6,600 research outputs found
Disk galaxy scaling relations at intermediate redshifts - I. The Tully-Fisher and velocity-size relations
We took spatially resolved slit spectra of 261 field disk galaxies at
redshifts up to z~1 using the FORS instruments of the ESO Very Large Telescope.
Our spectroscopy was complemented with HST/ACS imaging in the F814W filter. We
analyzed the ionized gas kinematics by extracting rotation curves from the 2-D
spectra. Taking into account all geometrical, observational and instrumental
effects, these rotation curves were used to derive the intrinsic Vmax.
Neglecting galaxies with disturbed kinematics or insufficient spatial rotation
curve extent, Vmax could be robustly determined for 124 galaxies covering
redshifts 0.05<z<0.97. This is one of the largest kinematic samples of distant
disk galaxies to date. We compared this data set to the local B-band
Tully-Fisher relation and the local velocity-size relation. The scatter in both
scaling relations is a factor of ~2 larger at z~0.5 than at z~0. The deviations
of individual distant galaxies from the local Tully-Fisher relation are
systematic in the sense that the galaxies are increasingly overluminous towards
higher redshifts, corresponding to an over-luminosity of -(1.2+-0.5) mag at
z=1. This luminosity evolution at given Vmax is probably driven by younger
stellar populations of distant galaxies with respect to their local
counterparts, potentially combined with modest changes in dark matter mass
fractions. The analysis of the velocity-size relation reveals that disk
galaxies of a given Vmax have grown in size by a factor of ~1.5 over the past
~8 Gyr, likely via accretion of cold gas and/or small satellites. Scrutinizing
the combined evolution in luminosity and size, we find that the galaxies which
show the strongest evolution towards smaller sizes at z~1 are not those which
feature the strongest evolution in luminosity, and vice versa. [abstract
abbreviated]Comment: A&A, accepted. 12 pages, 6 figures, 1 tabl
Disk galaxy scaling relations at intermediate redshifts - I. The Tully-Fisher and velocity-size relations
We took spatially resolved slit spectra of 261 field disk galaxies at
redshifts up to z~1 using the FORS instruments of the ESO Very Large Telescope.
Our spectroscopy was complemented with HST/ACS imaging in the F814W filter. We
analyzed the ionized gas kinematics by extracting rotation curves from the 2-D
spectra. Taking into account all geometrical, observational and instrumental
effects, these rotation curves were used to derive the intrinsic Vmax.
Neglecting galaxies with disturbed kinematics or insufficient spatial rotation
curve extent, Vmax could be robustly determined for 124 galaxies covering
redshifts 0.05<z<0.97. This is one of the largest kinematic samples of distant
disk galaxies to date. We compared this data set to the local B-band
Tully-Fisher relation and the local velocity-size relation. The scatter in both
scaling relations is a factor of ~2 larger at z~0.5 than at z~0. The deviations
of individual distant galaxies from the local Tully-Fisher relation are
systematic in the sense that the galaxies are increasingly overluminous towards
higher redshifts, corresponding to an over-luminosity of -(1.2+-0.5) mag at
z=1. This luminosity evolution at given Vmax is probably driven by younger
stellar populations of distant galaxies with respect to their local
counterparts, potentially combined with modest changes in dark matter mass
fractions. The analysis of the velocity-size relation reveals that disk
galaxies of a given Vmax have grown in size by a factor of ~1.5 over the past
~8 Gyr, likely via accretion of cold gas and/or small satellites. Scrutinizing
the combined evolution in luminosity and size, we find that the galaxies which
show the strongest evolution towards smaller sizes at z~1 are not those which
feature the strongest evolution in luminosity, and vice versa. [abstract
abbreviated]Comment: A&A, accepted. 12 pages, 6 figures, 1 tabl
Internal kinematics of isolated modelled disk galaxies
We present a systematic investigation of rotation curves (RCs) of fully
hydrodynamically simulated galaxies, including cooling, star formation with
associated feedback and galactic winds. Applying two commonly used fitting
formulae to characterize the RCs, we investigate systematic effects on the
shape of RCs both by observational constraints and internal properties of the
galaxies. We mainly focus on effects that occur in measurements of intermediate
and high redshift galaxies. We find that RC parameters are affected by the
observational setup, like slit misalignment or the spatial resolution and also
depend on the evolution of a galaxy. Therefore, a direct comparison of
quantities derived from measured RCs with predictions of semi-analytic models
is difficult. The virial velocity V_c, which is usually calculated and used by
semi-analytic models can differ significantly from fit parameters like V_max or
V_opt inferred from RCs. We find that V_c is usually lower than typical
characteristic velocities derived from RCs. V_max alone is in general not a
robust estimator for the virial mass.Comment: 9 pages, 15 figures, accepted for publication in A&
Individual Control of Risk: Seat Belt Use, Subjective Norms and the Theory of Reasoned Action
