arXiv subjects

Hélène M. Courtois

Publications and source records attributed to Hélène M. Courtois.

16 recordsLinked to original sources

arXiv2026

WALLABY pilot survey: accurate and automated linewidth measurements from global HI profiles

Current-generation 21-cm surveys of extragalactic neutral hydrogen (HI) with instruments such as FAST and ASKAP are providing detailed spectral and spatial information for over 10^5 galaxies. Future HI surveys with next-generation radio telescopes could provide sample sizes larger by orders of magnitude. There is therefore a need for accurate, automated, and reliable parameterisation of the HI emission from galaxies. We have developed an automated estimator for HI global profile widths to better enable studies of, for example, dynamical masses and Tully-Fisher distances. Our estimator is based on an implementation of the BusyFit profile-fitting algorithm, and converges for 95% of global profiles in the WALLABY pilot survey. Probability density functions are calculated for all profile parameters using Monte Carlo techniques, and example error parameterisations are given. We confirm that linewidth uncertainties depend primarily on the integrated signal-to-noise ratio, profile steepness, and the linewidth, consistent with previous studies. We compare several common linewidth definitions, and the width at 50% of the mean flux density (Wm50) is found to be the most robust measure of linewidth. We provide examples of the baryonic Tully-Fisher relation drawn from the WALLABY pilot survey.

astro-ph.GA↗

arXiv2026

Empirical signatures of velocity and density cascades in the Local Universe probed by the CosmicFlows4 dataset

Aims: Our aim is to characterise the multiscale statistical properties of the reconstructed velocity and density fields of the nearby Universe, identify possible scaling regimes, quantify intermittency, and assess indications for the transition towards large-scale homogeneity within the range probed by current data. Methods: We analysed the Cosmicflows-4 three-dimensional velocity and density-contrast cubes using absolute structure functions of arbitrary order, $q$. The analysis was performed within a volume extending to $z \lesssim 0.08$ ($\simeq 350~\mathrm{Mpc}$ $h^{-1}$). Structure function scaling exponents $ζ(q)$ were estimated from configuration-space statistics. Intermittency was characterised using the universal multifractal formalism, and the probability density functions of increments were examined. Results: Two regimes were detected. Small separations are dominated by reconstruction smoothing and show a nearly linear $ζ(q)$ behaviour. At larger separations, a scaling regime appears with $ζ_ρ(1)\simeq0.3$ ($D_ρ\approx3.7$) and $ζ_v(1)\simeq0.4$. The correlation function follows $ξ(r)\sim r^{-1.4}$ over $[45,250]~\mathrm{Mpc}\,h^{-1}$, implying $D_2\simeq1.6$. Non-linear $ζ(q)$ and Lévy-stable increment probability density functions (PDFs) indicate intermittency and strong non-Gaussianity. The velocity increments show a systematic negative skewness suggestive of a cascade-like asymmetry associated with amplification of negative compressive gradients.

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arXiv2026

On the Tully-Fisher Relation for Active Galaxies -- I: Evidence of Larger Scatter

We present an investigation of the Tully-Fisher (TF) relation solely for galaxies hosting an active galactic nucleus (AGN). Using 22 galaxies with primary, z-independent distances, we find that active galaxies exhibit significantly larger scatter about all TF relations compared to each respective calibration for (largely) inactive galaxies. The larger scatter persists despite removal of the AGN contamination from the photometry of the Type 1 AGNs via 1) careful surface brightness decompositions or 2) employing SEDs to constrain the light contribution of the AGN. These results suggest that the influence of an AGN on its host galaxy's surface brightness may extend beyond the nucleus. We also calculate the percentage difference between TF and primary distances, and find that TF-based distances are biased towards overestimation of the primary distances to active galaxies by anywhere from 5-10 percent for the optical/near-infrared and approximately 15 percent for distances predicted from inverting the Baryonic TF (BTF) relation. As TF-based distances (especially the I-band) are relied on heavily for analysis and modeling of the local peculiar velocity (Vpec) field, we suggest that active galaxies be removed from future Vpec modeling samples.

