Aims. DustPedia and Local Volume Legacy (LVL) are two samples representative of the local galaxy population, including in total ∼1000 unique objects of all morphological types, with a wide range of stellar masses and star formation activity, and a spectral coverage from the ultraviolet to the far-infrared. The purpose of this work is to show that these samples cover two complementary ranges in stellar mass and galaxy morphology, making them an ideal set for constraining the dominant processes in the evolution of the galactic dust content. Methods. Using the multi-wavelength data provided by the two surveys, we fitted the galaxies’ spectral energy distribution and estimated their physical properties, in particular the stellar mass, M*, the specific dust mass, sMdust = Mdust/M*, and the specific star formation rate, sSFR = SFR/M*. Results. By combining DustPedia and LVL, we highlight that the trend of log10(sMdust) with log10(M*) is not monotonic. Thanks to a large number of objects across a wide range of M*, we have been able to fit two smoothly joined linear correlations: a positive one for log10(M*/M⊙)≲9.5 (a range populated mostly by LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia, spirals (with early-type galaxies being distinct and more dispersed in the same mass regime). For log10(M*/M⊙) > 9.5, we confirm a strong correlation between sMdust and sSFR; dwarf galaxies, instead, lie below this trend, showing a large scatter of sMdust for −10.5 < log10(sSFR/yr−1) < − 9.0. By using chemical evolution models we find that the observed log10(sMdust)–log10(M*) and log10(sMdust)–log10(sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the galaxy ages, respectively. Low-mass Sm-Irr galaxies with low sMdust and a high sSFR can only be reproduced by the models by assuming a highly efficient photofragmentation rate of large grains, and/or low grain growth in clouds.

DustPedia and LVL are two samples representative of the local galaxy population, including in total 1011 unique objects of all morphological types, with a wide range of stellar masses (M_*) and star-formation activity, and a spectral coverage from the FUV to the FIR. The purpose of this work is to show that these samples cover two complementary ranges in M_* and morphology, making them an ideal set for constraining the dominant processes in the evolution of the galactic dust content. Using the multiwavelength data provided by the two surveys, we fitted the galaxies' spectral energy distribution and estimated their physical properties, in particular the M_*, sM_dust=M_dust/M_*, and sSFR = SFR/M_*. By combining DustPedia and LVL, we highlight that the log_10(sM_ dust)-log_10(M_*) trend is not monotonic. Thanks to a large number of objects across a wide range of M_*, we have been able to fit two smoothly-joined linear correlations: a positive for log_10(M_*/M_⊙)≲9.5 (mainly LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia spirals (early types are distinct and more dispersed in the same mass regime). For log_10(M_*/M_⊙)>9.5, we confirm a strong sM_dust-sSFR correlation; dwarf galaxies, instead, lie below this trend, with a large scatter of sM_ dust, for -10.5<log_10(sSFR/yr^-1)<-9.0. By using chemical evolution models we find that the observed log_10(sM_ dust)-log_10(M_*) and log_10(sM_ dust)-log_10(sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the galaxy ages, respectively. Low-mass Sm-Irr galaxies with low sM_ dust and high sSFR can only be reproduced by the models by assuming high photofragmentation rate of large grains, and/or low grain-growth in clouds.

Large high-quality samples of HII regions and their parent Giant Molecular Clouds (GMC) are now available for local galaxies. It is therefore possible to investigate links between the CO and Hα luminosity functions and whether massive stars form in GMCs of all masses. The CO luminosity functions (LF), representing the distribution of GMC masses, are consistently steeper than the Hα luminosity functions. The CO LF invariably steepens in the outer disk where fewer massive GMCs are present beyond the median cloud galactocentric distance. The Hα LF also steepens in the outer disk for most of the galaxies examined. Using Salpeter, Kroupa, and Chabrier Initial Mass Functions (IMF) along with stellar mass-luminosity-radius relations, we compute numerically the bolometric luminosity and Hα emission from young star clusters. The cluster masses are linked to the GMC mass by assuming that the cluster mass is a constant fraction (3%) of the parent cloud mass. In particular, results for a fully stochastic IMF are compared to suggestions that very massive stars only form in massive clusters or clouds. Within the limits of the observations – no small molecular clouds or low-luminosity HII regions can be detected at the typical ∼ 10 Mpc distance of the sample galaxies – we find no evidence for a maximum stellar mass which varies with cloud or cluster mass.

