118628300
Environmental effects on real-space and redshift-space galaxy clustering
Galaxy formation inside dark matter halos, as well as the formation of the halo itself, can be affected by the large-scale environment. Evaluating the imprint of environmental effects on galaxy clustering is crucial for construing precise cosmological constraints from galaxy redshift survey data. We investigate the environmental impact on both real-space and redshift-space galaxy clustering statistics using a semianalytic model (SAM) derived from the Millenium Simulation. We compare clustering statistics from original SAM galaxy samples to shuffled samples with the environmental influences on galaxy properties eliminated. Among the luminosity-threshold samples examined, the one with the lowest threshold luminosity (~0.2 -->L*) is the most affected by environmental effects, having a ~10% decrease in the real-space two-point correlation function (2PCF) after shuffling. By decomposing the 2PCF into five different components based on the source of pairs, we show that the change in the 2PCF can be explained by the age and richness (galaxy occupation number) dependence of halo clustering. The 2PCFs in redshift space are found to change in a similar manner after shuffling. If the environmental effects are neglected, halo occupation distribution modeling of the real-space and redshift-space clustering may have a less than 6.5% systematic uncertainty in constraining -->σ8Ωm0.6 from the most affected SAM sample, and substantially smaller uncertainties for the other, more luminous samples. We argue that the effect could be even smaller in reality. In the Appendix, we present a method to decompose the 2PCF, which can be applied to measure the two-point autocorrelation functions of galaxy subsamples in a volume-limited galaxy sample and their two-point cross-correlation functions in a single run using only one random catalog.
124560798
Lensing of 21cm Absorption "Halos" of First Galaxies
14026331
Redshift-space distortions with the halo occupation distribution – I. Numerical simulations
We show how redshift-space distortions of the galaxy correlation function or power spectrum can constrain the matter density parameter Ω m and the linear matter fluctuation amplitude σ 8 . We improve on previous treatments by adopting a fully non-linear description of galaxy clustering and bias, which allows us to achieve the accuracy demanded by larger galaxy redshift surveys and to break parameter degeneracies by combining large-scale and small-scale distortions. Given an observationally motivated choice of the initial power spectrum shape, we consider different combinations of Ω m and σ 8 and find parameters of the galaxy halo occupation distribution (HOD) that yield nearly identical galaxy correlation functions in real space. We use these HOD parameters to populate the dark matter haloes of large N-body simulations, from which we measure redshift-space distortions on small and large scales. We include a velocity bias parameter α v that allows the velocity dispersions of satellite galaxies in haloes to be systematically higher or lower than those of dark matter. Large-scale distortions are determined by the parameter combination β ≡ Ω 0.6 m /b g , where bg is the bias factor defined by the ratio of galaxy and matter correlation functions, in agreement with the linear theory prediction of parameter degeneracy. However, linear theory does not accurately describe the distortions themselves on scales accessible to our simulations. We provide fitting formulas to estimate β from measurements of the redshift-space correlation function or power spectrum, and we show that these formulas are significantly more accurate than those in the existing literature. On small scales, the 'FOG' distortions at projected separations ∼0.1 h -1 Mpc depend on Ω m α 2 v but are independent of as, while at intermediate separations they depend on σ 8 as well. One can thus use measurements of redshift-space distortions over a wide range of scales to separately determine Ω m , σ 8 , and α v .
15223533
Galaxy Evolution from Halo Occupation Distribution Modeling of DEEP2 and SDSS Galaxy Clustering
We model the luminosity-dependent projected two-point correlation function of DEEP2 (z ~ 1) and SDSS (z ~ 0) galaxies within the HOD framework. At both epochs, there is a tight correlation between central galaxy luminosity and halo mass, with the slope and scatter decreasing for larger halo masses, and the fraction of satellite galaxies decreases at higher luminosity. We find little evolution in the relation between mass scales of host halos for central galaxies and satellite galaxies above the same luminosity threshold. Combining these HOD results with theoretical predictions of the typical growth of halos, we establish an evolutionary connection between the galaxy populations at the two redshifts by linking z ~ 0 central galaxies to z ~ 1 central galaxies that reside in their progenitor halos. We find that the stellar mass growth of galaxies depends on halo mass. On average, the majority of the stellar mass in central galaxies residing in z ~ 0 low-mass halos (~5 × 1011 h-1 M☉) and only a small fraction of the stellar mass in central galaxies of high-mass halos (~1013 h-1 M☉) result from star formation between z ~ 1 and z ~ 0. In addition, the mass scale of halos where the star formation efficiency reaches a maximum is found to shift toward lower mass with time. Future work that combines HOD modeling of the clustering of galaxies at different redshifts with the assembly history and dynamical evolution of dark matter halos can lead to an understanding of the stellar mass growth due to both mergers and star formation as a function of host halo mass and provide powerful tests of galaxy formation theories.
