High-mass Haloes Research Articles

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: exploring the halo occupation distribution model for emission line galaxies

ABSTRACT We study the modelling of the halo occupation distribution (HOD) for the eBOSS DR16 emission line galaxies (ELGs). Motivated by previous theoretical and observational studies, we consider different physical effects that can change how ELGs populate haloes. We explore the shape of the average HOD, the fraction of satellite galaxies, their probability distribution function (PDF), and their density and velocity profiles. Our baseline HOD shape was fitted to a semi-analytical model of galaxy formation and evolution, with a decaying occupation of central ELGs at high halo masses. We consider Poisson and sub/super-Poissonian PDFs for satellite assignment. We model both Navarro–Frenk–White and particle profiles for satellite positions, also allowing for decreased concentrations. We model velocities with the virial theorem and particle velocity distributions. Additionally, we introduce a velocity bias and a net infall velocity. We study how these choices impact the clustering statistics while keeping the number density and bias fixed to that from eBOSS ELGs. The projected correlation function, wp, captures most of the effects from the PDF and satellites profile. The quadrupole, ξ2, captures most of the effects coming from the velocity profile. We find that the impact of the mean HOD shape is subdominant relative to the rest of choices. We fit the clustering of the eBOSS DR16 ELG data under different combinations of the above assumptions. The catalogues presented here have been analysed in companion papers, showing that eBOSS RSD+BAO measurements are insensitive to the details of galaxy physics considered here. These catalogues are made publicly available.

The stellar mass assembly of low-redshift, massive, central galaxies in SDSS and the TNG300 simulation

ABSTRACT The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim 90\, 000$ low-redshift, central galaxies selected from SDSS group catalogues ($M_{\rm Stellar}\gtrsim 10^{9.5}\, \mathrm{M}_{\odot }$, $M_{\rm Halo}\gtrsim 10^{12}\, \mathrm{M}_{\odot }$) as a function of both stellar mass and halo mass. We use estimates of the times at which 10, 50, and 90 per cent of the stellar mass were assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar mass and halo mass simultaneously, finding dependences of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a subsample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar mass or halo mass. However, some differences in the assembly times (of up to ∼3 Gyr) appear when considering both stellar mass and halo mass simultaneously, noticeably at intermediate stellar masses (MStellar ∼ 1011 M⊙). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode active galactic nucleus feedback implemented in TNG300.

Conditions for galaxy quenching at 0.5 < z < 2.5 from CANDELS: compact cores and environment

We investigate two classes of conditions for galaxy quenching at 0.5 < z < 2.5 based on the structural scaling relations of galaxies in the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields: the formation of a compact core and the environment. We confirm that in the entire redshift range, massive quiescent galaxies (M* > 1010 M⊙) have much higher stellar mass surface densities within the central 1 kpc (Σ1) and smaller sizes than star-forming galaxies in the same stellar mass range. In addition, the quiescent fractions significantly increase with the increase of Σ1 regardless of whether galaxies are centrals or satellites. In contrast, we find that the overall lower-mass quiescent galaxies (M* <∼ 1010 M⊙) have slightly higher Σ1 and comparable sizes compared to star-forming galaxies of the same mass and at the same redshift. At z < 1.5, satellites have higher halo masses and larger quiescent fractions than those of centrals at a given Σ1 (stellar mass). Our findings indicate that the significant growth of the galaxy cores is closely related to the quenching of massive galaxies since z ∼ 2.5, while the environmental effect plays an important role in the quenching of low-mass galaxies at z ≲ 1.5.

Galactic ionizing photon budget during the epoch of reionization in the Cosmic Dawn II simulation

