Herschel Space Observatory Research Articles

Observations of the temporal evolution of Saturn’s stratosphere following the Great Storm of 2010–2011

Context. Water vapour is delivered to Saturn’s stratosphere by Enceladus’ plumes and subsequent diffusion in the planet system. It is expected to condense into a haze in the middle stratosphere. The hot stratospheric vortex (the ‘beacon’) that formed as an aftermath of Saturn’s Great Storm of 2010 significantly altered the temperature, composition, and circulation in Saturn’s northern stratosphere. Previous photochemical models suggested haze sublimation and vertical winds as processes likely to increase the water vapour column density in the beacon. Aims. We aim to quantify the temporal evolution of stratospheric water vapour in the beacon during the storm. Methods. We mapped Saturn at 66.44 and 67.09 μm on seven occasions from July 2011 to February 2013 with the PACS instrument of the Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA). The observations probe the millibar levels, at which the water condensation region was altered by the warmer temperatures in the beacon. Using radiative transfer modelling, we tested several empirical and physically based models to constrain the cause of the enhanced water emission found in the beacon. Results. The observations show an increased emission in the beacon that cannot be reproduced only accounting for the warmer temperatures reported in the beacon. An additional source of water vapour is thus needed. We find a factor (7.5±1.6) increase in the water column in the beacon compared to pre-storm conditions using empirical models. Combining our results with a cloud formation model for July 2011, we evaluate the sublimation contribution to 45–85% of the extra column derived from the water emission increase in the beacon. Conclusions. The observations confirm that the storm conditions enhanced the water abundance at the millibar levels because of haze sublimation and vertical winds in the beacon. Future work on the haze temporal evolution during the storm will help to better constrain the sublimation contribution over time.

A probabilistic model to estimate number densities from column densities in molecular clouds

Constraining the physical and chemical evolution of molecular clouds is essential to our understanding of star formation. These investigations often necessitate knowledge of some local representative number density of the gas along the line of sight. However, constraining the number density is a difficult endeavor. Robust constraints on the number density often require line observations of specific molecules along with radiation transfer modeling, which provides densities traced by that specific molecule. Column density maps of molecular clouds are more readily available, with many high-fidelity maps calculated from dust emission and extinction, in particular from surveys conduction with the Herschel Space Observatory. We introduce a new probabilistic model which is based on the assumption that the total hydrogen nuclei column density along a line of sight can be decomposed into a turbulent component and a gravitationally dominated component. Therefore, for each pixel in a column density map, the line of sight was decomposed into characteristic diffuse (dubbed “turbulent”) and dense (dubbed “gravitational”) gas number densities from column density maps. The method thus exploits a physical model of turbulence to decouple the random turbulent column from gas in dense bound structures empirically using the observed column density maps. We find the model produces reasonable turbulent and gravitational densities in the Taurus L1495/B213 and Polaris Flare clouds. The model can also be used to infer an effective attenuating column density into the cloud, which is useful for astrochemical models of the clouds. We conclude by demonstrating an application of this method by predicting the emission of the [C II] 1900 GHz, [C I] 492 GHz, and CO (J = 1–0) 115 GHz lines across the Taurus L1495/B213 region at the native resolution of the column density map utilizing a grid of photodissociation-region models.

A deep neural network approach to compact source removal

Context. Analyzing extended emission in photometric observations of star-forming regions requires maps free from compact foreground, embedded, and background sources, which can interfere with various techniques used to characterize the interstellar medium. Within the framework of the NEMESIS project, we applied machine-learning techniques to improve our understanding of the star formation timescales, which involves the unbiased analysis of the extended emission in these regions. Aims. We present a deep learning-based method for separating the signals of compact sources and extended emission in photometric observations made by the Herschel Space Observatory, facilitating the analysis of extended emission and improving the photometry of compact sources. Methods. Central to our approach is a modified U-Net architecture with partial convolutional layers. This method enables effective source removal and background estimation across various flux densities, using a series of partial convolutional layers, batch normalization, and ReLU activation layers within blocks. Our training process utilized simulated sources injected into Herschel images, with controlled flux densities against known backgrounds. A dynamic, signal-to-noise ratio (S/N)-based adaptive masking system was implemented to assess how prominently a compact source stands out from the surrounding background. Results. The results demonstrate that our method can significantly improve the photometric accuracy in the presence of highly fluctuating backgrounds. Moreover, the approach can preserve all characteristics of the images, including the noise properties. Conclusions. The presented approach allows users to analyze extended emission without the interference of disturbing point sources or perform more precise photometry of sources located in complex environments. We also provide a Python tool with tutorials and examples to help the community effectively utilize this method.

