High frequency cluster radio galaxies and the Sunyaev-Zel’dovich Effect properties of galaxy clusters

Gupta, Nikhel (2018): High frequency cluster radio galaxies and the Sunyaev-Zel’dovich Effect properties of galaxy clusters. Dissertation, LMU München: Fakultät für Physik

Abstract

The high frequency mm-wave surveys by the South Pole Telescope (SPT), the Atacama Cosmology Telescope (ACT), and Planck have enabled the Sunyaev-Zel’dovich Effect (SZE) detection of large cluster samples and their use to constrain cosmological parameters. In these analyses the connection between the cluster SZE signature and the underlying halo mass described by the so-called observable-mass relation plays a central role. A calibration of this relation requires robust masses determined through the use of galaxy dynamics or weak gravitational lensing, whose biases can be calibrated using current structure formation simulations. Groups like the Planck collaboration that have attempted to employ masses derived using the assumption of Hydro-static Equilibrium (HSE) have found that their cosmological constraints are limited by the inaccuracy of this assumption. The cluster cosmology is also highly dependent on an understanding of the selection function, which in the SZE case can be impacted by radio emission from Active Galactic Nuclei (AGN) within the clusters. Although the high frequency SZE surveys listed above are working in a regime where radio AGN with sufficient flux to impact the SZE signature are rare, it it nevertheless important to study the luminosity functions of these cluster radio AGN to constrain their impact on incompleteness in SZE selected cluster samples. To begin with, we study the overdensity of point sources in the direction of X-ray- selected galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies (MCXC; ⟨z⟩ = 0.14) at SPT and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multi-frequency catalog of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster SZE signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogs. We find that the high frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 percent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. We note that with the MCXC sample we cannot place strong constraints on the redshift evolution of the high frequency radio galaxy LF. The most recent catalog of galaxy clusters for this purpose is constructed from the Dark Energy Survey first year observations (DES-Y1). Thus, we study the redshift and mass trends for the radio sources in the direction of optically selected catalog of galaxy clusters from DES. We measure luminosity functions (LFs) and Halo Occupation Numbers (HONs) for these radio sources by statistically correcting for the background population and effectively placing the radio sources at the redshift of clusters for all frequencies. We find that the number of sources depend on the cluster mass as N ∝ M^{B_H} with B_H = 0.83 ± 0.05, 0.92 ± 0.25 and 1.23 ± 0.15 for 0.843, 95 and 150 GHz datasets, respectively. The pure density evolution in LFs is estimated as (1+z)^{γ_D} , with power index γ_D = 2.32 ± 0.40, 6.68 ± 3.25 and 6.26 ± 2.60 at 0.843, 95 and 150 GHz, respectively. We repeat our exercise to estimate the sample incompleteness and bias in the observable-mass relation for 2500 deg2 of SPT- SZ like survey. We find that 10.7 ± 2.4 percent of the clusters would be lost from the cluster sample with detection significance ξ ≥ 5 and redshift range 0.25 < z < 1.55 due to radio source contamination. We are exploring the impact of the incompleteness on the cosmological parameters, and we expect that there could be some super-statistical shift in the best fit parameters, because the Poisson noise on the full cluster sample in the latest analysis is at the 5 percent level. We also explore the impact of the radio galaxy contamination on the observable–mass relation, finding that the shift in the parameters of the relation is well within the statistical uncertainties derived for these parameters in the most recent cosmological analysis; thus, it is not an important systematic for cosmological parameter estimation using cluster abundance. Moreover, in our cluster cosmology analysis approach we empirically calibrate the observable–mass relation, and therefore our approach is insensitive to this effect. In the past few years a lot of attention is offered towards investigations of the galaxy cluster observable-mass scaling relations. One method is to measure the mass from X- ray observations of the ICM combined with the assumption of HSE and to calibrate the observable-mass relation using these HSE masses. However, given that galaxy clusters are young objects still actively growing through accretion, it is unlikely that HSE pertains in these systems – particularly those systems having undergone recent major mergers. Thus, using these masses will produce misleading conclusions about the observable-mass scaling relation. It is important to quantify these systematics in the framework where true mass of cluster is known. We present a detailed study of the galaxy cluster thermal SZE signal Y and pressure profiles using Magneticum Pathfinder hydrodynamical simulations. With a sample of 50,000 galaxy clusters (M500c > 1.4 × 10^14 M⊙) out to z = 2, we find significant variations in the shape of the pressure profile with mass and redshift and present a new generalized NFW model that follows these trends. We show that the thermal pressure at R500c accounts for only 80 percent of the pressure required to maintain hydrostatic equilibrium, and therefore even idealized hydrostatic mass estimates would be biased at the 20 percent level. We compare the cluster SZE signal extracted from a sphere with different virial-like radii, a virial cylinder within a narrow redshift slice and the full light cone, confirming small scatter (σ_{ln Y} ≃ 0.087) in the sphere and showing that structure immediately surrounding clusters increases the scatter and strengthens non self-similar redshift evolution in the cylinder. Uncorrelated large scale structure along the line of sight leads to an increase in the SZE signal and scatter that is more pronounced for low mass clusters, resulting in non self-similar trends in both mass and redshift and a mass dependent scatter that is ~ 0.16 at low masses. The scatter distribution is consistent with log-normal in all cases. We present a model of the offsets between the center of the gravitational potential and the SZE center that follows the variations with cluster mass and redshift.

