Unveiling the Hidden Web: Calibrating Roman Galaxy Environments via IGM Tomography
| Program ID | 19107 |
|---|---|
| Science Category | Galaxies |
| Program Type | Analysis |
| Category | Medium |
| Principal Investigator | Nima Chartab |
| PI Institution | California Institute of Technology / IPAC |
| Co-Investigators |
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| Abstract | Understanding environmental galaxy evolution at cosmic noon (z ~ 2–3) is essential for resolving how present-day scaling relations were established. The Roman HLWAS Deep Tier grism survey will be transformative, covering 19 deg^2 and identifying ~200,000 emission-line galaxies. However, a fundamental environment measurement problem remains: spectroscopic samples at these redshifts rely predominantly on [O III]5008 selection, which preferentially favors galaxies with low gas-phase metallicity and high sSFR. This potentially leads to the systematic underrepresentation of quiescent or low-SFR structures. Furthermore, standard photometric redshifts lack the precision to resolve the ~10 cMpc/h scales where environmental processes act, often smearing compact protoclusters into the field background. This archival investigation addresses these limitations by using the Ly-a Tomography IMACS Survey (LATIS) as an empirical calibrator. LATIS provides a galaxy-independent 3D density map of the IGM, tracing the total matter field regardless of the specific galaxy population. We will calibrate the overdensity of [O III]-emitting galaxies against this matter field using the 0.8 deg^2 overlap between LATIS and the Roman Deep Tier in COSMOS. Once this [O III]-to-IGM transfer function is established, we will apply the calibration to the full 19 deg^2 footprint (COSMOS+XMM-LSS) to convert galaxy counts into robust physical overdensities. To ensure completeness and reliability, we will specifically test the recovery of UV-dim structures—massive halos lacking an overdensity of Lyman Break Galaxies—and quantify "[O III]-dim" analogs that might be missed or misidentified. This program will enable a calibrated census of ~475 protoclusters and investigate how galaxy properties correlate with these calibrated environments, providing the critical framework for all future Roman environment studies. |