Giant Cyclones in Gaseous Discs of Spiral Galaxies

We report detection of giant cyclonic vortices in the gaseous disc of the spiral galaxy NGC 3631 in the reference frame rotating with the spiral pattern. A presence of such structures was predicted by the authors for galaxies, where the radial gradient of the perturbed velocity exceeds that of the rotational velocity. This situation really takes place in NGC 3631.Comment: 13 pages, 4 EPS and 3 PS figure

Determination of the 57Co hyperfine field in Pd(57Co) from Mössbauer emission spectra in the regime of fast relaxation

Mössbauer emission spectra obtained on Pd(57Co) below ∼ 400 mK under an applied external magnetic field show a broadening of the 57Fe resonance lines and indicate an unexpectedly low polarization of the 57Co nucleus. The experimental data are consistently explained by a perpendicular component of relaxation acting on the 57Fe (I = 3/2) and (I = 5/2) nuclear levels.Les spectres d'émission Mössbauer obtenus pour Pd(57Co) au-dessous de ∼ 400 mK dans des champs magnétiques externes montrent une augmentation de la largeur de la raie résonnante de 57Fe et indiquent une polarisation de noyau de 57CO plus faible qu'attendu. Les résultats expérimentaux sont expliqués de façon consistante par une composante perpendiculaire de la relaxation opérant sur les niveaux (I = 3/2) et (I = 5/2) de noyau de 57Fe