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1.
With detections of the Sunyaev–Zel'dovich (SZ) effect induced by galaxy clusters becoming routine, it is crucial to establish accurate theoretical predictions. We use a hydrodynamical N -body code to generate simulated maps, of size 1 deg2, of the thermal SZ effect. This is done for three different cosmologies: the currently favoured low-density model with a cosmological constant, a critical-density model and a low-density open model. We stack simulation boxes corresponding to different redshifts in order to include contributions to the Compton y -parameter out to the highest necessary redshifts. Our main results are as follows.
(i) The mean y -distortion is around 4×10−6 for low-density cosmologies, and 1×10−6 for critical density. These are below current limits, but not by a wide margin in the former case.
(ii) In low-density cosmologies, the mean y -distortion is contributed across a broad range of redshifts, with the bulk coming from z ≲2 and a tail out to z ∼5. For critical-density models, most of the contribution comes from z <1.
(iii) The number of SZ sources above a given y depends strongly on instrument resolution. For a 1-arcmin beam, there are around 0.1 sources per deg2 with y >10−5 in a critical-density Universe, and around 8 such sources per deg2 in low-density models. Low-density models with and without a cosmological constant give very similar results.
(iv) We estimate that the Planck satellite will be able to see of order 25 000 SZ sources if the Universe has a low density, or around 10 000 if it has critical density.  相似文献   

2.
We examine the ability of the future Planck mission to provide a catalogue of galaxy clusters observed via their Sunyaev–Zel'dovich (SZ) distortion in the cosmic microwave background (CMB). For this purpose we produce full-sky SZ maps based on N -body simulations and scaling relations between cluster properties for several cosmological models. We extrapolate the N -body simulations by a mass function to high redshifts in order to obtain a realistic SZ background. The simulated Planck observations include, besides the thermal and kinematic SZ effects, contributions from the primordial CMB, extragalactic point sources as well as Galactic dust, free–free and synchrotron emission. A harmonic-space maximum-entropy method is used to separate the SZ signal from contaminating components in combination with a cluster detection algorithm based on thresholding and flux integration to identify clusters and to obtain their fluxes. We estimate a survey sensitivity limit (depending on the quality of the recovered cluster flux) and provide cluster survey completeness and purity estimates. We find that, given our modelling and detection algorithm, Planck will reliably detect at least several thousands of clusters over the full sky. The exact number depends on the particular cosmological model (up to 10 000 cluster detections in a concordance ΛCDM model with  σ8= 0.9  ). We show that the Galaxy does not significantly affect the cluster detection. Furthermore, the dependence of the thermal SZ power spectrum on the matter variance on scales of  8 h −1  Mpc and the quality of its reconstruction by the employed method are investigated. Our simulations suggest that the Planck cluster sample will not only be useful as a basis for follow-up observations, but also will have the ability to provide constraints on cosmological parameters.  相似文献   

3.
We show how future measurements of the Sunyaev–Zel'dovich effect (SZE) can be used to constrain the cosmological parameters. We combine the SZ information expected from the Planck full-sky survey, N ( S ), where no redshift information is included, with the N ( z ) obtained from an optically identified SZ-selected survey covering less than 1 per cent of the sky. We demonstrate how with a small subsample (≈300 clusters) of the whole SZ catalogue observed optically it is possible to reduce the degeneracy among the cosmological parameters drastically. We have studied the requirements for performing the optical follow-up and we show the feasibility of such a project. Finally, we have compared the cluster expectations for Planck with those expected for Newton–XMM during their lifetimes. It is shown that, owing to its larger sky coverage, Planck will detect a factor of ∼5 times more clusters than Newton–XMM and also provide a larger redshift coverage.  相似文献   

4.
A maximum entropy method (MEM) is presented for separating the emission resulting from different foreground components from simulated satellite observations of the cosmic microwave background radiation (CMBR). In particular, the method is applied to simulated observations by the proposed Planck Surveyor satellite. The simulations, performed by Bouchet &38; Gispert, include emission from the CMBR and the kinetic and thermal Sunyaev–Zel'dovich (SZ) effects from galaxy clusters, as well as Galactic dust, free–free and synchrotron emission. We find that the MEM technique performs well and produces faithful reconstructions of the main input components. The method is also compared with traditional Wiener filtering and is shown to produce consistently better results, particularly in the recovery of the thermal SZ effect.  相似文献   

