1,301 research outputs found
Non-Parametric Maximum Likelihood Density Estimation and Simulation-Based Minimum Distance Estimators
Indirect inference estimators (i.e., simulation-based minimum distance
estimators) in a parametric model that are based on auxiliary non-parametric
maximum likelihood density estimators are shown to be asymptotically normal. If
the parametric model is correctly specified, it is furthermore shown that the
asymptotic variance-covariance matrix equals the inverse of the
Fisher-information matrix. These results are based on uniform-in-parameters
convergence rates and a uniform-in-parameters Donsker-type theorem for
non-parametric maximum likelihood density estimators.Comment: minor corrections, some discussion added, some material remove
Non-Parametric Maximum Likelihood Density Estimation and Simulation-Based Minimum Distance Estimators
Indirect inference estimators (i.e., simulation-based minimum distance estimators) in a parametric model that are based on auxiliary non-parametric maximum likelihood density estimators are shown to be asymptotically normal. If the parametric model is correctly specified, it is furthermore shown that the asymptotic variance-covariance matrix equals the Cramér-Rao bound. These results are based on uniform-in-parameters convergence rates and a uniform-in-parameters Donsker-type theorem for non-parametric maximum likelihood density estimators.Indirect inference, simulation-based minimum distance estimation, non-parametric maximum likelihood, density estimation, efficiency
A kinematic study of the irregular dwarf galaxy NGC 2366 using HI and Halpha observations
Abridged. Context. The metal content of dwarf galaxies and the metal
enrichment of the intergalactic medium both suggest that mass loss from
galaxies is a significant factor for the chemical evolution history of
galaxies, in particular of dwarf galaxies. However, no clear evidence of a
blow-away in local dwarf galaxies has been found so far.
Aims. We therefore performed a detailed kinematic analysis of the neutral and
ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order
to make predictions about the fate of the gas and to get a more complete
picture of this galaxy.
Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366
were obtained. They were complemented by HI synthesis data from the THINGS
survey. We searched for line-splitting both in Halpha and HI by performing a
Gaussian decomposition. To get an idea whether the expansion velocities are
high enough for a gas blow-away, we used the pseudo-isothermal halo model,
which gives us realistic values for the escape velocities of NGC 2366. The good
data quality also allowed us to discuss some peculiarities of the morphology
and the dynamics in NGC 2366.
Results. A large red-shifted outflow north west of the giant extragalactic
HII region with an expansion velocity of up to 50 km/s is found in Halpha, but
not in HI. Additionally, a blue-shifted component north of the giant
extragalactic HII region was detected both in Halpha and HI with an expansion
velocity of up to 30 km/s. A comparison with the escape velocities of NGC 2366
reveals that the gas does not have enough kinetic energy to leave the
gravitational potential.Comment: 15 pages, 14 figures, accepted for publication by A&
GIRAFFE multiple integral field units at VLT: a unique tool to recover velocity fields of distant galaxies
The GIRAFFE spectrograph is unique in providing the integral field
spectroscopy of fifteen distant galaxies at the same time. It has been
successfully implemented at the second VLT unit within the FLAMES facility. We
present GIRAFFE observations acquired during the Guaranteed Time Observation of
the Paris Observatory, using total exposure times ranging from 6 to 12 hours.
