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We present the Catalogue of High Resolution Spectra of Obscured Sources (CHRESOS) from the XMM-Newton Science Archive. It comprises the emission-line luminosities of H- and He-like transitions from C to Si, and the Fe 3C and Fe 3G L-shell ones. Here, we concentrate on the soft X-ray OVII (f) and OVIII Lyα emission lines to shed light on to the physical processes with which their formation can be related to active galactic nucleus (AGN) versus star-forming regions. We compare their luminosity with that of two other important oxygen key lines [O III]lambda 5007 Å, in the optical, and [O IV] 25.89 mu m, in the infrared (IR). We also test OVII (f) and OVIII Lyα luminosities against that of continuum bands in the IR and hard X-rays, which point to different ionization processes. We probe into those processes by analysing photoionization and collisional ionization model predictions upon our lines. We show that both scenarios can explain the formation and observed intensities of OVII (f) and OVIII Lyα. By analysing the relationships between OVII (f) and OVIII Lyα, and all other observables: [OIII]lambda 5007 Å, [O IV] 25.89 mu m emission lines, and mid-infrared (MIR) 12 mu m, far-infrared (FIR) 60 and 100 mu m, 2-10 and 14-195 keV continuum bands, we conclude that the AGN radiation field is mainly responsible of the soft X-ray oxygen excitation., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Interstellar dust absorbs stellar light very efficiently and thus shapes the energetic output of galaxies. Studying the impact of different stellar populations on the dust heating remains hard because it requires decoupling the relative geometry of stars and dust, and involves complex processes as scattering and non-local dust heating. We aim to constrain the relative distribution of dust and stellar populations in the spiral galaxy M81 and create a realistic model of the radiation field that describes the observations. Investigating the dust-starlight interaction on local scales, we want to quantify the contribution of young and old stellar populations to the dust heating. We aim to standardise the setup and model selection of such inverse radiative transfer simulations so this can be used for comparable modelling of other nearby galaxies. We present a semi-automated radiative transfer modelling pipeline that implements the necessary steps such as the geometric model construction and the normalisation of the components through an optimisation routine. We use the Monte Carlo radiative transfer code SKIRT to calculate a self-consistent, panchromatic model of the interstellar radiation field. By looking at different stellar populations independently, we can quantify to what extent different stellar age populations contribute to the dust heating. Our method takes into account the effects of non-local heating. We obtain a realistic 3D radiative transfer model of the face-on galaxy M81. We find that only 50.2\% of the dust heating can be attributed to young stellar populations. We confirm a tight correlation between the specific star formation rate and the heating fraction by young stellar populations, both in sky projection and in 3D, also found for radiative transfer models of M31 and M51. We conclude that... (abridged), 23 pages, 16 figures, accepted for publication in A&A

The Radiation Explorer in the Far Infrared – Prototype for Applications and Development (REFIR-PAD) is a Fourier transform spectroradiometer that has been designed to operate from both stratospheric balloon platforms and the ground. It has been successfully deployed in a stratospheric balloon flight and several ground-based campaigns from high-altitude sites, including the current installation at the Italian–French Concordia Antarctic station. The instrument is capable of operating autonomously with only a limited need of remote control and monitoring and provides a multiyear dataset of spectrally resolved atmospheric downwelling radiances, measured in the 100–1500 cm−1 spectral range with 0.4 cm−1 resolution and a radiometric uncertainty of better than 0.85 mW(m2srcm-1)-1.

