M. Rowan-Robinson

Galaxy evolution and large-scale structure in the far-infrared. II, The IRAS Faint Source Survey

The new IRAS Faint Source Survey data base is used to confirm the conclusion of Hacking et al. (1987) that the 60 micron source counts fainter than about 0.5 Jy lie in excess of predictions based on nonevolving model populations. The existence of an anisotropy between the northern and southern Galactic caps discovered by Rowan-Robinson et al. (1986) and Needham and Rowan-Robinson (1988) is confirmed, and it is found to extend below their sensitivity limit to about 0.3 Jy in 60 micron flux density. The count anisotropy at f(60) greater than 0.3 can be interpreted reasonably as due to the Local Supercluster; however, no one structure accounting for the fainter anisotropy can be easily identified in either optical or far-IR two-dimensional sky distributions. The far-IR galaxy sky distributions are considerably smoother than distributions from the published optical galaxy catalogs. It is likely that structure of the large size discussed here have been discriminated against in earlier studies due to insufficient volume sampling. 105 refs.

Reconstruction analysis. I: Redshift-space deprojection in the quasi-non-linear regime

We present a new method for the extraction of the true three-dimensional velocity and density fields from the non-linear redshift-space projected density field. The method is based on the non-linear, non-local transformation of the density field. We assume a curl-free velocity field, although in the formulation presented here this assumption can be dropped. Toy models with special symmetry are used to test the intrinsic accuracy of the method compared with linear theory. Finding significant improvement, we then test the method in more detail on N-body simulations, considering the problems associated with sampling of the density field using sparse, magnitude-limited galaxy redshift surveys

The extragalactic distance scale

Developments in the extragalactic distance scale during the period 1983–1987 are reviewed. There have been many very significant improvements in our knowledge of the distance scale during this period, yet the overall shift in the distance scale from that adopted in Cosmological Distance Ladder (Rowan-Robinson, 1985, CDL) is small.The galactic calibration of Cepheids has been enormously improved by detailed work on the open clusters and associations containing Cepheids. The resulting shift from the calibration of Sandage and Tammann (1969) is small, though Strömgren-Hβ photometry gives discrepantly low distances in some cases. The number of galaxies outside the Local Group with distances determined from Cepheids has increased from 2 to 5 (N2403, M81, M101, N300, N3109).The nova method has, in a spectacular development, been pushed out to the Virgo cluster and gives a distance modulus in good agreement with that adopted in CDL. RR Lyrae stars have been studied in M31, again representing a more than 10-fold increase in the range of the method.The past five years has been a dramatic period for the supernova distance method. The rediscovery of Bertolas Type Ipec subclass, now known as Type Ib, has stimulated a burst of activity on the theoretical front. Models for Type Ia supernovae involving the deflagration of 0.4–1.0 M0 of a 1.4 M0 C-O white dwarf have reached a considerable degree of sophistication. Type Ibs are believed by most theorists to be the end-point of the evolution of a 20 M0 star which has previously lost its envelope by mass-loss. SN 1987a in the LMC was the astronomical event of the century and has already led to an independent estimate of the distance of the LMC in good agreement with other methods.The Tully-Fisher method has been the subject of intense study during the past five years but there is no clear explanation of why it gives lower distances than other methods. Malmquist bias has been invoked by several authors.A new method for estimating the distance to ellipticals, which is a modification of the older Faber-Jackson method, the Dn-σ method, has been applied to hundreds of ellipticals, giving distances in good agreement with those adopted in CDL.Weighted mean distances to groups have been calculated as in CDL and the resulting Hubble diagram, corrected for our motion through space, plotted. The best estimate of the Hubble constant is 66 ± 10 km s-1 Mpc-1, virtually unchanged from CDL. A prescription is suggested for bringing the Type Ia and infrared Tully-Fisher methods into line with other methods.

Models for IRAS Galaxies

We have modelled IRAS 12–100 µ observations of galaxies as a mixture of 3 components: a cool “disc” component, a warmer “starburst” component and a “Seyfert” component peaking at 25 µ.

