Distribution Of Galaxies Research Articles

Mini-quenching of z = 4–8 galaxies by bursty star formation

ABSTRACT The recent reported discovery of a low-mass z = 5.2 and an intermediate-mass z = 7.3 quenched galaxy with JWST/NIRSpec is the first evidence of halted star formation above z ≈ 5. Here, we show how bursty star formation at z = 4–8 gives rise to temporarily quenched, or mini-quenched galaxies in the mass range M⋆ = 107–109 M⊙ using four models of galaxy formation: the periodic box simulation IllustrisTNG, the zoom-in simulations vela and FirstLight and an empirical halo model. The main causes for mini-quenching are stellar feedback, lack of gas accretion onto galaxies, and galaxy–galaxy interactions. The abundance of (mini-)quenched galaxies agrees across the models: the population first appears below z ≈ 8, after which their proportion increases with cosmic time, from ∼0.5–1.0 per cent at z = 7 to ∼2–4 per cent at z = 4, corresponding to comoving number densities of ∼10−5 and ∼10−3 Mpc−3, respectively. These numbers are consistent with star formation rate duty cycles inferred for vela and FirstLight galaxies. Their star formation histories (SFHs) suggest that mini-quenching at z = 4–8 is short-lived with a duration of ∼20–40 Myr, which is close to the free-fall time-scale of the inner halo. However, mock spectral energy distributions of mini-quenched galaxies in IllustrisTNG and vela do not match JADES-GS-z7-01-QU photometry, unless their SFHs are artificially altered to be more bursty on time-scales of ∼40 Myr. Studying mini-quenched galaxies might aid in calibrating sub-grid models governing galaxy formation, as these may not generate sufficient burstiness at high redshift to explain the SFH inferred for JADES-GS-z7-01-QU.

The localization of galaxy groups in close proximity to galaxy clusters using cosmic web nodes

ABSTRACT We investigate the efficacy of using the cosmic web nodes identified by the DisPerSE topological filament finder to systematically identify galaxy groups in the infall regions around massive clusters. The large random motions and infall velocities of galaxies in the regions around clusters complicate the detection and characterisation of substructures through normal group-finding algorithms. Yet understanding the co-location of galaxies within filaments and/or groups is a key part of understanding the role of environment on galaxy evolution, particularly in light of next-generation wide-field spectroscopic surveys. Here we use simulated massive clusters from TheThreeHundred collaboration and compare the derived group catalogues, (haloes with σv > 300 h−1 km s−1) with the critical points from DisPerSE, ran on haloes with more than 100 particles. We find that in 3D, 56 per cent of DisPerSE nodes are correctly identified as groups (purity) while 68 per cent of groups are identified as nodes (completeness). The fraction of matches increases with group mass and with distance from the host cluster centre. This rises to a completeness of 100 per cent for the most massive galaxy groups (M > 1014 M⊙) in 3D, or 63 per cent when considering the projected 2D galaxy distribution. When a perfect match occurs between a cosmic web node and a galaxy group, the DisPerSE node density (δ) serves as an estimate of the group’s mass, albeit with significant scatter. We conclude that the use of a cosmic filament finder shows promise as a useful and straightforward observational tool for disentangling substructure within the infall regions of massive clusters.

Flat patterns in cosmic structure

ABSTRACT It is natural to wonder how far the flat pattern in the distribution of galaxies and clusters of galaxies around the de Vaucoueurs Local Supercluster extends, and whether there are other similarly extended flat patterns in the large-scale structure of the Universe. I present evidence of two extended flat and thin sheet-like patterns in the distributions of galaxies and clusters detected at redshift z < 0.021. Sheet A contains our position and is tilted 11° from the supergalactic pole, meaning the Local Supercluster is a moderately bent part of the more extended Sheet A. The continuation of this sheet is detected in the disjoint sample of galaxies at redshifts 0.021 < z < 0.041 and again in the disjoint samples of galaxies and clusters of galaxies at 0.042 < z < 0.085. Sheet B is 15 Mpc from us at its closest point. It is detected at z < 0.021 and at 0.021 < z < 0.041. These results make a serious case for the reality of signatures of close to flat and thin extended sheet-like patterns in cosmic structure, and an interesting challenge for the lambda-cold dark matter cosmology.

