arXiv subjects

Joaquín González-Nuevo

Publications and source records attributed to Joaquín González-Nuevo.

9 recordsLinked to original sources

arXiv2026

The Einstein Gap: an unrecognised strong lensing feature in weak lensing mass density profiles

Magnification bias cross-correlations between galaxy clusters and high-redshift submillimetre galaxies have recently revealed a characteristic signal deficit at intermediate angular scales, termed the Einstein Gap, that appears consistently across all lens types and cannot be explained by any single theoretical mass density profile. In this work we identify for the first time the most plausible physical origin of this feature through a combination of observational tests and improved lensing simulations. Using galaxy clusters to characterise the satellite population and as the lens sample, we show that the gap is detected at high statistical significance, accounting for the full covariance of the stacked profile. Then, we demonstrate that the Einstein Gap is robust across three independent estimators of the angular cross-correlation function, strengthens as the positional smoothing is reduced, and scales systematically with the bright central galaxy stellar mass. Finally, we show that the projected radial distribution of satellite galaxies is smooth and continuous at all angular scales with no depression corresponding to the gap, disfavouring both a statistical artifact and a genuine absence of mass as its origin. An improved magnification bias simulator incorporating full ray-tracing via the lens equation and a NFW+Sersic mass density profile reproduces the observed signal deficit, strongly supporting that the Einstein Gap is a strong lensing feature: background sources within the Einstein radius are displaced outward, creating a characteristic empty annulus whose angular size scales. This feature is consistent with features visible in previously published weak-lensing profiles that were not, however, interpreted as a strong-lensing signature. Its identification opens new possibilities for constraining halo masses and concentrations from magnification bias measurements alone.

astro-ph.GA↗

arXiv2026

Assessment of normalizing flows for parameter estimation on time-frequency representations of gravitational-wave data

The speed-up of parameter estimation is an active field of research in gravitational-wave data analysis. In this paper we present GP15, a deep-learning method that merges residual networks and normalizing flows into a general-purpose, image-based estimator of binary black hole (BBH) parameters. Building on our early work, we map BBH spectrograms from the Advanced LIGO and Advanced Virgo detectors to color channels in an RGB image amenable to be processed with residual networks. GP15 is trained on simulated data for BBH mergers obtained with the \texttt{IMRPhenomXPHM} waveform approximant and tested for all three-detector events from the GWTC-3 and GWTC-2.1 catalogs reported by the LIGO-Virgo-KAGRA (LVK) collaboration. Overall, our model yields good agreement with the LVK results over most parameters. Our simple model can produce large amounts of posterior samples in the order of a second, complementing existing approaches with normalizing flows based on time or frequency representation of gravitational-wave data. We also discuss current shortcomings of our model and possible improvements for future extensions (e.g. including noise conditioning from the detectors' PSD or splitting the parameter space into intrinsic and extrinsic subspaces).

gr-qc↗

arXiv2025

AtLAST -- Determination of Halo Mass Density Profiles at kpc Scales through Magnification Bias

Magnification bias, the lensing-induced modification of background source number counts, provides a uniquely powerful probe of the mass density profiles of galaxies and clusters down to kpc scales. Unlike shear-based weak lensing, magnification bias does not rely on galaxy shapes and thus avoids dominant small-scale systematics. Existing studies, however, are limited by sky coverage, positional uncertainty, and insufficiently deep, confusion-limited submillimetre (submm) surveys. A next-generation wide-field, high-throughput submm facility like the proposed 50m-telescope AtLAST is required to unlock this technique's full diagnostic power.

astro-ph.CO↗

arXiv2025

AtLAST -- A five fold increase in the number of identified Strongly Lensed Galaxies in the sub-millimetre and its consequences

Strong gravitational lensing is a powerful probe of cosmology, dark matter (DM), and high-redshift galaxy evolution, but current samples of strongly lensed galaxies (SLGs) remain far too small to exploit its full potential. $\textit{Herschel}$'s submillimeter (submm) surveys demonstrated that submm selection provides the most efficient and least biased route to identifying high-redshift SLGs, yet produced only a few hundred systems over limited, heterogeneous fields. Achieving the thousands of SLGs required for precision cosmology and detailed studies of distant dusty star-forming galaxies demands a new, wide-area, homogeneous sub-mm survey. A facility like AtLAST, capable of extending $\textit{Herschel}$-like methodologies to much larger areas, is uniquely positioned to deliver the order-of-magnitude increase in SLG numbers needed for transformative progress.

astro-ph.GA↗

arXiv2025

Cosmic magnification on high-redshift submillimeter galaxies

Weak lensing magnification probes the correlation between galaxies and the underlying matter field in a similar fashion to galaxy-galaxy lensing shear. Although it has long been sidelined in favor of the latter on the grounds of a poorer performance in terms of statistical significance, the provision of a large sample of high-redshift submillimeter galaxies by the \emph{Herschel} observatory has transformed the landscape of cosmic magnification due to their optimal physical properties for magnification analyses. This review aims to summarize the core principles and unique advantages of cosmic magnification on high-redshift submillimeter galaxies and discuss recent results applied for cosmological inference. The outlook and challenges of this observable are also outlined, with a focus on the ample scope for exploration and its potential to emerge as a competitive independent cosmological probe.

astro-ph.CO↗

arXiv2025

Candidate gravitationally lensed submillimeter galaxies in Herschel-ATLAS associated with WISE elliptical counterparts

