Modified Blackbody Model Research Articles

ALMA-IMF

Context. A crucial aspect in addressing the challenge of measuring the core mass function (CMF), that is pivotal for comprehending the origin of the initial mass function (IMF), lies in constraining the temperatures of the cores. Aims. We aim to measure the luminosity, mass, column density and dust temperature of star-forming regions imaged by the ALMA-IMF large program. These fields were chosen to encompass early evolutionary stages of massive protoclusters. High angular resolution mapping is required to capture the properties of protostellar and pre-stellar cores within these regions, and to effectively separate them from larger features, such as dusty filaments. Methods. We employed the point process mapping (PPMAP) technique, enabling us to perform spectral energy distribution fitting of far-infrared and submillimeter observations across the 15 ALMA-IMF fields, at an unmatched 2.5″ angular resolution. By combining the modified blackbody model with near-infrared data, we derived bolometric luminosity maps. We estimated the errors impacting values of each pixel in the temperature, column density, and luminosity maps. Subsequently, we employed the extraction algorithm getsf on the luminosity maps in order to detect luminosity peaks and measure their associated masses. Results. We obtained high-resolution constraints on the luminosity, dust temperature, and mass of protoclusters, that are in agreement with previously reported measurements made at a coarser angular resolution. We find that the luminosity-to-mass ratio correlates with the evolutionary stage of the studied regions, albeit with intra-region variability. We compiled a PPMAP source catalog of 313 luminosity peaks using getsf on the derived bolometric luminosity maps. The PPMAP source catalog provides constraints on the mass and luminosity of protostars and cores, although one source may encompass several objects. Finally, we compare the estimated luminosity-to-mass ratio of PPMAP sources with evolutionary tracks and discuss the limitations imposed by the 2.5″ beam.

Spatial Variations of Dust Opacity and Grain Growth in Dark Clouds: L1689, L1709, and L1712

The far-infrared (FIR) opacity of dust in dark clouds within the Ophiuchus molecular cloud is investigated through multiwavelength infrared observations from UKIDSS, Spitzer, and Herschel. Employing the infrared color excess technique with both near-infrared and mid-infrared photometric data, a high-resolution extinction map in the K band (A K ) is constructed for three dark clouds: L1689, L1709, and L1712. The derived extinction map has a resolution of 1′ and reaches a depth of A K ∼ 3 mag. The FIR optical depths τ 250 at a reference wavelength of 250 μm are obtained by fitting the Herschel PACS and SPIRE continuum data at 100, 160, 250, 350, and 500 μm using a modified blackbody model. The average dust opacity per unit gas mass at 250 μm, r κ 250, is determined through a pixel-by-pixel correlation of τ 250 with A K , yielding a value of approximately 0.09 cm2 g−1, which is about 2–3 times higher than the typical value in the diffuse interstellar medium. Additionally, an independent analysis across 16 subregions within the Ophiuchus cloud indicates spatial variations in dust opacity, with values ranging from 0.07 to 0.12 cm2 g−1. Although the observed trend of increasing dust opacity with higher extinction implies grain growth, our findings indicate that rapid grain growth has clearly not yet occurred in the dark clouds studied in this work.

BEYONDPLANCK

Using the Planck Low Frequency Instrument (LFI) and WMAP data within the global Bayesian BEYONDPLANCK framework, we constrained the polarized foreground emission between 30 and 70 GHz. We combined, for the first time, full-resolution Planck LFI time-ordered data with low-resolution WMAP sky maps at 33, 40, and 61 GHz. The spectral parameters were fit with a likelihood defined at the native resolution of each frequency channel. This analysis represents the first implementation of true multi-resolution component separation applied to CMB observations for both amplitude and spectral energy distribution (SED) parameters. For the synchrotron emission, we approximated the SED as a power-law in frequency and we find that the low signal-to-noise ratio of the current data strongly limits the number of free parameters that can be robustly constrained. We partitioned the sky into four large disjoint regions (High Latitude; Galactic Spur; Galactic Plane; and Galactic Center), each associated with its own power-law index. We find that the High Latitude region is prior-dominated, while the Galactic Center region is contaminated by residual instrumental systematics. The two remaining regions appear to be signal-dominated, and for these we derive spectral indices of βsSpur = −3.17 ± 0.06 and βsPlane = −3.03 ± 0.07, which is in good agreement with previous results. For the thermal dust emission, we assumed a modified blackbody model and we fit a single power-law index across the full sky. We find βd = 1.64 ± 0.03, which is slightly steeper than the value reported in Planck HFI data, but still statistically consistent at the 2σ confidence level.

