dataesr/scientific-paragraphs-categorization huggingface dataset:
While such modeling efforts facilitate the interpretation of the chemistry of sulfur-bearing hydrides, the abundance estimates are based on a limited number of detections in diffuse clouds. Observations of SH performed in the HyGAL program will provide high-quality spectra toward individual targets probing different sight lines. In combination with ancillary data on other small molecules containing sulfur, such as CS and H 2 S, they will provide key information about the overall sulfur chemistry in the diffuse and translucent clouds. Interpreted in the context of chemical models of shocks and turbulent dissipation regions, the observed abundances of sulfur-bearing molecules further promises to provide important constraints on the nature of interstellar turbulence.
Suitable background continuum sources were identified using the source catalog of the Hi-GAL Herschel key-guaranteed time project  (Molinari et al. 2010) , which provides continuum fluxes at 70, 160, 250, 350, and 500 μm. The set of sources targeted in this survey consists of 25 submillimeter continuum sources in the Galactic plane with 160 μm (1. 9 THz) continuum fluxes in excess of 2000 Jy for sources in the inner Galaxy and 1000 Jy for those in the outer Galaxy, as estimated from the Hi-GAL source catalog  (Elia et al. 2021). The positions of the background sources were checked against known millimeter-wave sources, H II regions and masers using the SIMBAD 17  astronomical database  (Wenger et al. 2000). In addition, the HyGAL source list also includes a few sources for which partial spectroscopic data are available from Herschel/HIFI, most often collected as a part of the PRISMAS 18  guaranteed time key program, but where the complete set of species targeted in HyGAL has not been observed.
Therefore, the completion of this legacy program will roughly double the number of sight lines along which the hydrides targeted in this survey have been observed; equally importantly, it will extend observations toward regions in the outer Galaxy that were previously unexplored. The HyGAL sources are situated over a wide range of Galactic longitude, lying at estimated distances from the Sun ranging from 1. 3 to 13 kpc. Table  2  provides an overview of the properties of the HyGAL source sample, and Figure  3  shows their distribution in the Galactic disk. Furthermore, a brief description of each source and its line-of-sight properties is given in Appendix A.
2012 ) and then converted to main-beam temperature scales, T MB , assuming a forward efficiency, η F , of 0. 97 and main-beam efficiencies, η MB , listed in Table  1. The calibrated spectra are subsequently processed using the GILDAS-CLASS software 19  and low order ( 2) polynomial baselines are removed. The spectra are further resampled to a uniform channel width of 0. 5 km s -1 (except for the OH + line toward NGC 7538 IRS1, for which the spectra are displayed with a velocity resolution of 1. 5 km s -1 for clarity). As of 2021 September, 39. 4% ( ≈ 32 hr) of the total planned observations for the HyGAL Legacy program have been performed. Table  3  summarizes the current status of the observations toward each source. The post-processed data products delivered to the SOFIA Science Center by the GREAT team will be publicly accessible via the NASA/IPAC InfraRed Science Archive 20  under Plan ID 08_0038.
Ancillary Data Sets In this section, we briefly summarize the ancillary data collected using various ground-based facilities, which have proven to be useful in interpreting previous observations of the FIR and submillimeter transitions of hydrides. Since many of the molecular ions targeted under the HyGAL Legacy program originate in diffuse atomic clouds where the H 2 fraction is small, absorption-line measurements of the 21 cm H I line have proven essential for their interpretation and the determination of their abundances within such clouds (see for example the use of such data as demonstrated in  Winkel et al. 2017). Therefore, in order to exploit the diagnostic powers of these species and provide essential information for our modeling efforts, we have carried out observations of the H I 21 cm line using the Karl G.
Analysis The observed spectral line features are modeled using an enhanced version of the eXtended CASA Line Analysis Software Suite (XCLASS; 22 Möller et al. 2017), which solves the 1D radiative transfer equation for an isothermal source assuming that the level populations are governed by Boltzmann statistics at a common temperature, T rot , such that the excitation Note. The rms noise level on the T MB scale is quoted for a spectral resolution of 0. 5 km s -1. (dN/dυ) rms represents the column density corresponding to T rms in units of [cm -2 /(km s -1 )]. For those species with hyperfine-structure splitting, (dN/dυ) rms is computed using the spectroscopic parameters of the strongest hyperfinestructure transition. temperature, T ex , is the same for all pairs of states. The spectral line profiles are fitted with multiple Gaussian components, taking into account the effects of optical depth on the line shape for a finite source size and dust attenuation using the automated fitting routine provided by MAGIX  (Möller et al.
