arXiv subjects

Cristiano Porciani

Publications and source records attributed to Cristiano Porciani.

At least 19 recordsLinked to original sources

arXiv2026

Environmental Quenching of High-Redshift Galaxies: Interpreting JWST Observations with Simulations

Recent observations of the high-redshift Universe, particularly with JWST, have revealed a population of quenched galaxies that challenges current galaxy formation models, which systematically underpredict their abundance. This discrepancy has been extensively studied for massive systems, motivating revisions to internal quenching mechanisms such as AGN feedback. However, the origin of quenching in lower-mass galaxies at high-z has received far less attention, largely due to previous observational limitations. JWST has now identified low-mass quenched galaxies (${M_{\star}}<10^{10}{\rm M_{\odot}}$). Given this emerging observational evidence, we investigate the viability of environmental quenching as the primary mechanism suppressing star formation in low-mass galaxies at $z>3$. We analyze several simulations, including L-GALAXIES, IllustrisTNG, SIMBA, and TNG-Cluster, jointly comprising more than half a million galaxies at z=5. Across all simulations, quenched systems are overwhelmingly satellites, despite representing less than 10\% of the total galaxy population. Satellite quenching increases with host halo mass and decreases with both stellar mass and halocentric distance, showing strong correlations with enhanced ram-pressure exposure and gas depletion. The simulations, particularly L-GALAXIES, produce low-mass quenched galaxies broadly consistent with those observed by JWST. Our results suggest that the recently discovered high-redshift quenched low-mass galaxies are possibly environmentally quenched systems residing in the vicinity of massive halos. According to the simulations, these galaxies are often only temporarily quenched: nearly 90\% of them merge within a few hundred megayears, and a small fraction rejuvenate and resume star formation. Extended samples from future observations will enable robust tests of the environmental origin of galaxy quenching in the early Universe.

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arXiv2026

The impact of our peculiar motion on primordial non-Gaussianity measurements using the LIGER4GAL framework

Current and forthcoming galaxy surveys will map the observable Universe with unprecedented depth, sky coverage, and precision. These maps are affected by relativistic redshift-space distortions (RSDs), which become increasingly relevant on ultra-large scales. Accurate modelling of these relativistic RSDs is essential to avoid systematic biases in key cosmological measurements, such as primordial non-Gaussianity (PNG). To address this, we introduce an updated implementation of the LIGER method, LIGER4GAL, which incorporates all linear-order relativistic RSDs directly at the tracer level of high-resolution N-body simulations. We demonstrate that LIGER4GAL improves upon previous iterations of the LIGER method by reproducing the expected non-linear clustering while maintaining accuracy for relativistic RSDs on large scales. We use the updated code to generate a DESI-like sample of luminous red galaxies from the Huge MultiDark Planck simulation. By measuring the power spectrum multipoles of this sample with and without the imprint of relativistic RSDs, we assess the impact of relativistic effects on measurements of the local PNG signal ($f_\mathrm{nl}$). We find that the omission of the''finger-of-the-observer'' (sourced by the peculiar velocity of the observer) effect in the power spectrum modelling can bias measurements of $f_{\rm nl}$ by more than $1$ ($0.25$) $ σ_{f_{\rm nl}}$ in 40% (80%) of the possible realizations of the universe if scales down to $k_\mathrm{min} = 0.0015\,h/\mathrm{Mpc}$ are included.

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arXiv2026

Coverage is not enough: Frequentist tests of simulation-based inference for primordial non-Gaussianity

(Abridged) Simulation-based inference (SBI) has emerged as a powerful framework for extracting cosmological information from complex, non-linear data where analytical likelihoods are unavailable. Its reliability is commonly assessed using coverage-based diagnostics under the prior predictive distribution, which probe calibration only in an averaged sense and do not constrain posterior behavior at fixed parameter value, the regime relevant for practical inference. We investigate these limitations in the context of primordial non-Gaussianity, parameterized by $f_\mathrm{NL}$, using simulations of the dark matter halo field. We compare SBI based on contrastive neural ratio estimation (CNRE) with likelihood-based inference (LBI) using the power spectrum, bispectrum, and wavelet scattering transform (WST) coefficients across 1000 realizations. SBI and LBI agree well on posterior means and skewness, while the variance agrees on average but shows weaker realization-by-realization consistency. Larger differences arise in the kurtosis, indicating discrepancies in the posterior tails. These effects are already present for the power spectrum - where the Gaussian likelihood assumed in LBI is best justified - and are most pronounced for the combined power spectrum and bispectrum, where SBI posteriors are often underconfident and can yield weaker constraints than either statistic individually, despite passing coverage tests. WST coefficients further tighten constraints on $f_\mathrm{NL}$, even when restricted to large scales. Our results highlight both the potential of higher-order statistics and the need for validation strategies that probe the posterior shape beyond standard coverage diagnostics.

