Source Number Counts Research Articles

Mass-sheet degeneracy: Fundamental limit on the cluster mass reconstruction from statistical (weak) lensing

Weak gravitational lensing is considered to be one of the most powerful tools to study the mass and the mass distribution of galaxy clusters. However, weak lensing mass reconstructions are plagued by the so-called mass-sheet degeneracy--the surface mass density \kappa of the cluster can be determined only up to a degeneracy transformation \kappa \to \kappa' = \lambda \kappa + (1 -\lambda), where \lambda is an arbitrary constant. This transformation fundamentally limits the accuracy of cluster mass determinations if no further assumptions are made. We describe here a method to break the mass-sheet degeneracy in weak lensing mass maps using distortion and redshift information of background galaxies and illustrate this by two simple toy models. Compared to other techniques proposed in the past, it does not rely on any assumptions on cluster potential; it can be easily applied to non-parametric mass-reconstructions and no assumptions on boundary conditions have to be made. In addition it does not make use of weakly constrained information (such as the source number counts, used in the magnification effect). Our simulations show that we are effectively able to break the mass-sheet degeneracy for supercritical lenses, but that for undercritical lenses the mass-sheet degeneracy is very difficult to be broken, even under idealised conditions.

Constraining cosmic microwave background consistent primordial voids with cluster evolution

Using cosmological simulations, we make predictions for the distribution of clusters in a plausible non-Gaussian model where primordial voids nucleated during inflation act together with scale-invariant adiabatic Gaussian fluctuations as seeds for the formation of large-scale structure. The parameters of the void network are constrained by the cosmic microwave background (CMB) fluctuations and by the abundance and size of the large empty regions seen in local galaxy redshift surveys. The model may account for the excess of CMB temperature anisotropy power measured on cluster scales by the Cosmic Background Imager. We show that the z = 0 cluster mass function differs little from predictions for a standard A cold dark matter cosmology with the same σ 8 , but that the evolution of the mass function at z ∼ 1 is slower than in a Gaussian model. Because massive clusters form much earlier in the 'void' scenario, we show that future integrated number counts of Sunyaev-Zel'dovich sources and simple statistics of strong lensing will provide additional constraints on this non-Gaussian model.

Fluctuation analysis of the far-infrared background - information from the confusion

We investigate the extent to which one can use a P(D) analysis to extract number counts of unclustered sources from maps of the far-infrared background. Such maps currently available, and those expected to emerge in the near future, are dominated by confusion noise resulting from poor resolution. We simulate background maps with an underlying two-slope model for N(S), and we find that, in an experiment of FIRBACK type, we can extract the high-flux slope with an error of a few per cent, whereas other parameters are not so well constrained. However, we find that, in a SIRTF-type experiment, all parameters of this N(S) model can be extracted with errors of only few per cent.

First‐Year Wilkinson Microwave Anisotropy Probe ( WMAP ) Observations: Tests of Gaussianity

We present limits to the amplitude of non-Gaussian primordial fluctuations in the WMAP 1 yr cosmic microwave background sky maps. A nonlinear coupling parameter, fNL, characterizes the amplitude of a quadratic term in the primordial potential. We use two statistics: one is a cubic statistic which measures phase correlations of temperature fluctuations after combining all configurations of the angular bispectrum. The other uses the Minkowski functionals to measure the morphology of the sky maps. Both methods find the WMAP data consistent with Gaussian primordial fluctuations and establish limits, -58 < fNL < 134, at 95% confidence. There is no significant frequency or scale dependence of fNL. The WMAP limit is 30 times better than COBE and validates that the power spectrum can fully characterize statistical properties of CMB anisotropy in the WMAP data to a high degree of accuracy. Our results also validate the use of a Gaussian theory for predicting the abundance of clusters in the local universe. We detect a point-source contribution to the bispectrum at 41 GHz, bsrc = (9.5 ± 4.4) × 10-5 μK3 sr2, which gives a power spectrum from point sources of csrc = (15 ± 6) × 10-3 μK2 sr in thermodynamic temperature units. This value agrees well with independent estimates of source number counts and the power spectrum at 41 GHz, indicating that bsrc directly measures residual source contributions.

The Resolved Fraction of the Cosmic X‐Ray Background

We present the X-ray source number counts in two energy bands (0.5-2 and 2-10 keV) from a very large source sample: we combine data of six different surveys, both shallow wide field and deep pencil beam, performed with three different satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating the flux distributions over this range and taking into account the (small) contribution of the brightest sources we derive the flux density generated by discrete sources in both bands. After a critical review of the literature values of the total Cosmic X--Ray Background (CXB) we conclude that, with the present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to discrete source emission. If we extrapolate the analytical form of the Log N--Log S distribution beyond the flux limit of our catalog in the soft band we find that the flux from discrete sources at ~3*10^-18 cgs is consistent with the entire CXB, whereas in the hard band it accounts for only 93% of the total CXB at most, hinting for a faint and obscured population to arise at even fainter fluxes.