We present new ASKAP/WALLABY HI observations of the nearby dwarf galaxy system ESO 179-013 (Kathryn's Wheel), the nearest known collisional ring galaxy, located 10 Mpc away in the Local Void. The system is composed of three previously known dwarf galaxies embedded in a large HI envelope, with a newly discovered fourth member identified through HI and radio continuum emission behind a bright foreground binary. Galaxy D exhibits the highest star formation rate in the group and deviates from the HI mass-diameter relation, suggesting it is a compact, gas-rich dwarf missed due to stellar foreground contamination. The HI data reveal for the first time an extended HI envelope around the whole system, the neutral gas counterpart of the star-forming ring and gas bridges among members, suggesting a more complex interaction history than the previously proposed collisional ring scenario. ESO 179-013 thus provides a rare opportunity to study hierarchical assembly and gas dynamics in underdense environments and demonstrates the power of blind HI surveys in identifying faint members of low-mass compact groups.

The surface densities of star formation, Sigma SFR, in 24 dwarf irregular (dIrr) galaxies from the LITTLE THINGS survey are combined with gas surface densities and midplane pressures to examine the correlations found previously for spiral galaxies. The pressure is the weight of the disk inside the gas layer, including gas, stars, and dark matter, which usually dominates disk gravity in dIrrs. We compare the results to the outer part of M33, which has similar local properties but a slightly higher metallicity, enabling the detection of CO. All the data are convolved to the H I beam, but to study the effects of resolution, the galaxies are examined first with average radial profiles, and then with maps having 1 .'' 5 pixels and 244 pc pixels. The correlations are found to be independent of resolution from 24 to 424 pc. The average ratio of molecular to atomic surface density is estimated to be 0.23 +/- 0.1, from the H2 surface density in M33 compared to the H I surface density at the same Sigma SFR in the dIrrs. With this ratio, the average star formation rate per molecule is about the same for all the dIrrs, and a factor of 2 less than the rate in M33. The pressure in dIrrs is so low that CO is essentially a dense gas tracer, with the same surface density threshold at the low metallicities of dIrrs as HCN has in spiral galaxies. As a result, CO regions in dIrrs should be strongly self-gravitating.

Molecular gas is the key ingredient in the star formation cycle, and tracing its dependencies on other galaxy properties is essential for understanding galaxy evolution. In this work, we explore the relation between the different phases of the interstellar medium (ISM), namely molecular gas, atomic gas, and dust, and galaxy properties using a sample of nearby late-type galaxies. To this end, we collected CO maps that cover at least 70% of the optical extent for 121 galaxies from the DustPedia project, which ensured an accurate determination of MH2, the global molecular gas mass. We investigated which scaling relations provide the best description of MH2, based on the strength of the correlation and its intrinsic dispersion. We found that the commonly used correlations between MH2 and star formation rate (SFR) and stellar mass (Mstar), respectively, are affected by large scatter, which accounts for galaxies that are experiencing quenching of their star formation activity. This issue can be partially mitigated by considering a "fundamental plane" of star formation, fitting together MH2, Mstar, and SFR. We confirm previous results from the DustPedia collaboration that the total gas mass has the tightest connection with the dust mass, and that the molecular component also establishes a good correlation with dust once map-based MH2 estimates are used. Although dust grains are necessary for the formation of hydrogen molecules, the strength of gravitational potential driven by the stellar component plays a key role in driving density enhancements and the atomic-to-molecular phase transition. By investigating the correlations between the various components of the ISM and monochromatic luminosities at different wavelengths, we propose mid- and far-IR luminosities as reliable proxies of LCO(1-0)' for those sources that lack dedicated millimeter observations. Luminosities in mid-IR photometric bands collecting PAH emission can be used to trace molecular gas and dust masses.

We investigate the star formation process across the disk of M33 using a multiwavelength dataset and disk dynamics. We computed numerically equilibrium values of gas densities and scale heights across the disk, taking into account dark matter and testing several analytic approximations that are often used to estimate these variables and the hydrostatic pressure. Orthogonal regressions and hierarchical Bayesian models, as well as random forest (RF) analyses, were used to establish the fundamental relations at physical scales from 160 pc to 1 kpc. The gas pressure, is the main driver of the star formation rate (SFR) surface density throughout the whole star-forming disk of M33. High-pressure regions enhance the atomic-to-molecular gas conversion, with the molecular hydrogen mass surface density being tightly correlated to pressure and a uniform scaling law throughout the M33 disk. The relation between pressure and SFR surface density differs, showing a change in slope from the inner to the outer disk. Scaling laws do not depend on the physical scale and brings out an intrinsic scatter linked to variations in the efficiency and relative age of the molecular gas-to-stars conversion. In the inner disk, where spiral arms are present and the stellar surface density dominates gravity, the pressure and SFR surface densidy establish an almost linear correlation with a smaller dispersion than that of the molecular gas – SFR surface density relation. In the atomic gas-dominated outer disk, the SFR density has a steeper dependence on pressure, which we propose could be the result of an increasing fraction of diffuse molecular gas that does not form stars.

