Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCosmological evolution of orientations of cluster-sized dark matter haloes and their central galaxies in the Horizon-AGN simulation
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
It is known observationally that the major axes of galaxy clusters and their brightest cluster galaxies are roughly aligned with each other. To understand the origin of the alignment, we identify 40 cluster-sized dark matter (DM) haloes with masses higher than $5times10^{13}~M_{odot}$ and their central galaxies (CGs) at $zapprox 0$ in the Horizon-AGN cosmological hydrodynamical simulation. We trace the progenitors at 50 different epochs between $0<z<5$. We then fit their shapes and orientations with a triaxial ellipsoid model. While the orientations of both DM haloes and CGs change significantly due to repeated mergers and mass accretions, their relative orientations are well aligned at each epoch even at high redshifts, $z>1$. The alignment becomes tighter with cosmic time; the major axes of the CGs and their host DM haloes at present are aligned on average within $sim 30^{circ}$ in the three dimensional space and $sim 20^{circ}$ in the projected plane. The orientations of the major axes of DM haloes on average follow one of the eigen-vectors of the surrounding tidal field that corresponds to the {it slowest collapsing} (or even stretching) mode, and the alignment with the tidal field also becomes tighter. This implies that the orientations of CGs and DM haloes at the present epoch are largely imprinted in the primordial density field of the Universe, whereas strong dynamical interactions such as mergers are important to explain their mutual alignment at each epoch.
rate research
Read More
Using a suite of three large cosmological hydrodynamical simulations, Horizon-AGN, Horizon-noAGN (no AGN feedback) and Horizon-DM (no baryons), we investigate how a typical sub-grid model for AGN feedback affects the evolution of the inner density profiles of massive dark matter haloes and galaxies. Based on direct object-to-object comparisons, we find that the integrated inner mass and density slope differences between objects formed in these three simulations (hereafter, H_AGN, H_noAGN and H_DM) significantly evolve with time. More specifically, at high redshift (z~5), the mean central density profiles of H_AGN and H_noAGN dark matter haloes tend to be much steeper than their H_DM counterparts owing to the rapidly growing baryonic component and ensuing adiabatic contraction. By z~1.5, these mean halo density profiles in H_AGN have flattened, pummelled by powerful AGN activity (quasar mode): the integrated inner mass difference gaps with H_noAGN haloes have widened, and those with H_DM haloes have narrowed. Fast forward 9.5 billion years, down to z=0, and the trend reverses: H_AGN halo mean density profiles drift back to a more cusped shape as AGN feedback efficiency dwindles (radio mode), and the gaps in integrated central mass difference with H_noAGN and H_DM close and broaden respectively. On the galaxy side, the story differs noticeably. Averaged stellar profile central densities and inner slopes are monotonically reduced by AGN activity as a function of cosmic time, resulting in better agreement with local observations. As both dark matter and stellar inner density profiles respond quite sensitively to the presence of a central AGN, there is hope that future observational determinations of these quantities can be used constrain AGN feedback models.
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses ($10^{8.75}$ to $10^{11.3} M_{odot}$) and redshifts ($0.2 < z < 0.8$) than previous weak lensing studies. At redshift $z sim 0.5$, the stellar-to-halo mass ratio (SHMR) reaches a maximum of $4.0pm0.2$ percent as a function of halo mass at $sim 10^{12.25} M_{odot}$. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from $4.5 pm 0.3$ percent at $z sim 0.7$ to $3.4 pm 0.2$ percent at $z sim 0.3$, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched downsizes with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well-fit by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic time.
We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on dark matter and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of $0.482pm 0.028$, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of $22.2pm 3.9$ deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of $0.11pm 0.03$. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold dark matter.
We apply our recently proposed quadratic genetic modification approach to generating and testing the effects of alternative mass accretion histories for a single $Lambda$CDM halo. The goal of the technique is to construct different formation histories, varying the overall contribution of mergers to the fixed final mass. This enables targeted studies of galaxy and dark matter halo formations sensitivity to the smoothness of mass accretion. Here, we focus on two dark matter haloes, each with four different mass accretion histories. We find that the concentration of both haloes systematically decreases as their merger history becomes smoother. This causal trend tracks the known correlation between formation time and concentration parameters in the overall halo population. At fixed formation time, we further establish that halo concentrations are sensitive to the order in which mergers happen. This ability to study an individual halos response to variations in its history is highly complementary to traditional methods based on emergent correlations from an extended halo population.
Early-type galaxies (ETGs) are observed to be more compact, on average, at $z gtrsim 2$ than at $zsimeq 0$, at fixed stellar mass. Recent observational works suggest that such size evolution could reflect the similar evolution of the host dark matter halo density as a function of the time of galaxy quenching. We explore this hypothesis by studying the distribution of halo central velocity dispersion ($sigma_0$) and half-mass radius ($r_{rm h}$) as functions of halo mass $M$ and redshift $z$, in a cosmological $Lambda$-CDM $N$-body simulation. In the range $0lesssim zlesssim 2.5$, we find $sigma_0propto M^{0.31-0.37}$ and $r_{rm h}propto M^{0.28-0.32}$, close to the values expected for homologous virialized systems. At fixed $M$ in the range $10^{11} M_odot lesssim Mlesssim 5.5 times 10^{14} M_odot$ we find $sigma_0propto(1+z)^{0.35}$ and $r_{rm h}propto(1+z)^{-0.7}$. We show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks $sigma_0propto M^{0.2}$ and $r_{rm h}propto M^{0.6}$, consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for. We compare the $N$-body data with ETGs observed at $0lesssim zlesssim3$ by populating the haloes with a stellar component under simple but justified assumptions: the resulting galaxies evolve consistently with the observed ETGs up to $z simeq 2$, but the model has difficulty reproducing the fast evolution observed at $zgtrsim 2$. We conclude that a substantial fraction of the size evolution of ETGs can be ascribed to a systematic dependence on redshift of the dark matter haloes structural properties.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