ABSTRACT Cosmic Dawn II yields the first statistically meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully coupled radiation-hydrodynamics simulation of the epoch of reionization large enough (∼100 Mpc) to model global reionization while resolving the formation of all galactic haloes above ${\sim}10^8 \, {\rm M}_{\odot }$. Cell transmission inside haloes is bi-modal – ionized cells are transparent, while neutral cells absorb the photons their stars produce – and the halo escape fraction fesc reflects the balance of star formation rate (SFR) between these modes. The latter is increasingly prevalent at higher halo mass, driving down fesc (we provide analytical fits to our results), whereas halo escape luminosity, proportional to fesc × SFR, increases with mass. Haloes with dark matter masses within $6\times 10^{8} \, {\rm M}_{\odot }\lt M_{\rm halo}\lt 3 \times 10^{10} \, {\rm M}_{\odot }$ produce ∼80 per cent of the escaping photons at z = 7, when the universe is 50 per cent ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10 per cent of the photon budget then, despite their high fesc. High-mass haloes are too few and too opaque, contributing &amp;lt;10 per cent despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z = 8.5, xH i = 0.9, $M_{\rm halo}\lt 5\times 10^9 \, {\rm M}_{\odot }$ haloes contributed ∼80 per cent). Galaxies with UV magnitudes MAB1600 between −12 and −19 dominated reionization between z = 6 and 8.

Structural diversity of disc galaxies originating in the cold gas inflow from cosmic webs

ABSTRACT Disc galaxies show a large morphological diversity with varying contribution of three major structural components: thin discs, thick discs, and central bulges. Dominance of bulges increases with the galaxy mass (Hubble sequence), whereas thick discs are more prominent in lower mass galaxies. Because galaxies grow with the accretion of matter, this observed variety should reflect diversity in accretion history. On the basis of the prediction by the cold-flow theory for galactic gas accretion and inspired by the results of previous studies, we put a hypothesis that associates different accretion modes with different components. Namely, thin discs form as the shock-heated hot gas in high-mass haloes gradually accretes to the central part, thick discs grow by the direct accretion of cold gas from cosmic webs when the halo mass is low, and finally bulges form by the inflow of cold gas through the shock-heated gas in high-redshift massive haloes. We show that this simple hypothesis reproduces the mean observed variation of galaxy morphology with the galaxy mass. This scenario also predicts that thick discs are older and poorer in metals than thin discs, in agreement with the currently available observations.

The stellar-to-halo mass relation over the past 12 Gyr

Aims. Understanding the link between the galaxy properties and the dark matter halos they reside in and their coevolution is a powerful tool for constraining the processes related to galaxy formation. In particular, the stellar-to-halo mass relation (SHMR) and its evolution throughout the history of the Universe provides insights on galaxy formation models and allows us to assign galaxy masses to halos in N-body dark matter simulations. To address these questions, we determine the SHMR throughout the entire cosmic history from z ∼ 4 to the present. Methods. We used a statistical approach to link the observed galaxy stellar mass functions on the COSMOS field to dark matter halo mass functions up to z ∼ 4 from the ΛCDM DUSTGRAIN-pathfinder simulation, which is complete for Mh &gt; 1012.5 M⊙, and extended this to lower masses with a theoretical parameterization. We propose an empirical model to describe the evolution of the SHMR as a function of redshift (either in the presence or absence of a scatter in stellar mass at fixed halo mass), and compare the results with several literature works and semianalytic models of galaxy formation. We also tested the reliability of our results by comparing them to observed galaxy stellar mass functions and to clustering measurements. Results. We derive the SHMR from z = 0 to z = 4, and model its empirical evolution with redshift. We find that M*/Mh is always lower than ∼0.05 and depends both on redshift and halo mass, with a bell shape that peaks at Mh ∼ 1012 M⊙. Assuming a constant cosmic baryon fraction, we calculate the star-formation efficiency of galaxies and find that it is generally low; its peak increases with cosmic time from ∼30% at z ∼ 4 to ∼35% at z ∼ 0. Moreover, the star formation efficiency increases for increasing redshifts at masses higher than the peak of the SHMR, while the trend is reversed for masses lower than the peak. This indicates that massive galaxies (i.e., galaxies hosted at halo masses higher than the SHMR peak) formed with a higher efficiency at higher redshifts (i.e., downsizing effect) and vice versa for low-mass halos. We find a large scatter in results from semianalytic models, with a difference of up to a factor ∼8 compared to our results, and an opposite evolutionary trend at high halo masses. By comparing our results with those in the literature, we find that while at z ∼ 0 all results agree well (within a factor of ∼3), at z &gt; 0 many differences emerge. This suggests that observational and theoretical work still needs to be done. Our results agree well (within ∼10%) with observed stellar mass functions (out to z = 4) and observed clustering of massive galaxies (M* &gt; 1011 M⊙ from z ∼ 0.5 to z ∼ 1.1) in the two-halo regime.

