Browsing by Subject "dark energy"

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  • Annila, Arto; Wikström, Mårten (2022)
    We reason that it is the gravitation of all ordinary matter, extending from the dense distant past to the sparse present, rather than dark matter, that shows up in galaxy rotation and velocity dispersion. Likewise, we argue that it is this gradient in the gravitational energy due to the expansion, rather than dark energy, that explains Type 1a supernovae brightness vs. redshift data. Our conclusions follow from statistical mechanics, the thermodynamic theory based on the atomistic axiom that everything comprises quanta. In line with the Einstein field equations, the vacuum quanta embodying gravitation, geometrized as spacetime, equate in dynamic balance to the quanta embodying the substance of the stress-energy tensor. In accordance with quantum field theory, the proposed ground-state field of paired light quanta complies with Bose-Einstein statistics and assumes an excited state around a particle.
  • Liu, Yun; Liao, Shihong; Liu, Xiangkun; Zhang, Jiajun; An, Rui; Fan, Zuhui (2022)
    The interacting dark energy (IDE) model, which considers the interaction between dark energy and dark matter, provides a natural mechanism to alleviate the coincidence problem and can also relieve the observational tensions under the ?CDM model. Previous studies have put constraints on IDE models by observations of cosmic expansion history, cosmic microwave background, and large-scale structures. However, these data are not yet enough to distinguish IDE models from ?CDM effectively. Because the non-linear structure formation contains rich cosmological information, it can provide additional means to differentiate alternative models. In this paper, based on a set of N-body simulations for IDE models, we investigate the formation histories and properties of dark matter haloes and compare with their ?CDM counterparts. For the model with dark matter decaying into dark energy and the parameters being the best-fitting values from previous constraints, the structure formation is markedly slowed down, and the haloes have systematically lower mass, looser internal structure, higher spin, and anisotropy. This is inconsistent with the observed structure formation, and thus this model can be safely ruled out from the perspective of non-linear structure formation. Moreover, we find that the ratio of halo concentrations between IDE and ?CDM counterparts depends sensitively on the interaction parameter and is independent of halo mass. This can act as a powerful probe to constrain IDE models. Our results concretely demonstrate that the interaction of the two dark components can affect the halo formation considerably, and therefore the constraints from non-linear structures are indispensable.
  • Euclid Collaboration; Scaramella, R.; Amiaux, J.; Gozaliasl, G.; Keihänen, E.; Kirkpatrick , C. C.; Kurki-Suonio, H.; Lindholm, Valtteri; Väliviita, J. (2022)
    Euclid is a mission of the European Space Agency that is designed to constrain the properties of dark energy and gravity via weak gravitational lensing and galaxy clustering. It will carry out a wide area imaging and spectroscopy survey (the Euclid Wide Survey: EWS) in visible and near-infrared bands, covering approximately 15 000 deg(2) of extragalactic sky in six years. The wide-field telescope and instruments are optimised for pristine point spread function and reduced stray light, producing very crisp images. This paper presents the building of the Euclid reference survey: the sequence of pointings of EWS, deep fields, and calibration fields, as well as spacecraft movements followed by Euclid as it operates in a step-and-stare mode from its orbit around the Lagrange point L2. Each EWS pointing has four dithered frames; we simulated the dither pattern at the pixel level to analyse the effective coverage. We used up-to-date models for the sky background to define the Euclid region-of-interest (RoI). The building of the reference survey is highly constrained from calibration cadences, spacecraft constraints, and background levels; synergies with ground-based coverage were also considered. Via purposely built software, we first generated a schedule for the calibrations and deep fields observations. On a second stage, the RoI was tiled and scheduled with EWS observations, using an algorithm optimised to prioritise the best sky areas, produce a compact coverage, and ensure thermal stability. The result is the optimised reference survey RSD_2021A, which fulfils all constraints and is a good proxy for the final solution. The current EWS covers approximate to 14 & x2006;500 deg(2). The limiting AB magnitudes (5 sigma point-like source) achieved in its footprint are estimated to be 26.2 (visible band I-E) and 24.5 (for near infrared bands Y-E, J(E), H-E); for spectroscopy, the H alpha line flux limit is 2 x 10(-16) erg(-1) cm(-2) s(-1) at 1600 nm; and for diffuse emission, the surface brightness limits are 29.8 (visible band) and 28.4 (near infrared bands) mag arcsec(-2).
  • Euclid Collaboration; Ilbert, O.; de la Torre, S.; Gozaliasl, G.; Keihänen, E.; Kurki-Suonio, H.; Väliviita, J.; Kirkpatrick , C. C. (2021)
    The analysis of weak gravitational lensing in wide-field imaging surveys is considered to be a major cosmological probe of dark energy. Our capacity to constrain the dark energy equation of state relies on an accurate knowledge of the galaxy mean redshift z. We investigate the possibility of measuring z with an accuracy better than 0.002 (1+z) in ten tomographic bins spanning the redshift interval 0.2 99.8%. The zPDF approach can also be successful if the zPDF is de-biased using a spectroscopic training sample. This approach requires deep imaging data but is weakly sensitive to spectroscopic redshift failures in the training sample. We improve the de-biasing method and confirm our finding by applying it to real-world weak-lensing datasets (COSMOS and KiDS+VIKING-450).
  • Euclid Collaboration; Moneti, A.; McCracken, H. J.; Gozaliasl, G.; Keihänen, E.; Kirkpatrick , C. C.; Kurki-Suonio, H.; Lindholm, Valtteri; Väliviita, J. (2022)
    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 mu m bands, and approximately 21.8 deg(2) in the 5.8 and 8 mu m bands. They reach at least 24 AB magnitude (measured to 5 sigma, in a 2 ''.5 aperture) in the 3.6 mu m band and up to similar to 5 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 less than or similar to 0 ''.15. The photometric calibration is in excellent agreement with previous WISE measurements. We extracted source number counts from the 3.6 mu m 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.
  • Ade, P. A. R.; Juvela, M.; Keihanen, E.; Kurki-Suonio, H.; Lähteenmäki, A.; Poutanen, T.; Suur-Uski, A. -S.; Tuovinen, J.; Valiviita, J.; Planck Collaboration (2014)