When the well runs dry: modelling environmental quenching of high-mass satellites in massive clusters at z ≳ 1

ABSTRACT We explore models of massive (>1010 M⊙) satellite quenching in massive clusters at z ≳ 1 using an MCMC framework, focusing on two primary parameters: Rquench (the host-centric radius at which quenching begins) and τquench (the time-scale upon which a satellite quenches after crossing Rquench). Our MCMC analysis shows two local maxima in the 1D posterior probability distribution of Rquench at approximately 0.25 and 1.0 R200. Analysing four distinct solutions in the τquench–Rquench parameter space, nearly all of which yield quiescent fractions consistent with observational data from the GOGREEN survey, we investigate whether these solutions represent distinct quenching pathways and find that they can be separated between ‘starvation’ and ‘core quenching’ scenarios. The starvation pathway is characterized by quenching time-scales that are roughly consistent with the total cold gas (H2 + H i) depletion time-scale at intermediate z, while core quenching is characterized by satellites with relatively high line-of-sight velocities that quench on short time-scales (∼0.25 Gyr) after reaching the inner region of the cluster (<0.30 R200). Lastly, we break the degeneracy between these solutions by comparing the observed properties of transition galaxies from the GOGREEN survey. We conclude that only the ‘starvation’ pathway is consistent with the projected phase-space distribution and relative abundance of transition galaxies at z ∼ 1. However, we acknowledge that ram pressure might contribute as a secondary quenching mechanism.

TRACING THE ASSEMBLY HISTORIES OF GALAXY CLUSTERS IN THE NEARBY UNIVERSE

We have compiled a sample of 67 nearby (z < 0.15) clusters of galaxies, for which on average more than 150 spectroscopic members are available and, by applying different methods to detect substructures in their galaxy distribution, we have studied their assembly history. Our analysis confirms that substructures are present in 70% of our sample, having a significant dynamical impact in 57% of them. A classification of the assembly state of the clusters based on the dynamical significance of their substructures is proposed. In 19% of our clusters, the originally identified brightest cluster galaxy is not the central gravitationally dominant galaxy (CDG), but turns out to be either the second-rank, or the dominant galaxy of a substructure (a SDG, in our classification), or even a possible “fossil” galaxy in the periphery of the cluster. Moreover, no correlation was found in general between the projected offset of the CDG from the X-ray peak and its peculiar velocity.

The DESI One-Percent survey: exploring the Halo Occupation Distribution of Emission Line Galaxies with AbacusSummit simulations

The One-Percent survey of the Dark Energy Spectroscopic Instrument collected ∼ 270k emission line galaxies (ELGs) at 0.8 < z < 1.6. The high completeness of the sample allowed the clustering to be measured down to scales never probed before, 0.04 Mpc/h in rp for the projected 2-point correlation function (2PCF) and 0.17 Mpc/h in galaxy pair separation s for the 2PCF monopole and quadrupole. The most striking feature of the measurements is a strong signal at the smallest scales, below 0.2 Mpc/h in rp and 1 Mpc/h in s.We analyse these datain the halo occupation distribution framework. We consider different distributions for central galaxies, a standard power law for satellites with no condition on the presence of a central galaxy and explore several extensions of these models. For all considered models, the mean halo mass of the sample is found to be log10 ⟨Mh ⟩ ∼ 11.9.We obtain a satellite mean occupation function which agrees with physically motivated ELG models only if we introduce central-satellite conformity, meaning that the satellite occupation is conditioned by the presence of central galaxies of the same type. To achieve in addition a good modelling of the clustering between 0.1 and 1 Mpc/h in rp , we allow for ELG positioning outside of the halo virial radius and find 0.5% of ELGs residingin the outskirts of halos. Furthermore, the satellite velocity dispersion inside halos is found to be ∼ 30% larger than that of the halo dark matter particles. These are the main findings of our work. We investigate assembly bias as a function of halo concentration, local density or local density anisotropies and observe no significant change in our results. We split the data sample in two redshift bins and report no significant evolution with redshift. Lastly, changing the cosmology in the modelling impacts only slightly our results.