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arXiv2026

Probing the warm dark matter mass with [C II] intensity mapping

The nature of dark matter (DM) is still debated. While cold DM (CDM) is the standard paradigm, warm DM (WDM) may ease some small-scale tensions in the $Λ$CDM framework. Line-intensity mapping (LIM) offers a novel probe of DM properties. To explore the potential of LIM surveys in constraining the WDM particle mass ($m_\mathrm{WDM}$) by means of the [C II] power spectrum (PS), we provide forecasts for the Deep Spectroscopic Survey (DSS) at $z\simeq3.6$ and extend the analysis to larger sky coverage, higher sensitivity, and/or increased spectral resolution. We developed a formulation for the [C II] PS based on the halo-model approach, incorporating the uncertainty in the luminosity function (LF) through two alternative parameterisations. We performed a Bayesian analysis on mock data to derive constraints on $m_\mathrm{WDM}$. In a CDM universe, the DSS yields lower limits on $m_\mathrm{WDM}$, at a $95\%$ credibility level, of $1.10$ keV and $0.58$ keV when considering the optimistic and pessimistic LF ($α= -1.1$), respectively. Ambitious surveys can improve these figures to $5.82$ keV and $1.90$ keV, and assuming a steeper faint-end slope ($α= -1.9$) further boosts these limits. A fivefold increase in spectral resolution enhances sensitivity to the damping scale associated with redshift-space distortions, tightening the constraints on $m_\mathrm{WDM}$ by a factor of up to $\sim1.8$. Finally, Bayesian inference on mock data with $m_\mathrm{WDM}=3$ keV results in a well-constrained and unbiased posterior only in futuristic survey setups. Upcoming LIM surveys can provide meaningful limits on $m_\mathrm{WDM}$, although the negligible contribution from small haloes reduces the constraining power of the [C II] PS. Future progress will benefit from combining multiple redshifts and emission lines, opening the way to competitive constraints on the nature of DM.

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arXiv2025

Segmenting proto-halos with vision transformers

The formation of dark-matter halos from small cosmological perturbations generated in the early universe is a highly non-linear process typically modeled through N-body simulations. In this work, we explore the use of deep learning to segment and classify proto-halo regions in the initial density field according to their final halo mass at redshift z=0. We compare two architectures: a fully convolutional neural network (CNN) based on the V-Net design and a U-Net transformer. We find that the transformer-based network significantly outperforms the CNN across all metrics, achieving sub-percent error in the total segmented mass per halo class. Both networks deliver much higher accuracy than the perturbation-theory-based model \textsc{pinocchio}, especially at low halo masses and in the detailed reconstruction of proto-halo boundaries. We also investigate the impact of different input features by training models on the density field, the tidal shear, and their combination. Finally, we use Grad-CAM to generate class-activation heatmaps for the CNN, providing preliminary yet suggestive insights into how the network exploits the input fields.

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arXiv2025

Detecting the signature of helium reionization through 3HeII 3.46cm line-intensity mapping

Helium reionization is the most recent phase change of the intergalactic medium, yet its timing and main drivers remain uncertain. Among the probes to trace its unfolding, the 3.46 cm hyperfine line of singly-ionized helium opens the study of helium reionization to upcoming radio surveys. We aim to evaluate the detectability of the 3.46,cm signal with radio surveys and the possible constraints it can place on helium reionization, in particular whether it can distinguish between early and late helium reionization scenarios. Moreover, we perform a comprehensive study of the advantages of single-dish vs. interferometric setup. Using hydrodynamical simulations post-processed with radiative transfer, we construct mock data cubes for two models of helium reionization. We compute the power spectrum of the signal and forecast the signal-to-noise ratio for SKA-1 MID, DSA-2000, and a PUMA-like survey, in both observational setups. The two scenarios produce distinct power spectra, but the faintness of the signal, largely caused by weak coupling between the spin temperature and the kinetic temperature in low-density regions of the IGM, combined with high instrumental noise, makes detection very difficult within realistic integration times for current surveys. A PUMA-like survey operating in single-dish mode could, however, detect the 3.46 cm signal with an integrated signal-to-noise ratio of a few in < 1000 h in both scenarios. Distinguishing helium reionization scenarios with 3.46 cm line-intensity mapping therefore remains challenging for current facilities. Our results, however, indicate that next-generation, high-sensitivity surveys with optimized observing strategies, especially when combined with complementary probes of the IGM, could begin to place meaningful constraints on the timing and morphology of helium reionization.