Multi-wavelength Properties of Radio- and Machine-learning-identified Counterparts to Submillimeter Sources in S2COSMOS

We identify multi-wavelength counterparts to 1,147 submillimeter sources from the S2COSMOS SCUBA-2 survey of the COSMOS field by employing a recently developed radio$+$machine-learning method trained on a large sample of ALMA-identified submillimeter galaxies (SMGs), including 260 SMGs identified in the AS2COSMOS pilot survey. In total, we identify 1,222 optical/near-infrared(NIR)/radio counterparts to the 897 S2COSMOS submillimeter sources with S$_{850}$>1.6mJy, yielding an overall identification rate of ($78\pm9$)%. We find that ($22\pm5$)% of S2COSMOS sources have multiple identified counterparts. We estimate that roughly 27% of these multiple counterparts within the same SCUBA-2 error circles very likely arise from physically associated galaxies rather than line-of-sight projections by chance. The photometric redshift of our radio$+$machine-learning identified SMGs ranges from z=0.2 to 5.7 and peaks at $z=2.3\pm0.1$. The AGN fraction of our sample is ($19\pm4$)%, which is consistent with that of ALMA SMGs in the literature. Comparing with radio/NIR-detected field galaxy population in the COSMOS field, our radio+machine-learning identified counterparts of SMGs have the highest star-formation rates and stellar masses. These characteristics suggest that our identified counterparts of S2COSMOS sources are a representative sample of SMGs at z<3. We employ our machine-learning technique to the whole COSMOS field and identified 6,877 potential SMGs, most of which are expected to have submillimeter emission fainter than the confusion limit of our S2COSMOS surveys (S$_{850}$<1.5mJy). We study the clustering properties of SMGs based on this statistically large sample, finding that they reside in high-mass dark matter halos ($(1.2\pm0.3)\times10^{13}\,h^{-1}\,\rm M_{\odot}$), which suggests that SMGs may be the progenitors of massive ellipticals we see in the local Universe.

G.A.S.

Context. Star formation in galaxies is inefficient, and understanding how star formation is regulated in galaxies is one of the most fundamental challenges of contemporary astrophysics. Radiative cooling, feedback from supernovae and active galactic nuclei (AGN), and large-scale dynamics and dissipation of turbulent energy act over various time and spatial scales and all regulate star formation in a complex gas cycle. Aims. This paper presents the physics implemented in a new semi-analytical model of galaxy formation and evolution called the Galaxy Assembler from dark-matter Simulation (G.A.S.). Methods. The fundamental underpinning of our new model is the development of a multiphase interstellar medium (ISM) in which energy produced by supernovae and AGN maintains an equilibrium between a diffuse, hot, and stable gas and a cooler, clumpy, and low-volume filling factor gas. The hot gas is susceptible to thermal and dynamical instabilities. We include a description of how turbulence leads to the formation of giant molecular clouds through an inertial turbulent energy cascade, assuming a constant kinetic energy transfer per unit volume. We explicitly modelled the evolution of the velocity dispersion at different scales of the cascade and accounted for thermal instabilities in the hot halo gas. Thermal instabilities effectively reduce the impact of radiative cooling and moderates accretion rates onto galaxies, and in particular, for those residing in massive haloes. Results. We show that rapid and multiple exchanges between diffuse and unstable gas phases strongly regulates star formation rates in galaxies because only a small fraction of the unstable gas is forming stars. We checked that the characteristic timescales describing the gas cycle, gas depletion timescale, and star-forming laws at different scales are in good agreement with observations. For high-mass haloes and galaxies, cooling is naturally regulated by the growth of thermal instabilities, so we do not need to implement strong AGN feedback in this model. Our results are also in good agreement with the observed stellar mass function from z ≃ 6.0 to z ≃ 0.5. Conclusion. Our model offers the flexibility to test the impact of various physical processes on the regulation of star formation on a representative population of galaxies across cosmic times. Thermal instabilities and the cascade of turbulent energy in the dense gas phase introduce a delay between gas accretion and star formation, which keeps galaxy growth inefficient in the early Universe. The main results presented in this paper, such as stellar mass functions, are available in the GALAKSIENN library.

