We study the dependence of galaxy clustering on H i mass using ∼16,000 galaxies with redshift in the range of 0.0025 < z < 0.05 and H i mass of M H I > 10 8 M ☉ , drawn from the 70% complete sample ...of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies with M H I above different thresholds and make volume-limited clustering measurements in terms of three statistics: the projected two-point correlation function, the projected cross-correlation function with respect to a reference sample, and the redshift-space monopole moment. In contrast to previous studies, which found no/weak H i mass dependence, we find both the clustering amplitudes on scales above a few megaparsecs and the bias factors to increase significantly with increasing H i mass for M H I > 10 9 M ☉ . For H i mass thresholds below ∼ 10 9 M ☉ , the inferred galaxy bias factors are systematically lower than the minimum halo bias from mass-selected halo samples. We extend the simple halo model, in which the galaxy content is only determined by halo mass, by including the halo formation time as an additional parameter. A model that puts H i-rich galaxies into halos that formed late can reproduce the clustering measurements reasonably well. We present the implications of our best-fitting model on the correlation of H i mass with halo mass and formation time, as well as the halo occupation distributions and H i mass functions for central and satellite galaxies. These results are compared with the predictions from semianalytic galaxy formation models and hydrodynamic galaxy formation simulations.
On halo formation times and assembly bias Li, Yun; Mo, H. J.; Gao, L.
Monthly notices of the Royal Astronomical Society,
09/2008, Volume:
389, Issue:
3
Journal Article
Peer reviewed
Open access
In this paper, we use the ‘Millennium Simulation’ to re-examine the mass assembly history of dark matter haloes and the age dependence of halo clustering. We use eight different definitions of halo ...formation times to characterize the different aspects of the assembly history of a dark matter halo. We find that these formation times have different dependence on halo mass. While some formation times characterize well the hierarchical nature of halo formation, in the sense that more massive haloes have later formation, the trend is reversed for other definitions of the formation time. In particular, the formation times that are likely to be related to the formation of galaxies in dark haloes show strong trends of ‘downsizing’, in that lower mass haloes form later. We also investigate how the correlation amplitude of dark matter haloes depends on the different formation times. We find that this dependence is quite strong for some definitions of formation time but weak or absent for other definitions. In particular, the correlation amplitude of haloes of a given mass is almost independent of their last major merger time. For the definitions that are expected to be more related to the formation of galaxies in dark haloes, a significant assembly bias is found only for haloes less massive than M*. We discuss our results in connection to the hierarchical assembly of dark matter haloes, the ‘archaeological downsizing’ observed in the galaxy population, and the observed colour-dependence of the clustering strength of galaxy groups and clusters.
ABSTRACT
We present a comparison of the physical properties of the ionized gas in the circumgalactic medium and intergalactic medium (IGM) at z ∼ 0 between observations and four cosmological ...hydrodynamical simulations: Illustris, TNG300 of the IllustrisTNG project, EAGLE, and one of the Magneticum simulations. For the observational data, we use the gas properties that are inferred from cross-correlating the Sunyaev–Zel’dovich effect (SZE) from the Planck CMB maps with haloes and large-scale structure. Both the observational and simulation results indicate that the integrated gas pressure in haloes deviates from the self-similar case, showing that feedback impacts haloes with $M_{500}\sim 10^{12\!-\!13}\, {\rm M_\odot }$. The simulations predict that more than half the baryons are displaced from haloes, while the gas fraction inferred from our observational data roughly equals the cosmic baryon fraction throughout the $M_{500}\sim 10^{12\!-\!14.5}\, {\rm M_\odot }$ halo mass range. All simulations tested here predict that the mean gas temperature in haloes is about the virial temperature, while that inferred from the SZE is up to one order of magnitude lower than that from the simulations (and also from X-ray observations). While a remarkable agreement is found for the average properties of the IGM between the observation and some simulations, we show that their dependence on the large-scale tidal field can break the degeneracy between models that show similar predictions otherwise. Finally, we show that the gas pressure and the electron density profiles from simulations are not well described by a generalized NFW profile. Instead, we present a new model with a mass-dependent shape that fits the profiles accurately.
