Euclid Quick Data Release (Q1): XXXIX. The evolution of the passive-density and morphology-density relations between z = 0.25 and z = 1

Abstract

The extent to which the environment affects galaxy evolution has been under scrutiny by researchers for decades. With the first data from Euclid, we can begin to systematically study a wide range of environments and their effects as a function of redshift, using 63 deg2 of space-based data. In this paper, we present results from the Euclid Quick Data Release, where we measured the passive-density and morphology-density relations in the redshift range z = 0.25–1. We determined if a galaxy is passive using the specific star formation rate, and we classified the morphologies of galaxies using the Sérsic index n and the u − r colours. We measured the local environmental density of each galaxy using the Nth-nearest neighbour method. We find that at a fixed stellar mass, the quenched fraction (the fraction of galaxies that have ceased star formation) increases with increasing local environmental density up to z = 1. This result is indicative of the separability of the effects from the stellar mass and the environment. Similarly, at all redshifts in this work, the early-type galaxy fraction increases with increasing density at fixed stellar mass, meaning the environment also transforms the morphology of the galaxy independently of stellar mass, up to M* ≲ 1010.8 M⊙. For M* ≳ 1010.8 M⊙, almost all galaxies are early-types, with minimal impact from the environment. At z > 0.75, the morphology depends mostly on stellar mass, with only low-mass galaxies being affected by the environment. Given that the morphology classifications use u − r colours, these are correlated to the star formation rate, and as such our morphology results should be taken with caution, yet future morphology classifications should help verify these results. To summarise, we successfully identify the passive-density and morphology-density relations at 0.25 < z < 1. Future Euclid data releases are key to confirm these trends at higher redshifts.