3D MC. II. X-Ray Echoes Reveal a Clumpy Molecular Cloud in the CMZ

Abstract X-ray observations collected over the past decades have revealed a strongly variable X-ray signal within the Milky Way’s Galactic center, interpreted as X-ray echoes from its supermassive black hole, Sgr A*. These echoes are traced by the strong Fe Kα fluorescent line at 6.4 keV, the intensity of which is proportional to the density of the illuminated molecular gas. Over time, the echo scans through molecular clouds (MCs) in our Galactic center, revealing their 3D structure and highlighting their densest parts. While previous studies have utilized spectral line Doppler shifts along with kinematic models to constrain the geometry of the Central Molecular Zone (CMZ) or to study the structure of individual clouds, these methods have limitations, particularly in the turbulent region of the CMZ. We use archival Chandra X-ray data to construct one of the first 3D representations of one prominent MC, the Stone cloud, located at (ℓ = 0 . ° 068, b = –0 . ° 076) at a distance of ∼20 pc from Sgr A* in projection. Using the Chandra X-ray Observatory, we followed the X-ray echo in this cloud from 2008 to 2017. We combine these data with 1.3 mm dust continuum emission observed with the Submillimeter Array (SMA) and the Herschel Space Observatory to reconstruct the 3D structure of the cloud and estimate the column densities for each year’s observed slice. The analysis of the X-ray echoes, along with velocities from SMA molecular line data, indicates that the structure of the Stone cloud can be described as a very diffuse background with multiple dense clumps throughout.

Environmental effects on nearby debris discs

Aims. We investigate the influence of the interstellar medium (ISM) on debris discs using a statistical approach. We probe the effect of the ISM on debris disc occurrence rates and on the morphologies of the discs. Methods. We used results from the Herschel Space Observatory DUNES and DEBRIS surveys of 295 nearby FGK dwarf stars imaged at 100 µm and 160 µm. Most of the 48 debris discs in this sample have small optical depths, making them more likely to be affected by the ISM compared to optically thick discs. Since the stars in our sample are located within the Local Interstellar Cloud, we can infer that their debris discs encounter similar conditions. This allows us to use the stellar space velocity, in particular the U component, as a single indicator of the forces that can act on the debris disc dust grains when they interact with the ISM. Because older stars show a larger dispersion of space velocity values, we investigated the impact of the debris disc ages on our results. Results. The observed debris disc occurrence rates seem to depend on the stellar space velocities, as expected under the hypothesis that stars with higher space velocities have a higher probability of losing their circumstellar dust. The percentage of sources with debris discs in our sample reaches a maximum of ≈25% for stars with low space velocity component values, |Urel|, relative to the local ISM, and decreases monotonically for larger |Urel| values down to the 10% level. A decrease in the average disc fractional luminosity as a function of |Urel| is also observed. These dependences do not disappear after accounting for the reported higher dispersion of U values with age. In extended discs, the impact of the ISM could also explain the links observed between the stellar space velocities and the debris disc’s projected ellipticities, position angles, and radii. The fractional luminosities of the debris discs appear to be correlated with their position angles, suggesting that the effect of the ISM on the dust content depends on the disc orientation. Although these indications may not be fully conclusive on their own, they collectively reinforce the hypothesis that the ISM influences the occurrence rates and morphologies of debris discs, thereby motivating additional research on the impact of the environment.