5.
The Planck mission is the most sensitive all-sky cosmic microwave background (CMB) experiment currently planned. The High-Frequency Instrument (HFI) will be especially suited for observing clusters of galaxies by their thermal Sunyaev–Zel'dovich (SZ) effect. In order to assess Planck 's SZ capabilities in the presence of spurious signals, a simulation is presented that combines maps of the thermal and kinetic SZ effects with a realization of the CMB, in addition to Galactic foregrounds (synchrotron emission, free–free emission, thermal emission from dust, CO-line radiation) as well as the submillimetric emission from celestial bodies of our Solar system. Additionally, observational issues such as the finite angular resolution and spatially non-uniform instrumental noise of Planck 's sky maps are taken into account, yielding a set of all-sky flux maps, the autocorrelation and cross-correlation properties of which are examined in detail. In the second part of the paper, filtering schemes based on scale-adaptive and matched filtering are extended to spherical data sets, that enable the amplification of the weak SZ signal in the presence of all contaminations stated above. The theory of scale-adaptive and matched filtering in the framework of spherical maps is developed, the resulting filter kernel shapes are discussed and their functionality is verified.  相似文献   

6.
We consider the distortion in the cosmic microwave background (CMB) resulting from galactic winds at high redshift. Winds outflowing from galaxies have been hypothesized to be possible sources of metals in the intergalactic medium, which is known to have been enriched to 10−2.5 Z⊙ at z ∼3. We model these winds as functions of mass of the parent galaxy and redshift, assuming that they activate at a common initial redshift, z in, and calculate the mean y -distortion and the angular power spectrum of the distortion in the CMB. We find that the thermal Sunyaev–Zel'dovich (SZ) effect resulting from the winds is consistent with previous estimates. The distortion arising from the kinetic SZ (kSZ) effect is, however, found to be more important than the thermal SZ (tSZ) effect. We find that the distortion resulting from galactic winds is an important contribution to the power spectrum of distortion at very small angular scales ( l ∼104). We also find that the power spectrum resulting from clustering dominates the Poisson power spectrum for l ≤(4–5)×105. We show explicitly how the combined power spectrum from wind dominates over that of clusters at 217 GHz, relevant for PLANCK . We also show how these constraints change when the efficiency of the winds is varied.  相似文献   

7.
We present deep near-infrared images, taken with the Subaru Telescope, of the region around the   z =1.08  radio source 3C 356 which show it to be associated with a poor cluster of galaxies. We discuss evidence that this cluster comprises two subclusters traced by the two galaxies previously proposed as identifications for 3C 356, which both seem to harbour active galactic nuclei, and which have the disturbed morphologies expected if they underwent an interpenetrating collision at the time the radio jets were triggered. We explain the high luminosity and temperature of the diffuse X-ray emission from this system as the result of shock heating of intracluster gas by the merger of two galaxy groups. Taken together with the results on other well-studied powerful radio sources, we suggest that the key ingredient for triggering a powerful radio source, at least at epochs corresponding to   z ∼1  , is a galaxy–galaxy interaction which can be orchestrated by the merger of their parent subclusters. This provides an explanation for the rapid decline in the number density of powerful radio sources since   z ∼1  . We argue that attempts to use distant radio-selected clusters to trace the formation and evolution of the general cluster population must address ways in which X-ray properties can be influenced by the radio source, both directly, by mechanisms such as inverse Compton scattering, and indirectly, by the fact that the radio source may be preferentially triggered at a specific time during the formation of the cluster.  相似文献   

