3,078 research outputs found
The stellar-subhalo mass relation of satellite galaxies
We extend the abundance matching technique (AMT) to infer the
satellite-subhalo and central-halo mass relations (MRs) of galaxies, as well as
the corresponding satellite conditional mass functions (CMFs). We use the
observed galaxy stellar mass function (GSMF) decomposed into centrals and
satellites and the LCDM halo/subhalo mass functions as inputs. We explore the
effects of defining the subhalo mass at the time of accretion (m_acc) vs. at
the time of observation (m_obs). We test the standard assumption that centrals
and satellites follow the same MRs, showing that this assumption leads to
predictions in disagreement with observations, specially for m_obs. Instead,
when the satellite-subhalo MRs are constrained following our AMT, they are
always different from the central-halo MR: the smaller the stellar mass (Ms),
the less massive is the subhalo of satellites as compared to the halo of
centrals of the same Ms. On average, for Ms<2x10^11Msol, the dark mass of
satellites decreased by 60-65% with respect to their masses at accretion time.
The resulting MRs for both definitions of subhalo mass yield satellite CMFs in
agreement with observations. Also, when these MRs are used in a HOD model, the
predicted correlation functions agree with observations. We show that the use
of m_obs leads to less uncertain MRs than m_acc, and discuss implications of
the obtained satellite-subhalo MR. For example, we show that the tension
between abundance and dynamics of MW satellites in LCDM gives if the slope of
the GSMF faint-end slope upturns to -1.6.Comment: 13, pages, 4 figures. Accepted for publication in ApJ. Minor changes
to previous versio
Evolution of basin and range structure in the Ruby Mountains and vicinity, Nevada
Results from various age dating techniques, seismic reflection profiling hydrocarbon maturation studies, and structural analysis were used to evaluate the Cenozoic deformation in the Ruby Mountains and adjoining ranges (pinyon Range and Cortez Range) in Elko and Eureka Counties, Nevada. Age dating techniques used include potassium-argon ages of biotites from granites published by Kistler et al. (1981) and fission track ages from apatite and zircon. Fission track ages from apatite reflect a closing temperature of 100 plus or minus 20 deg C. Zircon fission track ages reflect a closing temperature of 175 plus or minus 25 deg C and potassium-argon ages from brotite reflect a closing temperature of 250 plus or minus 30 deg C. Thus these results allow a reasonably precise tracking of the evolution of the ranges during the Cenozoic. Seismic reflection data are available from Huntington Valley. Access to seismic reflection data directly to the west of the Harrison Pass Pluton in the central Ruby Mountains was obtained. In addition results are available from several deep exploration holes in Huntington Valley
Self-trapping at the liquid vapor critical point
Experiments suggest that localization via self-trapping plays a central role
in the behavior of equilibrated low mass particles in both liquids and in
supercritical fluids. In the latter case, the behavior is dominated by the
liquid-vapor critical point which is difficult to probe, both experimentally
and theoretically. Here, for the first time, we present the results of
path-integral computations of the characteristics of a self-trapped particle at
the critical point of a Lennard-Jones fluid for a positive particle-atom
scattering length. We investigate the influence of the range of the
particle-atom interaction on trapping properties, and the pick-off decay rate
for the case where the particle is ortho-positronium.Comment: 12 pages, 3 figures, revtex4 preprin
Angular momentum distribution of hot gas and implications for disk galaxy formation
We study the angular momentum profiles both for dark matter and for gas
within virialized halos, using a statistical sample of halos drawn from
cosmological hydrodynamics simulations. Three simulations have been analyzed,
one is the ``non-radiative'' simulation, and the other two have radiative
cooling. We find that the gas component on average has a larger spin and
contains a smaller fraction of mass with negative angular momentum than its
dark matter counterpart in the non-radiative model. As to the cooling models,
the gas component shares approximately the same spin parameter as its dark
matter counterpart, but the hot gas has a higher spin and is more aligned in
angular momentum than dark matter, while the opposite holds for the cold gas.
