arXiv subjects

Diego Garcia Lambas

Publications and source records attributed to Diego Garcia Lambas.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting the CMB homogeneity scale: low multipoles removal effect and extragalactic foreground masking

The Cosmic Microwave Background (CMB) reaches homogeneity at relatively modest angular scales compared to the expectation of the standard $Λ$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 $θ= 90^\circ$. We find that the removal of low multipoles, in particular the quadrupole, from both the data and the $Λ$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 $Λ$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.

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arXiv2026

Evidence for a sign change of the ISW effect in the very recent universe? hot voids and cold overdensities at $z<0.03$

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.

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arXiv2026

Cosmic filaments confirm unexplained CMB temperature decrements in two independent redshift ranges

Recent papers have reported an unexplained cooling of CMB photons passing through galaxies in nearby cosmic filaments $z<0.02$ at the $>5σ$ 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 $3-4σ$ detection of a CMB temperature decrement trend towards 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 $z<0.04$.

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arXiv2026

The connection between surface brightness and satellite systems for central galaxies through Illustris TNG

We analyse different properties of central low-surface-brightness galaxies (LSBGs) and their satellite systems using the simulation Illustris TNG-100, in order to deepen our understanding of the formation mechanism of LSBGs in a $Λ$CDM cosmology. We find differences in the spin and the concentrations of the LSBGs haloes and the host haloes of high-surface-brightness galaxies (HSBGs), consistent with previous studies. By analysing their spatial and kinematical distribution of satellites, we find that LSBGs tend to have a larger number of satellites than HSBGs and with a larger velocity dispersion. Moreover, we obtain a continuous relation between the number of satellites and surface brightness, particularly for massive central galaxies. We also find a relation between surface brightness and the relative tangential velocity of the satellites. For a given stellar mass, the existence of LSBGs is strongly correlated with their satellite system dominated by rotation. Furthermore, the satellite system is systematically in counter-rotation with respect to the primary disc in LSBGs. We propose that this fact reflects that these galaxies have not experienced a significantly high rate of mergers, which are more likely associated with radial orbits expected in systems of galaxies with a high surface brightness.

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arXiv2025

Are CMB derived cosmological parameters affected by foregrounds associated to nearby galaxies?

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.

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arXiv2025

A p<0.0001 detection of CMB cooling in galactic halos and its possible relation to dark matter

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 $Λ$CDM 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 ($\ell<16$) 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.

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arXiv2024

Galaxy Pairs in Cosmic Voids

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, $ΔV <$ 500 kms$^{-1}$ in the redshift range z<0.1. The different results for this pair sample are compared 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 pair galaxies in voids tend to have bluer optical colors than the corresponding galaxies in wall an field, regardless of their stellar mass and concentration, which indicates a more recent formation of the bulk of stars. We also obtain larger mid--IR colors for the void paired galaxies with respect to the corresponding matched samples in the wall and in field environments. However, we find significantly larger differences for galaxies with high mass and concentration. We also notice that mid--IR color--color diagram shows void pair members consistent with the locus of star--forming galaxies, in contrast with the other environments that exhibit a bimodal behavior comprising both passive and star--forming objects. The D$_n$(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 larger efficiency for void paired galaxies. We notice that the star formation efficiency is larger for void paired galaxies with high stellar mass and concentration. We also find that the efficiency of star formation associated to galaxy interactions is significantly larger in pairs residing in cosmic voids. This larger star formation activity could be associated to both the expected richer gas environment and a more gentle dynamical behavior typical of void environments.

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arXiv2023

Void Probability Function inside cosmic voids: evidence for hierarchical scaling of high-order correlations in real space

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.

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arXiv2023

The CMB Cold Spot as predicted by foregrounds around nearby galaxies

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.

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arXiv2023

A CMB lensing analysis of the extended mass distribution of clusters

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 centered on SDSS DR8 redMaPPer clusters within the redshift range [0.4, 0.5]. We obtain mean radial profiles of the convergence parameter k finding strong signals at scales as large as 40 Mpc/h. 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% 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.

