We find a significant CMB temperature excess in the direction of local underdensities within z<0.03. By contrast, less than 0.2% of simulated CMB maps show a similarly significant temperature excess in nearby voids. Combined with earlier findings showing a >5σ cooling of CMB photons in galactic filaments in the same redshift range, we now may have possible evidence for a negative Integrated Sachs-Wolfe (ISW) effect in the very recent Universe. In addition to having opposite sign, the observed amplitude is an order of magnitude larger than the predicted Rees-Sciama and ISW effects, pointing to an unknown physical process, possibly related with a non-standard model of dark energy. We discuss the results in light of the latest Data Release 2 results of the Dark Energy Spectroscopic Instrument (DESI) showing hints for dynamical dark energy. Removing the quadrupole, we find the CMB temperatures measured in nearby voids to a large degree uncorrelated with the temperature measured around nearby galaxies and the observed mean difference between these temperatures is almost 6.5σ larger than found in simulations.

Recent papers have reported an unexplained cooling of cosmic microwave background (CMB) photons passing through galaxies in nearby cosmic filaments z <0.02 at the > 5 sigma level. Here we show for the first time that this effect is also present at higher redshifts 0.02 < z < 0.04. Instead of calculating the CMB temperature around individual galaxies as in previous works, we analyze mean CMB temperature profiles associated to cosmic filaments in three dimensions. We have considered different thresholds in the linear K-band luminosity density of the filaments as a proxy to mass density. Furthermore, we have analyzed the dependence of the results on the average orientation of filaments with respect to the line of sight. These studies were implemented to test the expected dependence on mass density as well as on photon trajectory length within the cosmic filaments. We find a 3 - 4 sigma detection of a CMB temperature decrement trend toward the spine of the filaments, the larger the mass and the more radially oriented the filament, the stronger the CMB temperature decrement. This trend is seen independently in both redshift ranges 0.004 < z <0.02 and 0.02 < z <0.04. We therefore conclude that our results provide strong evidence for a lower CMB temperature along massive cosmic filaments in the nearby Universe z <0.04.

We find that CMB photons passing through local voids ($z&lt;0.03$) are hotter than expected at the $2.7-3.6\sigma$ level. Combined with earlier findings showing a $&gt;5\sigma$ cooling of CMB photons in galactic filaments in the same redshift range, we now have possible evidence for a negative Integrated Sachs-Wolfe (ISW) effect in the very recent universe. In addition to having opposite sign, the observed amplitude is an order of magnitude larger than the predicted Rees-Sciama and ISW effects for the nearby universe. An altered growth of gravitational potentials at very low redshift, as predicted by some dark energy and modified gravity models, could give rise to the observed sign change. We discuss the results in light of the latest Data Release 2 results of the Dark Energy Spectroscopic Instrument (DESI) showing evidence for dynamical dark energy. When removing the CMB quadrupole, we find the temperatures measured in voids to a large degree uncorrelated with the temperature measured in galaxies and the observed mean difference of $41\mu$K between void and galaxy temperatures is about $6.5\sigma$ larger than found in simulations.

We present a statistical analysis of different astrophysical properties of a sample of galaxy pairs in cosmic voids. The sample consists of 72 galaxy pairs with projected separations and relative radial velocities rp < 100 h(-1) kpc, Delta V < 500 km s(-1) in the redshift range z < 0.1. We compared the different results for this pair sample to those derived for matched samples configured in absolute magnitude, stellar mass, and concentration residing in void, wall, and global averaged environments. We find that the pair galaxies in voids tend to have bluer optical colors than the corresponding galaxies in the wall and field environments, regardless of their stellar mass and concentration, which indicates a more recent formation of the bulk of stars. We also obtained larger mid-IR color indices for the void paired galaxies with respect to the corresponding matched samples in the wall and field environments. However, we found significantly larger differences for galaxies with a high mass and concentration. We also note that a mid-IR color-color diagram of the results showed void pair members consistent with the locus of star forming galaxies, in contrast to the other environments that exhibit a bimodal behavior comprising both passive and star forming objects. The Dn(4000) parameter also shows a significant younger stellar population in paired galaxies in voids. This is also reflected in the higher star formation rate values, which show a greater efficiency for void paired galaxies. We note that the star formation efficiency is greater for void paired galaxies with a high stellar mass and concentration. We also find that the efficiency of star formation associated with galaxy interactions is significantly greater in pairs residing in cosmic voids. This increased star formation activity could be associated with the expected richer gas environment and a gentler dynamical behavior as compared to the more eccentric orbits and stronger interactions and mergers more likely to occur in the wall and field environments.