Unraveling the Dusty Environment around RT Vir

Abstract Infrared (IR) studies of asymptotic giant branch (AGB) stars are critical to our understanding of the formation of cosmic dust. In this investigation, we explore the mid- to far-IR emission of the oxygen-rich AGB star RT Virginis. This optically thin dusty environment has unusual spectral features when compared to other stars in its class. To explore this enigmatic object we use the one-dimensional radiative transfer modeling code DUSTY. Modeled spectra are compared with observations from the Infrared Space Observatory, InfraRed Astronomical Satellite, the Herschel Space Observatory, and a host of other sources to determine the properties of RT Vir's circumstellar material. Our models suggest a set of two distant and cool dust shells at low optical depths (τ V,inner = 0.16, τ V,outer = 0.06), with inner dust temperatures T 1 = 330 K, T 3 = 94 K. Overall, these dust shells exhibit a chemical composition consistent with dust typically found around O-rich AGB stars. However, the distribution of materials differs significantly. The inner shell consists of a mixture of silicates, Al2O3, FeO, and Fe, while the outer shell primarily contains crystalline Al2O3 polymorphs. This chemical change is indicative of two distinct epochs of dust formation around RT Vir. These changes in dust composition are driven by either changes in the pressure–temperature conditions around the star or by a decrease in the C/O ratio due to hot-bottom burning.

Detection of the [O i] 63 µm emission line from the z = 6.04 quasar J2054–0005

Abstract We report the highest-redshift detection of [O i] 63 $\mu$m from a luminous quasar, J2054$-$0005, at $z=6.04$ based on the Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 9 observations. The [O i] 63 $\mu$m line luminosity is $(4.5\pm 1.5) \times 10^{9} L_{\odot }$, corresponding to the [O i] 63 $\mu$m-to-far-infrared luminosity ratio of $\approx$6.7 $\times 10^{-4}$, which is consistent with the value obtained in the local Universe. Remarkably, [O i] 63 $\mu$m is as bright as [C ii] 158 $\mu$m, resulting in the [O i]-to-[C ii] line luminosity ratio of $1.3\pm 0.5$. Based on a careful comparison of the luminosity ratios of [O i] 63 $\mu$m, [C ii] 158 $\mu$m, and dust continuum emission to models of photodissociation regions, we find that J2054$-$0005 has a gas density $\log (n_{\rm H}/{\rm cm}^{-3}) = 3.7\pm 0.3$ and an incident far-ultraviolet radiation field of $\log (G/G_{\rm 0}) = 3.0\pm 0.1$, showing that [O i] 63 $\mu$m serves as an important coolant of the dense and warm gas in J2054$-$0005. A close examination of the [O i] and [C ii] line profiles suggests that the [O i] line may be partially self-absorbed; however, deeper observations are needed to verify this conclusion. Regardless, the gas density and incident radiation field are in broad agreement with the values obtained in nearby star-forming galaxies and objects with [O i] 63 $\mu$m observations at $z=1$–3 with the Herschel Space Observatory. These results demonstrate the power of ALMA high-frequency observations targeting [O i] 63 $\mu$m to examine the properties of photodissociation regions in high-redshift galaxies.

Supernova Shocks in Molecular Clouds: Shocks Driven into Dense Cores in IC 443 and 3C 391

Supernova shocks into dense molecular cores in IC 443 (clumps B, C, and G) and 3C 391 were observed using the Stratospheric Observatory for Infrared Astronomy and complemented by archival data from the Herschel Space Observatory. The pure rotational transitions 0–0 S(1) and S(5) of H2, and the ground-state 110–101 transition of H2O, are all broadened, arising from molecules that survive the passage of the shock front. Theoretical models from the Paris–Durham shock code were analyzed to generate velocity profiles that approximately match the observations. The observations can be fit with two shock conditions, which approximate the range of densities in the preshock molecular cloud. The width and brightness of the S(5) lines require shocks into gas with a density of order 2000 cm−3, into which the IC 443 blast wave drives shocks with speed 60 km s−1. The brightness and narrower width of the S(1) lines requires different shocks, into gas with density of order 105 cm−3, with shock speeds of 10 km s−1. The H2O velocity distribution is also consistent with these shocks. The existence of shocks into dense gas shows that the bright shocked clumps in IC 443 were prestellar cores. It is unlikely that they will form stars soon after the passage of the shock front, given the input of kinetic and thermal energy from the shocks.

