115 research outputs found
Euclid preparation : XVI. Exploring the ultra-low surface brightness Universe with Euclid/VIS
Context. While Euclid is an ESA mission specifically designed to investigate the nature of dark energy and dark matter, the planned unprecedented combination of survey area (similar to 15000 deg(2)), spatial resolution, low sky-background, and depth also make Euclid an excellent space observatory for the study of the low surface brightness Universe. Scientific exploitation of the extended low surface brightness structures requires dedicated calibration procedures that are yet to be tested. Aims. We investigate the capabilities of Euclid to detect extended low surface brightness structure by identifying and quantifying sky-background sources and stray-light contamination. We test the feasibility of generating sky flat-fields to reduce large-scale residual gradients in order to reveal the extended emission of galaxies observed in the Euclid survey. Methods. We simulated a realistic set of Euclid/VIS observations, taking into account both instrumental and astronomical sources of contamination, including cosmic rays, stray-light, zodiacal light, interstellar medium, and the cosmic infrared background, while simulating the effects of background sources in the field of view. Results. We demonstrate that a combination of calibration lamps, sky flats, and self-calibration would enable recovery of emission at a limiting surface brightness magnitude of mu(lim) = 29.5(-0.27)(+0.08) mag arcsec(-2) (3 sigma, 10 x 10 arcsec(2)) in theWide Survey, and it would reach regions deeper by 2 mag in the Deep Surveys. Conclusions. Euclid/VIS has the potential to be an excellent low surface brightness observatory. Covering the gap between pixel-to-pixel calibration lamp flats and self-calibration observations for large scales, the application of sky flat-fielding will enhance the sensitivity of the VIS detector at scales larger than 1 '', up to the size of the field of view, enabling Euclid to detect extended surface brightness structures below mu(lim) = 31 mag arcsec(-2) and beyond.Peer reviewe
Kinematic Clues to Bar Evolution for Galaxies in the Local Universe: Why the Fastest Rotating Bars are Rotating Most Slowly
We have used Spitzer images of a sample of 68 barred spiral galaxies in the local universe to make systematic measurements of bar length and bar strength. We combine these with precise determinations of the corotation radii associated with the bars, taken from our previous study, which used the phase change from radial inflow to radial outflow of gas at corotation, based on high-resolution two-dimensional velocity fields in Hα taken with a Fabry-Pérot spectrometer. After presenting the histograms of the derived bar parameters, we study their dependence on the galaxy morphological type and on the total stellar mass of the host galaxy, and then produce a set of parametric plots. These include the bar pattern speed versus bar length, the pattern speed normalized with the characteristic pattern speed of the outer disk versus the bar strength, and the normalized pattern speed versus R, the ratio of corotation radius to bar length. To provide guidelines for our interpretation, we used recently published simulations, including disk and dark matter halo components. Our most striking conclusion is that bars with values of R < 1.4, previously considered dynamically fast rotators, can be among the slowest rotators both in absolute terms and when their pattern speeds are normalized. The simulations confirm that this is because as the bars are braked, they can grow longer more quickly than the outward drift of the corotation radius. We conclude that dark matter halos have indeed slowed down the rotation of bars on Gyr timescales. © 2017. The American Astronomical Society. All rights reserved.
Extragalactic magnetism with SOFIA (SALSA Legacy Program). VI. The magnetic fields in the multi-phase interstellar medium of the Antennae galaxies
Mergers are thought to be a fundamental channel for galaxy growth, perturbing
the gas dynamics and the magnetic fields (B-fields) in the interstellar medium
(ISM). However, the mechanisms that amplify and dissipate B-fields during a
merger remain unclear. We characterize the morphology of the ordered B-fields
in the multi-phase ISM of the closest merger of two spiral galaxies, the
Antennae galaxies. We compare the inferred B-fields using m thermal
dust and cm radio synchrotron emission polarimetric observations. We find
that the m B-fields are more ordered across the Antennae galaxies than
the cm B-fields. The turbulent-to-ordered m B-field increases at
the galaxy cores and star-forming regions. The relic spiral arm has an ordered
spiral m B-field, while the cm B-field is radial. The m
B-field may be dominated by turbulent dynamos with high CO(1-0) velocity
dispersion driven by star-forming regions, while the cm B-field is
cospatial with high HI velocity dispersion driven by galaxy interaction. This
result shows the dissociation between the warm gas mainly disturbed by the
merger, and the dense gas still following the dynamics of the relic spiral arm.
