33 research outputs found
Line Profiles from Discrete Kinematic Data
We develop a method to extract the shape information of line profiles from
discrete kinematic data. The Gauss-Hermite expansion, which is widely used to
describe the line of sight velocity distributions extracted from absorption
spectra of elliptical galaxies, is not readily applicable to samples of
discrete stellar velocity measurements, accompanied by individual measurement
errors and probabilities of membership. We introduce two parameter families of
probability distributions describing symmetric and asymmetric distortions of
the line profiles from Gaussianity. These are used as the basis of a maximum
likelihood estimator to quantify the shape of the line profiles. Tests show
that the method outperforms a Gauss-Hermite expansion for discrete data, with a
lower limit for the relative gain of approx 2 for sample sizes N approx 800. To
ensure that our methods can give reliable descriptions of the shape, we develop
an efficient test to assess the statistical quality of the obtained fit. As an
application, we turn our attention to the discrete velocity datasets of the
dwarf spheroidals of the Milky Way. In Sculptor, Carina and Sextans the
symmetric deviations are consistent with velocity distributions more peaked
than Gaussian. In Fornax, instead, there is an evolution in the symmetric
deviations of the line profile from a peakier to more flat-topped distribution
on moving outwards. These results suggest a radially biased orbital structure
for the outer parts of Sculptor, Carina and Sextans. On the other hand,
tangential anisotropy is favoured in Fornax. This is all consistent with a
picture in which Fornax may have had a different evolutionary history to
Sculptor, Carina and Sextans.Comment: MNRAS, accepted for publication, minor change
Neural field model for measuring and reproducing time intervals
The continuous real-time motor interaction with our environment requires the capacity to measure and produce time intervals in a highly flexible manner. Recent neurophysiological evidence suggests that the neural computational principles supporting this capacity may be understood from a dynamical systems perspective: Inputs and initial conditions determine how a recurrent neural network evolves from a “resting state” to a state triggering the action. Here we test this hypothesis in a time measurement and time reproduction experiment using a model of a robust neural integrator based on the theoretical framework of dynamic neural fields. During measurement, the temporal accumulation of input leads to the evolution of a self-stabilized bump whose amplitude reflects elapsed time. During production, the stored information is used to reproduce on a trial-by-trial basis the time interval either by adjusting input strength or initial condition of the integrator. We discuss the impact of the results on our goal to endow autonomous robots with a human-like temporal cognition capacity for natural human-robot interactions.The work received financial support from FCT through the PhD fellowship
PD/BD/128183/2016, the project ”Neurofield” (POCI-01-0145-FEDER-031393)
and the research centre CMAT within the project UID/MAT/00013/2013
Equation of state for Universe from similarity symmetries
In this paper we proposed to use the group of analysis of symmetries of the
dynamical system to describe the evolution of the Universe. This methods is
used in searching for the unknown equation of state. It is shown that group of
symmetries enforce the form of the equation of state for noninteracting scaling
multifluids. We showed that symmetries give rise the equation of state in the
form and energy density
, which
is commonly used in cosmology. The FRW model filled with scaling fluid (called
homological) is confronted with the observations of distant type Ia supernovae.
We found the class of model parameters admissible by the statistical analysis
of SNIa data. We showed that the model with scaling fluid fits well to
supernovae data. We found that and (), which can correspond to (hyper) phantom fluid, and to a
high density universe. However if we assume prior that
then the favoured model is close to concordance
CDM model. Our results predict that in the considered model with
scaling fluids distant type Ia supernovae should be brighter than in
CDM model, while intermediate distant SNIa should be fainter than in
CDM model. We also investigate whether the model with scaling fluid is
actually preferred by data over CDM model. As a result we find from
the Akaike model selection criterion prefers the model with noninteracting
scaling fluid.Comment: accepted for publication versio
A combined measurement of cosmic growth and expansion from clusters of galaxies, the CMB and galaxy clustering
Combining galaxy cluster data from the ROSAT All-Sky Survey and the Chandra
X-ray Observatory, cosmic microwave background data from the Wilkinson
Microwave Anisotropy Probe, and galaxy clustering data from the WiggleZ Dark
Energy Survey, the 6-degree Field Galaxy Survey and the Sloan Digital Sky
Survey III, we test for consistency the cosmic growth of structure predicted by
General Relativity (GR) and the cosmic expansion history predicted by the
cosmological constant plus cold dark matter paradigm (LCDM). The combination of
these three independent, well studied measurements of the evolution of the mean
energy density and its fluctuations is able to break strong degeneracies
between model parameters. We model the key properties of cosmic growth with the
normalization of the matter power spectrum, sigma_8, and the cosmic growth
index, gamma, and those of cosmic expansion with the mean matter density,
Omega_m, the Hubble constant, H_0, and a kinematical parameter equivalent to
that for the dark energy equation of state, w. For a spatially flat geometry,
w=-1, and allowing for systematic uncertainties, we obtain sigma_8=0.785+-0.019
and gamma=0.570+0.064-0.063 (at the 68.3 per cent confidence level). Allowing
both w and gamma to vary we find w=-0.950+0.069-0.070 and gamma=0.533+-0.080.
