David L. Clements

We present a resolved far-infrared/sub-millimetre study of dust in the nearby spiral galaxy M 81 using Herschel PACS/SPIRE and JCMT SCUBA-2 observations from 70 to 850 μm. We model the dust emission using both single-temperature modified blackbody (SMBB) fits and point process mapping (PPMAP), comparing pixel-by-pixel SED-fitting with image cubes of dust surface density as a function of position and temperature. For fixed β = 1.9 and a dust opacity of κ350μm = 1.92 cm2 g−1, SMBB gives an integrated dust mass of (1.77 ± 0.09) × 107M⊙, while PPMAP gives (2.65 ± 0.13) × 107M⊙. The higher PPMAP mass is expected because real lines of sight contain dust over a range of temperatures, whereas SMBB assumes a single effective temperature and can underestimate the dust mass. Both methods show enhanced dust surface densities along the spiral arms and a radially declining dust temperature, with the warmest dust in the central region. Variable-β fits indicate only moderate spatial variation in β for well-constrained pixels, but the strong T–β degeneracy motivates a fixed emissivity index for the main analysis. Combining the dust maps with H i data, we find a positive radial gas-to-dust ratio gradient, with dlog10(GDR)/dR = 0.065 dex kpc−1. Comparison with M 81’s metallicity gradient implies a declining dust-to-metals ratio, potentially consistent with more efficient grain growth in the inner disc. The star formation rate is modest, ~0.27 M⊙ yr−1, and is strongly concentrated along the spiral arms. These results suggest that the dust, gas, and star-forming structures of M 81 are strongly shaped by its spiral arms, while the central region hosts the warmest dust in the disc.

Source detection and photometry with Herschel-SPIRE is fundamentally limited by confusion rather than instrumental noise, with 1 σ confusion noises of ∼5–7 mJy across the 250–500 μ m bands. We apply XID+, a probabilistic Bayesian deblender, to the Herschel-SPIRE Dark Field, the deepest SPIRE image obtained, using positional priors from a Spitzer-MIPS 24 μ m catalog of 2625 sources over a 225 arcmin ² overlap region. Euclidean-normalized differential number counts are recovered at 250, 350, and 500 μ m and compared against an independent P ( D ) fluctuation analysis of the same field, the SIDES+uchuu simulation, and published literature counts. XID+ recovers counts below the 1 σ confusion noise in all three bands, in good agreement with P ( D ) and HerMES+stacking to ∼2 mJy. These results validate prior-based deblending and motivate its adoption for next-generation far-infrared surveys with NASA’s PRIMA.

Context. Current investigations of cold gas in the interstellar medium are limited by selection biases, as most samples are derived from optical or near-infrared surveys that preferentially select massive, low-obscuration galaxies. While previous research has established key scaling relations for the main sequence (MS), these studies often exclude gas-rich passive systems and inefficient star-forming populations that are not identified by conventional color-selection criteria. Overcoming these limitations requires a large-volume molecular-line survey that identifies galaxies based on their molecular gas reservoirs rather than stellar luminosity. Aims. This study provides a census of molecular gas content in galaxies spanning a broad cosmic range (0.5 > z > 5) through a spectral search within the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA) ALMA Band 4 observations. Methods. The spectral axis of ALMA data in the Ex-MORA field, covering 577 arcmin ² , enabled a dual-strategy molecular line search: an unbiased search for high-significance line emitters and a targeted search utilizing spectroscopic redshift priors. In total, we detected 52 galaxies in CO or [C I ] line transitions, 2 of which exhibited two distinct lines. We derived physical properties using CIGALE with nonparametric star formation history modeling, and estimated molecular gas masses using metallicity-dependent conversion factors. Results. Our sample is dominated by MS systems characterized by high stellar masses (median log M _⋆ /M _⊙ = 10.83) and substantial molecular gas reservoirs (>10 ¹⁰ M _⊙ ). The gas fraction ( μ _gas ) increases with redshift among active populations; however, this trend may be influenced by environmental factors, particularly a significant bias at high redshifts due to a gas-rich protocluster at z ≈ 2.4. In contrast, the overdensity at z ≈ 0.73 is indistinguishable from the field population and does not bias the results. We identified five transitional green valley sources, all of which exhibit a peak in μ _gas at cosmic noon. This peak could potentially be due to stellar feedback during this epoch that suppresses star formation by heating the gas rather than immediate reservoir depletion. Trying to conclude that this process happens to all green valley galaxies is beyond the scope and capabilities of our survey, but our results show that at least some GV galaxies could be affected by feedback. Our kinematic analysis of resolved sources indicates a predominance of rotating disk structures. Conclusions. Large-area line searches are highly effective at recovering gas-massive galaxies across diverse evolutionary states, including transitional phases often missed by traditional surveys. The prevalence of MS systems and high gas masses underscores this approach’s ability to identify and characterize the most prominent gas reservoirs.

