INSPIRE: INvestigating Stellar Population In RElics

III. Second data release (DR2): testing the systematics on the stellar velocity dispersion^★

¹ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
e-mail: gdago@astro.puc.cl
² Sub-Dep. of Astrophysics, Dep. of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
³ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁵ Universita degli studi dell’Insubria, via Valleggio 11, 22100 Como, Italy
⁶ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de LaLaguna, E-38206 La Laguna, Tenerife, Spain
⁸ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁹ INAF – Osservatorio Astronomico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹⁰ School for Physics and Astronomy, Sun Yat-sen University, Guangzhou 519082, Zhuhai Campus, PR China
¹¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹² INAF – Osservatorio astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
¹³ INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
¹⁴ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Received: 23 November 2022
Accepted: 23 January 2023

Abstract

Context. The project called INvestigating Stellar Population In RElics (INSPIRE) is based on VLT/X-shooter data from the homonymous on-going ESO Large Program. It targets 52 ultra-compact massive galaxies at 0.1 < z < 0.5 with the goal of constraining their kinematics and stellar population properties in great detail and of analysing their relic nature.

Aims. This is the second INSPIRE data release (DR2), comprising 21 new systems with observations completed before March 2022. For each system, we release four one-dimensional (1D) spectra to the ESO Science Archive, one spectrum for each arm of the X-Shooter spectrograph. They are at their original resolution. We also release a combined and smoothed spectrum with a full width at half maximum resolution of 2.51 Å. In this paper, we focus on the line-of-sight velocity distribution, measuring integrated stellar velocity dispersions from the spectra, and assessing their robustness and the associated uncertainties.

Methods. For each of the 21 new systems, we systematically investigated the effect of the parameters and set-ups of the full spectral fitting on the stellar velocity dispersion (σ) measurements. In particular, we tested how σ changes when several parameters of the fit as well as the resolution and spectral coverage of the input spectra are varied.

Results. We found that the effect that causes the largest systematic uncertainties on σ is the wavelength range used for the fit, especially for spectra with a lower signal-to-noise ratio (S/N ≤ 30). When using blue wavelengths (UVB arm) one generally underestimates the velocity dispersion (by ~15 km s⁻¹). The values obtained from the near-IR (NIR) arm present a larger scatter because the quality of the spectra is lower. We finally compared our results with those in literature, finding a very good agreement overall.

Conclusions. Joining results obtained in DR1 with those presented here, INSPIRE contains 40 ultra-compact massive galaxies, corresponding to 75% of the whole survey. By plotting these systems in a stellar mass-velocity dispersion diagram, we identify at least four highly reliable relic candidates among the new systems. Their velocity dispersion is larger than that of normal-sized galaxies of similar stellar mass.