21,361 research outputs found
The Minimum Amount of Stars a Galaxy Will Form
We present an analysis of the atomic hydrogen and stellar properties of 38
late-type galaxies in the local Universe covering a wide range of HI
mass-to-light ratios (M_HI/L_B), stellar luminosities, and surface
brightnesses. From these data we have identified an upper envelope for the
M_HI/L_B as a function of galaxy luminosity. This implies an empirical relation
between the minimum amount of stars a galaxy will form and its initial baryonic
mass. While the stellar mass of a galaxy seems to be only loosely connected to
its baryonic mass, the latter quantity is strongly linked to the galaxy's
dynamical mass as it is observed in the baryonic Tully-Fisher relation. We find
that dwarf irregular galaxies with generally high M_HI/L_B-ratios follow the
same trend as defined by lower M_HI/L_B giant galaxies, but are underluminous
for their rotation velocity to follow the trend in a stellar mass Tully-Fisher
relation, suggesting that the baryonic mass of the dwarf galaxies is normal but
they have failed to produced a sufficient amount of stars. Finally, we present
a three dimensional equivalent to the morphology-density relation which shows
that high M_HI/L_B galaxies preferentially evolve and/or survive in low-density
environments. We conclude that an isolated galaxy with a shallow dark matter
potential can retain a large portion of its baryonic matter in the form of gas,
only producing a minimum quantity of stars necessary to maintain a stable gas
disk.Comment: 37 Pages, 7 Figures. Accepted for publication in A
The cognitive organization of music knowledge: a clinical analysis
Despite much recent interest in the clinical neuroscience of music processing, the cognitive organization of music as a domain of non-verbal knowledge has been little studied. Here we addressed this issue systematically in two expert musicians with clinical diagnoses of semantic dementia and Alzheimer’s disease, in comparison with a control group of healthy expert musicians. In a series of neuropsychological experiments, we investigated associative knowledge of musical compositions (musical objects), musical emotions, musical instruments (musical sources) and music notation (musical symbols). These aspects of music knowledge were assessed in relation to musical perceptual abilities and extra-musical neuropsychological functions. The patient with semantic dementia showed relatively preserved recognition of musical compositions and musical symbols despite severely impaired recognition of musical emotions and musical instruments from sound. In contrast, the patient with Alzheimer’s disease showed impaired recognition of compositions, with somewhat better recognition of composer and musical era, and impaired comprehension of musical symbols, but normal recognition of musical emotions and musical instruments from sound. The findings suggest that music knowledge is fractionated, and superordinate musical knowledge is relatively more robust than knowledge of particular music. We propose that music constitutes a distinct domain of non-verbal knowledge but shares certain cognitive organizational features with other brain knowledge systems. Within the domain of music knowledge, dissociable cognitive mechanisms process knowledge derived from physical sources and the knowledge of abstract musical entities
- …