To further tighten the constraints on the expansion parameters, we also include
supernova, Cepheid variable and baryon acoustic oscillation data. For w=-1, we
have gamma=0.616+-0.061. For our most general model with a free w, we measure
Omega_m=0.278+0.012-0.011, H_0=70.0+-1.3 km s^-1 Mpc^-1 and
w=-0.987+0.054-0.053 for the expansion parameters, and sigma_8=0.789+-0.019 and
gamma=0.604+-0.078 for the growth parameters. These results are in excellent
agreement with GR+LCDM (gamma~0.55; w=-1) and represent the tightest and most
robust simultaneous constraint on cosmic growth and expansion to date.Comment: 14 pages, 5 figures, 1 table. Matches the accepted version for MNRAS.
New sections 3 and 6 added, containing 2 new figures. Table extended. The
results including BAO data have been slightly modified due to an updated BAO
analysis. Conclusions unchange
Dark energy problem: from phantom theory to modified Gauss-Bonnet gravity
The solution of dark energy problem in the models without scalars is
presented. It is shown that late-time accelerating cosmology may be generated
by the ideal fluid with some implicit equation of state. The universe evolution
within modified Gauss-Bonnet gravity is considered. It is demonstrated that
such gravitational approach may predict the (quintessential, cosmological
constant or transient phantom) acceleration of the late-time universe with
natural transiton from deceleration to acceleration (or from non-phantom to
phantom era in the last case).Comment: LaTeX 8 pages, prepared for the Proceedings of QFEXT'05, minor
correctons, references adde
SN 2021hpr and its two siblings in the Cepheid calibrator galaxy NGC 3147: A hierarchical BayeSN analysis of a Type Ia supernova trio, and a Hubble constant constraint
To improve Type Ia supernova (SN Ia) standardisability, the consistency of
distance estimates to siblings -- SNe in the same host galaxy -- should be
investigated. We present Young Supernova Experiment Pan-STARRS-1
photometry of SN 2021hpr, the third spectroscopically confirmed SN Ia in the
high-stellar-mass Cepheid-calibrator galaxy NGC 3147. We analyse NGC 3147's
trio of SN Ia siblings: SNe 1997bq, 2008fv and 2021hpr, using a new version of
the BayeSN model of SN Ia spectral-energy distributions, retrained
simultaneously using optical-NIR (0.35--1.8 m) data. The
distance estimates to each sibling are consistent, with a sample standard
deviation 0.01 mag, much smaller than the total intrinsic scatter in
the training sample: mag. Fitting normal SN Ia siblings
in three additional galaxies, we estimate a 90% probability that the
siblings' intrinsic scatter is smaller than . We build a new
hierarchical model that fits light curves of siblings in a single galaxy
simultaneously; this yields more precise estimates of the common distance and
the dust parameters. Fitting the trio for a common dust law shape yields
. Our work motivates future hierarchical modelling of more
siblings, to tightly constrain their intrinsic scatter, and better understand
SN-host correlations. Finally, we estimate the Hubble constant, using a Cepheid
distance to NGC 3147, the siblings trio, and 109 Hubble flow () SNe Ia; marginalising over the siblings' and population's
intrinsic scatters, and the peculiar velocity dispersion, yields
.Comment: Submitted to MNRAS; 30 pages, 22 figure
The stellar and sub-stellar IMF of simple and composite populations
The current knowledge on the stellar IMF is documented. It appears to become
top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr
pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing
metallicity and in increasingly massive early-type galaxies. It declines quite
steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars
having their own IMF. The most massive star of mass mmax formed in an embedded
cluster with stellar mass Mecl correlates strongly with Mecl being a result of
gravitation-driven but resource-limited growth and fragmentation induced
starvation. There is no convincing evidence whatsoever that massive stars do
form in isolation. Various methods of discretising a stellar population are
introduced: optimal sampling leads to a mass distribution that perfectly
represents the exact form of the desired IMF and the mmax-to-Mecl relation,
while random sampling results in statistical variations of the shape of the
IMF. The observed mmax-to-Mecl correlation and the small spread of IMF
power-law indices together suggest that optimally sampling the IMF may be the
more realistic description of star formation than random sampling from a
universal IMF with a constant upper mass limit. Composite populations on galaxy
scales, which are formed from many pc scale star formation events, need to be
described by the integrated galactic IMF. This IGIMF varies systematically from
top-light to top-heavy in dependence of galaxy type and star formation rate,
with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and
Galactic Structure, Vol.5, Springer. This revised version is consistent with
the published version and includes additional references and minor additions
to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-
A neural integrator model for planning and value-based decision making of a robotics assistant
