ΛCDM Simulations Research Articles

How Do Primordial Black Holes Change the Halo Mass Function and Structure?

We examine the effects of massive primordial black holes (PBHs) on cosmic structure formation, employing both a semianalytical approach and cosmological simulations. Our simulations incorporate PBHs with a monochromatic mass distribution centered around 106 M ⊙, constituting a fraction of 10−2 to 10−4 of the dark matter (DM) in the Universe, with the remainder being collisionless particle DM. Additionally, we conduct a ΛCDM simulation for comparative analysis with runs that include PBHs. At smaller scales, halos containing PBHs exhibit similar density and velocity dispersion profiles to those without PBHs. Conversely, at larger scales, PBHs can expedite the formation of massive halos and reside at their centers owing to the “seed effect.” To analyze the relative distribution of PBH host halos compared to non-PBH halos, we apply nearest neighbor statistics. Our results suggest that PBH host halos, through gravitational influence, significantly impact the structure formation process, compared to the ΛCDM case, by attracting and engulfing nearby newly formed minihalos. Should PBHs constitute a fraction of DM significantly larger than ∼10−3, almost all newly formed halos will be absorbed by PBH-seeded halos. Consequently, our simulations predict a bimodal feature in the halo mass function, with most of the massive halos containing at least one PBH at their core and the rest being less massive non-PBH halos.

Fast simulation mapping: From standard to modified gravity cosmologies using the bias assignment method

Context. We assess the effectiveness of a non-parametric bias model in generating mock halo catalogues for modified gravity (MG) cosmologies, relying on the distribution of dark matter from either MG or Λ cold dark matter (ΛCDM) simulations. Aims. We aim to generate halo catalogues that effectively capture the distinct impact of MG, ensuring high accuracy in both two- and three-point statistics for a comprehensive analysis of large-scale structures. We investigated the inclusion of MG in non-local bias to directly map the tracers onto ΛCDM fields, which would significantly reduce computational costs. Methods. We employed the bias assignment method (BAM) to model halo distribution statistics by leveraging seven high-resolution COLA simulations of MG cosmologies. Taking cosmic-web dependences into account when learning the bias relations, we designed two experiments to map the MG effects: one utilising the consistent MG density fields and the other employing the benchmark ΛCDM density field. Results. BAM generates MG halo catalogues from both calibration experiments with excellent summary statistics, achieving a ~1% accuracy in the power spectrum across a wide range of k modes, with minimal differences well below 10% for modes subject to cosmic variance, particularly below k < 0.07 h Mpc−1. The reduced bispectrum remains consistent with the reference catalogues within 10% for the studied configuration. Our results demonstrate that a non-linear and non-local bias description can model the effects of MG starting from a ΛCDM field.

The satellite galaxy plane of NGC 4490 in light of ΛCDM

Context. The system of galaxies around NGC 4490 was recently highlighted to display a flattened, kinematically correlated structure reminiscent of planes of satellite galaxies around other hosts. Aims. Since known satellite planes are in tension with expectations from cosmological simulations in the Λ cold dark matter (ΛCDM) model, we aim to quantitatively assess for the first time the tension posed by the NGC 4490 system. Methods. We measured the on-sky flattening as the major-to-minor axis ratio b/a of the satellite distribution and their line-of-sight kinematic correlation. Analogs to the system were selected in the TNG50 simulation and their flattening and correlation were similarly measured. Results. We confirm the strong kinematic coherence of all 12 observed satellite objects with available line-of-sight velocities (of 14 in total): the northern ones approach and the southern ones recede relative to the host. The spatial distribution of all 14 objects is substantially flattened with b/a = 0.38 (0.26 considering only the 12 objects with available velocities). Such extreme arrangements are rare in the ΛCDM simulation, at a level of 0.21 to 0.35%. This fraction of analogs would drop further if at least one of the two satellite objects without velocities is confirmed to follow the kinematic trend, and would become zero if both are rejected as non-members. We also identify a likely galaxy pair in the observed system, and find a similar pair in the best-matching simulated analog. Conclusions. Our measurements establish NGC 4490 as another strong example of a satellite plane in the Local Volume. This emphasizes that planes of satellites are a more general issue faced by ΛCDM also beyond the Local Group. The tension with typical systems drawn from simulations suggests that the observed one requires a specific formation scenario, potentially connected to the larger-scale galaxy alignment in its vicinity. The presence of galaxy pairs in the observed and a simulated system hints at the importance such groupings may have to understand satellite planes.