The first Euclid Quick Data Release (Q1) contains millions of galaxies with excellent optical and near-infrared (IR) coverage. To complement this dataset, we investigate the average far-IR properties of Euclid -selected main sequence (MS) galaxies using existing Herschel and SCUBA-2 data. We used 17.6 deg ² (2.4 deg ² ) of overlapping Herschel (SCUBA-2) data, containing 2.6 million (240 000) MS galaxies. We binned the Euclid catalogue by stellar mass and photometric redshift and performed a stacking analysis following SimStack , which accounts for galaxy clustering and bin-to-bin correlations. We detected stacked far-IR flux densities across a significant fraction of the bins. We fitted modified blackbody spectral energy distributions in each bin and derived mean dust temperatures ( T _d ), dust masses ( M _d ), and star-formation rates (SFRs). We find similar mean SFRs compared to the Euclid catalogue, and we show that the average dust-to-stellar mass ratios decreased from z ≃ 1 to the present day. Average dust temperatures are largely independent of stellar mass and are well-described by the function T ₂ + ( T ₁ − T ₂ ) e ^{− t / τ} , where t is the age of the Universe, T ₁ = (79.7 ± 7.4) K, T ₂ = (23.2 ± 0.1) K, and τ = (1.6 ± 0.1) Gyr. We argue that since the dust temperatures converge to a non-zero value below z = 1, the dust is now primarily heated by the existing cooler and older stellar population, as opposed to hot young stars in star-forming regions at higher redshifts. We show that since the dust temperatures are independent of stellar mass, the correlation between dust temperature and SFR depends on stellar mass. Lastly, we estimate the contribution of the Euclid catalogue to the cosmic IR background (CIB), finding that it accounts for > 60% of the CIB at 250, 350, and 500 μm. As the Euclid mission progresses, larger catalogues will allow us to probe the far-IR properties of MS galaxies out to higher redshifts and lower stellar masses, potentially recovering the complete CIB.

The Herschel-SPIRE Dark Field (SDF), originally observed for calibration of the SPIRE instrument, is the deepest far-infrared (FIR) field to date (equivalent exposure time of ∼700 hr deg⁻¹) at wavelengths 250–500 μm, probing below the SPIRE confusion limit. We present SCUBA-2 850 μm observations covering the central Deep Region, detecting 36 sources with number counts consistent with previous surveys at this wavelength. Cross-identification with multiwavelength catalogues reveals 20 SPIRE-dropouts, whose stacked SPIRE fluxes suggest a photometric redshift of z ∼ 4. Photo-z estimates from the magphys, bagpipes and mmpz tools are consistent within the uncertainties for 3 sources (z ∼ 1–2), while 13 are inconsistent, and 20 lack sufficient data due to counterpart ambiguity or non-detections. We flag a total of 9 sources as potentially lensed and 15 as potential multiples. SED fitting yields average properties for SPIRE-detected sources of log₁₀(L_FIR / L_⊙) = 13.6 ± 0.1, log₁₀(M_dust / M_⊙) = 8.1 ± 0.1, and SFR_obsc = 7000 ± 1900 M_⊙ yr⁻¹. The stacked dropouts yield log₁₀(L_FIR / L|$_{\odot }) = 12.8^{+0.5}_{-0.7} [12.5^{+0.4}_{-0.6}]$|⁠, log₁₀(M_dust / M|$_{\odot }) = 6.52^{+0.33}_{-0.41} [6.71^{+0.19}_{-0.23}]$|⁠, and SFR|$_{\textrm{obsc}} = 700^{+1500}_{-560} [350^{+420}_{-250}]\,$| M_⊙ yr⁻¹ at a derived |$z = 6.7^{+2.4}_{-3.0}$| [at a fixed |$z = 4.0^{+0.1}_{-0.6}$|] contributing ∼15 [∼2] per cent of the cosmic SFRD at that epoch. We find an excess at z ∼ 1 in the SFRD of SPIRE-detected sources, consistent with the sub-mJy bump in SPIRE number counts previously identified in this field, possibly tracing large-scale structure.

We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned extension of the survey duration to 2035, this expansion will significantly enhance SO's search for a B -mode signal in the polarisation of the cosmic microwave background, a potential signature of gravitational waves produced in the very early Universe. Assuming a 1/ f noise model with knee multipole ℓ _knee = 50 and a moderately complex model for Galactic foregrounds, we forecast a 1 σ (or 68% confidence level) constraint on the tensor-to-scalar ratio r of σ _r = 1.2 × 10 ^-3 , assuming no primordial B-modes are present. This forecast assumes that 70% of the B -mode lensing signal can ultimately be removed using high resolution observations from the SO Large Aperture Telescope (LAT) and overlapping large-scale structure surveys. For more optimistic assumptions regarding foregrounds and noise, and assuming the same level of delensing, this forecast constraint improves to σ _r = 7 × 10 ^-4 . These forecasts represent a major improvement in SO's constraining power, being a factor of around 2.5 times better than what could be achieved with the originally planned campaign, which assumed the existing three SATs would conduct a five-year survey.