We find a kpc scale ordered B-field connecting the two galaxies. The
base of the tidal tail is cospatial with the HI and CO(1-0) emission and
has compressed and/or sheared m and cm B-fields driven by the
merger. We suggest that amplify B-fields, with respect to the rest of the
system and other spiral galaxies, may be supporting the gas flow between both
galaxies and the tidal tail.Comment: 11 pages, 5 figures, Accepted for publication in ApJ Letter
Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- V: First results on the magnetic field orientation of galaxies
We present the analysis of the magnetic field (-field) structure of
galaxies measured with far-infrared (FIR) and radio (3 and 6 cm) polarimetric
observations. We use the first data release of the Survey on extragALactic
magnetiSm with SOFIA (SALSA) of 14 nearby ( Mpc) galaxies with resolved (5
arcsec-18 arcsec; pc-- kpc) imaging polarimetric observations using
HAWC+/SOFIA from to \um. We compute the magnetic pitch angle
() profiles as a function of the galactrocentric radius. We introduce
a new magnetic alignment parameter () to estimate the
disordered-to-ordered -field ratio in spiral -fields. We find FIR and
radio wavelengths to not generally trace the same -field morphology in
galaxies. The profiles tend to be more ordered with galactocentric
radius in radio () than in FIR
(). For spiral galaxies, FIR -fields
are \% more turbulent than the radio -fields. For starburst galaxies,
we find that FIR polarization is a better tracer of the -fields along the
galactic outflows than radio polarization. Our results suggest that the
-fields associated with dense, dusty, turbulent star-forming regions, those
traced at FIR, are less ordered than warmer, less-dense regions, those traced
at radio, of the interstellar medium. The FIR -fields seem to be more
sensitive to the activity of the star-forming regions and the morphology of the
molecular clouds within a vertical height of few hundred pc in the disk of
spiral galaxies than the radio -fields.Comment: 26 pages, 13 figure
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A tomographic view of far infrared and radio polarimetric observations through MHD simulations of galaxies
The structure of magnetic fields in galaxies remains poorly constrained,
despite the importance of magnetism in the evolution of galaxies. Radio
synchrotron and far-infrared dust polarization (FIR) polarimetric observations
are the best methods to measure galactic scale properties of magnetic fields in
galaxies beyond the Milky Way. We use synthetic polarimetric observations of a
simulated galaxy to identify and quantify the regions, scales, and interstellar
medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of
magnetohydrodynamical cosmological zoom-in simulations features
high-resolutions (10 pc full-cell size) and multiple magnetization models. Our
synthetic observations have a striking resemblance to those of observed
galaxies. We find that the total and polarized radio emission extends to
approximately double the altitude above the galactic disk (half-intensity disk
thickness of kpc)
relative to the FIR total and polarized emission that are concentrated in the
disk midplane ( kpc).
Radio emission traces magnetic fields at scales of pc, whereas
FIR emission probes magnetic fields at the smallest scales of our simulations.
These scales are comparable to our spatial resolution and well below the
spatial resolution ( pc) of existing FIR polarimetric measurements.
Finally, we confirm that synchrotron emission traces a combination of the warm
neutral and cold neutral gas phases, whereas FIR emission follows the densest
gas in the cold neutral phase in the simulation. These results are independent
of the ISM magnetic field strength. The complementarity we measure between
radio and FIR wavelengths motivates future multiwavelength polarimetric
observations to advance our knowledge of extragalactic magnetism.Comment: Submitted to ApJ. 32 pages, 15 figure
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
Einstein--de 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 mass-observation relations; with the only notable exception
of the effect due to the halo finder, that could lead to biased cosmological
inference.Comment: 24 pages, 21 figures, 5 tables, 3 appendixes
Euclid preparation TBD. The effect of baryons on the Halo Mass Function
The Euclid photometric survey of galaxy clusters stands as a powerful
cosmological tool, with the capacity to significantly propel our understanding
of the Universe. Despite being sub-dominant to dark matter and dark energy, the
baryonic component in our Universe holds substantial influence over the
structure and mass of galaxy clusters. This paper presents a novel model to
precisely quantify the impact of baryons on galaxy cluster virial halo masses,
using the baryon fraction within a cluster as proxy for their effect.