Characterizing line-of-sight variability of polarized dust emission with future CMB experiments

ABSTRACT While Galactic dust emission is often accounted for in cosmic microwave background (CMB) analyses by fitting a two-parameter modified blackbody (MBB) model in each pixel, typically a number of such clouds are found along each line of sight and within each angular pixel, resulting in a superposition of their spectra. We study the effects of this superposition on pixel-based foreground fitting strategies by modeling the spectral energy distribution (SED) in each pixel as the integral of individual MBB spectra over various physically motivated statistical distributions of dust cloud properties. We show that fitting these SEDs with the two-parameter MBB model generally results in unbiased estimates of the CMB Stokes Q and U amplitudes per pixel, unless there are significant changes in both the dust SED and polarization angle along the line of sight, in which case significant (>10σ) biases are observed in an illustrative model. We find that the best-fitting values of the dust temperature, Td, and spectral index, βd, are significantly biased from the mean/median of the corresponding statistical distributions when the distributions are broad, suggesting that MBB model fits can give an unrepresentative picture of the physical properties of dust at microwave wavelengths if not interpreted carefully. Using Fisher matrix analysis, we determine the experimental sensitivity required to recover the parameters of the Td and βd distributions by fitting a probabilistic MBB model, finding that only the parameters of broad distributions can be measured by SED fitting on a single line of sight.

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.

Evidence for Large-scale Excesses Associated with Low H i Column Densities in the Sky. I. Dust Excess

Where dust and gas are uniformly mixed, atomic hydrogen can be traced through the detection of far-infrared (FIR) or UV emission of dust. We considered, for the origin of discrepancies observed between various direct and indirect tracers of gas outside the Galactic plane, possible corrections to the zero levels of the Planck High Frequency Instrument (HFI) detectors. We set the zero levels of the Planck-HFI skymaps as well as the 100 μm map from COBE/DIRBE and IRAS from the correlation between FIR emission and atomic hydrogen column density excluding regions of lowest gas column density. A modified blackbody model fit to those new zero-subtracted maps led to significantly different maps of the opacity spectral index β and temperature T and an overall increase in the optical depth at 353 GHz τ 353 of 7.1 × 10−7 compared to the data release 2 Planck map. When comparing τ 353 and the H i column density, we observed a uniform spatial distribution of the opacity outside regions with dark neutral gas and CO except in various large-scale regions of low N H i that represent 25% of the sky. In those regions, we observed an average dust column density 45% higher than predictions based on N H i with a maximum of 250% toward the Lockman Hole region. From the average opacity σ e353 = (8.9 ± 0.1) × 10−27 cm2, we deduced a dust-to-gas mass ratio of 0.53 × 10−2. We did not see evidence of dust associated with a Reynolds layer of ionized hydrogen. We measured a far-ultraviolet isotropic intensity of 137 ± 15 photons s−1 cm−2 sr−1 Å−1 in agreement with extragalactic flux predictions and a near-ultraviolet isotropic intensity of 378 ± 45 photons s−1 cm−2 sr−1 Å−1 corresponding to twice the predicted flux.

Mitigating Bias in CMB B-modes from Foreground Cleaning Using a Moment Expansion

One of the primary challenges facing upcoming cosmic microwave background (CMB) polarization experiments aiming to measure the inflationary B-mode signal is the removal of polarized foregrounds. The thermal dust foreground is often modeled as a single modified blackbody; however, overly simplistic foreground models can bias measurements of the tensor-to-scalar ratio r. As CMB polarization experiments become increasingly sensitive, thermal dust emission models must account for greater complexity in the dust foreground while making minimal assumptions about the underlying distribution of dust properties within a beam. We use Planck dust temperature data to estimate the typical variation in dust properties along the line of sight and examine the impact of these variations on the bias in r if a single modified blackbody model is assumed. We then assess the ability of the moment method to capture the effects of spatial averaging and to reduce bias in the tensor-to-scalar ratio for different possible toy models of dust emission. We find that the expected bias due to temperature variations along the line of sight is significant compared to the target sensitivities of future CMB experiments, and that the use of the moment method could reduce bias as well as shed light into the distribution of dust physical parameters.

