Browsing by Subject "BARYONS"

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  • Schewtschenko, J. A.; Baugh, C. M.; Wilkinson, R. J.; Boehm, C.; Pascoli, S.; Sawala, T. (2016)
    In the thermal dark matter (DM) paradigm, primordial interactions between DM and Standard Model particles are responsible for the observed DM relic density. In Boehm et al., we showed that weak-strength interactions between DM and radiation (photons or neutrinos) can erase small-scale density fluctuations, leading to a suppression of the matter power spectrum compared to the collisionless cold DM (CDM) model. This results in fewer DM subhaloes within Milky Way-like DM haloes, implying a reduction in the abundance of satellite galaxies. Here we use very high-resolution N-body simulations to measure the dynamics of these subhaloes. We find that when interactions are included, the largest subhaloes are less concentrated than their counterparts in the collisionless CDM model and have rotation curves that match observational data, providing a new solution to the 'too big to fail' problem.
  • Ahoranta, Jussi; Nevalainen, Jukka; Wijers, Nastasha; Finoguenov, Alexis; Bonamente, Massilimiano; Tempel, Elmo; Tilton, Evan; Schaye, Joop; Kaastra, Jelle; Gozaliasl, Ghassem (2020)
    Aims. We explore the high spectral resolution X-ray data towards the quasar 3C 273 to search for signals of hot (similar to 10^(6-7) K) X-ray-absorbing gas co-located with two established intergalactic far-ultraviolet (FUV) OVI absorbers. Methods. We analyze the soft X-ray band grating data of all XMM-Newton and Chandra instruments to search for the hot phase absorption lines at the FUV predicted redshifts. The viability of potential line detections is examined by adopting the constraints of a physically justified absorption model. The WHIM hypothesis is investigated with a complementary 3D galaxy distribution analysis and by detailed comparison of the measurement results to the WHIM properties in the EAGLE cosmological, hydrodynamical simulation. Results. At one of the examined FUV redshifts, 0.09017 +/- 0.00003, we measured signals of two hot ion species, ;VIII and x202f;IX, with a 3.9 sigma combined significance level. While the absorption signal is only marginally detected in individual co-added spectra, considering the line features in all instruments collectively and assuming collisional equilibrium for absorbing gas, we were able to constrain the temperature (kT = 0.26 +/- 0.03 keV) and the column density cm(-2)) of the absorber. Thermal analysis indicates that FUV and X-ray absorption relate to different phases, with estimated temperatures, T-FUV & x2004;3 x 10(5), and, T(X - ray)x2004;3 x 10(6) K. These temperatures match the EAGLE predictions for WHIM at the FUV/X-ray measured N-ion-ranges. We detected a large scale galactic filament crossing the sight-line at the redshift of the absorption, linking the absorption to this structure. Conclusions. This study provides observational insights into co-existing warm and hot gas within a WHIM filament and estimates the ratio of the hot and warm phases. Because the hot phase is thermally distinct from the OVI gas, the estimated baryon content of the absorber is increased, conveying the promise of X-ray follow-up studies of FUV detected WHIM in refining the picture of the missing baryons.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    An analysis of the bottom baryon decay Lambda(b) -> J/psi(-> mu(+)mu(-))Lambda( -> p pi(-)) is performed to measure the Lambda(b) polarization and three angular parameters in data from pp collisions at root s = 7 and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The Lambda(b) polarization is measured to be 0.00 +/- 0.06(stat) +/- 0.06(syst) and the parity-violating asymmetry parameter is determined to be 0.14 +/- 0.14(stat) +/- 0.10(syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.
  • Bigazzi, Francesco; Cotrone, Aldo L.; Järvinen, Matti; Kiritsis, Elias (2020)
    Among the possible CP-odd couplings of the axion to ordinary matter, the most relevant ones for phenomenology are the Yukawa couplings to nucleons. We analyze such non-derivative couplings within three different approaches: standard effective field theory, the Skyrme model and holographic QCD. In all the cases, the couplings can be related to the CP-odd non-derivative couplings to nucleons of the low-lying mesons and the eta '. Using the effective field theory approach we discuss how to derive the expressions for the CP-odd interaction terms as functions of the parameters of the effective Lagrangian at generic number of colors N-c and flavors N-f. Then, we compute the CP-odd couplings to nucleons of the axion, the eta ' and the pseudo-Goldstone mesons in both the Skyrme and the holographic QCD model with N-f = 2, 3. We present model-independent expressions for the coefficients of the non-derivative axion-nucleon couplings. This allows us to provide quantitative estimates of these couplings.