To cite this article: Mo J-H, Kang E-K, Quan S-H, Rhee C-S, Lee CH, Kim D-Y. Anti-tumor necrosis factor-alpha treatment reduces allergic responses in an allergic rhinitis mouse model. Allergy 2011; ...66: 279-286. ABSTRACT: Background: Tumor necrosis factor (TNF)-α is a principal mediator of the acute inflammatory response, including allergic rhinitis. TNF-α inhibitors are widely used for the treatment of inflammatory conditions such as rheumatoid arthritis and inflammatory bowel diseases; however, the effects of TNF-α inhibitors on allergic rhinitis are not well established. We aimed to investigate the effects of infliximab, a TNF-α inhibitor, on allergic rhinitis in a mouse model. Methods: BALB/c mice were sensitized with ovalbumin (OVA) and alum, and challenged intranasally with OVA. The TNF-α inhibitor, infliximab was administered intraperitoneally, and multiple parameters of allergic responses were evaluated to determine the effects of infliximab. Results: Infliximab reduced allergic symptoms and eosinophilic infiltration into the nasal mucosa. It also suppressed total and OVA-specific IgE levels, and inhibited local Th2 cytokine transcription in the nasal mucosa and systemic Th2 cytokine production by splenocytes. Furthermore, the expression of E-selectin, neither intercellular adhesion molecule 1 (ICAM-1) nor vascular cell adhesion molecule 1 (VCAM-1), in the nasal mucosa was suppressed in the infliximab-treated group when compared to the nontreated group. Conclusion: This study shows that the TNF-α inhibitor infliximab induces anti-allergic effects by decreasing local and systemic Th2 cytokine (IL-4) production, total and OVA-specific IgE levels, adhesion molecule (E-selectin) expression, and eosinophil infiltration into the nasal mucosa in an allergic rhinitis model. Therefore, infliximab should be considered as a potential agent in treating allergic rhinitis.
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Using a statistically representative sample of 911 central galaxies (CENs) from the Sloan Digital Sky Survey (SDSS) Data Release 4 group catalogue, we study how the structure (shape and size) of the ...first rank (by stellar mass) group and cluster members depends on (1) galaxy stellar mass (Mstar), (2) the global environment defined by the dark matter halo mass (Mhalo) of the host group and (3) the local environment defined by their special halocentric position. We quantify the structure of SDSS galaxies with a galfit-based pipeline that fits two-dimensional Sérsic models to the r-band image data. Through tests with simulated and real galaxy images, we demonstrate that our pipeline can recover Sérsic parameters without significant bias. We find that the fitting results are most sensitive to the background sky level determination, and we strongly recommend using the SDSS global value. We also find that uncertainties in the background sky level translate into a strong covariance between the total magnitude, the half-light radius (r50) and the Sérsic index (n), especially for bright/massive galaxies. Applying our pipeline to the CEN sample, we find that n of CENs depends strongly on Mstar, but only weakly or not at all on Mhalo. The n–Mstar relation holds for CENs over the full range of halo masses that we consider. Less massive CENs tend to be disc like and high-mass systems are typically spheroids, with a considerable scatter in n at all galaxy masses. Similarly, CEN sizes depend on galaxy stellar mass and luminosity, with early- and late-type galaxies exhibiting different slopes for the size–luminosity (r50–L) and the size–stellar mass (r50–Mstar) scaling relations. Moreover, to test the impact of local environment on CENs, we compare the structure of CENs with that satellite galaxies (SATs) of comparable Mstar. We find that low-mass (<1010.75 h−2 M⊙) SATs have somewhat larger median Sérsic indices than CENs of a similar Mstar. Furthermore, low-mass, late-type SATs are moderately smaller in size than late-type CENs of the same stellar mass. However, we find no size differences between early-type CENs and SATs and no structural differences between CENs and SATs when they are matched in both optical colour and stellar mass. The similarity in the structure of massive SATs and CENs demonstrates that the halocentric distinction has no significant impact on the structure of spheroids. We conclude that Mstar is the most fundamental property determining the basic structural shape and size of a galaxy. In contrast, the lack of a significant n–Mhalo relation rules out a clear distinct group mass for producing spheroids. The existence of spheroid CENs in low- and high-mass groups suggests that the morphological transformation processes that produce spheroids must occur at the centres of groups spanning a wide range of masses.