The Hubble Deep Field South Flanking Fields

As part of the Hubble Deep Field South program, a set of shorter two-orbit observations were obtained of the area adjacent to the deep fields. The WFPC2 flanking fields cover a contiguous solid angle of 48 arcmin2. Parallel observations with the STIS and NICMOS instruments produce a patchwork of additional fields with optical and near-infrared (1.6 μm) response. Deeper parallel exposures with WFPC2 and NICMOS were obtained when STIS observed the NICMOS deep field. These deeper fields are offset from the rest, and an extended low surface brightness object is visible in the deeper WFPC2 flanking field. In this data paper, which serves as an archival record of the project, we discuss the observations and data reduction and present SExtractor source catalogs and number counts derived from the data. Number counts are broadly consistent with previous surveys from both ground and space. Among other things, these flanking field observations are useful for defining slit masks for spectroscopic follow-up over a wider area around the deep fields, for studying large-scale structure that extends beyond the deep fields, for future supernova searches, and for number counts and morphological studies, but their ultimate utility will be defined by the astronomical community.

The Chandra Deep Field–South: The 1 Million Second Exposure

We present the main results from our 940 ks observation of the Chandra Deep Field-South using the source catalog described in an accompanying paper by Giacconi et al. We extend the measurement of source number counts to 5.5 × 10-17 ergs cm-2 s-1 in the soft 0.5-2 keV band and 4.5 × 10-16 ergs cm-2 s-1 in the hard 2-10 keV band. The hard-band log N-log S shows a significant flattening (slope 0.6) below ≈10-14 ergs cm-2 s-1, leaving at most 10%-15% of the X-ray background to be resolved, the main uncertainty lying in the measurement of the total flux of the X-ray background (XRB). On the other hand, the analysis in the very hard 5-10 keV band reveals a relatively steep log N-log S (slope 1.3) down to 10-15 ergs cm-2 s-1. Together with the evidence of a progressive flattening of the average X-ray spectrum near the flux limit, this indicates that there is still a nonnegligible population of faint hard sources to be discovered at energies not well probed by Chandra, which possibly contributes to the 30 keV bump in the spectrum of the XRB. We use optical redshifts and identifications, obtained with the Very Large Telescope, for one-quarter of the sample to characterize the combined optical and X-ray properties of the Chandra Deep Field-South sample. Different source types are well separated in a parameter space that includes X-ray luminosity, hardness ratio, and R-K color. Type II objects, while redder on average than the field population, have colors that are consistent with being hosted by a range of galaxy types. Type II active galactic nuclei are mostly found at z 1, in contrast with predictions based on active galactic nucleus population synthesis models, thus suggesting a revision of their evolutionary parameters.

Synchrotron Emission from Hot Accretion Flows and the Cosmic Microwave Background Anisotropy

Current estimates of number counts of radio sources in the frequency range where the most sensitive Cosmic Microwave Background (CMB) experiments are carried out significantly under-represent sources with strongly inverted spectra. Hot accretion flows around supermassive black holes in the nuclei of nearby galaxies are expected to produce inverted radio spectra by thermal synchrotron emission. We calculate the temperature fluctuations and power spectra of these sources in the Planck Surveyor 30 GHz energy channel, where their emission is expected to peak. We find that their potential contribution is generally comparable to the instrumental noise, and approaches the CMB anisotropy level at small angular scales. Forthcoming CMB missions, which will provide a large statistical sample of inverted-spectra sources, will be crucial for determining the distribution of hot accretion flows in nearby quiescent galactic nuclei. Detection of these sources in different frequency channels will help constrain their spectral characteristics, hence their physical properties.

Lensing‐induced Structure of Submillimeter Sources: Implications for the Microwave Background

We consider the effect of lensing by galaxy clusters on the angular distribution of submillimeter wavelength objects. While lensing does not change the total flux and number counts of submillimeter sources, it can affect the number counts and fluxes of flux-limited samples. Therefore imposing a flux cut on point sources not only reduces the overall Poisson noise, but imprints the correlations between lensing clusters on the unresolved flux distribution. Using a simple model, we quantify the lensing anisotropy induced in flux-limited samples and compare this to Poisson noise. We find that while the level of induced anisotropies on the scale of the cluster angular correlation length is comparable to Poisson noise for a slowly evolving cluster model, it is negligible for more realistic models of cluster evolution. Thus the removal of point sources is not expected to induce measurable structure in the microwave or far-infrared backgrounds.