Benchmarking Dust Emission Models in M101

Abstract We present a comparative study of four physical dust models and two single-temperature modified blackbody models by fitting them to the resolved WISE, Spitzer, and Herschel photometry of M101 (NGC 5457). Using identical data and a grid-based fitting technique, we compare the resulting dust and radiation field properties derived from the models. We find that the dust mass yielded by the different models can vary by up to a factor of 3 (factor of 1.4 between physical models only), although the fits have similar quality. Despite differences in their definition of the carriers of the mid-IR aromatic features, all physical models show the same spatial variations for the abundance of that grain population. Using the well-determined metallicity gradient in M101 and resolved gas maps, we calculate an approximate upper limit on the dust mass as a function of radius. All physical dust models are found to exceed this maximum estimate over some range of galactocentric radii. We show that renormalizing the models to match the same Milky Way high-latitude cirrus spectrum and abundance constraints can reduce the dust mass differences between models and bring the total dust mass below the maximum estimate at all radii.

Resolving the Dust-to-Metals Ratio and CO-to-H2 Conversion Factor in the Nearby Universe

Abstract We investigate the relationship between the dust-to-metals ratio (D/M) and the local interstellar medium environment at ∼2 kpc resolution in five nearby galaxies: IC 342, M31, M33, M101, and NGC 628. A modified blackbody model with a broken power-law emissivity is used to model the dust emission from 100 to 500 μm observed by Herschel. We utilize the metallicity gradient derived from auroral line measurements in H i regions whenever possible. Both archival and new CO rotational line and H i 21 cm maps are adopted to calculate gas surface density, including new wide-field CO and H i maps for IC 342 from IRAM and the VLA, respectively. We experiment with several prescriptions of the CO-to-H2 conversion factor and compare the resulting D/M–metallicity and D/M–density correlations, both of which are expected to be nonnegative from depletion studies. The D/M is sensitive to the choice of the conversion factor. The conversion factor prescriptions based on metallicity only yield too much molecular gas in the center of IC 342 to obtain the expected correlations. Among the prescriptions tested, the one that yields the expected correlations depends on both metallicity and surface density. The 1σ range of the derived D/M spans 0.40–0.58. Compared to chemical evolution models, our measurements suggest that the dust growth timescale is much shorter than the dust destruction timescale. The measured D/M is consistent with the D/M in galaxy-integrated studies derived from infrared dust emission. Meanwhile, the measured D/M is systematically higher than the D/M derived from absorption, which likely indicates a systematic offset between the two methods.

Planck intermediate results

We describe an extension of the most recent version of the Planck Catalogue of Compact Sources (PCCS2), produced using a new multi-band Bayesian Extraction and Estimation Package (BeeP). BeeP assumes that the compact sources present in PCCS2 at 857 GHz have a dust-like spectral energy distribution (SED), which leads to emission at both lower and higher frequencies, and adjusts the parameters of the source and its SED to fit the emission observed in Planck’s three highest frequency channels at 353, 545, and 857 GHz, as well as the IRIS map at 3000 GHz. In order to reduce confusion regarding diffuse cirrus emission, BeeP’s data model includes a description of the background emission surrounding each source, and it adjusts the confidence in the source parameter extraction based on the statistical properties of the spatial distribution of the background emission. BeeP produces the following three new sets of parameters for each source: (a) fits to a modified blackbody (MBB) thermal emission model of the source; (b) SED-independent source flux densities at each frequency considered; and (c) fits to an MBB model of the background in which the source is embedded. BeeP also calculates, for each source, a reliability parameter, which takes into account confusion due to the surrounding cirrus. This parameter can be used to extract sub-samples of high-frequency sources with statistically well-understood properties. We define a high-reliability subset (BeeP/base), containing 26 083 sources (54.1% of the total PCCS2 catalogue), the majority of which have no information on reliability in the PCCS2. We describe the characteristics of this specific high-quality subset of PCCS2 and its validation against other data sets, specifically for: the sub-sample of PCCS2 located in low-cirrus areas; the Planck Catalogue of Galactic Cold Clumps; the Herschel GAMA15-field catalogue; and the temperature- and spectral-index-reconstructed dust maps obtained with Planck’s Generalized Needlet Internal Linear Combination method. The results of the BeeP extension of PCCS2, which are made publicly available via the Planck Legacy Archive, will enable the study of the thermal properties of well-defined samples of compact Galactic and extragalactic dusty sources.