8.
We present the results of an initial search for clusters of galaxies at z ∼ 1 and above, using data from 2.9 square degrees of XMM–Newton images. By selecting weak potentially extended X-ray sources with faint or no identifications in deep, ground-based optical imaging, we have constructed a starting sample of 19 high-redshift cluster candidates. Near-IR and R , z ' imaging of these fields identified nine of them as high-redshift systems. Six of these were confirmed spectroscopically, three at z ∼ 1.0 and the other three in the  0.8 < z < 0.92  range. The remaining three systems have solid photometric evidence to be at   z phot∼ 0.8, 1.0  and 1.3. The present sample significantly increases the number of such clusters. The measured density of z ≳ 1 clusters, after discarding 'low'-redshift systems at z ≲ 0.92 is about 1.7 deg−2 (with 68 per cent confidence interval equal to [1.0, 2.9]) for   fX ≳ 2.5  10−15 erg cm−2 s−1  ([0.5–2] keV) and this is a lower limit, having screened not all potential z ∼ 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.  相似文献   

9.
Motivated by recent observational studies of the environment of   z ∼ 6  QSOs, we have used the Millennium Run (MR) simulations to construct a very large  (∼4°× 4°)  mock redshift survey of star-forming galaxies at   z ∼ 6  . We use this simulated survey to study the relation between density enhancements in the distribution of i 775-dropouts and Lyα emitters, and their relation to the most massive haloes and protocluster regions at   z ∼ 6  . Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1°, much larger than probed by current surveys. Approximately one-third of all   z ∼ 6  haloes hosting i -dropouts brighter than   z = 26.5  mag  (≈ M *UV, z =6)  become part of   z = 0  galaxy clusters. i -dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i -dropouts and Lyα emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six   z ∼ 6  QSO fields observed with Hubble Space Telescope show no significant enhancements in their i 775-dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at   z ∼ 6  .  相似文献   

10.
The next generation of X-ray telescopes have the potential to detect faint quasars at very high redshift and probe the early growth of massive black holes (BHs). We present modelling of the evolution of the optical and X-ray active galactic nucleus (AGN) luminosity function at  2 < z < 6  based on a cold dark matter (CDM) merger-driven model for the triggering of nuclear activity combined with a variety of fading laws. We extrapolate the merger-driven models to   z > 6  for a range of BH growth scenarios. We predict significant numbers of sources at   z ∼ 6  with fluxes just an order of magnitude below the current detection limits and thus detectable with XEUS and Constellation-X , relatively independently of the fading law chosen. The predicted number of sources at even higher redshift depends sensitively on the early growth history of BHs. For passive evolution models in which BHs grow constantly at their Eddington limit, detectable BHs may be rare beyond   z ∼ 10  even with Generation-X . However, in the more probable scenario that BH growth at   z > 6  can be described by passive evolution with a small duty cycle, or by our merger-driven accretion model, then we predict that XEUS and Generation-X will detect significant numbers of BHs out to   z ∼ 10  and perhaps beyond.  相似文献   

11.
We consider constraints on the structure formation model based on non-Gaussian fluctuations generated during inflation, which have     distributions. Using three data sets, the abundance of the clusters at z =0, moderate z and the correlation length, we show that constraints on the non-Gaussianity and the amplitude of fluctuations and the density parameter can be obtained. We obtain an upper bound for m, and a lower bound for the non-Gaussianity and the amplitude of the fluctuations. Using the abundance of clusters at z 0.6, for the spectrum parametrized by cold dark matter (CDM) shape parameter =0.23, we obtain an upper bound for the density parameter of m0.5 and lower bounds for the amplitude of 80.7 and for the non-Gaussianity of fluctuations of G 2 ( m 200), where G =1 for Gaussian.  相似文献   

12.
We present an analysis of the X-ray point source populations in 182 Chandra images of galaxy clusters at   z > 0.1  with exposure time >10 ks, as well as 44 non-cluster fields. The analysis of the number and flux of these sources, using a detailed pipeline to predict the distribution of non-cluster sources in each field, reveals an excess of X-ray point sources associated with the galaxy clusters. A sample of 148 galaxy clusters at  0.1 < z < 0.9  , with no other nearby clusters, shows an excess of 230 cluster sources in total, an average of ∼1.5 sources per cluster. The lack of optical data for these clusters limits the physical interpretation of this result, as we cannot calculate the fraction of cluster galaxies hosting X-ray sources. However, the fluxes of the excess sources indicate that over half of them are very likely to be active galactic nuclei (AGN), and the radial distribution shows that they are quite evenly distributed over the central 1 Mpc of the cluster, with almost no sources found beyond this radius. We also use this pipeline to successfully reproduce the results of previous studies, particularly the higher density of sources in the central 0.5 Mpc of a few cluster fields, but show that these conclusions are not generally valid for this larger sample of clusters. We conclude that some of these differences may be due to the sample properties, such as the size and redshift of the clusters studied, or a lack of publications for cluster fields with no excess sources. This paper also presents the basic X-ray properties of the galaxy clusters, and in subsequent papers in this series the dependence of the AGN population on these cluster properties will be evaluated.
In addition the properties of over 9500 X-ray point sources in the fields of galaxy clusters are tabulated in a separate catalogue available online or at http://www.sc.eso.org~rgilmour .  相似文献   

