arXiv subjects

Athanasia Gkogkou

Publications and source records attributed to Athanasia Gkogkou.

9 recordsLinked to original sources

arXiv2026

JESSNet: Joint dEconvolution and Sparse Separation Network for HI 21 cm foreground cleaning

Foreground cleaning is a major challenge for H\,{\sc i} 21 cm intensity mapping, particularly in the presence of a chromatic instrumental beam that couples angular foreground structure into the frequency direction and under incomplete sky coverage. We introduce JESSNet, a beam-aware, mask-compatible foreground-cleaning framework for single-dish intensity mapping. Building on SDecGMCA, JESSNet introduces three main extensions: a multiscale angular decomposition with scale-dependent mixing matrices and channel selection, a learned spherical-wavelet ''learnlet'' sparse regularization operator, and a mask-constrained reconstruction applicable to Galactic masks and survey footprints. We test JESSNet on simulated SKA-MID-like observations over $900\text{-}1300\,{\rm MHz}$ ($z\simeq0.09\text{-}0.58$), including H\,{\sc i} emission, Galactic and extragalactic foregrounds, thermal noise, and an oscillating MeerKAT-inspired chromatic beam. The multiscale reconstruction accurately recovers the angular and frequency power spectra of the input H\,{\sc i} signal, improves the recovery at low and intermediate angular scales relative to a single-scale implementation, and reduces residual beam-induced spectral features. JESSNet also remains effective for a synthetic survey footprint, preserving the H\,{\sc i} power spectra under incomplete sky coverage. The code and analysis pipeline are publicly released to facilitate reproducibility and future applications to simulated and observational data.

astro-ph.CO↗

arXiv2026

Non-linear halo bias for accurate modelling of cosmic infrared background anisotropies

Halo models provide the standard framework for interpreting cosmic infrared background (CIB) anisotropies and inferring the connection between dusty star-forming galaxies and their host dark matter halos. Recent studies have shown that inaccuracies in the modelling of halo clustering may bias the inferred parameters governing star formation in dark matter halos. In this work, we investigate whether a more detailed description of halo clustering can alleviate these shortcomings. We incorporate a scale-dependent, non-linear correction to the halo bias within a halo-model framework based on a simple SFR-halo mass parametrisation. We consider both a full mass-dependent implementation and a computationally efficient approximation. We also investigate the impact of updated (sub)halo mass functions. We validate the revised framework using mock observations derived from a dedicated simplified version of the SIDES-Uchuu simulation, combining the SIDES empirical galaxy model with the Uchuu N-body simulation, specifically designed to match the SFR prescriptions adopted in our halo-model. The corrections modify the predicted CIB clustering by up to 30% on intermediate scales, while the effective implementation reproduces the full treatment at the sub-percent level. The updated model removes the scale-dependent discrepancies previously identified and accurately reproduces the measured power spectra over the full multipole range. In MCMC analyses, the input SFR parameters are recovered with substantially reduced biases, with all input parameters recovered within their $1σ$ confidence intervals. Our results demonstrate that accurately modelling non-linear halo clustering is essential not only to reproduce CIB anisotropies, but also to reliably recover the underlying galaxy-halo connection. The framework presented here provides a validated foundation for future analyses of observational data.

astro-ph.CO↗

arXiv2026

Methodological Frontiers in 21-cm Intensity Mapping: the Treatment of Systematics and Foreground Contamination

The distribution of neutral hydrogen (HI) in the post-reionization universe traces the cosmic large-scale structure and therefore serves as a powerful cosmological probe. An efficient way to measure its distribution over wide sky areas and redshift ranges is through single-dish intensity mapping, which exploits the autocorrelation signal of each dish in a telescope array while scanning the same sky patch. Thanks to its broad frequency coverage and technical capabilities, SKA-Mid will enable measurements of the integrated 21 cm emission from HI up to redshift $z\sim3$, making single-dish intensity mapping a key observable for probing dark matter and dark energy. Isolating the faint 21 cm cosmological signal without introducing biases is, however, challenging. The 21 cm signal is several orders of magnitude weaker than the astrophysical foregrounds, and its analysis is further affected by instrumental systematics. Overcoming these difficulties requires detailed modelling together with continuous improvements and innovations in data-analysis techniques. Over the past decade, the international community has developed and tested new methods to address current observational challenges and prepare for forthcoming SKA-Mid observations. This chapter reviews recent advances in map-making and component-separation techniques, with particular emphasis on telescope-specific systematics such as beam response and correlated noise. We focus on results obtained in controlled simulation environments, providing a valuable framework for assessing the strengths and limitations of different approaches. Developing robust algorithms capable of accurately handling instrumental effects and sky-model uncertainties is a crucial step toward fully exploiting the cosmological potential of HI intensity-mapping surveys in the SKA Observatory era.