We perform cosmological parameters estimation on Planck Cosmic Microwave Background (CMB) maps masking the recently discovered foreground related to nearby spiral galaxies. In addition, we also analyse the association between these foreground regions and recent claims of cosmological causal horizons in localized CMB parameter estimates. Our analysis shows consistent cosmological parameter values regardless of the masking approach, though reduced sky areas introduce larger uncertainties. By modelling the new extragalactic foreground, we identify a resemblance with local parameter variation maps with a statistical significance at the 3 sigma level, suggesting that a simplified foreground model partially accounts, (40-50)% correlation with 15% uncertainty, for the observed causal horizons. These findings add new evidence to the existence of the new foreground associated with large spiral galaxies and show that estimates of cosmological parameters on smaller patches on the sky can be largely affected by these foregrounds, but that the parameters taken over the full sky are unaltered.

The Cosmic Microwave Background (CMB) reaches homogeneity at relatively modest angular scales compared to the expectation of the standard Lambda CDM model revealing an important challenge to the theoretical predictions. We analyze this inconsistency through the homogeneity scale H and the slope of the homogeneity index at theta = 90 degrees. We find that the removal of low multipoles, in particular the quadrupole, from both the data and the Lambda CDM synthetic CMB maps, significantly improve the consistency between models and observations. This adds to indications of the relevant contribution of the low value of the CMB quadrupole to the observed anomalies in the homogeneity scale. Due to the presence of a new extragalactic foreground in the CMB maps, we have performed statistical analyses with different masking taking into account the regions mostly affected. In particular we consider galaxies in the local neighborhood which are expected to affect more significantly the large angular scales. We find that by masking these regions, the analysis cannot solve the discrepancy between the observations and the Lambda CDM model in spite of a small improvement of their mutual consistency. The studies with both foreground masking and low-& ell; removed CMB maps show similar results than those of the full CMB map indicating that the main discrepancy between theory and observations is associated to the quadrupole anomaly and may require more exhaustive analysis.

We compare the reduced void probability function (VPF) inside and outside of cosmic voids in the TNG300-1 simulation, both in real and simulated redshift space. The VPF is a special case of the counts-in-cells approach for extracting information of high-order clustering that is crucial for a full understanding of the distribution of galaxies. Previous studies have validated the hierarchical scaling paradigm of galaxy clustering moments, in good agreement with the "negative binomial" model, in redshift surveys, but have also reported that this paradigm is not valid in real space. However, in this work we find that hierarchical scaling can indeed be found in real space inside cosmic voids. This is well fitted by the negative binomial model. We find this result to be robust against changes in void identification, galaxy mass, random dilutions, and redshift. We also obtain that the VPF in real space at high redshift approaches the negative binomial model, and therefore it is similar to the VPF inside voids at the present time. This study points, for the first time, towards evidence of hierarchical scaling of high-order clustering of galaxies in real space inside voids, preserving the pristine structure formation processes of the Universe.

We confirm at the $5.7\sigma$ level previous studies reporting Cosmic Microwave Background (CMB) temperatures being significantly lower around nearby spiral galaxies than expected in the $\Lambda$CDM model. The significance reported in our earlier work was disputed by Addison 2024, who reported lower signficances when including pixels at distances far beyond the galactic halos while disregarding pixels close to the galaxies where the main signal is seen. Here we limit the study to pixels well within the galactic halos, focus on galaxies in dense cosmic filaments and improve on signal-to-noise compared to previous studies. The average CMB temperature in discs around these galaxies is always much lower in Planck data than in any of the 10.000 Planck-like CMB simulations. Even when correcting for the look-elsewhere-effect, the detection is still at the $3-4\sigma$ level. We further show that the largest scales ($\ell<16$) of the Planck CMB fluctuations are more correlated with the distribution of nearby galaxies than $99.99\%$ of simulated CMB maps. We argue that the existence of a new CMB foreground cannot be ignored and a physical interaction mechanism, possibly involving dark matter, as well as linked to intergalactic magnetic fields, should be sought.