astro-ph.GA↗

arXiv2026

The CAVITY project. The spatially resolved SFR of galaxies in voids

The mass in the Universe is distributed non-uniformly, originating the Large Scale Structure (LSS), characterised by clusters, filaments, walls and voids. Galaxies in voids are bluer, later type, less massive, and have slower evolution than galaxies in denser environments. The effect of the void environment on properties such as star formation rate (SFR) is still under discussion. We tackle this by estimating spatially-resolved SFR from extinction-corrected Halpha luminosities of 220 void galaxies from the CAVITY survey. These observations consist of optical integral field unit data cubes from the PMAS/PPaK spectrograph at Calar Alto Observatory. We measure the continuum-subtracted emission lines to obtain maps of SFR, specific star formation rate (sSFR) and extinction. We assess global properties and radial profiles up to 2 half-light radii. We compare with galaxies in filaments and walls from the CALIFA survey using the same methodology, building a control sample matched in morphology and stellar mass. We find no significant differences in SFR and sSFR, although void galaxies tend to have larger SFR, especially for early spirals. This effect is present for Sa galaxies at all galactocentric distances, and in the outer parts of late-type spirals, evidencing slower transition to quiescence and less evolved discs. Void late-type galaxies have lower extinction. Using extinction normalised by stellar mass surface density as a proxy for gas mass fraction, we find it larger for void early spirals, especially in outer regions. This indicates the effect of the void environment on the transition from star forming to passive.

astro-ph.GA↗

arXiv2025

The Velocity Field Olympics: Assessing velocity field reconstructions with direct distance tracers

The peculiar velocity field of the local Universe provides direct insights into its matter distribution and the underlying theory of gravity, and is essential in cosmological analyses for modelling deviations from the Hubble flow. Numerous methods have been developed to reconstruct the density and velocity fields at $z \lesssim 0.05$, typically constrained by redshift-space galaxy positions or by direct distance tracers such as the Tully-Fisher relation, the fundamental plane, or Type Ia supernovae. We introduce a validation framework to evaluate the accuracy of these reconstructions against catalogues of direct distance tracers. Our framework assesses the goodness-of-fit of each reconstruction using Bayesian evidence, residual redshift discrepancies, velocity scaling, and the need for external bulk flows. Applying this framework to a suite of reconstructions -- including those derived from the Bayesian Origin Reconstruction from Galaxies (BORG) algorithm and from linear theory -- we find that the non-linear BORG reconstruction consistently outperforms others. We highlight the utility of such a comparative approach for supernova or gravitational wave cosmological studies, where selecting an optimal peculiar velocity model is essential. Additionally, we present calibrated bulk flow curves predicted by the reconstructions and perform a density--velocity cross-correlation using a linear theory reconstruction to constrain the growth factor, yielding $S_8 = 0.793 \pm 0.035$. The result is in good agreement with both weak lensing and Planck, but is in strong disagreement with some peculiar velocity studies.

astro-ph.CO↗

arXiv2025

Revealing Hidden Cosmic Flows through the Zone of Avoidance with Deep Learning

We present a refined deep-learning-based method to reconstruct the three-dimensional dark matter density, gravitational potential, and peculiar velocity fields in the Zone of Avoidance (ZOA), a region near the galactic plane with limited observational data. Using a convolutional neural network (V-Net) trained on A-SIM simulation data, our approach reconstructs density or potential fields from galaxy positions and radial peculiar velocities. The full 3D peculiar velocity field is then derived from the reconstructed potential. We validate the method with mocks that mimic the spatial distribution of the Cosmicflows-4 (CF4) catalog and apply it to actual data. Given CF4's significant observational uncertainties and since our model does not yet account for them, we use peculiar velocities corrected via an existing Hamiltonian Monte Carlo reconstruction, rather than raw catalog distances. Our results demonstrate that the reconstructed density field recovers known galaxy clusters detected in an H \textsc{i} survey of the ZOA, despite this dataset not being used in the reconstruction. This agreement underscores the potential of our method to reveal structures in data-sparse regions. Most notably, streamline convergence and watershed analysis identify a mass concentration consistent with the Great Attractor, at $(l, b) = (308.4^\circ \pm 2.4^\circ, 29.0^\circ \pm 1.9^\circ)$ and $cz = 4960.1 \pm 404.4,{\rm km/s}$, for 64\% of realizations. Our method is particularly valuable as it does not rely on data point density, enabling accurate reconstruction in data-sparse regions and offering strong potential for future surveys with more extensive galaxy datasets.

