Host Halo Research Articles

The VST ATLAS Quasar Survey – III. Halo mass function via quasar clustering and quasar-CMB lensing cross-clustering

ABSTRACT We exploit the VST ATLAS quasar (QSO) catalogue to perform three measurements of the quasar halo mass profile. First, we make a new estimate of the angular autocorrelation function of ≈230 000 ATLAS quasars with $z_{\rm photo}\lesssim 2.5$ and $17 < g < 22$. By comparing with the $\Lambda$CDM mass clustering correlation function, we measure the quasar bias to be $b_{\rm Q}\approx 2.1$, implying a quasar halo mass of $M_{\rm halo} \approx 8.5\times 10^{11}\,h^{-1}\,{\rm M}_\odot$. Second, we cross-correlate these $z\approx 1.7$ ATLAS quasars with the Planck cosmic microwave background (CMB) lensing maps, detecting a somewhat stronger signal at $4\,{\rm arcmin} < \theta < 60\,{\rm arcmin}$ than previous authors. Scaling these authors’ model fit to our data, we estimate a quasar host halo mass of $M_{\rm halo}\approx 8.3\times 10^{11}\,h^{-1}\,{\rm M}_\odot$. Third, we fit halo occupation sistribution (HOD) model parameters to our quasar autocorrelation function and from the derived halo mass function, we estimate a quasar halo mass of $M_{\rm halo}\approx 2.5\times 10^{12}\,h^{-1}\,{\rm M}_\odot$. We then compare our HOD model prediction to our quasar-CMB lensing result, confirming their consistency. We find that most (≈2/3) QSOs have halo masses within a factor of ≈3 of this average mass. An analysis based on the probability of X-ray detections of AGN in galaxies and the galaxy stellar mass function gives a similarly small mass range. Finally, we compare the quasar halo mass and luminosity functions and suggest that gravitational growth may produce the constant space density with redshift seen in the quasar luminosity function.

Investigating the Kinematics of Central and Satellite Galaxies Using Normalizing Flows

Galaxy clustering contains information on cosmology, galaxy evolution, and the relationship between galaxies and their dark matter hosts. On small scales, the detailed kinematics of galaxies within their host halos determines the galaxy clustering. In this paper, we investigate the dependence of the central and satellite galaxy kinematics on θ , the intrinsic host halo properties (mass, spin, concentration), cosmology (Ωm, σ 8), and baryonic feedback from active galactic nuclei and supernovae (A AGN1, A AGN2, A SN1, A SN2). We utilize 2000 hydrodynamic simulations in CAMELS run using IllustrisTNG and SIMBA galaxy formation models. Focusing on central and satellite galaxies with M * > 109 M ⊙, we apply neural density estimation (NDE) with normalizing flows to estimate their p(Δr ∣ θ ) and p(Δv ∣ θ ), where Δr and Δv are the magnitudes of the halocentric spatial and velocity offsets. With NDE, we accurately capture the dependence of galaxy kinematics on each component of θ . For central galaxies, we identify significant spatial and velocity biases dependent on halo mass, concentration, and spin. For satellite distributions, we find significant deviations from a Navarro–Frenk–White profile and evidence that they consist of distinct orbiting and infalling populations. However, we find no strong dependence on θ besides a weak dependence on host halo spin. For both central and satellite galaxies, there is no notable dependence on cosmological parameters and baryonic feedback. These results provide key insights for improving the current halo occupation distribution (HOD) models. This work is the first in a series that will reexamine and develop HOD frameworks for improved modeling of galaxy clustering at smaller scales.

The Mass and Redshift Dependence of Halo Star Clustering

We adopt the two-point correlation function (2PCF) as a statistical tool to quantify the spatial clustering of halo stars for galaxy systems spanning a wide range in host halo virial mass ( 11.25<log10M200c/M⊙<15 ) and redshifts (0 < z < 1.5) from the IllustrisTNG simulations. Consistent with a previous study, we identify clear correlations between the strength of the 2PCF signals and galaxy formation redshifts, but over a much wider mass range. We find that such correlations are slightly stronger at higher redshifts and get weakened with the increase of host halo mass. We demonstrate that the spatial clustering of halo stars is affected by two factors: (1) the clustering gets gradually weakened as time passes (phase mixing); (2) newly accreted stars at more recent times would increase the clustering. For more massive galaxy systems, they assemble late, and the newly accreted stars would increase the clustering. The late assembly of massive systems may also help to explain the weaker correlations between the 2PCF signals and the galaxy formation redshifts in massive halos, as their 2PCFs are affected more by recently accreted stars, while formation redshift characterizes mass accretion on a much longer timescale. We find that the orbits of satellite galaxies in more massive halos maintain larger radial anisotropy, reflecting the more active accretion state of their hosts while also contributing to their stronger mass loss rates.

