1,859 research outputs found
Adversarial recovery of agent rewards from latent spaces of the limit order book
Inverse reinforcement learning has proved its ability to explain state-action
trajectories of expert agents by recovering their underlying reward functions
in increasingly challenging environments. Recent advances in adversarial
learning have allowed extending inverse RL to applications with non-stationary
environment dynamics unknown to the agents, arbitrary structures of reward
functions and improved handling of the ambiguities inherent to the ill-posed
nature of inverse RL. This is particularly relevant in real time applications
on stochastic environments involving risk, like volatile financial markets.
Moreover, recent work on simulation of complex environments enable learning
algorithms to engage with real market data through simulations of its latent
space representations, avoiding a costly exploration of the original
environment. In this paper, we explore whether adversarial inverse RL
algorithms can be adapted and trained within such latent space simulations from
real market data, while maintaining their ability to recover agent rewards
robust to variations in the underlying dynamics, and transfer them to new
regimes of the original environment.Comment: Published as a workshop paper on NeurIPS 2019 Workshop on Robust AI
in Financial Services. 33rd Conference on Neural Information Processing
Systems (NeurIPS 2019), Vancouver, Canad
Obscured Starburst Activity in High Redshift Clusters and Groups
Using Spitzer-MIPS 24um imaging and Keck spectroscopy we examine the nature
of the obscured star forming population in three clusters and three groups at
z~0.9. These six systems are components of the Cl1604 supercluster, the largest
structure imaged by Spitzer at redshifts near unity. We find that the average
density of 24um-detected galaxies within the Cl1604 clusters is nearly twice
that of the surrounding field and that this overdensity scales with the
cluster's dynamical state. The 24um-bright members often appear optically
unremarkable and exhibit only moderate [OII] line emission due to severe
obscuration. Their spatial distribution suggests they are an infalling
population, but an examination of their spectral properties, morphologies and
optical colors indicate they are not simply analogs of the field population
that have yet to be quenched. Using stacked composite spectra, we find the
24um-detected cluster and group galaxies exhibit elevated levels of Balmer
absorption compared to galaxies undergoing normal, continuous star formation. A
similar excess is not observed in field galaxies with equivalent infrared
luminosities, indicating a greater fraction of the detected cluster and group
members have experienced a burst of star formation in the recent past compared
to their counterparts in the field. Our results suggest that gas-rich galaxies
at high redshift experience a temporary increase in their star formation
activity as they assemble into denser environments. Using HST-ACS imaging we
find that disturbed morphologies are common among the 24um-detected cluster and
group members and become more prevalent in regions of higher galaxy density. We
conclude that mergers are the dominant triggering mechanism responsible for the
enhanced star formation found in the Cl1604 groups, while a mix of harassment
and mergers are likely driving the activity of the cluster galaxies.Comment: 18 pages, 19 figures, submitted to Ap
Making school happen: children-parent-teacher
The exercise of citizenship is today understood as a duty and as a right to be
enjoyed within any educational context. Within the school, all of its protagonists are
invited to exercise practices of citizenship. No one is excluded; even the less important
parties have the right to participate in decisions that, for some reason, may have an
influence on their academic life. The citizenship of the child is, thus, a challenge to the
changing political, social and educational structures, to the transformation of institutions
and to cultural renewal. The existence of harmonious relations between the educational
community, the school, the children and the family is dependent on everyoneâs ability to
understand and communicate with each other. Parents and teachers have made a
commitment to a fruitful and unison dialogue on behalf of the quality of education. In this
article, we set out from an analysis of the new social realities and of the different meanings
assigned to education, to afterwards reflect upon the current educational values and upon
the practices that are consistent with those purposes. Citizenship, as well as autonomy, rise,
thus, as central concepts, in which each educational community finds reasons for Making
School Happen.CIEC â Research Centre on Child Studies, UM (FCT R&D 317
NGC 2770 - a supernova Ib factory?
