The galaxy cluster mass scale and its impact on cosmological constraints from the cluster population (1902.10837v1)

Abstract: The total mass of a galaxy cluster is one of its most fundamental properties. Together with the redshift, the mass links observation and theory, allowing us to use the cluster population to test models of structure formation and to constrain cosmological parameters. Building on the rich heritage from X-ray surveys, new results from Sunyaev-Zeldovich and optical surveys have stimulated a resurgence of interest in cluster cosmology. These studies have generally found fewer clusters than predicted by the baseline Planck LCDM model, prompting a renewed effort on the part of the community to obtain a definitive measure of the true cluster mass scale. Here we review recent progress on this front. Our theoretical understanding continues to advance, with numerical simulations being the cornerstone of this effort. On the observational side, new, sophisticated techniques are being deployed in individual mass measurements and to account for selection biases in cluster surveys. We summarise the state of the art in cluster mass estimation methods and the systematic uncertainties and biases inherent in each approach, which are now well identified and understood, and explore how current uncertainties propagate into the cosmological parameter analysis. We discuss the prospects for improvements to the measurement of the mass scale using upcoming multi-wavelength data, and the future use of the cluster population as a cosmological probe.

The Influence of Galaxy Cluster Mass Scale on Cosmological Constraints

The research paper under consideration explores the assessment of galaxy cluster masses and explores its implications for cosmological models. This investigation is particularly significant as galaxy clusters are among the largest gravitationally bound structures in the universe, serving as critical probes for testing cosmic formation models and constraining parameters of cosmology such as matter density and the amplitude of matter fluctuations, commonly denoted as $\sigma_8$.

Context and Background

Galaxy clusters, composed predominantly of dark matter, hot ionized gas, and stars, provide a wealth of information about the large-scale structure of the universe. The mass of these clusters, intertwined with their redshift, offers a concrete link between observational data and theoretical frameworks. Traditionally, X-ray surveys have been at the forefront of these studies, revealing a lower-than-anticipated cluster count when compared against predictions from the standard $\Lambda$CDM model. This discrepancy has heightened the focus on accurately determining the mass scale of galaxy clusters.

Current Developments and Methodological Advances

The paper emphasizes recent efforts aimed at refining mass estimation techniques. Notably, numerical simulations have become indispensable in advancing theoretical comprehension, serving as the foundation for these efforts. Parallelly, diverse observational methodologies—ranging from galaxy kinematics to gravitational lensing—are being honed to individually measure cluster masses while addressing selection biases within cluster surveys. Each method comes with unique systematic uncertainties; hence, understanding these biases remains critical to enhancing the accuracy of mass estimations.

Findings and Theoretical Insights

The paper reviews current techniques in estimating mass scales and provides insights into systematic errors and uncertainties. Simulations indicate that assumptions inherent in each method could introduce biases, impacting the derived cosmological parameters. For instance, non-thermal pressures within clusters need careful consideration to avoid significant biases in mass calculations. The sophistication in mass estimation is also pivotal in reconciling the mismatch between cluster counts from observations and theoretical predictions.

Prospects for Multi-Wavelength Data

There is potential for progress via upcoming multi-wavelength datasets which promise improvements in measuring the mass scale. Such datasets are anticipated to refine the calibration of mass-observable relations further. Precise multi-wavelength observations could mitigate existing uncertainties, allowing for more stringent constraints on cosmological parameters using galaxy clusters as cosmological probes.

Conclusion

Ultimately, the paper underscores the centrality of accurate mass scale determination in clusters for cosmology. By reviewing the state of the art in mass estimation methodologies and detailing their systematic uncertainties, the paper outlines the current understanding and progress in cluster cosmology. It also offers a look ahead at future advancements, as additional and refined observations enhance the constraints on cosmological models. These developments underscore the integral role of galaxy cluster mass measurement in understanding the universe's structure and evolution.

In conclusion, the continued improvement in understanding galaxy cluster masses not only aids in addressing observational-theoretical discrepancies but also sharpens the precision of the universe's cosmological parameters, quintessential for unraveling cosmic mysteries.