The SAGA Survey. IV. The Star Formation Properties of 101 Satellite Systems around Milky Way–mass Galaxies

Abstract We present the star-forming properties of 378 satellite galaxies around 101 Milky Way analogs in the Satellites Around Galactic Analogs (SAGA) Survey, focusing on the environmental processes that suppress or quench star formation. In the SAGA stellar mass range of 106−10 M ⊙, we present quenched fractions, star-forming rates, gas-phase metallicities, and gas content. The fraction of SAGA satellites that are quenched increases with decreasing stellar mass and shows significant system-to-system scatter. SAGA satellite quenched fractions are highest in the central 100 kpc of their hosts and decline out to the virial radius. Splitting by specific star formation rate (sSFR), the least star-forming satellite quartile follows the radial trend of the quenched population. The median sSFR of star-forming satellites increases with decreasing stellar mass and is roughly constant with projected radius. Star-forming SAGA satellites are consistent with the star formation rate–stellar mass relationship determined in the Local Volume, while the median gas-phase metallicity is higher and median H i gas mass is lower at all stellar masses. We investigate the dependence of the satellite quenched fraction on host properties. Quenched fractions are higher in systems with larger host halo mass, but this trend is only seen in the inner 100 kpc; we do not see significant trends with host color or star formation rate. Our results suggest that lower-mass satellites and satellites inside 100 kpc are more efficiently quenched in a Milky Way–like environment, with these processes acting sufficiently slowly to preserve a population of star-forming satellites at all stellar masses and projected radii.

Dual Active Galactic Nuclei: Precursors of Binary Supermassive Black Hole Formation and Mergers

The presence of dual active galactic nuclei (AGNs) on scales of a few tens of kiloparsecs can be used to study merger-induced accretion on supermassive black holes (SMBHs) and offer insights about SMBH mergers, using dual AGNs as merger precursors. This study uses the Romulus25 cosmological simulation to investigate the properties and evolution of dual AGNs. We first analyze the properties of AGNs (L bol > 1043 erg s−1) and their neighboring SMBHs (any SMBHs closer than 30 pkpc to an AGN) at z ≤ 2. This is our underlying population. We then applied the luminosity threshold of L bol > 1043 erg s−1 to the neighboring SMBHs thereby identifying dual and multiple AGNs. Our findings indicate an increase in the number of both single and dual AGNs from lower to higher redshifts. We also find that the number of dual AGNs with separations of 0.5–4 kpc is twice the number of duals with separations of 4–30 kpc. All dual AGNs in our sample resulted from major mergers. Compared to single AGNs, duals have a lower black hole-to-halo mass ratio. We found that the properties of dual AGN host halos, including halo mass, stellar mass, star formation rate, and gas mass, are generally consistent with those of single AGN halos, albeit tending toward the higher end of their respective property ranges. Our analysis uncovered a diverse array of evolutionary patterns among dual AGNs, including rapidly evolving systems, slower ones, and instances where SMBH mergers are ineffective.

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.

Weak Gravitational Lensing around Low Surface Brightness Galaxies in the DES Year 3 Data

