[Paper Review] The VANDELS ESO public spectroscopic survey: final Data Release of 2087 spectra and spectroscopic measurements

B. Garilli, R. J. McLure+95 more|University of Groningen research database (University of Groningen / Centre for Information Technology)|Jan 19, 2021

Astronomy and Astrophysical Research70 references4 citations

TL;DR

This paper presents the final public data release of the VANDELS survey, delivering 2,087 spectroscopic redshifts for galaxies at 1 < z < 6.5, achieved through deep VIMOS observations with signal-to-noise ratios >7 for 80% of targets brighter than i_AB = 26. The survey achieves a 98% spectroscopic success rate and redshift accuracy of 0.0007, with SED fitting providing stellar mass, star formation rate, and dust attenuation measurements across a mass range of 8.3 < log(M*/M⊙) < 11.7.

ABSTRACT

VANDELS is an ESO Public Spectroscopic Survey designed to build a sample of high signal to noise, medium resolution spectra of galaxies at redshift between 1 and 6.5. Here we present the final Public Data Release of the VANDELS Survey, comprising 2087 redshift measurements. We give a detailed description of sample selection, observations and data reduction procedures. The final catalogue reaches a target selection completeness of 40% at iAB = 25. The high Signal to Noise ratio of the spectra (above 7 in 80% of the spectra) and the dispersion of 2.5Å allowed us to measure redshifts with high precision, the redshift measurement success rate reaching almost 100%. Together with the redshift catalogue and the reduced spectra, we also provide optical mid-IR photometry and physical parameters derived through SED fitting. The observed galaxy sample comprises both passive and star forming galaxies covering a stellar mass range 8.3&lt; Log(M*/Msolar)&lt;11.7. All catalogues and spectra are accessible through the survey database (http://vandels.inaf.it) where all information can be queried interactively, and via the ESO Archive (https://www.eso.org/qi/).

Motivation & Objective

• To deliver the final public data release of the VANDELS ESO spectroscopic survey, providing high-fidelity spectroscopic measurements for high-redshift galaxies.
• To ensure the completeness and reliability of redshift measurements across a wide redshift range (1 < z < 6.5), particularly for faint and passive galaxies.
• To characterize galaxy intrinsic properties through SED fitting, including stellar mass, star formation rate, dust attenuation, and star formation history.
• To validate that target selection and redshift measurement processes do not introduce significant biases relative to photometric redshifts.
• To make line fluxes, equivalent widths, and Lick indices available in future releases, enhancing the utility of the dataset for detailed physical analysis.

Proposed method

• Target selection was based on photometric redshifts and magnitude limits, with priority given to galaxies at 1 < z < 6.5, including passive and star-forming types.
• Deep VIMOS spectroscopic observations were conducted over up to 80 hours per field, using the VIMOS instrument on the ESO Very Large Telescope.
• Data reduction included 2D and 1D spectral extraction, sky subtraction, and flux calibration using standard stars and sky fibers.
• Redshifts were measured via cross-correlation and manual fitting of emission and absorption lines, with confidence flags assigned based on signal-to-noise and line quality.
• SED fitting was performed using full photometric coverage from HST, ground-based, and IRAC data, fitting with stellar population synthesis models to derive physical parameters.
• Systematic uncertainties in redshifts were estimated via internal comparisons between repeated observations of the same targets.

Experimental results

Research questions

• RQ1 What is the spectroscopic redshift success rate and accuracy of the VANDELS survey across the redshift range 1 < z < 6.5?
• RQ2 How do the signal-to-noise ratios of the spectra vary with magnitude, and what is the completeness of the survey for faint and passive galaxies?
• RQ3 To what extent do the target selection and redshift measurement processes introduce biases relative to photometric redshifts?
• RQ4 What are the derived physical properties (e.g., stellar mass, SFR, dust attenuation) of the galaxies in the sample, and how do they vary with redshift?
• RQ5 How do the SED fitting results compare with the original photometric redshift estimates, and what is the reliability of the derived parameters?

Key findings

• The VANDELS survey achieved a spectroscopic redshift success rate of 98% across all redshift measurements, with 86% reliability for redshifts flagged as high-confidence.
• For targets with i_AB < 26, 80% of spectra have a signal-to-noise ratio per resolution element above 7, and 70% of fainter targets (i_AB > 26) still achieve S/N > 5.
• The redshift accuracy is estimated at 0.0007, based on internal comparisons between repeated observations of the same targets.
• The survey successfully targets passive galaxies down to i_AB = 24.5 and star-forming galaxies down to i_AB = 24, with a target sampling rate exceeding 45% in both cases.
• Stellar masses in the sample span 8.3 < log(M*/M⊙) < 11.7, with star formation rates (SFR) averaged over the last 100 Myr and dust attenuation (Av) derived from SED fitting.
• No significant biases were introduced in redshift or physical property measurements relative to the original photometric redshift selection, confirming the robustness of the survey.