7,203 research outputs found
Dark Matter Halos: The Dynamical Basis of Effective Empirical Models
We investigate the dynamical basis of the classic empirical models
(specifically, Sersic-Einasto and generalized NFW) that are widely used to
describe the distributions of collisionless matter in galaxies. We submit that
such a basis is provided by our \alpha-profiles, shown to constitute solutions
of the Jeans dynamical equilibrium with physical boundary conditions. We show
how to set the parameters of the empirical in terms of the dynamical models; we
find the empirical models, and specifically Sersic-Einasto, to constitute a
simple and close approximation to the dynamical models. Finally, we discuss how
these provide an useful baseline for assessing the impact of the small-scale
dynamics that may modulate the density slope in the central galaxy regions.Comment: 11 pages, 2 figures, Accepted by Advances in Astronom
Marine Fungi of Iceland: A Preliminary Account of Ascomycetes
This paper reports, for the first time, 25 species of marine pyrenomycetes from Icelandic waters. Taxonomic notes are included for certain species.
Surtsey, a submarine volcanic upthrust off the south coast of Iceland (Thorarinsson, 1967), is a current center for cooperative geophysical, geochemical, and biological investigations on an international scale. The mycological portion of the total biological research effort of the Surtsey project has emphasized a survey of the marine and freshwater mycoflora on the mainland of Iceland itself as a necessary prerequisite to ecological studies on Surtsey. With the exception of two reports on aquatic phycomycetes (Larsen, 1931, and Johnson, 1966), the aquatic mycoflora of Iceland is unknown. Thus Iceland, rather than Surtsey, has become the immediate focal point for mycological investigations
The History of Cosmic Baryons: X-ray Emission vs. Star Formation Rate
We relate the star formation from cold baryons in virialized structures to
the X-ray properties of the associated diffuse, hot baryonic component. Our
computations use the standard ``semi-analytic'' models to describe i) the
evolution of dark matter halos through merging after the hierarchical
clustering, ii) the star formation governed by radiative cooling and by
supernova feedback, iii) the hydro- and thermodynamics of the hot gas, rendered
with our Punctuated Equilibria model. So we relate the X-ray observables
concerning the intra-cluster medium to the thermal energy of the gas pre-heated
and expelled by supernovae following star formation, and then accreted during
the subsequent merging events. We show that at fluxes fainter than erg/cm s (well within the reach of next generation X-ray
observatories) the X-ray counts of extended extragalactic sources (as well as
the faint end of the luminosity function, the contribution to the soft X-ray
background, and the correlation at the group scales) increase
considerably when the star formation rate is enhanced for z>1 as indicated by
growing optical/infrared evidence. Specifically, the counts in the range 0.5-2
keV are increased by factors when the the feedback is decreased and
star formation is enhanced as to yield a flat shape of the star formation rate
for 2<z<4.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Two New Species of Leafblight Fungi on Kalmia Latifolia
The evergreen shrub, Kalmia latifolia L., commonly known as mountain laurel, calico bush, or sheep-kill, grows widely on rocky, acid soils in the eastern United States. Whether growing in its natural habit or in cultivation, mountain laurel appears to be equally subject to attack by fungi. The following account characterizes and discusses two of these fungi. One of them has not been described previously and additional observations have been made regarding the developmental morphology of the other one.
Both pathogens are Pyrenomycetes, one a Physalospora and the other a Diaporthe. Each produces a leafblight disease. Tiny brown discolorations on young leaves characterize the early stages of attack by both organisms. These small lesions gradually enlarge and become irregular brown spots that may encompass the major portion of the leaf surface. The invaded tissues are darkest near the margins of the lesions, but a reddish zone lies between the darker border and the surrounding green tissues. Severely attacked leaves are deformed and shed prematurely.
The reproductive structures of the Physalospora occur on the lower surface and begin to develop before the leaves are shed. The pycnidial stromata of the Diaporthe elevate the epidermis and caticle, and consequently produce grayish spots on the leaf surface. Both fungi continue to develop after the leaves have fallen, and since the mycelia extend beyond the margins of the lesions, perithecia ultimately may occupy most of the leaf surface. [excerpt
The SZ Effect as a Probe of Non-Gravitational Entropy in Groups and Clusters of Galaxies
We investigate how strongly and at what scales the Sunyaev- Zel'dovich effect
reflects the shifting balance between the two processes that compete for
governing the density and the thermodynamic state of the hot intra-cluster
medium pervading clusters and groups of galaxies: the hierarchical clustering
of the DM; the non-gravitational energy and momentum fed back into the ICM by
the condensing baryons. We base on a SAM of galaxy formation and clustering to
describe how the baryons are partitioned among the hot, the cool and the
stellar phase; the partition shifts as the galaxies cluster hierarchically, and
as the feedback by stellar winds and SN explosions follows the star formation.
Their impact is amplified by the same large scale accretion shocks that
thermalize the gravitational energy of gas falling into the growing potential
wells. We compute the Compton parameter , and find a relation of with
the ICM temperature, the relation, which departs from the self-similar
scaling and bends down at temperatures typical of galaxy groups. We
model-independently relate this with the analogous behaviour of the L_x - T
relation, and discuss to what extent our results are generic of the
hierarchical models of galaxy formation and clustering.Comment: 24 pages, 6 figures, submitted to MNRAS; typos correcte
Imbedding estimates and elliptic equations with discontinuous coefficients in unbounded domains
In this paper we deal with the multiplication operator u ∈ W^{k,p} (Ω) → gu ∈ L^q (Ω), with g belonging to a space of Morrey type. We apply our results in order to establish an a-priori bound for the solutions of the Dirichlet problem concerning elliptic equations with discontinuous coefficients
- …