ESA Science & Technology - Publication Archive
Context: The morphology of massive star formation in the central regions of galaxies is an important tracer of the dynamical processes that govern the evolution of disk, bulge, and nuclear activity.
Aims: We present optical imaging of the central regions of a sample of 73 spiral galaxies in the H-a line and in optical broad bands, and derive information on the morphology of massive star formation.
Methods:We obtained images with theWilliam Herschel Telescope, mostly at a spatial resolution of below one second of arc. For most galaxies, no H-a imaging is available in the literature.We outline the observing and data reduction procedures, list basic properties, and present the I-band and continuum-subtracted H-a images. We classify the morphology of the nuclear and circumnuclear H-a emission and explore trends with host galaxy parameters.
Results: We confirm that late-type galaxies have a patchy circumnuclear appearance in H-a, and that nuclear rings occur primarily in spiral types Sa-Sbc. We identify a number of previously unknown nuclear rings, and confirm that nuclear rings are predominantly hosted by barred galaxies.
Conclusions: Other than in stimulating nuclear rings, bars do not influence the relative strength of the nuclear H-a peak, nor the circumnuclear H-a morphology. Even considering that our selection criteria led to an over-abundance of galaxies with close massive companions, we do not find any significant influence of the presence or absence of a close companion on the relative strength of the nuclear H-a peak, nor on the H-a morphology around the nucleus.
Enthusiasm and commitment for a strong European scientific programme are expressed in Giovanni Bignami's book "Explorer l'Espace pour Remonter le Temps' (Exploring space to go back in time), by Odile Jacob, Paris, published in January 2006. This book follows his other book "La Storia nello Spazio" (History in Space), published in Italian by Mursia, Milano, in 2001.
His latest book tells science stories of several past, present and future space missions (Giotto, Galileo, Cassini, BeppoSAX, RossiXTE, BepiColombo) of the ESA, NASA and ASI space agencies.
These missions address a vast panorama of science in space, from planets to comets and from black holes to explosive events in the Universe. Bignami also gives room to the lives, times and innovative spirit of each mission namesakes, from the early 1300s, with a taste of Giottos painting (including Halleys comet) in the Papal Europe, to the 1600s of Galileo and Gian Domenico Cassini, who left Bologna to go to Paris in the service of the Roi Soleil.
The overview moves onto the twentieth century, with Beppo Occhialini, Italian physicist at the Fermi school, and Bruno Rossi, who fled Fascist Italy to become the founder, in the United States, of astronomy in space. Finally, the book moves onto Bepi Colombo, the great scientist and celestial mechanics visionary of the University of Padova.
G.F. Bignami is chairman of ESA's Space Science Advisory Committee. He is the Director of the Centre d'Etude Spatiale des Rayonnements (CNRS-Universitè de Toulouse) and Professor of Astronomy at the University of Pavia. He is a member of the Accademia dei Lincei and of the Academia Europaea.
Here we report the first three-dimensional spatial spectrum of the low frequency magnetic turbulence obtained from the four Cluster spacecraft in the terrestrial magnetosheath close to the magnetopause. We show that the turbulence is compressible and dominated by mirror structures, its energy is injected at a large scale k × rho ~ 0.3 (l~2000 km) via a mirror instability well predicted by linear theory, and cascades nonlinearly and unexpectedly up to k × rho ~ 3.5 (l~150 km), revealing a new power law in the inertial range not predicted by any turbulence theory, and its strong anisotropy is controlled by the static magnetic field and the magnetopause normal.