The Heterodyne Spectroscopy Instrument (HSI) is a focal plane array receiver (FPA) for the Far-IR Spectroscopy Space Telescope (FIRSST), a proposal submitted to NASA's APEX call. Though FIRSST was not selected for further study, the receiver design allowed us to quantitatively demonstrate that small (few to few tens of pixels) heterodyne FPAs are now feasible for space missions, can be built with high TRL components, are reliable and fit within the mass/volume/power constraints of medium to large missions. The design also identified the challenges and critical design considerations, in particular that great care needs to be taken to minimize the cryogenic heat load of the cryogenic IF amplifiers and to keep the power consumption of the spectrometer backends low. The HSI was designed primarily to study the trail of water from the Interstellar Medium (ISM) to planets and to observe the important low-lying transitions of water and its isotopes between 500 and 2000 GHz undetectable from the ground due to Earth's atmosphere. HSI has a spectral resolving power of up to 107 (0.03 km/s), ideal for kinematic studies or line tomography. HSI has six 5-pixel-arrays covering 3 frequency bands and 2 linear polarizations. The concept study showed that heterodyne array receivers such as HSI can be built today even for fast missions and that they are powerful and versatile instruments, with low-risk technology capable of opening up the THz sky at very high spectral resolving power for new discoveries.

One of the greatest challenges in galaxy evolution over the last decade has been constraining the prevalence of heavily dust-obscured galaxies in the early Universe. At z > 3, these galaxies are increasingly rare, and difficult to identify, as they are interspersed among the more numerous dust-obscured galaxy population at z = 1–3, making efforts to secure confident spectroscopic redshifts expensive, and sometimes unsuccessful. In this work, we present the Extended Mapping Obscuration to Reionization with the Atacama Large Millimeter/submillimeter Array (ALMA; Ex-MORA) Survey—a 2 mm blank-field survey in the COSMOS-Web field, and the largest ever ALMA blank-field survey to date, covering 577 arcmin ² . Ex-MORA is an expansion of the MORA survey designed to identify primarily z > 3 dusty, star-forming galaxies while simultaneously filtering out the more numerous z < 3 population by leveraging the very negative K -correction at observed-frame 2 mm. We identify 37 significant (>5 σ ) sources, 33 of which are robust thermal dust emitters. We measure a median redshift of 〈 z 〉 = 3 . 8 − 1.52 + 1.7 , with two-thirds of the sample at z > 3, and just under half at z > 4, demonstrating the overall success of the 2 mm selection technique. The total integrated z > 3 volume density of Ex-MORA sources is ∼1–3 × 10 ⁻⁵ Mpc ⁻³ , consistent with other surveys of infrared luminous galaxies at similar epochs. We also find that techniques using rest-frame optical emission (or lack thereof) to identify z > 3 heavily dust-obscured galaxies miss at least half of Ex-MORA galaxies. This supports the idea that the dusty galaxy population is heterogeneous, and that synergies across observatories spanning multiple energy regimes are critical to understanding their formation and evolution at z > 3.

Luminous infrared (IR) galaxies are key sites of obscured stellar mass assembly at z > 0.5. Their star formation rates (SFRs) are often estimated using the luminosities of the 6.2 and 11.2 μ m polycyclic aromatic hydrocarbon (PAH) features or those of the [Ne ii ] and [Ne iii ] fine-structure lines, as they are minimally affected by obscuration. It is uncertain whether the calibration of these features as SFR tracers depends on the starburst bolometric luminosity or the level of active galactic nucleus (AGN) activity. We here investigate the relationship between the luminosities of PAH and neon lines with SFR for highly luminous objects using radiative transfer modeling and archival observations of 42 local ultraluminous (≥10 ¹² L _⊙ ) IR galaxies (ULIRGs). We find that PAH and [Ne ii ] features arise mainly in star-forming regions, with small contributions from the AGN or host, but that the [Ne iii ] line has a mixed contribution from both star formation and AGN activity. We present relations between L _PAH and L _{[Ne II ]} , and both starburst luminosity and SFR. We find relations for lower-luminosity ( L _IR ≃ 10 ¹⁰ –10 ¹² L _⊙ ) systems underestimate the SFRs in local ULIRGs by up to ∼1 dex. The 6.2 and 11.2 μ m PAH features, and the [Ne ii ] line, are thus good tracers of SFR in ULIRGs. We do not find that a more luminous AGN affects the relationship between SFR and PAH or neon luminosity but that it can make PAH emission harder to discern. Our results and derived relations are relevant to studies of star-forming and composite galaxies at z < 3 with the James Webb Space Telescope.