NGC 2770 has been the host of three supernovae of Type Ib during the last 10
years, SN 1999eh, SN 2007uy and SN 2008D. SN 2008D attracted special attention
due to the serendipitous discovery of an associated X-ray transient. In this
paper, we study the properties of NGC 2770 and specifically the three SN sites
to investigate whether this galaxy is in any way peculiar to cause a high
frequency of SNe Ib. We model the global SED of the galaxy from broadband data
and derive a star-formation and SN rate comparable to the values of the Milky
Way. We further study the galaxy using longslit spectroscopy covering the major
axis and the three SN sites. From the spectroscopic study we find subsolar
metallicities for the SN sites, a high extinction and a moderate star-formation
rate. In a high resolution spectrum, we also detect diffuse interstellar bands
in the line-of-sight towards SN 2008. A comparison of NGC 2770 to the global
properties of a galaxy sample with high SN occurance (at least 3 SN in the last
100 years) suggests that NGC 2770 is not particularly destined to produce such
an enhancement of observed SNe observed. Its properties are also very different
from gamma-ray burst host galaxies. Statistical considerations on SN Ib
detection rates give a probability of ~1.5% to find a galaxy with three Ib SNe
detected in 10 years. The high number of rare Ib SNe in this galaxy is
therefore likely to be a coincidence rather than special properties of the
galaxy itself. NGC 2770 has a small irregular companion, NGC 2770B, which is
highly starforming, has a very low mass and one of the lowest metallicities
detected in the nearby universe as derived from longslit spectroscopy. In the
most metal poor part, we even detect Wolf-Rayet features, against the current
models of WR stars which require high metallicities.Comment: 15 pages, 10 figures, submitted to Ap
Infrared properties of the SDSS-maxBCG galaxy clusters
The physics of galaxy clusters has proven to be influenced by several
processes connected with their galactic component which pollutes the ICM with
metals, stars and dust. However, it is not clear whether the presence of
diffuse dust can play a role in clusters physics since a characterisation of
the IR properties of galaxy clusters is yet to be completely achieved. We focus
on the recent work of Giard et al. (2008) who performed a stacking analysis of
the IRAS data in the direction of several thousands of galaxy clusters,
providing a statistical characterisation of their IR luminosity and redshift
evolution. We model the IR properties of the galactic population of the
SDSS-maxBCG clusters (0.1<z<0.3) in order to check if it accounts for the
entire observed signal and to constrain the possible presence of other
components, like dust in the ICM. Starting from the optical properties of the
galaxy members, we estimate their emission in the 60 and 100 micron IRAS bands
making use of modeled SEDs of different spectral types (E/S0, Sa, Sb, Sc and
starburst). We also consider the evolution of the galactic
population/luminosity with redshift. Our results indicate that the galactic
emission, which is dominated by the contribution of star-forming galaxies, is
consistent with the observed signal. In fact, our model slightly overestimates
the observed fluxes, with the excess being concentrated in low-redshift
clusters (z <~ 0.17). This indicates that, if present, the IR emission from
intracluster dust must be very small. We obtain an upper limit on the
dust-to-gas mass ratio in the ICM of Z_d <~ 5 10^-5. The excess in luminosity
obtained at low redshift constitutes an indication that the cluster environment
is driving a process of star-formation quenching in its galaxy members.Comment: 12 pages, 6 figures, 2 tables. Accepted for publication in A&
Another thread in the tapestry of stellar feedback: X-ray binaries
We consider X-ray binaries (XBs) as potential sources of stellar feedback.
XBs observationally appear able to deposit a high fraction of their power
output into their local interstellar medium, which may make them a
non-negligible source of energy input. The formation rate of the most luminous
XBs rises with decreasing metallicity, which should increase their significance
during galaxy formation in the early universe. We also argue that stochastic
effects are important to XB feedback (XBF) and may dominate the systematic
changes due to metallicity in many cases. Large stochastic variation in the
magnitude of XBF at low absolute star formation rates provides a natural reason
for diversity in the evolution of dwarf galaxies which were initially almost
identical, with several percent of such halos experiencing energy input from
XBs roughly two orders of magnitude above the most likely value. These
probability distributions suggest that the effect of XBF is most commonly
significant for total stellar masses between ~10^7 and 10^8 Msun, which might
resolve a current problem with modelling populations of such galaxies. We
explain how XBs might inject energy before luminous supernovae (SNe) contribute
significantly to feedback and how XBs can assist in keeping gas hot long after
the last core-collapse SN has exploded. [...] XBF could be especially important
to some dwarf galaxies, potentially heating gas without expelling it; the
properties of XBF also match those previously derived as allowing episodic star
formation. We also argue that the efficiency of SN feedback (SNF) might be
reduced when XBF has had the opportunity to act first. In addition, we note
that the effect of SNF is unlikely to be scale-free; galaxies smaller than ~100
pc might well experience less effective SNF. (Slightly abbreviated to fit arXiv
size limit.)Comment: Very belatedly updated to include a note added in proof and
additional reference. The definitive version is at:
mnras.oxfordjournals.org/content/423/2/164
Observation of light driven band structure via multi-band high harmonic spectroscopy
Intense light-matter interactions have revolutionized our ability to probe
and manipulate quantum systems at sub-femtosecond time scales, opening routes
to all-optical control of electronic currents in solids at petahertz rates.
