The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submillimetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform integral-field spectroscopy and imaging photometry in the 60−210 μm wavelength regime. In photometry mode, it simultaneously images two bands, 60−85 μm or 85−125 μm and 125−210 μm, over a field of view of ∼1.75 × 3.5 , with close to Nyquist beam sampling in each band. In spectroscopy mode, it images a field of 47 × 47 , resolved into 5 × 5 pixels, with an instantaneous spectral coverage of ∼ 1500 km s −1 and a spectral resolution of ∼175 km s −1 . We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the performance verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions. Key words. space vehicles: instruments -instrumentation: photometers -instrumentation: spectrographsHerschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Spitzer Space Telescope and Herschel Space Observatory imaging of M31 is used, with a physical dust model, to construct maps of dust surface density, dust-to-gas ratio, starlight heating intensity, and polycyclic aromatic hydrocarbon (PAH) abundance, out to R ≈ 25 kpc. The global dust mass is M d = 5.4 × 10 7 M , the global dust/H mass ratio is M d /M H = 0.0081, and the global PAH abundance is q PAH = 0.039. The dust surface density has an inner ring at R = 5.6 kpc, a maximum at R = 11.2 kpc, and an outer ring at R ≈ 15.1 kpc. The dust/gas ratio varies from M d /M H ≈ 0.026 at the center to ∼0.0027 at R ≈ 25 kpc. From the dust/gas ratio, we estimate the interstellar mediu (ISM) metallicity to vary by a factor ∼10, from Z/Z ≈ 3 at R = 0 to ∼ 0.3 at R = 25 kpc. The dust heating rate parameter U peaks at the center, with U ≈ 35, declining to U ≈ 0.25 at R = 20 kpc. Within the central kiloparsec, the starlight heating intensity inferred from the dust modeling is close to what is estimated from the stars in the bulge. The PAH abundance reaches a peak q PAH ≈ 0.045 at R ≈ 11.2 kpc. When allowance is made for the different spectrum of the bulge stars, q PAH for the dust in the central kiloparsec is similar to the overall value of q PAH in the disk. The silicate-graphite-PAH dust model used here is generally able to reproduce the observed dust spectral energy distribution across M31, but overpredicts 500µm emission at R ≈ 2-6 kpc, suggesting that at R = 2-6 kpc, the dust opacity varies more steeply with frequency (with β ≈ 2.3 between 200 and 600µm) than in the model. Subtraction of foreground and background emission has been carried out following methods described in Aniano et al. (2012), with automatic identification of background pixels and fitting of a "tilted plane" background model (with three parameters -zero point, tilt, and tilt orientation) for 3 IRAC images in bands 1-4 were multiplied by extended source calibration factors 0.91, 0.94, 0.66, 0.74 (Reach et al. 2005). 4 MIPS images were generated by the Mips enhancer v3.10 pipeline on 2007 Jul 3. 5 The PACS and SPIRE images were processed by HIPE v9, and the Level 1 HIPE images were then processed by Scanamorphos v18.0 (Roussel 2013). We used the calibration files in HIPE v9 (version 42 for PACS, and version 10.0 for SPIRE). Intensities in the SPIRE bands were obtained by dividing the HIPE v9 flux density per beam by effective beam solid angles Ω = (1.103, 1.944, 4.183) × 10 −8 sr for SPIRE250, 350, and 500, as recommended by Griffin et al. (2013).

Abstract. Infrared to millimetre spectral energy distributions (SEDs) have been obtained for 41 bright ultraluminous infrared galaxies (ULIRGs). The observations were carried out with ISOPHOT between 10 and 200 µm and supplemented for 16 sources with JCMT/SCUBA at 450 and 850 µm and with SEST at 1.3 mm. In addition, seven sources were observed at 1.2 and 2.2 µm with the 2.2 m telescope on Calar Alto. These new SEDs represent the most complete set of infrared photometric templates obtained so far on ULIRGs in the local universe. The SEDs peak at 60-100 µm and show often a quite shallow Rayleigh-Jeans tail. Fits with one single modified blackbody yield a high FIR opacity and small dust emissivity exponent β < 2. However, this concept leads to conflicts with several other observational constraints, like the low PAH extinction or the extended filamentary optical morphology. A more consistent picture is obtained using several dust components with β = 2, low to moderate FIR opacity and cool (50 K > T > 30 K) to cold (30 K > T > 10 K) temperatures. This provides evidence for two dust stages, the cool starburst dominated one and the cold cirrus-like one. The third stage with several hundred Kelvin warm dust is identified in the AGN dominated ULIRGs, showing up as a NIR-MIR powerlaw flux increase. While AGNs and SBs appear indistinguishable at FIR and submm wavelengths, they differ in the NIR-MIR. This suggests that the cool FIR emitting dust is not related to the AGN, and that the AGN only powers the warm and hot dust. In comparison with optical and MIR spectroscopy, a criterion based on the SED shapes and the NIR colours is established to reveal AGNs among ULIRGs. Also the possibility of recognising evolutionary trends among the ULIRGs via the relative amounts of cold, cool and warm dust components is investigated.