Dissecting the Global Cold Dust Properties and Possible Submillimeter Excess of 13 Nearby Spiral Galaxies from the NGLS

Abstract We select 13 nearby spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) project and perform spectral energy distribution fitting for each galaxy applying two-component modified blackbody models on a global scale aim to probe the potential submillimeter (submm) excess. We find that NGC 2976, NGC 3351, and NGC 4631 show excess emission at 850 μm when using β c = 2.0. The contributions of CO(3–2), free–free emission or synchrotron radiation cannot explain their 850 μm excess. Our results suggest that a submm excess at 850 μm may be more easily detected for galaxies with faint total infrared luminosity and low cold dust mass. The colder temperature of cold dust, the more radiation of dust there is at 850 μm. The submm excess are prone to be detected in spiral galaxies with low stellar mass. As the metallicity of galaxies become poor, the submm excess is more obvious.

Infrared study of IRAS 18316-0602 star-forming region

We present the results of the investigation of ISM and the young stellar population in the IRAS 18316-0602 star-forming region which is referred to as UCHII (G25.65+1.05). Single temperature modified blackbody model shows that values of N(H2) hydrogen column density and Td dust temperature are in ranges 2 - 7 x 1023 cm-2 and 12 - 30 K, respectively. The analysis of infrared photometric data allowed to reveal about 50 young stellar objects in the G25.65+1.05 UCHII region.

Molecular gas and dust properties of galaxies from the Great Observatories All-sky LIRG Survey

We present IRAM-30 m Telescope 12CO and 13CO observations of a sample of 55 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in the local universe. This sample is a subset of the Great Observatory All-Sky LIRG Survey (GOALS), for which we use ancillary multi-wavelength data to better understand their interstellar medium and star formation properties. Fifty-three (96%) of the galaxies are detected in 12CO, and 29 (52%) are also detected in 13CO above a 3σ level. The median full width at zero intensity (FWZI) velocity of the CO line emission is 661 km s−1, and ∼54% of the galaxies show a multi-peak CO profile. Herschel photometric data is used to construct the far-IR spectral energy distribution of each galaxy, which are fit with a modified blackbody model that allows us to derive dust temperatures and masses, and infrared luminosities. We make the assumption that the gas-to-dust mass ratio of (U)LIRGs is comparable to local spiral galaxies with a similar stellar mass (i.e., gas/dust of mergers is comparable to their progenitors) to derive a CO-to-H2 conversion factor of ⟨α⟩ = 1.8−0.8+1.3 M⊙ (K km s−1 pc2)−1; such a value is comparable to that derived for (U)LIRGs based on dynamical mass arguments. We derive gas depletion times of 400 − 600 Myr for the (U)LIRGs, compared to the 1.3 Gyr for local spiral galaxies. Finally, we re-examine the relationship between the 12CO/13CO ratio and dust temperature, confirming a transition to elevated ratios in warmer systems.

No signs of star formation being regulated in the most luminous quasars at z ∼ 2 with ALMA

ABSTRACT We present ALMA Band 7 observations at $850\, \mu$m of 20 luminous ($\log \, L_{\rm bol}\,\gt\, 46.9$ [erg s−1]) unobscured quasars at z ∼ 2. We detect continuum emission for 19/20 quasars. After subtracting an AGN contribution, we measure the total far-IR luminosity for 18 quasars, assuming a modified blackbody model, and attribute the emission as indicative of the star formation rate (SFR). Our sample can be characterized with a lognormal SFR distribution having a mean of 140 M⊙ yr−1 and a dispersion of 0.5 dex. Based on an inference of their stellar masses, the SFRs are similar, in both the mean and dispersion, with star-forming main-sequence galaxies at the equivalent epoch. Thus, there is no evidence for a systematic enhancement or suppression (i.e. regulation or quenching) of star formation in the hosts of the most luminous quasars at z ∼ 2. These results are consistent with the Magneticum cosmological simulation, while in disagreement with a widely recognized phenomenological model that predicts higher SFRs than observed here based on the high bolometric luminosities of this sample. Furthermore, there is only a weak relation between SFR and accretion rate on to their supermassive black holes both for average and individual measurements. We interpret these results as indicative of star formation and quasar accretion being fed from the available gas reservoir(s) in their host with a disconnect due to their different physical sizes, temporal scales, and means of gas processing.