The reduced 3D cube of each galaxy has been deconvolved using our new package
DisGal3D. This software has been written using the only assumption that UV
light traces the emission line regions. The comparison between GIRAFFE spectra
and HST imagery allows us to recover details on velocity fields as small as
0.3-0.4 arcsec. It has been successfully tested using Fabry Perot observations
of nearby galaxies purposely redshifted to large distances. We present here
preliminary results for three distant galaxies at 0.45< z < 0.65, whose
velocity fields have been derived with exquisite spectral (R=10000) and spatial
resolutions. Observed velocity fields range from disturbed fields expected in
major merger events to those of regular spiral with minor perturbations. For
the latter, one could accurately derive the dynamical major axis and the
maximal rotational velocity. We conclude that dynamical properties of a large
number of distant galaxies can be routinely derived at VLT. This opens a new
avenue towards the understanding of the galaxy formation and evolution during
the last 8 Gyr.Comment: 4 pages, 3 jpeg figures. to appear in A&
An improved method for statistical studies of the internal kinematics of HII regions: the case of M 83
We present the integrated Halpha emission line profile for 157 HII regions in
the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot
interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the
importance of a good characterization of the instrumental response function for
the study of line profile shapes. The luminosity-velocity dispersion relation
is also studied, and in the log(L)-log(sigma) plane we do not find a linear
relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For
the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity
L=10^38.5 ergs, in full agreement with previous studies of other galaxies,
reinforcing the idea of using HII regions as standard candles.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Spiral inflow feeding the nuclear starburst in M83, observed in H-alpha emission with the GHAFAS Fabry-Perot interferometer
We present observations of the nearby barred starburst galaxy, M83 (NGC5236),
with the new Fabry-Perot interferometer GHAFAS mounted on the 4.2 meter William
Herschel Telescope on La Palma. The unprecedented high resolution observations,
of 16 pc/FWHM, of the H-alpha-emitting gas cover the central two kpc of the
galaxy. The velocity field displays the dominant disk rotation with signatures
of gas inflow from kpc scales down to the nuclear regions. At the inner Inner
Lindblad Resonance radius of the main bar and centerd at the dynamical center
of the main galaxy disk, a nuclear rapidly
rotating disk with scale length of pc has formed. The nuclear
starburst is found in the vicinity as well as inside this nuclear disk, and our
observations confirm that gas spirals in from the outer parts to feed the
nuclear starburst, giving rise to several star formation events at different
epochs, within the central 100 pc radius of M83.Comment: Accepted for publication in ApJ Letters. High-resolution version can
be found at http://www.astro.su.se/~kambiz/DOC/paper-M83.pd
GHASP : An Halpha kinematic survey of spiral and irregular galaxies - VI. New Halpha data cubes for 108 galaxies
We present the Fabry-Perot observations obtained for a new set of 108
galaxies that completes the GHASP survey (Gassendi HAlpha survey of SPirals).
The GHASP survey consists of 3D Ha data cubes for 203 spiral and irregular
galaxies, covering a large range in morphological types and absolute
magnitudes, for kinematics analysis. The GHASP sample is by now the largest
sample of Fabry-Perot data ever published. We have derived Ha data cubes from
which are computed Ha maps, radial velocity fields as well as residual velocity
fields, position-velocity diagrams, rotation curves and the kinematical
parameters for almost all galaxies. Original improvements in the determination
of the kinematical parameters, rotation curves and their uncertainties have
been implemented in the reduction procedure. This new method is based on the
whole 2D velocity field and on the power spectrum of the residual velocity
fieldrather than the classical method using successive crowns in the velocity
field. Among the results, we point out that morphological position angles have
systematically higher uncertainties than kinematical ones, especially for
galaxies with low inclination. Morphological inclination of galaxies having no
robust determination of their morphological position angle cannot be
constrained correctly. Galaxies with high inclination show a better agreement
between their kinematical inclination and their morphological inclination
computed assuming a thin disk. The consistency of the velocity amplitude of our
rotation curves have been checked using the Tully-Fisher relationship. Our data
are in good agreement with previous determinations found in the literature.
Nevertheless, galaxies with low inclination have statistically higher
velocities than expected and fast rotators are less luminous than expected.Comment: accepted in MNRAS for publication, 60 pages, 25 figures, usues
biblio.bib for bibliography (.bbl included in the archive), natbib.sty,
epsfig.st
An Evolutionary Sequence of Expanding Hydrogen Shells in Galaxy Discs
Large HI shells, with diameters of hundreds of pc and expansion velocities of
10-20kms-1 are well observed features of local gas rich galaxies. These shells
could well be predicted as a result of the impact of OB associations on the
ISM, but doubt has been cast on this scenario by the apparent absence of OB
stars close to the centres of a large fraction of these shells in recent
observations of the SMC. Using Fabry-Perot scanned Halpha emission line mapping
of nearby galaxy discs we have detected, in all the HII regions where the
observations yield sufficient angular resolution and S:N ratio, dominant Halpha
shells with radii a few tens of pc, expanding at velocities of 50-100kms-1. We
have applied a simple dynamically consistent framework in which we can
extrapolate the properties of the observed Halpha shells to a few 10^7yr after
the formation of the OB stars. The framework includes the dynamical inputs of
both winds and SNe on the surrounding ISM. The results give quantitative
statistical support to the hypothesis that the Halpha emitting shells are
generic progenitors of the HI shells. During the time taken for an expanding
shell to reach the size of a typical HI shell, the OB association may well lose
its most luminous stars so the absence of such stars near the centres of many
of the HI shells is well explained in this scenario.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
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