The Galaxy–Galaxy Strong Lensing Cross Section and the Internal Distribution of Matter in ΛCDM Substructure

Strong gravitational lensing offers a powerful probe of the detailed distribution of matter in lenses, while magnifying and bringing faint background sources into view. Observed strong lensing by massive galaxy clusters, which are often in complex dynamical states, has also been used to map their dark matter (DM) substructures on smaller scales. Deep high-resolution imaging has revealed the presence of strong lensing events associated with these substructures, namely galaxy-scale sub-halos. However, an inventory of these observed galaxy–galaxy strong lensing (GGSL) events is noted to be discrepant with state-of-the-art ΛCDM simulations. Cluster sub-halos appear to be over-concentrated compared to their simulated counterparts yielding an order-of-magnitude higher value of GGSL. In this paper, we explore the possibility of resolving this observed discrepancy by redistributing the mass within observed cluster sub-halos in ways that are consistent within the ΛCDM paradigm of structure formation. Lensing mass reconstructions from data provide constraints on the mass enclosed within apertures and are agnostic to the detailed mass profile within them. Therefore, as the detailed density profile within cluster sub-halos currently remains unconstrained by data, we are afforded the freedom to redistribute the enclosed mass. We investigate if rearranging the mass to a more centrally concentrated density profile helps alleviate the GGSL discrepancy. We report that refitting cluster sub-halos to the ubiquitous ΛCDM-motivated Navarro–Frenk–White profile, and further modifying them to include significant baryonic components, does not resolve this tension. A resolution to this persisting GGSL discrepancy may require more careful exploration of alternative DM models.

Multiple Beads on a String: Dark-matter-deficient Galaxy Formation in a Mini-Bullet Satellite–Satellite Galaxy Collision

Dark-matter-deficient galaxies (DMDGs) discovered in the survey of ultra-diffuse galaxies (UDGs), in apparent conflict with standard cold dark matter, may be produced by high-velocity galaxy–galaxy collisions, the so-called Mini-Bullet scenario. Recent observations of an aligned trail of 7–11 UDGs near NGC 1052, including DMDGs DF2 and DF4, suggesting a common formation event, ∼8.9 ± 1.5 Gyr ago, provide a test.Hydro/N-body simulations, supplemented by galaxy orbit integrations, demonstrate that satellite–satellite collisions outside the host-galaxy virial radius can reproduce the observed UDGs in the NGC 1052 group. A trail of ∼10 DMDGs is shown to form, including 2 massive ones that replicate the observed motions of DF2 and DF4. The linear relation, v = A x + v 0, conjectured previously to relate positions ( x ) and velocities ( v ) of the aligned DMDGs as a signature of the collision event, is approximately obeyed, but individual DMDGs can deviate significantly from it. The progenitors whose collision spawned the trail of DMDGs survive the collision without themselves becoming DMDGs. We predict that one progenitor is located at the end of the trail, which can be tested by observing the difference between its stars, formed pre-collision, from those of the DMDGs, formed post-collision. By contrast, stellar ages and metallicities of the DMDGs are nearly identical. We further offer a hint that the tidal field of host NGC 1052 may contribute to making DMDGs diffuse. ΛCDM simulation in a 100 cMpc box finds our required initial conditions ∼10 times at z < 3. These results indicate current observations are consistent with the Mini-Bullet scenario.