Determining thermal dust emission from Planck HFI data using a sparse, parametric technique

Context. The Planck data releases have provided the community with submillimetre and full-sky radio observations at unprecedented resolutions. We make use of the Planck 353, 545, and 857 GHz maps alongside the IRAS 3000 GHz map. These maps contain information on the cosmic microwave background (CMB), cosmic infrared background (CIB), extragalactic point sources, and diffuse thermal dust emission. Aims. We aim to determine the modified black-body (MBB) model parameters of thermal dust emission in total intensity and produce all-sky maps of pure thermal dust, having separated this Galactic component from the CMB and CIB. Methods. This separation is completed using a new, sparsity-based, parametric method, Parameter Recovery Exploiting Model Informed Sparse Estimates (premise). The method is comprised of three main stages: 1) filtering the raw data to reduce the effect of the CIB on the MBB fit; 2) fitting an MBB model to the filtered data across super-pixels of various sizes determined by the algorithm itself; and 3) refining these super-pixel estimates into full-resolution maps of the MBB parameters. Results. We present our maps of MBB temperature, spectral index, and optical depth at 5 arcmin resolution and compare our estimates to those of GNILC and to the two-step MBB fit presented by the Planck Collaboration in 2013. Conclusions. By exploiting sparsity we avoid the need for smoothing, enabling us to produce the first full-resolution MBB parameter maps from intensity measurements of thermal dust emission. We consider the premise parameter estimates to be competitive with the existing state-of-the-art solutions, outperforming these methods within low signal-to-noise regions as we account for the CIB without removing thermal dust emission through oversmoothing.

Mitigating Complex Dust Foregrounds in Future Cosmic Microwave Background Polarization Experiments

Abstract Polarized Galactic foregrounds are one of the primary sources of systematic error in measurements of the B-mode polarization of the cosmic microwave background (CMB). Experiments are becoming increasingly sensitive to complexities in the foreground frequency spectra that are not captured by standard parametric models, potentially affecting our ability to efficiently separate out these components. Employing a suite of dust models encompassing a variety of physical effects, we simulate observations of a future seven-band CMB experiment to assess the impact of these complexities on parametric component separation. We identify configurations of frequency bands that minimize the “model errors” caused by fitting simple parametric models to more complex “true” foreground spectra, which bias the inferred CMB signal. We find that: (a) fits employing a simple two-parameter modified blackbody (MBB) dust model tend to produce significant bias in the recovered polarized CMB signal in the presence of physically realistic dust foregrounds; (b) generalized MBB models with three additional parameters reduce this bias in most cases, but non-negligible biases can remain, and can be hard to detect; (c) line-of-sight effects, which give rise to frequency decorrelation, and the presence of iron grains are the most problematic complexities in the dust emission for recovering the true CMB signal. More sophisticated simulations will be needed to demonstrate that future CMB experiments can successfully mitigate these more physically realistic dust foregrounds.

HERUS: the far-IR/submm spectral energy distributions of local ULIRGs and photometric atlas

We present the Herschel-SPIRE photometric atlas for a complete flux limited sample of 43 local ultraluminous infrared galaxies (ULIRGs), selected at 60 μm by IRAS, as part of the HERschel ULIRG Survey (HERUS). Photometry observations were obtained using the SPIRE instrument at 250, 350, and 500 μm. We describe these observations, present the results, and combine the new observations with data from IRAS to examine the far-infrared spectral energy distributions (SEDs) of these sources. We fit the observed SEDs of HERUS objects with a simple parametrized modified blackbody model, where temperature and emissivity β are free parameters. We compare the fitted values to those of non-ULIRG local galaxies, and find, in agreement with earlier results, that HERUS ULIRGs have warmer dust (median temperature T = 37.9 ± 4.7 K compared to 21.3 ± 3.4 K) but a similar β distribution (median β = 1.7 compared to 1.8) to the Herschel reference sample (HRS, Cortese et al. 2014) galaxies. Dust masses are found to be in the range of 107.5–109 M⊙, significantly higher than that of HRS sources. We compare our results for local ULIRGs with higher redshift samples selected at 250 and 850 μm. These latter sources generally have cooler dust and/or redder 100-to-250 μm colours than our 60 μm-selected ULIRGs. We show that this difference may in part be the result of the sources being selected at different wavelengths rather than being a simple indication of rapid evolution in the properties of the population.