An extended galactic population of low-luminosity x-ray sources (CVs?) and the diffuse x-ray background

view Abstract Citations (10) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Extended Galactic Population of Low-Luminosity X-Ray Sources (CVs?) and the Diffuse X-Ray Background Maoz, Eyal ; Grindlay, Jonathan E. Abstract Summary of abstract: The existence of a new population of yet unrecognized x-ray sources has been often suggested to resolve some pecularities in the properties of the x-ray background (XRB), and has recently been indicated by an analysis of resolved sources in deep ROSAT observations (Hasinger \etal 1993). We investigate the possibility that the indicated new population of x-ray sources is Galactic in origin, and derive its properties which would resolve the discrepancy found in the number counts of faint sources, and be consistent with observational constraints on the total background intensity, the XRB anisotropy, the number of unidentified bright sources, the Galaxy's total x-ray luminosity, and with the results of fluctuation analyses of the unresolved XRB. We find that a flattened Galactic halo (or a thick disk) distribution with a scale height of a few Kpc satisfies all the above requirements. The typical x-ray luminosity of the sources is $\approx 10^{30-31}$ erg/s in the 0.5-2 KeV band, the number density of sources in the Solar vicinity is $\sim 10^{-4.5} pc^{-3}$, their total number in the Galaxy is $\sim 10^{8.5}$, and they contribute $\sim 10^{39}$ erg/s to the Galaxy's total x-ray luminosity. We discuss the possible nature of these sources (subdwarfs, LMXBs, old neutron stars), and argue that the inferred x-ray and optical luminosities of the sources, their $\sim 2-4$ KeV spectrum, and the derived local number density and spatial distribution are all consistent with them being intrinsicly faint cataclysmic variables with low accretion rates. We discuss the possible origin of such population, including an origin from disrupted globular clusters or dark clusters, make predictions, and suggest observational tests. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175593 arXiv: arXiv:astro-ph/9408100 Bibcode: 1995ApJ...444..183M Keywords: Background Radiation; Diffuse Radiation; Galactic Structure; Milky Way Galaxy; Populations; X Ray Astronomy; X Ray Sources; Cataclysmic Variables; Faint Objects; Galactic Evolution; Galactic Halos; Neutron Stars; X Ray Stars; Astronomy; COSMOLOGY: DIFFUSE RADIATION; GALAXIES: STELLAR CONTENT; GALAXY: HALO; STARS: NOVAE; CATACLYSMIC VARIABLES; X-RAYS: GALAXIES; X-RAYS: STARS; Astrophysics E-Print: 20 pages, PostScript file (330K including figures), submitted to ApJ full text sources arXiv | ADS |

A search for associations of distant radio-bright quasars with Abell clusters: an effect of gravitational amplification bias?

The theory predicts that the effect of gravitational lensing by the matter associated with clusters of galaxies can magnify background sources, leading to an enhancement of source number density around foreground clusters of galaxies. We conduct a search for the associations of distant radio-bright quasars with Abell clusters using the 1-Jy and 2-Jy all-sky catalogs. Statistics turns to be very poor on the basis of the 1-Jy sample, which shows no correlations between the distant radio quasars with the foreground Abell clusters above $1\sigma$ level. However, an apparent association ($>1\sigma$) of the 2-Jy radio sources with the foreground Abell clusters has been detected on scale of $\sim20$ arcminutes. We point out that this enhancement is unlikely to be produced by the statistical gravitational lensing hypothesis utilizing the matter associated with a population of isolated clusters unless (1)their velocity dispersion is a few times larger than the presently adopted value and/or (2)the intrinsic counts of the radio-bright sources with flux have a steeper slope than the presently observed ones. This indicates that (1)the observed associations, if real, can be the integrated result of all the matter along the line of sight to the distant quasars, namely, the weak lensing effect of clusters of galaxies that trace large-scale structures of the universe, and/or (2)the number counts of the radio-bright sources have been seriously contaminated by lensing.

