Spectrophotometric Redshifts for z ∼ 1 Galaxies and Predictions for Number Densities with WFIRST and Euclid

Abstract

We investigate the accuracy of 4000Å/Balmer-break based redshifts by combining Hubble Space Telescope (HST) grism data with photometry. The grism spectra are from the Probing Evolution And Reionization Spectroscopically (PEARS) survey with HST using the G800L grism on the Advanced Camera for Surveys (ACS). The photometric data come from a compilation by the 3D-HST collaboration of imaging from multiple surveys (notably CANDELS and 3D-HST). We show evidence that spectrophotometric redshifts (SPZs) typically improve the accuracy of photometric redshifts by ∼17-60%. Our SPZ method is a template fitting based routine which accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism and also accounts for galaxy morphology along the dispersion direction. We show that the robustness of the SPZ is directly related to the fidelity of the D4000 measurement. We also estimate the accuracy of continuumbased redshifts, i.e., for galaxies that do not contain strong emission lines, based on the grism data alone (σ NMAD ∆z/(1+z) 0.06). Given that future space-based observatories like WFIRST and Euclid will spend a significant fraction of time on slitless spectroscopic observations, we estimate number densities for objects with |∆z/(1 + z s )| ≤ 0.02. We predict ∼700-4400 galaxies/degree 2 for galaxies with D4000>1.1 and |∆z/(1 + z s )| ≤ 0.02 to a limiting depth of i AB =24 mag. This is especially important in the absence of an accompanying rich photometric dataset like the existing one for the CANDELS fields, where redshift accuracy from future surveys will rely only on the presence of a feature like the 4000Å/Balmer breaks or the presence of emission lines within the grism spectra.

The PAU Survey: Measurements of the 4000 Å spectral break with narrow-band photometry

“…7, andHaines et al (2017), table 1. Far more examples can be find in the literature: e.g., Moresco et al (2012) displays the decreasing D4000 dependency on physical parameters vs redshift for early-type galaxies from different surveys in 0.15 < 𝑧 < 1.35 (separated in stellar mass bins), while Joshi et al (2019) and Borghi et al (2021) find the same trend in a redshift range similar to this work, for passive galaxies only and for a high-quality sample without any specific galaxy property cuts, respectively. This consistent decreasing trend is a consequence of the D4000 increasing with stellar age, and is noticeable in Fig.…”

“…The dependency of the D4000 versus redshift, stellar mass and SFR has also been evaluated. For the former, we have computed linear fits to the full sample, and find that the average D4000 decreases as redshift increases (as largely demonstrated in the literature, e.g., Moresco et al 2012;Joshi et al 2019;Borghi et al 2021). Despite the low SNR, the linear fit to PAUS direct is fully compatible with the trend found in VIPERS D4000.…”

The PAU survey: measurements of the 4000 Å spectral break with narrow-band photometry

“…7, andHaines et al ( 2017 ), table 1 (far more examples can be found in literature at different redshifts, e.g. Moresco et al 2012 ;Joshi et al 2019 ;Borghi et al 2021 ).…”

A Critical Examination of the Standard Cosmological Model: Toward a Modified Framework for Explaining Cosmic Structure Formation and Evolution

“…Research into the correlation between galaxy numbers and redshift is a key focus in astrophysics. This area of study is instrumental in unraveling the intricate dynamics and formation of structures within the universe [50][51][52][53].…”