Letter to the Editor

The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory^*

A. Poglitsch¹, C. Waelkens², N. Geis¹, H. Feuchtgruber¹, B. Vandenbussche², L. Rodriguez³, O. Krause⁴, E. Renotte⁵, C. van Hoof⁶, P. Saraceno⁷, J. Cepa⁸, F. Kerschbaum⁹, P. Agnèse¹⁰, B. Ali¹¹, B. Altieri¹², P. Andreani^13,14, J.-L. Augueres³, Z. Balog⁴, L. Barl¹, O. H. Bauer¹, N. Belbachir¹⁵, M. Benedettini⁷, N. Billot³, O. Boulade³, H. Bischof¹⁶, J. Blommaert², E. Callut⁵, C. Cara³, R. Cerulli⁷, D. Cesarsky¹, A. Contursi¹, Y. Creten⁶, W. De Meester², V. Doublier¹, E. Doumayrou³, L. Duband¹⁷, K. Exter², R. Genzel¹, J.-M. Gillis⁵, U. Grözinger⁴, T. Henning⁴, J. Herreros⁸, R. Huygen², M. Inguscio¹⁸, G. Jakob^1,13, C. Jamar⁵, C. Jean², J. de Jong¹, R. Katterloher¹, C. Kiss¹⁹, U. Klaas⁴, D. Lemke⁴, D. Lutz¹, S. Madden³, B. Marquet⁵, J. Martignac³, A. Mazy⁵, P. Merken⁶, F. Montfort⁵, L. Morbidelli²⁰, T. Müller¹, M. Nielbock⁴, K. Okumura³, R. Orfei⁷, R. Ottensamer^9,16, S. Pezzuto⁷, P. Popesso¹, J. Putzeys⁶, S. Regibo², V. Reveret³, P. Royer², M. Sauvage³, J. Schreiber⁴, J. Stegmaier⁴, D. Schmitt³, J. Schubert¹, E. Sturm¹, M. Thiel¹, G. Tofani²⁰, R. Vavrek¹², M. Wetzstein¹, E. Wieprecht¹ and E. Wiezorrek¹

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany e-mail: alpog@mpe.mpg.de
² Institute of Astronomy KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
³ Commissariat à l'Energie Atomique, IRFU, Orme des Merisiers, Bât. 709, 91191 Gif/Yvette, France
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Centre Spatial de Liège, Parc Scientifique du Sart Tilman, Avenue du Pré-Aily, 4031 Angleur-Liège, Belgium
⁶ Interuniversity Microelectronics Center, Kapeldreef 75, 3001 Leuven, Belgium
⁷ Istituto di Fisica dello Spazio Interplanetario, Via del Fosso del Cavaliere, 00133 Roma, Italy
⁸ Instituto de Astrofisica de Canarias, C/via Lactea s/n, La Laguna, 38200 Santa Cruz de Tenerife, Spain
⁹ Institut für Astronomie der Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria
¹⁰ Commissariat à l'Energie Atomique, LETI, 17 rue des Martyrs, 38054 Grenoble, France
¹¹ NASA Herschel Science Center, Pasadena, USA
¹² European Space Astronomy Centre (ESAC), Camino bajo del Castillo, s/n, Villanueva de la Cañada, 28692 Madrid, Spain
¹³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁴ Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁵ AIT Austrian Institute of Technology, Donau-City-Straße 1, 1220 Wien, Austria
¹⁶ Institute of Computer Vision and Graphics, Graz University of Technology, Inffeldgasse 16/II, 8010 Graz, Austria
¹⁷ Commissariat à l'Energie Atomique, INAC/SBT, 17 rue des Martyrs, 38054 Grenoble, France
¹⁸ LENS - European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, 50019 Sesto-Fiorentino (Firenze), Italy
¹⁹ Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
²⁰ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Received: 29 March 2010
Accepted: 28 April 2010

Abstract

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.