The Three Hundred: Msub–Vcirc relation

ABSTRACT In this study, we investigate a recent finding based on strong lensing observations, which suggests that the sub-haloes observed in clusters exhibit greater compactness compared to those predicted by ΛCDM simulations. To address this discrepancy, we compare the cumulative sub-halo mass function and the Msub–Vcirc relation between observed clusters and 324 simulated clusters from $\rm \small {The\,Three\,\,Hundred}$ project, focusing on the hydrodynamic resimulations using $\rm \small {Gadget-X}$ and $\rm \small {Gizmo-Simba}$ baryonic models. The cumulative sub-halo mass function of $\rm \small {Gizmo-Simba}$ simulated clusters aligns with observations, while $\rm \small {Gadget-X}$ simulations exhibit discrepancies in the lower sub-halo mass range, possibly due to its strong supernova feedback. Both $\rm \small {Gadget-X}$ and $\rm \small {Gizmo-Simba}$ simulations demonstrate a redshift evolution of the sub-halo mass function and the Vcirc function, with slightly fewer sub-haloes observed at lower redshifts. Neither the $\rm \small {Gadget-X}$ nor $\rm \small {Gizmo-Simba}$ (albeit a little closer) simulated clusters’ predictions for the Msub–Vcirc relation align with the observational result. Further investigations on the correlation between sub-halo/halo properties and the discrepancy in the Msub–Vcirc relation reveal that the sub-halo’s half mass radius and galaxy stellar age, the baryon fraction, and sub-halo distance from the cluster’s centre, as well as the halo relaxation state, play important roles on reproducing this relation. Nonetheless, challenges persist in accurately reproducing the observed Msub–Vcirc relationship within our current hydrodynamic cluster simulation that adheres to the standard ΛCDM cosmology. These challenges may stem from shortcomings in our baryon modelling, numerical intricacies within the simulation, or even potential limitations of the ΛCDM framework.

The e-MANTIS emulator: fast predictions of the non-linear matter power spectrum in f(R)CDM cosmology

ABSTRACT In order to probe modifications of gravity at cosmological scales, one needs accurate theoretical predictions. N-body simulations are required to explore the non-linear regime of structure formation but are very time consuming. In this work, we release a new public emulator, dubbed e-mantis, that performs an accurate and fast interpolation between the predictions of f(R) modified gravity cosmological simulations, run with ecosmog. We sample a wide 3D parameter space given by the current background scalar field value $10^{-7}\lt \left|f_{R_0}\right|\lt 10^{-4}$, matter density 0.24 &amp;lt; Ωm &amp;lt; 0.39, and primordial power spectrum normalization 0.6 &amp;lt; σ8 &amp;lt; 1.0, with 110 points sampled from a Latin hypercube. For each model we perform pairs of f(R)CDM and ΛCDM simulations covering an effective volume of $\left(560 \, h^{-1}\, \mathrm{Mpc}\right)^3$ with a mass resolution of ∼2 × 1010h−1M⊙. We build an emulator for the matter power spectrum boost B(k) = Pf(R)(k)/PΛCDM(k) using a Gaussian process regression method. The boost is mostly independent of h, ns, and Ωb, which reduces the dimensionality of the relevant cosmological parameter space. Additionally, it is more robust against statistical and systematic errors than the raw power spectrum, thus strongly reducing our computational needs. According to our dedicated study of numerical systematics, the resulting emulator has an estimated maximum error of 3 per cent across the whole cosmological parameter space, for scales $0.03 \ h\, \mathrm{Mpc}^{-1} \lt k \lt 7 \ h\, \mathrm{Mpc}^{-1}$, and redshifts 0 &amp;lt; z &amp;lt; 2, while in most cases the accuracy is better than 1 per cent. Such an emulator could be used to constrain f(R) gravity with weak lensing analyses.

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 exploited the gravitational velocity field computed using the CosmicFlows-4 catalog of galaxy distances in order to delineate superclusters as watersheds, publishing for the first time their size, shape, main streams of matter, and the location of their central attractor. We confirm the size of Laniakea, our home supercluster, to be 2 × 106 (Mpc h−1)3. We dynamically define five more known superclusters in the same way as Laniakea: Apus, Hercules, Lepus, Perseus-Pisces, and Shapley. Additionally, we found the central repellers of the Bootes and Sculptor voids, and based on our analysis, the Dipole and Cold Spot repellers appear as a single gigantic entity. Interestingly, the observed superclusters are an order of magnitude larger than the theoretical ones predicted by cosmological ΛCDM simulations.