Glass-like random catalogues for two-point estimates on the light-cone

ABSTRACT We introduce grlic, a publicly available Python tool for generating glass-like point distributions with a radial density profile n(r) as it is observed in large-scale surveys of galaxy distributions on the past light-cone. Utilizing these glass-like catalogues, we assess the bias and variance of the Landy–Szalay (LS) estimator of the first three two-point correlation function (2PCF) multipoles in halo and particle catalogues created with the cosmological N-body code gevolution. Our results demonstrate that the LS estimator calculated with the glass-like catalogues is biased by less than 10−4 with respect to the estimate derived from Poisson-sampled random catalogues, for all multipoles considered and on all but the smallest scales. Additionally, the estimates derived from glass-like catalogues exhibit significantly smaller standard deviation σ than estimates based on commonly used Poisson-sampled random catalogues of comparable size. The standard deviation of the estimate depends on a power of the number of objects NR in the random catalogue; we find a power law $\sigma \propto N_\mathit{R}^{-0.9}$ for glass-like catalogues as opposed to $\sigma \propto N_\mathit{R}^{-0.48}$ using Poisson-sampled random catalogues. Given a required precision, this allows for a much reduced number of objects in the glass-like catalogues used for the LS estimate of the 2PCF multipoles, significantly reducing the computational costs of each estimate.

Search for a possible quasi-periodic structure based on data of the SDSS DR12 LOWZ

ABSTRACT We carry out a statistical analysis of the spatial distribution of galaxies at cosmological redshifts 0.16 ≤ z ≤ 0.47 based on the SDSS DR12 LOWZ catalogue. Our aim is to search and study possible large-scale quasi-regular structures embedded in the cosmic web. We calculate projections of the Cartesian galaxy coordinates on different axes (directions), densely covering certain regions in the sky to look for special directions along which 1D distributions of the projections contain significant quasi-periodic components. These components appear as peaks in the power spectra and lie in a narrow range of wave numbers 0.05 &amp;lt; k &amp;lt; 0.07. Particular attention is paid to the evaluation of the significance of the peaks. It is found that the significance of the dominant peaks for some selected directions exceeds (4–5)σ. In order to reduce possible selection effects, we create a mock homogeneous catalogue of spatial distribution of galaxies by adding a random set of artificial objects (points) to the real galaxies under study. The power spectrum of this cumulative model data also demonstrates significant peak corresponding to approximately the same scale. As a result we assume the existence of an anisotropic cosmological quasi-periodic structure with characteristic scale (116 ± 10) h−1 Mpc.

The origin of the observed Ly α EW distribution of dwarf galaxies at z ∼ 2

ABSTRACT We present a rest-UV-selected sample of 32 lensed galaxies at z ∼ 2 observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed ($-19 \le {M_{\rm UV}} \le -17$) at this redshift. The fraction of dwarf galaxies identified as Ly α emitters ($\rm EW \ge 20$ Å) is ${X_{\rm LAE}}=33^{+17}_{-12}\,{\rm per\, cent}$. We use the Balmer lines and UV continuum to estimate both the intrinsic EW and the Ly α escape fraction to determine their relative importance in dictating the observed EW distribution. Fainter galaxies (MUV &amp;gt; −19) show larger intrinsic EWs and escape fractions than brighter galaxies. Only galaxies with intrinsic EWs greater than 40 Å have escape fractions larger than 5 per cent. We find little to no anticorrelation between the escape fraction and dust in dwarf galaxies. The volumetric escape fraction of our sample is $f_{\rm esc}^{\rm Ly\alpha } = 4.6^{+2.0}_{-1.4}\,{\rm per\, cent}$ in agreement with measurements found elsewhere in the literature. 60 per cent of the total integrated Ly α luminosity density comes from galaxies with EWobs &amp;gt; 20 Å.