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arXiv2023

A possible common explanation for several cosmic microwave background (CMB) anomalies: A strong impact of nearby galaxies on observed large-scale CMB fluctuations

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.

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arXiv2022

Galaxy populations in haloes in high-density environments

There are hints suggesting that properties of galaxy populations in dark matter haloes may depend on their large-scale environment. Recent works point out that very low-density environments influence halo occupation distribution (HOD), however there is not a similar analysis focused on high-density environments. Here we use a simulated set of future virialized superstructures (FVS) to analyse the occupation of galaxies in haloes within these high globally dense regions. We use a publicly available simulated galaxy set constructed with a semi-analytical model to identify FVS in the simulation. Then, we computed the HOD within these superstructures for different absolute magnitude thresholds and make several analysis including the comparison to the global HOD results. We study the dependence on the results on properties of the FVS such as density and volume as well as consider the morphology of galaxies. We also analysed the properties of the stellar content of galaxies and the formation time of the haloes inside FVS. We find a significant increase in the HOD inside FVS. This result is present for all absolute magnitude thresholds explored. The effect is larger in the densest regions of FVS, but does not depend on the volume of the superstructure. We also find that the stellar-mass content of galaxies considerably differs inside the superstructures. Low mass haloes have their central and satellite galaxies with a higher stellar mass content (50%), and exhibit mean star ages (20%) older than average. For massive haloes in FVS we find that only the stellar mass of satellite galaxies varies considerably corresponding to a decrease of 50%. We find a significant statistical difference between the formation times of haloes in FVS and the average population. Haloes residing in superstructures formed earlier, a fact that leads to several changes in the HOD and their member galaxy properties.

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arXiv2022

How do galaxies populate halos in extreme density environments? An analysis of the Halo Occupation Distribution in SDSS

Recent works have shown that the properties of galaxy populations in dark matter halos vary with large-scale environments. These results suggest a variation in the halo occupation distribution (HOD) in extreme density environments. To analyse these effects, we identify cosmic voids and future virialised structures (FVS) in the SDSS-DR12 and estimate the HOD within these superstructures using group catalogues as dark matter halo proxies. Our goal is to use observational galaxy data to characterise the HOD within voids and FVS, explore the different properties of these galaxies populations and compare them with the general results outside these superstructures. Using a galaxy group catalogue we compute the HOD within both types of superstructures. We also study the dependence on the results on the main void and FVS properties. We also analysed the mean stellar age of the galaxies inside these regions. In all cases, we compare the results with those derived from the Field sample. Inside voids, we find a strong decrease in HOD concerning the Field results. The mean number of satellites fall to 50%. Inside FVS, the HOD shows a significant increase to the Field, with a 40% excess in the mean number of satellites. In both regions, the differences with respect to the Field increases for the extreme values of the density environments. We obtain no signs of variations related to intrinsic characteristics of voids and FVS. We find that the cumulative distribution of the mean age of stars of the central galaxy also varies in these regions. Finally, we explore the HOD for the 25% youngest (oldest) galaxies. We find that for the low-mass groups the youngest galaxies are only present inside voids. On the other hand, for the high-mass groups the FVS environments show the same increase in the HOD concerning the Field. We find that cosmic voids lack of oldest galaxies.

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arXiv2021

The impact of void environment on AGN

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$_{\rm void}$) smaller than 0.8, comprising overdensities lesser than -0.9, an intermediate/transition shell region (namely void--wall) 0.8 $<$ distance/r$_{\rm void} <$ 1.2, and a region sufficiently distant from voids, the field: distance/r$_{\rm void} >$ 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.