Densities and mass assembly histories of the Milky Way satellites are not a challenge to ΛCDM

ABSTRACT We use the GRUMPY galaxy formation model based on a suite of zoom-in, high-resolution, dissipationless Λ Cold Dark Matter (ΛCDM) simulations of the Milky Way (MW) sized haloes to examine total matter density within the half-mass radius of stellar distribution, ρtot(&amp;lt; r1/2), of satellite dwarf galaxies around the MW hosts and their mass assembly histories. We compare model results to ρtot(&amp;lt; r1/2) estimates for observed dwarf satellites of the Milky Way spanning their entire luminosity range. We show that observed MW dwarf satellites exhibit a trend of decreasing total matter density within a half-mass radius, ρtot(&amp;lt; r1/2), with increasing stellar mass. This trend is in general agreement with the trend predicted by the model. None of the observed satellites are overly dense compared to the results of our ΛCDM-based model. We also show that although the halo mass of many satellite galaxies is comparable to the halo mass of the MW progenitor at z ≳ 10, at these early epochs halos that survive as satellites to z = 0 are located many virial radii away from the MW progenitors and thus do not have a chance to merge with it. Our results show that neither the densities estimated in observed Milky Way satellites nor their mass assembly histories pose a challenge to the ΛCDM model. In fact, the broad agreement between density trends with the stellar mass of the observed and model galaxies can be considered as yet another success of the model.

Learning Neutrino Effects in Cosmology with Convolutional Neural Network

Measuring the sum of the three active neutrino masses, M ν , is one of the most important challenges in modern cosmology. Massive neutrinos imprint characteristic signatures on several cosmological observables, in particular, on the large-scale structure of the universe. In order to maximize the information that can be retrieved from galaxy surveys, accurate theoretical predictions in the nonlinear regime are needed. Currently, one way to achieve those predictions is by running cosmological numerical simulations. Unfortunately, producing those simulations requires high computational resources—several hundred to thousand core hours for each neutrino mass case. In this work, we propose a new method, based on a deep-learning network (D3M), to quickly generate simulations with massive neutrinos from standard ΛCDM simulations without neutrinos. We computed multiple relevant statistical measures of deep-learning generated simulations and conclude that our approach is an accurate alternative to the traditional N-body techniques. In particular the power spectrum is within ≃6% down to nonlinear scales k = 0.7 h Mpc−1. Finally, our method allows us to generate massive neutrino simulations 10,000 times faster than the traditional methods.

A test of invariance of dark matter halo surface density using multiwavelength mock galaxy catalogues

ABSTRACT A large number of observations have shown that the dark matter halo surface density, given by the product of halo core radius and core density, is nearly constant for a diverse suite of galaxies. Although this invariance of the halo surface density is violated at galaxy cluster and group scales, it is still an open question on whether the aforementioned constancy on galactic scales can be explained within Lambda cold dark matter (ΛCDM). For this purpose, we probe the variation of halo surface density as a function of mass using multiwavelength mock galaxy catalogues from ΛCDM simulations, where the adiabatic contraction of dark matter haloes in the presence of baryons has been taken into account. We find that these baryonified ΛCDM haloes were best fitted with a generalized Navarro–Frenk–White profile, and the halo surface density from these haloes has a degeneracy with respect to both the halo mass and the virial concentration. We find that the correlation with mass when averaged over concentration is consistent with a constant halo surface density. However, a power-law dependence as a function of halo mass also cannot be ruled out.