We present galaxy-galaxy lensing measurements using a sample of low surface brightness galaxies (LSBGs) drawn from the Dark Energy Survey Year 3 (Y3) data as lenses. LSBGs are diffuse galaxies with a surface brightness dimmer than the ambient night sky. These dark-matter-dominated objects are intriguing due to potentially unusual formation channels that lead to their diffuse stellar component. Given the faintness of LSBGs, using standard observational techniques to characterize their total masses proves challenging. Weak gravitational lensing, which is less sensitive to the stellar component of galaxies, could be a promising avenue to estimate the masses of LSBGs. Our LSBG sample consists of 23,790 galaxies separated into red and blue color types at g−i≥0.60 and g−i&lt;0.60, respectively. Combined with the DES Y3 shear catalog, we measure the tangential shear around these LSBGs and find signal-to-noise ratios of 6.67 for the red sample, 2.17 for the blue sample, and 5.30 for the full sample. We use the clustering redshifts method to obtain redshift distributions for the red and blue LSBG samples. Assuming all red LSBGs are satellites, we fit a simple model to the measurements and estimate the host halo mass of these LSBGs to be . We place a 95% upper bound on the subhalo mass at . By contrast, we assume the blue LSBGs are centrals, and place a 95% upper bound on the halo mass at log(Mhost/M⊙)&lt;11.84. We find that the stellar-to-halo mass ratio of the LSBG samples is consistent with that of the general galaxy population. This work illustrates the viability of using weak gravitational lensing to constrain the halo masses of LSBGs.

A unified model for the clustering of quasars and galaxies at z ≈ 6

ABSTRACT Recent observations from the EIGER JWST program have measured for the first time the quasar–galaxy cross-correlation function at $z\approx 6$. The autocorrelation function of faint $z\approx 6$ quasars was also recently estimated. These measurements provide key insights into the properties of quasars and galaxies at high redshift and their relation with the host dark matter haloes. In this work, we interpret these data building upon an empirical quasar population model that has been applied successfully to quasar clustering and demographic measurements at $z\approx 2\!-\!4$. We use a new, large-volume N-body simulation with more than a trillion particles, FLAMINGO-10k, to model quasars and galaxies simultaneously. We successfully reproduce observations of $z\approx 6$ quasars and galaxies (i.e. their clustering properties and luminosity functions), and infer key quantities such as their luminosity–halo mass relation, the mass function of their host haloes, and their duty cycle/occupation fraction. Our key findings are (i) quasars reside on average in $\approx 10^{12.5}\, {\rm M}_{\odot }$ haloes (corresponding to $\approx 5\sigma$ fluctuations in the initial conditions of the linear density field), but the distribution of host halo masses is quite broad; (ii) the duty cycle of (UV-bright) quasar activity is relatively low ($\approx 1~{{\ \rm per\ cent}}$); (iii) galaxies (that are bright in [O iii]) live in much smaller haloes ($\approx 10^{10.9}\, {\rm M}_{\odot }$) and have a larger duty cycle (occupation fraction) of $\approx 13~{{\ \rm per\ cent}}$. Finally, we focus on the inferred properties of quasars and present a homogeneous analysis of their evolution with redshift. The picture that emerges reveals a strong evolution of the host halo mass and duty cycle of quasars at $z\approx 2\!-\!6$, and calls for new investigations of the role of quasar activity across cosmic time.

Subhalos in Galaxy Clusters: Coherent Accretion and Internal Orbits

Subhalo dynamics in galaxy cluster host halos govern the observed distribution and properties of cluster member galaxies. We use the IllustrisTNG simulation to investigate the accretion and orbits of subhalos found in cluster-size halos. We find that the median change in the major axis direction of cluster-size host halos is approximately 80° between a ∼ 0.1 and the present day. We identify coherent regions in the angular distribution of subhalo accretion, and ∼68% of accreted subhalos enter their host halo through ∼38% of the surface area at the virial radius. The majority of galaxy clusters in the sample have ∼2 such coherent regions. We further measure angular orbits of subhalos with respect to the host major axis and use a clustering algorithm to identify distinct orbit modes with varying oscillation timescales. The orbit modes correlate with subhalo accretion conditions. Subhalos in orbit modes with shorter oscillations tend to have lower peak masses and accretion directions somewhat more aligned with the major axis. One orbit mode, exhibiting the least oscillatory behavior, largely consists of subhalos that accrete near the plane perpendicular to the host halo major axis. Our findings are consistent with expectations from inflow from major filament structures and internal dynamical friction: most subhalos accrete through coherent regions, and more massive subhalos experience fewer orbits after accretion. Our work offers a unique quantification of subhalo dynamics that can be connected to how the intracluster medium strips and quenches cluster galaxies.