Prominent Mid-infrared Excess of the Dwarf Planet (136472) Makemake Discovered by JWST/MIRI Indicates Ongoing Activity

We report on the discovery of a very prominent mid-infrared (18–25 μm) excess associated with the trans-Neptunian dwarf planet (136472) Makemake. The excess, detected by the Mid-Infrared Instrument of the James Webb Space Telescope, along with previous measurements from the Spitzer and Herschel space telescopes, indicates the occurrence of temperatures of ∼150 K, much higher than what solid surfaces at Makemake’s heliocentric distance could reach by solar irradiation. We identify two potential explanations: a continuously visible, currently active region powered by subsurface upwelling and possibly cryovolcanic activity covering ≤1% of Makemake’s surface or an as-yet-undetected ring containing very small carbonaceous dust grains, which have not been seen before in trans-Neptunian or Centaur rings. Both scenarios point to unprecedented phenomena among trans-Neptunian objects and could greatly impact our understanding of these distant worlds.

ALMA Detection of Masers and Dasars in the Hydrogen Recombination Lines of the Planetary Nebula Mz3

The hydrogen recombination lines H30α, H40α, H42α, H50β, and H57γ and the underlying bremsstrahlung continuum emission were detected with ALMA in the bipolar nebula Mz3. The source was not spatially resolved, but the velocity profile of the H30α line shows clear indication of maser amplification, confirming previous reports of laser amplification in the far-infrared H recombination lines observed with Herschel Space Observatory. Comparison between the flux densities of the H50β, H40α, and H42α lines show overcooling, or darkness amplification by stimulated absorption (dasar effect) at the LSR velocity of about −25 km s−1, which constrains the density of the absorbing region to about 103 cm−3. The H30α line, on the other hand, presents maser lines at LSR velocities of −69 and −98 km s−1, which indicates ionized gas with densities close to 107 cm−3. Although the source of emission was not resolved, it was possible to find the central position of the images for each velocity interval, which resulted in a well defined position–velocity distribution.

Nitrogen Abundance Distribution in the Inner Milky Way

We combine a new Galactic plane survey of hydrogen radio recombination lines (RRLs) with far-infrared surveys of ionized nitrogen, N+, to determine nitrogen abundance across Galactic radius. RRLs were observed with the NASA Deep Space Network Station 43 70 m antenna and the Green Bank Telescope in 108 lines of sight spanning −135°< l < 60°, at b = 0°. These positions were also observed in [N ii] 122 μm and 205 μm lines with the Herschel Space Observatory. Combining RRL and [N ii] 122 μm and 205 μm observations in 41 of 108 samples with high signal-to-noise ratio, we studied the ionized nitrogen abundance distribution across Galactocentric distances of 0–8 kpc. Combined with existing solar neighborhood and outer Galaxy N/H abundance determinations, we studied this quantity’s distribution within the Milky Way’s inner 17 kpc for the first time. We found a nitrogen abundance gradient extending from Galactocentric radii of 4–17 kpc in the Galactic plane, while within 0–4 kpc the N/H distribution remained flat. The gradient observed at large Galactocentric distances supports inside-out galaxy growth, with the additional steepening resulting from variable star formation efficiency and/or radial flows in the Galactic disk, while the inner 4 kpc flattening, coinciding with the Galactic bar’s onset, may be linked to radial flows induced by the bar potential. Using SOFIA/FIFI-LS and Herschel/PACS, we observed the [N iii] 57 μm line to trace doubly ionized gas contribution in a subsample of sight lines. We found negligible N++ contributions along these sight lines, suggesting mostly singly ionized nitrogen originating from low-ionization H ii region outskirts.