Since the molecular gas column traced along the sight lines discussed is greater than or equivalent to the atomic gas column, the overall trends observed when comparing the column densities of the different species studied with that of molecular hydrogen and the total gas column, are consistent with one another (see Figures  11  and 13 ). The main difference arises from the fact that there are fewer atomic gas components measured toward NGC 7538 IRS1. This is because the H I spectrum toward NGC 7538 IRS1 is extracted from a neighboring region G111. 61 + 0. 37  (Lebrón et al. 2001) , and therefore we can only assume that the foreground material along the lines-of-sight toward both clouds is the same. Eliminating such uncertainties the auxiliary data collected using the JVLA under the umbrella of the HyGAL program (see Section 3.
Summary In this paper, we introduced the SOFIA Legacy program HyGAL aimed at characterizing the Galactic ISM through absorption-line studies of six key hydrides (ArH + , p-H 2 O + , OH + , SH, OH, and CH) and two atomic species C + and O toward 25 bright Galactic background continuum sources. Concerned with the life cycle of molecular material in the universe, the HyGAL program addresses questions related to the formation of molecular clouds and investigates the processes responsible for the phase transition from atomic to molecular gas. This is achieved by making use of the wellestablished diagnostic powers of the different targeted hydrides, which range from tracers of the atomic gas and cosmic-ray ionization rates such as ArH + , p-H 2 O + , and molecular and CO-dark H 2 gas tracers, like CH and OH, to tracers of the dissipation of turbulence such as SH.
These goals are realized by taking advantage of the unique capabilities and high resolution provided by the upGREAT and 4GREAT instruments on board the SOFIA telescope. Here, we presented the observing strategy and data reduction techniques used as well as illustrated the potential analysis through the example of three sources in our sample-W3(OH), W3 IRS5, and NGC 7538 IRS1. For all three sources, the observed hydride spectra reveal widespread absorption not only at the velocities of the molecular cloud but also along its lines of sight, except for SH likely because of the species lower Figure  17. 12 C/ 13 C isotopic abundance ratio as a function of Galactocentric distance, R GAL (kpc) adapted from  Jacob et al. (2020a). The teal star represents the 12 C/ 13 C ratio obtained using C + (this paper).
The black solid line represents the weighted fit to the data except that from this work with the gray shaded region demarcating the 1σ interval of this fit. abundances toward these sight lines. The spectra of the atomic species, C + and O, are more complex showing a combination of emission and absorption features toward the hot core, in addition to the line-of-sight absorption features. Despite local variations in abundances, the column densities and column density ratios with respect to both atomic and molecular hydrogen derived over specific velocity intervals that correspond to spiral arm crossings are similar for all three sources. Extending this analysis to the complete HyGAL data set will provide column density distribution profiles for all the species observed, toward all sources studied to systematically investigate the properties of the diffuse gas sight lines over Galactic scales.
The joint analysis of the SOFIA HyGAL data along with the H I data obtained from the JVLA, the 3 mm lines obtained from the IRAM 30 m telescope and chemical models will not only address the questions we set out to answer, but will also provide a wealth of knowledge about the background continuum sources making this survey of valuable legacy for future ISM studies. A. 6. G328. 307+00. 423 The G328. 307+00. 423 cluster harbors massive young stellar objects that are highly concentrated within the central region, with intermediate-mass young stellar objects more spread out. Situated in the fourth quadrant, G328. 307+00. 423 is a bright ATLASGAL  (Schuller et al. 2009)  870 μm source at a distance of 5. 8 kpc  (Urquhart et al. 2018 ) and located in the Norma spiral arm. The sight line toward this source contains contributions from the molecular cloud and the near side of the Norma arm between -110 and -75 km s -1 , the Scutum-Centaurus arm between -62 and -50 km s -1 and the Sagittarius arm between -45 and -35 km s -1.