The Three Hundred: The existence of massive dark matter-deficient satellite galaxies in cosmological simulations

The observation of a massive galaxy with an extremely low dark matter content (i.e. NGC 1277) has posed questions about how such objects form and evolve in a hierarchical universe. We here report on the finding of several massive, dark matter-deficient galaxies in a set of 324 galaxy clusters theoretically modelled by means of full-physics hydrodynamical simulations. We first focus on two example galaxies selected amongst the most massive and dark matter-deficient ones. By tracing the evolution of these galaxies, we find that their lack of dark matter is a result of multiple pericentre passages. While orbiting their host halo, tidal interactions gradually strip away dark matter while preserving the stellar component. A statistical analysis of all massive satellite galaxies in the simulated clusters shows that the stellar-to-total mass ratio today is strongly influenced by the number of orbits and the distance at pericentres. Galaxies with more orbits and closer pericentres are more dark matter-deficient. Additionally, we find that massive, dark matter-deficient galaxies at the present day are either the remnants of very massive galaxies at infall or former central galaxies of infalling groups. We conclude that such massive yet dark matter-deficient galaxies exist and are natural by-products of typical cluster galaxy evolution, with no specific requirement for an exotic formation scenario.

Survival of gas in subhalos and its impact on the 21 cm forest signals: insights from hydrodynamic simulations

Understanding the survival of gas within subhalos under various astrophysical processes is crucial for elucidating cosmic structure formation and evolution. We study the resilience of gas in subhalos, focusing on the impact of tidal and ram pressure stripping through hydrodynamic simulations. Our results uncover significant gas stripping primarily driven by ram pressure effects, which also profoundly influence the gas distribution within these subhalos. Notably, despite their vulnerability to ram pressure effects, the low-mass subhalos can play a pivotal role in influencing the observable characteristics of cosmic structures due to their large abundance. Specifically, we explore the application of our findings to the 21 cm forest, showing how the survival dynamics of gas in subhalos can modulate the 21 cm optical depth, a key probe for detecting minihalos in the pre-reionization era. Our previous study demonstrated that the 21 cm optical depth can be enhanced by the subhalos, but the effects of tidal and ram pressure stripping on the subhalo abundance have not been fully considered. In this work, we further investigate the contribution of subhalos to the 21 cm optical depth with hydrodynamic simulations, particularly highlighting the trajectories and fates of subhalos within mass ranges of 104-6 M ⊙ h -1 in a host halo of 107 M ⊙h-1, and subhalos within mass range of 104-5 M ⊙h-1 in a host halo of 106 M ⊙h-1. Despite their susceptibility to ram pressure stripping, the contribution of abundant low-mass subhalos to the 21 cm optical depth is more significant than that of their massive counterparts primarily due to their greater abundance. We find that the 21 cm optical depth can be increased by a factor of approximately two due to the abundant low-mass subhalos. However, this enhancement is about twice as low as previously estimated in our earlier study, a discrepancy attributed to the effects of ram pressure stripping. Our work provides critical insights into the gas dynamics within subhalos in the early universe, highlighting their resilience against environmental stripping effects, and their impact on observable 21 cm signals.

EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6

We expect luminous (M 1450 ≲ −26.5) high-redshift quasars to trace the highest-density peaks in the early Universe. Here, we present observations of four z ≳ 6 quasar fields using JWST/NIRCam in the imaging and wide-field slitless spectroscopy mode and report a wide range in the number of detected [O iii]-emitting galaxies in the quasars’ environments, ranging between a density enhancement of δ ≈ 65 within a 2 cMpc radius—one of the largest protoclusters during the Epoch of Reionization discovered to date—to a density contrast consistent with zero, indicating the presence of a UV-luminous quasar in a region comparable to the average density of the Universe. By measuring the two-point cross-correlation function of quasars and their surrounding galaxies, as well as the galaxy autocorrelation function, we infer a correlation length of quasars at 〈z〉 = 6.25 of r0QQ=22.0−2.9+3.0cMpch−1 , while we obtain a correlation length of the [O iii]-emitting galaxies of r0GG=4.1±0.3cMpch−1 . By comparing the correlation functions to dark-matter-only simulations we estimate the minimum mass of the quasars’ host dark matter halos to be log10(Mhalo,min/M⊙)=12.43−0.15+0.13 (and log10(Mhalo,min[OIII]/M⊙)=10.56−0.03+0.05 for the [O iii] emitters), indicating that (a) luminous quasars do not necessarily reside within the most overdense regions in the early Universe, and that (b) the UV-luminous duty cycle of quasar activity at these redshifts is f duty ≪ 1. Such short quasar activity timescales challenge our understanding of early supermassive black hole growth and provide evidence for highly dust-obscured growth phases or episodic, radiatively inefficient accretion rates.