An Observational View of Structure in Protostellar Systems

The envelopes and disks that surround protostars reflect the initial conditions of star and planet formation and govern the assembly of stellar masses. Characterizing these structures requires observations that span the near-IR to centimeter wavelengths. Consequently, the past two decades have seen progress driven by numerous advances in observational facilities across this spectrum, including the Spitzer Space Telescope, Herschel Space Observatory, the Atacama Large Millimeter/submillimeter Array, and a host of other ground-based interferometers and single-dish radio telescopes. ▪Nearly all protostars have well-formed circumstellar disks that are likely to be rotationally supported; the ability to detect a disk around a protostar is more a question of spatial resolution rather than whether or not a disk is present.▪The disks around protostars have inherently higher millimeter/submillimeter luminosities as compared to disks around more-evolved pre-main-sequence stars, though there may be systematic variations between star-forming regions.▪The envelopes around protostars are inherently asymmetric, and streamers emphasize that mass flow through the envelopes to the disks may not be homogeneous.▪The current mass distribution of protostars may be impacted by selection bias given that it is skewed toward solar-mass protostars, which is inconsistent with the stellar initial mass function.

Cold Water Emission Cannot Be Used to Infer Depletion of Bulk Elemental Oxygen [O/H] in Disks

We reexamine the constraints provided by Herschel Space Observatory data regarding cold water emission from protoplanetary disks. Previous disk models that were used to interpret observed water emission concluded that oxygen (O/H) is depleted by at least 2 orders of magnitude if a standard, interstellar gas/dust mass ratio is assumed in the disk. In this work, we use model results from a recent disk parameter survey and show that most of the Herschel constraints obtained for cold water (i.e., for transitions with an upper energy level E up < 200 K, where the bulk of the disk water lies) can be explained with disk models adopting interstellar medium-like oxygen elemental abundance (i.e., O/H = 3.2 × 10−4) and the canonical gas/dust mass ratio of 100. We show that cold water vapor is mainly formed by photodesorption of water ice at the interface between the molecular layer and the midplane, and that its emission is relatively independent of the main disk properties like the disk gas mass and gas/dust mass ratio. We find that the abundance of water vapor in the outer disk is set by photoprocesses and depends on the (constant) vertical column density of water ice needed to attenuate the far-ultraviolet photon flux, resulting in roughly constant emission for the parameters (gas mass, dust mass, disk radius) varied in our survey. Importantly, water line emission is found to be optically thick and hence sensitive to temperature more than abundance, possibly driving previous inferences of large-scale oxygen depletion.

Abundances of trace constituents in Jupiter’s atmosphere inferred from Herschel/PACS observations

Context. On October 31, 2009, the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory observed far-infrared spectra of Jupiter in the wavelength range between 50 and 220 µm as part of the program “Water and Related Chemistry in the Solar System”. The spectra have an effective spectral resolution between 900 and 3500, depending on the wavelength and grating order. Aims. We investigate the disk-averaged chemical composition of Jupiter’s atmosphere as a function of height using these observations. Methods. We used the Planetary Spectrum Generator and the least-squares fitting technique to infer the abundances of trace constituents. Results. The PACS data include numerous spectral lines attributable to ammonia (NH3), methane (CH4), phosphine (PH3), water (H2O), and deuterated hydrogen (HD) in the Jovian atmosphere and probe the chemical composition from p ~ 275 mbar to p ~ 900 mbar. From the observations, we infer an ammonia abundance profile that decreases from a mole fraction of (1.7 ± 0.8) × 10−4 at p ~ 900 mbar to (1.7 ± 0.9) × 10−8 at p ~ 275 mbar, following a fractional scale height of about 0.114. For phosphine, we find a mole fraction of (7.2 ± 1.2) × 10−7 at pressures higher than (550 ± 100) mbar and a decrease of its abundance at lower pressures following a fractional scale height of (0.09 ± 0.02). Our analysis delivers a methane mole fraction of (1.49 ± 0.09) × 10−3. Analyzing the HD R(0) line at 112.1 µm yields a new measurement of Jupiter’s D/H ratio, D/H = (1.5 ± 0.6) × 10−5. Finally, the PACS data allow us to put the most stringent 3σ upper limits yet on the mole fractions of hydrogen halides in the Jovian troposphere. These new upper limits are &lt;1.1 × 10−11 for hydrogen fluoride (HF), &lt;6.0 × 10−11 for hydrogen chloride (HCl), &lt;2.3 × 10−10 for hydrogen bromide (HBr) and &lt;1.2 × 10−9 for hydrogen iodide (HI) and support the proposed condensation of hydrogen halides into ammonium halide salts in the Jovian troposphere.