After the mass of negative angular momentum is excluded, the angular momentum
profile of the hot gas component approximately follows the universal function
originally proposed by Bullock et al. for dark matter, though the shape
parameter is much larger for hot gas and is comfortably in the range
required by observations of disk galaxies. Since disk formation is related to
the distribution of hot gas that will cool, our study may explain the fact that
the disk component of observed galaxies contains a smaller fraction of low
angular momentum material than dark matter in halos.Comment: 30 pages, 12 figures, 4 tables, accepted for publication in Ap
Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution
We discuss the dissipation of turbulent kinetic energy Ek in the global ISM
by means of 2-D, MHD, non-isothermal simulations in the presence of model
radiative heating and cooling. We argue that dissipation in 2D is
representative of that in three dimensions as long as it is dominated by shocks
rather than by a turbulent cascade. Energy is injected at a few isolated sites
in space, over relatively small scales, and over short time periods. This leads
to the coexistence of forced and decaying regimes in the same flow. We find
that the ISM-like flow dissipates its turbulent energy rapidly. In simulations
with forcing, the input parameters are the radius l_f of the forcing region,
the total kinetic energy e_k each source deposits into the flow, and the rate
of formation of those regions, sfr_OB. The global dissipation time t_d depends
mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g
u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and
u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >=
1.5x10^7 yr. The global dissipation time is consistently smaller than the
crossing time of the largest energy-containing scales. In decaying simulations,
Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with
distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If
applicable to the vertical direction, our results support models of galaxy
evolution in which stellar energy injection provides significant support for
the gas disk thickness, but not models of galaxy formation in which this energy
injection is supposed to reheat an intra-halo medium at distances of up to
10-20 times the optical galaxy size, as the dissipation occurs on distances
comparable to the disk height.Comment: 23 pages, including figures. To appear in ApJ. Abstract abridge
Revisiting Clifford algebras and spinors III: conformal structures and twistors in the paravector model of spacetime
This paper is the third of a series of three, and it is the continuation of
math-ph/0412074 and math-ph/0412075. After reviewing the conformal spacetime
structure, conformal maps are described in Minkowski spacetime as the twisted
adjoint representation of the group Spin_+(2,4), acting on paravectors.
Twistors are then presented via the paravector model of Clifford algebras and
related to conformal maps in the Clifford algebra over the lorentzian R{4,1}$
spacetime. We construct twistors in Minkowski spacetime as algebraic spinors
associated with the Dirac-Clifford algebra Cl(1,3)(C) using one lower spacetime
dimension than standard Clifford algebra formulations, since for this purpose
the Clifford algebra over R{4,1} is also used to describe conformal maps,
instead of R{2,4}. Although some papers have already described twistors using
the algebra Cl(1,3)(C), isomorphic to Cl(4,1), the present formulation sheds
some new light on the use of the paravector model and generalizations.Comment: 17 page
The Formal Description of Minimal Basic
The purpose of this formal description of Minimal Basic is to provide an operational description which is not subject to the ambiguities of interpretation of natural language specifications
Assessing the Effects of Banana Pingers as a Bycatch Mitigation Device for Harbour Porpoises (Phocoena phocoena)
This is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement:
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, to any qualified researcher.Bycatch is a significant cause of population declines of marine megafauna globally. While numerous bycatch mitigation strategies exist, acoustic alarms, or pingers, are the most widely adopted strategy for small cetaceans. Although pingers have been shown to be an effective measure for numerous species, there are some concerns about their long-term use. Bycatch is recognized as a persistent problem in waters around Cornwall, United Kingdom, where several cetacean species are resident, with harbour porpoises (Phocoena phocoena) being the most-commonly sighted. In this study, we assessed the effects of a Banana Pinger (Fishtek Marine Limited) on harbour porpoises in Cornwall between August 2012 and March 2013. Two passive acoustic loggers (C-PODs; Chelonia Limited) were deployed 100 m apart to record cetacean activity during cycles of active and inactive pinger periods. Harbour porpoises were 37% less likely to be detected at the C-POD near the pinger when the pinger was active, while they were only 9% less likely to be detected 100 m further away. The effect of the pinger was constant over the study period at both C-PODs despite the temporal variation in harbour porpoise detections. In addition, we found no evidence of reduced pinger effect with changing environmental conditions. Furthermore, harbour porpoise detections at the C-POD near the pinger did not depend on the time elapsed since the pinger turned off, with harbour porpoises returning to the ensonified area with no delay. Together these results suggest that (1) harbour porpoises did not habituate to the pinger over an 8-month period, (2) the pinger effect is very localized, and (3) pinger use did not lead to harbour porpoise displacement over the study period, suggesting an absence of long-term behavioral effects. We suggest that the deployment of pingers on fishing nets would likely reduce net-porpoise interactions, thereby mitigating bycatch of harbour porpoises and potentially other cetacean species. As the small-scale fishery dominates in United Kingdom waters, there is an acute need for cost-effective mitigation strategies with concurrent monitoring to be implemented rapidly in order to address the problem of harbour porpoise, and more generally, cetacean bycatch.Whale and Dolphin ConservationFishtek Marine Limite
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