From Halos to Galaxies. IX. Estimate of Halo Assembly History for SDSS Galaxy Groups

The properties of the galaxies are tightly connected to their host halo mass and halo assembly history. Accurate measurement of the halo assembly history in observation is challenging but crucial to the understanding of galaxy formation and evolution. The stellar-to-halo mass ratio (M */M h) for the centrals has often been used to indicate the halo assembly time t h,50 of the group, where t h,50 is the lookback time at which a halo has assembled half of its present-day virial mass. Using mock data from the semi-analytic models, we find that M */M h shows a significant scatter with t h,50, with a strong systematic difference between the group with a star-forming central (blue group) and passive central (red group). To improve the accuracy, we develop machine learning models to estimate t h,50 for galaxy groups using only observable quantities in the mocks. Since star formation quenching will decouple the co-growth of the dark matter and baryon, we train our models separately for blue and red groups. Our models have successfully recovered t h,50, within an accuracy of ∼1.09 Gyr. With careful calibrations of individual observable quantities in the mocks with Sloan Digital Sky Survey (SDSS) observations, we apply the trained models to the SDSS Yang et al. groups and derive the t h,50 for each group for the first time. The derived SDSS t h,50 distributions are in good agreement with that in the mocks, in particular for blue groups. The derived halo assembly history, together with the halo mass, make an important step forward in studying the halo–galaxy connections in observation.

Formation of Galactic Disks. II. The Physical Drivers of Disk Spin-up

Using a representative sample of Milky Way (MW)–like galaxies from the TNG50 cosmological simulation, we investigate physical processes driving the formation of galactic disks. A disk forms as a result of the interplay between inflow and outflow carrying angular momentum in and out of the galaxy. Interestingly, the inflow and outflow have remarkably similar distributions of angular momentum, suggesting an exchange of angular momentum and/or outflow recycling, leading to continuous feeding of prealigned material from the corotating circumgalactic medium. We show that the disk formation in TNG50 is correlated with stellar bulge formation, in qualitative agreement with a recent theoretical model of disk formation facilitated by steep gravitational potentials. Disk formation is also correlated with the formation of a hot circumgalactic halo with around half of the inflow occurring at subsonic and transonic velocities corresponding to Mach numbers of ≲2. In the context of recent theoretical works connecting disk settling and hot halo formation, our results imply that the subsonic part of the inflow may settle into a disk while the remaining supersonic inflow will perturb this disk via the chaotic cold accretion. We find that disks tend to form when the host halos become more massive than ∼(1–2) × 1011 M ⊙, consistent with previous theoretical findings and observational estimates of the predisk protogalaxy remnant in the MW. Our results do not prove that either corotating outflow recycling, gravitational potential steepening, or hot halo formation cause disk formation, but they show that all these processes occur concurrently and may play an important role in disk growth.

The Massive and Distant Clusters of WISE Survey 2: A Stacking Analysis Investigating the Evolution of Star Formation Rates and Stellar Masses in Groups and Clusters

The evolution of galaxies depends on their masses and local environments; understanding when and how environmental quenching starts to operate remains a challenge. Furthermore, studies of the high-redshift regime have been limited to massive cluster members, owing to sensitivity limits or small fields of view when the sensitivity is sufficient, intrinsically biasing the picture of cluster evolution. In this work, we use stacking to investigate the average star formation history of more than 10,000 groups and clusters drawn from the Massive and Distant Clusters of WISE Survey 2. Our analysis covers near-ultraviolet to far-infrared wavelengths, for galaxy overdensities at 0.5 ≲ z ≲ 2.54. We employ spectral energy distribution fitting to measure the specific star formation rates (sSFRs) in four annular apertures with radii between 0 and 1000 kpc. At z ≳ 1.6, the average sSFR evolves similarly to the field in both the core and the cluster outskirts. Between z¯=1.60 and z¯=1.35 , the sSFR in the core drops sharply, and it continues to fall relative to the field sSFR at lower redshifts. We interpret this change as evidence that the impact of environmental quenching dramatically increases at z ∼ 1.5, with the short time span of the transition suggesting that the environmental quenching mechanism dominant at this redshift operates on a rapid timescale. We find indications that the sSFR may decrease with increasing host halo mass, but lower-scatter mass tracers than the signal-to-noise ratio are needed to confirm this relationship.