In this paper, we investigate the physical associations between blended far-infrared (FIR)-emitting galaxies, in order to identify the level of line-of-sight projection contamination in the single-dish Herschel data. Building on previous work, and as part of the Herschel Extragalactic Legacy Project (HELP), we identify a sample of galaxies in the COSMOS field which are found to be both FIR-bright (typically $\sim 15$ mJy) and blended within the Herschel 250 $\mu$m beam. We identify a spectroscopic or photometric redshift for each FIR-bright source. We conduct a joint probability distribution analysis on the redshift probability density functions to determine the fraction of the FIR sources with multiple FIR-bright counterparts which are likely to be found at consistent ($\Delta z$ $< 0.01$) redshifts. We find that only 3 (0.4 per cent) of the pair permutations between counterparts are $>50$ per cent likely to be at consistent redshifts. A majority of counterparts (72 per cent) have no overlap in their redshift probability distributions whatsoever. This is in good agreement with the results of recent simulations, which indicate that single-dish observations of the FIR sky should be strongly contaminated by line of sight projection effects. We conclude that for our sample of 3.6- and 24-$\mu$m selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multi-component FIR systems are line of sight projections within the 18.1 arcsec Herschel beam, rather than physical associations., Comment: Accepted for publication in MNRAS. 12 pages excluding Appendix; 16 pages total. 6 figures, 3 tables

We present results from a deep 2'x3' (comoving scale of 3.7 Mpc x 5.5 Mpc at z=3) survey at 1.1 mm taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 micro-Jy/beam at a spatial resolution of 0".7. We detect 18 robust ALMA sources at a signal-to-noise ratio (SNR) > 5. Comparison between the ALMA map and a 1.1 mm map taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE) indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least ten of our 18 ALMA SMGs have spectroscopic redshifts of z = 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with SNR > 10 have a median intrinsic angular size of 0".32+0".13-0".06 (2.4+1.0-0.4 physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected the source counts show a possible excess compared to the counts in the general fields at S_1.1mm >= 1.0 mJy due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies., 16 pages, 11 figures, accepted for publication in ApJ

We study the correlation between far-infared/submm dust emission and atomic gas column density in order to derive the properties of the high Galactic latitude, low density, Milky Way cirrus in the foreground of the Virgo cluster of galaxies. Dust emission maps from 60 to 850 um are obtained from SPIRE observations carried out within the Herschel Virgo Cluster Survey, complemented by IRAS-IRIS and Planck-HFI maps. Data from the Arecibo legacy Fast ALFA Survey is used to derive atomic gas column densities for two broad velocity components, low and intermediate velocity clouds. Dust emissivities are derived for each gas component and each far-infared/submm band. For the low velocity clouds, we measure an average emissivity 0.79 +/- 0.08 times 1E-20 MJy sr^-1 cm^2 at 250 um. After fitting a modified blackbody to the available bands, we estimated a dust absorption cross-section 0.49 +/- 0.13 times 1E-25 cm^2 H^-1 at 250 um (with dust temperature T = 20.4 +/- 1.5 K and spectral index beta = 1.53 +/- 0.17). The results are in excellent agreement with those obtained by Planck over a much larger coverage of the high Galactic latitude cirrus (50% of the sky vs 0.2% in our work). For dust associated with intermediate velocity gas, we confirm earlier Planck results and find a higher temperature and lower emissivity and cross-section. After subtracting the modelled components, we find regions at scales smaller than 20' where the residuals deviate significantly from the average, cosmic-infrared-background dominated, scatter. These large residuals are most likely due to local variations in the cirrus dust properties (and/or the dust/atomic-gas correlation) or to high-latitude molecular clouds with average N_H2, Comment: 25 pages, 19 figures, A&A accepted

The quantity of dust in a spiral disk can be estimated using the dust's typical emission or the extinction of a known source. In this paper we compare two techniques, one based on emission and one on absorption, applied to sections of 14 disk galaxies. The two measurements reflect, respectively, the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small-scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative contributions of different stellar populations, and dust emissivity are all free parameters in galaxy spectral energy distribution ( SED) models; they are also sometimes degenerate, depending on wavelength coverage. Our aim is to constrain the typical ISM geometry. The apparent optical depth measurement comes from the number of distant galaxies seen in Hubble Space Telescope (HST) images through the foreground disk, calibrated with the synthetic field method (SFM). We discuss what can be learned from the SFM measurement alone regarding ISM geometry. We measure the IR flux in images from the Spitzer Infrared Nearby Galaxy Survey in the same section of the disk that was covered by HST. A physical model of the dust is fit to the SED to estimate the dust surface density, mean temperature, and brightness in these disk sections. The surface density is subsequently converted into the average optical depth estimate. The two measurements generally agree, and the SED model finds mostly cold dust ( T