A possible dwarf galaxy satellite-of-satellite problem in ΛCDM

Dark matter clusters on all scales, and it is therefore expected that even substructure should host its own substructure. Using the Extragalactic Distance Database, we searched for dwarf-galaxy satellites of dwarf galaxies, that is, satellite-of-satellite galaxies, corresponding to these substructures of substructure. From investigation of Hubble Space Telescope data for 117 dwarf galaxies, we report the discovery of a previously unknown dwarf galaxy around the ultra-diffuse M96 companion M96-DF6 at 10.2 Mpc in the Leo-I group. We confirm its dwarf-galaxy nature as a stellar overdensity. Modeling its structural parameters with a growth-curve analysis, we find that it is an ultrafaint dwarf galaxy with a luminosity of 1.5 × 105 L⊙, which is 135 times fainter than its host. Based on its close projection to M96-DF6, it is unlikely that their association occurs simply by chance. We compare the luminosity ratio of this and three other known satellite-of-satellite systems with results from two different cosmological sets of ΛCDM simulations. For the observed stellar mass range of the central dwarf galaxies, the simulated dwarfs have a higher luminosity ratio between the central dwarf and its first satellite (≈10 000) than observed (≈100), excluding the Large and Small Magellanic Cloud (LMC/SMC) system. No simulated dwarf analog at these observed stellar masses has the observed luminosity ratio. This cannot be due to missing resolution, because it is the brightest subhalos that are missing. This may indicate that there is a satellite-of-satellite (SoS) problem for ΛCDM in the stellar-mass range between 106 and 108 M⊙, the regime of the classical dwarf galaxies. However, simulated dwarf models at both a lower (&lt; 106 M⊙) and higher (&gt; 108 M⊙) stellar mass have comparable luminosity ratios. For the higher-stellar-mass systems, the LMC/SMC system is reproduced by simulations; for the lower stellar masses, no observed satellite-of-satellite system has been observed to date. More observations and simulations of satellite-of-satellite systems are needed to assess whether the luminosity ratio is at odds with ΛCDM.

Lopsided Satellite Distributions around Isolated Host Galaxies in a ΛCDM Universe

A recent observational study found that the projected spatial distributions of the satellites of bright, isolated host galaxies tend to be lopsided with respect to the locations of the hosts. Here, we examine the spatial distributions of the satellites of a large number of bright, isolated host galaxies that were obtained from mock redshift surveys of a Λ-cold dark matter (ΛCDM) simulation. Host galaxies and their satellites were identified using selection criteria that are identical to those used in the observational study, allowing for a direct comparison of the results for the simulated and observed systems. To characterize the spatial distribution of the satellites, we adopt two statistics: (1) the pairwise clustering of the satellites and (2) the mean resultant length. In agreement with the observational study, we find a strong tendency for satellites in the simulation to be located on the same side of their host, and the signal is most pronounced for the satellites of blue hosts. These lopsided satellite distributions are not solely attributable to incompleteness of the observed satellite catalog or the presence of objects that have been falsely identified as satellites. In addition, satellites that joined their hosts’ halos in the distant past (≳8 Gyr) show a pronounced lopsidedness in their spatial distributions and, therefore, the lopsidedness is not solely attributable to the late-time accretion of satellites.

The Concentration–Mass relation of massive, dynamically relaxed galaxy clusters: agreement between observations and ΛCDM simulations

ABSTRACT The relationship linking a galaxy cluster’s total mass with the concentration of its mass profile and its redshift is a fundamental prediction of the Cold Dark Matter (CDM) paradigm of cosmic structure formation. However, confronting those predictions with observations is complicated by the fact that simulated clusters are not representative of observed samples where detailed mass profile constraints are possible. In this work, we calculate the symmetry-peakiness-alignment (SPA) morphology metrics for maps of X-ray emissivity from the three hundred project hydrodynamical simulations of galaxy clusters at four redshifts, and thereby select a sample of morphologically relaxed, simulated clusters, using observational criteria. These clusters have on average earlier formation times than the full sample, confirming that they are both morphologically and dynamically more relaxed than typical. We constrain the concentration–mass–redshift relation of both the relaxed and complete sample of simulated clusters, assuming power-law dependences on mass (κm) and 1 + z (κζ), finding κm = −0.12 ± 0.07 and κζ = −0.27 ± 0.19 for the relaxed subsample. From an equivalently selected sample of massive, relaxed clusters observed with Chandra, we find κm = −0.12 ± 0.08 and κζ = −0.48 ± 0.19, in good agreement with the simulation predictions. The simulated and observed samples also agree well on the average concentration at a pivot mass and redshift providing further validation of the ΛCDM paradigm in the properties of the largest gravitationally collapsed structures observed. This also represents the first clear detection of decreasing concentration with redshift, a longstanding prediction of simulations in data.