We confirm at the 5.7σ level previous studies reporting Cosmic Microwave Background (CMB) temperatures being significantly lower around nearby spiral galaxies than expected in the ΛCDM model. Results from our earlier work was disputed in a recent paper, but in that paper, areas far beyond the galactic halos were included in the analysis while the neighborhood of the galaxies where the main signal is seen was disregarded. Here we limit the study to pixels well within the galactic halos, focus on galaxies in dense cosmic filaments and improve on signal-to-noise compared to previous studies. The average CMB temperature in discs around these galaxies is always much lower in Planck data than in any of the 10.000 Planck-like CMB simulations. Even when correcting for the look-elsewhere-effect, the detection is still at the 3-4σ level. We further show that the largest scales (ℓ<16) of the Planck CMB fluctuations are more correlated with the distribution of nearby galaxies than 99.99% of simulated CMB maps. We argue that the existence of a new CMB foreground cannot be ignored and a physical interaction mechanism, possibly involving dark matter, as well as linked to intergalactic magnetic fields, should be sought.

Self-interacting dark matter (SIDM) is an alternative to the standard collisionless cold dark matter model (CDM), allowing for interactions between the dark matter particles through the introduction of a self-scattering cross-section. However, the observable effects between these two scenarios are hard to detect. In this work we present a detailed analysis of an application of galaxy-galaxy lensing to measure with high precision the shapes of cluster halos and how this approach can be used to obtain information regarding the nature of the dark matter particle. Using two sets of simulated data, SIDM and CDM simulations, we compute stacked shear maps centred on several subsets of halos with masses $\gtrsim 10^{13.5} M_\odot$. From these maps, we obtain the quadrupole profiles related to the mean projected elongation of the particle distribution from which the shape parameters are derived. Accounting for a radial shape variation, this technique provides an enhancement of the observed differences between the simulated data-sets. In particular, we obtain a higher slope of the power law for the shape-radial relation for the halos identified in the SIDM simulation, which are rounder towards the centre. Also, as approaching to the mean virial radius, the projected semi-axis ratios converge to similar values than in the CDM simulation. Moreover, we account for the impact of the neighbouring mass, where more strongly elongated distributions are found for the halos in the SIDM simulation, indicating that under dark matter self interaction, the large scale structure imprints a more coherent accretion process.

The detection of anisotropies with respect to a given direction in a vector field is a common problem in astronomy. Several methods have been proposed that rely on the distribution of the acute angles between the data and a reference direction. Different approaches use Monte Carlo methods to quantify the statistical significance of a signal, although often lacking an analytical framework. Here we present two methods to detect and quantify alignment signals and test their statistical robustness. The first method considers the deviance of the relative fraction of vector components in the plane perpendicular to a reference direction with respect to an isotropic distribution. We also derive the statistical properties and stability of the resulting estimator, and therefore does not rely on Monte Carlo simulations to assess its statistical significance. The second method is based on a fit over the residuals of the empirical cumulative distribution function with respect to that expected for a uniform distribution, using a small set of harmonic orthogonal functions, which does not rely on any binning scheme. We compare these methods with others commonly used in the literature, using Monte Carlo simulations, finding that the proposed statistics allow the detection of alignment signals with greater significance.

Using a new statistical approach we study the alignment signal of galactic spins with respect to the center of voids identified in the TNG-300 simulation. We explore this signal in different samples of galaxies, varying their distance from the void center, mass, spin norm, local density, and velocity. We find a strong tendency (>9 sigma) of massive, high-spin, and low radial velocity galaxies to be aligned perpendicularly to the void-centric direction in a wide range of distances corresponding to 0.9 to 1.4 void radii. Furthermore, we find that in these subdense environments, local density is irrelevant in the amplitude of spin alignment, while the largest impact is associated to the galaxy void-centric radial velocity in the sense that those at the lowest expansion rate are more strongly aligned perpendicularly to the center of the void. Our results suggest that further analysis at understanding intrinsic alignments and their relation to large scale structures may probe key for weak lensing studies in upcoming large surveys such as Euclid and LSST.

The non-Gaussian Cold Spot (CS) surrounded by its hot ring is one of the most striking features of the CMB. It has been speculated that either new physics or ISW effect induced by the presence of a cosmic void at high redshift can account for the observations. Here we investigate if the systematic decrease in CMB temperature in the neighbourhood of nearby galaxies may create such a strong temperature depression. In particular, we note that the Eridanus supergroup and its neighbouring groups, is in the CS area. Our goal is to analyse observational galaxy data to characterise the neighbourhood of the CS, explore the properties of these galaxies and thereby make a prediction of the CMB temperature decrement in this region. We use the Planck SMICA maps and the galaxy catalogues 2MRS, 6dF and HIPASS as foreground tracers. We apply mean temperature profiles to model the temperature decrement from the galaxies in the CS area. Even after correcting for the mean low temperature of the CS region, we find that the temperature decrement around galaxies is significantly stronger than the mean decrement in other parts of the sky. We discuss whether this could be attributed to the fact that the CS area coincides with one of the regions populated by the most HI deficient galaxies. Modelling the foreground temperature profile, we find a particularly strong temperature decrement due to the presence of the late-type overabundant largest group complex in the nearby universe. A CS shape, which to a large degree overlaps with the CMB CS, is observed. We conclude that the coincidence of the only nearby spiral rich group complex located in the CS region, and the success of the modelling performed, adds strong evidence to the existence of a local extragalactic foreground which could account for the observed temperature depression, alleviating the tension with an otherwise Gaussian field expected in the CMB.

