arXiv subjects

A. Kashlinsky

Publications and source records attributed to A. Kashlinsky.

65 records · Page 4Linked to original sources

arXiv1998

Determining $Ω$ from cluster correlation function

It is shown how data on the cluster correlation function can be used in order to reconstruct the density of the pregalactic density field on the cluster mass scale. The method is applied to the data on the cluster correlation amplitude -- richness dependence. The spectrum of the recovered density field has the same shape as the density field derived from data on the galaxy correlation function which is measured as function of linear scales. Matching the two amplitudes relates the mass to the comoving scale it contains and thereby leads to a direct determination of $Ω$. The resultant density parameter turns out to be $Ω$=0.25.

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arXiv1997

Reconstructing the spectrum of the pregalactic density field from astronomical data

In this paper we evaluate the spectrum of the pregalactic density field on scales $1h^{-1}Mpc < r < 100h^{-1}$Mpc from a variety of astronomical data. APM data on $w(θ)$ in six narrow magnitude is used, after correcting to possible evolutionary effects, to constrain the spectrum of galaxy clustering on scales $10h^{-1}Mpc < r < 50-100h^{-1}Mpc$. Fitting power spectra of CDM models to the data at all depths requires $Ωh=0.2$ if the primordial index $n=1$ and $Ωh=0.3$ if the spectrum is tilted with $n=0.7$. Then we compare the peculiar velocity field predicted by the APM spectrum of galaxy (light) distribution with the actual velocity data. The two fields are consistent and the comparison suggests that the bias factor is scale independent with $Ω^{0.6}/b\simeq$(0.2-0.3). The next dataset used comes from the cluster correlation data. We calculate in detail the amplification of the cluster correlation function due to gravitational clustering and use the data on both the slope of the cluster correlation function and its amplitude-richness dependence. Cluster masses are normalized using the Coma cluster. We find that CDM models are hard to reconcile with all the three datasets: APM data on $w(θ)$, the data on cluster correlation function, and the data on the latter's amplitude-richness dependence. We show that the data on the amplitude-richness dependence can be used directly to obtain the spectrum of the pregalactic density field. Applying the method to the data, we recover the density field on scales between 5 and 25$h^{-1}$Mpc whose slope is in good agreement with the APM data on the same scales. Requiring the two amplitudes to be the same, fixes the value of $Ω$ to be 0.3 in agreement with observations of the dynamics of the Coma cluster. Finally we use the data

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arXiv1997

Limits on the cosmic infrared background from clustering in COBE/DIRBE maps

We discuss a new method of estimating the cosmic infrared background (CIB) from the spatial properties of infrared maps and give the limits on the CIB from applying it to the COBE/DIRBE maps. The strongest limits are obtained at mid- to far-IR where foregrounds are bright, but smooth. If the CIB comes from matter clustered like galaxies, the smoothness of the maps implies CIB levels less than $\sim$(10-15) nW/m$^2$/sr over this wavelength range.

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arXiv1996

High-z objects and cold-dark-matter cosmogonies: the case of 53W091

The recently discovered high redshift galaxy, 53W091, with accurate age measurements (Dunlop et al 1996) provides a measure of the small-scale power of the primordial density field and, as we show, a crucial test of the inflation-inspired models. It allows $Ω$=1 cosmologies only for low values of $H_0$, but then pushes formation of that galaxy to redshift much greater than allowed for by the cold-dark-matter density field. Cold-dark-matter (CDM) models with cosmological constant ($Λ$) and low $Ω$ would decrease the redshift at which this galaxy has collapsed. However, in CDM models decreasing $Ω$ suppresses the small scale power in the density field and this effect turns out to be dominant. We estimate the mass of the galaxy and show that it represents a very rare and unlikely event in the density field of such models. Similar problems would occur in other modifications of the CDM cosmogonies.

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arXiv1996

Modified Cold-Dark-Matter models in light of 53W091 an old galaxy at high z

The epoch of galaxy formation provides an important additional test of cosmological theories. Cold-dark-matter (CDM) models with cosmological constant ($Λ$) are designed to account for the observed excess power in galaxy distribution, but at the same time suppress the power on small scales pushing galaxy formation to recent epochs. We point out that the recently discovered high redshift galaxy, 53W091, with accurate age measurements (Dunlop et al 1996) provides a particularly important test of these models. In the flat $Λ$-dominated Universe, the redshift of formation of 53W091 decreases with decreasing $Ω$. However, in the modified CDM models decreasing $Ω$ suppresses the small scale power in the density field and this effect turns out to be dominant. We estimate the mass of the galaxy and show that it represents a very rare and unlikely event in the density field of such models. Similar problems would occur in other modifications of the CDM cosmogonies.