Aims. We investigate the star formation process across M33, which is characterized by a low molecular content and can be sampled with high spatial resolution out to regions where star formation activity drops. Methods. We used a multiwavelength dataset and disk dynamics to extract the local physical parameters across the M33 disk, such as the atomic, molecular, stellar and dust mass surface densities, dark matter densities, and hydrostatic pressure. We computed numerically equilibrium values of gas densities and scale heights across the disk, testing several analytic approximations that are often used to estimate these variables. Orthogonal regressions and hierarchical Bayesian models, as well as random forest (RF) analyses, were used to establish the fundamental relations at physical scales from 160 pc to 1 kpc. Results. The gas hydrostatic pressure, Phy, which balances the local weight, is the main driver of the star formation rate surface density, SigmaSFR, throughout the whole star-forming disk of M33. High-pressure regions enhance the atomic-to-molecular gas conversion, with the molecular hydrogen mass surface density, SigmaH2, being tightly correlated to Phy and a uniform scaling law throughout the M33 disk. The Phy-SigmaSFR relation differs, showing a change in slope from the inner to the outer disk. Our use of an accurate analytic expression and database to compute Phy for a multicomponent disk minimizes observational scatter. This points to scaling laws that do not depend on the physical scale and brings out an intrinsic scatter linked to variations in the efficiency and relative age of the molecular gas-to-stars conversion. In the inner disk, where spiral arms are present and the stellar surface density dominates gravity, Phy and SigmaSFR establish an almost linear correlation with a smaller dispersion than in the SigmaH2-SigmaSFR relation. In the atomic gas-dominated outer disk, SigmaSFR has a steeper dependence on Phy, which we propose could be the result of an increasing fraction of diffuse molecular gas that does not form stars.

We present the extended ALMA MaNGA QUEnching and STar formation survey, a combination of the original 46 ALMaQUEST galaxies plus new ALMA observations for a further 20 interacting galaxies. Three well-studied scaling relations are fit to the 19,999 star-forming spaxels in the extended sample, namely the resolved Schmidt-Kennicutt (rSK) relation, the resolved star forming main sequence (rSFMS) and the resolved molecular gas main sequence (rMGMS). We additionally investigate the relationship between the dynamical equilibrium pressure (PDE) and star formation rate surface density (Sigma_SFR), which we refer to as the resolved PDE (rPDE) relation. Contrary to previous studies that have focussed on normal star-forming galaxies and found an approximately linear rPDE relation, the presence of more vigourously star-forming galaxies in the extended ALMaQUEST sample reveals a marked turnover in the relation at high pressures. Although the scatter around the linear fit to the rPDE relation is similar to the other three relations, a random forest analysis, which can extract non-linear dependences, finds that PDE is unambiguously more important than either Sigma_H2 or Sigma_star for predicting Sigma_SFR. We compare the observed rPDE relation to the prediction of the pressure-regulated feedback-modulated (PRFM) model of star formation, finding that galaxies residing on the global SFMS do indeed closely follow the rPDE relation predicted by the PRFM theory. However, galaxies above and below the global SFMS show significant deviations from the model. Galaxies with high SFR are instead consistent with models that include other contributions to turbulence in addition to the local star formation feedback.

We investigate a possible close encounter between M33 and M31 in the past to understand the role of galaxy-galaxy interactions in shaping the matter distribution in galaxy outskirts. We recovered possible orbital trajectories of M33, M31 and the Milky Way in the past, which are compatible with the Early Third Data Release of the Gaia mission and with mass estimates of Local Group spirals, after tuning mass losses and the dynamical friction term with the help of N-body numerical simulations. A close encounter of M33 and M31 in the past has a low but non-negligible probability. If the two galaxies had been closer in the past, their minimum distance would be of the order of 100 kpc or larger, and this happened earlier than 3 Gyr ago. During this encounter, 35-40% of the dark matter mass of M33 might have been removed from the halo due to tidal stripping. A detailed comparison of the results of test-particle simulations with the observed disk warp or with the spatial distribution of candidate dark satellites of M33 suggests that a closer passage of M33 around M31 cannot, however, be responsible for the observed morphological features. We suggest that more recent gas accretion events, possibly from a cosmic filament, might cause the misalignment of the outer disk of M33 after the rapid inner disk formation.

