Structure in galaxy clusters revealed through Sunyaev-Zel’dovich observations : A multi-aperture synthesis approach

As the largest bound objects in the universe, galaxy clusters are unique targets to study astrophysical processes, as well as powerful probes for precision cosmology. Galaxy clusters are dynamically young and their merger history and energetic feedback from galaxies leave significant traces in the pressure or entropy distribution of the intra-cluster medium (ICM), the hot plasma that contains most of the baryonic mass in clusters. A detailed understanding of how ICM observables relate to cluster mass at different cosmic epochs is also crucial to reduce the systematic uncertainties in the measurement of cosmological parameters from cluster observations. Through analysis of new observational data, mock observations, and modelling, I explore how current and future millimeter-wavelength interferometer observations of the Sunyaev-Zel’dovich effect (SZE) allow detailed studies of the ICM structure and physics. The SZE is a change in the emission spectrum of the Cosmic Microwave Background (CMB) caused by the scattering of CMB photons off the hot ICM free electrons. The SZE signal is proportional to the electron pressure and thus allows a measure of the thermal energy content and morphology of the ICM. I focus on the projected triaxial cluster morphology, whose extended structure is best observed at millimeter-wavelengths with a combination of interferometer and single-dish imaging observations. Interferometric observations provide good spatial resolution but suffer from sparse spatial sampling, which may hamper non-spherical cluster pressure profile constraints. Single dish observations are naturally limited in spatial resolution and commonly do not resolve the interesting cluster core regions or shocks in the ICM. My interferometric CARMA/SZA SZE observations of the galaxy cluster MS0451 complement our prior single-dish APEX observations. While the small-dish interferometric SZA data offer better precision in spherical pressure profile fits, they suffer from insufficient interferometric spatial sampling, which does not allow to constrain the projected elliptical shape and orientation of MS0451. APEX-SZ data thus complement the interferometric fits, as they can constrain the non-spherical projected morphology. The ICM in the core regions of clusters retains signatures of AGN energy feedback and merger-induced disturbance. The unrivaled high resolution and sensitivity of the new Atacama Large Millimeter Array (ALMA) and its compact sub-array (ACA) offer unique capabilities to study cluster cores and merger-induced shock fronts. Through mock simulations of ALMA and SZA observations and using my Bayesian MCMC code, I show that it is possible to distinguish different morphological states of clusters through their characteristic, observable pressure profiles. In addition, I quantify how future ALMA lower frequency (Band 1) observations can strengthen the present capability to measure the cluster pressure distribution. My simulations also outline how ALMA observations provide detailed views on shock fronts in the ICM. The famous Bullet Cluster is taken as an example case, for which ALMA/ACA Cycle 2 configuration simulations illustrate how the merger-induced bow shock structure can indeed be imaged

ALMA FITS header keywords: a study from the archive User perspective

ALMA products are stored in the Science Archive in the form of FITS images. It is a common idea that the FITS image headers should collect in their keywords all the information that an archive User might want to search for in order to quickly select, compare, or discard datasets. With this perspective in mind, we first present a short description of the current status of the ALMA FITS archive and images. We realized that at the moment most of the parameters that could be useful for a general User are still missing in the archived data. We then provide a CASA task generating the image header keywords that we suggest to be relevant for the scientific exploitation of the ALMA archival data. The proposed tool could be also applied to several types of interferometer data and part of it is implemented in a web interface. An example of the scientific application of the keywords is also discussed.Comment: 20 pages, 6 figures, ALMA Memo 613 https://library.nrao.edu/public/memos/alma/main/memo613.pd

The ALMA Re-imaging Project Study

In the first 6 years of ALMA operations, data for more than 1700 projects have been calibrated and manually imaged for quality assessment purposes before being delivered to the PI and being added to the ALMA Science Archive. However, imaging is a time-consuming process and therefore the data-reducers have only created image products for a small fraction of the original data for quality control purposes. We study the feasibility and cost of a potential ALMA Re-Imaging project which would use the newly developed ALMA imaging pipeline to create image products for all the existing data. We here report about the concept and the currrent state of this study

KAFE: the Key-analysis Automated FITS-images Explorer

We present KAFE—the Key-analysis Automated FITS-images Explorer. KAFE is a web-based FITS image postprocessing analysis tool designed to be applicable in the radio to sub-mm wavelength domain. KAFE was developed to complement selected FITS files with metadata based on a uniform image analysis approach as well as to provide advanced image diagnostic plots. It is ideally suited for data mining purposes and multiwavelength/multi-instrument data samples that require uniform data diagnostic criteria. We present the code structure and interface, the keyword definitions, the products generated for selected users’ science cases, and application examples

Square Kilometre Array Science Data Challenge 1: analysis and results

As the largest radio telescope in the world, the Square Kilometre Array (SKA) will lead the next generation of radio astronomy. The feats of engineering required to construct the telescope array will be matched only by the techniques developed to exploit the rich scientific value of the data. To drive forward the development of efficient and accurate analysis methods, we are designing a series of data challenges that will provide the scientific community with high-quality data sets for testing and evaluating new techniques. In this paper, we present a description and results from the first such Science Data Challenge 1 (SDC1). Based on SKA MID continuum simulated observations and covering three frequencies (560, 1400, and 9200 MHz) at three depths (8, 100, and 1000 h), SDC1 asked participants to apply source detection, characterization, and classification methods to simulated data. The challenge opened in 2018 November, with nine teams submitting results by the deadline of 2019 April. In this work, we analyse the results for eight of those teams, showcasing the variety of approaches that can be successfully used to find, characterize, and classify sources in a deep, crowded field. The results also demonstrate the importance of building domain knowledge and expertise on this kind of analysis to obtain the best performance. As high-resolution observations begin revealing the true complexity of the sky, one of the outstanding challenges emerging from this analysis is the ability to deal with highly resolved and complex sources as effectively as the unresolved source population

KAFE - a flexible image analysis tool

We present KAFE, the Keywords of Astronomical FITS-Images Explorer - a web-based FITS images post-processing analysis tool designed to be applicable in the radio to sub-mm wavelength domain. KAFE was developed to enrich selected FITS files with metadata based on a uniform image analysis approach as well as to provide advanced image diagnostic plots. It is ideally suited for data mining purposes and multi-wavelength/multi-instrument data samples that require uniform data diagnostic criteria

SZ contribution to characterize the shape of galaxy cluster haloes

We present the on-going activity to characterize the geometrical properties of the gas and dark matter haloes using multi-wavelength observations of galaxy clusters. The role of the SZ signal in describing the gas distribution is discussed for the pilot case of the CLASH object MACS J1206.2-0847

Combination of single dish and interferometer data

I will review techniques how to combine single dish and interferometric data in the radio regime. Packages such as MIRIAD and GILDAS will also be compared to how this is currently done in CASA. An associated tutorial will focus and compare solutions in CASA using the QAC frontend, for which scripts are available in the github repository

SZ contribution to characterize the shape of galaxy cluster haloes

We present the on-going activity to characterize the geometrical properties of the gas and dark matter haloes using multi-wavelength observations of galaxy clusters. The role of the SZ signal in describing the gas distribution is discussed for the pilot case of the CLASH object MACS J1206.2-0847