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The dust mass absorption coefficient, κd is the conversion function used to infer physical dust masses from observations of dust emission. However, it is notoriously poorly constrained, and it is highly uncertain how it varies, either between or within galaxies. Here we present the results of a proof-of-concept study, using the DustPedia data for two nearby face-on spiral galaxies M 74 (NGC 628) and M 83 (NGC 5236), to create the first ever maps of κd in galaxies. We determine κd using an empirical method that exploits the fact that the dust-to-metals ratio of the interstellar medium is constrained by direct measurements of the depletion of gas-phase metals. We apply this method pixel-by-pixel within M 74 and M 83, to create maps of κd. We also demonstrate a novel method of producing metallicity maps for galaxies with irregularly sampled measurements, using the machine learning technique of Gaussian process regression. We find strong evidence for significant variation in κd. We find values of κd at 500  |$\mu$| m spanning the range 0.11–0.25  |${\rm m^{2}\, kg^{-1}}$| in M 74, and 0.15–0.80  |${\rm m^{2}\, kg^{-1}}$| in M 83. Surprisingly, we find that κd shows a distinct inverse correlation with the local density of the interstellar medium. This inverse correlation is the opposite of what is predicted by standard dust models. However, we find this relationship to be robust against a large range of changes to our method – only the adoption of unphysical or highly unusual assumptions would be able to suppress it. [ABSTRACT FROM AUTHOR]

Aims. We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods. We used Herschel observations and atomic and molecular gas masses to estimate ϵ(250 μm), the disc-averaged dust emissivity at 250 μm, and from this, the absorption cross section per H atom σ(250 μm) and per dust mass κ(250 μm). The emissivity ϵ(250 μm) requires one assumption, which is the CO-to-H2 conversion factor, and the dust temperature is additionally required for σ(250 μm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for κ(250 μm). Results. We find ϵ(250 μm) = 0.82 ± 0.07 MJy sr−1 (1020 H cm−2)−1 for galaxies with 4 <  F(250 μm)/F(500 μm) < 5. This depends only weakly on the adopted CO-to-H2 conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, for F(250 μm)/F(500 μm) > 6, ϵ(250 μm) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values for σ(250 μm) and κ(250 μm) at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made. [ABSTRACT FROM AUTHOR]

We use a sub-set of the DustPedia galaxy sample (461 galaxies) to investigate the effect the environment has had on galaxies. We consider Virgo cluster and field samples and also assign a density contrast parameter to each galaxy, as defined by the local density of SDSS galaxies. We consider their chemical evolution (using MDust/MBaryon and MGas/MBaryon), their specific star formation rate (SFR/MStars), star formation efficiency (SFR/MGas), stars-to-dust mass ratio (MStars/MDust), gas-to-dust mass ratio (MGas/MDust) and the relationship between star formation rate per unit mass of dust and dust temperature (SFR/MDust and TDust). Late type galaxies (later than Sc) in all of the environments can be modelled using simple closed box chemical evolution and a simple star formation history (SFR(t) ∝ t exp−t/τ). For earlier type galaxies the physical mechanisms that give rise to their properties are clearly much more varied and require a more complicated model (mergers, gas in or outflow). However, we find little or no difference in the properties of galaxies of the same morphological type within the cluster, field or with different density contrasts. It appears that it is morphology, how and whenever this is laid down, and consistent internal physical processes that primarily determine the derived properties of galaxies in the DustPedia sample and not processes related to differences in the local environment. [ABSTRACT FROM AUTHOR]

The stellar initial mass function (IMF) regulates the baryonic cycle within galaxies, and is a key ingredient for translating observations into physical quantities. Although it was assumed to be universal for decades, there is now growing observational evidence showing that the center of massive early-type galaxies hosts a larger population of low-mass stars than is expected based on observations from the Milky Way. Moreover, these variations in the IMF have been found to be related to radial metallicity variations in massive galaxies. We present here a two-dimensional stellar population analysis of the massive lenticular galaxy FCC 167 (NGC 1380) as part of the Fornax3D project. Using a newly developed stellar population fitting scheme, we derive a full two-dimensional IMF map of an early-type galaxy. This two-dimensional analysis allows us go further than a radial analysis, showing how the metallicity changes along a disk-like structure while the IMF follows a distinct, less disky distribution. Thus, our findings indicate that metallicity cannot be the sole driver of the observed radial IMF variations. In addition, a comparison with the orbital decomposition shows suggestive evidence of a coupling between stellar population properties and the internal dynamical structure of FCC 167, where metallicity and IMF maps seem to track the distribution of cold and warm orbits, respectively. [ABSTRACT FROM AUTHOR]