We carry out sensitive searches for the CO J=1-0 and J=2-1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas metallicities are close to solar but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations. We use the IRAM-30m telescope to observe eleven regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached a spectral noise between 1 and 5 mK for at least one observed frequencies at 2 km/s spectral resolution. We marginally detect two CO J=1-0 lines in the star forming region Clump 1 of the Leo ring, whose radial velocities are consistent with those of Halpha lines but line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths and the extremely low number densities suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt-Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.

ABSTRACT Studying the interplay between massive star formation and the interstellar medium (ISM) is paramount to understand the evolution of galaxies. Radio continuum (RC) emission serves as an extinction-free tracer of both massive star formation and the energetic components of the ISM. We present a multiband RC survey of the Local Group galaxy M 33 down to ≃30 pc linear resolution observed with the Karl G. Jansky Very Large Array (VLA). We calibrate the star formation rate surface density and investigate the impact of diffuse emission on this calibration using a structural decomposition. Separating the thermal and non-thermal emission components, the correlation between different phases of the ISM, and the impact of massive star formation are being investigated. Radio sources with sizes ≲200 pc constitute about 36 per cent (46 per cent) of the total RC emission at 1.5 GHz (6.3 GHz) in the inner 18 × 18 arcmin2 (or 4 kpc × 4 kpc) disc of M 33. The non-thermal spectral index becomes flatter with increasing star formation rate surface density, indicating the escape of cosmic ray electrons from their birth places. The magnetic field strength also increases with star formation rate following a bi-modal relation, indicating that the small-scale turbulent dynamo acts more efficiently at higher luminosities and star formation rates. Although the correlations are tighter in star-forming regions, the non-thermal emission is also correlated with the more quiescent molecular gas in the ISM. An almost linear molecular star formation law exists in M 33 when excluding diffuse structures. Massive star formation amplifies the magnetic field and increases the number of high-energy cosmic ray electrons, which can help the onset of winds and outflows.

Context. The far-infrared (FIR) and sub-millimeter (submm) emissivity, ϵν, of the Milky Way (MW) cirrus is an important benchmark for dust grain models. Dust masses in other galaxies are generally derived from the FIR/submm using the emission properties of these MW-calibrated models. Aims. We seek to derive the FIR/submm ϵν in nine nearby spiral galaxies to check its compatibility with MW cirrus measurements. Methods. We obtained values of ϵν at 70–500 μm, using maps of dust emission from the Herschel satellite and of gas surface density from the THINGS and HERACLES surveys on a scale generally corresponding to 440 pc. We studied the variation of ϵν with the surface brightness ratio Iν(250 μm)/Iν(500 μm), a proxy for the intensity of the interstellar radiation field heating the dust. Results. We find that the average value of ϵν agrees with MW estimates for pixels sharing the same color as the cirrus, namely, for Iν(250 μm)/Iν(500 μm)=4.5. For Iν(250 μm)/Iν(500 μm)> 5, the measured emissivity is instead up to a factor ∼2 lower than predicted from MW dust models heated by stronger radiation fields. Regions with higher Iν(250 μm)/Iν(500 μm) are preferentially closer to the galactic center and have a higher overall (stellar+gas) surface density and molecular fraction. The results do not depend strongly on the adopted CO-to-molecular conversion factor and do not appear to be affected by the mixing of heating conditions. Conclusions. Our results confirm the validity of MW dust models at low density, but are at odds with predictions for grain evolution in higher density environments. If the lower-than-expected ϵν at high Iν(250 μm)/Iν(500 μm) is the result of intrinsic variations in the dust properties, it would imply an underestimation of the dust mass surface density of up to a factor ∼2 when using current dust models.

