. We measure the optical depth of the [CII] line and perform radiative transfer computations for all observed transitions. By comparing the line intensities with the far-infrared continuum we can assess the total cooling budget and measure the gas heating efficiency. The main emission of fine structure lines in S 140 stems from a 8.3'' region close to the infrared source IRS 2 that is not prominent at any other wavelength. It can be explained by a photon-dominated region (PDR) structure around the embedded cluster if we assume that the [OI] line intensity is reduced by a factor seven due to self-absorption. The external cloud interface forms a second PDR at an inclination of 80-85 degrees illuminated by an UV field of 60 times the standard interstellar radiation field. The main radiation source in the cloud, IRS 1, is not prominent at all in the fine structure lines. We measure line-to-continuum cooling ratios below 10^(-4), i.e. values lower than in any other Galactic source, rather matching the far-IR line deficit seen in ULIRGs. In particular the low intensity of the [CII] line can only be modeled by an extreme excitation gradient in the gas around IRS 1. We found no explanation why IRS 1 shows no associated fine-structure line peak, while IRS 2 does. The inner part of S 140 mimics the far-IR line deficit in ULIRGs thereby providing a template that may lead to a future model.Comment: Accepted for publication in Astronomy & Astrophysic

The water abundance behind interstellar shocks: results from HerschelHerschel/PACS and SpitzerSpitzer/IRS observations of H2_2O, CO, and H2_2

We have investigated the water abundance in shock-heated molecular gas, making use of $Herschel$ measurements of far-infrared CO and H$_2$O line emissions in combination with $Spitzer$ measurements of mid-IR H$_2$ rotational emissions. We present far-infrared line spectra obtained with $Herschel$'s PACS instrument in range spectroscopy mode towards two positions in the protostellar outflow NGC 2071 and one position each in the supernova remnants W28 and 3C391. These spectra provide unequivocal detections, at one or more positions, of 12 rotational lines of water, 14 rotational lines of CO, 8 rotational lines of OH (4 lambda doublets), and 7 fine-structure transitions of atoms or atomic ions. We first used a simultaneous fit to the CO line fluxes, along with H$_2$ rotational line fluxes measured previously by $Spitzer$, to constrain the temperature and density distribution within the emitting gas; and we then investigated the water abundances implied by the observed H$_2$O line fluxes. The water line fluxes are in acceptable agreement with standard theoretical models for nondissociative shocks that predict the complete vaporization of grain mantles in shocks of velocity $v \sim 25$ km/s, behind which the characteristic gas temperature is $\sim 1300$ K and the H$_2$O/CO ratio is 1.2Comment: 42 pages, 15 figures, accepted for publication in the Astrophysical Journa

Detection of [O III] at z~3: A Galaxy above the Main Sequence, Rapidly Assembling its Stellar Mass

We detect bright emission in the far infrared fine structure [O III] 88$\mu$m line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z=3.127, using the $\rm 2^{nd}$ generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a sub-millimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of $7.1\times10^{9}\,\rm(\frac{10}{\mu})\,\rm{L_{\odot}}\,$ likely arises from HII regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of $(1.2-5.2)\times10^{6}\,\rm(\frac{10}{\mu})$ equivalent O5.5 or higher stars; where $\mu$ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of $\sim 2\times 10^{8}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$ in ionized gas, that is $0.33\%$ of the estimated total molecular gas mass of $6\times10^{10}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$. We compile multi-band photometry tracing rest-frame UV to millimeter continuum emission to further constrain the properties of this dusty high redshift star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 $\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,\rm{yr^{-1}}$ and already has a stellar mass of $8\times 10^{10}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$. We also constrain the age of the current starburst to be $\leqslant$ 5 million years, making G12v2.43 a gas rich galaxy lying above the star-forming main sequence at z$\sim$3, undergoing a growth spurt and, could be on the main sequence within the derived gas depletion timescale of $\sim$66 million years.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical Journa