The nature of assembly bias – II. Halo spin Lacerna, Ivan; Padilla, Nelson
Monthly Notices of the Royal Astronomical Society Letters,
October 2012, Volume:
426, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT
We study an assembly‐type bias parametrized by the dimensionless spin parameter that affects massive structures. In numerical simulations, higher spin haloes are more strongly clustered than ...lower spin haloes of equal mass. We detect a difference of over 30 per cent in the clustering strength for dark matter haloes of 1013–1014 h−1 M⊙, which is similar to the result of Bett et al. We explore whether the dependence of clustering strength on halo spin is removed if we apply the redefinition of overdensity peak height proposed by Lacerna & Padilla (Paper I) obtained using assembly ages. We find that this is not the case due to two reasons. First, only a few objects of low virial mass are moved into the mass range where the spin introduces an assembly‐type bias after using this redefinition. Secondly, this formalism does not alter the mass of massive objects. In other words, the sample of haloes with redefined mass M in the high‐mass regime is practically the same as before the redefinition of peak height, and thus the clustering behaviour is the same. We then repeat the process of finding the redefined peak height of Paper I but using the spin. In this case, the new masses show no spin‐related assembly bias but they introduce a previously absent assembly bias with respect to relative age. From this result, we conclude that the assembly‐type bias with respect to the halo spin has a different origin from that with respect to the assembly age. The former may be due to the material from filaments, which is accreted by massive haloes, and enhanced in high‐density environments, thus causing more extreme spin values without significantly changing the formation age of the halo. In addition, the estimates of the mass of collapsed structures in numerical simulations could be lower than the true mass, even in cluster‐size haloes. High‐mass objects may correspond, in some cases, to a different peak height from that suggested by their virial mass, providing a possible explanation for the assembly‐type bias with respect to the spin.
We analyse galaxies in groups in the Sloan Digital Sky Survey (SDSS) and find a weak but significant assembly-type bias, where old central galaxies have a higher clustering amplitude (61 ± 9 per ...cent) at scales >1 h
−1 Mpc than young central galaxies of equal host halo mass (Mh
∼ 1011.8 h
− 1 M⊙). The observational sample is volume limited out to z = 0.1 with M
r
− 5 log (h) ≤ −19.6. We construct a mock catalogue of galaxies that shows a similar signal of assembly bias (46 ± 9 per cent) at the same halo mass. We then adapt the model presented by Lacerna & Padilla (Paper I) to redefine the overdensity peak height, which traces the assembly bias such that galaxies in equal density peaks show the same clustering regardless of their stellar age, but this time using observational features such as a flux limit. The proxy for peak height, which is proposed as a better alternative than the virial mass, consists in the total mass given by the mass of neighbour host haloes in cylinders centred at each central galaxy. The radius of the cylinder is parameterized as a function of stellar age and virial mass. The best-fitting sets of parameters that make the assembly bias signal lower than 5–15 per cent for both SDSS and mock central galaxies are similar. The idea behind the parameterization is not to minimize the bias, but it is to use this method to understand the physical features that produce the assembly bias effect. Even though the tracers of the density field used here differ significantly from those used in Paper I, our analysis of the simulated catalogue indicates that the different tracers produce correlated proxies, and therefore the reason behind assembly bias is the crowding of peaks in both simulations and the SDSS.
The large Integral Field Spectroscopy surveys have allowed the classification of ionizing sources of emission lines on sub-kiloparsec scales. In this work, we define two non-parametric parameters, ...quiescence (Fq) and its concentration (Cq), to quantify the strength and the spatial distribution of the quenched areas, respectively, traced by the LI(N)ER regions with low EW(H ). With these two measurements, we classify MaNGA galaxies into inside-out and outside-in quenching types according to their locations on the Fq versus Cq plane and we measure the fraction of inside-out (outside-in) quenching galaxies as a function of halo mass. We find that the fraction of galaxies showing inside-out quenching increases with halo mass, irrespective of stellar mass or galaxy type (satellites versus centrals). In addition, high-stellar-mass galaxies exhibit a greater fraction of inside-out quenching compared to low-stellar-mass ones in all environments. In contrast, the fraction of outside-in quenching does not depend on halo mass. Our results suggest that morphological quenching may be responsible for the inside-out quenching seen in all environments. On the other hand, the flat dependence of the outside-in quenching on halo mass could be a mixed result of ram pressure stripping and galaxy mergers. Nevertheless, for a given environment and stellar mass, the fraction of inside-out quenching is systematically greater than that of outside-in quenching, suggesting that inside-out quenching is the dominant quenching mode in all environments.