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arXiv1996

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. An all-sky survey of $C(0)$

We measure the smoothness of the infrared sky using the COBE DIRBE maps, and obtain interesting limits on the production of the diffuse cosmic infrared background (CIB) light by matter clustered like galaxies. The predicted fluctuations of the CIB with the DIRBE beam size of 0.7° are of the order of 10\%, and the maps are smooth at the level of $δνI_ν\sim $ a few \nwm2sr rms from 2.2 to 100 \um. The lowest numbers are achieved at mid- to far-IR where the foreground is bright but smooth; they are $\sqrt{C(0)}$$\leq$$(1-1.5)$ \nwm2sr at $λ=$ 10-100 \um. If the CIB comes from clustered matter evolving according to typical scenarios, then the smoothness of the maps implies CIB levels less than $\sim (10-15) $ \nwm2sr over this wavelength range.

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arXiv1996

Clustering of Diffuse Infrared Background Light

The cosmic infrared background from galaxies should have a minimum fluctuation of the order of 10\% on angular scales probed by the DIRBE (Diffuse Infrared Background Experiment) on board COBE (Cosmic Background Explorer). We present the theoretical basis for the analysis and discuss the all-sky all-wavelengths survey that we conducted. We further show that a linear combination of maps at different wavelengths can greatly reduce the fluctuations produced by foreground stars in the near-IR, while not eliminating the fluctuations of the background from high redshift galaxies. The method is potentially very powerful, especially at wavelengths in the mid- to far-IR where the foreground is bright but smooth.

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arXiv1996

Clustering of DIRBE Light and IR Background

We outline a new method for estimating the cosmic infrared background using the spatial and spectral correlation properties of infrared maps. The cosmic infrared background from galaxies should have a minimum fluctuation of the order of 10\% on angular scales of the order of 1°. We show that a linear combination of maps at different wavelengths can greatly reduce the fluctuations produced by foreground stars, while not eliminating the fluctuations of the background from high redshift galaxies. The method is potentially very powerful, especially at wavelengths where the foreground is bright but smooth.

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arXiv1996

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. I. $C(0)$ and limits on the near-IR background

This paper is devoted to studying the CIB through its correlation properties. We studied the limits on CIB anisotropy in the near IR (1.25, 2.2, and 3.5 \um, or $J,\;K,\;L$) bands at a scale of 0.7° using the COBE\footnote{ The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the {\it COBE}. Scientific guidance is provided by the {\it COBE} Science Working Group. GSFC is also responsible for the development of the analysis software and for the production of the mission data sets.} Diffuse Infrared Background Experiment (DIRBE) data. In single bands we obtain the upper limits on the zero-lag correlation signal $C(0)= \langle(νδI_ν)^2\rangle < 3.6 \times 10^{-16},\; 5.1 \times 10^{-17},\; 5.7 \times 10^{-18}$ \w2m4sr2 for the $J,K,L$ bands respectively. The DIRBE data exhibit a clear color between the various bands with a small dispersion. On the other hand most of the CIB is expected to come from redshifted galaxies and thus should have different color properties. We use this observation to develop a `color subtraction' method of linear combinations of maps at two different bands. This method is expected to suppress the dominant fluctuations from foreground stars and nearby galaxies, while not reducing (or perhaps even amplifying) the extragalactic contribution to $C(0)$. Applying this technique gives significantly lower and more isotropic limits.

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arXiv1994

Microwave background anisotropy in low-$Ω_0$ inflationary models and the scale of homogeneity in the Universe

We study the microwave background anisotropy due to superhorizon-size perturbations (the Grischuk-Zel'dovich effect) in open universes with negative spatial curvature. Using COBE results on the low-order temperature multipole moments, we find that if the homogeneity of the observable Universe arises from an early epoch of inflation, the present density parameter cannot differ from unity by more than the observed quadrupole anisotropy, $|1-Ω_0| \alt Q \simeq 5\times 10^{-6}$. Thus, inflation models with low $Ω_0$ either do not fit the microwave background observations or they do not solve the horizon problem.

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arXiv1993

Microwave backgropund anisotropies, large-scale structure and cosmological parameters

We review how the various large-scale data constrain cosmological parameters and, consequently, theories for the origin of large-scale structure in the Universe. We discuss the form of the power spectrum implied by the correlation data of galaxies and argue by comparing the velocity field implied by the distribution of light with the observed velocity flows that the bias parameter, $b$, is likely to be constant in the linear regime. This then allows one to estimate the density parameter, $Ω$, and $b$ directly from the \underline{data} on $ξ(r)$ and the velocity fields. We show that it is consistent with low values of $Ω^{0.6}/b$. We discuss the ways to normalise the optical data at $z\sim0$ directly to the COBE (or other microwave background) data. The data on high-$z$ \underline{galaxies} allows one to further constrain the shape of the \underline{primordial} power spectrum at scales which are non-linear today ($< 8h^{-1}$Mpc) and we discuss the consistency of the data with inflationary models normalised to the large-scale structure observations.

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