Tracing the quenching history of cluster galaxies in the EAGLE simulation

ABSTRACT We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical simulation to trace the quenching history of galaxies in its 10 most massive clusters. We use two criteria to identify moments when galaxies suffer significant changes in their star formation activity: (i) the instantaneous star formation rate (SFR) strongest drop, $\Gamma _{\rm SFR}^{\rm SD}$, and (ii) a ‘quenching’ criterion based on a minimum threshold for the specific SFR of ≲10$^{-11}\,\rm yr^{-1}$. We find that a large fraction of galaxies (${\gtrsim} 60\,{\rm per\,cent}$) suffer their $\Gamma _{\rm SFR}^{\rm SD}$ outside the cluster’s R200. This ‘pre-processed’ population is dominated by galaxies that are either low mass and centrals or inhabit low-mass hosts (1010.5 ≲ Mhost ≲ 1011.0 M⊙). The host mass distribution is bimodal, and galaxies that suffered their $\Gamma _{\rm SFR}^{\rm SD}$ in massive hosts ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.0}\, \mathrm{M}_{\odot }$) are mainly processed within the clusters. Pre-processing mainly limits the total stellar mass with which galaxies arrive in the clusters. Regarding quenching, galaxies preferentially reach this state in high-mass haloes ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.5}\, \mathrm{M}_{\odot }$). The small fraction of galaxies that reach the cluster already quenched have also been pre-processed, linking both criteria as different stages in the quenching process of those galaxies. For the z = 0 satellite populations, we find a sharp rise in the fraction of quenched satellites at the time of first infall, highlighting the role played by the dense cluster environment. Interestingly, the fraction of pre-quenched galaxies rise with final cluster mass. This is a direct consequence of the hierarchical cosmological model used in these simulations.

Elliptical galaxies/stellar halos connection

AbstractCosmological simulations predict that early-type galaxies (ETGs) are the results of extended mass accretion histories. The latter are characterized by different numbers of mergers, mergers’ mass ratios and gas fractions, and timing. Depending on the sequence and nature of these mergers that follow the first phase of the in-situ star formation, these accretion histories may lead to ETGs that have low or high mass halos, and that rotate fast or slow. Since the stellar halos maintain the fossil records of the events that led to their formation, a discontinuity may be in place between the inner regions of ETGs and their outer halos, because the time required for the halos’ stars to exchange their energies and momenta is very long compared with the age of these systems. Exquisite deep photometry and extended spectroscopy for significant samples of ETGs are then used to quantify the occurrence and significance of such a transition in the galaxies’ structural and kinematical parameters. Once this transition radius is measured, its dependency with the effective radius of the galaxies’ light distribution and total stellar masses can be investigated. Such correlations can then be compared with the predictions of accreted, i.e. ex-situ vs. in-situ components from cosmological simulations to validate such models.

The Cosmic Ballet II: spin alignment of galaxies and haloes with large-scale filaments in the EAGLE simulation

We investigate the alignment of galaxies and haloes relative to cosmic web filaments using the EAGLE hydrodynamical simulation. We identify filaments by applying the NEXUS+ method to the mass distribution and the Bisous formalism to the galaxy distribution. Both web finders return similar filamentary structures that are well aligned and that contain comparable galaxy populations. EAGLE haloes have an identical spin alignment with filaments as their counterparts in dark matter only simulations: a complex mass dependent trend with low mass haloes spinning preferentially parallel to and high mass haloes spinning preferentially perpendicular to filaments. In contrast, galaxy spins do not show such a spin transition and have a propensity for perpendicular alignments at all masses, with the degree of alignment being largest for massive galaxies. This result is valid for both NEXUS+ and Bisous filaments. When splitting by morphology, we find that elliptical galaxies show a stronger orthogonal spin--filament alignment than spiral galaxies of similar mass. The same is true of their haloes, with the host haloes of elliptical galaxies having a larger degree of orthogonal alignment than the host haloes of spirals. Due to the misalignment between galaxy shape and spin, galaxy minor axes are oriented differently with filaments than galaxy spins. We find that the galaxies whose minor axis is perpendicular to a filament are much better aligned with their host haloes. This suggests that many of the same physical processes determine both the galaxy--filament and the galaxy--halo alignments.