Constructed on the premise of quasi-adiabaticity, the model includes two
parameters calibrated using non-radiative cosmological hydrodynamical
simulations and a single large-scale simulation from the Magneticum set, which
includes the physical processes driving galaxy formation. As a main result of
our analysis, we demonstrate that this model delivers a remarkable one percent
relative accuracy in determining the virial dark matter-only equivalent mass of
galaxy clusters, starting from the corresponding total cluster mass and baryon
fraction measured in hydrodynamical simulations. Furthermore, we demonstrate
that this result is robust against changes in cosmological parameters and
against varying the numerical implementation of the sub-resolution physical
processes included in the simulations. Our work substantiates previous claims
about the impact of baryons on cluster cosmology studies. In particular, we
show how neglecting these effects would lead to biased cosmological constraints
for a Euclid-like cluster abundance analysis. Importantly, we demonstrate that
uncertainties associated with our model, arising from baryonic corrections to
cluster masses, are sub-dominant when compared to the precision with which
mass-observable relations will be calibrated using Euclid, as well as our
current understanding of the baryon fraction within galaxy clusters.Comment: 18 pages, 10 figures, 4 tables, 1 appendix, abstract abridged for
arXiv submissio
Euclid preparation. TBD. The effect of linear redshift-space distortions in photometric galaxy clustering and its cross-correlation with cosmic shear
Cosmological surveys planned for the current decade will provide us with
unparalleled observations of the distribution of galaxies on cosmic scales, by
means of which we can probe the underlying large-scale structure (LSS) of the
Universe. This will allow us to test the concordance cosmological model and its
extensions. However, precision pushes us to high levels of accuracy in the
theoretical modelling of the LSS observables, in order not to introduce biases
in the estimation of cosmological parameters. In particular, effects such as
redshift-space distortions (RSD) can become relevant in the computation of
harmonic-space power spectra even for the clustering of the photometrically
selected galaxies, as it has been previously shown in literature studies. In
this work, we investigate the contribution of linear RSD, as formulated in the
Limber approximation by arXiv:1902.07226, in forecast cosmological analyses
with the photometric galaxy sample of the Euclid survey, in order to assess
their impact and quantify the bias on the measurement of cosmological
parameters that neglecting such an effect would cause. We perform this task by
producing mock power spectra for photometric galaxy clustering and weak
lensing, as expected to be obtained from the Euclid survey. We then use a
Markov chain Monte Carlo approach to obtain the posterior distributions of
cosmological parameters from such simulated observations. We find that
neglecting the linear RSD leads to significant biases both when using galaxy
correlations alone and when these are combined with cosmic shear, in the
so-called 32pt approach. Such biases can be as large as
-equivalent when assuming an underlying CDM cosmology. When
extending the cosmological model to include the equation-of-state parameters of
dark energy, we find that the extension parameters can be shifted by more than
.Comment: 15 pages, 5 figures. To be submitted in A&
Euclid Preparation. XXVIII. Forecasts for ten different higher-order weak lensing statistics
Recent cosmic shear studies have shown that higher-order statistics (HOS)
developed by independent teams now outperform standard two-point estimators in
terms of statistical precision thanks to their sensitivity to the non-Gaussian
features of large-scale structure. The aim of the Higher-Order Weak Lensing
Statistics (HOWLS) project is to assess, compare, and combine the constraining
power of ten different HOS on a common set of -like mocks, derived from
N-body simulations. In this first paper of the HOWLS series, we computed the
nontomographic (, ) Fisher information for the
one-point probability distribution function, peak counts, Minkowski
functionals, Betti numbers, persistent homology Betti numbers and heatmap, and
scattering transform coefficients, and we compare them to the shear and
convergence two-point correlation functions in the absence of any systematic
bias. We also include forecasts for three implementations of higher-order
moments, but these cannot be robustly interpreted as the Gaussian likelihood
assumption breaks down for these statistics. Taken individually, we find that
each HOS outperforms the two-point statistics by a factor of around two in the
precision of the forecasts with some variations across statistics and
cosmological parameters. When combining all the HOS, this increases to a
times improvement, highlighting the immense potential of HOS for cosmic shear
cosmological analyses with . The data used in this analysis are
publicly released with the paper.Comment: 33 pages, 24 figures, main results in Fig. 19 & Table 5, version
published in A&
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