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arXiv2024

CAVITY: Calar Alto Void Integral-field Treasury surveY. I. First public data release

The Calar Alto Void Integral-field Treasury surveY (CAVITY) is a legacy project aimed at characterising the population of galaxies inhabiting voids, which are the most under-dense regions of the cosmic web, located in the Local Universe. This paper describes the first public data release (DR1) of CAVITY, comprising science-grade optical data cubes for the initial 100 out of a total of $\sim$300 galaxies in the Local Universe ($0.005 < z < 0.050$). These data were acquired using the integral-field spectrograph PMAS/PPak mounted on the 3.5m telescope at the Calar Alto observatory. The DR1 galaxy sample encompasses diverse characteristics in the color-magnitude space, morphological type, stellar mass, and gas ionisation conditions, providing a rich resource for addressing key questions in galaxy evolution through spatially resolved spectroscopy. The galaxies in this study were observed with the low-resolution V500 set-up, spanning the wavelength range 3745-7500 Å, with a spectral resolution of 6.0 Å (FWHM). Here, we describe the data reduction and characteristics and data structure of the CAVITY datasets essential for their scientific utilisation, highlighting such concerns as vignetting effects, as well as the identification of bad pixels and management of spatially correlated noise. We also provide instructions for accessing the CAVITY datasets and associated ancillary data through the project's dedicated database.

astro-ph.GA↗

arXiv2024

The CAVITY project. The spatially resolved stellar population properties of galaxies in voids

The Universe is shaped as a web-like structure, formed by clusters, filaments, and walls that leave large volumes in between named voids. Galaxies in voids have been found to be of a later type, bluer, less massive, and to have a slower evolution than galaxies in denser environments (filaments and walls). However, the effect of the void environment on their stellar population properties is still unclear. We aim to address this question using 118 optical integral field unit datacubes from the Calar Alto Void Integral-field Treasury surveY (CAVITY), observed with the PMAS/PPaK spectrograph at the 3.5m telescope at the Calar Alto Observatory (Almería, Spain). We used the non-parametric full spectral fitting code STARLIGHT to estimate their stellar population properties: stellar mass, stellar mass surface density, age, star formation rate (SFR), and specific star formation rate (sSFR). We analysed the results through the global and spatially resolved properties. Then, we compared them with a control sample of galaxies in filaments and walls from the CALIFA survey, matched in stellar mass and morphological type. Key findings include void galaxies having a slightly higher half-light radius (HLR), lower stellar mass surface density, and younger ages across all morphological types, and slightly elevated SFR and sSFR (only significant enough for Sas). Many of these differences appear in the outer parts of spiral galaxies in voids (HLR > 1), which are younger and exhibit a higher sSFR, indicative of less evolved discs. This trend is also found for early-type spirals, suggesting a slower transition from star-forming to quiescent states in voids. Our analysis indicates that void galaxies, influenced by their surroundings, undergo a more gradual evolution, especially in their outer regions, with a more pronounced effect for low-mass galaxies.

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arXiv2023

Dynamic cosmography of the local Universe: Laniakea and five more watershed superclusters

This article delivers the dynamical cosmography of the Local Universe within z=0.1 (1 giga light-years). We exploit the gravitational velocity field computed using the CosmicFlows-4 catalog of galaxy distances to delineate superclusters as watersheds, publishing for the first time their size, shape, main streams of matter and the location of their central attractor. Laniakea, our home supercluster's size is confirmed to be 2 $\times 10^6$ (Mpc $h^{-1}$)$^3$. Five more known superclusters are now dynamically defined in the same way: Apus, Hercules, Lepus, Perseus-Pisces and Shapley. Also, the central repellers of the Bootes and Sculptor voids are found and the Dipole and Cold Spot repellers now appear as a single gigantic entity. Interestingly the observed superclusters are an order of magnitude larger than the theoretical ones predicted by cosmological $Λ$CDM simulations.