Milky Way-est: Cosmological Zoom-in Simulations with Large Magellanic Cloud and Gaia–Sausage–Enceladus Analogs

We present Milky Way-est, a suite of 20 cosmological cold-dark-matter-only zoom-in simulations of Milky Way (MW)-like host halos. Milky Way-est hosts are selected such that they (i) are consistent with the MW’s measured halo mass and concentration, (ii) accrete a Large Magellanic Cloud (LMC)-like (≈1011 M ⊙) subhalo within the last 2 Gyr on a realistic orbit, placing them near 50 kpc from the host center at z ≈ 0, and (iii) undergo a >1:5 sub-to-host halo mass ratio merger with a Gaia–Sausage–Enceladus (GSE)-like system at early times (0.67 < z < 3). Hosts satisfying these LMC and GSE constraints constitute <1% of all halos in the MW’s mass range, and their total masses grow rapidly at late times due to LMC analog accretion. Compared to hosts of a similar final halo mass that are not selected to include LMC and GSE analogs, Milky Way-est hosts contain 22% more subhalos with present-day virial masses above 108 M ⊙ throughout the virial radius, on average. This enhancement reaches ≈80% in the inner 100 kpc and is largely, if not entirely, due to LMC-associated subhalos. These systems also induce spatial anisotropy in Milky Way-est subhalo populations, with ≈60% of the total subhalo population within 100 kpc found in the current direction of the LMC. Meanwhile, we find that GSE-associated subhalos do not significantly contribute to present-day Milky Way-est subhalo populations. These results provide context for our Galaxy’s dark matter structure and subhalo population and will help interpret a range of measurements that are currently only possible in the MW.

Impact of astrophysical scatter on the epoch of reionization [H i]21 bispectrum

It is believed that the first star-forming galaxies are the main drivers of cosmic reionization. It is usually assumed that there is a one-to-one relationship between the star formation rate (SFR) inside a galaxy and the host halo mass in semi-analytical/numerical modeling of large-scale ionization maps during the epoch of reionization. However, more accurate simulations and observations suggest that the SFR and ionizing luminosity in galaxies may vary considerably even if the host halo mass is the same. This astrophysical scatter can introduce an additional non-Gaussianity in the [H i]21cm signal, which might not be captured adequately in the power spectrum. In this work, we have studied the impact of the scatter on the [H i]21cm bispectrum using semi-numerical simulations. We find that the scatter primarily affects small ionized regions, whereas the large ionized bubbles remain largely unaffected. Although, the fractional change in the [H i]21cm bispectra due to the scatter is found to be more than a factor of 10 at large scales (k 1 ≲ 1 Mpc-1) for z=7.4, it is found to be statistically insignificant. However, at small scales (k 1 ~ 2.55 Mpc-1), we have found the impact due to the scatter to be high in magnitude (|〈Δ B 〉/B no-scatter| ~ 1) and statistically significant (|〈Δ B〉/σ ΔB| ≳ 5) at neutral fraction, x̅HI ~ 0.8 for z=7.4. The impact due to scatter is found to be even more prominent (|〈Δ B 〉/B no-scatter| ≳ 10) at small scales for z=10 and x̅HI ~ 0.8, but with reduced statistical significance to some extent (|〈Δ B〉/σ ΔB| ~ 3), compared to z=7.4 at the same neutral fraction. We have also found that in the most optimistic scenario, SKA1-Low might be able to detect these signatures of astrophysical scatter, at ~ 3σ and ~ 5σ detection significance for x̅HI ~ 0.8 and 0.9 respectively, for the equilateral [H i]21cm bispectrum at z=7.4.