2 0. 52 2 Π 3/2 , N = 2 -1 3 --2 + 2 --1 + 2514. 3167(9) b 2514. 3532(9) 0. 1368 0. 1231 CH 3/2 -1/2 1 --1 + 2006. 74886(6) 0. 0111 96. 31 LFA 13. 5 0. 66 2 Π 3/2 , N = 2 -1 1 --0 + 2 --1 + 2006. 76258(6) 2006. 79906(6) b 0. 0223 0. 0335 C II 2 P 3/2 -2 P 1/2 O I 3 P 1 -3 P 2 2 -1 2 -1 L L 1900. 5369(13) 4744. 7775(1) 2. 32 × 10 -6 8. 91 × 10 -5 91. 21 227. 76 LFA HFA 14. 1 6. 3 0. 66 0. 65 Muller et al. 2016)opic data are taken from the Cologne Database for Molecular Spectroscopy (CDMS;Müller et al. 2005). The H 2 O + frequencies were refined considering astronomical observations (see Appendix A ofMuller et al. 2016)for which the upper level energies are given with respect to the ground state of p-H 2 O +.
Noise level and sensitivity Noise maps of all three fields are presented in Figures A. 1, A. 2 and A. 3 in Appendix A. In general, we are able to achieve the nominal WALLABY noise level of 1. 6 mJy per 30 beam and 18. 5 kHz frequency channel across the inner regions of all tiles (typically the inner 4 • × 4 • of a single tile) unless individual primary beams or entire footprints are missing. The noise does vary slightly across the sky depending on data quality and flagging fraction. While there is a strong increase in the noise level towards the edges of each field, this issue will not affect the full WALLABY survey which will have a contiguous sky coverage with adequate overlap between tiles. The noise level does vary as a function of frequency as well, as is shown in Figure  2  for a location in the eastern tile of the Norma field.
Image deconvolution In the current WALLABY data reduction pipeline, image deconvolution is carried out on each individual primary beam and prior to mosaicking of all 36 beams of a footprint and combination of two footprints into a single tile. As a result, faint sidelobes which are below the noise level in an individual primary beam may resurface after mosaicking due to the lower noise floor in the mosaicked tile. While this is not generally a problem for WALLABY pilot survey data due to the low intrinsic sidelobe levels of ASKAP's synthesised beam and the faintness of the majority of the sources detected by the survey, sidelobes were picked up by the source finding pipeline near individual bright and extended objects, most notably around the bright galaxy NGC 3137 (WALLABY J100903-290239) in the Hydra field.
Another intrinsic issue related to deconvolution in general is the fact that only bright emission above the noise level can be deconvolved, while faint emission sitting below the noise level at the original spatial and spectral resolution of the data will remain convolved with the dirty beam. As a result, faint and bright sources in the same deconvolved image could be characterised by rather different beams (or possibly even a combination of the clean and dirty beam) which poses a challenge for the accurate recovery of the integrated flux of a source, in particular as the dirty beam will generally vary with frequency. This problem is not specific to WALLABY, but affects any blind interferometric survey. We discuss the resulting consequences in more detail in Section 6. This specific problem was first noted in the Hydra internal team release 1 (Hydra TR1) data which has a restoring beam size of 30 , but a dirty beam size that is somewhat smaller and slightly elliptical, ranging from about 28.
Residual continuum emission All phase 1 pilot survey data cubes still contain residual radio continuum emission as a result of imperfect continuum subtraction by the ASKAP data reduction pipeline. These residuals manifest themselves as a periodic bandpass ripple feature in the direction of bright radio continuum sources and their sidelobes. The severity of the continuum artefacts is a function of angular distance from the position of the continuum source and also depends on whether the continuum source is located inside the field (in which case it will have been imaged and subtracted by the data reduction pipeline) or not. In addition, due to the declination-dependence of ASKAP's UV coverage, the amplitude of continuum residuals is expected to be generally higher near the celestial equator due to elevated beam sidelobe levels.
