306 research outputs found
RACE-OC Project: Rotation and variability in young stellar associations within 100 pc
Our goal is to determine the rotational and magnetic-related activity
properties of stars at different stages of evolution. We have focussed our
attention on 6 young loose stellar associations within 100 pc and ages in the
range 8-70 Myr: TW Hydrae (~8 Myr), beta Pictoris (~10 Myr), Tucana/Horologium,
Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional data on alpha
Persei and the Pleiades from the literature is also considered. Rotational
periods of stars showing rotational modulation due to photospheric magnetic
activity (i.e. starspots) have been determined applying the Lomb-Scargle
periodogram technique to photometric time-series obtained by the All Sky
Automated Survey (ASAS). The magnetic activity level has been derived from the
amplitude of the V lightcurves. We detected the rotational modulation and
measured the rotation periods of 93 stars for the first time, and confirmed the
periods of 41 stars already known from the literature. For further 10 stars we
revised the period determinations by other authors. The sample was augmented
with periods of 21 additional stars retrieved from the literature. In this way,
for the first time we were able to determine largest set of rotation periods at
ages of ~8, ~10 and ~30 Myr, as well as increase by 150\% the number of known
periodic members of AB Dor.The analysis of the rotation periods in young
stellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC2264
data from the literature, has allowed us to find that in the 0.6 - 1.2 solar
masses range the most significant variations of the rotation period
distribution are the spin-up between 9 and 30 Myr and the spin-down between 70
and 110 Myr. Variations between 30 and 70 Myr are rather doubtful, despite the
median period indicates a significant spin-up.Comment: Accepted by Astronomy and Astrophysic
A benchmark for multi-conjugated AO: VLT-MAD observations of the young massive cluster Trumpler 14
MAD is the first multi-conjugated adaptive optics system at the VLT. We
present H and Ks observations of the young massive cluster Trumpler 14
revealing the power of MCAO systems by providing a homogeneous Strehl ratio
over a large field of view. Mean Strehl ratios of 6.0 and 5.9 per cent with
maximum Strehl ratios of 9.8 and 12.6 per cent in H and Ks, respectively, show
significant improvement of the spatial PSF stability compared to
single-conjugated adaptive optics systems. Photometry of our observations cover
a dynamic range of ~10 mag including 2-3 times more sources than comparable
seeing-limited observations. The colour-magnitude diagram reveals that the
massive cluster originated in a recent starburst-like event 1+/-0.5 Myr ago. We
tentatively detect hints for an older population of 3 Myr suggesting that low
intensity star formation might have been going on in the HII region for a few
Myr. We derive the luminosity function and mass function between 0.1 M_sun and
3.2 M_sun and identify a change of the power law slope of the mass function at
m_c~0.53(+0.12/-0.10) M_sun. The MF appears shallow with power law slopes of
Gamma1=-0.50+/-0.11 above m_c and Gamma2=0.63+/-0.32 below m_c.Comment: Accepted for publication in MNRAS, 12 pages, 10 figures, 2 table
Euclid preparation: XVII. Cosmic Dawn Survey: Spitzer Space Telescope observations of the Euclid deep fields and calibration fields
We present a new infrared survey covering the three Euclid deep fields and four other Euclid calibration fields using Spitzer Space Telescope's Infrared Array Camera (IRAC). We combined these new observations with all relevant IRAC archival data of these fields in order to produce the deepest possible mosaics of these regions. In total, these observations represent nearly 11 % of the total Spitzer Space Telescope mission time. The resulting mosaics cover a total of approximately 71.5 deg^{2} in the 3.6 and 4.5 ÎŒm bands, and approximately 21.8 deg^{2} in the 5.8 and 8 ÎŒm bands. They reach at least 24 AB magnitude (measured to 5Ï, in a 2âłââ.5 aperture) in the 3.6 ÎŒm band and up to âŒ5 mag deeper in the deepest regions. The astrometry is tied to the Gaia astrometric reference system, and the typical astrometric uncertainty for sources with 16 "< "[3.6]< 19 is âČ 0âłââ.15. The photometric calibration is in excellent agreement with previous WISE measurements. We extracted source number counts from the 3.6 ÎŒm band mosaics, and they are in excellent agreement with previous measurements. Given that the Spitzer Space Telescope has now been decommissioned, these mosaics are likely to be the definitive reduction of these IRAC data. This survey therefore represents an essential first step in assembling multi-wavelength data on the Euclid deep fields, which are set to become some of the premier fields for extragalactic astronomy in the 2020s
Euclid preparation: VII. Forecast validation for Euclid cosmological probes
Aims: The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. The estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on various individual methodologies and numerical implementations, which were developed for different observational probes and for the combination thereof. In this paper we present validated forecasts, which combine both theoretical and observational ingredients for different cosmological probes. This work is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts.
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Methods: We describe in detail the methods adopted for Fisher matrix forecasts, which were applied to galaxy clustering, weak lensing, and the combination thereof. We estimated the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations, some of which are made publicly available, in different programming languages, together with a reference training-set of input and output matrices for a set of specific models. These can be used by the reader to validate their own implementations if required.
