The fundamental properties of the postulated dark matter (DM) affect the internal structure of gravitationally bound structures. In the cold dark matter paradigm, DM particles interact only via... Show moreThe fundamental properties of the postulated dark matter (DM) affect the internal structure of gravitationally bound structures. In the cold dark matter paradigm, DM particles interact only via gravity. Their distribution is well represented by an Einasto profile with shape parameter alpha approximate to 0.18 in the smallest dwarf galaxies or the most massive galaxy clusters alike. Conversely, if DM particles self-interact via additional forces, we expect the mass density profiles of DM halos to flatten in their central regions, thereby increasing the Einasto shape parameter. We measured the structural properties of 12 massive galaxy clusters from observations of their hot gaseous atmosphere, using the X-ray observatory XMM-Newton, and of the Sunyaev-Zel'dovich effect using the Planck all-sky survey. After removing morphologically disturbed systems, we measured Einasto shape parameters with mean =0.19 +/- 0.03 and intrinsic scatter sigma(alpha)=0.06, which is in close agreement with the prediction of the cold dark matter paradigm. We used cosmological hydrodynamical simulations of cluster formation with self-interacting DM (BAHAMAS-SIDM) to determine how the Einasto shape parameter depends on the self-interaction cross section. We used the fitted relation to turn our measurements of alpha into constraints on the self-interaction cross section, which imply sigma/m< 0.19 cm(2) g(-1) (95% confidence level) at collision velocity v(DM - DM)similar to 1000 km s(-1). This is lower than the interaction cross section required for DM self-interactions to solve the core-cusp problem in dwarf spheroidal galaxies, unless the cross section is a strong function of velocity. Show less
Context. The evolution of galaxies is influenced by many physical processes, which may vary depending on their environment.Aims. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic... Show moreContext. The evolution of galaxies is influenced by many physical processes, which may vary depending on their environment.Aims. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic Explorer (MUSE) data of galaxies at 0.25 less than or similar to z less than or similar to 1.5 to probe the impact of environment on the size-mass relation, the main sequence (MS) relation, and the Tully-Fisher relation (TFR).Methods. We perform a morpho-kinematics modelling of 593 [O II] emitters in various environments in the COSMOS area from the MUSE-gAlaxy Groups In Cosmos survey. The HST F814W images are modelled with a bulge-disk decomposition to estimate their bulge-disk ratio, effective radius, and disk inclination. We use the [O II] lambda lambda 3727, 3729 doublet to extract the galaxies' ionised gas kinematics maps from the MUSE cubes, and we model those maps for a sample of 146 [O II] emitters, including bulge and disk components constrained from morphology and a dark matter halo.Results. We find an offset of 0.03 dex (1 sigma - significant) on the size-mass relation zero point between the field and the large structure sub-samples, with a richness threshold of N = 10 to separate between small and large structures, and of 0.06 dex (2 sigma) with N = 20. Similarly, we find a 0.1 dex (2 sigma) difference on the MS relation with N = 10 and 0.15 dex (3 sigma) with N = 20. These results suggest that galaxies in massive structures are smaller by 14% and have star formation rates reduced by a factor of 1.3-1.5 with respect to field galaxies at z approximate to 0.7. Finally, we do not find any impact of the environment on the TFR, except when using N = 20 with an offset of 0.04 dex (1 sigma). We discard the effect of quenching for the largest structures, which would lead to an offset in the opposite direction. We find that, at z approximate to 0.7, if quenching impacts the mass budget of galaxies in structures, these galaxies would have been affected quite recently and for roughly 0.7-1.5 Gyr. This result holds when including the gas mass but vanishes once we include the asymmetric drift correction. Show less
Aims. Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary gamma-ray emission from gamma-ray interactions with extragalactic... Show moreAims. Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary gamma-ray emission from gamma-ray interactions with extragalactic background light. Lower bounds on the magnetic field in the voids were derived from the nondetection of this emission. It is not clear a priori what kind of magnetic field is responsible for the suppression of the secondary gamma-ray flux: a cosmological magnetic field that might be filling the voids, or the field spread by galactic winds driven by star formation and active galactic nuclei. Methods. We used IllustrisTNG cosmological simulations to study the effect of magnetized galactic wind bubbles on the secondary gamma-ray flux. Results. We show that within the IllustrisTNG model of baryonic feedback, galactic wind bubbles typically provide energy-independent secondary flux suppression at a level of about 10%. The observed flux suppression effect has to be due to the cosmological magnetic field in the voids. This might not be the case for the special case when the primary gamma-ray source has a hard intrinsic gamma-ray spectrum that peaks in the energy range above 50 TeV. In this case, the observational data may be strongly affected by the magnetized bubble that is blown by the source host galaxy. Show less