13.
N -body/hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a Λ cold dark matter (ΛCDM) cosmology are used in order to follow the building-up of the colour–magnitude relation in two clusters and in 12 groups. We have found that galaxies, starting from the more massive, move to the red sequence (RS) as they get aged over times and eventually set upon a 'dead sequence' (DS) once they have stopped their bulk star formation activity. Fainter galaxies keep having significant star formation out to very recent epochs and lie broader around the RS. Environment plays a role as galaxies in groups and cluster outskirts hold star formation activity longer than the central cluster regions. However, galaxies experiencing infall from the outskirts to the central parts keep star formation on until they settle on to the DS of the core galaxies. Merging contributes to mass assembly until z ∼ 1, after which major events only involve the brightest cluster galaxies.
The emerging scenario is that the evolution of the colour–magnitude properties of galaxies within the hierarchical framework is mainly driven by star formation activity during dark matter haloes assembly. Galaxies progressively quenching their star formation settle to a very sharp 'red and dead' sequence, which turns out to be universal, its slope and scatter being almost independent of the redshift (since at least z ∼ 1.5) and environment.
Differently from the DS, the operatively defined RS evolves more evidently with z , the epoch when it changes its slope being closely corresponding to that at which the passive galaxies population takes over the star-forming one: this goes from z ≃ 1 in clusters down to 0.4 in normal groups.  相似文献   

14.
With the Planck and Herschel satellite missions of the European Space Agency, the far-infrared and submillimeter window will offer new investigation tools toward clusters of galaxies in the distant Universe. These are the Sunyaev Zel'dovich (SZ) effect of the cosmic microwave background and the thermal emission of dust grains. The power of the SZ effect is such that Planckis expected to discover thousands of new clusters at redshifts larger than 0.2, where only a few tens are known today. The dust can be present at large scale in the intracluster medium, and we show that even at very low abundances it is able to be a major cooling agent for the whole cluster. However the dominating dust emission will be that of the background infrared star forming galaxies. In all cases, the data processing of space borne sensitive submillimeter observations of clusters of galaxies such as the one that Planck and Herschel will provide, will require a very carefull combined analysis of the SZ effect and dust thermal emission.  相似文献   

15.
We report an overdensity of bright submillimetre galaxies (SMGs) in the 0.15 deg2 AzTEC/COSMOS survey and a spatial correlation between the SMGs and the optical-IR galaxy density at   z ≲ 1.1  . This portion of the COSMOS field shows a  ∼3σ  overdensity of robust SMG detections when compared to a background, or 'blank-field', population model that is consistent with SMG surveys of fields with no extragalactic bias. The SMG overdensity is most significant in the number of very bright detections (14 sources with measured fluxes   S 1.1 mm > 6  mJy), which is entirely incompatible with sample variance within our adopted blank-field number densities and infers an overdensity significance of  ≫ 4σ  . We find that the overdensity and spatial correlation to optical-IR galaxy density are most consistent with lensing of a background SMG population by foreground mass structures along the line of sight, rather than physical association of the SMGs with the   z ≲ 1.1  galaxies/clusters. The SMG positions are only weakly correlated with weak-lensing maps, suggesting that the dominant sources of correlation are individual galaxies and the more tenuous structures in the survey region, and not the massive and compact clusters. These results highlight the important roles cosmic variance and large-scale structure can play in the study of SMGs.  相似文献   