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arXiv2025

Constraining the [CII] luminosity function from the power spectrum of line-intensity maps at redshift 3.6

Forthcoming measurements of the line-intensity mapping (LIM) power spectrum (PS) are expected to provide valuable constraints on astrophysical and cosmological quantities. We focus on the [CII] luminosity function (LF) at high redshift, which remains poorly constrained, especially at the faint end. We present forecasts for the Deep Spectroscopic Survey (DSS) that is to be conducted with the Fred Young Submillimeter Telescope (FYST) at $z\simeq3.6$. We also make predictions for surveys with a ten times larger sky coverage and/or a $\sqrt{10}$ times higher sensitivity, accounting for the Lorentzian spectral profile of Fabry-Pérot interferometers and the impact of their resolving power $R$. Motivated by the halo-occupation properties of [CII] emitters in the MARIGOLD simulations, we derived a luminosity-mass relation by abundance matching two ALPINE LFs to the halo mass function. This relation was then used in a halo-model framework to predict the PS and its uncertainty. Bayesian inference on mock PS data provided forecasts for the first two LF moments and Schechter parameters. Depending on the true LF, the DSS is expected to be able to detect clustering and shot-noise components with signal-to-noise ratios of $\gtrsim2$. At $R=100$, spectral smoothing masks redshift-space distortions, rendering the damping scale $σ$ unmeasurable. For $R\gtrsim500$, $σ$ is distinguishable from instrumental effects, though degeneracies with amplitude parameters increase. Joint fits to the PS and LF yield precise constraints on the Schechter normalisation and cutoff luminosity, while the faint-end slope remains uncertain (unless the true value approaches $-2$). An increased survey sensitivity offers greater gains than a wider area. A higher spectral resolution improves the access to physical parameters, but intensifies degeneracies. This highlights key design trade-offs in LIM surveys.

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arXiv2025

The [C II] line emission as an interstellar medium probe in the MARIGOLD galaxies

The [C II] fine-structure line at 157.74 $μ$m is one of the brightest far-infrared emission lines and an important probe of galaxy properties like the star formation rate (SFR) and the molecular gas mass ($M_{\mathrm{mol}}$). Using high-resolution numerical simulations, we test the reliability of the [C II] line as a tracer of $M_{\mathrm{mol}}$ in high-redshift galaxies and investigate secondary dependences of the [C II]-$M_{\mathrm{mol}}$ relation on the SFR and metallicity. We investigate the time evolution of the [C II] luminosity function (LF) and the relative spatial extent of [C II] emission and star formation. We post-process galaxies from the MARIGOLD simulations at redshifts $3 \le z \leq 7$ to obtain their [C II] emission. These simulations were performed with the sub-grid chemistry model, HYACINTH, to track the non-equilibrium abundances of $\mathrm{H_2}$, $\mathrm{CO}$, $\rm C$ and $\mathrm{C^+}$ on the fly. Based on a statistical sample of galaxies at these redshifts, we investigate correlations between the [C II] line luminosity, L([C II]), and the SFR, the $M_{\mathrm{mol}}$, the total gas mass and the metal mass in gas phase ($M_{\mathrm{metal}}$). We find that accounting for secondary dependencies in the L([C II])-$M_{\mathrm{mol}}$ relation improves the $M_{\mathrm{mol}}$ prediction by a factor of 2.3. The [C II] emission in our simulated galaxies shows the tightest correlation with $M_{\mathrm{metal}}$. About 20% (10%) of our simulated galaxies at $z=5$ ($z=4$) have [C II] emission extending $\geq 2$ times farther than the star formation activity. The [C II] LF evolves rapidly and is always well approximated by a double power law that does not show an exponential cutoff at the bright end. We record a 600-fold increase in the number density of L([C II]) $\sim 10^9 \, \mathrm{L_{\odot}}$ emitters in 1.4 Gyr.