Morganti, R.; Oosterloo, T.A.; Brienza, M.; Jurlin, N.; Prandoni, I.; Orru, E.; ... ; Ziemke, J. 2021
Super massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding... Show moreSuper massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of the images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of similar to 15 arcsec) for all the sources within an approximately 6 deg(2) area of the Lockman Hole region. In this way, we were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent cases of radio sources in the remnant or the restarted phases of their life cycle. Our findings confirm that these objects are not as rare as previously thought, suggesting a relatively fast cycle. They also show a variety of properties that can be relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the "off" (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with the results of simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), possibly suggesting different types of progenitors. The present work sets the stage for exploiting the powerful tool of low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys. Show less
Stangret, M.; Pallé, E.; Casasayas Barris, N.; Oshagh, M.; Bello-Arufe, A.; Luque, R.; ... ; Tronsgaard, R. 2021
Context. Benford’s law states that for scale- and base-invariant data sets covering a wide dynamic range, the distribution of the first significant digit is biased towards low values. This has been... Show moreContext. Benford’s law states that for scale- and base-invariant data sets covering a wide dynamic range, the distribution of the first significant digit is biased towards low values. This has been shown to be true for wildly different datasets, including financial, geographical, and atomic data. In astronomy, earlier work showed that Benford’s law also holds for distances estimated as the inverse of parallaxes from the ESA HIPPARCOS mission.Aims. We investigate whether Benford’s law still holds for the 1.3 billion parallaxes contained in the second data release of Gaia (Gaia DR2). In contrast to previous work, we also include negative parallaxes. We examine whether distance estimates computed using a Bayesian approach instead of parallax inversion still follow Benford’s law. Lastly, we investigate the use of Benford’s law as a validation tool for the zero-point of the Gaia parallaxes.Methods. We computed histograms of the observed most significant digit of the parallaxes and distances, and compared them with the predicted values from Benford’s law, as well as with theoretically expected histograms. The latter were derived from a simulated Gaia catalogue based on the Besançon galaxy model.Results. The observed parallaxes in Gaia DR2 indeed follow Benford’s law. Distances computed with the Bayesian approach of Bailer-Jones et al. (2018, AJ, 156, 58) no longer follow Benford’s law, although low-value ciphers are still favoured for the most significant digit. The prior that is used has a significant effect on the digit distribution. Using the simulated Gaia universe model snapshot, we demonstrate that the true distances underlying the Gaia catalogue are not expected to follow Benford’s law, essentially because the interplay between the luminosity function of the Milky Way and the mission selection function results in a bi-modal distance distribution, corresponding to nearby dwarfs in the Galactic disc and distant giants in the Galactic bulge. In conclusion, Gaia DR2 parallaxes only follow Benford’s Law as a result of observational errors. Finally, we show that a zero-point offset of the parallaxes derived by optimising the fit between the observed most-significant digit frequencies and Benford’s law leads to a value that is inconsistent with the value that is derived from quasars. The underlying reason is that such a fit primarily corrects for the difference in the number of positive and negative parallaxes, and can thus not be used to obtain a reliable zero-point. Show less
By means of a fully connected artificial neural network, we identified asteroids with the potential to impact Earth. The resulting instrument, named the Hazardous Object Identifier (HOI), was... Show moreBy means of a fully connected artificial neural network, we identified asteroids with the potential to impact Earth. The resulting instrument, named the Hazardous Object Identifier (HOI), was trained on the basis of an artificial set of known impactors which were generated by launching objects from Earth's surface and integrating them backward in time. HOI was able to identify 95.25% of the known impactors simulated that were present in the test set as potential impactors. In addition, HOI was able to identify 90.99% of the potentially hazardous objects identified by NASA, without being trained on them directly. Show less