astro-ph.CO↗

arXiv2022

Cosmicflows-4

With Cosmicflows-4, distances are compiled for 55,877 galaxies gathered into 38,065 groups. Eight methodologies are employed, with the largest numbers coming from the correlations between the photometric and kinematic properties of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise from degenerate progenitors (type Ia Sne) are an important overlapping component. Smaller contributions come from distance estimates from the surface brightness fluctuations of elliptical galaxies and the luminosities and expansion rates of core collapse supernovae (SNII). Cepheid period-luminosity relation and tip of the red giant branch observations founded on local stellar parallax measurements along with the geometric maser distance to NGC 4258 provide the absolute scaling of distances. The assembly of galaxies into groups is an important feature of the study in facilitating overlaps between methodologies. Merging between multiple contributions within a methodology and between methodologies is carried out with Bayesian Markov chain Monte Carlo procedures. The final assembly of distances is compatible with a value of the Hubble constant of $H_0=74.6$ km s$^{-1}$ Mpc$^{-1}$ with the small statistical error of $\pm 0.8$ km s$^{-1}$ Mpc$^{-1}$ but a large potential systematic error of ~3 km s$^{-1}$ Mpc$^{-1}$. Peculiar velocities can be inferred from the measured distances. The interpretation of the field of peculiar velocities is complex because of large errors on individual components and invites analyses beyond the scope of this study.

astro-ph.CO↗

arXiv2022

WALLABY Pre-Pilot and Pilot Survey: the Tully Fisher Relation in Eridanus, Hydra, Norma and NGC4636 fields

The WALLABY pilot survey has been conducted using the Australian SKA Pathfinder (ASKAP). The integrated 21-cm HI line spectra are formed in a very different manner compared to usual single-dish spectra Tully-Fisher measurements. It is thus extremely important to ensure that slight differences (e.g. biases due to missing flux) are quantified and understood in order to maximise the use of the large amount of data becoming available soon. This article is based on four fields for which the data are scientifically interesting by themselves. The pilot data discussed here consist of 614 galaxy spectra at a rest wavelength of 21cm. Of these spectra, 472 are of high enough quality to be used to potentially derive distances using the Tully-Fisher relation. We further restrict the sample to the 251 galaxies whose inclination is sufficiently close to edge-on. For these, we derive Tully-Fisher distances using the deprojected WALLABY velocity widths combined with infrared (WISE W1) magnitudes. The resulting Tully-Fisher distances for the Eridanus, Hydra, Norma and NGC 4636 clusters are 21.5, 53.5, 69.4 and 23.0 Mpc respectively, with uncertainties of 5--10\%, which are better or equivalent to the ones obtained in studies using data obtained with giant single dish telescopes. The pilot survey data show the benefits of WALLABY over previous giant single-dish telescope surveys. WALLABY is expected to detect around half a million galaxies with a mean redshift of $z = 0.05 (200 Mpc)$. This study suggests that about 200,000 Tully-Fisher distances might result from the survey.

astro-ph.GA↗

arXiv2022

Anisotropic satellite accretion onto the Local Group with HESTIA

How the cosmic web feeds halos, and fuels galaxy formation is an open question with wide implications. This study explores the mass assembly in the Local Group within the context of the local cosmography by employing simulations whose initial conditions have been constrained to reproduce the local environment. The goal of this study is to inspect whether the direction of accretion of satellites on to the Milky Way and Andromeda galaxies, is related to the cosmic web. The analysis considers the three high-resolution simulations available in the HESTIA simulation suite, as well as the derived velocity shear and tidal tensors. We notice two eras in the Local Group accretion history, delimited by an epoch around $z \approx 0.7$. We also find that satellites can travel up to $\sim 4$ Mpc, relative to their parent halo before crossing its viral radius $R_{200}$. Finally, we observe a strong alignment of the infall direction with the axis of slowest collapse $\vec{e_3}$ of both tidal and shear tensors, implying satellites of the Local Group originated from one particular region of the cosmic web and were channeled towards us via the process of accretion.This alignment is dominated by the satellites that enter during the early infall era, i.e $z>0.7$.

astro-ph.GA↗

arXiv2021

Tully-Fisher Distances and Dynamical Mass Constraints for 24 Host Galaxies of Reverberation-Mapped AGN