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arXiv2025

Measuring our peculiar velocity from spectroscopic redshift surveys

Our peculiar velocity imprints a dipole on galaxy density maps derived from redshift surveys. The dipole gives rise to an oscillatory signal in the multipole moments of the observed power spectrum which we indicate as the finger-of-the-observer (FOTO) effect. Using a suite of large mock catalogues mimicking ongoing and future $\textrm{H}α$- and $\textrm{H}\scriptstyle\mathrm{I}$-selected surveys, we demonstrate that the oscillatory features can be measured with a signal-to-noise ratio of up to 7 (depending on the sky area coverage and provided that observational systematics are kept under control on large scales). We also show that the FOTO effect cannot be erased by correcting the individual galaxy redshifts. On the contrary, by leveraging the power of the redshift corrections, we propose a novel method to determine both the magnitude and the direction of our peculiar velocity. After applying this technique to our mock catalogues, we conclude that it can be used to either test the kinematic interpretation of the temperature dipole in the cosmic microwave background or to extract cosmological information such as the matter density parameter and the equation of state of dark energy.

astro-ph.CO↗

arXiv2024

Connecting stellar and galactic scales: Energetic feedback from stellar wind bubbles to supernova remnants

Energy and momentum feedback from stars is a key element of models for galaxy formation and interstellar medium dynamics, but resolving the relevant length scales to directly include this feedback remain out of reach of current-generation simulations. We aim to constrain the energy feedback by winds, photoionisation and supernovae (SNe) from massive stars. We measure the thermal and kinetic energy imparted to the interstellar medium on various length scales, calculated from high-resolution 1D radiation-hydrodynamics simulations. Our grid of simulations covers a broad range of densities, metallicities, and state-of-the-art evolutionary models of single and binary stars. We find that a single star or binary system can carve a cavity of tens-of-pc size into the surrounding medium. During the pre-SN phase, post-main-sequence stellar winds and photoionisation dominate. While SN explosions dominate the total energy budget, the pre-SN feedback is of great importance by reducing the circumstellar gas density and delaying the onset of radiative losses in the SN remnant. Contrary to expectations, the metallicity dependence of the stellar wind has little effect on the cumulative energy imparted by feedback to the ISM; the only requirement is the existence of a sufficient level of pre-SN radiative and mechanical feedback. The ambient medium density determines how much and when feedback energy reaches to distance $\gtrsim 10-20$ pc and affects the division between kinetic and thermal feedback. Our results can be used as a sub-grid model for feedback in large-scale simulations of galaxies. The results reinforce that the uncertain mapping of stellar evolution sequences to SN explosion energy is very important to determining the overall feedback energy from a stellar population.

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arXiv2024

The universal multiplicity function: counting halos and voids

We present a novel combination of the excursion-set approach with the peak theory formalism in Lagrangian space and provide accurate predictions for halo and void statistics over a wide range of scales. The set-up is based on an effective moving barrier. Besides deriving the corresponding numerical multiplicity function, we introduce a new analytical formula reaching the percent level agreement with the exact numerical solution obtained via Monte Carlo realizations down to small scales, $\sim 10^{12} h^{-1}\mathrm{M_\odot}$. In the void case, we derive the dependence of the effective moving barrier on the void formation threshold, $δ_{\rm v}$, by comparison against the Lagrangian void size function measured in the Dark Energy and Massive Neutrinos Universe simulations. We discuss the mapping from Lagrangian to Eulerian space for both halos and voids; adopting the spherical symmetry approximation, we obtain a strong agreement at intermediate and large scales. Finally, using the effective moving barrier, we derive Lagrangian void density profiles accurately matching measurements from cosmological simulations, a major achievement towards using void profiles for precision cosmology with the next generation of galaxy surveys.

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arXiv2024

The streaming model for the three-point correlation function and its connection to standard perturbation theory

Redshift-space distortions present a significant challenge in building models for the three-point correlation function (3PCF). We compare two possible lines of attack: the streaming model and standard perturbation theory (SPT). The two approaches differ in their treatment of the non-linear mapping from real to redshift space: SPT expands this mapping perturbatively, while the streaming model retains its non-linear form but relies on simplifying assumptions about the probability density function (PDF) of line-of-sight velocity differences between pairs or triplets of tracers. To assess the quality of the predictions and the validity of the assumptions of these models, we measure the monopole of the matter 3PCF and the first two moments of the pair- and triplewise velocity PDF from a suite of N-body simulations. We also evaluate the large-scale limit of the streaming model and determine under which conditions it aligns to SPT. On scales $>10\,h^{-1}\mathrm{Mpc}$, we find that the streaming model for the 3PCF monopole is dominated by the first two velocity moments, making the exact shape of the PDF irrelevant. This model can match the accuracy of a Stage-IV galaxy survey, if the velocity moments are measured directly from the simulations. However, replacing the measurements with perturbative expressions to leading order generates large errors already on scales of $60-70 h^{-1}\mathrm{Mpc}$. This is the main drawback of the streaming model. Conversely, the SPT model for the 3PCF cannot account for the significant velocity dispersion that is present at all scales, and consequently provides predictions with limited accuracy. We demonstrate that this issue can be addressed by isolating the large-scale limit of the dispersion, which leads to typical Fingers-of-God damping functions. Overall, the SPT model with a damping function provides the best deal in terms of accuracy and computing time.