Statistics of Highly Magnified Gravitational Images in Clusters of Galaxies. II. Implications for the Sources

view Abstract Citations (32) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Statistics of Highly Magnified Gravitational Images in Clusters of Galaxies. II. Implications for the Sources Miralda-Escude, Jordi Abstract The probability of observing images of background galaxies gravitationally lensed by clusters of galaxies, in the form of elongated arcs, is studied as a function of the arc length. A numerical calculation is performed for isothermal lenses with a spherical component and a quadrupole component, and with finite core radius. The number of arcs is calculated for several models of the number counts and angular size of the sources being lensed, and assuming that the detectability of an arc depends only on its observed surface brightness, but taking into account the reduction of the surface brightness produced by seeing. It is shown that the number of arcs expected in lensing clusters depends mostly on the angular size of the sources, basically because a lower magnification is needed to produce an arc of fixed length for a larger source. From the available observations of the number of arcs, we tentatively conclude that most of the sources should have typical scale-lengths larger than 0".5. This constraint on the angular sizes could be made much more secure with a homogeneous sample of arcs with well-known detection limits, and a precise definition of the arc length in terms of the surface brightness profile. We also show how such a homogeneous sample can be used to infer the number counts of sources that are too faint to be observed in the field. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172221 Bibcode: 1993ApJ...403..509M Keywords: COSMOLOGY: GRAVITATIONAL LENSING; COSMOLOGY: THEORY; GALAXIES: CLUSTERING; GALAXIES: EVOLUTION full text sources ADS | data products SIMBAD (2) Related Materials (1) Part 1: 1993ApJ...403..497M

The statistics of multiple gravitational lensing and the application of a single lensing approximation

The statistics of multiple gravitational lensing in a locally inhomogeneous universe is taken into account, based on the expansion of the mean amplification into the summation of various lenses and the pointlike models for both background sources and lensing objects. By comparing the deviation of the effects of various lenses from mean amplification, the redshift ranges over which different lenses dominate are investigated. In particular, the accuracy of a single lensing approximation, which has been widely used in previous statistical lensing, is demonstrated. As the application of a single lensing approximation, the lowest correction to the Mattig's relation due to the inhomogeneities in universe and the lowest effect on the number counts of background sources due to amplification bias are reconsidered. It is emphasized the fact that the effect of statistical lensing, even in a single lensing approximation, is of significance for modern observational cosmology.

X-Ray and Optical Observations of Quasars

The first Einstein observations established that quasars, as a class, are luminous X-ray emitters (Tananbaum et al. 1979). Since then, one of our major programs has been to carry out further X-ray and optical observations to improve our estimate of the contribution of quasars to the 2 keV extragalactic isotropic X-ray background and also to reconcile number counts of discrete X-ray sources with reported optical number counts of quasars (cf. Zamorani et al. 1981 and references therein). This paper is a preliminary report on our observations of the 1.7 square degree field studied originally by Braccesi and his colleagues (Formiggini et al. 1980 and Braccesi et al. 1980). A more detailed presentation of our results is in preparation (Marshall et al., 1981).

Effects of a rotation of the universe on the number counts of radio sources - Goedel's universe

By using Goedel's (1949) rotating universe model, it is shown that vorticity alone in a homogeneous universe could have an effect on the (number-count)/(flux density) relation. This effect is the same as evolutionary effects. The effect also shows in expanding models, where a spatial gradient also appears, generating an anisotropy in the number counts. The possible existence of a global vorticity of the universe is discussed.

Radio Background as a Criterion for Cosmological Models

As I have recently shown1, the number counts of extragalactic radio sources according to the latest Cambridge survey2 imply that in an evolutionary cosmology there is a minimum rate of evolution of the power of the radio sources, which depends on the time variation assumed for the spatial density of the sources. The particular cases when the spatial density of the sources is always proportional to that of ordinary galaxies and, alternatively, to the square of that of the galaxies, were found to require a diminution of mean source power exceeding 1.4 and 0.2 per cent per 108 years, respectively, at the present epoch. More generally, when no definite assumption was made regarding mean source density n(t) and mean source power P(t), it was found that agreement with the Cambridge results required a minimum present rate of diminution of the product n(t)P2(t) equal to 5 per cent per 108 years. In these calculations the Hubble time T was taken to be 1.3 × 1010 years.

The Preparation of the Revised 3C Catalogue of Radio Sources

New observational data are used to make a complete revision of the 3C catalogue, which should now provide a complete and reliable list for all sources with flux greater than |$9 \times 10^{-26}\enspace \text {w.m}^{-2} \enspace(\text {c/s})^{-1}$| at 178 Mc/s and for which δ > −05°. The correction of the observations for the effects of confusion is described in detail, and the analysis of these errors is verified by comparison of the original 3C measurements with new measurements now available. The new catalogue is compared with the original, and it is shown that the number counts of sources remain almost unchanged, in agreement with new observations by Scott and Ryle.