The opacity of spiral galaxy disks, from counts of distant galaxies, is compared to HI column densities. The opacity measurements are calibrated using the ``Synthetic Field Method'' from Gonzalez et al (1998) and Holwerda et al. (2005a). When compared for individual disks, the HI column density and dust opacity do not seem to be correlated as HI and opacity follow different radial profiles. To improve statistics, an average radial opacity profile is compared to an average HI profile. Compared to dust-to-HI estimates from the literature, more extinction is found in this profile. This difference may be accounted for by an underestimate of the dust in earlier measurements due to their dependence on dust temperature. Since the SFM is insensitive to the dust temperature, the ratio between the SFM opacity and HI could very well be indicative of the true ratio. Earlier claims for a radially extended cold dust disk were based on sub-mm observations. A comparison between sub-mm observations and counts of distant galaxies is therefore desirable. We present the best current example of such a comparison, M51, for which the measurements seem to agree. However, this remains an area where improved counts of distant galaxies, sub-mm observations and our understanding of dust emissivity are needed., 8 pages, 5 figures, 1 table, accepted by A&A

Deep far-infrared (FIR) imaging data obtained with ISOPHOT at 90 mum, 150 mum, and 200 mum detected the thermal emission from cold dust in the northern shell region of NGC5128 (Centaurus A), where previously neutral hydrogen and molecular gas has been found. A somewhat extended FIR emission region is present in both the 150 mum and 200 mum map, while only an upper flux limit could be derived from the 90 mum data. The FIR spectral energy distribution can be reconciled with a modified blackbody spectrum with very cold dust color temperatures and emissivity indices in the range 13K beta > 1, respectively, where the data favor the low temperature end. A representative value for the associated dust mass is M(Dust) approximate to 7 x 10(4) M(.), which together with the HI gas mass gives a gas-to-dust ratio of approximate to300, close the average values of normal inactive spiral galaxies. This value, in conjunction with the atomic to molecular gas mass ratio typical for a spiral galaxy, indicates that the interstellar medium (ISM) from the inner part of a captured disk galaxy is likely the origin of the outlying gas and dust. These observations are in agreement with recent theoretical considerations that in galaxy interactions leading to stellar shell structures the less dissipative clumpy component of the ISM from the captured galaxy can lead to gaseous shells. Alternatively, the outlying gas and dust could be a rotating ring structure resulting from an interaction or even late infall of tidal material of a merger in the distant past. With all three components ( atomic gas, molecular gas, dust) of the ISM present in the northern shell region, local star formation may account for the chains of young blue stars surrounding the region to the east and north. The dust cloud may also be involved in the disruption of the large scale radio jet before entering the brighter region of the northern radio lobe.

The symbiosis of nuclear activity and star-formation in galaxies, as manifested in their spectral energy distributions (SEDs) is reviewed. Attention is drawn to an Hertzsprung-Russell diagram - equivalent for such objects, as well as to the importance of the SEDs in cosmological context. (C) 2001 Elsevier Science B.V. All rights reserved.

In order to study the nature of the far-infrared emission observed in radio-loud active galaxies, we have obtained 1.2 mill observations with the IRAM 30 m telescope for a sample of eight radio-loud active galaxies. In all objects we find that the 1.2 mm emission is dominated by non-thermal emission. An extrapolation of the non-thermal radio spectrum indicates that the contribution of synchrotron emission to the far-infrared is less than 10% in quasars. and negligible ill the radio galaxies. The quasars in the sample show signs of relativistic beaming at millimeter wavelengths, and the quasar 3C 334 shows evidence for strong variability.