Such control typically requires electric field amplitudes , when
the voltage drop across a lattice site becomes comparable to the characteristic
band gap energies. In this regime, intense light-matter interaction induces
significant modifications of electronic and optical properties, dramatically
modifying the crystal band structure. Yet, identifying and characterizing such
modifications remains an outstanding problem. As the oscillating electric field
changes within the driving field's cycle, does the band-structure follow, and
how can it be defined? Here we address this fundamental question, proposing
all-optical spectroscopy to probe laser-induced closing of the band-gap between
adjacent conduction bands. Our work reveals the link between nonlinear light
matter interactions in strongly driven crystals and the sub-cycle modifications
in their effective band structure
SPIDER - IV. Optical and NIR color gradients in Early-type galaxies: New Insights into Correlations with Galaxy Properties
We present an analysis of stellar population gradients in 4,546 Early-Type
Galaxies with photometry in along with optical spectroscopy. A new
approach is described which utilizes color information to constrain age and
metallicity gradients. Defining an effective color gradient, ,
which incorporates all of the available color indices, we investigate how
varies with galaxy mass proxies, i.e. velocity dispersion,
stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and
alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age
gradients and decreasing metallicity gradients wrt mass, metallicity, and
enhancement. We find that velocity dispersion and alpha/Fe are the main drivers
of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10
M_odot, show no correlation of age, metallicity, and color gradients wrt mass,
although color gradients still correlate with stellar population parameters,
and these correlations are independent of each other. In both mass regimes, the
striking anti-correlation between color gradient and alpha-enhancement is
significant at \sim 4sigma, and results from the fact that metallicity gradient
decreases with alpha/Fe. This anti-correlation may reflect the fact that star
formation and metallicity enrichment are regulated by the interplay between the
energy input from supernovae, and the temperature and pressure of the hot X-ray
gas in ETGs. For all mass ranges, positive age gradients are associated with
old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at
low-mass, the age gradient tends to be anti-correlated with the Age parameter,
with more positive gradients at younger ages.Comment: Accepted for Publication in the Astronomical Journa
A nearby GRB host prototype for z~7 Lyman-break galaxies: Spitzer-IRS and X-shooter spectroscopy of the host galaxy of GRB031203
Gamma-ray burst (GRB) host galaxies have been studied extensively in optical
photometry and spectroscopy. Here we present the first mid-infrared spectrum of
a GRB host, HG031203. It is one of the nearest GRB hosts at z=0.1055, allowing
both low and high-resolution spectroscopy with Spitzer-IRS. Medium resolution
UV-to-K-band spectroscopy with the X-shooter spectrograph on the VLT is also
presented, along with Spitzer IRAC and MIPS photometry, as well as radio and
sub-mm observations. These data allow us to construct a UV-to-radio spectral
energy distribution with almost complete spectroscopic coverage from 0.3-35
micron of a GRB host galaxy for the first time, potentially valuable as a
template for future model comparisons. The IRS spectra show strong,
high-ionisation fine structure line emission indicative of a hard radiation
field in the galaxy, suggestive of strong ongoing star-formation and a very
young stellar population. The selection of HG031203 via the presence of a GRB
suggests that it might be a useful analogue of very young star-forming galaxies
in the early universe, and hints that local BCDs may be used as more reliable
analogues of star-formation in the early universe than typical local
starbursts. We look at the current debate on the ages of the dominant stellar
populations in z~7 and z~8 galaxies in this context. The nebular line emission
is so strong in HG031203, that at z~7, it can reproduce the spectral energy
distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 micron
fluxes without the need to invoke a 4000A break.Comment: Published in ApJ. 9 pages, 6 figures, emulateapj styl
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