UniverseMachine: The correlation between galaxy growth and dark matter halo assembly from z = 0−10

ABSTRACTWe present a method to flexibly and self-consistently determine individual galaxies’ star formation rates (SFRs) from their host haloes’ potential well depths, assembly histories, and redshifts. The method is constrained by galaxies’ observed stellar mass functions, SFRs (specific and cosmic), quenched fractions, ultraviolet (UV) luminosity functions, UV–stellar mass relations, IRX–UV relations, auto- and cross-correlation functions (including quenched and star-forming subsamples), and quenching dependence on environment; each observable is reproduced over the full redshift range available, up to 0 &lt; z &lt; 10. Key findings include the following: galaxy assembly correlates strongly with halo assembly; quenching correlates strongly with halo mass; quenched fractions at fixed halo mass decrease with increasing redshift; massive quenched galaxies reside in higher-mass haloes than star-forming galaxies at fixed galaxy mass; star-forming and quenched galaxies’ star formation histories at fixed mass differ most at z &lt; 0.5; satellites have large scatter in quenching time-scales after infall, and have modestly higher quenched fractions than central galaxies; Planck cosmologies result in up to 0.3 dex lower stellar – halo mass ratios at early times; and, none the less, stellar mass–halo mass ratios rise at z &gt; 5. Also presented are revised stellar mass – halo mass relations for all, quenched, star-forming, central, and satellite galaxies; the dependence of star formation histories on halo mass, stellar mass, and galaxy SSFR; quenched fractions and quenching time-scale distributions for satellites; and predictions for higher-redshift galaxy correlation functions and weak lensing surface densities. The public data release (DR1) includes the massively parallel (&gt;105 cores) implementation (the UniverseMachine), the newly compiled and remeasured observational data, derived galaxy formation constraints, and mock catalogues including lightcones.

Alignment between Filaments and Galaxy Spins from the MaNGA Integral-field Survey

Abstract Halos and galaxies acquire their angular momentum during the collapse of the surrounding large-scale structure. This process imprints alignments between galaxy spins and nearby filaments and sheets. Low-mass halos grow by accretion onto filaments, aligning their spins with the filaments, whereas high-mass halos grow by mergers along filaments, generating spins perpendicular to the filament. We search for this alignment signal using filaments identified with the “Cosmic Web Reconstruction” algorithm applied to the Sloan Digital Sky Survey Main Galaxy Sample and galaxy spins from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) integral-field unit survey. MaNGA produces a map of the galaxy’s rotational velocity, allowing direct measurement of the galaxy’s spin direction, or unit angular momentum vector projected onto the sky. We find no evidence for alignment between galaxy spins and filament directions. We do find hints of a mass-dependent alignment signal, which is in 2σ–3σ tension with the mass-dependent alignment signal in the MassiveBlack-II and Illustris hydrodynamical simulations. However, the tension vanishes when galaxy spin is measured using the Hα emission line velocity rather than stellar velocity. Finally, in simulations we find that the mass-dependent transition from aligned to anti-aligned dark matter halo spins is not necessarily present in stellar spins: we find a stellar spin transition in Illustris but not in MassiveBlack-II, highlighting the sensitivity of spin-filament alignments to feedback prescriptions and subgrid physics.

Is the Stellar Mass–Stellar Metallicity Relation Universal in the Milky Way Satellites and Beyond?