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arXiv2021

Dynamical analysis of clusters of galaxies from cosmological simulations

Studies of cluster mass and velocity anisotropy profiles are useful tests of dark matter models, and of the assembly history of clusters of galaxies. These studies might be affected by unknown systematics caused by projection effects. We aim at testing observational methods for the determination of mass and velocity anisotropy profiles of clusters of galaxies. Particularly, we focus on the MAMPOSSt technique (Mamon et al. 2013). We use results from two semi-analytic models of galaxy formation coupled with high-resolution N-body cosmological simulations, the catalog of De Lucia & Blaizot (2007) and the FIRE catalog based on the new GAlaxy Evolution and Assembly model. We test the reliability of the Jeans equation in recovering the true mass profile when full projected phase-space information is available. We examine the reliability of the MAMPOSSt method in estimating the true mass and velocity anisotropy profiles of the simulated halos when only projected phase-space information is available, as in observations. The spherical Jeans equation provides a reliable tool for the determination of cluster mass profiles, also for subsamples of tracers separated by galaxy color. Results are equally good for prolate and oblate clusters. Using only projected phase-space information, MAMPOSSt provides estimates of the mass profile with a standard deviation of 35-69 %, and a negative bias of 7-17 %, nearly independent of radius, and that we attribute to the presence of interlopers in the projected samples. The bias changes sign, that is, the mass is over-estimated, for prolate clusters with their major axis aligned along the line-of-sight. MAMPOSSt measures the velocity anisotropy profiles accurately in the inner cluster regions, with a slight overestimate in the outer regions, both for the whole sample of observationally-identified cluster members and separately for red and blue galaxies.

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arXiv2020

Brightest Cluster Galaxies: the centre can(not?) hold

We explore the persistence of the alignment of brightest cluster galaxies (BCGs) with their local environment. We find that a significant fraction of BCGs do not coincide with the centroid of the X-ray gas distribution and/or show peculiar velocities (they are not at rest with respect to the cluster mean). Despite this, we find that BCGs are generally aligned with the cluster mass distribution even when they have significant offsets from the X-ray centre and significant peculiar velocities. The large offsets are not consistent with simple theoretical models. To account for these observations BCGs must undergo mergers preferentially along their major axis, the main infall direction. Such BCGs may be oscillating within the cluster potential after having been displaced by mergers or collisions, or the dark matter halo itself may not yet be relaxed.

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arXiv2020

Measuring the surface mass density ellipticity of redMaPPer galaxy clusters using weak-lensing

In this work we study the shape of the projected surface mass density distribution of galaxy clusters using weak-lensing stacking techniques. In particular, we constrain the average aligned component of the projected ellipticity, $ε$, for a sample of redMaPPer clusters ($0.1 \leq z < 0.4$). We consider six different proxies for the cluster orientation and measure $ε$ for three ranges of projected distances from the cluster centres. The mass distribution in the inner region (up to $700\,$kpc) is better traced by the cluster galaxies with a higher membership probability, while the outer region (from $700\,$kpc up to $5\,$Mpc) is better traced by the inclusion of less probable galaxy cluster members. The fitted ellipticity in the inner region is $ε= 0.21 \pm 0.04$, in agreement with previous estimates. We also study the relation between $ε$ and the cluster mean redshift and richness. By splitting the sample in two redshift ranges according to the median redshift, we obtain larger $ε$ values for clusters at higher redshifts, consistent with the expectation from simulations. In addition, we obtain higher ellipticity values in the outer region of clusters at low redshifts. We discuss several systematic effects that might affect the measured lensing ellipticities and their relation to the derived ellipticity of the mass distribution.

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arXiv2020

Evolution and Role of Mergers in the BCG-Cluster Alignment. A View from Cosmological Hydro-Simulations

Contradictory results have been reported on the time evolution of the alignment between clusters and their Brightest Cluster Galaxy (BCG). We study this topic by analyzing cosmological hydro-simulations of 24 massive clusters with $M_{200}|_{z=0} \gtrsim 10^{15}\, M_\odot$, plus 5 less massive with $1 \times 10^{14} \lesssim M_{200}|_{z=0} \lesssim 7 \times 10^{14}\, M_\odot$, which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift $z=0$, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20$^\circ$. The BCG alignment with the DM halo is even tighter. The alignment persists up to $z\lesssim2$ with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter ($3R_{200}$) is already in place at $z\sim4$ with a typical angle of $35^\circ$, before the BCG-Cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG-Cluster alignment occurs in an outside-in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent major mergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis.

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