ABSTRACT Galaxy pairs constitute the initial building blocks of galaxy evolution, which is driven through merger events and interactions. Thus, the analysis of these systems can be valuable in understanding galaxy evolution and studying structure formation. In this work, we present a new publicly available catalogue of close galaxy pairs identified using photometric redshifts provided by the Physics of the Accelerating Universe Survey (PAUS). To efficiently detect them, we take advantage of the high-precision photo−z (σ68 < 0.02) and apply an identification algorithm previously tested using simulated data. This algorithm considers the projected distance between the galaxies (rp < 50 kpc), the projected velocity difference (ΔV < 3500 km s−1) and an isolation criterion to obtain the pair sample. We applied this technique to the total sample of galaxies provided by PAUS and to a subset with high-quality redshift estimates. Finally, the most relevant result we achieved was determining the mean mass for several subsets of galaxy pairs selected according to their total luminosity, colour, and redshift, using galaxy–galaxy lensing estimates. For pairs selected from the total sample of PAUS with a mean r-band luminosity 1010.6 h−2 L⊙, we obtain a mean mass of M200 = 1012.2 h−1 M⊙, compatible with the mass–luminosity ratio derived for elliptical galaxies. We also study the mass-to-light ratio M/L as a function of the luminosity L and find a lower M/L (or steeper slope with L) for pairs than the one extrapolated from the measurements in groups and galaxy clusters.

ABSTRACT The aim of this work is to study the anisotropic weak lensing signal associated with the mass distribution of massive clusters of galaxies using the cosmic microwave background (CMB) data. For this purpose, we stack patches of the Planck Collaboration (2018) CMB lensing convergence map centred on SDSS DR8 redMaPPer clusters within the redshift range [0.4, 0.5]. We obtain mean radial profiles of the convergence parameter κ finding strong signals at scales as large as 40 Mpch−1. By orienting the clusters along their major axis defined through the galaxy member distribution, we find a significant difference between the parallel and perpendicular-oriented convergence profiles. The amplitude of the profile along the parallel direction is about 50 per cent larger than that along the perpendicular direction, indicating that the clusters are well aligned with the surrounding mass distribution. From a model with an anisotropic surface mass density, we obtain a suitable agreement for both mass and ellipticities of clusters compared to results derived from weak lensing shear estimates, finding strong evidence of the correlation between the galaxy cluster member distribution and the large-scale mass distribution.

In Luparello et al. 2023, a new and hitherto unknown CMB foreground was detected. A systematic decrease in Cosmic Microwave Background (CMB) temperatures around nearby large spiral galaxies points to an unknown interaction with CMB photons in a sphere up to several projected Mpc around these galaxies. We investigate to which extent this foreground may impact the CMB fluctuations map and create the so-called CMB anomalies. Using the observed temperature decrements around the galaxies, and making some general assumptions about the unknown interaction, we propose a common radial temperature profile. By assigning this profile to nearby galaxies in the redshift range $z=[0.004,0.02]$ we create a foreground map model. We find a remarkable resemblance between this temperature model map based on nearby galaxies and the Planck CMB map. Out of 1000 simulated maps, none of them show such a strong correlation with the foreground map over both large and small angular scales. In particular, the quadrupole, octopole, as well as $\ell=4$ and $\ell=5$ modes correlate with the foreground map to high significance. Furthermore, one of the most prominent temperature decrements in the foreground map coincides with the position of the CMB cold spot. The largest scales of the CMB and thereby the cosmological parameters, may have important changes after proper corrections of this foreground component. However, a reliable corrected CMB map can only be derived when suitable physical mechanisms are proposed and tested.