We have obtained 2.5-45 mu m spectra of a sample of compact H II regions, YSOs and evolved stars in order to study the origin and evolution of interstellar Polycyclic Aromatic Hydrocarbon molecules (PAHs). Besides the well-known, strong PAH bands at 3.3, 6.2, 7.7, 8.6, and 11.2 mu m, these spectra reveal for the first time, a ubiquitous emission plateau from 15 to 20 mu m While the overall shape of this plateau is very similar in all sources, the detailed profiles vary from source to source. In particular, some sources show a distinct emission feature at 16.4 mu m. Moreover, the integrated intensity of this plateau varies relative to the PAH emission features by a factor 10 in our sample.We attribute this 15-20 mu m plateau to a blend of many emission features due to the interstellar or circumstellar PAH family present in these sources. Laboratory studies and quantum chemical calculations show that PAH molecules invariably possess emission features in this wavelength region, arising from C-CC bending modes which cause in- and out-of-plane distortion of the carbon skeleton. These modes are very sensitive to the molecular structure of the specific PAHs present and hence different molecules emit at different wavelengths. Analysis of the available data on the IR characteristics of PAHs show that a collection of PAHs will give rise to a broad plateau in this region.We have analyzed the size distribution of PAHs giving rise to the IR emission spectra of the sources in our samples. While much of the 15-20 mu m plateau is thought to arise in relatively large PAHs and PAH clusters, we attribute the 16.4 mu m feature to the small end of the interstellar PAH size distribution. We conclude that the observed increased strength of the 15-20 mu m plateau relative to the shorter wavelength IR emission features in regions of massive star formation is caused by a preponderance of larger PAHs and PAH clusters in those sources. Possibly this reflects the importance of coagulation in the dense molecular cloud environment from which these stars are formed.

Herschel far-infrared (FIR) observations are used to construct Virgo cluster galaxy luminosity functions and to show that the cluster lacks the very bright and the numerous faint sources detected in field galaxy surveys. The FIR spectral energy distributions are fitted to obtain dust masses and temperatures and the dust mass function. The cluster is overdense in dust by about a factor of 100 compared to the field. The same emissivity (beta)-temperature relation applies for different galaxies as that found for different regions of M31. We use optical and H i data to show that Virgo is overdense in stars and atomic gas by about a factor of 100 and 20, respectively. Metallicity values are used to measure the mass of metals in the gas phase. The mean metallicity is similar to 0.7 solar, and similar to 50 per cent of the metals are in the dust. For the cluster as a whole, the mass density of stars in galaxies is eight times that of the gas and the gas mass density is 130 times that of the metals. We use our data to consider the chemical evolution of the individual galaxies, inferring that the measured variations in the effective yield are due to galaxies having different ages, being affected to varying degrees by gas loss. Four galaxy scaling relations are considered: mass-metallicity, mass-velocity, mass-star formation rate and mass-radius - we suggest that initial galaxy mass is the prime driver of a galaxy's ultimate destiny. Finally, we use X-ray observations and galaxy dynamics to assess the dark and baryonic matter content compared to the cosmological model.

We present Herschel spatially resolved images of the debris disc orbiting the subgiant Kappa CrB. Not only are these the first resolved images of a debris disc orbiting a subgiant, but Kappa CrB is a rare example of an intermediate mass star where a detailed study of the structure of the planetary system can be made, including both planets and planetesimal belt(s). The only way to discover planets around such stars using the radial velocity technique is to observe 'retired' A stars, which are cooler and slower rotators compared to their main-sequence counterparts. A planetary companion has already been detected orbiting the subgiant Kappa CrB, with revised parameters of m sin i = 2.1MJ and apl = 2.8AU (Johnson et al. 2008a). We present additional Keck I HIRES radial velocity measurements that provide evidence for a second planetary companion, alongside Keck II AO imaging that places an upper limit on the mass of this companion. Modelling of our Herschel images shows that the dust is broadly distributed, but cannot distinguish between a single wide belt (from 20 to 220AU) or two narrow dust belts (at around 40 and 165AU). Given the existence of a second planetary companion beyond approximately 3AU it is possible that the absence of dust within approximately 20AU is caused by dynamical depletion, although the observations are not inconsistent with depletion of these regions by collisional erosion, which occurs at higher rates closer to the star., Updated abstract