The time evolution of bias

ABSTRACT We investigate the time evolution of bias of cosmic density fields. We perform numerical simulations of the evolution of the cosmic web for the conventional Λ cold dark matter (ΛCDM) model. The simulations cover a wide range of box sizes $L=256\rm{-}1024\,h^{-1}\, {\rm Mpc}$, and epochs from very early moments z = 30 to the present moment z = 0. We calculate spatial correlation functions of galaxies, ξ(r), using dark matter particles of the biased Lambda cold dark mattter (ΛCDM) simulation. We analyse how these functions describe biasing properties of the evolving cosmic web. We find that for all cosmic epochs the bias parameter, defined through the ratio of correlation functions of selected samples and matter, depends on two factors: the fraction of matter in voids and in the clustered population, and the luminosity (mass) of galaxy samples. Gravity cannot evacuate voids completely, thus there is always some unclustered matter in voids, and the bias parameter of galaxies is always greater than unity, over the whole range of evolution epochs. We find that for all cosmic epochs bias parameter values form regular sequences, depending on galaxy luminosity (particle density limit), and decreasing with time.

Bar formation in submaximal discs: a challenge for ΛCDM

ABSTRACT Bar formation in cosmological simulations of galaxy formation remains challenging. It was previously shown that the fraction of barred galaxies at low stellar masses (M* &amp;lt; 1010.5 M⊙) in TNG50 is too low compared to the observations. Here, we highlight another tension, also observed at higher stellar masses, namely that barred galaxies in TNG50 appear to be maximal discs, in the sense that the majority of the gravitational acceleration is accounted for by baryons at the peak radius of the baryonic rotation curve, while observations account for a substantial fraction of barred submaximal discs. In this letter, we compare the barred fraction of submaximal discs in the local Universe from the SPARC catalogue with that in the TNG50 simulation. We show that, although SPARC tends to select against barred galaxies, the fraction of barred submaximal discs in this data set is significantly larger than in TNG50. This result adds to the list of challenges related to predicting the right statistics and properties of barred galaxies in ΛCDM simulations of galaxy formation.

Distinguishing between ΛCDM and f(R) gravity models using halo ellipticity correlations in simulations

ABSTRACT There is a growing interest in utilizing intrinsic alignment (IA) of galaxy shapes as a geometric and dynamical probe of cosmology. In this paper, we present the first measurements of IA in a modified gravity model using the gravitational shear-intrinsic ellipticity correlation (GI) and intrinsic ellipticity-ellipticity correlation (II) functions of dark-matter haloes from f(R) gravity simulations. By comparing them with the same statistics measured in Lambda cold dark matter (ΛCDM) simulations, we find that the IA statistics in different gravity models show distinguishable features, with a trend similar to the case of conventional galaxy clustering statistics. Thus, the GI and II correlations are found to be useful in distinguishing between the ΛCDM and f(R) gravity models. More quantitatively, IA statistics enhance detectability of the imprint of f(R) gravity on large-scale structures by $\sim 40{{\ \rm per\ cent}}$ when combined with the conventional halo clustering in redshift space. We also find that the correlation between the axial ratio and orientation of haloes becomes stronger in f(R) gravity than that in ΛCDM. Our results demonstrate the usefulness of IA statistics as a probe of gravity beyond a consistency test of ΛCDM and general relativity.

Solitons in the dark: First approach to non-linear structure formation with fuzzy dark matter

We present the results of a full cosmological simulation with the new codeSCALAR, where dark matter is in the form of fuzzy dark matter (FDM), described by a light scalar field with a mass ofmB = 2.5 × 10−22eV and evolving according to the Schrödinger-Poisson system of equations. In comoving units, the simulation volume is 2.5 h−1Mpc on a side, with a resolution of 20 h−1pc at the highest refinement level. While the resulting large-scale resolution prevents us from studying the general properties of the FDM structure formation, the extremely high small-scale resolution allows a detailed analysis of the formation and evolution of central solitonic cores, which are found to leave their imprints on dark matter density profiles, resulting in shallower central densities, and on rotation curves, producing an additional circular velocity peak at small radii from the centre. Despite the limitations on the large-scale resolution, we find that the suppression of structures due to the quantum nature of the scalar field reveals indications of a shallower halo mass function in the low-mass end compared to the case of a ΛCDM simulation, in which dark matter is expected to cluster at all mass scales even if it was evolved with the same initial conditions as used for FDM. Furthermore, we verify the scaling relations characterising the solution to the Schrödinger–Poisson system for both isolated and merging haloes, and we find that they are preserved by merging processes. We characterise each FDM halo in terms of the dimensionless quantity Ξ ∝ Ehalo/Mhalo3, and we show that the core mass is tightly linked to the halo mass by the core–halo mass relationMcore/Mhalo ∝ Ξ1/3. We also show that the core surface density of the simulated FDM haloes does not follow the scaling with the core radius, as observed for dwarf galaxies. This is a challenge for the FDM model as the sole explanation of core formation.