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Results: We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setting, for example flat or non-flat spatial cosmologies, or different cuts at non-linear scales. The numerical implementations are now reliable for these settings. We present the results for an optimistic and a pessimistic choice for these types of settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy figure of merit by at least a factor of three
Euclid: Covariance of weak lensing pseudo-C_ell estimates. Calculation, comparison to simulations, and dependence on survey geometry
An accurate covariance matrix is essential for obtaining reliable
cosmological results when using a Gaussian likelihood. In this paper we study
the covariance of pseudo-C_ estimates of tomographic cosmic shear power
spectra. Using two existing publicly available codes in combination, we
calculate the full covariance matrix, including mode-coupling contributions
arising from both partial sky coverage and non-linear structure growth. For
three different sky masks, we compare the theoretical covariance matrix to that
estimated from publicly available N-body weak lensing simulations, finding good
agreement. We find that as a more extreme sky cut is applied, a corresponding
increase in both Gaussian off-diagonal covariance and non-Gaussian super-sample
covariance is observed in both theory and simulations, in accordance with
expectations. Studying the different contributions to the covariance in detail,
we find that the Gaussian covariance dominates along the main diagonal and the
closest off-diagonals, but further away from the main diagonal the super-sample
covariance is dominant. Forming mock constraints in parameters describing
matter clustering and dark energy, we find that neglecting non-Gaussian
contributions to the covariance can lead to underestimating the true size of
confidence regions by up to 70 per cent. The dominant non-Gaussian covariance
component is the super-sample covariance, but neglecting the smaller connected
non-Gaussian covariance can still lead to the underestimation of uncertainties
by 10--20 per cent. A real cosmological analysis will require marginalisation
over many nuisance parameters, which will decrease the relative importance of
all cosmological contributions to the covariance, so these values should be
taken as upper limits on the importance of each component
Euclid preparation: XXIV. Calibration of the halo mass function in (?)CDM cosmologies
Euclid s photometric galaxy cluster survey has the potential to be a very competitive cosmological probe. The main cosmological probe with observations of clusters is their number count, within which the halo mass function (HMF) is a key theoretical quantity. We present a new calibration of the analytic HMF, at the level of accuracy and precision required for the uncertainty in this quantity to be subdominant with respect to other sources of uncertainty in recovering cosmological parameters from Euclid cluster counts. Our model is calibrated against a suite of N-body simulations using a Bayesian approach taking into account systematic errors arising from numerical effects in the simulation. First, we test the convergence of HMF predictions from different N-body codes, by using initial conditions generated with different orders of Lagrangian Perturbation theory, and adopting different simulation box sizes and mass resolution. Then, we quantify the effect of using different halo finder algorithms, and how the resulting differences propagate to the cosmological constraints. In order to trace the violation of universality in the HMF, we also analyse simulations based on initial conditions characterised by scale-free power spectra with different spectral indexes, assuming both Einsteinde Sitter and standard CDM expansion histories. Based on these results, we construct a fitting function for the HMF that we demonstrate to be sub-percent accurate in reproducing results from 9 different variants of the CDM model including massive neutrinos cosmologies. The calibration systematic uncertainty is largely sub-dominant with respect to the expected precision of future massobservation relations; with the only notable exception of the effect due to the halo finder, that could lead to biased cosmological inference
Euclid preparation: VIII. The Complete Calibration of the ColourâRedshift Relation survey: VLT/KMOS observations and data release
The Complete Calibration of the ColourâRedshift Relation survey (C3R2) is a spectroscopic effort involving ESO and Keck facilities designed specifically to empirically calibrate the galaxy colourâredshift relation â P(z|C) to the Euclid depth (iABâ=â24.5) and is intimately linked to the success of upcoming Stage IV dark energy missions based on weak lensing cosmology. The aim is to build a spectroscopic calibration sample that is as representative as possible of the galaxies of the Euclid weak lensing sample. In order to minimise the number of spectroscopic observations necessary to fill the gaps in current knowledge of the P(z|C), self-organising map (SOM) representations of the galaxy colour space have been constructed. Here we present the first results of an ESO@VLT Large Programme approved in the context of C3R2, which makes use of the two VLT optical and near-infrared multi-object spectrographs, FORS2 and KMOS. This data release paper focuses on high-quality spectroscopic redshifts of high-redshift galaxies observed with the KMOS spectrograph in the near-infrared H- and K-bands. A total of 424 highly-reliable redshifts are measured in the 1.3ââ€âzââ€â2.5 range, with total success rates of 60.7% in the H-band and 32.8% in the K-band. The newly determined redshifts fill 55% of high (mainly regions with no spectroscopic measurements) and 35% of lower (regions with low-resolution/low-quality spectroscopic measurements) priority empty SOM grid cells. We measured Hα fluxes in a 1.âł2 radius aperture from the spectra of the spectroscopically confirmed galaxies and converted them into star formation rates. In addition, we performed an SED fitting analysis on the same sample in order to derive stellar masses, E(Bâ