Context. Edge-on spiral galaxies with prominent dust lanes provide us with an excellent opportunity to study the distribution and properties of the dust within them. The HEROES project was set up to observe a sample of seven large edge-on galaxies across various wavelengths for this investigation. Aims. Within this first paper, we present the Herschel observations and perform a qualitative and quantitative analysis on them, and we derive some global properties of the far infrared and submillimetre emission. Methods. We determine horizontal and vertical profiles from the Herschel observations of the galaxies in the sample and describe the morphology. Modified black-body fits to the global fluxes, measured using aperture photometry, result in dust temperatures and dust masses. The latter values are compared to those that are derived from radiative transfer models taken from the literature. Results. On the whole, our Herschel flux measurements agree well with archival values. We find that the exponential horizontal dust distribution model often used in the literature generally provides a good description of the observed horizontal profiles. Three out of the seven galaxies show signatures of extended vertical emission at 100 and 160 {\mu}m at the 5{\sigma} level, but in two of these it is probably due to deviations from an exactly edge-on orientation. Only for NGC 4013, a galaxy in which vertically extended dust has already been detected in optical images, we can detect vertically extended dust, and the derived scaleheight agrees with the value estimated through radiative transfer modelling. Our analysis hints at a correlation between the dust scaleheight and its degree of clumpiness, which we infer from the difference between the dust masses as calculated from modelling of optical data and from fitting the spectral energy distribution of Herschel datapoints., Comment: 21 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics

We examine Herschel Space Observatory images of one nearby prototypical outer ring galaxy, NGC 1291, and show that the ring becomes more prominent at wavelengths longer than 160um. The mass of cool dust in the ring dominates the total dust mass of the galaxy, accounting for at least 70% of it. The temperature of the emitting dust in the ring (T=19.5+/-0.3K) is cooler than that of the inner galaxy (T=25.7+/-0.7K). We discuss several explanations for the difference in dust temperature, including age and density differences in the stellar populations of the ring versus the bulge., Accepted to ApJ, 9 pages, 6 figures

We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 {\mu}m, as well as new CO J = 3-2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ~30 K towards the centre of the disk and a smoothly decreasing trend to ~20 K with increasing radius. We find a total dust mass of (1.59 \pm 0.05) \times 10^7 M\odot, and a total gas mass of (2.7 \pm 0.2) \times 10^9 M\odot. The average gas-to-dust mass ratio is 103 \pm 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the XCO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations., Comment: Accepted for publication in MNRAS; 11 pages, 8 figures, 1 table

The quantity of dust in a spiral disk can be estimated using the dust's typical emission or the extinction of a known source. In this paper, we compare two techniques, one based on emission and one on absorption, applied on sections of fourteen disk galaxies. The two measurements reflect, respectively the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative contributions of different stellar populations and dust emissivity are all free parameters in galaxy Spectral Energy Distribution (SED) models; they are also sometimes degenerate, depending on wavelength coverage. Our aim is to constrain typical ISM geometry. The apparent optical depth measurement comes from the number of distant galaxies seen in HST images through the foreground disk. We measure the IR flux in images from the {\it Spitzer} Infrared Nearby Galaxy Survey in the same section of the disk that was covered by HST. A physical model of the dust is fit to the SED to estimate the dust surface density, mean temperature, and brightness in these disk sections. The surface density is subsequently converted into the average optical depth estimate. The two measurements generally agree. The ratios between the measured average and apparent optical depths of the disk sections imply optically thin clouds in these disks. Optically thick disks, are likely to have more than a single cloud along the line-of-sight., Comment: 31 pages, 5 figures, 4 tables, accepted for publication in AJ

The symbiosis of nuclear activity and star-formation in galaxies, as manifested in their spectral energy distributions (SEDs) is reviewed. Attention is drawn to an Hertzsprung-Russell diagram-equivalent for such objects, as well as to the importance of the SEDs in cosmological context., Invited review for FIRSED2000 Workshop (Groningen, April 2000)