On the dust properties of the UV galaxies in the redshift range z ∼ 0.6–1.2

ABSTRACT Far-infrared observations from the Herschel Space Observatory are used to estimate the infrared (IR) properties of ultraviolet-selected galaxies. We stack the PACS (100, 160 $\mu$m) and SPIRE (250, 350, and 500 $\mu$m) maps of the Chandra deep field south (CDFS) on a source list of galaxies selected in the rest-frame ultraviolet (UV) in a redshift range of 0.6–1.2. This source list is created using observations from the XMM–OM telescope survey in the CDFS using the UVW1 (2910 Å) filter. The stacked data are binned according to the UV luminosity function of these sources, and the average photometry of the UV-selected galaxies is estimated. By fitting modified black bodies and IR model templates to the stacked photometry, average dust temperatures and total IR luminosity are determined. The luminosity-weighted average temperatures are consistent with a weak trend of increasing temperature with redshift found by previous studies. Infrared excess, unobscured, and obscured star formation rate (SFR) values are obtained from the UV and IR luminosities. We see a trend in which dust attenuation increases as UV luminosity decreases. It remains constant as a function of IR luminosities at fixed redshift across the luminosity range of our sources. In comparison to local luminous infrared galaxies with similar SFRs, the higher redshift star-forming galaxies in the sample show a lesser degree of dust attenuation. Finally, the inferred dust attenuation is used to correct the unobscured SFR density in the redshift range 0.6–1.2. The dust-corrected SFR density is consistent with measurements from IR-selected samples at similar redshifts.

Orbit/Attitude Control for Rendezvous and Docking at the Herschel Space Observatory

Orbit/Attitude Control for Rendezvous and Docking at the Herschel Space Observatory

Characterization of Herschel-selected strong lens candidates through HST and sub-mm/mm observations

ABSTRACT We have carried out Hubble Space Telescope (HST) snapshot observations at 1.1 μm of 281 candidate strongly lensed galaxies identified in the wide-area extragalactic surveys conducted with the Herschel Space Observatory. Our candidates comprise systems with flux densities at $500\, \mu$m, S500 ≥ 80 mJy. We model and subtract the surface brightness distribution for 130 systems, where we identify a candidate for the foreground lens candidate. After combining visual inspection, archival high-resolution observations, and lens subtraction, we divide the systems into different classes according to their lensing likelihood. We confirm 65 systems to be lensed. Of these, 30 are new discoveries. We successfully perform lens modelling and source reconstruction on 23 systems, where the foreground lenses are isolated galaxies and the background sources are detected in the HST images. All the systems are successfully modelled as a singular isothermal ellipsoid. The Einstein radii of the lenses and the magnifications of the background sources are consistent with previous studies. However, the background source circularized radii (between 0.34 and 1.30 kpc) are ∼3 times smaller than the ones measured in the sub-millimetre/millimetre for a similarly selected and partially overlapping sample. We compare our lenses with those in the Sloan Lens Advanced Camera for Surveys (ACS) Survey confirming that our lens-independent selection is more effective at picking up fainter and diffuse galaxies and group lenses. This sample represents the first step towards characterizing the near-infrared properties and stellar masses of the gravitationally lensed dusty star-forming galaxies.