Using the stellar ages and metallicities of galaxies in the Sloan Digital Sky Survey (SDSS) obtained by Gallazzi et al. and the SDSS galaxy group catalogue of Yang et al., we study how the stellar ...ages and metallicities of central and satellite galaxies depend on stellar mass, M*, and halo mass, Mh. We find that satellites are older and metal richer than centrals of the same stellar mass, and this difference increases with decreasing M*. In addition, the slopes of the age–stellar mass and metallicity–stellar mass relations are found to become shallower in denser environments (more massive haloes). This is due to the fact that the average age and metallicity of low-mass satellite galaxies (M*≲ 1010 h−2 M⊙) increase with the mass of the halo in which they reside. In order to gain understanding of the physical origin of these trends, we compare our results with the semi-analytical model of Wang et al. The model, which predicts stellar mass functions and two-point correlation functions in good overall agreement with observations, also reproduces the fact that satellites are older than centrals of the same stellar mass and that the age difference increases with the halo mass of the satellite. This is a consequence of the fact that satellites are stripped of their hot gas reservoir shortly after they are accreted by their host haloes (strangulation). The ensuing quenching of star formation leaves the stellar populations of satellites to evolve passively, while the prolonged star formation activity of centrals keeps their average ages younger. The resulting age offset is larger in more massive environments because their satellites were accreted earlier. The model does not reproduce he halo mass dependence of the metallicities of low-mass satellites, yields metallicity–stellar mass and age–stellar mass relations that are too shallow and predicts that satellite galaxies have the same metallicities as centrals of the same stellar mass, in disagreement with the data. We argue that these discrepancies are likely to indicate the need to (i) modify the recipes of both supernova feedback and active galactic nucleus feedback, (ii) use a more realistic description of strangulation and (iii) include a proper treatment of the tidal stripping, heating and destruction of satellite galaxies.
ABSTRACT We study how halo intrinsic dynamical properties are linked to their formation processes for halos in two mass ranges, and , and how both are correlated with the large-scale tidal field ...within which the halos reside at present. We identify infall halos that are about to merge with their hosts. We find that the tangential infall velocity increases significantly with the strength of the tidal field, but no strong correlation is found for the radial component. These results can be used to explain the environmental dependence of internal velocity anisotropy and spin of halos. The position vectors and velocities of infall halos are aligned with the principal axes of the tidal field, and the alignment depends on the strength of the tidal field. Opposite accretion patterns are found in weak and strong tidal fields, showing that in a weak field the accretion flow is dominated by radial motion within the local structure, while a large tangential component is present in a strong field. These findings can be used to understand the strong alignments we find between the principal axes of the internal velocity ellipsoids of halos and the tidal field, and their dependence on the strength of the tidal field. We further find that only in weak tidal fields does the spin-tidal field alignment follow the prediction of the tidal torque theory. We discuss how our results may be used to understand the spins of disk galaxies and velocity structures of elliptical galaxies and their correlations with large-scale structure.