Lopsidedness as a tracer of early galactic assembly history

ABSTRACT Large-scale asymmetries (i.e. lopsidedness) are a common feature in the stellar density distribution of nearby disc galaxies both in low- and high-density environments. In this work, we characterize the present-day lopsidedness in a sample of 1435 disc-like galaxies selected from the TNG50 simulation. We find that the percentage of lopsided galaxies (10 per cent–30 per cent) is in good agreement with observations if we use similar radial ranges to the observations. However, the percentage (58 per cent) significantly increases if we extend our measurement to larger radii. We find a mild or lack of correlation between lopsidedness amplitude and environment at z = 0 and a strong correlation between lopsidedness and galaxy morphology regardless of the environment. Present-day galaxies with more extended discs, flatter inner galactic regions, and lower central stellar mass density (i.e. late-type disc galaxies) are typically more lopsided than galaxies with smaller discs, rounder inner galactic regions, and higher central stellar mass density (i.e. early-type disc galaxies). Interestingly, we find that lopsided galaxies have, on average, a very distinct star formation history within the last $10\, \mathrm{Gyr}$, with respect to their symmetric counterparts. Symmetric galaxies have typically assembled at early times (∼8–$6\, \mathrm{Gyr}$ ago) with relatively short and intense bursts of central star formation, while lopsided galaxies have assembled on longer time-scales and with milder initial bursts of star formation, continuing building up their mass until z = 0. Overall, these results indicate that lopsidedness in present-day disc galaxies is connected to the specific evolutionary histories of the galaxies that shaped their distinct internal properties.

A Multiwavelength Investigation of Dust and Stellar Mass Distributions in Galaxies: Insights from High-resolution JWST Imaging

We study the morphological properties of mid-infrared selected galaxies at 1.0 < z < 1.7 in the SMACS J0723.3-7327 cluster field to investigate the mechanisms of galaxy mass assembly and structural formation at cosmic noon. We develop a new algorithm to decompose the dust and stellar components of individual galaxies by using high-resolution images in the MIRI F770W and NIRCam F200W bands. Our analysis reveals that a significant number of galaxies with stellar masses between 109.5 < M */M ⊙ < 1010.5 exhibit dust cores that are relatively more compact than their stellar cores. Specifically, within this mass range, the nonparametric method indicates that the dust cores are 1.23 (±0.05) times more compact than the stellar cores on average when evaluated with flux concentration of the two components within a fixed radius. Similarly, the parametric method yields an average compactness ratio of 1.27 (±0.06). Notably, the most massive galaxy (M * ∼ 1010.9 M ⊙) in our sample demonstrates a comparable level of compactness between its stellar core and dust, with a dust-to-stellar ratio of 0.86 (0.89) as derived from nonparametric (parametric) method. The observed compactness of the dust component is potentially attributed to the presence of a (rapidly growing) massive bulge that in some cases is associated with elevated star formation. Expanding the sample size through a joint analysis of multiple Cycle 1 deep-imaging programs can help to confirm the inferred picture. Our pilot study highlights that MIRI offers an efficient approach to studying the structural formation of galaxies from cosmic noon to the modern Universe.

Dynamical Hotness, Star Formation Quenching, and Growth of Supermassive Black Holes