In order to study the nature of the far-infrared emission observed in radio-loud active galaxies, we have obtained 1.2 mm observations with the IRAM 30 m telescope for a sample of eight radio-loud active galaxies. In all objects we find that the 1.2 mm emission is dominated by non-thermal emission. An extrapolation of the non-thermal radio spectrum indicates that the contribution of synchrotron emission to the far-infrared is less than 10% in quasars, and negligible in the radio galaxies. The quasars in the sample show signs of relativistic beaming at millimeter wavelengths, and the quasar 3C334 shows evidence for strong variability., 6 pages, 1 figure, accepted by A&A

We have obtained 2.5-45 mu m spectra of a sample of compact H II regions, YSOs and evolved stars in order to study the origin and evolution of interstellar Polycyclic Aromatic Hydrocarbon molecules (PAHs). Besides the well-known, strong PAH bands at 3.3, 6.2, 7.7, 8.6, and 11.2 mu m, these spectra reveal for the first time, a ubiquitous emission plateau from 15 to 20 mu m While the overall shape of this plateau is very similar in all sources, the detailed profiles vary from source to source. In particular, some sources show a distinct emission feature at 16.4 mu m. Moreover, the integrated intensity of this plateau varies relative to the PAH emission features by a factor 10 in our sample. We attribute this 15-20 mu m plateau to a blend of many emission features due to the interstellar or circumstellar PAH family present in these sources. Laboratory studies and quantum chemical calculations show that PAH molecules invariably possess emission features in this wavelength region, arising from C-CC bending modes which cause in- and out-of-plane distortion of the carbon skeleton. These modes are very sensitive to the molecular structure of the specific PAHs present and hence different molecules emit at different wavelengths. Analysis of the available data on the IR characteristics of PAHs show that a collection of PAHs will give rise to a broad plateau in this region. We have analyzed the size distribution of PAHs giving rise to the IR emission spectra of the sources in our samples. While much of the 15-20 mu m plateau is thought to arise in relatively large PAHs and PAH clusters, we attribute the 16.4 mu m feature to the small end of the interstellar PAH size distribution. We conclude that the observed increased strength of the 15-20 mu m plateau relative to the shorter wavelength IR emission features in regions of massive star formation is caused by a preponderance of larger PAHs and PAH clusters in those sources. Possibly this reflects the importance of coagulation in the dense molecular cloud environment from which these stars are formed.

We present Herschel observations of 62 Early-Type Galaxies (ETGs), including 39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as ellipticals using SPIRE at 250, 350 and 500 microns (and PACS 100 and 160 microns for 19 sources) as part of the volume-limited Herschel Reference Survey. We detect dust emission in 24% of the ellipticals and 62% of the S0s. The mean temperature of the dust is 23.9+/-0.8 K, warmer than that found for late-type galaxies in the Virgo Cluster. Including the non-detections, the mean dust mass is log(Mdust) = 5.9+/-0.1 and 5.2+/-0.1 Msun for the S0s and elliptical galaxies respectively. The mean dust-to-stellar mass is log(Mdust/Mstar) = -4.4+/-0.1 (S0s) and -5.8+/-0.1 (ellipticals). Virtually all the galaxies lie close to the red sequence yet the large number of detections of cool dust, the gas-to-dust ratios and the ratios of far-infrared to radio emission all suggest that many ETGs contain a cool interstellar medium similar to that in late-type galaxies. The mean dust-to-stellar mass ratio for S0s is approximatly a factor of ten less than for early-type spirals and the sizes of the dust sources in the S0s are also much smaller. We show that the difference cannot be explained by either the different bulge-to-disk ratios or environmental effects such as ram-pressure stripping. The wide range in the dust-to-stellar mass ratio for ETGs and the lack of a correlation between dust mass and optical luminosity suggest that much of the dust in the ETGs detected by Herschel has been acquired as the result of gravitational interactions; these interactions are unlikely to have had a major effect on the stellar masses of the ETGs. The Herschel observations tentatively suggest that in the most massive ETGs, the mass of the interstellar medium is unconnected to the evolution of the stellar populations., Comment: 28 Pages, 12 Figures. Submitted to ApJ December 2011; accepted January 2012