Open accessJournal Article

# Analytical halo models of cosmic tidal fields

02 Mar 2021-Monthly Notices of the Royal Astronomical Society (Oxford University Press (OUP))-Vol. 502, Iss: 4, pp 5210-5226
Abstract: The non-linear cosmic web environment of dark matter haloes plays a major role in shaping their growth and evolution, and potentially also affects the galaxies that reside in them. We develop an analytical (halo model) formalism to describe the tidal field of anisotropic halo-centric density distributions, as characterised by the halo-centric tidal tensor $\langle T_{ij} \rangle( ... read more Topics: Virial theorem (60%), Halo (52%) ##### Citations More 8 results found Open accessJournal Article Xiaoju Xu1, Idit Zehavi1, Sergio Contreras2Institutions (2) Abstract: Understanding the galaxy-halo connection is fundamental for contemporary models of galaxy clustering. The extent to which the haloes' assembly history and environment impact galaxy clustering (a.k.a. galaxy assembly bias; GAB), remains a complex and challenging problem. Using a semi-analytic galaxy formation model, we study the individual contributions of different secondary halo properties to the GAB signal. These are obtained by comparing the clustering of stellar-mass selected samples to that of shuffled samples where the galaxies are randomly reassigned to haloes of fixed mass and a specified secondary halo property. We explore a large range of internal halo properties and environmental measures. We find that commonly-used properties like the halo age or concentration amount to only 20-30% of the signal, while the smoothed matter density or the tidal anisotropy can explain the full level of GAB (though care should be given to the specific definition). For the successful'' measures, we examine the occupancy variations and the associated changes in the halo occupation function parameters. These are used to create mock catalogues which reproduce the full level of GAB. Finally, we propose a practical modification of the standard halo occupation distribution model, which can be tuned to any level of assembly bias. Fitting the parameters to our semi-analytic model, we demonstrate that the corresponding mock catalogue recovers the target level of GAB as well as the occupancy variations. Our results enable producing realistic mock catalogues and directly inform theoretical modelling of assembly bias and attempts to detect it in the Universe. ... read more Topics: , Halo (54%), ... read more 31 Citations Open accessJournal Article Abstract: At$z=0$, higher-spin haloes with masses above$\log(\text{M}_{\text{c}}/h^{-1}\text{M}_\odot)\simeq 11.5$have a higher bias than lower-spin haloes of the same mass. However, this trend is known to invert below this characteristic crossover mass,$\text{M}_{\text{c}}$. In this paper, we measure the redshift evolution and scale dependence of halo spin bias at the low-mass end and demonstrate that the inversion of the signal is entirely produced by the effect of splashback haloes. These low-mass haloes tend to live in the vicinity of significantly more massive haloes, thus sharing their large-scale bias properties. We further show that the location of the redshift-dependent crossover mass scale$\text{M}_{\text{c}}(z)$is completely determined by the relative abundance of splashbacks in the low- and high-spin subpopulations. Once splashback haloes are removed from the sample, the intrinsic mass dependence of spin bias is recovered. Since splashbacks have been shown to account for some of the assembly bias signal at the low-mass end, our results unveil a specific link between two different secondary bias trends: spin bias and assembly bias. ... read more 12 Citations Open accessJournal Article Abstract: We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias$b_1$and$b_2$on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy$\alpha$to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work which exploits the near-Lognormal shape of the distribution of$\alpha$and results in very high precision calibrations. We present convenient fitting functions for the dependence of$b_1$and$b_2$on$\alpha$over a wide range of halo mass for redshifts$0\leq z\leq1$. Our calibration of$b_2(\alpha)$is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results which showed that$\alpha$is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of$b_1$and$b_2$on any such secondary property which has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using$\alpha$as a segregating variable in multi-tracer analyses. ... read more Topics: Halo (58%), Halo effect (53%), Dark matter (52%) 10 Citations Open accessJournal Article Abstract: We explore the potential of the kinetic Sunyaev-Zel'dovich (kSZ) effect as the cornerstone of a future observational probe for halo spin bias, the secondary dependence of halo clustering on halo spin at fixed halo mass. Using the IllustrisTNG magneto-hydrodynamical cosmological simulation, we measure both the kSZ and the thermal SZ (tSZ) effects produced by the baryonic content of more than 50,000 haloes within the halo mass range$11 < \log_{10} ({\rm M_{vir}}/ h^{-1} {\rm M_{\odot}}) \lesssim 14.5$. First, we confirm that the magnitude of both effects depends strongly on the total gas and virial mass of the haloes, and that the integrated kSZ signal displays a significant correlation with the angular momentum of the intra-halo gas, particularly for massive haloes. Second, we show that both the integrated kSZ signal and the ratio of the integrated kSZ and tSZ signals trace total halo spin, even though significant scatter exists. Finally, we demonstrate that, in the absence of observational and instrumental uncertainties, these SZ-related statistics can be used to recover most of the underlying IllustrisTNG halo spin bias signal. Our analysis represents the first attempt to develop a future observational probe for halo spin bias, bringing forward alternative routes for measuring the secondary bias effects. ... read more Topics: Halo (58%), 6 Citations Open accessPosted Content Abstract: The environment-dependent bimodality of the distribution of stellar mass ($M_\ast$) and specific star formation rate (sSFR) of galaxies, and its explanation in terms of the central-satellite dichotomy, form a cornerstone of our current understanding of galaxy evolution in the hierarchical structure formation paradigm. We revisit this framework in the IllustrisTNG simulation in the context of the most extreme local tidal anisotropy$\alpha_{\rm peak}$experienced by each galaxy over cosmic time, which is an excellent proxy for environmental influence. We show that, while sharing a common monotonic$M_\ast$-$v_{\rm peak}$relation, central, satellite and `splashback' galaxies define a hierarchy of increasing$\alpha_{\rm peak}$. We also find that the sSFR of objects in small haloes unaffected by feedback from an active nucleus typically decreases with increasing$\alpha_{\rm peak}$. Our results support an alternate viewpoint in which a galaxy can be identified by the value of$\alpha_{\rm peak}\$; i.e., rather than being placed on the central-satellite dichotomy, a galaxy is better classified by its location in a continuum of tidal environments. This conceptual shift can potentially yield a more robust understanding of galaxy evolution and the galaxy-dark matter connection, e.g., in accurately modelling subtle effects such as sSFR-induced secondary clustering.

Topics: , Galaxy (54%), Star formation (51%)

5 Citations

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Abstract: We use high-resolution N-body simulations to study the equilibrium density profiles of dark matter halos in hierarchically clustering universes. We find that all such profiles have the same shape, independent of the halo mass, the initial density fluctuation spectrum, and the values of the cosmological parameters. Spherically averaged equilibrium profiles are well fitted over two decades in radius by a simple formula originally proposed to describe the structure of galaxy clusters in a cold dark matter universe. In any particular cosmology, the two scale parameters of the fit, the halo mass and its characteristic density, are strongly correlated. Low-mass halos are significantly denser than more massive systems, a correlation that reflects the higher collapse redshift of small halos. The characteristic density of an equilibrium halo is proportional to the density of the universe at the time it was assembled. A suitable definition of this assembly time allows the same proportionality constant to be used for all the cosmologies that we have tested. We compare our results with previous work on halo density profiles and show that there is good agreement. We also provide a step-by-step analytic procedure, based on the Press-Schechter formalism, that allows accurate equilibrium profiles to be calculated as a function of mass in any hierarchical model.

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Abstract: High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r -2 near the center and steeper than r -2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.

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