A stellar system is dynamically hot when its kinetic energy is dominated by random motion represented by the velocity dispersion σ hot. We use MaNGA data to obtain the inner and outer dispersion of a galaxy, σ in and σ out, to characterize its dynamical status and study its connection with star formation quenching and the growth of its supermassive black hole (SMBH). We divide galaxies into fully quenched (FQGs), partially quenched (PQGs), and fully star-forming (FSGs) populations, and identify quenched central cores (QCCs) in PQGs. The galaxy distribution in (σ in/σ hot)–(σ out/σ hot) diagram is L-shaped, consisting of a horizontal sequence (σ out/σ hot ∼ 0) and a vertical sequence (σ in/σ hot ∼ 1). FQGs and QCCs are located at the top of the vertical sequence, σ out/σ hot ∼ 1, and are thus dynamically hot over their entire bodies. PQGs reside along the vertical sequence, so they have hot centers but cold outskirts. FSGs are diverse and can be found in both sequences. Galaxy structural properties, star formation, and AGN activities make a transition along the horizontal sequence at σ in/σ hot ∼ 0.5, and along the vertical sequence at σ out/σ hot ∼ 0.5. The fractions of optical AGNs and barred galaxies increase rapidly in the first transition and decline rapidly in the second; radio galaxies are located at the top of the vertical sequence. Our results demonstrate that star formation quenching and SMBH growth are effective only in dynamically hot systems. A simple model along this line can reproduce the observed SMBH scaling relations. We discuss how secular processes and strong interactions can make a system dynamically hot, and lead to the SMBH growth and star formation quenching.

Improved GALEX UV Photometry for 700,000 SDSS Galaxies

The Galaxy Evolution Explorer (GALEX) satellite performed the first and only large-area UV survey, which in tandem with the Sloan Digital Sky Survey (SDSS) has facilitated modeling of the spectral energy distributions of low-redshift galaxies and the determination of various galaxy properties, in particular the star formation rate. However, the relatively crude angular resolution of GALEX (5″) made its images susceptible to blending of sources, resulting in potentially biased far-UV and near-UV (NUV) pipeline photometry. To remedy this issue and take advantage of model-fit photometry, we use the EMphot software to obtain forced GALEX photometry for ∼700,000 SDSS galaxies at z < 0.3. Positional priors of target galaxies and potentially contaminating neighbors were taken from SDSS. New photometry is based on the best-fitting of three model profiles: optical-like, exponential, and flat. New photometry mitigates blending present in the original pipeline catalogs, which affected 16% of galaxies at a level of >0.2 mag and 2% at a level of >1 mag. Pipeline NUV magnitudes are severely affected (≳1 mag) when the neighbor is brighter than the target galaxy and within 10″, or when the neighbor is fainter and within ∼3″ of the target. New photometry fixes edge-of-detector bias, which affected pipeline photometry by up to 0.1 mag in NUV. We present catalogs with new photometry for GALEX observations of different depths, corresponding to the all-sky imaging survey (AIS), medium imaging survey, and deep imaging survey. Catalogs feature combined magnitudes for multiple detections of the same galaxy in a survey.

Simulation-guided galaxy evolution inference: A case study with strong lensing galaxies

Understanding the evolution of galaxies provides crucial insights into a broad range of aspects in astrophysics, including structure formation and growth, the nature of dark energy and dark matter, baryonic physics, and more. It is, however, infeasible to track the evolutionary processes of individual galaxies in real time given their long timescales. As a result, galaxy evolution analyses have been mostly based on ensembles of galaxies that are supposed to be from the same population according to usually basic and crude observational criteria. We propose a new strategy of evaluating the evolution of an individual galaxy by identifying its descendant galaxies as guided by cosmological simulations. As a proof of concept, we examined the evolution of the total mass distribution of a target strong lensing galaxy atz = 0.884 using the proposed strategy. We selected 158 galaxies from the TNG300 simulation that we identified as analogs of the target galaxy. We followed their descendants and found 11 observed strong lensing galaxies that match in stellar mass and size with the descendants at their redshifts. The observed and simulated results are discussed, although no conclusive assessment is made given the low statistical significance due to the small sample size. Nevertheless, the test confirms that our proposed strategy is already feasible with existing data and simulations. We expect it to play an even more important role in studying galaxy evolution as more strong lens systems and larger simulations become available with the advent of next-generation survey programs and cosmological simulations.