Observations of evolution in the dust-to-metal ratio allow us to constrain the dominant dust processing mechanisms. In this work, we present a study of the dust-to-metal and dust-to-gas ratios in a sub-sample of ~500 DustPedia galaxies. Using literature and MUSE emission line fluxes, we derived gas-phase metallicities (oxygen abundances) for over 10 000 individual regions and determine characteristic metallicities for each galaxy. We study how the relative dust, gas, and metal contents of galaxies evolve by using metallicity and gas fraction as proxies for evolutionary state. The global oxygen abundance and nitrogen-to-oxygen ratio are found to increase monotonically as galaxies evolve. Additionally, unevolved galaxies (gas fraction >60%, metallicity 12 + log(O∕H) < 8.2) have dust-to-metal ratios that are about a factor of 2.1 lower (a factor of six lower for galaxies with gas fraction >80%) than the typical dust-to-metal ratio (Md∕MZ ~ 0.214) for more evolved sources. However, for high gas fractions, the scatter is larger due to larger observational uncertainties as well as a potential dependence of the dust grain growth timescale and supernova dust yield on local conditions and star formation histories. We find chemical evolution models with a strong contribution from dust grain growth describe these observations reasonably well. The dust-to-metal ratio is also found to be lower for low stellar masses and high specific star formation rates (with the exception of some sources undergoing a starburst). Finally, the metallicity gradient correlates weakly with the HI-to-stellar mass ratio, the effective radius and the dust-to-stellar mass ratio, but not with stellar mass. [ABSTRACT FROM AUTHOR]

Most radiative transfer models assume that dust in spiral galaxies is distributed exponentially. In this paper our goal is to verify this assumption by analysing the two-dimensional large-scale distribution of dust in galaxies from the DustPedia sample. For this purpose, we have made use of Herschel imaging in five bands, from 100 to 500 μm, in which the cold dust constituent is primarily traced and makes up the bulk of the dust mass in spiral galaxies. For a subsample of 320 disc galaxies, we successfully performed a simultaneous fitting with a single Sérsic model of the Herschel images in all five bands using the multi-band modelling code GALFITM. We report that the Sérsic index n, which characterises the shape of the Sérsic profile, lies systematically below 1 in all Herschel bands and is almost constant with wavelength. The average value at 250 μm is 0.67 ± 0.37 (187 galaxies are fitted with n250 ≤ 0.75, 87 galaxies have 0.75 < n250 ≤ 1.25, and 46 – with n250 >  1.25). Most observed profiles exhibit a depletion in the inner region (at r <  0.3−0.4 of the optical radius r25) and are more or less exponential in the outer part. We also find breaks in the dust emission profiles at longer distances (0.5−0.6) r25 which are associated with the breaks in the optical and near-infrared. We assumed that the observed deficit of dust emission in the inner galaxy region is related to the depression in the radial profile of the HI surface density in the same region because the atomic gas reaches high enough surface densities there to be transformed into molecular gas. If a galaxy has a triggered star formation in the inner region (for example, because of a strong bar instability, which transfers the gas inwards to the centre, or a pseudobulge formation), no depletion or even an excess of dust emission in the centre is observed. [ABSTRACT FROM AUTHOR]

The Herschel Space Observatory has had a tremendous impact on the study of extragalactic dust. Specifically, early-type galaxies (ETG) have been the focus of several studies. In this paper, we combine results from two Herschel studies - a Virgo cluster study Herschel Virgo Cluster Survey (HeViCS) and a broader, low-redshift Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS)/Galaxy and Mass Assembly (GAMA) study - and contrast the dust and associated properties for similar mass galaxies. This comparison is motivated by differences in results exhibited between multiple Herschel studies of ETG. A comparison between consistent modified blackbody derived dust mass is carried out, revealing strong differences between the two samples in both dust mass and dust-to-stellar mass ratio. In particular, the HeViCS sample lacks massive ETG with as high a specific dust content as found in H-ATLAS. This is most likely connected with the difference in environment for the two samples. We calculate nearest neighbour environment densities in a consistent way, showing that H-ATLAS ETG occupy sparser regions of the local Universe, whereas HeViCS ETG occupy dense regions. This is also true for ETG that are not Herschel-detected but are in the Virgo and GAMA parent samples. Spectral energy distributions are fit to the panchromatic data. From these, we find that in H-ATLAS the specific star formation rate anticorrelates with stellar mass and reaches values as high as in our Galaxy. On the other hand HeViCS ETG appear to have little star formation. Based on the trends found here, H-ATLAS ETG are thought to have more extended star formation histories and a younger stellar population than HeViCS ETG. [ABSTRACT FROM AUTHOR]

