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The High Latitude Spectroscopic Survey (HLSS) is the reference baseline spectroscopic survey for NASA's Nancy Grace Roman Space Telescope, measuring redshifts of ∼10M H α emission line galaxies over a 2000 deg2 footprint at z  = 1–2. In this work, we use a realistic Roman galaxy mock catalogue to explore optimal phenomenological modelling of the measured power spectrum. We consider two methods for modelling the redshift-space distortions (Kaiser squashing and another with a window function on β that selects out the coherent radial infall pairwise velocities, |$\mathcal {M}_A$| and |$\mathcal {M}_B$|⁠ , respectively), two models for the non-linear impact of baryons that smear the baryon acoustic oscillation signal (a fixed ratio between the smearing scales in the perpendicular and parallel dimensions and another where these smearing scales are kept as free parameters, Pdw(k | k *) and Pdw(k |Σ⊥, Σ∥), respectively), and two analytical emulations of non-linear growth (one employing the halo model and another formulated from simulated galaxy clustering of a semi-analytical model, |$\mathcal {F}_{HM}$| and |$\mathcal {F}_{\it SAM}$|⁠ , respectively). We find that the best model combination employing |$\mathcal {F}_{HM}$| is |$P_{dw}(k|k_*)*\mathcal {F}_{HM}*\mathcal {M}_B$|⁠ , while the best combination employing |$\mathcal {F}_{\it SAM}$| is |$P_{dw}(k|k_*)*\mathcal {F}_{\it SAM}*\mathcal {M}_B$|⁠ , which leads to unbiased measurements of cosmological parameters. We compare these to the Effective Field Theory of Large-Scale Structure perturbation theory model PEFT (k |Θ), and find that our simple phenomenological models are comparable across the entire redshift range for k max = 0.25 and 0.3 h  Mpc−1. We expect the tools that we have developed to be useful in probing dark energy and testing gravity using Roman in an accurate and robust manner. [ABSTRACT FROM AUTHOR]

The Nancy Grace Roman Space Telescope will conduct a High Latitude Spectroscopic Survey (HLSS) over a large volume at high redshift, using the near-IR grism (1.0â€"1.93 ÎĽ m, R = 435â€"865) and the 0.28 deg2 wide-field camera. We present a reference HLSS that maps 2000 deg2 and achieves an emission-line flux limit of 10âˆ'16 erg sâˆ'1 cmâˆ'2 at 6.5 σ, requiring ∼0.6 yr of observing time. We summarize the flowdown of the Roman science objectives to the science and technical requirements of the HLSS. We construct a mock redshift survey over the full HLSS volume by applying a semianalytic galaxy formation model to a cosmological N -body simulation and use this mock survey to create pixel-level simulations of 4 deg2 of HLSS grism spectroscopy. We find that the reference HLSS would measure ∼10 million H α galaxy redshifts that densely map large-scale structure at z = 1â€"2 and 2 million [O iii ] galaxy redshifts that sparsely map structures at z = 2â€"3. We forecast the performance of this survey for measurements of the cosmic expansion history with baryon acoustic oscillations and the growth of large-scale structure with redshift-space distortions. We also study possible deviations from the reference design and find that a deep HLSS at f line > 7 Ă— 10âˆ'17 erg sâˆ'1 cmâˆ'2 over 4000 deg2 (requiring ∼1.5 yr of observing time) provides the most compelling stand-alone constraints on dark energy from Roman alone. This provides a useful reference for future optimizations. The reference survey, simulated data sets, and forecasts presented here will inform community decisions on the final scope and design of the Roman HLSS. [ABSTRACT FROM AUTHOR]

We present measurements of the linear galaxy bias of Hα and [O  iii ] emission-line galaxies (ELGs) for the High Latitude Spectroscopic Survey (HLSS) of Nancy Grace Roman Space Telescope (or Roman), using galaxy mocks constructed using semi-analytical model for galaxy formation, Galacticus , with a large cosmic volume and redshift coverage. We compute the two-point statistics of galaxies in configuration space and measure linear bias within scales of 10–50  h −1 Mpc. We adopt different selection algorithms to investigate the impact of the Roman line flux cut, as well as the effect of dust model used to calibrate Galacticus, on the bias measurements. We consider galaxies with Hα and [O  iii ] emissions over the redshift range 1 < z < 3, as specified by the current baseline for the Roman HLSS. We find that the linear bias for the Hα and [O  iii ] ELGs can be expressed as a linear function with respect to redshift: b ≃ 0.9 z + 0.5 for H |$\alpha \, (1\lt z\lt 2)$|⁠ , and b ≃ z + 0.5 for [O  iii ] (2 < z < 3). We have also measured the halo occupation distributions of these Hα and [O  iii ] ELGs to understand their distribution within dark matter haloes. Our results provide key input to enable the reliable forecast of dark energy and cosmology constraints from Roman. [ABSTRACT FROM AUTHOR]

We present a realistic 2000 deg2 H α galaxy mock catalogue with 1 < z < 2 for the Nancy Grace Roman Space Telescope (Roman) galaxy redshift survey, the High Latitude Spectroscopic Survey (HLSS), created using Galacticus, a semi-analytical galaxy formation model, and high-resolution cosmological N -body simulations. Galaxy clustering can probe dark energy and test gravity via baryon acoustic oscillation (BAO) and redshift space distortion (RSD) measurements. Using our realistic mock as the simulated Roman HLSS data, and a covariance matrix computed using a large set of approximate mocks created using ezmock , we investigate the expected precision and accuracy of the BAO and RSD measurements using the same analysis techniques used in analysing real data. We find that the Roman H α galaxy survey alone can measure the angular diameter distance with 2 per cent uncertainty, the Hubble parameter with 3–6 per cent uncertainty, and the linear growth parameter with 7 per cent uncertainty, in each of four redshift bins. Our realistic forecast illustrates the power of the Roman galaxy survey in probing the nature of dark energy and testing gravity. [ABSTRACT FROM AUTHOR]

We perform a simulation with Galacticus, a semi-analytical galaxy formation model, to predict the number counts of H α and [O  iii ] emitting galaxies. With a state-of-the-art N -body simulation, UNIT, we first calibrate Galacticus with the current observation of H α luminosity function. The resulting model coupled with a dust attenuation model, can reproduce the current observations, including the H α luminosity function from HiZELS and number density from WISP. We extrapolate the model prediction to higher redshift and the result is found to be consistent with previous investigations. We then use the same galaxy formation model to predict the number counts for [O  iii ] emitting galaxies. The result provides further validation of our galaxy formation model and dust model. We present number counts of H α and [O  iii ] emission line galaxies for three different line flux limits: 5 × 10−17erg s−1 cm−2, 1 × 10−16 erg s−1 cm−2 (6.5σ nominal depth for WFIRST GRS), and 2 × 10−16 erg s−1 cm−2 (3.5σ depth of Euclid GRS). At redshift 2 < z < 3, our model predicts that WFIRST can observe hundreds of [O  iii ] emission line galaxies per square degree with a line flux limit of 1 × 10−16 erg s−1 cm−2. This will provide accurate measurement of large-scale structure to probe dark energy over a huge cosmic volume to an unprecedented high redshift. Finally, we compare the flux ratio of H α/[O  iii ] within the redshift range of 0 < z < 3. Our results show the known trend of increasing H α/[O  iii ] flux ratio with H α flux at low redshift, which becomes a weaker trend at higher redshifts. [ABSTRACT FROM AUTHOR]