Determining the dark matter distribution in simulated galaxies with deep learning

ABSTRACTWe present a novel method of inferring the dark matter (DM) content and spatial distribution within galaxies, using convolutional neural networks (CNNs) trained within state-of-the-art hydrodynamical simulations (Illustris–TNG100). Within the controlled environment of the simulation, the framework we have developed is capable of inferring the DM mass distribution within galaxies of mass ∼1011–$10^{13} \, M_\odot$ from the gravitationally baryon-dominated internal regions to the DM-rich, baryon-depleted outskirts of the galaxies, with a mean absolute error always below ≈0.25 when using photometrical and spectroscopic information. With respect to traditional methods, the one presented here also possesses the advantages of not relying on a pre-assigned shape for the DM distribution, to be applicable to galaxies not necessarily in isolation, and to perform very well even in the absence of spectroscopic observations.

WALLABY pilot survey: the potential polar ring galaxies NGC 4632 and NGC 6156

ABSTRACT We report on the discovery of two potential polar ring galaxies (PRGs) in the WALLABY Pilot Data Release 1 (PDR1). These untargeted detections, cross-matched to NGC 4632 and NGC 6156, are some of the first galaxies where the H i observations show two distinct components. We used the iDaVIE virtual reality software to separate the anomalous gas from the galactic gas and found that the anomalous gas comprises ∼50 per cent of the total H i content of both systems. We have generated plausible 3D kinematic models for each galaxy, assuming that the rings are circular and inclined at 90° to the galaxy bodies. These models show that the data are consistent with PRGs but do not definitively prove that the galaxies are PRGs. By projecting these models at different combinations of main disc inclinations, ring orientations, and angular resolutions in mock data cubes, we have further investigated the detectability of similar PRGs in WALLABY. Assuming that these galaxies are indeed PRGs, the detectability fraction, combined with the size distribution of WALLABY PDR1 galaxies, implies an incidence rate of ∼1–3 per cent. If this rate holds true, the WALLABY survey will detect hundreds of new polar ring galaxies.

Can Cuspy Dark-matter-dominated Halos Hold Cored Stellar Mass Distributions?

According to the current concordance cosmological model, dark matter (DM) particles are collisionless and produce self-gravitating structures with a central cusp, which, generally, is not observed. The observed density tends to a central plateau or core, explained within the cosmological model through the gravitational feedback of baryons on DM. This mechanism becomes inefficient when decreasing the galaxy’s stellar mass so that in the low-mass regime (M ⋆ ≪ 106 M ⊙) the energy provided by the baryons is insufficient to modify cusps into cores. Thus, if cores exist in these galaxies they have to reflect departures from the collisionless nature of DM. Measuring the DM mass distribution in these faint galaxies is extremely challenging; however, their stellar mass distribution can be characterized through deep photometry. Here we provide a way of using only the stellar mass distribution to constrain the underlying DM distribution. The so-called Eddington inversion method allows us to discard pairs of stellar distributions and DM potentials requiring (unphysical) negative distribution functions in the phase space. In particular, cored stellar density profiles are incompatible with the Navarro–Frenk–White (NFW) potential expected from collisionless DM if the velocity distribution is isotropic and the system spherically symmetric. Through a case-by-case analysis, we are able to relax these assumptions to consider anisotropic velocity distributions and systems that do not have exact cores. In general, stellar distributions with radially biased orbits are difficult to reconcile with NFW-like potentials, and cores in the baryon distribution tend to require cores in the DM distribution.

Simulating the LOcal Web (SLOW)