16.
We analyse the effects of the detector response time on bolometric measurements of the anisotropy of the cosmic microwave background (CMB). We quantify the effect in terms of a single dimensionless parameter L defined as the ratio between the time the beam sweeps its own size and the bolometer response time. As L decreases below ∼ 2.5, the point-source response of the experiment becomes elongated. We introduce a window function matrix based on the timestream data to assess the effects of the elongated beam. We find that the values of the window function matrix elements decrease slowly as a function of L . Our analysis and results apply to other cases of beam asymmetry. For the High Frequency Instrument on board the Planck Surveyor satellite we show that, for a broad range of L , the ability of the experiment to extract the cosmological parameters is not degraded. Our analysis enhances the flexibility in tuning the design parameters of CMB anisotropy experiments.  相似文献   

17.
The Planck Satellite will survey the entire sky in 9 millimeter/submillimeter bands and detect thousands of galaxy clusters via their thermal Sunyaev‐Zel'dovich (SZ) effect. The unprecedented volume of the survey will permit the construction of a unique catalog of massive clusters out to redshifts of order unity. We describe the expected contents of this catalog and use an empirical model of the intra‐cluster gas to predict the X‐ray properties of Planck SZ clusters. Using this information we show how a ∼10 Ms follow‐up program on XMM‐Newton could increase by ∼100‐fold the number of clusters with measured temperatures in the redshift range z = 0.5–1. Such a large sample of well‐studied massive clusters at these redshifts would be a powerful cosmological tool and a significant legacy for XMM‐Newton. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
We present the results of a continuing survey to detect Lyα emitting galaxies at redshifts   z ∼ 9  : the ' z equals nine' (ZEN) survey. We have obtained deep VLT Infrared Spectrometer and Array Camera observations in the narrow J -band filter NB119 directed towards three massive lensing clusters: Abell clusters 1689, 1835 and 114. The foreground clusters provide a magnified view of the distant Universe and permit a sensitive test for the presence of very high redshift galaxies. We search for   z ∼ 9 Lyα  emitting galaxies displaying a significant narrow-band excess relative to accompanying J -band observations that remain undetected in Hubble Space Telescope ( HST )/Advanced Camera for Surveys (ACS) optical images of each field. No sources consistent with this criterion are detected above the unlensed 90 per cent point-source flux limit of the narrow-band image,   F NB= 3.7 × 10−18 erg s−1 cm−2  . To date, the total coverage of the ZEN survey has sampled a volume at   z ∼ 9  of approximately 1700 comoving Mpc3 to a Lyα emission luminosity of  1043 erg s−1  . We conclude by considering the prospects for detecting   z ∼ 9 Lyα  emitting galaxies in light of both observed galaxy properties at   z < 7  and simulated populations at   z > 7  .  相似文献   

19.
We discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21-cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST) to be built in China. We consider issues related to the estimation of the source counts and optimizations of the survey, and discuss the constraints on cosmological models that such a survey could provide. We find that a survey taking around two years could detect ∼107 galaxies with an average redshift of ∼0.15 making the survey complementary to those already carried out at optical wavelengths. These conservative estimates have used the   z = 0  H  i mass function and have ignored the possibility of evolution. The results could be used to constrain  Γ=Ωm h   to 5 per cent and the spectral index, n s, to 7 per cent independent of cosmic microwave background data. If we also use simulated power spectra from the Planck satellite, we can constrain w to be within 5 per cent of −1.  相似文献   

20.
I apply the well controlled hydro-PM (HPM) approximation of Gnedin &38; Hui to model the column density distribution of the Ly α forest for 25 different flat cosmological scenarios, including variants of the standard cold dark matter (CDM), tilted CDM, CDM with a cosmological constant, and cold + hot dark matter (CHDM) models. I show that, within the accuracy of the HPM approximation, the slope of the column density distribution reflects the degree of non-linearity of the cosmic gas distribution and is a function of the rms linear density fluctuation at the characteristic filtering scale only. The amplitude of the column density distribution, expressed as the value for the ionizing intensity, is derived as a function of the cosmological parameters (to about 40 per cent accuracy). The observational data are currently consistent with the value for the ionizing intensity being constant in the redshift interval z  ∼ −4.  相似文献   

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