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arXiv2024

Testing the assumptions of the Effective Field Theory of Large-Scale Structure

The Effective Field Theory of Large-Scale Structure (EFTofLSS) attempts to amend some of the shortcomings of the traditional perturbative methods used in cosmology. It models the evolution of long-wavelength perturbations above a cutoff scale without the need for a detailed description of the short-wavelength ones. Short-scale physics is encoded in the coefficients of a series of operators composed of the long-wavelength fields, and ordered in a systematic expansion. As applied in the literature, the EFTofLSS corrects a summary statistic (such as the power spectrum) calculated from standard perturbation theory by matching it to $N$-body simulations or observations. This `bottom-up' construction is remarkably successful in extending the range of validity of perturbation theory. In this work, we compare this framework to a `top-down' approach, which estimates the EFT coefficients from the stress tensor of an $N$-body simulation, and propagates the corrections to the summary statistic. We consider simple initial conditions, viz. two sinusoidal, plane-parallel density perturbations with substantially different frequencies and amplitudes. We find that the leading EFT correction to the power spectrum in the top-down model is in excellent agreement with that inferred from the bottom-up approach which, by construction, provides an exact match to the numerical data. This result is robust to changes in the wavelength separation between the two linear perturbations. However, in our setup, the leading EFT coefficient does not always grow linearly with the cosmic expansion factor as assumed in the literature based on perturbative considerations. Instead, it decreases after orbit crossing takes place.

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arXiv2024

HYACINTH: HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations

Aims. We present a new sub-grid model, HYACINTH -- HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations -- for computing the non-equilibrium abundances of ${\rm H_2}$ and its carbon-based tracers, namely ${\rm CO}$, ${\rm C}$, and ${\rm C^+}$, in cosmological simulations of galaxy formation. Methods. The model accounts for the unresolved density structure in simulations using a variable probability distribution function of sub-grid densities and a temperature-density relation. Included is a simplified chemical network that has been tailored for hydrogen and carbon chemistry within molecular clouds and easily integrated into large-scale simulations with minimal computational overhead. As an example, we applied HYACINTH to a simulated galaxy at redshift $z \sim 2.5$ in post-processing and compared the resulting abundances with observations. Results. The chemical predictions from HYACINTH are in reasonable agreement with high-resolution molecular-cloud simulations at different metallicities. By post-processing a galaxy simulation with HYACINTH, we reproduced the $\rm H\,I-{\rm H_2}$ transition as a function of the hydrogen column density $N_{\rm H}$ for both Milky-Way-like and Large-Magellanic-Cloud-like conditions. Column density maps reveal that ${\rm CO}$ is concentrated in the peaks of the ${\rm H_2}$ distribution, while atomic carbon more broadly traces the bulk of ${\rm H_2}$ in our post-processed galaxy. Based on both the column density maps and the surface density profiles of the different gas species in the post-processed galaxy, we find that ${\rm C^+}$ maintains a substantially high surface density out to $\sim 10 \, \rm kpc$ as opposed to other components that exhibit a higher central concentration. This is similar to the extended $[\rm C\,II]$ emission found in some recent observations at high redshifts.

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arXiv2022

Window function convolution with deep neural network models

Traditional estimators of the galaxy power spectrum and bispectrum are sensitive to the survey geometry. They yield spectra that differ from the true underlying signal since they are convolved with the window function of the survey. For the current and future generations of experiments, this bias is statistically significant on large scales. It is thus imperative that the effect of the window function on the summary statistics of the galaxy distribution is accurately modelled. Moreover, this operation must be computationally efficient in order to allow sampling posterior probabilities while performing Bayesian estimation of the cosmological parameters. In order to satisfy these requirements, we built a deep neural network model that emulates the convolution with the window function, and we show that it provides fast and accurate predictions. We trained (tested) the network using a suite of 2000 (200) cosmological models within the cold dark matter scenario, and demonstrate that its performance is agnostic to the precise values of the cosmological parameters. In all cases, the deep neural network provides models for the power spectra and the bispectrum that are accurate to better than 0.1 per cent on a timescale of 10 $μ$s.