We present Tully-Fisher distances for 24 AGN host galaxies with black hole mass ($M_\textrm{BH}$) measurements from reverberation mapping, as well as the first calibration of the $V-$band Tully-Fisher relation. Combining our measurements of HI 21cm emission with $HST$ and ground-based optical and near-infrared images allows multiple distance measurements for 19 galaxies and single measurements for the remaining 5. Separation of the nucleus from its host galaxy via surface brightness decomposition yields galaxy-only luminosities, thus allowing measurements of the distance moduli free of contamination from the AGN. For 14 AGN hosts, these are the first reported distances independent of redshift, and hence independent of peculiar velocities. For the remaining galaxies, we show good agreement between our distances and those previously reported from surface brightness fluctuations (SBF) and Cepheids. We also determine the total galaxy mass enclosed within the estimated HI radius, which when compared to the baryonic content allows for constraints on the dark matter masses. We find a typical mass fraction of $M_{\textrm{DM}}$/$M_{\textrm{DYN}}$ = 62\%, and find significant correlations between $M_{\textrm{BH}}$ $-$ $M_{\textrm{DYN}}$ and $M_{\textrm{BH}}$ $-$ $M_{\textrm{DM}}$. Finally, we scale our galaxy radii based on estimated relationships between visible and halo radii and assume a flat rotation curve out to the halo radius to approximate $M_{\textrm{HALO}}$. Over the range of $M_{\textrm{BH}}$ and $M_{\textrm{HALO}}$ in this sample, we find good agreement with observationally-constrained relationships between $M_{\textrm{BH}}$ and $M_{\textrm{HALO}}$ and with hydrodynamical simulations.

astro-ph.GA↗

arXiv2019

HI Spectroscopy of Reverberation-Mapped Active Galactic Nuclei

We present HI 21 cm spectroscopy from the GBT for the host galaxies of 31 nearby AGNs with direct M$_{\textrm{BH}}$ measurements from reverberation mapping. These are the first published HI detections for 12 galaxies, and the spectral quality is generally an improvement over archival data for the remainder of the sample. We present measurements of emission-line fluxes, velocity widths, and recessional velocities from which we derive HI mass, total gas mass, and redshifts. Combining M$_{\textrm{GAS}}$ with constraints on M$_{\textrm{STARS}}$ allows exploration of the baryonic content of these galaxies. We find a typical M$_{\textrm{GAS}}$/M$_{\textrm{STARS}}$ fraction of 10%, with a few reaching $\sim$30-50%. We also examined several relationships between M$_{\textrm{STARS}}$, M$_{\textrm{GAS}}$, M$_{\textrm{BH}}$, baryonic mass, and morphological type. We find a weak preference for galaxies with larger M$_{\textrm{GAS}}$ to host more massive black holes. We also find gas-to-stellar fractions to weakly correlate with later types in unbarred spirals, with an approximately constant fraction for barred spirals. Consistent with previous studies, we find declining M$_{\textrm{GAS}}$/M$_{\textrm{STARS}}$ with increasing M$_{\textrm{STARS}}$, with a slope suggesting the gas reservoirs have been replenished. Finally, we find a clear relationship for M$_{\textrm{BH}}$-M$_{\textrm{BARY}}$ with a similar slope as M$_{\textrm{BH}}$-M$_{\textrm{STARS}}$ reported by Bentz & Manne-Nicholas (2018). The dwarf Seyfert NGC 4395 appears to follow this relationship as well, even though it has a significantly higher gas fraction and smaller M$_{\textrm{BH}}$ than the remainder of our sample.

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arXiv2018

The quasi-linear nearby Universe

The local Universe provides a unique opportunity for testing cosmology and theories of structure formation. To facilitate this opportunity we present a new method for the reconstruction of the quasi-linear matter density and velocity fields from galaxy peculiar velocities and apply it to the Cosmicflows-2 data. The method consists of constructing an ensemble of cosmological simulations, constrained by the standard cosmological model and the observational data. The quasi-linear density field is the geometric mean and variance of the fully non-linear density fields of the simulations. The main nearby clusters (Virgo, Centaurus, Coma), superclusters (Shapley, Perseus-Pisces) and voids (Dipole Repeller) are robustly reconstructed. Galaxies are born biased with respect to the underlying dark matter distribution. Using our quasi-linear framework we demonstrate that the luminosity-weighted density field derived from the 2M++ redshift compilations is non-linearly biased with respect to the matter density field. The bias diminishes in the linear regime.

astro-ph.CO↗

arXiv2010

Cosmological Simulations on a Grid of Computers

The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in GALICS and MOMAF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling efficiencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values. The computation time needed is so large, that we need to run on a grid of computers. Hence, we model GALICS and MOMAF execution time and output files size, and run the simulation using a grid middleware: DIET. All the complexity of accessing resources, scheduling simulations and managing data is harnessed by DIET and hidden behind a web portal accessible to the users.

astro-ph.IM↗