This review examines the relationship between black hole activity and kinematic gas–star misalignment in brightest group galaxies (BGGs) with different merger rates. The formation history of galaxy ...groups is assessed through “age-dating” as an indicator of distinct major mergers involving the BGGs. BGGs within groups characterized by a higher frequency of major mergers are more likely to host active SMBHs. A consistent correlation is identified between the level of black hole activity, as indicated by the 1.4 GHz and 325 MHz radio emissions, and the degree of kinematic misalignment between the gas and stellar components in BGGs. In dynamically fossil groups, where black hole accretion rate is relatively (∼1 dex) lower due to the lack of recent (≤1 Gyr) major mergers, there is reduced (∼30%) misalignment between the gas and stellar components of BGGs compared to non-fossil groups. Additionally, this study reveals that BGGs in non-fossil groups show higher levels of star formation rate and increased occurrence of mergers, contributing to observed color differences. Exploring the properties and dynamics of the gas disk influenced by mechanical AGN feedback through hydrodynamic simulations suggests that AGN wind-induced effects further lead to the persistent gas misalignment in the disk around the supermassive black hole.
Abstract
Using dark-matter-only
N
-body cosmological simulations, we measure the pericentre distance of dark matter halos on their first infall into group and cluster halos. We find that the ...pericentre distance (
R
peri
) is an important parameter as it significantly affects the strength of tidal mass loss in dense environments, and likely other environmental mechanisms as well. We examine what determines the
R
peri
value and find that, for most infallers, the dominant parameter is
V
⊥
, the tangential component of the orbital velocity as the halo enters the group/cluster halo for the first time. This means that the strength of tidal stripping acting near the cores of groups/clusters are strongly influenced by the external peculiar velocity field of the large-scale structure surrounding them, which differs between clusters and is sensitive to the mass ratio of infaller to host. We find that filament feeding also partially contributes to feeding in low-
V
⊥
halos. Dynamical friction can also play a role in reducing
R
peri
but this is only significant for those few relatively massive infallers (>10% of the mass of their host). These results highlight how the response of galaxies to dense environments will sensitively depend on dynamics inherited from far outside those dense environments.
Abstract
We describe new efforts to model radio active galactic nuclei (AGN) in a cosmological context using the Semi-Analytic Galaxy Evolution (SAGE) semi-analytic galaxy model. Our new method ...tracks the physical properties of radio jets in massive galaxies including the evolution of radio lobes and their impact on the surrounding gas. This model also self consistently follows the gas cooling–heating cycle that significantly shapes star formation and the life and death of many galaxy types. Adding jet physics to SAGE adds new physical properties to the model output, which in turn allows us to make more detailed predictions for the radio AGN population. After calibrating the model to a set of core observations we analyse predictions for jet power, radio cocoon size, radio luminosity and stellar mass. We find that the model is able to match the stellar mass-radio luminosity relation at z ∼ 0 and the radio luminosity function out to z ∼ 1. This updated model will make possible the construction of customised AGN-focused mock survey catalogues to be used for large-scale observing programs.
Using high-resolution hydrodynamical cosmological simulations, we study the gas accretion history of low-mass halos located in a field-like, low-density environment. We track their evolution ...individually from the early, pre-reionization era, through reionization, and beyond until z = 0. Before reionization, low-mass halos accrete cool cosmic-web gas at a very rapid rate, often reaching the highest gas mass they will ever have. But when reionization occurs, we see that almost all halos lose significant quantities of their gas content, although some respond less quickly than others. We find that the response rate is influenced by halo mass first, and secondarily by their internal gas density at the epoch of reionization. Reionization also fully ionizes the cosmic-web gas by z ∼ 6. As a result, the lowest mass halos (M ∼ 106 h−1 M at z = 6) can never again re-accrete gas from the cosmic web, and by z ∼ 5 have lost all their internal gas to ionization, resulting in a halt in star formation at this epoch. However, more massive halos can recover from their gas mass loss, and re-accrete ionized cosmic-web gas. We find the efficiency of this re-accretion is a function of halo mass first, followed by local surrounding gas density. Halos that are closer to the cosmic-web structure can accrete denser gas more rapidly. We find that our lower mass halos have a sweet spot for rapid, dense gas accretion at distances of roughly 1-5 virial radii from the most massive halos in our sample (>108 h−1 M ), as these tend to be embedded deeply within the cosmic web.