Abstract
We combine an unprecedented MaNGA sample of over 3000 passive galaxies in the stellar mass range 10
9
–10
12
M
⊙
with the Sloan Digital Sky Survey group catalog by Tinker to quantify how ...central and satellite formation, quantified by radial profiles in stellar age, Fe/H, and Mg/Fe, depends on the stellar mass of the galaxy (
M
*
) and the mass of the host halo (
M
h
). After controlling for
M
*
and
M
h
, the stacked spectra of centrals and satellites beyond the effective radius (
r
e
) show small, yet significant differences in multiple spectral features at the 1% level. According to spectral fitting with the code
alf
, a primary driver of these differences appears to be Mg/Fe variations, suggesting that stellar populations in the outskirts of satellites formed more rapidly than the outer populations of centrals. To probe the physical mechanisms that may be responsible for this signal, we examined how satellite stellar populations depend on
M
h
. We find that satellites in high-
M
h
halos show older stellar ages, lower Fe/H, and higher Mg/Fe compared to satellites in low-
M
h
halos, especially for
M
*
= 10
9.5
–10
10.5
M
⊙
. These signals lend support to environmentally driven processes that quench satellite galaxies, although variations in the merger histories of central and satellite galaxies also emerge as a viable explanation.
The galaxy integrated H star formation rate-stellar mass relation, or SFR(global)-M*(global) relation, is crucial for understanding star formation history and evolution of galaxies. However, many ...studies have dealt with SFR using unresolved measurements, which makes it difficult to separate out the contamination from other ionizing sources, such as active galactic nuclei and evolved stars. Using the integral field spectroscopic observations from SDSS-IV MaNGA, we spatially disentangle the contribution from different H powering sources for ∼1000 galaxies. We find that, when including regions dominated by all ionizing sources in galaxies, the spatially resolved relation between H surface density ( H (all)) and stellar mass surface density ( *(all)) progressively turns over at the high *(all) end for increasing M*(global) and/or bulge dominance (bulge-to-total light ratio, B/T). This in turn leads to the flattening of the integrated H (global)-M*(global) relation in the literature. By contrast, there is no noticeable flattening in both integrated H (H ii)-M*(H ii) and spatially resolved H (H ii)- *(H ii) relations when only regions where star formation dominates the ionization are considered. In other words, the flattening can be attributed to the increasing regions powered by non-star-formation sources, which generally have lower ionizing ability than star formation. An analysis of the fractional contribution of non-star-formation sources to total H luminosity of a galaxy suggests a decreasing role of star formation as an ionizing source toward high-mass, high-B/T galaxies and bulge regions. This result indicates that the appearance of the galaxy integrated SFR-M* relation critically depends on their global properties (M*(global) and B/T) and relative abundances of various ionizing sources within the galaxies.
We present a new proxy for the overdensity peak height for which the large-scale clustering of haloes of a given mass does not vary significantly with the assembly history. The peak height, usually ...taken to be well represented by the virial mass, can instead be approximated by the mass inside spheres of different radii, which in some cases can be larger than the virial radius and therefore include mass outside the individual host halo. The sphere radii are defined as
where δt is the age relative to the typical age of galaxies hosted by haloes with virial mass M
vir, M
nl is the non-linear mass, and a= 0.2 and b=−0.02 are the free parameters adjusted to trace the assembly bias effect. Note that r depends on both halo mass and age. In this new approach, some of the objects which were initially considered low-mass peaks (i.e. which had low virial masses) belong to regions with higher overdensities. At large scales, i.e. in the two-halo regime, this model properly recovers the simple prescription where the bias responds to the height of the mass peak alone, in contrast to the usual definition (virial mass) that shows a strong dependence on additional halo properties such as formation time. The dependence on the age in the one-halo term is also remarkably reduced with the new definition. The population of galaxies whose 'peak height' changes with this new definition consists mainly of old stellar populations and are preferentially hosted by low-mass haloes located near more massive objects. The latter is in agreement with recent results which indicate that old, low-mass haloes would suffer truncation of mass accretion by nearby larger haloes or simply due to the high density of their surroundings, thus showing an assembly bias effect. The change in mass is small enough that the Sheth et al. mass function is still a good fit to the resulting distribution of new masses.