We present a new and independent methodology for identifying gravitational lens candidates using data from the H-ATLAS and AllWISE surveys. Unlike previous approaches, which are typically biased toward bright, strongly lensed submillimeter galaxies (SMGs), our method uncovers fainter systems with lower magnifications. This enables the identification and individual study of lensing events that would otherwise only be accessible through statistical weak lensing analyses. Our approach focuses on high-redshift SMGs from H-ATLAS in the range $1.2 < z < 4.0$, and searches for associated AllWISE sources within an angular distance of 18 arcsec. Candidate lenses are selected based on their WISE colors ($0.5 < \mathrm{W2} - \mathrm{W3} < 1.5$ mag), consistent with those of elliptical galaxies, and further filtered using $J-\mathrm{W1}$ color and photometric redshift cuts to reduce stellar contamination. This conservative selection yields 68 new lens candidates. We then performed SED fitting with CIGALE across UV to submillimeter wavelengths to estimate the physical properties of both the lenses and the background SMGs, and to assess the lensing nature of these candidates. Despite the uncertainties, we were able to constrain key parameters such as stellar and dust masses, infrared luminosities, and star formation rates. In addition, the estimated magnifications for most candidates are modest, consistent with the weak lensing regime ($μ\simeq 1{-}1.5$), although a few sources may require more precise modeling. Future efforts could refine this methodology to recover potential candidates outside our selection, and high-resolution follow-up observations will be essential to confirm the lensing nature of these sources and to further investigate their physical properties.

astro-ph.GA↗

arXiv2024

Methodological refinement of the submillimeter galaxy magnification bias. I. Cosmological analysis with a single redshift bin

The main goal of this work, the second in a three-paper series, is to test the impact of a methodological improvement in measuring the magnification bias signal on a sample of submillimeter galaxies and its implications for constraining cosmological parameters. The analysis considers the angular cross-correlation function between a foreground sample of GAMA galaxies ($0.2<z<0.8$) and a background sample of H-ATLAS submillimeter galaxies ($1.2<z<4.0$). A refined methodology, discussed extensively in Paper I, is used. By interpreting the weak lensing signal within the halo model and employing an MCMC algorithm, the posterior distribution of the halo occupation distribution (HOD) and cosmological parameters is obtained for a flat $Λ$CDM model. The analysis incorporates the foreground angular auto-correlation function to account for galaxy clustering. The results demonstrate a remarkable improvement in uncertainties for both HOD and cosmological parameters compared to previous studies. However, when using the cross-correlation data alone, the estimation of $σ_8$ depends on prior knowledge of $β$, the logarithmic slope of the background number counts. Assuming a physically motivated prior distribution for $β$, mean values of $Ω_m=0.18^{+0.03}{-0.03}$ and $σ_8=1.04^{+0.11}{-0.07}$ are obtained. These results may however be subject to an inherent bias in the data due to anomalous behavior observed in the G15 field. After excluding the G15 region, the mean values shift to $Ω_m=0.30^{+0.05}{-0.06}$ and $σ_8=0.92^{+0.07}{-0.07}$. This becomes more apparent when adding the clustering of the foreground sample, but the dependence on $β$ information disappears, mitigating the aforementioned issue. Excluding the G15 region, the joint analysis yields mean values of $Ω_m=0.36^{+0.03}{-0.07}$, $σ_8=0.90^{+0.03}{-0.03}$, and $h=0.76^{+0.14}_{-0.14}$.

astro-ph.CO↗

arXiv2024

Cosmic Insights from Galaxy Clusters: Exploring Magnification Bias on Sub-millimeter Galaxies

Magnification bias, an observational effect of gravitational lensing in the weak regime, allows testing the cosmological model through angular correlations of sources at different redshifts. This effect has been observed in various contexts, particularly with sub-millimeter galaxies (SMGs), offering astrophysical and cosmological insights. The study aims to investigate the magnification bias effect exerted by galaxy clusters on SMGs and its implications for astrophysical and cosmological parameters within the $Λ$CDM model. Magnification bias was explored through quantifying the cross-correlation function, utilised to derive constraints on cosmological and astrophysical parameters with a Markov Chain Monte Carlo algorithm. Two distinct galaxy cluster samples were used to assess result robustness and understand the influence of sample characteristics. Cluster samples show higher cross-correlation values than galaxies, with an excess at larger scales suggesting contributions from additional large-scale structures. The parameters obtained, while consistent with galaxies, are less constrained due to broader redshift distributions and limited cluster statistics. Results align with weak lensing studies, hinting at slightly lower $σ_8$ and $Ω_m$ values than \emph{Planck}'s CMB data, emphasizing the need for enhanced precision and alternative low-redshift universe tests. While yielding constraints compatible with the $Λ$CDM model, limitations include broader redshift distributions and a limited number of lenses, resulting in less constrained parameters compared to previous galaxy studies. Nonetheless, the study underscores the potential of using galaxy clusters as lenses for magnification bias studies, capitalising on their elevated mass, providing a promising avenue to test current Cosmology theories. Further progress can be made by expanding the lens sample size.

astro-ph.CO↗

arXiv2019

Confusion noise due to clustered extragalactic point sources. Application of logarithmic cumulants for parameter estimation

The calculation of the characteristic function of the signal fluctuations due to clustered astrophysical sources is performed in this paper. For the typical case of power-law differential number counts and two-point angular correlation function, we present an extension of Zolotarev's theorem that allows us to compute the cumulants of the logarithm of the absolute value of the intensity. As a test, simulations based on recent observations of radio galaxies are then carried out, showing that these cumulants can be very useful for determining the fundamental parameters defining the number counts and the correlation. If the angular correlation scale of the observed source population is known, the method presented here is able to obtain estimators of the amplitude and slope of the power-law number counts with mean absolute errors that are one order of magnitude better than previous techniques, that did not take into account the correlation. Even if the scale of correlation is not well known, the method is able to estimate it and still performs much better than if the effect of correlations is not considered.

astro-ph.CO↗