ABSTRACT We present the first study of the evolution of galaxy groups in the Illustris simulation. We focus on dynamically relaxed and unrelaxed galaxy groups representing dynamically evolved and ...evolving galaxy systems, respectively. The evolutionary state of a group is probed from its luminosity gap and separation between the brightest group galaxy and the center of mass of the group members. We find that the Illustris simulation overproduces galaxy systems with a large luminosity gap, known as fossil systems, in comparison to observations and the probed semi-analytical predictions. However, this simulation is just as successful as the probed semi-analytic model in recovering the correlation between luminosity gap and offset of the luminosity centroid. We find evolutionary tracks based on luminosity gap that indicate that a group with a large luminosity gap is rooted in one with a small luminosity gap, regardless of the position of the brightest group galaxy within the halo. This simulation helps to explore, for the first time, the black hole mass and its accretion rate in galaxy groups. For a given stellar mass of the brightest group galaxies, the black hole mass is larger in dynamically relaxed groups with a lower rate of mass accretion. We find this to be consistent with the latest observational studies of radio activity in the brightest group galaxies in fossil groups. We also find that the intragalactic medium in dynamically evolved groups is hotter for a given halo mass than that in evolving groups, again consistent with earlier observational studies.
We study the stellar populations of the brightest group galaxies (BGGs) in groups with different dynamical states, using Galaxy And Mass Assembly survey data. We use two independent, ...luminosity-dependent indicators to probe the relaxedness of their groups: the magnitude gap between the two most luminous galaxies (ΔM12), and the offset between BGGs and the luminosity center (Doffset) of the group. Combined, these two indicators were previously found useful for identifying relaxed and unrelaxed groups. We find that the BGGs of unrelaxed groups have significantly bluer near-ultraviolet-r colors than in relaxed groups. This is also true at the fixed sersic index. We find the bluer colors cannot be explained away by differing dust fraction, suggesting there are real differences in their stellar populations. Star formation rates derived from spectral energy distribution (SED) fitting tend to be higher in unrelaxed systems. This is in part because of a greater fraction of BGGs with non-elliptical morphology, but also because unrelaxed systems have larger numbers of mergers, some of which may bring fuel for star formation. The SED-fitted stellar metallicities of BGGs in unrelaxed systems also tend to be higher by around 0.05 dex, perhaps because their building blocks were more massive. We find that the ΔM12 parameter is the most important parameter behind the observed differences in the relaxed/unrelaxed groups, in contrast with the previous study of Trevisan et al. We also find that groups selected to be unrelaxed using our criteria tend to have higher velocity offsets between the BGG and their group.
Abstract
We have examined the star formation history (SFH) of Andromeda VII (And VII), the brightest and most massive dwarf spheroidal (dSph) satellite of the Andromeda galaxy (M31). Although M31 is ...surrounded by several dSph companions with old stellar populations and low metallicity, it has a metal-rich stellar halo with an age of 6–8 Gyr. This indicates that any evolutionary association between the stellar halo of M31 and its dSph system is frail. Therefore, the question is whether And VII (a high-metallicity dSph located ∼220 kpc from M31) can be associated with M31's young, metal-rich halo. Here we perform the first reconstruction of the SFH of And VII employing long-period variable (LPV) stars. As the most evolved asymptotic giant branch and red supergiant stars, the birth mass of LPVs can be determined by connecting their near-infrared photometry to theoretical evolutionary tracks. We found 55 LPV candidates within two half-light radii, using multiepoch imaging with the Isaac Newton Telescope in the
i
and
V
bands. Based on their birth mass function, the star formation rate (SFR) of And VII was obtained as a function of cosmic time. The main epoch of star formation occurred ≃ 6.2 Gyr ago with an SFR of 0.006 ± 0.002
M
⊙
yr
−1
. Over the past 6 Gyr, we find slow star formation, which continued until 500 Myr ago with an SFR ∼ 0.0005 ± 0.0002
M
⊙
yr
−1
. We determined And VII’s stellar mass
M
= (13.3 ± 5.3) × 10
6
M
⊙
within a half-light radius
and metallicity
Z
= 0.0007, and we also derived its distance modulus of
μ
= 24.38 mag.
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