We have used the Very Large Array to image a single field in a set of adjacent frequency bands around 333.0 MHz in an attempt to detect 21 cm emission from large scale H I inhomogeneities at a redshift of z = 3.3. Following the subtraction of continuum radio sources, the absence of any spectral signals apart from that expected due to the system thermal noise has been used to derive constraints on the evolutionary scenario leading to the formation of the present day clusters of galaxies. The observations rule out the existence of H I protoclusters atz = 3.3 with masses ≃3.5 × 10¹⁴M_⊙ in H I gas and space density exceeding (74 Mpc)⁻³. This indicates that the present day rich clusters of galaxies either formed as gaseous protocluster condensates prior toz = 3.3 or else they formed through the clustering of their constituent galaxies.

Observations have been conducted using the Ooty Radio Telescope in order to place constraints on the evolutionary scenario leading to the formation of the present day superclusters. The experiment attempted to detect 21 cm emission from massive neutral hydrogen condensates at a redshift ofz = 3.3. In an Einstein de-Sitter universe with baryon density Ω = 0.05, about ten condensates were expected in the volume surveyed if superclusters, having H I masses ≃5 × 10₁₅M_⊙, were the first objects to separate out of the Hubble expansion. The sensitivity of our experiment rules out the existence of these condensates atz = 3.3 unless their lifetimes are less than one-tenth the dispersion in their epoch of formation or the proto-superclusters subtend angles greater than 6 arcmin. The result indicates that superclusters form at z > 3.3 if indeed they were the first objects to condense out of the Hubble flow.

The discovery of the 3K microwave background radiation (MBR) and its interpretation as a relict of the hot big bang was probably the most important observation that led to the elevation of the hot big bang model to the status of a ‘Standard Model’. The temperature of this background is consistent with the primordial nucleosynthesis hypothesis. Detailed measurements of the spectrum and angular anisotropy of this radiation background have been found — within the measurement errors - to be consistent with the expectations of the Standard Model and with the formation of structure from the gravitational growth of primordial seed density perturbations within this framework.

The absolute temperature of the cosmic microwave background (CMB) has been measured at a frequency of 1280 MHz. The observation was made with a modified version of the L-band receiver used in the Giant Metre wavelength Radio Telescope (GMRT): the feed horn was replaced by a corrugated plate and the receiver was placed on the ground, directed at zenith, and shielded from ground radiation by an aluminium screen with corrugated edges. Novel techniques have been adopted for

The thermodynamic temperature of the CMB is estimated to be 3.45 ± 0.78 K.

We present 18 GHz observations of the Bullet cluster using the Austalia Telescope Compact Array (ATCA), which show structure in the Sunyaev–Zeldovich effect; in particular, a deep, compact feature which does not correspond to any bright feature in X-ray, optical or lensing maps. In general, the relatively deeper SZE features appear to avoid the regions with the most intense X-ray emission. SZE displaced from X-ray centres implies that modeling cluster dynamics is non-trivial. The SZE distribution in the western parts of the cluster are co-spatial with the radio halo indicative of a common origin for the hot and relativistic electrons in the turbulent wake of the Bullet.