Star formation towards the Galactic H II region RCW 120

Context. The expansion of H ii regions can trigger the formation of stars. An overdensity of young stellar objects is observed at the edges of H ii regions but the mechanisms that give rise to this phenomenon are not clearly identified. Moreover, it is difficult to establish a causal link between H ii -region expansion and the star formation observed at the edges of these regions. A clear age gradient observed in the spatial distribution of young sources in the surrounding might be a strong argument in favor of triggering. Aims. We aim to characterize the star formation observed at the edges of H ii regions by studying the properties of young stars that form there. We aim to detect young sources, derive their properties and their evolution stage in order to discuss the possible causal link between the first-generation massive stars that form the H ii region and the young sources observed at their edges. Methods. We have observed the Galactic H ii region RCW 120 with Herschel PACS and SPIRE photometers at 70, 100, 160, 250, 350 and 500 μm. We produced temperature and H2 column density maps and use the getsources algorithm to detect compact sources and measure their fluxes at Herschel wavelengths. We have complemented these fluxes with existing infrared data. Fitting their spectral energy distributions with a modified blackbody model, we derived their envelope dust temperature and envelope mass. We computed their bolometric luminosities and discuss their evolutionary stages. Results. The overall temperatures of the region (without background subtraction) range from 15 K to 24 K. The warmest regions are observed towards the ionized gas. The coldest regions are observed outside the ionized gas and follow the emission of the cold material previously detected at 870 μm and 1.3 mm. The H2 column density map reveals the distribution of the cold medium to be organized in filaments and highly structured. Column densities range from 7 × 1021 cm-2 up to 9 × 1023 cm-2 without background subtraction. The cold regions observed outside the ionized gas are the densest and host star formation when the column density exceeds 2 × 1022 cm-2. The most reliable 35 compact sources are discussed. Using existing CO data and morphological arguments we show that these sources are likely to be associated with the RCW 120 region. These sources’ volume densities range from 2 × 105 cm-3 to 108 cm-3. Five sources have envelope masses larger than 50 M⊙ and are all observed in high column density regions (>7 × 1022 cm-2). We find that the evolutionary stage of the sources primarily depends on the density of their hosting condensation and is not correlated with the distance to the ionizing star. Conclusions. The Herschel data, with their unique sampling of the far infrared domain, have allowed us to characterize the properties of compact sources observed towards RCW 120 for the first time. We have also been able to determine the envelope temperature, envelope mass and evolutionary stage of these sources. Using these properties we have shown that the density of the condensations that host star formation is a key parameter of the star-formation history, irrespective of their projected distance to the ionizing stars.

On the redshift distribution and physical properties of ACT-selected DSFGs

We present multi-wavelength detections of nine candidate gravitationally-lensed dusty star-forming galaxies (DSFGs) selected at 218GHz (1.4mm) from the ACT equatorial survey. Among the brightest ACT sources, these represent the subset of the total ACT sample lying in Herschel SPIRE fields, and all nine of the 218GHz detections were found to have bright Herschel counterparts. By fitting their spectral energy distributions (SEDs) with a modified blackbody model with power-law temperature distribution, we find the sample has a median redshift of (68 per cent confidence interval), as expected for 218GHz selection, and an apparent total infrared luminosity of , which suggests that they are either strongly lensed sources or unresolved collections of unlensed DSFGs. The effective apparent diameter of the sample is , further evidence of strong lensing or multiplicity, since the typical diameter of dusty star-forming galaxies is 1.0-2.5 kpc. We emphasize that the effective apparent diameter derives from SED modelling without the assumption of optically thin dust (as opposed to image morphology). We find that the sources have substantial optical depth. to dust around the peak in the modified blackbody spectrum (λ obs ⩽ 500μm), a result that is robust to model choice.

Gas-to-dust ratios in massive star-forming galaxies at z ∼ 1.4

Abstract We present results of 12CO(J = 2–1) observations toward four massive star-forming galaxies at z ∼ 1.4 with the Nobeyama 45 m radio telescope. The galaxies are detected with Spitzer/MIPS in 24 μm and Herschel/SPIRE in 250 μm and 350 μm, and they mostly reside in the main sequence. Their gas-phase metallicities derived by the N2 method using the Hα and [N ii]λ 6584 emission lines are near the solar value. CO lines are detected toward three galaxies. The molecular-gas masses obtained are (9.6–35) × 1010 M⊙ by adopting the Galactic CO-to-H2 conversion factor and a CO(2–1)/CO(1–0) flux ratio of 3. The dust masses derived from the modified blackbody model (assuming a dust temperature of 35 K and an emissivity index of 1.5) are (2.4–5.4) × 108 M⊙. Resulting gas-to-dust ratios (not accounting for H i mass) at z ∼ 1.4 are 220–1450, which are several times larger than those in local star-forming galaxies. A dependence of the gas-to-dust ratio on the far-infrared luminosity density is not clearly seen.