The central region of the Coma cluster of galaxies was observed in the energy band from 0.065 to 0.245 kiloelectron volts by the Deep Survey telescope aboard the Extreme Ultraviolet Explorer. A diffuse emission halo of angular diameter approximately 30 arc minutes was detected. The extreme-ultraviolet (EUV) emission level exceeds that expected from the x-ray temperature gas in Coma. This halo suggests the presence of two more phases in the emitting gas, one at a temperature of approximately 2 x 10(6) kelvin and the other at approximately 8 x 10(5) kelvin. The latter phase cools rapidly and, in steady state, would have produced cold matter with a mass of approximately 10(14) solar masses within the EUV halo. Although a similar EUV enhancement was discovered in the Virgo cluster, this detection in Coma applies to a noncooling flow system.

An observation of M87, the central galaxy of the Virgo Cluster, was performed by the deep survey telescope aboard the Extreme-Ultraviolet Explorer, in the 0.065-0.245 keV energy band. A point source and an extended emission halo of radius 120Ј are clearly visible in the data, and represent the first detection of cluster gas emission in the EUV. The emission cannot be explained by the well-known cluster gas at X-ray temperatures. Instead, it is necessary to introduce a second gas component, with temperature between 5 ϫ 10 5 and 10 6 K. The rapid cooling of plasmas at such temperatures implies a mass accretion rate of more than 300 M J yr Ϫ1 . It is unlikely that the phenomenon is directly related to a cooling flow, which involves a much lower accretion rate of 110 M J yr Ϫ1 .

The excess extreme-ultraviolet (EUV) emission detected in the Virgo and Coma clusters is explained by inverse Compton scattering of cosmic microwave background photons, which are scattered by the relativistic electrons that account for the extended radio synchrotron emission of these clusters. The lower limits of the average magnetic fields of these clusters estimated from the EUV excess are close to the equipartition magnetic fields derived from radio observations, indicating that the electron energies and magnetic field energies might be close to equipartition. The excess emission suggests energy reservoirs of approximately 10(61) and approximately 10(60) ergs for the Coma and Virgo clusters, respectively.

Aims. The stochastic acceleration of subrelativistic electrons from a background plasma is studied in order to find a possible explanation of the hard X-ray emission detected from the Coma cluster. Methods. We calculate the necessary energy supply as a function of the plasma temperature and of the electron energy, and we show that, for the same value of the hard X-ray flux, the energy supply changes gradually from its high value for the case when emitting particle are non-thermal to lower values when the electrons are thermal. The kinetic equations we use include terms describing particle thermalization as well as momentum diffusion due to the Fermi II acceleration. Results. We show that the temporal evolution of the particle distribution function has, at its final stationary stage, a rather specific form. This distribution function cannot be described by simple exponential or power-law expressions. A broad transfer region is formed by Coulomb collisions at energies between the Maxwellian and power-law parts of the distribution functions. In this region the radiative lifetime of a single quasi-thermal electron differs greatly from the lifetime of the distribution function as a whole. For a plasma temperature of 8 keV, the particles emitting bremsstrahlung at 20−80 keV lie in this quasi-thermal regime. We show that the energy supply required by quasi-thermal electrons to produce the observed hard X-ray flux from Coma is one or two orders of magnitude smaller than the value derived from the assumption of a nonthermal origin of the emitting particles. This result may solve the problem of rapid cluster overheating by nonthermal electrons raised by Petrosian (2001): while Petrosian's estimates are correct for nonthermal particles, they are inapplicable in the quasi-thermal range. We finally analyze the change in Coma's Sunyaev-Zeldovich effect caused by the implied distortions of the Maxwellian spectrum of electrons, and we show that evidence for the acceleration of subrelativistic electrons can, in principle, be derived from detailed spectral measurements.

We present CO(3-2) interferometric observations of the central region of the Seyfert 2 galaxy NGC 1068 using the Submillimeter Array, together with CO(1-0) data taken with the Owens Valley Radio Observatory Millimeter Array. Both the CO(3-2) and CO(1-0) emission lines are mainly distributed within ∼ 5 arcsec of the nucleus and along the spiral arms, but the intensity distributions show differences; the CO(3-2) map peaks in the nucleus, while the CO(1-0) emission is mainly located along the spiral arms. The CO(3-2)/CO(1-0) ratio is about 3.1 in the nucleus, which is four times as large as the average line ratio in the spiral arms, suggesting that the molecular gas there must be affected by the radiation arising from the AGN. On the other hand, the line ratios in the spiral arms vary over a wide range from 0.24 to 2.34 with a average value around 0.75, which is similar to the line ratios of star-formation regions, indicating that the molecular gas is affected by star formation. Besides, we see a tight correlation between CO(3-2)/(1-0) ratios in the spiral arms and star formation rate surface densities derived from Spitzer 8 µm dust flux densities. We also compare the CO(3-2)/(1-0) ratio and the star formation rate at different positions within the spiral arms; both are found to decrease as the radius from the nucleus increases.