The beyond-halo mass effects of the cosmic web environment on galaxies

ABSTRACT Galaxy properties primarily depend on their host halo mass. Halo mass, in turn, depends on the cosmic web environment. We explore if the effect of the cosmic web on galaxy properties is entirely transitive via host halo mass, or if the cosmic web has an effect independent of mass. The secondary galaxy bias, sometimes referred to as ‘galaxy assembly bias’, is the beyond-mass component of the galaxy–halo connection. We investigate the link between the cosmic web environment and the secondary galaxy bias in simulations. We measure the secondary galaxy bias through the following summary statistics: projected two-point correlation function, $w_{\mathrm{p}}(r_{\mathrm{p}})$, and counts-in-cylinders statistics, $P(N_{\mathrm{CIC}})$. First, we examine the extent to which the secondary galaxy bias can be accounted for with a measure of the environment as a secondary halo property. We find that the total secondary galaxy bias preferentially places galaxies in more strongly clustered haloes. In particular, haloes at fixed mass tend to host more galaxies when they are more strongly associated with nodes or filaments. This tendency accounts for a significant portion, but not the entirety, of the total secondary galaxy bias effect. Secondly, we quantify how the secondary galaxy bias behaves differently depending on the host halo proximity to nodes and filaments. We find that the total secondary galaxy bias is relatively stronger in haloes more associated with nodes or filaments. We emphasize the importance of removing halo mass effects when considering the cosmic web environment as a factor in the galaxy–halo connection.

A two-phase model of galaxy formation – II. The size–mass relation of dynamically hot galaxies

ABSTRACT In Paper-I, we developed a two-phase model to connect dynamically hot galaxies (such as ellipticals and bulges) with the formation of self-gravitating gas clouds (SGCs) associated with the fast assembly of dark matter haloes. Here, we explore the implications of the model for the size–stellar mass relation of dynamically hot galaxies. Star-forming sub-clouds resulting from the fragmentation of the turbulent SGC inherit its spatial structure and dynamical hotness, producing a ‘homologous’ relation, $r_{\rm f}\approx \, 100\, r_{\rm bulge}$, between the size of a dynamically hot galaxy ($r_{\rm bulge}$) and that of its host halo assembled in the fast regime ($r_{\rm f}$), independent of redshift and halo mass. This relation is preserved by the ‘dry’ expansion driven by dynamical heating when a galaxy becomes gas-poor due to inefficient cooling, and is frozen due to the stop of bulge growth during the slow assembly regime of the halo. The size–stellar mass relation is thus a simple combination of the galaxy–halo homology and the non-linear stellar mass–halo mass relation. Using a set of halo assembly histories, we reproduce all properties in the observed size–mass relation of dynamically hot galaxies, including the flattening in the low-mass end and the upturn in the massive end. The prediction matches observational data currently available to $z \approx 4$, and can be tested in the future at higher z. Our results indicate that the sizes of dynamically hot galaxies are produced by the dissipation and collapse of gas in haloes to establish SGCs in which stars form.

LIGHTS. Survey Overview and a Search for Low Surface Brightness Satellite Galaxies

We present an overview of the LBT Imaging of Galactic Halos and Tidal Structures survey, which currently includes 25 nearby galaxies that are on average ∼1 mag fainter than the Milky Way, and a catalog of 54 low central surface brightness (24 < μ 0,g /mag arcsec−2 < 28) satellite galaxy candidates, most of which were previously uncatalogued. The depth of the imaging exceeds the full 10 yr depth of the Rubin Observatory’s Legacy Survey of Space and Time. We find, after applying completeness corrections, rising numbers of candidate satellites as we approach the limiting luminosity (M r ∼ −8 mag) and central surface brightness (μ 0,g ∼ 28 mag arcsec−2). Over the parameter range we explore, each host galaxy (excluding those that are in overdense regions, apparently groups) has nearly four such candidate satellites to a projected radius of ∼100 kpc. These objects are mostly just at or beyond the reach of spectroscopy unless they are H i rich or have ongoing star formation. We identify three, possibly four, ultra-diffuse satellite galaxies (effective radius >1.5 kpc). This incidence rate falls within expectations of the extrapolation of the published relationship between the number of ultra-diffuse satellite galaxies and host halo mass. Last, we visually identify 12 candidate satellites that host a nuclear star cluster (NSC). The NSC occupation fraction for the sample (12/54) matches that published for satellites of early-type galaxies, suggesting that the parent’s morphological type plays at most a limited role in determining the NSC occupation fraction.