Joint Modelling of Dust Scattering and Thermal Emission: The Spider Complex

Observations across the electromagnetic spectrum of radiative processes involving interstellar dust—emission, absorption, and scattering—are used to constrain the parameters of dust models and more directly to aid in foreground removal of dust for extragalactic and cosmological observations. Dust models can benefit from more independent constraints from complementary observations. Here, we quantify the relationship between scattered light and thermal emission from dust in a diffuse (cirrus) intermediate-latitude cloud, Spider, using data from the Dragonfly Telephoto Array and the Herschel Space Observatory. A challenge for optical observations of faint diffuse cirrus is accurate removal of a contaminating, spatially varying sky. We present a technique to analyze two images of the same cirrus field concurrently, correlating pixel values to capture the relationship and simultaneously fitting the sky-related signal as a complex noncorrelating additive component. For the Spider, we measure a color g − r = 0.644 ± 0.024 and ratios of visible-wavelength to 250 μm intensity of γ g,250 = (0.855 ± 0.025) × 10−3 and γ r,250 = (1.55 ± 0.08) × 10−3 for the g and r-bands, respectively. We show how to use any dust model that matches the thermal dust emission to predict an upper limit to the amount of scattered light. The actual brightness of the cirrus will be fainter than this limit because of anisotropic scattering by the dust combined with anisotropy of the incident interstellar radiation field (ISRF). Using models of dust and the ISRF in the literature, we illustrate that the predicted brightness is indeed lower, though not as faint as the observations indicate.

The Lockman-SpReSO project

Context. Extragalactic surveys are a key tool for better understanding the evolution of galaxies. Both deep and wide-field surveys serve to provide a clearer emerging picture of the physical processes that take place in and around galaxies, and to identify which of these processes are the most important in shaping the properties of galaxies. Aims. The Lockman Spectroscopic Redshift Survey using Osiris (Lockman-SpReSO) aims to provide one of the most complete optical spectroscopic follow-ups of the far-infrared (FIR) sources detected by the Herschel Space Observatory in the Lockman Hole (LH) field. The optical spectroscopic study of the FIR-selected galaxies supplies valuable information about the relation between fundamental FIR and optical parameters, including extinction, star formation rate, and gas metallicity. In this article, we introduce and provide an in-depth description of the Lockman-SpReSO project and of its early results. Methods. We selected FIR sources from Herschel observations of the central 24 arcmin ×24 arcmin of the LH field with an optical counterpart up to 24.5 RC(AB). The sample comprises 956 Herschel FIR sources, plus 188 additional interesting objects in the field. These are point X-ray sources, cataclysmic variable star candidates, high-velocity halo star candidates, radio sources, very red quasi-stellar objects, and optical counterparts of sub-millimetre galaxies. The faint component of the catalogue (RC(AB) ≥ 20) was observed using the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias in multi-object spectroscopy (MOS) mode. The bright component was observed using two multi-fibre spectrographs: the AF2-WYFFOS at the William Herschel Telescope and the HYDRA instrument at the WYIN telescope. Results. From an input catalogue of 1144 sources, we measured a secure spectroscopic redshift in the range 0.03 ≲ z ≲ 4.96 for 357 sources with at least two identified spectral lines. In addition, for 99 sources that show only one emission or absorption line, a spectroscopic redshift was postulated based on the line and object properties, and photometric redshift. In both cases, properties of emission and absorption lines were measured. Furthermore, to characterize the sample in more depth with determined spectroscopic redshifts, spectral energy distribution (SED) fits were performed using the CIGALE software. The IR luminosity and the stellar mass estimations for the sample are also presented as a preliminary description.

Herschel Optimized Tau and Temperature (HOTT) Maps: Uncertainty Analysis and Robust Parameter Extraction

We introduce the HOTT dust optical depth and temperature maps parameterizing thermal dust emission. Such maps have revolutionized studies of the distribution of matter in molecular clouds and processes relevant to star formation, including virial stability. HOTT maps for a suite of fields, including the Herschel Gould Belt Survey, are available online. The standardization of our robust pipeline for modified blackbody fitting of the spectral energy distribution (SED) of high-quality archival submillimeter data from the Herschel Space Observatory is based on a thorough analysis and quantification of the uncertainties of the data. This enables proper weighting in the SED fits. The uncertainties assessed fall into four main categories: instrument noise; the cosmic infrared background anisotropy, a contaminating sky signal; gradient-related noise arising because of dust signal morphology; and calibration uncertainty, scaling with the signal strength. Zero-level adjustments are important too. An analysis of residuals from the SED fits across many fields supports the overall appropriateness of the assumed modified blackbody model and points to where it breaks down. Finding χ 2 distributions close to the theoretical expectation boosts confidence in the pipeline and the optimized quality of the parameter maps and their estimated uncertainties. We compared our HOTT parameter maps to those from earlier studies to understand and quantify the potential for systematic differences.