  • Vacca, V.; Murgia, M.; Govoni, F.; Loi, F.; Vazza, F.; Finoguenov, A.; Carretti, E.; Feretti, L.; Giovannini, G.; Concu, R.; Melis, A.; Gheller, C.; Paladino, R.; Poppi, S.; Valente, G.; Bernardi, G.; Boschin, W.; Brienza, M.; Clarke, T. E.; Colafrancesco, S.; Ensslin, T. A.; Ferrari, C.; de Gasperin, F.; Gastaldello, F.; Girardi, M.; Gregorini, L.; Johnston-Hollitt, M.; Junklewitz, H.; Orru, E.; Parma, P.; Perley, R.; Taylor, G. B. (2018)
    We report the detection of diffuse radio emission which might be connected to a large-scale filament of the cosmic web covering a 8 degrees x 8 degrees area in the sky, likely associated with a z approximate to 0.1 overdensity traced by nine massive galaxy clusters. In this work, we present radio observations of this region taken with the Sardinia Radio Telescope. Two of the clusters in the field host a powerful radio halo sustained by violent ongoing mergers and provide direct proof of intracluster magnetic fields. In order to investigate the presence of large-scale diffuse radio synchrotron emission in and beyond the galaxy clusters in this complex system, we combined the data taken at 1.4 GHz with the Sardinia. Radio Telescope with higher resolution data taken with the NRAO VIA Sky Survey. We found 28 candidate new sources with a size larger and X-ray emission fainter than known diffuse large-scale synchrotron cluster sources for a given radio power. This new population is potentially the tip of the iceberg of a class of diffuse large-scale synchrotron sources associated with the filaments of the cosmic web. In addition, we found in the field a candidate new giant radio galaxy.
  • Hattori, Shiho; Ota, Naomi; Zhang, Yu-Ying; Akamatsu, Hiroki; Finoguenov, Alexis (2017)
    We present the results from Suzaku satellite observations of the surrounding region of a galaxy cluster, A 2744, at z = 0.3. To search for oxygen emission lines from the warm-hot intergalactic medium (WHIM), we analyzed X-ray spectra from two northeastern regions 2.2-3.3 and 3.3-4.4 Mpc from the center of the cluster, which offers the first test on the presence of a WHIM near the typical accretion shock radius (similar to 2 r(200)) predicted by hydrodynamical simulations. For the 2.2-3.3 Mpc region, the spectral fit significantly (99.2% significance) improved when we included O-VII and O-VIII lines in the spectralmodel. A comparable WHIM surface brightness was obtained in the 3.3-4.4 Mpc region and the redshift of the O-VIII line is consistent with z=0.3 with in errors. The present results support that the observed soft X-ray emission originated from the WHIM. However, considering both statistical and systematic uncertainties, OVIII detection in the northeast regions was marginal. The surface brightnesses of the O-VIII line in 10(-7) photons cm(-2) s(-1) arcmin(-2) for the 2.2-3.3 and 3.3-4.4 Mpc regions were measured to be 2.7 +/- 1.0 and 2.1 +/- 1.2, giving upper limits on the baryon overdensity of delta = 319(<442) and 284(<446), respectively. This is comparable with previous observations of cluster outskirts and their theoretical predictions. The future prospect for WHIM detection using the Athena X-IFU micro-calorimeter is briefly discussed here. In addition, we also derived the intracluster medium temperature distribution of A 2744 to detect a clear discontinuity at the location of the radio relic. This suggests that the cluster has undergone strong shock heating by mass accretion along the filament.
  • Nevalainen, J.; Tempel, E.; Ahoranta, J.; Liivamägi, L. J.; Bonamente, M.; Tilton, E.; Kaastra, J.; Fang, T.; Heinämäki, P.; Saar, E.; Finoguenov, A. (2019)
    The cosmological missing baryons at z <1 most likely hide in the hot (T greater than or similar to 10(5.5) K) phase of the warm hot intergalactic medium (WHIM). While the hot WHIM is hard to detect due to its high ionisation level, the warm (T less than or similar to 10(5.5) K) phase of the WHIM has been very robustly detected in the far-ultraviolet (FUV) band. We adopted the assumption that the hot and warm WHIM phases are co-located and therefore used the FUV-detected warm WHIM as a tracer for the cosmologically interesting hot WHIM. We performed an X-ray follow-up in the sight line of the blazar PKS 2155-304 at the redshifts where previous FUV measurements of O VI, Si IV, and broad Lyman-alpha (BLA) absorption have indicated the existence of the warm WHIM. We looked for the O VII Hc alpha and O VIII Ly alpha absorption lines, the most likely hot WHIM tracers. Despite the very large exposure time (approximate to 1 Ms), the Reflection Grating Spectrometer unit 1 (RGS1) on-board XMM-Newton data yielded no significant detection which corresponds to upper limits of log N(O VII (cm(-2)))