When faced with a risk for which an inexpensive solution is available, individuals often choose the risk rather than the solution. Protection from certain kinds of risks, e.g., using seat belts or condoms or insulating against radon, is largely under personal control, but individuals often choose not to comply with behaviors which would reduce the risk. The Theory of Reasoned Action (TRA) has been used to predict when individuals will comply. The authors attempted to validate aspects of the TRA by the use of scenarios. Factor analysis of their data supports the theory that intention is a major determinate of behavior but fails to establish the influence of scenarios on subjects\u27 intention to wear seat belts
Self-administration of edible Δ9-tetrahydrocannabinol and associated behavioral effects in mice
Background
With increasing access to legal cannabis across the globe, it is imperative to more closely study its behavioral and physiological effects. Furthermore, with the proliferation of cannabis use, modes of consumption are changing, with edible formulations becoming increasingly popular. Nevertheless, there are relatively few animal models of self-administration of the primary psychoactive component of cannabis, Δ9-tetrahydrocannabinol (THC), and almost all incorporate routes of administration other than those used by humans. The aim of the current study was to develop a model of edible THC self-administration and assess its impact on CB1 receptor-mediated behaviors in female and male mice.
Methods
Mice were given limited access to a palatable dough which occasionally contained THC in doses ranging from 1 to 10 mg/kg. Following dough consumption, mice were assessed for home cage locomotor activity, body temperature, or analgesia. Locomotor activity was also assessed in conjunction with the CB1 receptor antagonist SR141716A.
Results
Dough was well-consumed, but consumption decreased at the highest THC concentrations. Edible THC produced dose-dependent decreases in locomotor activity and body temperature in both sexes, and these effects were more pronounced in male mice. Hypolocomotion induced by edible THC was attenuated by SR141716A, indicating mediation by CB1 receptor activation.
Conclusions
In contrast to other cannabinoid self-administration models, edible THC is relatively low in stress and uses a route of administration analogous to one used by humans. Potential applications include chronic THC self-administration, determining THC reward/reinforcement, and investigating consequences of oral THC use
Light spin-1/2 or spin-0 Dark Matter particles
We recall and precise how light spin-0 particles could be acceptable Dark
Matter candidates, and extend this analysis to spin-1/2 particles. We evaluate
the (rather large) annihilation cross sections required, and show how they may
be induced by a new light neutral spin-1 boson U. If this one is vectorially
coupled to matter particles, the (spin-1/2 or spin-0) Dark Matter annihilation
cross section into e+e- automatically includes a v_dm^2 suppression factor at
threshold, as desirable to avoid an excessive production of gamma rays from
residual Dark Matter annihilations. We also relate Dark Matter annihilations
with production cross sections in e+e- scatterings. Annihilation cross sections
of spin-1/2 and spin-0 Dark Matter particles are given by exactly the same
expressions. Just as for spin-0, light spin-1/2 Dark Matter particles
annihilating into e+e- could be responsible for the bright 511 keV gamma ray
line observed by INTEGRAL from the galactic bulge.Comment: 10 page
Internal kinematics of modelled interacting disc galaxies
We present an investigation of galaxy-galaxy interactions and their effects
on the velocity fields of disc galaxies in combined N-body/hydrodynamic
simulations, which include cooling, star formation with feedback, and galactic
winds. Rotation curves (RCs) of the gas are extracted from these simulations in
a way that follows the procedure applied to observations of distant, small, and
faint galaxies as closely as possible. We show that galaxy-galaxy mergers and
fly-bys disturb the velocity fields significantly and hence the RCs of the
interacting galaxies, leading to asymmetries and distortions in the RCs.
Typical features of disturbed kinematics are significantly rising or falling
profiles in the direction of the companion galaxy and pronounced bumps in the
RCs. In addition, tidal tails can leave strong imprints on the rotation curve.
All these features are observable for intermediate redshift galaxies, on which
we focus our investigations. We use a quantitative measure for the asymmetry of
rotation curves to show that the appearance of these distortions strongly
depends on the viewing angle. We also find in this way that the velocity fields
settle back into relatively undisturbed equilibrium states after unequal mass
mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no
severe distortions anymore. These results are consistent with previous
theoretical and observational studies. As an illustration of our results, we
compare our simulated velocity fields and direct images with rotation curves
from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find
remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some
improvements and changes, main conclusions are unaffecte
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