35692275
Constraints on radiative dark-matter decay from the cosmic microwave background
If dark matter decays to electromagnetically interacting particles, it can inject energy into the baryonic gas and thus affect the processes of recombination and reionization. This leaves an imprint on the cosmic microwave background (CMB): the large-scale polarization is enhanced, and the small-scale temperature fluctuation is damped. We use the Wilkinson Microwave Anisotropy Probe (WMAP) three-year data combined with galaxy surveys to constrain radiatively decaying dark matter. Our new limits to the dark-matter decay width are about 10 times stronger than previous limits. For dark-matter lifetimes that exceed the age of the Universe, a limit of zetaGammachi<1.7×10^-25 s^-1 (95% C.L.) is derived, where zeta is the efficiency of converting decay energy into ionization energy. Limits for lifetimes short compared with the age of the Universe are also derived. We forecast improvements expected from the Planck satellite.
14336682
Interpreting the Observed Clustering of Red Galaxies at z ~ 3
Daddi et al. have recently reported strong clustering of a population of red galaxies at z � 3 in the Hubble Deep Field-South. Fitting the observed angular clustering with a power law of index � 0.8, they infer a comoving correlation length r0 � 8 h � 1 Mpc; for a standard cosmology, this r0 would imply that the red galaxies reside in rare, M � 10 13 h � 1 Mhalos, with each halo hosting � 100 galaxies to match the number density of the pop- ulation. Using the framework of the halo occupation distribution (HOD) in a CDM universe, we show that the Daddi et al. data can be adequately reproduced by less surprising models, e.g., models with galaxies residing in halos of mass M > Mmin ¼ 6:3;10 11 h � 1 Mand a mean occupation Navg(M) ¼ 1:4(M =Mmin) 0:45 above this cutoff. The resultant correlation functions do not follow a strict power law, showing instead a clear transition from the one-halo-dominated regime, where the two galaxies of each pair reside in the same dark matter halo, to the two-halo-dominated regime, where the two galaxies of each pair are from different halos. The observed high- amplitude data points lie in the one-halo-dominated regime, so these HOD models are able to explain the observations despite having smaller correlation lengths, r0 � 5 h � 1 Mpc. HOD parameters are only loosely constrained by the current data because of large sample variance and the lack of clustering information on scales that probe the two-halo regime. If our explanation of the data is correct, then future observations covering a larger area should show that the large-scale correlations lie below a � � 1:8 extrapolation of the small-scale points. Our models of the current data suggest that the red galaxies are somewhat more strongly clustered than UV-selected Lyman break galaxies and have a greater tendency to reside in small groups. Subject heading gs: galaxies: halos — galaxies: high-redshift — large-scale structure of universe
117560042
A z ∼ 5.7 Lyα EMISSION LINE WITH AN ULTRABROAD RED WING
Using the Ly? emission line as a tracer of high-redshift, star-forming galaxies, hundreds of Ly? emission line galaxies (LAEs) at z > 5 have been detected. These LAEs are considered to be low-mass young galaxies, critical to the re-ionization of the universe and the metal enrichment of the circumgalactic medium (CGM) and the intergalactic medium (IGM). It is assumed that outflows in LAEs can help both ionizing photons and Ly? photons escape from galaxies. However, we still know little about the outflows in high-redshift LAEs due to observational difficulties, especially at redshift >5. Models of Ly? radiative transfer predict asymmetric Ly? line profiles with broad red wings in LAEs with outflows. Here, we report a z ~ 5.7 Ly? emission line with a broad red wing extending to >1000?km s?1 relative to the peak of Ly? line, which has been detected in only a couple of z > 5 LAEs until now. If the broad red wing is ascribed to gas outflow instead of active galactic nucleus activity, the outflow velocity could be larger than the escape velocity (~500?km s?1) of a typical halo mass of z ~ 5.7 LAEs, which is consistent with the idea that outflows in LAEs disperse metals to CGM and IGM.
197531110
Ring Structure and Warp of NGC 5907: Interaction with Dwarf Galaxies
The edge-on, nearby spiral galaxy NGC 5907 has long been used as the prototype of a “noninteracting” warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC 5907 close to one of the ring’s foci. This suggests that the ring material is in orbit around NGC 5907. No gaseous component to the ring has been detected either with deep Ha images or in Very Large Array H i 21 cm line maps. The visible material in the ring has an integrated luminosity •10 8 L,, and its brightest part has a color . R 2 I » 0.9 All of these properties are consistent with the ring being a tidally disrupted dwarf spheroidal galaxy. Second, we find that NGC 5907 has a dwarf companion galaxy, PGC 54419, which is projected to be only 36.9 kpc from the center of NGC 5907, close in radial velocity ( km s 21 ) to the giant spiral galaxy. This dwarf DV 5 45 is seen at the tip of the H i warp and in the direction of the warp. Hence, NGC 5907 can no longer be considered noninteracting but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies. Subject headings: galaxies: individual (NGC 5907, PGC 054419) — galaxies: interactions — galaxies: photometry — galaxies: spiral — radio lines: galaxies