We report and analyse the presence of foregrounds in the cosmic microwave background (CMB) radiation associated to extended galactic halos. Using the cross correlation of Planck and WMAP maps and the 2MRS galaxy catalogue, we find that the mean temperature radial profiles around nearby galaxies at $cz\le 4500~\rm{km~s^{-1}}$ show a statistically significant systematic decrease of $\sim 15~\mu \rm{K}$ extending up to several galaxy radii. This effect strongly depends on the galaxy morphological type at scales within several tens of times the galaxy size, becoming nearly independent of galaxy morphology at larger scales. The effect is significantly stronger for the more extended galaxies, with galaxy clustering having a large impact on the results. Our findings indicate the presence of statistically relevant foregrounds in the CMB maps that should be considered in detailed cosmological studies. Besides, we argue that these can be used to explore the intergalactic medium surrounding bright late-type galaxies and allow for diverse astrophysical analyses.

We study the population of active galaxies in void environment in the SDSS. We use optical spectroscopic information to analyze characteristics of the emission lines of galaxies, accomplished by WHAN and BPT diagrams. Also, we study WISE mid-IR colours to assess AGN activity. We investigate these different AGN classification schemes, both optical and mid-IR, and their dependence on the spatial location with respect to the void centres. To this end, we define three regions: void, the spherical region defined by voidcentric distance relative to void radius (distance/r_ void) smaller than 0.8, comprising overdensities lesser than -0.9, an intermediate/transition shell region (namely void–wall) 0.8 < distance/r_ void < 1.2, and a region sufficiently distant from voids, the field: distance/r_ void > 2. We find statistical evidence for a larger fraction of AGN and star–forming galaxies in the void region, regardless of the classification scheme addressed (either BPT, WHAN or WISE). Moreover, we obtain a significantly stronger nuclear activity in voids compared to the field. We find an unusually large fraction of the most massive black holes undergoing strong accretion when their host galaxies reside in voids. Our results suggest a strong influence of the void environment on AGN mechanisms associated with galaxy evolution.

Context. Evidence shows that properties of dark matter haloes may vary with large-scale environment. Studying the halo occupation distribution in cosmic voids makes it possible to obtain useful information that can shed light on the subject. The history of the formation of the haloes and galaxies residing in these regions is likely to differ from the global behaviour given their extreme environment. Aims. Our goal is to characterise the halo occupation distribution in the interior of cosmic voids and compare with the general results to unveil the way galaxies populate haloes in simulated galaxy catalogues. Methods. We used two publicly accessible simulated galaxy catalogues constructed with different methods: a semi-analytical model and a hydrodynamic simulation. In both cases, we identified cosmic voids, and we measured the halo occupation distribution inside these regions for different absolute magnitude thresholds. We compared these determinations with the overall results, and we studied the dependence of different characteristics of the voids. We also analysed the stellar content and the formation time of the haloes inside voids and confronted the general halo population results. Results. Inside the voids, we find a significantly different halo occupation distribution with respect to the general results. This is present in all absolute magnitude ranges explored. We obtain no signs of variation related to void characteristics, indicating that the effects depend only on the density of the large-scale environment. Additionally, we find that the stellar-mass content also differs within voids that host haloes with less massive central galaxies (∼10%), as well as satellites with significantly lower stellar-mass content (∼30%). Finally, we find a slight difference between the formation times of the younger haloes in voids than the average population. These characteristics indicate that haloes populating voids have had a different formation history, inducing significant changes on the halo occupation distribution.

ABSTRACT We study the impact of the environment on galaxies as they fall in and orbit in the potential well of a Local Group (LG) analogue, following them with high cadence. The analysis is performed on eight disc satellite galaxies from the CIELO suite of hydrodynamical simulations. All galaxies have stellar masses within the range $[10^{8.1}\!-\!10^{9.56}] \, \mathrm{M}_{\odot }\, {\rm h}^{-1}$. We measure tidal torques, ram pressure, and specific star formation rates (sSFRs) as a function of time, and correlate them with the amount of gas lost by satellites along their orbits. Stronger removal episodes occur when the disc plane is oriented perpendicular to the direction of motion. More than one peripassage is required to significantly modify the orientations of the discs with respect to the orbital plane. The gas removed during the interaction with the central galaxies may also be found opposite to the direction of motion, depending on the orbital configuration. Satellites are not totally quenched when the galaxies reach their first peripassage and continue forming about $10{{\ \rm per\ cent}}$ of the final stellar mass after this event. The fraction of removed gas is found to be the product of the joint action of tidal torque and ram pressure, which can also trigger new star formation activity and subsequent supernova feedback.