The Triangulum Australis cluster is one of about a dozen nearby massive cluster systems which contribute to the gravitational pull behind the so-called Great Attractor that is dominated by the nearby ...Shapley Supercluster mass, which conforms the galaxy velocity flows observed in that general direction. Here, we study the structure and dynamical mass of the Triangulum Australis cluster together with the neighbouring cluster AS0794. We present a set of 131 velocities collected in the regions of the two clusters with the 2.5 m Du Pont telescope at Las Campanas Observatory (Chile). For the Triangulum Australis cluster we find a dynamical mass of about Mv = 4.2 (±1.3) × 1015 M⊙ and for AS0794 a value of about Mv = 1.7 (±1.3) × 1013 M⊙. These values are consistent with the observed X-ray luminosities of these clusters. Combined with velocities already known we reanalyse the structure and dynamics of this general region, finding that both clusters, together with at least eight other ones, form a large supercluster, centered on TriAus (which dominates in terms of mass). We find that this supercluster is part of a large-scale structure filament linked to the Shapley supercluster (SSC). Uncertainties remain on the richness and detailed structure of this filament and the TriAus supercluster because parts of it remain hidden behind the Galaxy disk. Based on observations made with the 2.50 m Du Pont Telescope at the Las Campanas Observatory (Chile).
The Triangulum Australis cluster is one of about a dozen nearby massive cluster systems which contribute to the gravitational pull behind the so-called Great Attractor that is dominated by the nearby ...Shapley Supercluster mass, which conforms the galaxy velocity flows observed in that general direction. Here, we study the structure and dynamical mass of the Triangulum Australis cluster together with the neighbouring cluster AS0794. We present a set of 131 velocities collected in the regions of the two clusters with the 2.5 m Du Pont telescope at Las Campanas Observatory (Chile). For the Triangulum Australis cluster we find a dynamical mass of about
M
v
= 4.2 (±1.3) × 10
15
M
⊙
and for AS0794 a value of about
M
v
= 1.7 (±1.3) × 10
13
M
⊙
. These values are consistent with the observed X-ray luminosities of these clusters. Combined with velocities already known we reanalyse the structure and dynamics of this general region, finding that both clusters, together with at least eight other ones, form a large supercluster, centered on TriAus (which dominates in terms of mass). We find that this supercluster is part of a large-scale structure filament linked to the Shapley supercluster (SSC). Uncertainties remain on the richness and detailed structure of this filament and the TriAus supercluster because parts of it remain hidden behind the Galaxy disk.
ABSTRACT
We use the improved IllustrisTNG300 magnetohydrodynamical cosmological simulation to revisit the effect that secondary halo bias has on the clustering of the central galaxy population. With ...a side length of 205 h−1 Mpc and significant improvements on the subgrid model with respect to previous Illustris simulations, IllustrisTNG300 allows us to explore the dependencies of galaxy clustering over a large cosmological volume and halo mass range. We show at high statistical significance that the halo assembly bias signal (i.e. the secondary dependence of halo bias on halo formation redshift) manifests itself on the clustering of the galaxy population when this is split by stellar mass, colour, specific star formation rate, and surface density. A significant signal is also found for galaxy size: at fixed halo mass, larger galaxies are more tightly clustered than smaller galaxies. This effect, in contrast to the rest of the dependencies, seems to be uncorrelated with halo formation time, with some small correlation only detected for halo spin. We also explore the transmission of the spin bias signal, i.e. the secondary dependence of halo bias on halo spin. Although galaxy spin retains little information about the total halo spin, the correlation is enough to produce a significant galaxy spin bias signal. We discuss possible ways to probe this effect with observations.
ABSTRACT
We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce, and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the Northern and ...Southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous data set, largest to date, allows us to discuss the intrinsic Fe spread, the shape, and statistics of Al-Mg and N-C anti-correlations as a function of cluster mass, luminosity, age, and metallicity for all 31 clusters. We find that the Fe spread does not depend on these parameters within our uncertainties including cluster metallicity, contradicting earlier observations. We do not confirm the metallicity variations previously observed in M22 and NGC 1851. Some clusters show a bimodal Al distribution, while others exhibit a continuous distribution as has been previously reported in the literature. We confirm more than two populations in ω Cen and NGC 6752, and find new ones in M79. We discuss the scatter of Al by implementing a correction to the standard chemical evolution of Al in the Milky Way. After correction, its dependence on cluster mass is increased suggesting that the extent of Al enrichment as a function of mass was suppressed before the correction. We observe a turnover in the Mg-Al anticorrelation at very low Mg in ω Cen, similar to the pattern previously reported in M15 and M92. ω Cen may also have a weak K-Mg anticorrelation, and if confirmed, it would be only the third cluster known to show such a pattern.
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