We use the conditional luminosity function (CLF) and data from the 2-degree Field Galaxy Redshift Survey (2dFGRS) to constrain the average relation between light and mass in a Lambda cold dark matter ...(ΛCDM) cosmology with Ωm= 0.23 and σ8= 0.74 (hereafter WMAP3 cosmology). Reproducing the observed luminosity dependence of the galaxy two-point correlation function results in average mass-to-light ratios that are ∼35 per cent lower than those in a ΛCDM cosmology with Ωm= 0.3 and σ8= 0.9 (hereafter WMAP1 cosmology). This removes an important problem with previous halo occupation models which had a tendency to predict cluster mass-to-light ratios that were too high. For the WMAP3 cosmology, our model yields average mass-to-light ratios, central galaxy luminosities, halo occupation numbers, satellite fractions and luminosity-gap statistics, that are all in excellent agreement with those obtained from a 2dFGRS group catalogue and from other independent studies. We also use our CLF model to compute the probability distribution P(M | Lcen), that a central galaxy of luminosity Lcen resides in a halo of mass M. We find this distribution to be much broader than what is typically assumed in halo occupation distribution models, which has important implications for the interpretation of satellite kinematics and galaxy–galaxy lensing data. Finally, reproducing the luminosity dependence of the pairwise peculiar velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios for clusters and a satellite fraction that decreases strongly with increasing luminosity. This is only marginally consistent with the constraints obtained from the luminosity dependence of the galaxy two-point correlation function. We argue that a cosmology with parameters between those of the WMAP1 and WMAP3 cosmologies is likely to yield results with a higher level of consistency.
The general large‐scale synthesis of a family of single‐crystalline transition metal tungstate nanorods/nanowires is easily realized by a hydrothermal crystallization technique under mild conditions ...using cheap and simple inorganic salts as precursors. Uniform tungstate nanorods/nanowires such as MWO4 (M = Zn, Mn, Fe), Bi2WO6, Ag2WO4, and Ag2W2O7 with diameters of 20–40 nm, lengths of up to micrometers, and controlled aspect ratios can be readily obtained by hydrothermal transformation and recrystallization of amorphous particulates. This novel and efficient pathway toward various kinds of related low‐dimensional tungstate nanocrystals under mild conditions could open new opportunities for further investigating the novel properties of tungstate materials.
Large‐scale synthesis of a family of single‐crystalline transition metal tungstate nanorods/ nanowires by a mild hydrothermal crystallization technique using inorganic salts as precursors is reported. Uniform tungstate nanorods/nanowires, such as MWO4 (M = Zn, Mn, Fe (as shown in the Figure)), Bi2WO6, Ag2WO4, and Ag2W2O7 with diameters of 20–40 nm, lengths of up to micrometers, and controlled aspect ratios can be readily obtained.
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Using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey Data Release 2, we investigate the correlation between various galaxy properties and halo mass. We split the ...population of galaxies in early-types, late-types and intermediate-types, based on their colour and specific star formation rate. At fixed luminosity, the late- (early-)type fraction of galaxies increases (decreases) with decreasing halo mass. Most importantly, this mass dependence is smooth and persists over the entire mass range probed, without any break or feature at any mass-scale. We argue that the previous claim of a characteristic feature on galaxy group scales is an artefact of the environment estimators used. At fixed halo mass, the luminosity dependence of the type fractions is surprisingly weak, especially over the range 0.25 ≲ L/L* ≲ 2.5: galaxy type depends more strongly on halo mass than on luminosity. In agreement with previous studies, the late- (early-)type fraction increases (decreases) with increasing halocentric radius. However, we find that this radial dependence is present in haloes of all masses probed (down to 1012 h−1 M⊙), while previous studies did not find any radial dependence in haloes with M≲ 1013.5 h−1 M⊙. We argue that this discrepancy owes to the fact that we have excluded central galaxies from our analysis. We also find that the properties of satellite galaxies are strongly correlated with those of their central galaxy. In particular, the early-type fraction of satellites is significantly higher in a halo with an early-type central galaxy than in a halo of the same mass but with a late-type central galaxy. This phenomenon, which we call ‘galactic conformity’, is present in haloes of all masses and for satellites of all luminosities. Finally, the fraction of intermediate-type galaxies is always ∼20 per cent, independent of luminosity, independent of halo mass, independent of halocentric radius, and independent of whether the galaxy is a central galaxy or a satellite galaxy. We discuss the implications of all these findings for galaxy formation and evolution.
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