astro-ph.CO↗

arXiv2022

The Halo Bispectrum Multipoles in Redshift Space

We present the analysis of the halo bispectrum in redshift-space in terms of its multipoles, monopole, quadrupole and hexadecapole, measured from a large set of simulations. We fit such measurements with a tree-level model in perturbation theory that depends on linear and nonlinear bias parameters as well as on the growth rate $f$ of density fluctuations. The likelihood analysis takes advantage of a very large set of mock catalogs, enabling a robust estimation of the covariance properties for all multipoles. We compare the numerical estimate of the covariance matrix to its Gaussian prediction finding discrepancies of 10% or less for all configurations with the sole exception of the squeezed triangles in the monopole case. We find the range of validity of the tree-level model, for the total simulation volume of about 1000 $h^{-3}\, {\rm Gpc}^3$, reaches a maximum wavenumber of $0.08 \, h \, {\rm Mpc}^{-1}$ for the monopole, while it is limited to $0.06$ and $0.045\, h \, \rm{Mpc}^{-1}$ respectively for quadrupole and hexadecapole. Despite this, the addition of the quadrupole to the analysis allows for significant improvements on the determination of the model parameters and specifically on $f$, similarly to the power spectrum case. Finally, we compare our numerical estimate for the full covariance with its theoretical prediction in the Gaussian approximation and find the latter to work remarkably well in the context of simulation boxes with periodic boundary condition.

astro-ph.CO↗

arXiv2022

Mechanical feedback from stellar winds with an application to galaxy formation at high redshift

We compute different sets of stellar evolutionary tracks in order to quantify the energy, mass, and metals yielded by massive main-sequence and post-main-sequence winds. Our aim is to investigate the impact of binary systems and of a metallicity-dependent distribution of initial rotational velocities on the feedback by stellar winds. We find significant changes compared to the commonly used non-rotating, single-star scenario. The largest differences are noticeable at low metallicity, where the mechanical-energy budget is substantially increased. So as to establish the maximal (i.e. obtained by neglecting dissipation in the near circumstellar environment) influence of winds on the early stages of galaxy formation, we use our new feedback estimates to simulate the formation and evolution of a sub-$L_*$ galaxy at redshift 3 (hosted by a dark-matter halo with a mass of $1.8\times 10^{11}$ M$_\odot$) and compare the outcome with simulations in which only supernova (SN) feedback is considered. Accounting for the continuous energy injection by winds reduces the total stellar mass, the metal content, and the burstiness of the star-formation rate as well as of the outflowing gas mass. However, our numerical experiment suggests that the enhanced mechanical feedback from the winds of rotating and binary stars has a limited impact on the most relevant galactic properties compared to the non-rotating single-star scenario. Eventually, we look at the relative abundance between the metals entrained in winds and those ejected by SNe and find that it stays nearly constant within the simulated galaxy and its surrounding halo.

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arXiv2021

The large-scale monopole of the power spectrum in a Euclid-like survey: wide-angle effects, lensing, and the `finger of the observer'

Radial redshift-space distortions due to peculiar velocities and other light-cone effects shape the maps we build of the Universe. We address the open question of their impact onto the monopole moment of the galaxy power spectrum, $P_0(k)$. Specifically, we use an upgraded numerical implementation of the LIGER method to generate $140$ mock galaxy density fields for a full Euclid-like survey and we measure $P_0(k)$ in each of them utilising a standard estimator. We compare the spectra obtained by turning on and off different effects. Our results show that wide-angle effects due to radial peculiar velocities generate excess power above the level expected within the plane-parallel approximation. They are detectable with a signal-to-noise ratio of 2.7 for $k<0.02\,h$ Mpc$^{-1}$. Weak-lensing magnification also produces additional power on large scales which, if the current favourite model for the luminosity function of H$α$ emitters turns out to be realistic, can only be detected with a signal-to-noise ratio of 1.3 at best. Finally, we demonstrate that measuring $P_0(k)$ in the standard of rest of the observer generates an additive component reflecting the kinematic dipole overdensity caused by the peculiar velocity. This component is characterised by a damped oscillatory pattern on large scales. We show that this `finger of the observer' effect is detectable in some redshift bins and suggest that its measurement could possibly open new research directions in connection with the determination of the cosmological parameters, the properties of the galaxy population under study, and the dipole itself.

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