Millimetre and Submillimetre Observations in Cosmology
Total Page:16
File Type:pdf, Size:1020Kb
Millimetre and Submillimetre Observations in Cosmology by David Leigh Clements A Thesis Submitted for the Degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College February 1991 Astrophysics Group Imperial College of Science, Technology and Medicine London SW7 2BZ 1 A bstract This thesis describes two investigations in observational cosmology at mil limetre and submillimetre wavelengths: observations of recently discovered high redshift radio galaxies in search of dust emission, and observations of the Cosmic Background Radiation (CBR) is search of the Sunyaev-Zeldovich Effect. High redshift radio galaxies such as 0902+34 appear to be essentially nor mal high luminosity radio galaxies but at large redshift. Their optical properties suggest that they are forming stars very rapidly, and that there may be some interaction between the radio jet and the star forming process. If they are form ing stars in a manner similar to nearby starburst galaxies, or if their far infrared properties are similar to the nearby high power radio galaxy (Cygnus A) observed by IRAS, then redshifted far infrared radiation should be detectable at millime- tre/submillimetre wavelengths. Predicted fluxes in the 800 fim window at the JCMT are of order 10 mJy. The observations fail to detect this radiation, and 2 <r upper limits of 7 and 10 mJy are set for 3C257 and 3C326.1 respectively. These limits are not sufficiently stringent to discount models for theses objects based on nearby galaxies, but future miflimetre/submiflimetre observations may provide a crucial test of the nature of these objects. The Sunyaev-Zeldovich (S-Z) effect is a spectral distortion of the CBR caused by inverse Compton scattering of CBR photons by the hot gas in clusters of galaxies. It is predicted to have a distinct spectral signature in the millime- tre/submillimetre waveband, but this has yet to be detected. Observations at UKIRT using UKT-14 are used here in an attempt to detect the S-Z effect at 1.1 mm. After a detailed scheme to select good data from the observations, which were severely affected by bad weather, we find that our observations indicate an S-Z effect in 0016+16 of 0.9 db 1.2 mK Rayleigh-Jeans equivalent temperature decrement. We thus fail to detect the effect, and also fail to place any useful lim its on the effect when compared to the latest radio measurements. The behaviour of the data as observations over 17 days are combined are also investigated, and it is found that the noise continues to integrate down as expected for Gaussian statistics as long as sufficient care is taken to select the best data and to remove systematic errors. The construction, testing and first observations with an instrument specifically 1 designed to observe the S-Z effect are dealt with in the next chapters. This instrument has 2 observational channels and a third to monitor and subtract sky noise. The design is reviewed with special emphasis placed on the data acquisition system. The results of observations at the 1.5 m TIRGO telescope with the instrument are then discussed. These observations were severely contaminated with a source of noise correlated between the channels, and a noise subtraction technique originally developed to remove sky noise is tested on this with some degree of success. 2 Acknowledgements A PhD is never wholly the work of one person, as the help and experience of a host of others are called upon in its completion. I must therefore take this chance to thank all those who have contributed to this work or my time at the IC Astro group. First and foremost must come R.D Joseph, my supervisor, for all his help and encouragement. Without his care and expertise it is doubtful that much of this work would have been completed, or even attempted, and my knowledge of astronomy would be sorely lacking. His departure to Hawaii was a severe blow to both his students and IC, and I wish him luck at the IRTF. Almost as important is Simon Chase, responsible for the 3 Channel Instru ment’s design. His introduction to the mysteries of Helium systems and instru mentation in general will provide a background for all my future work. Good luck to you and your family in Italy! Work on the instrument would not have been possible without the expertise of the Astro Group technical team. Haxry, Mark and Victor and all your apprentices put in sterling service, at some very awkward times, and have taken the sting out of many problems for me. Mick Bartholemew must also be thanked in his absence. On the more concrete side, much of the instrument would not have been built without Bill and the workshop crew. Thank you all! Our collaborators, Peter Ade, Kandiah Shivanandan and J-P Torre have also been invaluable. Operations at