Abstract Observations reveal a universal stellar mass–stellar metallicity relation (MZR) existing in Local Group dwarfs of different types, Z * ∝ M * α with α = 0.30 ± 0.02. In this work, we investigate the “universality” of the MZRs for both satellites and central galaxies in a large number of different host dark matter halos covering a large mass range of 109–1015 h −1 M ⊙ , by using a semianalytical galaxy formation and evolution model. We obtain the following results: (1) The exponents (α) for the MZRs of the satellites in halos with the same mass as the Milky Way halo, but different individual assembly histories, are mostly ∼0.2–0.4, i.e., having a scatter of ∼0.2; and the scatter of α increases with decreasing halo masses. (2) The MZR relations are changed little by the variation of halo masses and the classification between central galaxies and satellites, if many halos with the same mass are stacked together. (3) A double power law exists in the MZR relations for both central galaxies and stacked satellites, with α ∼ 0.2–0.4 at 103 M ⊙ ≲ M * ≲ 108 M ⊙ and a relatively higher α ∼ 0.5 at 108 M ⊙ ≲ M * ≲ 1011 M ⊙ . (4) The high-mass satellites (M * ≳ 108 M ⊙ ) existing mostly in high-mass halos can lead to an apparent increase of α (from ∼0.2 to ∼0.4) with increasing host halo masses shown in the single-power-law fitting results of stacked satellites. The universality of the MZR suggests the common physical processes in stellar formation and chemical evolution of galaxies can be unified over a large range of galaxy masses and halo masses.

The Effect of Dark Matter–Dark Radiation Interactions on Halo Abundance: A Press–Schechter Approach

Abstract We study halo mass functions with the Press–Schechter formalism for interacting dark matter models, where matter power spectra are damped due to dark acoustic oscillations in the early universe. After adopting a smooth window function, we calibrate the analytical model with numerical simulations from the “effective theory of structure formation” (ETHOS) project and fix the model parameters in the high-mass regime, M h ≳ 3 × 1010 M ⊙. We also perform high-resolution cosmological simulations with halo masses down to M h ∼ 108 M ⊙ to cover a wide mass range for comparison. Although the model is calibrated with ETHOS1 and cold dark matter simulations for high halo masses at redshift z = 0, it successfully reproduces simulations for two other ETHOS models in the low-mass regime at low and high redshifts. As an application, we compare the cumulative number density of halos to that of observed galaxies at z = 6, and find that the interacting dark matter models with a kinetic decoupling temperature below 0.5 keV is disfavored. We also perform the abundance-matching analysis and derive the stellar–halo mass relation for these models at z = 4. Suppression in halo abundance leads to less massive halos that host observed galaxies in the stellar mass range M * ≃ 10 5 – 10 7 M ⊙ .

Stellar populations and ionised gas in central spheroidal galaxies

We investigate the stellar populations and ionised gas properties of a sample of central spheroidal galaxies in order to better constrain their history of star formation and gas excitation mechanism. We select galaxies from Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER) catalogue and separate these galaxies in different regimes of halo and galaxy mass. To characterise the stellar population properties of these galaxies we use the stellar population synthesis method with the Starlight code, and the presence of ionised gas is identified by measurements of the Hα equivalent width. We analyse how these properties behave as a function of the galaxy stellar mass and the parent halo mass. A trend is observed in the sense of increased ionised gas emission for low-mass centrals in high-mass halos. We interpret this trend in a scenario of intracluster medium (ICM) cooling versus active galactic nuclei (AGN) feedback in a Bondi accretion context.

The interplay of self-interacting dark matter and baryons in shaping the halo evolution

We use high-resolution hydrodynamical simulation to test the difference of halo properties in cold dark matter (CDM) and a self-interacting dark matter (SIDM) scenario with a constant cross-section of $\sigma^\text{T}/m_{\chi}=1\;\text{cm}^{2}\text{g}^{-1}$. We find that the interplay between dark matter self-interaction and baryonic physics induces a complex evolution of the halo properties, which depends on the halo mass and morphological type, as well as on the halo mass accretion history. While high mass haloes, selected as analogues of early-type galaxies, show cored profiles in the SIDM run, systems of intermediate mass and with a significant disk component can develop a profile that is similar or cuspier than in CDM. The final properties of SIDM haloes - measured at z=0.2 - correlate with the halo concentration and formation time, suggesting that the differences between different systems are due to the fact that we are observing the impact self-interaction. We also search for signatures of self-interacting dark matter in the lensing signal of the main haloes and hints of potential differences in the distribution of Einstein radii, which suggests that future wide-field survey might be able to distinguish between CDM and SIDM models on this basis. Finally, we find that the subhalo abundances are not altered in the adopted SIDM model with respect to CDM.