astro-ph.CO↗

arXiv2025

Foreground removal in HI 21 cm intensity mapping under frequency-dependent beam distortions

Neutral hydrogen (HI) intensity mapping with single-dish experiments is a powerful approach for probing cosmology in the post-reionization epoch. However, the presence of bright foregrounds over four orders of magnitude stronger than the HI signal makes its extraction highly challenging. While all methods perform well when assuming a Gaussian beam degraded to the worst resolution, most of them degrade significantly in the presence of a more realistic beam model. In this work, we investigate the performance of SDecGMCA. This method extends DecGMCA to spherical data, combining sparse component separation with beam deconvolution. Our goal is to evaluate this method in comparison with established foreground removal techniques, assessing its ability to recover the cosmological HI signal from single-dish intensity mapping observations under varying beam conditions. We use simulated HI signal and foregrounds, covering the frequency ranges relevant to MeerKAT and SKA-Mid. The foreground removal techniques tested fall into two main categories: model-fitting methods (polynomial and parametric) and blind source separation methods (PCA, ICA, GMCA, and SDecGMCA). Their effectiveness is evaluated based on the recovery of the HI angular and frequency power spectra under progressively more realistic beam conditions. While all methods perform adequately under a uniform degraded beam, SDecGMCA remains robust when frequency-dependent beam distortions are introduced. In the oscillating beam case, SDecGMCA suppresses the spurious spectral peak at $k_ν\sim 0.3$ and achieves $\lesssim 5\%$ accuracy at intermediate angular scales ($10 < \ell < 200$), outperforming other methods. Beam inversion, however, remains intrinsically unstable beyond $\ell \sim 200$, setting a practical limit on the method.

astro-ph.CO↗

arXiv2025

Challenges of standard halo models in constraining galaxy properties from CIB anisotropies

The halo model, combined with halo occupation distribution (HOD) prescriptions, is widely used to interpret cosmic infrared background (CIB) anisotropies and connect star-forming galaxies to large-scale structure. Recent implementations adopt more physical parameterizations, but it remains unclear whether these models reliably recover astrophysical quantities. We test whether current CIB halo models can constrain the star formation efficiency, $η(M_h,z)$, and the halo mass where it peaks, $M_{\rm max}$, when fitted to mock data. We examine whether discrepancies arise from emission assumptions (the HOD ingredients) or from more fundamental components, such as bias and matter clustering. Using the M21 CIB HOD model within the halo framework, we fit mock CIB power spectra and star formation rate density (SFRD) data from the SIDES-Uchuu simulation, then repeat the analysis with a simplified simulation (SSU) matched to the HOD assumptions. Comparing best-fit parameters to known inputs, we find that although the M21 model fits the mock data well, it fails to recover intrinsic parameters, especially $M_{\rm max}$, even when applied to data generated with consistent assumptions. Emission-related quantities (SFRD, emissivity) agree within 5%, but the two-halo term shows a redshift- and scale-dependent offset exceeding 20%, likely due to the linear treatment of halo bias and matter clustering. Scatter in the SFR-halo mass relation and spectral energy distributions significantly impacts shot noise ($\sim 50\%$) but only modestly ($<10\%$) the clustered signal. We conclude that robust recovery of physical parameters from CIB clustering requires improved cosmological ingredients in halo models, including scale-dependent halo bias and nonlinear matter power spectra, alongside refined emission modeling.

astro-ph.CO↗

arXiv2024

A$^3$COSMOS and A$^3$GOODSS: Continuum Source Catalogues and Multi-band Number Counts

Galaxy submillimetre number counts are a fundamental measurement in our understanding of galaxy evolution models. Most early measurements are obtained via single-dish telescopes with substantial source confusion, whereas recent interferometric observations are limited to small areas. We used a large database of ALMA continuum observations to accurately measure galaxy number counts in multiple (sub)millimetre bands, thus bridging the flux density range between single-dish surveys and deep interferometric studies. We continued the Automated Mining of the ALMA Archive in the COSMOS Field project (A$^3$COSMOS) and extended it with observations from the GOODS-South field (A$^3$GOODSS). The database consists of ~4,000 pipeline-processed continuum images from the public ALMA archive, yielding 2,050 unique detected sources. To infer galaxy number counts, we constructed a method to reduce the observational bias inherent to targeted pointings that dominate the database. This method comprises a combination of image selection, masking, and source weighting. The effective area was calculated by accounting for inhomogeneous wavelengths, sensitivities, and resolutions and for spatial overlap between images. We tested and calibrated our method with simulations. We derived the number counts in a consistent and homogeneous way in four different ALMA bands covering a relatively large area. The results are consistent with number counts from the literature within the uncertainties. In Band 7, at the depth of the inferred number counts, ~40% of the cosmic infrared background is resolved into discrete sources. This fraction, however, decreases with wavelength, reaching ~4% in Band 3. Finally, we used the number counts to test models of dusty galaxy evolution, and find a good agreement within the uncertainties.

