Astrophysics

We constrain the coupling between axionlike particles (ALPs) and photons, measured with the superconducting resonant detection circuit of a cryogenic Penning trap. By searching the noise spectrum of our fixed-frequency resonant circuit for peaks caused by dark matter ALPs converting into photons in the strong magnetic field of the Penning-trap magnet, we are able to constrain the coupling of ALPs with masses around 2.7906??.7914 neV/c 2 to g aγ <1? 10 ??1 GeV ?? . This is more than one order of magnitude lower than the best laboratory haloscope and approximately 5 times lower than the CERN axion solar telescope (CAST), setting limits in a mass and coupling range which is not constrained by astrophysical observations. Our approach can be extended to many other Penning-trap experiments and has the potential to provide broad limits in the low ALP mass range.

We present limits on the parameters of the o Λ CDM, w 0 CDM, and w 0 w a CDM models obtained from the joint analysis of the full-shape, baryon acoustic oscillations (BAO), big bang nucleosynthesis (BBN) and supernovae data. Our limits are fully independent of the data on the cosmic microwave background (CMB) anisotropies, but rival the CMB constraints in terms of parameter error bars. We find the spatial curvature consistent with a flat universe Ω k =− 0.043 +0.036 −0.036 ( 68% C.L.); the dark-energy equation of state parameter w 0 is measured to be w 0 =− 1.031 +0.052 −0.048 ( 68% C.L.), consistent with a cosmological constant. This conclusion also holds for the time-varying dark energy equation of state, for which we find w 0 =− 0.98 +0.099 −0.11 and w a =− 0.33 +0.63 −0.48 (both at 68% C.L.). The exclusion of the supernovae data from the analysis does not significantly weaken our bounds. This shows that using a single external BBN prior, the full-shape and BAO data can provide strong CMB-independent constraints on the non-minimal cosmological models.

Both the absolute magnitude of type Ia supernovae (SNe Ia) and the luminosity distance of them are modified in the context of the minimally extended varying speed of light (meVSL) model compared to those of general relativity (GR). We have analyzed the likelihood of various dark energy models under meVSL by using the Pantheon SNe Ia data. Both ? CDM and CPL parameterization dark energy models indicate a cosmic variation of the speed of light at the 1- ? level. For ٠m0 =0.30,0.31 , and 0.32 with ( ? 0 , ? a )=(??,0) , 1- ? range of c ~ ? 0 / c ~ 0 ( 10 ??3 yr ?? ) are (-8.76 \,, -0.89), (-11.8 \,, 3.93), and (-14.8 \,, -6.98), respectively. Meanwhile, 1- ? range of c ~ ? 0 / c ~ 0 ( 10 ??2 yr ?? ) for the CPL dark energy models with ??.05??? 0 ?��?0.95 and 0.28??٠m0 ??.32 , are (-6.31\,, -2.98). The value of c ~ at z=3 can be larger than that of the present by 0.2?? \% for ? CDM models and 5??3 \% for CPL models. We also obtain ??5.6??G ~ ? 0 / G ~ 0 ( 10 ??2 yr ?? )?��?0.36 for viable models except for CPL model for ٠m0 =0.28 . We obtain the increasing rate of the gravitational constant as 1.65??G ~ ? 0 / G ~ 0 ( 10 ??2 yr ?? )??.79 for that model.

We study the structure of galactic halos within a scalar dark matter model, endowed with a repulsive quartic self-interaction, capable of undergoing the superfluid phase transition in high-density regions. We demonstrate that the thermalized cores are prone to fragmentation into superfluid droplets due to the Jeans instability. Furthermore, since cores of astrophysical size may be generated only when most of the particles comprising the halo reside in a highly degenerate phase-space, the well-known bound on the dark matter self-interaction cross section inferred from the collision of clusters needs to be revised, accounting for the enhancement of the interaction rate due to degeneracy. As a result, generation of kpc-size superfluid solitons, within the parameter subspace consistent with the Bullet Cluster bound, requires dark matter particles to be ultra-light.

The core mass of galaxy clusters is an important probe of structure formation. Here, we evaluate the use of a Single-Halo model (SHM) as an efficient method to estimate the strong lensing cluster core mass, testing it with ray-traced images from the `Outer Rim' simulation. Unlike detailed lens models, the SHM represents the cluster mass distribution with a single halo and can be automatically generated from the measured lensing constraints. We find that the projected core mass estimated with this method, M SHM , has a scatter of 8.52% and a bias of 0.90% compared to the "true" mass within the same aperture. Our analysis shows no systematic correlation between the scatter or bias and the lens-source system properties. The bias and scatter can be reduced to 3.26% and 0.34% , respectively, by excluding models that fail a visual inspection test. We find that the SHM success depends on the lensing geometry, with single giant arc configurations accounting for most of the failed cases due to their limiting constraining power. When excluding such cases, we measure a scatter and bias of 3.88% and 0.84% , respectively. Finally, we find that when the source redshift is unknown, the model-predicted redshifts are overestimated, and the M SHM is underestimated by a few percent, highlighting the importance of securing spectroscopic redshifts of background sources. Our analysis provides a quantitative characterization of M SHM , enabling its efficient use as a tool to estimate the strong lensing cluster core masses in the large samples, expected from current and future surveys.