telescopes are essential for this sort of work, so it is my pleasures to thank all those who have helped me abroad: Dolores, Gillian and Thor at UKIRT, Rusty and Tom at JCMT, and Areste, Nere, Alfonso and everyone at TIRGO. Apologies for the spelling! Beyond direct assistance, life has been made more worth while by all those I have known in the Astro Group. Geoff and Tim, whose fault it was in the first place, Phil who sorted me out, Andrea, Rene, Martyn, Sepi and Arvind who have had to share offices and lab space with me, Natasha, Tanya, Peter, Phil H., Lee, Peter M. Graeme, Sunil and all the others who have kept the atmosphere fresh and interesting; thank you all. 3 I’d also like to thank those who have helped in the production of this thesis. Bob, Amanda and Natasha for reading bits, Sunil, Graeme and Martyn for keeping the machines running. Science is a creative process, and so the strangest things can contribute. In this sphere I must thank those who’ve kept me sane during my time here: Amanda, Simon B, Tom the Madhatter, The Waveguide, ICSF and ICU, though at times it didn’t seem like it! The best to all of you, wherever you are. This work was supported by SERC. 4 To my parents, without whom it wouldn’t have been possible. And to Amanda, who maae it much better. r C ontents 1 Introduction 15 1.1 Observations in C osm ology.................................................................. 16 1.1.1 Fundamental Observations in Modern Cosmology ................ 17 1.1.2 The Hubble F low ........................................................................ 17 1.1.3 Primordial Nucleosynthesis of Light Elem ents ....................... 17 1.1.4 The Cosmic Background R adiation......................................... 18 1.2 The Early History of the Universe..................................................... 18 1.2.1 The Geometry of the U n iv e rse ............................................... 20 1.2.2 The Evolution of the Universe ............................................... 22 1.3 The Cosmic Background R adiation ..................................................... 24 1.4 Dark Matter ........................................................................................... 25 1.5 Primordial Fluctuations: The Origin of Large Scale Structure . 26 1.5.1 The Nature and Spectrum of Initial Fluctuations ................. 26 1.5.2 Galaxy Formation and Large Scale S tru c tu re ...................... 29 1.6 Confrontation of Theories with Cosmological Observations ............. 31 1.6.1 CBR O bservations..................................................................... 31 1.6.2 Distant O bjects........................................................................... 33 1.6.3 Large Scale S tru c tu re ............................................................... 33 1.7 The Role of this Thesis ........................................................................ 34 2 Millimetre and Submillimetre Observations of Distant Galaxies 35 2.1 Introduction.............................................................................................. 35 2.2 High Redshift Galaxies........................................................................... 35 2.2.1 D iscovery..................................................................................... 35 5 2.3 The Properties of High Redshift Radio Galaxies ............................... 37 2.3.1 Radio P ro p erties........................................................................ 37 2.3.2 Optical and Infrared Properties............................................... 39 2.3.3 The Nature of High Redshift Radio G a la x ie s ...................... 43 2.4 Motivation for Observations.................................................................. 45 2.4.1 Target Objects for these O bservations................................... 45 2.4.2 Millimetre/Submillimetre synchrotron emission from a HRRG 46 2.4.3 Dust Emission from a neaxby radio galaxy model of a HRRG 48 2.4.4 Dust Emission from a Starburst Model of a HRRG ............. 48 2.4.5 Limitations of these Models ..................................................... 50 2.5 The Observations.................................................................................... 51 2.5.1 The UK.T-14 Continuum R e c e iv e r......................................... 52 2.6 C a lib ratio n .............................................................................................. 55 2.7 Data Reduction ....................................................................................... 57 2.7.1 Demodulation of D a ta .............................................................. 57 2.7.2 Atmospheric Transmission ........................................................ 58 2.7.3 Removal of S p ik e s ....................................................................