astro-ph.GA↗

arXiv2024

Separation of dust emission from the Cosmic Infrared Background in Herschel observations with Wavelet Phase Harmonics

The low brightness dust emission at high Galactic latitude is of interest to study the interplay between physical processes in shaping the structure of the interstellar medium (ISM), as well as to statistically characterize dust emission as a foreground to the Cosmic Microwave Background (CMB). Progress in this avenue of research have been hampered by the difficulty of separating the dust emission from the Cosmic Infrared Background (CIB). We demonstrate that dust and CIB may be effectively separated based on their different structure on the sky and use the separation to characterize the structure of diffuse dust emission on angular scales where CIB is a significant component in terms of power. We use scattering transform statistics, the Wavelet Phase Harmonics (WPH), to perform a statistical component separation using Herschel SPIRE observations. This component separation is done only from observational data using non-Gaussian properties as a lever arm, and is done at a single 250 microns frequency. This method, that we validate on mock data, gives us access to non-Gaussian statistics of the interstellar dust and an output dust map essentially free from CIB contamination. Our statistical modelling characterizes the non-Gaussian structure of the diffuse ISM down to the smallest scales observed by Herschel. We recover the power-law shape of the dust power spectrum up to a wavenumber of 2 arcmin$^{-1}$ where the dust signal represents 2 percent of the total power. The output dust map reveals coherent structures at the smallest scales which were hidden by the CIB anisotropies. It opens new observational perspectives on the formation of structure in the diffuse ISM which we discuss with reference to past work. We have succeeded to perform a statistical separation from observational data only at a single frequency by using non-Gaussian statistics.

astro-ph.GA↗

arXiv2023

A plausible link between dynamically unsettled molecular gas and the radio jet in NGC 6328

We report the detection of outflowing molecular gas at the center of the nearby radio galaxy NGC6328 (z=0.014), which has a gigahertz-peaked spectrum radio core and a compact (2 pc) young double radio lobe tracing jet. Utilizing Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) and CO(3-2) observations, as well as a novel code developed to fit the 3D gas distribution and kinematics, to study the molecular gas kinematics, we find that the bulk of the gas is situated within a highly warped disk structure, most likely the result of a past merger event. Our analysis further uncovers, within the inner regions of the gas distribution (R<300 pc) and at a position angle aligning with that of the radio jet (150 degrees), the existence of two anti-diametric molecular gas structures kinematically detached from the main disk. These structures most likely trace a jet-induced cold gas outflow with a total lower limit mass of $2\times 10^6\,\mathrm{M_\odot}$ mass, corresponding to an outflow rate of $2\,\mathrm{M_\odot\,yr^{-1}}$ and a kinetic power of $2.7\times 10^{40}\,\mathrm{erg\,s^{-1}}$. The energy required to maintain such a molecular outflow is aligned with the mechanical power of the jet.

astro-ph.GA↗

arXiv2023

Extragalactic CO emission lines in the CMB experiments: a forgotten signal and a foreground

High resolution cosmic microwave background (CMB) experiments have allowed us to precisely measure the CMB temperature power spectrum down to very small scales (multipole $\ell \sim 3000$). Such measurements at multiple frequencies enable separating the primary CMB anisotropies with other signals like CMB lensing, thermal and kinematic Sunyaev-Zel'dovich effects (tSZ and kSZ), and cosmic infrared background (CIB). In this paper, we explore another signal of interest at these frequencies that should be present in the CMB maps: extragalactic CO molecular rotational line emissions, which are the most widely used tracers of molecular gas in the line intensity mapping experiments. Using the SIDES simulations adopted for top hat bandpasses at 150 and 220 GHz, we show that the cross-correlation of the CIB with CO lines has a contribution similar to the CIB-tSZ correlation and the kSZ power, thereby contributing a non-negligible amount to the total power at these scales. This signal, therefore, may significantly impact the recently reported $\geq 3σ$ detection of the kSZ power spectrum from the South Pole Telescope (SPT) collaboration, as the contribution of the CO lines is not considered in such analyses. Our results also provide a new way of measuring the CO power spectrum in cross-correlation with the CIB. Finally, these results show that the CO emissions present in the CMB maps will have to be accounted for in all the CMB auto-power spectrum and cross-correlation studies involving a LSS tracer.

astro-ph.CO↗