Hyper Suprime-Cam view of the CMASS galaxy sample

Aims. We wish to determine the distribution of dark matter halo masses as a function of the stellar mass and the stellar mass profile for massive galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) constant-mass (CMASS) sample. Methods. We used grizy photometry from the Hyper Suprime-Cam (HSC) to obtain Sérsic fits and stellar masses of CMASS galaxies for which HSC weak-lensing data are available. This sample was visually selected to have spheroidal morphology. We applied a cut in stellar mass, log M*/M⊙ &gt; 11.0, and selected ∼10 000 objects thus. Using a Bayesian hierarchical inference method, we first investigated the distribution of Sérsic index and size as a function of stellar mass. Then, making use of shear measurements from HSC, we measured the distribution of halo mass as a function of stellar mass, size, and Sérsic index. Results. Our data reveal a steep stellar mass-size relation Re ∝ M*βR, with βR larger than unity, and a positive correlation between Sérsic index and stellar mass: n ∝ M*0.46. The halo mass scales approximately with the 1.7 power of the stellar mass. We do not find evidence for an additional dependence of halo mass on size or Sérsic index at fixed stellar mass. Conclusions. Our results disfavour galaxy evolution models that predict significant differences in the size growth efficiency of galaxies living in low- and high-mass halos.

Tidal stripping and post-merger relaxation of dark matter haloes: causes and consequences of mass-loss

We study the properties of distinct dark matter halos (i.e., those that are not subhalos) that have a final virial mass $M_{\mathrm{vir}}$ at $z = 0$ less than their peak mass ($M_{\mathrm{peak}}$) in the Bolshoi-Planck cosmological simulation. We identify two primary causes of halo mass loss: relaxation after a major merger and tidal stripping by a massive neighbouring halo. Major mergers initially boost $M_{\mathrm{vir}}$ and typically cause the final halo to become more prolate and less relaxed and to have higher spin and lower NFW concentration. As the halo relaxes, high energy material from the recent merger gradually escapes beyond the virial radius, temporarily resulting in a net negative accretion rate that reduces the halo mass by $5-15\%$ on average. Halos that experience a major merger around $z = 0.4$ typically reach a minimum mass near $z = 0$. Tidal stripping mainly occurs in dense regions, and it causes halos to become less prolate and have lower spins and higher NFW concentrations. Tidally stripped halos often lose a large fraction of their peak mass ($> 20\%$) and most never recover (or even reattain a positive accretion rate). Low mass halos can be strongly affected by both post-merger mass loss and tidal stripping, while high mass halos are predominantly influenced by post-merger mass loss and show few signs of significant tidal stripping.

Morphology rather than environment drives the SFR–mass relation in the local universe

Exploiting a sample of 680 star-forming galaxies from the Padova-Millennium GalaxyGroup Catalog (PM2GC) (Calvi et al. 2011) in the range 0.038<z<0.104, we present a detailed analysis of the Star Formation Rate (SFR)-stellar mass (M_star) and specific SFR(SSFR)-M_star relations as a function of environment. We adopt three different parameterizations of environment, to probe different scales. We consider separately 1) galaxies in groups, binary and single systems, defined in terms of a Friends-of-Friends algorithm, 2) galaxies located at different projected local densities, 3) galaxies in haloes of different mass. Overall, above logM_ast/M_sun>10.25 and SSFR>10^{-12} yr^{-1}, the SFR-M_ast and SSFR-M_ast relations do not depend on environment, when the global environment is used, while when the halo mass is considered, high mass haloes might have a systematically lower (S)SFR-M_ast relation. Finally, when local densities are exploited, at any given mass galaxies in less dense environments have systematically higher values of SFR. All the relations are characterized by a large scatter ({\sigma}~0.6), which is dueto the coexistence of galaxies of different morphological types. Indeed, at any given mass, late-types are characterized by systematically higher values of SFR and SSFR than S0s and ellipticals. Galaxies of the same morphology show similar trends in all the environments, but their incidence strongly depends on environment and on the environmental parametrization adopted, with late-types generally becoming less common in denser environments, contrasted by the increase of ellipticals and/or S0s. Our results suggest that in the local universe morphology and local interactions, probed by the local density parameterization, have dominant roles in driving the characteristics of the SFR-M_ast relation.