Abstract.Mining the ISO data archive we provide the complete ISO view of PG quasars containing 64 infrared spectral energy distributions between 5 and 200 µm. About half of the sample was supplemented by MAMBO and SCUBA (sub-)millimetre data. Since the PG quasars were selected optically, the high infrared detection rate of more than 80% suggests that every quasar possesses luminous to hyperluminous dust emission with dust masses comparable to Seyferts and ultraluminous IR galaxies (ULIRGs). The gas-to-dust mass ratio (of those sources where CO measurements are available in the literature) is consistent with the galactic value providing further evidence for the thermal nature of the IR emission of radio quiet quasars. The SEDs represent templates of unprecedented detail and sensitivity. The power-law like near-to mid-IR SEDs (F ν ∝ ν α ) are smooth up to far-infrared wavelengths, favouring dust heating by the central AGN, and we conclude that, in particular for our hyperluminous quasars at z = 1, starbursts play only a minor role for powering the dust emission, even in the FIR. The IR spectral slopes α 1−10 µm range from -0.9 to -2.2 with a mean of −1.3 ± 0.3. They neither correlate with the optical spectral slope α 0.3−1 µm , nor with the IR luminosity, nor with the FIR/MIR luminosity ratio, nor with inclination-dependent extinction effects in the picture of a dusty torus. We suggest that the diversity of the SEDs reflects largely the evolution of the dust distribution, and we propose a classification of the SED shapes as well as an evolutionary scheme in which this variety can be understood. During the evolution the surrounding dust redistributes, settling more and more into a torus/disk like configuration, while the SEDs show an initial FIR bump, then an increasing MIR emission and a steeper near-to mid-infrared slope, both of which finally also decrease. Strikingly, based on the sensitive ISO data now we do not only see the coarse IR differences between ULIRGs and quasars, but also the details and a possible evolution of the dust distribution and emission even among the optically selected PG sample. Regarding cosmic evolution, our hyperluminous quasars in the "local" universe at z = 1 do not show the hyperluminous (L FIR > ∼ 10 13 L ) starburst activity inferred for z = 4 quasars detected in several (sub-)millimetre surveys. In view of several caveats this difference should be established further, but it already suggests that in the early dense universe stronger merger events led to more powerful starbursts accompanying the quasar phenomenon, while at later cosmic epochs any coeval starbursts obviously do not reach that high power and are outshone by the AGN.

We present spectral energy distributions (SEDs) of 69 QSOs at z > 5, covering a rest frame wavelength range of 0.1 µm to ∼80 µm, and centered on new Spitzer and Herschel observations. The detection rate of the QSOs with Spitzer is very high (97% at λ rest 4 µm), but drops towards the Herschel bands with 30% detected in PACS (rest frame mid-infrared) and 15% additionally in the SPIRE (rest frame far-infrared; FIR). We perform multi-component SED fits for Herschel-detected objects and confirm that to match the observed SEDs, a clumpy torus model needs to be complemented by a hot (∼1300K) component and, in cases with prominent FIR emission, also by a cold (∼50K) component. In the FIR detected cases the luminosity of the cold component is on the order of 10 13 L which is likely heated by star formation. From the SED fits we also determine that the AGN dust-to-accretion disk luminosity ratio declines with UV/optical luminosity. Emission from hot (∼1300K) dust is common in our sample, showing that nuclear dust is ubiquitous in luminous QSOs out to redshift 6. However, about 15% of the objects appear under-luminous in the near infrared compared to their optical emission and seem to be deficient in (but not devoid of) hot dust. Within our full sample, the QSOs detected with Herschel are found at the high luminosity end in L UV/opt and L NIR and show low equivalent widths (EWs) in Hα and in Lyα. In the distribution of Hα EWs, as determined from the Spitzer photometry, the high-redshift QSOs show little difference to low redshift AGN.