CII] line intensity mapping the epoch of reionization with the Prime-Cam on FYST

Aims. We predict the three-dimensional intensity power spectrum (PS) of the [CII] 158 μm line throughout the epoch of (and post) reionization at redshifts from ≈3.5 to 8. We study the detectability of the PS in a line intensity mapping (LIM) survey with the Prime-Cam spectral-imager on the Fred Young Submillimeter Telescope (FYST). Methods. We created mock [CII] tomographic scans in redshift bins at z ≈ 3.7, 4.3, 5.8, and 7.4 using the Illustris TNG300-1 ΛCDM simulation and adopting a relation between the star formation activity and the [CII] luminosity (L[CII]) of galaxies. A star formation rate (SFR) was assigned to a dark matter halo in the Illustris simulation in two ways: (i) we adopted the SFR computed in the Illustris simulation and, (ii) we matched the abundance of the halos with the SFR traced by the observed dust-corrected ultraviolet luminosity function of high-redshift galaxies. The L[CII] is related to the SFR from a semi-analytic model of galaxy formation, from a hydrodynamical simulation of a high-redshift galaxy, or from a high-redshift [CII] galaxy survey. The [CII] intensity PS was computed from mock tomographic scans to assess its detectability with the anticipated observational capability of the FYST. Results. The amplitude of the predicted [CII] intensity power spectrum varies by more than a factor of 10, depending on the choice of the halo-to-galaxy SFR and the SFR-to-L[CII] relations. In the planned 4° ×4° FYST LIM survey, we expect a detection of the [CII] PS up to z ≈ 5.8, and potentially even up to z ≈ 7.4. The design of the envisioned FYST LIM survey enables a PS measurement not only in small (&lt; 10 Mpc) shot noise-dominated scales, but also in large (&gt; 50 Mpc) clustering-dominated scales making it the first LIM experiment that will place constraints on the SFR-to-L[CII] and the halo-to-galaxy SFR relations simultaneously.

The High Fraction of Thin Disk Galaxies Continues to Challenge ΛCDM Cosmology

Abstract Any viable cosmological framework has to match the observed proportion of early- and late-type galaxies. In this contribution, we focus on the distribution of galaxy morphological types in the standard model of cosmology (Lambda cold dark matter, ΛCDM). Using the latest state-of-the-art cosmological ΛCDM simulations known as Illustris, IllustrisTNG, and EAGLE, we calculate the intrinsic and sky-projected aspect ratio distribution of the stars in subhalos with stellar mass M * &gt; 1010 M ⊙ at redshift z = 0. There is a significant deficit of intrinsically thin disk galaxies, which however comprise most of the locally observed galaxy population. Consequently, the sky-projected aspect ratio distribution produced by these ΛCDM simulations disagrees with the Galaxy And Mass Assembly (GAMA) survey and Sloan Digital Sky Survey at ≥12.52σ (TNG50-1) and ≥14.82σ (EAGLE50) confidence. The deficit of intrinsically thin galaxies could be due to a much less hierarchical merger-driven build-up of observed galaxies than is given by the ΛCDM framework. It might also arise from the implemented sub-grid models, or from the limited resolution of the above-mentioned hydrodynamical simulations. We estimate that an 85 times better mass resolution realization than TNG50-1 would reduce the tension with GAMA to the 5.58σ level. Finally, we show that galaxies with fewer major mergers have a somewhat thinner aspect ratio distribution. Given also the high expected frequency of minor mergers in ΛCDM, the problem may be due to minor mergers. In this case, the angular momentum problem could be alleviated in Milgromian dynamics because of a reduced merger frequency arising from the absence of dynamical friction between extended dark matter halos.