On-dish calibrator Another artefact discovered in the data during source finding is a faint spectral ripple feature that can be seen in several of the ASKAP primary beams and is most prominent in some of the corner beams of the 6 × 6 beam footprint. Tests later established that this ripple was caused by the telescope's on-dish calibrators (ODC) which were left switched on during the observations. Tests during phase 2 of ASKAP pilot observations have confirmed that the ripple disappears when the ODCs remain powered off during science observations. In order to minimise the impact of the ODC ripple on our automated source finding, we identified the most severely affected primary beams in the Hydra field and removed them from the final mosaic. This results in the loss of sensitivity in small areas of the field around the three corner beams that had to be removed, but at the benefit of being able to obtain a much cleaner and overall more complete H I source catalogue.
Preconditioning At the start of the source finding process, each data cube was multiplied by the square root of the weights cube supplied by the ASKAP data reduction pipeline to normalise noise levels across the entire cube. Noise variations would typically result from effects such as primary beam attenuation, system temperature variation, variable data flagging fraction or missing data in specific primary beams and/or frequency ranges. In addition to applying the weights cube, we also used SoFiA's built-in noise normalisation module to measure and divide by the local noise level in a running window of size 51 × 51 spatial pixels and 51 spectral channels. This ensures that the noise is constant throughout the entire data cube to allow a constant source detection threshold to be applied later on.
In addition, we specifically flagged a radius of 5 pixels around the positions of all radio continuum sources brighter than about 100-150 mJy to remove faint bandpass ripples associated with weaker continuum sources that the auto-flagger would not have removed. Continuum source positions were either extracted from the NVSS catalogue  (Condon et al. 1998)  where possible, or otherwise from the ASKAP radio continuum image of the field itself. In the case of the eastern tile of the Norma field we additionally ran SoFiA's ripple removal filter to reduce the ODC-generated bandpass ripple that was noticeable in some of the edge and corner beams of the mosaic. The filter works by subtracting the median of the data from a running window, the size of which was set to 91 × 91 spatial pixels (9 ) and 41 spectral channels (760 kHz) to ensure that the filter was large enough to not be affacted by H I emission from galaxies.
The basic linker settings used for each field are also listed in Table  2. The final step in SoFiA was the removal of false positives using the reliability module. Reliability filtering works by comparing the density of detections with net positive and negative flux in a userdefined parameter space and discarding all positive detections that have a reliability of less than a user-specified minimum threshold. The method is described in detail in  Serra et al. (2012). The basic settings used for the different fields are again given in Table  2. After source finding, linking and reliability filtering, SoFiA writes out the resulting source catalogue and other relevant data products such as integrated source spectra and moment maps. Each detection was then visually assessed by inspecting the 0 th and 1 st moment, the integrated spectrum and an optical image from the Digitized Sky Survey (DSS) in an attempt to identify and discard any false positives caused by noise peaks or artefacts.
Hydra TR1 and TR2 The Hydra field was subject to two blind source finding runs internally released to the WALLABY team. The catalogues from both runs are included in this public data release. The first run (Hydra TR1) was carried out on a smaller subregion of the full field centred on the Hydra cluster itself. This subregion is relatively clean and not as severely affected by continuum residuals and ODC ripples as the rest of the Hydra field, allowing us to extract a fairly deep source catalogue. A second run (Hydra TR2) on the full field was carried out with slightly modified SoFiA settings to limit the number of artefacts in the preliminary catalogue, but at the cost of a slightly reduced completeness at low SNR. As a result, 119 out of the 148 sources from Hydra TR1 are also included in Hydra TR2, while the remaining 29 H I sources from Hydra TR1 are missing from Hydra TR2 due to the slightly lower completeness of the SoFiA run on the full Hydra field.
NGC 4636 Due to severe continuum artefacts from the bright quasar 3C 273 near the edge of the region, we were unable to carry out a blind H I source finding run on either of the two tiles of the NGC 4636 field. We instead ran SoFiA locally on small subregions of the cube at the positions of previously detected optical and H I sources with known redshifts (Lin et al. , in preparation) using slightly modified SoFiA settings as listed in Table  2. For this purpose, galaxy positions and redshifts for the entire NGC 4636 field were extracted from DR16 of the Sloan Digital Sky Survey (SDSS;  Ahumada et al. 2020) , DR3 of the 6dF Galaxy Survey (6dFGS;  Jones et al. 2004 Jones et al. , 2009)) , the Cosmicflows-3 database  (Tully et al. 2016 ) and the Arecibo Legacy Fast ALFA Survey (ALFALFA;  Haynes et al.