Modern manufacturing and assembly environments are characterized by a high variability in the built process which challenges human–robot cooperation. To reduce the cognitive workload of the operator, the robot should not only be able to learn from experience but also to plan and decide autonomously. Here, we present an approach based on Dynamic Neural Fields that apply brain-like computations to endow a robot with these cognitive functions. A neural integrator is used to model the gradual accumulation of sensory and other evidence as time-varying persistent activity of neural populations. The decision to act is modeled by a competitive dynamics between neural populations linked to different motor behaviors. They receive the persistent activation pattern of the integrators as input. In the first experiment, a robot learns rapidly by observation the sequential order of object transfers between an assistant and an operator to subsequently substitute the assistant in the joint task. The results show that the robot is able to proactively plan the series of handovers in the correct order. In the second experiment, a mobile robot searches at two different workbenches for a specific object to deliver it to an operator. The object may appear at the two locations in a certain time period with independent probabilities unknown to the robot. The trial-by-trial decision under uncertainty is biased by the accumulated evidence of past successes and choices. The choice behavior over a longer period reveals that the robot achieves a high search efficiency in stationary as well as dynamic environments.The work received financial support
from FCT through the PhD fellowships PD/BD/128183/2016
and SFRH/BD/124912/2016, the project “Neurofield”
(PTDC/MAT-APL/31393/2017) and the research centre
CMAT within the project UID/MAT/00013/2013
LensWatch: I. Resolved HST Observations and Constraints on the Strongly-Lensed Type Ia Supernova 2022qmx ("SN Zwicky")
Supernovae (SNe) that have been multiply-imaged by gravitational lensing are
rare and powerful probes for cosmology. Each detection is an opportunity to
develop the critical tools and methodologies needed as the sample of lensed SNe
increases by orders of magnitude with the upcoming Vera C. Rubin Observatory
and Nancy Grace Roman Space Telescope. The latest such discovery is of the
quadruply-imaged Type Ia SN 2022qmx (aka, "SN Zwicky"; Goobar et al. 2022) at z
= 0.3544. SN Zwicky was discovered by the Zwicky Transient Facility (ZTF) in
spatially unresolved data. Here we present follow-up Hubble Space Telescope
observations of SN Zwicky, the first from the multi-cycle "LensWatch" program
(www.lenswatch.org). We measure photometry for each of the four images of SN
Zwicky, which are resolved in three WFC3/UVIS filters (F475W, F625W, F814W) but
unresolved with WFC3/IR F160W, and produce an analysis of the lensing system
using a variety of independent lens modeling methods. We find consistency
between time delays estimated with the single epoch of HST photometry and the
lens model predictions constrained through the multiple image positions, with
both inferring time delays of <1 day. Our lens models converge to an Einstein
radius of (0.168+0.009-0.005)", the smallest yet seen in a lensed SN. The
"standard candle" nature of SN Zwicky provides magnification estimates
independent of the lens modeling that are brighter by ~1.5 mag and ~0.8 mag for
two of the four images, suggesting significant microlensing and/or additional
substructure beyond the flexibility of our image-position mass models
The Young Supernova Experiment: Survey Goals, Overview, and Operations
Time domain science has undergone a revolution over the past decade, with
tens of thousands of new supernovae (SNe) discovered each year. However,
several observational domains, including SNe within days or hours of explosion
and faint, red transients, are just beginning to be explored. Here, we present
the Young Supernova Experiment (YSE), a novel optical time-domain survey on the
Pan-STARRS telescopes. Our survey is designed to obtain well-sampled
light curves for thousands of transient events up to . This
large sample of transients with 4-band light curves will lay the foundation for
the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope,
providing a critical training set in similar filters and a well-calibrated
low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy
science. As the name suggests, YSE complements and extends other ongoing
time-domain surveys by discovering fast-rising SNe within a few hours to days
of explosion. YSE is the only current four-band time-domain survey and is able
to discover transients as faint 21.5 mag in and 20.5 mag in
, depths that allow us to probe the earliest epochs of stellar explosions.
YSE is currently observing approximately 750 square degrees of sky every three
days and we plan to increase the area to 1500 square degrees in the near
future. When operating at full capacity, survey simulations show that YSE will
find 5000 new SNe per year and at least two SNe within three days of
explosion per month. To date, YSE has discovered or observed 8.3% of the
transient candidates reported to the International Astronomical Union in 2020.
We present an overview of YSE, including science goals, survey characteristics
and a summary of our transient discoveries to date.Comment: ApJ, in press; more information at https://yse.ucsc.edu