The large-scale structure of the Universe is a cosmic web of interconnected clusters, filaments, and sheets of matter. This PhD comprises two complementary projects investigating the cosmic web using correlations between three different tracers: the cosmic microwave background (CMB), supernovae (SNe), and large quasar groups (LQGs). In the first project we re-analyse the apparent correlation between CMB temperature and SNe redshift reported by Yershov, Orlov and Raikov. They presented evidence that the WMAP/Planck CMB pixel-temperatures at SNe locations tend to increase with increasing redshift. They suggest this could be caused by the Integrated Sachs-Wolfe effect and/or by residual foreground contamination. Our analysis supports the prima facie existence of the correlation but attributes it instead to a composite selection bias caused by the chance alignment of seven deep survey fields with CMB hotspots. These seven fields contain just 9.2% of the SNe sample. We estimate the likelihood of their falling on CMB hotspots by chance is approximately 1 in 11. In the second project we investigate for the first time the apparent coherent alignment of LQGs in the redshift range 1.0 <= z <= 1.8. We find that the position angles (PAs) of LQGs are correlated, specifically aligned and orthogonal, with a maximum significance of ~2.4 sigma at typical angular (comoving) separations of ~30 degrees (~1.6 Gpc). Spatial coincidence between our LQG sample and regions of quasar polarization alignment first reported by Hutsemekers, and the similarity between LQG PAs and radio polarization angles reported by Pelgrims and Hutsemekers, suggest an interesting result.

Recent X-ray observations have revealed remarkable correlations between the masses of central supermassive black holes (SMBHs) and the X-ray properties of the hot atmospheres permeating their host galaxies, thereby indicating the crucial role of the atmospheric gas in tracing SMBH growth in the high-mass regime. We examine this topic theoretically using the IllustrisTNG cosmological simulations and provide insights to the nature of this SMBH -- gaseous halo connection. By carrying out a mock X-ray analysis for a mass-selected sample of TNG100 simulated galaxies at z=0 , we inspect the relationship between the masses of SMBHs and the hot gas temperatures and luminosities at various spatial and halo scales -- from galactic ( ∼ R e ) to group/cluster scales ( ∼ R 500c ). We find strong SMBH-X-ray correlations mostly in quenched galaxies and find that the correlations become stronger and tighter at larger radii. Critically, the X-ray temperature ( k B T X ) at large radii ( r≳5 R e ) traces the SMBH mass with a remarkably small scatter ( ∼0.2 dex). The relations emerging from IllustrisTNG are broadly consistent with those obtained from recent X-ray observations. Overall, our analysis suggests that, within the framework of IllustrisTNG, the present-time M BH − k B T X correlations at the high-mass end ( M BH ≳ 10 8 M ⊙ ) are fundamentally a reflection of the SMBH mass -- halo mass relation, which at such high masses is set by the hierarchical assembly of structures. The exact form, locus, and scatter of those scaling relations are, however, sensitive to feedback processes such as those driven by star formation and SMBH activity.

Pulsar timing data used to provide upper limits on a possible stochastic gravitational wave background (SGWB). However, the NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gμ∈(4× 10 −11 , 10 −10 ) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers. The SGWB produced by cosmic strings with such values of Gμ would be beyond the reach of LIGO, but could be measured by other planned and proposed detectors such as SKA, LISA, TianQin, AION-1km, AEDGE, Einstein Telescope and Cosmic Explorer.

Inferring line-of-sight distances from redshifts in and around galaxy clusters is complicated by peculiar velocities, a phenomenon known as the "Fingers of God" (FoG). This presents a significant challenge for finding filaments in large observational data sets as these artificial elongations can be wrongly identified as cosmic web filaments by extraction algorithms. Upcoming targeted wide-field spectroscopic surveys of galaxy clusters and their infall regions such as the WEAVE Wide-Field Cluster Survey motivate our investigation of the impact of FoG on finding filaments connected to clusters. Using zoom-in resimulations of 324 massive galaxy clusters and their outskirts from The ThreeHundred project, we test methods typically applied to large-scale spectroscopic data sets. This paper describes our investigation of whether a statistical compression of the FoG of cluster centres and galaxy groups can lead to correct filament extractions in the cluster outskirts. We find that within 5 R200 (~15 Mpc/h) statistically correcting for FoG elongations of virialized regions does not achieve reliable filament networks compared to reference filament networks based on true positions. This is due to the complex flowing motions of galaxies towards filaments in addition to the cluster infall, which overwhelm the signal of the filaments relative to the volume we probe. While information from spectroscopic redshifts is still important to isolate the cluster regions, and thereby reduce background and foreground interlopers, we expect future spectroscopic surveys of galaxy cluster outskirts to rely on 2D positions of galaxies to extract cosmic filaments.

Forthcoming surveys will extend the understanding of cosmological large scale structures up to unprecedented redshift. According to this perspective, we present a fully relativistic framework to evaluate the impact of stochastic inhomogeneities on the determination of the Hubble constant. To this aim, we work within linear perturbation theory and relate the fluctuations of the luminosity distance-redshift relation, in the Cosmic Concordance model, to the intrinsic uncertainty associated to the measurement of H 0 from high-redshift surveys ( 0.15?�z??.85 ). We first present the detailed derivation of the luminosity distance-redshift relation 2-point correlation function and then provide analytical results for all the involved relativistic effects, such as peculiar velocity, lensing, time delay and (integrated) Sachs-Wolfe, and their angular spectra. Hence, we apply our analytical results to the study of high-redshift Hubble diagram, according to what has been recently claimed in literature. Following the specific of Euclid Deep Survey and LSST, we conclude that the cosmic variance associated with the measurement of the Hubble constant is at most of 0.1 %. Our work extends the analysis already done in literature for closer sources, where only peculiar velocity has been taken into account. We then conclude that deep surveys will provide an estimation of the H 0 which will be more precise than the one obtained from local sources, at least in regard of the intrinsic uncertainty related to a stochastic distribution of inhomogeneities.