Distances to Virgo and Beyond

New distance measurements to Virgo and beyond are reviewed. The discrepancy between the Type la supernova and infrared Tully-Fisher methods remains unresolved. Two new distance methods based on the luminosity function for planetary nebulae and on surface brightness fluctuations in ellipticals and lenticulars are briefly discussed. Analysis of IRAS maps of 100 µm emission from interstellar dust appear to resolve the controversy about extinction towards the Galactic poles. A new model for the local flow based on the QDOT IRAS galaxy redshift survey is applied to the analysis of the Hubble diagram. The implications of the current best estimates of Ho and Ωo for inflation are discussed.

Axially Symmetric Radiative Transfer Models of Low Mass Protostars

In this paper we present a modification to the method of Efstathiou and Rowan-Robinson (1989) for the solution of the axially symmetric radiative transfer problem in dust clouds, which is more appropriate for modeling protostellar candidates. In contrast to previous attempts to solve the axisymmetric problem, the method integrates the equation of radiative transfer exactly in the sense that it does not neglect any terms in the equation and treats multiple anisotropic scattering. The results of several computed models are presented showing the dependence of the emergent spectrum on the model parameters and viewing angle. We also present a very good fit to the observed spectrum of IRS5 LI551 and compare it with previous work.

Cosmological Implications of the Infrared Background Radiation

We review some exciting new observational developments in the infrared background (1 – 1000 µm). The Nagoya-Berkeley collaboration have made accurate measurements of the infrared background intensity between 100 and 1000 µm and have detected excess radiation, compared to a 2.74 K blackbody, peaking at 700 µm. New detailed studies of the IRAS background data show the clear possibility of a cosmological background at 100 µm, though there is still not a concensus on the correct model for the foreground zodiacal emission. Finally, the Nagoya group claim a significant background intensity at 2 µm. Possible interpretations of the far infrared background as radiation from starburst galaxies undergoing strong cosmological evolution are discussed. The spectrum of the 700 µm excess does not agree well with such a model. More promising are models involving a pregalactic generation of stars which make dust and light. The expected infrared background from a variety of pregalactic sources (primeval galaxies, Population III stars, accreting black holes, large-scale structure formation, decaying elementary particles) are discussed in detail. These backgrounds would generally appear in the near infrared unless they have been absorbed by galactic or intergalactic dust, in which case they should have been reprocessed to the far infrared.

Distribution of IRAS Galaxies

Infrared wavelengths are free of several of the problems that plague optical galaxy surveys. At high galactic latitude >99% of 60µ sources in the IRAS Point Source Catalog, after deletion of obvious stars, are galaxies. At lower latitudes care has to be taken to avoid confusion with emission from interstellar dust (the’cirrus’). IRAS galaxies have been used to determined the direction of the gravitational acceleration acting on the Local Group due to galaxies and clusters within about 200 Mpc. This agrees well with the direction of the microwave background dipole. The density of matter in the universe, distributed like IRAS galaxies, needed to account for the observed velocity of the Local Group, corresponds to Ωo = 1.0 ± 0.2. In the standard hot Big Bang model, 90–95% of this matter would have to be non-baryonic.

Models of IRAS Observations of Circumstellar Shells

We have modelled the IRAS observations of the circumstellar dustshells around late-type stars previously studied by Rowan-Robinson and Harris (1982, 1983a, b), using only high quality IRAS fluxes which do not appear extended in the raw data. Figure 1a, b shows the IRAS 12-26-60 colour colour diagrams for late M and carbon stars, together with the predictions of simple model sequences. Figure 2a, b show the spectra of a sample of the stars.

Models for IRAS observations of galactic HII regions

We have investigated the transfer of radiation through a spherically symmetric distribution of dust surrounding a centrally located hot star. Comparison with observation is made via IRAS colour-colour diagrams for compact HII regions.