2018). This strategy enabled us to extract the H I emission from 147 galaxies across the NGC 4636 field, but at the expense of missing galaxies that are not included in any of the four redshift surveys used to select our target regions. In addition to this selection bias, several galaxies detected in the NGC 4636 field are still affected to some degree by strong continuum artefacts, and users are advised to exercise caution when using the NGC 4636 data in their scientific analysis.
Position and redshift Position and redshift in the source catalogue are derived from the flux density-weighted centroid position, (x, y, z), across the source mask in the original pixel coordinate system of the data cube: x = 1 S sum i x i S i (1) and likewise for y and z, where S i is the flux density in pixel i, S sum = i S i is the summed flux density, and the summation is over all pixels of the source mask with positive flux density. The resulting pixel-based centroid is entirely arbitrary and therefore converted to more meaningful world coordinates (right ascension, declination and barycentric frequency) using WCS information from the FITS file header. Our position accuracy is illustrated in Figure  4  where we plot the relative position offset between the H I detections from WALLABY and their optical counterparts retrieved from the NASA/IPAC Extragalactic Database (NED) for 159 galaxies from the Hydra field.
2016; Abbott et al. 2017; Planck Collaboration et al. 2020 ). However, given that the WALLABY pilot survey specifically targets nearby groups and clusters, many of the measured redshifts are likely to be dominated by peculiar motions. Hence, we caution against using the catalogued Hubble distances in any scientific analysis and instead recommend obtaining redshift-independent distances where possible. We also provide statistical uncertainties of the pixel-based centroid position assuming Gaussian error propagation and additionally taking into consideration the spatial correlation of pixels due to the finite beam size: σ 2 x = σ 2 rms S 2 sum i (x i -x) 2 (3) and likewise for σ y and σ z , where σ x is the standard deviation in x, is the synthesised beam solid angle in units of pixels, and σ rms is the local RMS noise level in the data cube.
Flux and H I mass In addition to position and redshift, the integrated flux of a source is another critical parameter of any H I survey, as it is needed to derive the H I mass of a galaxy. WALLABY fluxes are calculated as F = νS sum ( 4 ) where ν = 1/54 MHz is the native channel width of WALLABY data which corresponds to a velocity width of approximately 4 km s -1 at z = 0. According to Equation (  4 ), accurate flux measurements require knowledge of the beam solid angle,. All catalogued fluxes were calculated assuming the solid angle of the Gaussian restoring beam used during deconvolution, = πϑ a ϑ b 4 ln(2) (5) where ϑ a and ϑ b denote the FWHM of the major and minor axis of the restoring beam in units of pixels. In the case of WALLABY data, the restoring beam is very close to 30 in size, hence ϑ a = ϑ b = 5 for the 6 pixel size set in the imaging pipeline.
Kinematic major axis We also supply a basic estimate of the position angle of the kinematic major axis of each source on the sky, although we note that this value may not be meaningful for sources that do not show a noticeable velocity gradient, for example, due to small angular size, face-on geometry or a genuine absence of rotation. The position angle is calculated by measuring the centroid of the H I emission on the sky in each individual spectral channel across the source mask and then carrying out an orthogonal regression to the line of centroids on the sky. The resulting kinematic major axis position angle will point towards the approaching side of the object and is measured counter-clockwise, with 0 • pointing up (in the direction of increasing y). It is important to note that the position angle has not been corrected for the effects of beam smearing and will be relative to the pixel grid of the data cube, not the sky coordinate system.
This makes WALLABY data ideal for large-scale statistical and cosmological studies, but will limit the ability to carry out detailed morphological studies of galaxies. Nevertheless, the full survey is expected to detect several thousand spatially well-resolved galaxies across the southern sky. In addition, we intend to image several thousand selected galaxies from the full WALLABY survey at a higher angular resolution of up to 10 to enable more detailed studies of their interstellar medium. The resulting H I mass plot as a function of luminosity distance in a flat CDM Universe with H 0 = 70 km s -1 Mpc -1 and a local matter density of m = 0. 3 is shown in Figure  7 , colourcoded by field. The theoretical detection limit for a 5σ signal across a bandwidth of 1 MHz based on the median local RMS noise level of 1.