Context. Several observations of the Local Universe point toward the existence of very prominent structures: massive galaxy clusters and local superclusters on the one hand, but also large local voids and underdensities on the other. However, it is highly nontrivial to connect such different observational selected tracers to the underlying dark matter (DM) distribution. Aims. Therefore, constructing mock catalogs of such observable tracers using cosmological hydrodynamics simulations is needed. These simulations have to follow galaxy formation physics and also have to be constrained to reproduce the Local Universe. Such constraints should be based on observables that directly probe the full underlying gravitational field, such as the observed peculiar velocity field, to provide an independent test on the robustness of these distinctive structures. Methods. We used a 500 h−1 Mpc constrained simulation of the Local Universe to investigate the anomalies in the local density field, as found in observations. Constructing the initial conditions based on peculiar velocities derived from the CosmicFlows-2 catalog makes the predictions of the simulations completely independent from the distribution of the observed tracer population, and following galaxy formation physics directly in the hydrodynamics simulations also allows the comparison to be based directly on the stellar masses of galaxies or X-ray luminosity of clusters. We also used the 2668 h−1 Mpc large cosmological box from the Magneticum simulations to evaluate the frequency of finding such anomalies in random patches within simulations. Results. We demonstrate that halos and galaxies in our constrained simulation trace the local dark matter density field very differently. Thus, this simulation reproduces the observed 50% underdensity of galaxy clusters and groups within the sphere of ≈100 Mpc when applying the same mass or X-ray luminosity limit used in the observed cluster sample (CLASSIX), which is consistent with a ≈1.5σ feature. At the same time, the simulation reproduces the observed overdensity of massive galaxy clusters within the same sphere, which on its own also corresponds to a ≈1.5σ feature. Interestingly, we find that only 44 out of 15 635 random realizations (i.e., 0.28%) match both anomalies, thus making the Local Universe a ≈3σ environment. We finally compared a mock galaxy catalog with the observed distribution of galaxies in the Local Universe, finding a match to the observed factor of 2 overdensity at ∼16 Mpc as well as the observed 15% underdensity at ∼40 Mpc. Conclusions. Constrained simulations of the Local Universe which reproduce the main features of the local density field open a new window for local field cosmology, where the imprint of the specific density field and the impact on the bias through the observational specific tracers can be investigated in detail.

Toward an Optimal Reconstruction of the Shear Field with PDF-folding

Weak lensing provides a direct way of mapping the density distribution in the Universe. To reconstruct the density field from the shear catalog, an important step is to build the shear field from the shear catalog, which can be quite nontrivial due to the inhomogeneity of the background galaxy distribution and the shape noise. We propose the PDF-folding method as a statistically optimal way of reconstructing the shear field. It is an extention of the PDF-SYM method, which was previously designed for optimizing the stacked shear signal as well as the shear-shear correlation for the Fourier_Quad shear estimators. PDF-folding does not require smoothing kernels as in traditional methods, therefore it suffers less information loss on small scales and avoids possible biases due to the spatial variation in the shear on the scale of the kernel. We show with analytic reasoning as well as numerical examples that the new method can reach the optimal signal-to-noise ratio on the reconstructed shear map under general observing conditions, i.e., with inhomogeneous background densities or masks. We also show the performance of the new method on real data around foreground galaxy clusters.

Probing massive neutrinos with the Minkowski functionals of the galaxy distribution

The characteristic signatures of massive neutrinos on large-scale structure (LSS), if fully captured, can be used to put a stringent constraint on their mass sum, Mν . Previous work utilizing N-body simulations has shown the Minkowski functionals (MFs) of LSS can reveal the imprints of massive neutrinos on LSS, provide important complementary information to two-point statistics, and significantly improve constraints on Mν . In this work, we take a step forward and apply the statistics to the biased tracers of LSS, i.e. the galaxies, and in redshift space. We perform a Fisher matrix analysis and quantify the constraining power of the MFs by using the Molino mock galaxy catalogs, which are constructed based on the halo occupation distribution (HOD) framework with parameters for the SDSS Mr < -21.5 and -22 galaxy samples. We find the MFs give tighter constraints on all of the cosmological parameters that we consider than the power spectrum. The constraints on Ωm, Ωb, h, ns , σ 8, and Mν from the MFs are better by a factor of 1.9, 2.9, 3.7, 4.2, 2.5, and 5.7, respectively, after marginalizing over the HOD parameters. Specifically, for Mν , we obtain a 1σ 8 constraint of 0.059 eV with the MFs alone for a volume of only (1h -1Gpc)3.