9,529 research outputs found
Verifying the mass-metallicity relation in damped Lyman-alpha selected galaxies at 0.1<z<3.2
A scaling relation has recently been suggested to combine the galaxy
mass-metallicity (MZ) relation with metallicities of damped Lyman-alpha systems
(DLAs) in quasar spectra. Based on this relation the stellar masses of the
absorbing galaxies can be predicted. We test this prediction by measuring the
stellar masses of 12 galaxies in confirmed DLA absorber - galaxy pairs in the
redshift range 0.1<z<3.2. We find an excellent agreement between the predicted
and measured stellar masses over three orders of magnitude, and we determine
the average offset = 0.44+/-0.10 between absorption
and emission metallicities. We further test if could depend on the
impact parameter and find a correlation at the 5.5sigma level. The impact
parameter dependence of the metallicity corresponds to an average metallicity
difference of -0.022+/-0.004 dex/kpc. By including this metallicity vs. impact
parameter correlation in the prescription instead of , the scatter
reduces to 0.39 dex in log M*. We provide a prescription how to calculate the
stellar mass (M*,DLA) of the galaxy when both the DLA metallicity and DLA
galaxy impact parameter is known. We demonstrate that DLA galaxies follow the
MZ relation for luminosity-selected galaxies at z=0.7 and z=2.2 when we include
a correction for the correlation between impact parameter and metallicity.Comment: 15 pages, 6 figures. Major revision. Accepted for publication in
MNRA
What controls the large-scale magnetic fields of M dwarfs?
Observations of active M dwarfs show a broad variety of large-scale magnetic
fields encompassing dipole-dominated and multipolar geometries. We detail the
analogy between some anelastic dynamo simulations and spectropolarimetric
observations of 23 M stars. In numerical models, the relative contribution of
inertia and Coriolis force in the global force balance -estimated by the
so-called local Rossby number- is known to have a strong impact on the magnetic
field geometry. We discuss the relevance of this parameter in setting the
large-scale magnetic field of M dwarfs.Comment: 4 pages, 3 figures, conference proceeding, IAUS 302 'Magnetic Fields
Throughout the Stellar Evolution', (26-30 Aug 2013, Biarritz, France
What controls the magnetic geometry of M dwarfs?
Context: observations of rapidly rotating M dwarfs show a broad variety of
large-scale magnetic fields encompassing dipole-dominated and multipolar
geometries. In dynamo models, the relative importance of inertia in the force
balance -- quantified by the local Rossby number -- is known to have a strong
impact on the magnetic field geometry. Aims: we aim to assess the relevance of
the local Rossby number in controlling the large-scale magnetic field geometry
of M dwarfs. Methods: we explore the similarities between anelastic dynamo
models in spherical shells and observations of active M-dwarfs, focusing on
field geometries derived from spectropolarimetric studies. To do so, we
construct observation-based quantities aimed to reflect the diagnostic
parameters employed in numerical models. Results: the transition between
dipole-dominated and multipolar large-scale fields in early to mid M dwarfs is
tentatively attributed to a Rossby number threshold. We interpret late M dwarfs
magnetism to result from a dynamo bistability occurring at low Rossby number.
By analogy with numerical models, we expect different amplitudes of
differential rotation on the two dynamo branches.Comment: 4 pages, 4 figures, accepted for publication in A&
Magnetic polarizability of hadrons from lattice QCD in the background field method
We present a calculation of hadron magnetic polarizability using the
techniques of lattice QCD. This is carried out by introducing a uniform
external magnetic field on the lattice and measuring the quadratic part of a
hadron's mass shift. The calculation is performed on a lattice with
standard Wilson actions at beta=6.0 (spacing fm) and pion mass down to
about 500 MeV. Results are obtained for 30 particles covering the entire baryon
octet (, , , , , , ,
) and decuplet (, , , ,
, , , , ,
), plus selected mesons (, , , , ,
, , , , , , ). The
results are compared with available values from experiments and other
theoretical calculations.Comment: 30 pages, 23 figures, 5 table
On the mass-metallicity relation, velocity dispersion and gravitational well depth of GRB host galaxies
We analyze a sample of 16 absorption systems intrinsic to long duration GRB
host galaxies at for which the metallicities are known. We
compare the relation between the metallicity and cold gas velocity width for
this sample to that of the QSO-DLAs, and find complete agreement. We then
compare the redshift evolution of the mass-metallicity relation of our sample
to that of QSO-DLAs and find that also GRB hosts favour a late onset of this
evolution, around a redshift of . We compute predicted stellar
masses for the GRB host galaxies using the prescription determined from QSO-DLA
samples and compare the measured stellar masses for the four hosts where
stellar masses have been determined from SED fits. We find excellent agreement
and conclude that, on basis of all available data and tests, long duration
GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the
same underlying population. GRB host galaxies and QSO-DLAs are found to have
different impact parameter distributions and we briefly discuss how this may
affect statistical samples. The impact parameter distribution has two effects.
First any metallicity gradient will shift the measured metallicity away from
the metallicity in the centre of the galaxy, second the path of the sightline
through different parts of the potential well of the dark matter halo will
cause different velocity fields to be sampled. We report evidence suggesting
that this second effect may have been detected.Comment: 11 pages, 6 figures, 6 tables. Accepted for publication in MNRAS Main
Journal. For the definitive version visit http://mnras.oxfordjournals.org
A magnetic field evolution scenario for brown dwarfs and giant planets
Very little is known about magnetic fields of extrasolar planets and brown
dwarfs. We use the energy flux scaling law presented by Christensen et al.
(2009) to calculate the evolution of average magnetic fields in extrasolar
planets and brown dwarfs under the assumption of fast rotation, which is
probably the case for most of them. We find that massive brown dwarfs of about
70 M_Jup can have fields of a few kilo-Gauss during the first few hundred
Million years. These fields can grow by a factor of two before they weaken
after deuterium burning has stopped. Brown dwarfs with weak deuterium burning
and extrasolar giant planets start with magnetic fields between ~100G and ~1kG
at the age of a few Myr, depending on their mass. Their magnetic field weakens
steadily until after 10Gyr it has shrunk by about a factor of 10. We use
observed X-ray luminosities to estimate the age of the known extrasolar giant
planets that are more massive than 0.3M_Jup and closer than 20pc. Taking into
account the age estimate, and assuming sun-like wind-properties and radio
emission processes similar to those at Jupiter, we calculate their radio flux
and its frequency. The highest radio flux we predict comes out as 700mJy at a
frequency around 150MHz for Boob, but the flux is below 60mJy for the
rest. Most planets are expected to emit radiation between a few Mhz and up to
100MHz, well above the ionospheric cutoff frequency.Comment: 7 pages, accepted by A&
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