Aims. We perform a homogeneous analysis of an unprecedented set of spatially resolved scaling relations (SRs) between interstellar medium (ISM) components, that is to say dust, gas, and gas-phase metallicity, and other galaxy properties, such as stellar mass ( M star ), total baryonic content, and star-formation rate (SFR), in a range of physical scales between 0.3 and 3.4 kpc. We also study some ratios between galaxy components: dust-to-stellar, dust-to-gas, and dust-to-metal ratios. Methods. We use a sample of 18 large, spiral, face-on DustPedia galaxies. The sample consists of galaxies with spatially resolved dust maps corresponding to 15 Herschel -SPIRE 500 μm resolution elements across the optical radius, with the morphological stage spanning from T = 2 to 8, M star from 2 × 10 9 to 1 × 10 11 M ⊙ , SFR from 0.2 to 13 M ⊙ yr −1 , and oxygen abundance from 12 + log(O/H) = 8.3 to 8.8. Results. All the SRs are moderate or strong correlations except the dust-H I SR that does not exist or is weak for most galaxies. The SRs do not have a universal form but each galaxy is characterized by distinct correlations, affected by local processes and galaxy peculiarities. The SRs hold, on average, starting from the scale of 0.3 kpc, and if a breaking down scale exists it is below 0.3 kpc. By evaluating all galaxies together at the common scale of 3.4 kpc, differences due to peculiarities of individual galaxies are cancelled out and the corresponding SRs are consistent with those of whole galaxies. By comparing subgalactic and global scales, the most striking result emerges from the SRs involving ISM components: the dust-total gas SR is a good correlation at all scales, while the dust-H 2 and dust-H I SRs are good correlations at subkiloparsec/kiloparsec and total scales, respectively. For the other explored SRs, there is a good agreement between small and global scales and this may support the picture where the main physical processes regulating the properties and evolution of galaxies occur locally. In this scenario, our results are consistent with the hypothesis of self-regulation of the star-formation process. The analysis of subgalactic ratios between galaxy components shows that they are consistent with those derived for whole galaxies, from low to high redshift, supporting the idea that also these ratios could be set by local processes. Conclusions. Our results highlight the heterogeneity of galaxy properties and the importance of resolved studies on local galaxies in the context of galaxy evolution. They also provide fundamental observational constraints to theoretical models and updated references for high-redshift studies.

Chemical abundances in the Leo ring, the largest HI cloud in the local Universe, have recently been determined to be close or above solar, incompatible with a previously claimed primordial origin of the ring. The gas, pre-enriched in a galactic disk and tidally stripped, did not manage to form stars very efficiently in intergalactic space. We map nebular lines in 3 dense HI clumps of the Leo ring and complement these data with archival stellar continuum observations to investigate the slow building up of a sparse population of stars in localized areas of the ring. Individual young stars as massive as O7-types are powering some HII regions. The average star formation rate density is of order of 10^-5 Msun/yr/kpc^2 and proceeds with local bursts a few hundred parsecs in size, where loose stellar associations of 500-1000 Msun occasionally host massive outliers. The far ultraviolet-to-Halpha emission ratio in nebular regions implies recent stellar bursts, from 2 to 7 Myr ago. The relation between the local HI gas density and the star formation rate in the ring is similar to what is found in dwarfs and outer disks with gas depletion times as long as 100 Gyrs. We find a candidate planetary nebula in a compact and faint Halpha region with [OIII]/Halpha line enhancement, consistent with the estimated mean stellar surface brightness of the ring. The presence of 1 kpc partial ring emitting weak Halpha lines around the brightest and youngest HII region suggests that local shocks might be the triggers of new star forming events.

The origin and fate of the most extended extragalactic neutral cloud known in the local Universe, the Leo ring, is still debated 38 years after its discovery. Its existence is alternatively attributed to leftover primordial gas with some low level of metal pollution versus enriched gas stripped during a galaxy-galaxy encounter. Taking advantage of MUSE (Multi Unit Spectroscopic Explorer) operating at the VLT, we performed optical integral field spectroscopy of 3 HI clumps in the Leo ring where ultraviolet continuum emission has been found. We detected, for the first time, ionized hydrogen in the ring and identify 4 nebular regions powered by massive stars. These nebulae show several metal lines ([OIII],[NII],[SII]) which allowed reliable measures of metallicities, found to be close to or above the solar value. Given the faintness of the diffuse stellar counterparts, less than 3 percent of the observed heavy elements could have been produced locally in the main body of the ring and not much more than 15 percent in the HI clump towards M96. This inference, and the chemical homogeneity among the regions, convincingly demonstrates that the gas in the ring is not primordial, but has been pre-enriched in a galaxy disk, then later removed and shaped by tidal forces and it is forming a sparse population of stars.