Abstract

Die Hochfrequenz-Millimeterwellen Durchmusterungen durch das South Pole Telescope (SPT), das Atacama Cosmology Telescope (ACT) und der ESA Satellitenmission Planck ermo ̈glichen die Sunyaev-Zeldovitsch-Effekt-Detektion (SZE) grosser Galaxienhaufenkata- loge und deren Nutzung zur Bestimmung der kosmologischen Parameter. Das Verha ̈ltnis des SZE Signals zur zugrundeliegenden Halonenmasses des Galaxienhaufens - die soge- nannte mass-observable relation - ist von zentraler Bedeutung fu ̈r diese Untersuchungen. Die Bestimmung der kosmologischen Parameter ist insbesondere stark von der Annahme des hydrostatischen Gleichgewichts (hydrostatic equilibrium, HSE) abha ̈ngig. Mit Hilfe der hydrodynamischen Magneticum Pathfinder Simulationen bestimmen wir anhand eines simulierten Galaxienhaufenkataloges die Abha ̈ngigkeit des Druckprofiles von der Halonen- masse und der Rotverschiebung des Haufens. Wir weisen nach, dass der thermische Druck nur 80Neben der mass-observable relation ha ̈ngt die Bestimmung der kosmologischen Pa- rameter durch Galaxienhaufenkataloge auch von der Selektion der Kataloge ab. Insbeson- dere kann die Anwesenheit von punktfo ̈rmigen Radioquellen in einem Galaxienhaufen zu einer Verringerung des SZE Signals, und folglich einer Nichtdetektion, fu ̈hren. Um den Ein- fluss dieses Effekts auf die Anzahl Haufen im SPT-Katalog zu bestimmen, untersuchen wir die Ha ̈ufigkeit von punktfo ̈rmigen Radioquellen in einem Ro ̈ntgen- und einem optisch se- lektiertem Haufenkatalog. Wir bestimmen die Leuchtkraftverteilung (luminosity function) der Radioquellen, und untersuchen dessen Entwicklung mit Rotverschiebung. Die daraus folgende Anzahl nichtdetektierter Quellen ist kleiner als der Poissonfehler auf der Anzahl Haufen im SPT-Katalog, und fu ̈hrt somit zu keiner signifikanten Fehlbestimmung der kos- mologischen Parameter. Zusammenfassend stellen wir fest, dass die Galaxienhaufenselek- tion durch den SZE Effekt eine ausreichende Vollsta ̈ndigkeit der Kataloge sicherstellt. Die Annahme von HSE fu ̈hrt jedoch zu einer 20-prozentigen Fehlscha ̈tzung der Halonenmassen der Haufen. Anhand unserer Arbeit kann diese Fehlscha ̈tzung kalibriert und korrigiert werden.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Galaxies, Galaxy Clusters, Luminosity function, Mass function, Submillimeter galaxies, Cosmology, Observations, Simulations
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 2. März 2018
• 1. Bericht­erstatter:in: Mohr, Joseph