We examined variations in the 160/250 and 250/350 μm surface brightness ratios within 24 nearby (<30 Mpc) face-on spiral galaxiesobserved with the Herschel Space Observatory to identify the heating mechanisms for dust emitting at these wavelengths. The analysis consisted of both qualitative and quantitative comparisons of the 160/250 and 250/350 μm ratios to Hα and 24 μm emission, which trace the light from star-forming regions, and 3.6 μm emission, which traces the light from the older stellar populations of the galaxies. We find broad variations in the heating mechanisms for the dust. In one subset of galaxies, we found evidence that emission at ≤160 μm (and in rare cases potentially at ≤350 μm) originates from dust heated by star-forming regions. In another subset, we found that the emission at ≥250 μm (and sometimes at ≥160 μm) originates from dust heated by the older stellar population. In the rest of the sample, either the results are indeterminate or both of these stellar populations may contribute equally to the global dust heating. The observed variations in dust heating mechanisms do not necessarily match what has been predicted by dust emission and radiative transfer models, which could lead to overestimated dust temperatures, underestimated dust masses, false detections of variability in dust emissivity, and inaccurate star formation rate measurements. [ABSTRACT FROM AUTHOR]

We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby, edge-on spiral galaxy, NGC 891: [Cii] 158 μm, [Nii] 122, 205 μm, [Oi] 63, 145 μm, and [Oiii] 88 μm. We find that the photoelectric heating efficiency of the gas, traced via the ([Cii]+[Oi]63)/FTIR ratio, varies from a mean of 3.5 × 10-3 in the centre up to 8 × 10-3 at increasing radial and vertical distances in the disc. A decrease in ([Cii]+[Oi]63)/FTIR but constant ([Cii]+[Oi]63)/FPAH with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, G0. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891's disc have hydrogen densities of 1 < log?(n/ cm-3) < 3.5 experiencing an incident FUV radiation field with strengths of 1.7 < log?G0 < 3. Although these values we derive for most of the disc are consistent with the gas properties found in PDRs in the spiral arms and inter-arm regions of M?51, observed radial trends in n and G0 are shown to be sensitive to varying optical thickness in the lines, demonstrating the importance of accurately accounting for optical depth effects when interpreting observations of high inclination systems. Increasing the coverage of our analysis by using an empirical relationship between the MIPS 24 μm and [Nii] 205 μm emission, we estimate an enhancement of the FUV radiation field strength in the far north-eastern side of the disc relative to the rest of the disc that coincides with the above-average star formation rate surface densities and gas-to-dust ratios. However, an accurate interpretation remains difficult due to optical depth effects, confusion along the line-of-sight and observational uncertainties. [ABSTRACT FROM AUTHOR]

Observations of evolution in the dust-to-metal ratio allow us to constrain the dominant dust processing mechanisms. In this work, we present a study of the dust-to-metal and dust-to-gas ratios in a sub-sample of ~500 DustPedia galaxies. Using literature and MUSE emission line fluxes, we derived gas-phase metallicities (oxygen abundances) for over 10 000 individual regions and determine characteristic metallicities for each galaxy. We study how the relative dust, gas, and metal contents of galaxies evolve by using metallicity and gas fraction as proxies for evolutionary state. The global oxygen abundance and nitrogen-to-oxygen ratio are found to increase monotonically as galaxies evolve. Additionally, unevolved galaxies (gas fraction >60%, metallicity 12 + log(O∕H) < 8.2) have dust-to-metal ratios that are about a factor of 2.1 lower (a factor of six lower for galaxies with gas fraction >80%) than the typical dust-to-metal ratio (Md∕MZ ~ 0.214) for more evolved sources. However, for high gas fractions, the scatter is larger due to larger observational uncertainties as well as a potential dependence of the dust grain growth timescale and supernova dust yield on local conditions and star formation histories. We find chemical evolution models with a strong contribution from dust grain growth describe these observations reasonably well. The dust-to-metal ratio is also found to be lower for low stellar masses and high specific star formation rates (with the exception of some sources undergoing a starburst). Finally, the metallicity gradient correlates weakly with the HI-to-stellar mass ratio, the effective radius and the dust-to-stellar mass ratio, but not with stellar mass. [ABSTRACT FROM AUTHOR]

In this paper we present a catalog of giant molecular clouds (GMCs) in the Andromeda (M31) galaxy extracted from the Herschel Exploitation of Local Galaxy Andromeda (HELGA) data set. GMCs are identified from the Herschel maps using a hierarchical source extraction algorithm. We present the results of this new catalog and characterize the spatial distribution and spectral energy properties of its clouds based on the radial dust/gas properties found by Smith et al. A total of 326 GMCs in the mass range 104-107M☼ are identified; their cumulative mass distribution is found to be proportional to M–2.34, in agreement with earlier studies. The GMCs appear to follow the same correlation of cloud mass to LCO observed in the Milky Way. However, comparison between this catalog and interferometry studies also shows that the GMCs are substructured below the Herschel resolution limit, suggesting that we are observing associations of GMCs. Following Gordon et al., we study the spatial structure of M31 by splitting the observed structure into a set of spiral arms and offset rings. We fit radii of 10.3 and 15.5 kpc to the two most prominent rings. We then fit a logarithmic spiral with a pitch angle of 8.°9 to the GMCs not associated with either ring. Last, we comment on the effects of deprojection on our results and investigate the effect different models for M31's inclination will have on the projection of an unperturbed spiral arm system. [ABSTRACT FROM AUTHOR]