The origin of the most extended intergalactic cloud of the local Universe, the Leo ring, has been debated for about 40 years. It has a gas mass equivalent to that of a galaxy but no extended optical counterpart. Recent observations with integral field spectroscopy have localized small star formation sites with young, massive stars in the cloud. The light from the hot gas in their proximity has the footprints of heavy elements with abundances close to solar ones, unveiling the long-standing mystery of the origin of this giant ring.

Aims. We investigate thermal and nonthermal radio emission associated with the early formation and evolution phases of young stellar clusters (YSCs) selected by their mid-infrared (MIR) emission at 24 μm in M 33. We consider regions in their early formation period, which are compact and totally embedded in the molecular cloud, and in the more evolved and exposed phase. Methods. Thanks to recent radio continuum surveys between 1.4 and 6.3 GHz we are able to find radio source counterparts to more than 300 star forming regions of M 33. We identify the thermal free–free component for YSCs and their associated molecular complexes using the Hα line emission. Results. A cross-correlation of MIR and radio continuum is established from bright to very faint sources, with the MIR-to-radio emission ratio that shows a slow radial decline throughout the M 33 disk. We confirm the nature of candidate embedded sources by recovering the associated faint radio continuum luminosities. By selecting exposed YSCs with reliable Hα flux, we establish and discuss the tight relation between Hα and the total radio continuum at 5 GHz over four orders of magnitude. This holds for individual YSCs as well as for the giant molecular clouds hosting them, and allows us to calibrate the radio continuum–star formation rate relation at small scales. On average, about half of the radio emission at 5 GHz in YSCs is nonthermal with large scatter. For exposed but compact YSCs and their molecular clouds, the nonthermal radio continuum fraction increases with source brightness, while for large HII regions the nonthermal fraction is lower and shows no clear trend. This has been found for YSCs with and without identified supernova remnants and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.

Aims. The purpose of this work is the characterization of the main scaling relations between all of the interstellar medium (ISM) components, namely dust, atomic, molecular, and total gas, and gas-phase metallicity, as well as other galaxy properties, such as stellar mass (Mstar) and galaxy morphology, for late-type galaxies in the Local Universe.Methods. This study was performed by extracting late-type galaxies from the entire DustPedia sample and by exploiting the large and homogeneous dataset available thanks to the DustPedia project. The sample consists of 436 galaxies with morphological stage spanning from T = 1−10, Mstar from 6 × 107 to 3 × 1011 M⊙, star formation rate from 6 × 10−4 to 60 M⊙ yr−1, and oxygen abundance from 12 + log(O/H) = 8−9.5. Molecular and atomic gas data were collected from the literature and properly homogenized. All the masses involved in our analysis refer to the values within the optical disks of galaxies. The scaling relations involving the molecular gas are studied by assuming both a constant and a metallicity-dependent CO-to-H2 conversion factor (XCO). The analysis was performed by means of the survival analysis technique, in order to properly take into account the presence of both detection and nondetection in the data.Results. We confirm that the dust mass correlates very well with the total gas mass, and find –for the first time– that the dust mass correlates better with the atomic gas mass than with the molecular one. We characterize important mass ratios such as the gas fraction, the molecular-to-atomic gas mass ratio, the dust-to-total gas mass ratio (DGR), and the dust-to-stellar mass ratio, and study how they relate to each other, to galaxy morphology, and to gas-phase metallicity. Only the assumption of a metallicity-dependent XCO reproduces the expected decrease of the DGR with increasing morphological stage and decreasing gas-phase metallicity, with a slope of about 1. The DGR, the gas-phase metallicity, and the dust-to-stellar mass ratio are, for our galaxy sample, directly linked to galaxy morphology. The molecular-to-atomic gas mass ratio and the DGR show a positive correlation for low molecular gas fractions, but for galaxies rich in molecular gas this trend breaks down. To our knowledge, this trend has never been found before, and provides new constraints for theoretical models of galaxy evolution and a reference for high-redshift studies. We discuss several scenarios related to this finding.Conclusions. The DustPedia database of late-type galaxies is an extraordinary tool for the study of the ISM scaling relations, thanks to its homogeneous collection of data for the different ISM components. The database is made publicly available to the whole community.

We carried out deep searches for CO line emission in the outer disk of M 33, at R > 7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular cloud throughout the disk of M 33. We used the IRAM-30 m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M 33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M 33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R > 7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7 +/- 0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.