ââ
V), total magnitudes, and SFRs. We combine the results obtained from the spectra with those derived via SED fitting, and we show that the spectroscopic failures come from either weakly star-forming galaxies (at zâ â2 galaxies
Euclid: Covariance of weak lensing pseudo-Cl estimates: Calculation, comparison to simulations, and dependence on survey geometry
An accurate covariance matrix is essential for obtaining reliable cosmological results when using a Gaussian likelihood. In this paper we study the covariance of pseudo-Cestimates of tomographic cosmic shear power spectra. Using two existing publicly available codes in combination, we calculate the full covariance matrix, including mode-coupling contributions arising from both partial sky coverage and non-linear structure growth. For three different sky masks, we compare the theoretical covariance matrix to that estimated from publicly available N-body weak lensing simulations, finding good agreement. We find that as a more extreme sky cut is applied, a corresponding increase in both Gaussian off-diagonal covariance and non-Gaussian super-sample covariance is observed in both theory and simulations, in accordance with expectations. Studying the different contributions to the covariance in detail, we find that the Gaussian covariance dominates along the main diagonal and the closest off-diagonals, but farther away from the main diagonal the super-sample covariance is dominant. Forming mock constraints in parameters that describe matter clustering and dark energy, we find that neglecting non-Gaussian contributions to the covariance can lead to underestimating the true size of confidence regions by up to 70 per cent. The dominant non-Gaussian covariance component is the super-sample covariance, but neglecting the smaller connected non-Gaussian covariance can still lead to the underestimation of uncertainties by 10-20 per cent. A real cosmological analysis will require marginalisation over many nuisance parameters, which will decrease the relative importance of all cosmological contributions to the covariance, so these values should be taken as upper limits on the importance of each component
Euclid: Discovering pair-instability supernovae with the Deep Survey
Pair-instability supernovae are theorized supernovae that have not yet been
observationally confirmed. They are predicted to exist in low-metallicity
environments. Because overall metallicity becomes lower at higher redshifts,
deep near-infrared transient surveys probing high-redshift supernovae are
suitable to discover pair-instability supernovae. The Euclid satellite, which
is planned to be launched in 2023, has a near-infrared wide-field instrument
that is suitable for a high-redshift supernova survey. Although no dedicated
supernova survey is currently planned during the Euclid's 6 year primary
mission, the Euclid Deep Survey is planned to make regular observations of
three Euclid Deep Fields (40 deg2 in total) spanning six years. While the
observations of the Euclid Deep Fields are not frequent, we show that the
predicted long duration of pair-instability supernovae would allow us to search
for high-redshift pair-instability supernovae with the Euclid Deep Survey.
Based on the current observational plan of the Euclid mission, we conduct
survey simulations in order to estimate the expected numbers of
pair-instability supernova discoveries. We find that up to several hundred
pair-instability supernovae at z < ~ 3.5 can be discovered by the Euclid Deep
Survey. We also show that pair-instability supernova candidates can be
efficiently identified by their duration and color that can be determined with
the current Euclid Deep Survey plan. We conclude that the Euclid mission can
lead to the first confident discovery of pair-instability supernovae if their
event rates are as high as those predicted by recent theoretical studies. We
also update the expected numbers of superluminous supernova discoveries in the
Euclid Deep Survey based on the latest observational plan.Comment: 12 pages, 13 figures, 2 tables, submitted to Astronomy & Astrophysic
Euclid: Forecast constraints on consistency tests of the â§cDM model
Context. The standard cosmological model is based on the fundamental assumptions of a spatially homogeneous and isotropic universe on large scales. An observational detection of a violation of these assumptions at any redshift would immediately indicate the presence of new physics. Aims. We quantify the ability of the Euclid mission, together with contemporary surveys, to improve the current sensitivity of null tests of the canonical cosmological constant ⧠and the cold dark matter (⧠CDM) model in the redshift range 0 < 1.8. Methods. We considered both currently available data and simulated Euclid and external data products based on a â§CDM fiducial model, an evolving dark energy model assuming the Chevallier-Polarski-Linder parameterization or an inhomogeneous LemaĂźtre-Tolman-Bondi model with a cosmological constant â§, and carried out two separate but complementary analyses: A machine learning reconstruction of the null tests based on genetic algorithms, and a theory-Agnostic parametric approach based on Taylor expansion and binning of the data, in order to avoid assumptions about any particular model. Results. We find that in combination with external probes, Euclid can improve current constraints on null tests of the â§CDM by approximately a factor of three when using the machine learning approach and by a further factor of two in the case of the parametric approach. However, we also find that in certain cases, the parametric approach may be biased against or missing some features of models far from â§CDM. Conclusions. Our analysis highlights the importance of synergies between Euclid and other surveys. These synergies are crucial for providing tighter constraints over an extended redshift range for a plethora of different consistency tests of some of the main assumptions of the current cosmological paradigm
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