0 Assigned ID: 2944 ----- Attempting Submission 1 (Thu Mar 24 04:25:52 GMT 2022) ----- One of the biggest unsolved problems in galaxy formation is the physical mechanism that quenches star formation in massive systems, giving rise to the observed dichotomy between blue star-forming galaxies and red-and-dead ellipticals. In order to reproduce it, all modern cosmological simulations implement some variant of AGN feedback, driving powerful galactic scale outflows that suppress star-formation in massive galaxies at late times. Simulations show that these outflows can expel baryons into the circumgalactic and intergalacticmedia (IGM and CGM) resulting in Mpc-scale bubbles of tenuous hot (T > 10^6 K) gas surrounding massivegalaxies. The degree to which AGN feedback contributes to the number of baryons in the so-called warm-hot intergalactic medium (WHIM), adding to the inevitable contribution from gas shock-heated by structure formation, is at the heart of the long-standing missing baryon problem. We propose to use an archival sample of 94 HST/COS background QSO spectra probing the massive halos hosting 3193 foreground SDSS luminous red galaxies (LRGs; z < 0.5) to statistically characterize the Ly-alpha forest absorption profile at impact parameters from 0.1 to 10 pMpc. By performing an end-to-end feasibility study of our proposed analysis using state-of-the-art cosmological simulations and realistic mock COS spectra, we demonstrate that the abundance of HI Ly-alpha forest lines (N_HI < 10^14 cm^-2) in this dataset provides a precision probe of AGN feedback models and the fraction of baryons in the WHIM. The proposal team is composed of a combination of researchers with extensive experience in (1) high-resolution ultraviolet and optical spectroscopy of QSO absorption systems, and (2) theoretical studies of the Ly-alpha forest, the intergalactic and circumgalactic medium (IGM and CGM), and cosmological hydrodynamical simulations. Besides, our team has direct access to the National Energy Research Scientific Computing Center (NERSC) and an ample amount of supercomputing resources. Principal Investigator Khaire is an expert in the theoretical studies of IGM and CGM, analyzing HST/COS data and cosmological hydrodynamical simulations. In his recent paper (Khaire et. al. 2019) he published a high precision Ly-alpha forest power spectrum at z < 0.5 using the HST/COS archival dataset which resulted in precise measurements of the low-z metagalactic UV background. Using the results of it, he has also published synthesis models of the metagalactic UV background (Khaire & Srianand 2019) that are implemented in the cloudy photoionization software helping researchers to use it in the CGM studies. In addition to this, he has co-authored 8 IGM/CGM papers that use HST/COS data. He has experience in measuring the UV background and thermal state of the IGM (Khaire et. al in prep) which are the important nuisance parameters that we will also determine for the data and simulations in our proposed analysis. Co-investigators Hennawi, Burchett, and Tejos are expert QSO absorption-line researchers with established track records and important publications on a variety of specific topics in this general area. Dr. Joseph Burchett and Prof. Nicolas Tejos are experts in dealing with HST/COS QSO spectra. They will be leading the efforts for preparing the dataset of QSO-LRG pairs, continuum fitting QSO spectra, and identifying metal lines. Co-investigators Dr. Koki Kakiichi, Dr. Suk Sien Tie, and Teng Hu are experts in analyzing large datasets of Ly-alpha forest as well as simulating those in cosmological hydrodynamic simulations. Recently, Teng Hu has proposed a new approach to estimate the thermal state of the intergalactic medium using the Doppler width column density (b-NHI) distribution using likelihood free inference and machine learning (Hu et al 2022, under review in MNRAS). Co-investigator Prof. Joseph Hennawi (along with his former Ph.D. student Dr. Hector Hiss) has developed automated Voigt profile fitting codes (Hiss et al. 2019) and measured z > 2 thermal states of the IGM (also used in Walther et al.2019). We are using the same automated Voigt profile fitting code, modified to work on HST/COS spectra. Teng Hu has used the same code in his recent paper Hu et al. 2020 as mentioned above. In addition to this, Prof. Hennawi, PI Khaire, and co-I Teng Hu have all the tools to analyze different hydrodynamical simulations, create forward model spectra and perform sophisticated parameter estimations as demonstrated by many published works. Co-investigator Pro. Zarija Lukic is a world-leading expert in the hydrodynamical simulations of the intergalactic medium. He pioneered the massively parallel grid simulation Nyx which is extremely fast and efficient. Nyx simulations have been used in many IGM studies, including PI Khaire's power-spectrum analysis, CO-I Prof. Hennawi's thermal state measurements, and CO-I Teng Hu's new approach for measuring low-redshift thermal state. Prof. Lukic has recently implemented AGN feedback models into the Nyx code. We will be using Nyx to create a suite of simulations by tuning the strength of AGN feedback. Prof. Lukic has direct access to the NERSC supercomputer and ample resources to perform these simulations Intergalactic Medium and the Circumgalactic Medium Large Scale Structure of the Universe 0 Regular false false false false false false SUPPORTED