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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 500µm as part of the volume-limited Herschel Reference Survey (HRS). We detect dust emission in 24% of the ellipticals and 62% of the S0s. The mean temperature of the dust is Td 23.9±0.8 K,warmer than that found for late-type galaxies in the Virgo Cluster. The mean dust mass for the entire detected early-type sample is logMd = 6.1 ± 0.1 Mʘ with a mean dust-to-stellar-mass ratio of log(Md / M*) = -4.3 ± 0.1. Including the non-detections, these parameters are logMd = 5.6 ± 0.1 and log(Md /M*) = -5.1 ± 0.1, respectively. The average dust-to-stellar-mass ratio for the early-type sample is fifty times lower, with larger dispersion, than the spiral galaxies observed as part of the HRS, and there is an order-of-magnitude decline in Md / M* between the S0s and ellipticals. We use UV and optical photometry to show that 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. We show that the sizes of the dust sources in S0s are much smaller than those in early-type spirals and the decrease in the dust-to-stellar-mass ratio from early-type spirals to S0s cannot simply be explained by an increase in the bulge-to-disk ratio. These results suggest that the disks in S0s contain much less dust (and presumably gas) than the disks of early-type spirals and this cannot be explained simply by current 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 interactions, although we show these 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 systems, the mass of interstellar medium is unconnected to the evolution of the stellar populations in these galaxies. [ABSTRACT FROM AUTHOR]

We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to ∼4000 quasi-independent pixels with spatial resolution of ∼140 pc and find that a variable dust-emissivity index (β) is required to fit the data. We find no significant long-wavelength excess above this model, suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from ∼20 in the center to ∼70 in the star-forming ring at 10 kpc, consistent with the metallicity gradient. In the 10 kpc ring the average β is ∼1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in β, which increases from 1.9 at 10 kpc to ∼2.5 at a radius of 3.1 kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10 kpc ring (ranging from 17 to 20 K), but increases strongly in the bulge to ∼30 K. Within 3.1 kpc we find the dust temperature is highly correlated with the 3.6 μm flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for “dark gas” in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimizing the dispersion in the gas-to-dust ratio, obtaining a value of (1.9 ± 0.4) × 1020 cm–2 [K km s–1]–1. [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]

We search for variations in the disk of Centaurus A of the emission from atomic fine structure lines using Herschel PACS and SPIRE spectroscopy. In particular, we observe the [C II](158 μm), [N II](122 and 205 μm), [O I](63 and 145 μm), and [O III](88 μm) lines, which all play an important role in cooling the gas in photo-ionized and photodissociation regions (PDRs). We determine that the ([C II]+[O I]63)/FTIR line ratio, a proxy for the heating efficiency of the gas, shows no significant radial trend across the observed region, in contrast to observations of other nearby galaxies. We determine that 10%-20% of the observed [C II] emission originates in ionized gas. Comparison between our observations and a PDR model shows that the strength of the far-ultraviolet radiation field, G0, varies between 101.75 and 102.75 and the hydrogen nucleus density varies between 102.75 and 103.75 cm–3, with no significant radial trend in either property. In the context of the emission line properties of the grand-design spiral galaxy M51 and the elliptical galaxy NGC 4125, the gas in Cen A appears more characteristic of that in typical disk galaxies rather than elliptical galaxies. [ABSTRACT FROM AUTHOR]