Evolutionary paths among different red galaxy types at 0.3 < z < 1.5 and the late buildup of massive E-S0s through major mergers

Abstract

Some recent observations seem to disagree with hierarchical theories of galaxy formation about the role played by major mergers in the late buildup of massive E-S0's. We re-address this question by analysing the morphology, structural distortion level, and star formation enhancement of a sample of massive galaxies (M * > 5 × 10 10 M ⊙ ) lying on the Red Sequence and its surroundings at 0.3 < z < 1.5. We have used an initial sample of ∼1800 sources with K s < 20.5 mag over an area ∼ 155 arcmin 2 on the Groth Strip, combining data from the Rainbow Extragalactic Database and the GOYA Survey. Red galaxy classes that can be directly associated to intermediate stages of major mergers and to their final products have been defined. We report observational evidence of the existence of a dominant evolutionary path among massive red galaxies at 0.6 < z < 1.5, consisting in the conversion of irregular disks into irregular spheroids, and of these ones into regular spheroids. This result implies: 1) the massive red regular galaxies at low redshifts derive from the irregular ones populating the Red Sequence and its neighbourhood at earlier epochs up to z ∼ 1.5; 2) the progenitors of the bulk of present-day massive red regular galaxies have been disks that seem to have migrated to the Red Sequence mostly through major mergers at 0.6 < z < 1.2 (these mergers thus starting at z ∼ 1.5); and 3) the formation of E-S0's that end up with M * > 10 11 M ⊙ at z = 0 through gas-rich major mergers has frozen since z ∼ 0.6. All these facts support that major mergers have played a dominant role in the definitive buildup of present-day E-S0's with M * > 10 11 M ⊙ at 0.6 < z < 1.2, in good agreement with hierarchical scenarios of galaxy formation.

Evolution induced by dry minor mergers onto fast-rotator S0 galaxies

“…Additionally, recent observations have reported the existence of some S0s that clearly derive from major merger events in which the disc-rebuilding has been successful, so this mechanism cannot be ignored even though the properties of present-day S0s seem too relaxed and smooth to have been formed through a mechanism as violent as a major merger (Peirani et al 2009;Yang et al 2009;Hammer et al 2009aHammer et al ,b, 2010. In fact, many studies find that major mergers may have played a key role in the definitive build-up of the bulk of the massive ETG population (both ellipticals and S0s) in low-to-intermediate density environments at 0.6 < z < 1, in agreement with standard hierarchical models of galaxy formation (see Eliche-Moral et al 2010a,b;Bernardi et al 2011b,a;Prieto et al 2013). This is why it is so relevant to develop methods for quantifying the cumulative effects of mergers in the settlement of the dynamical status of current galaxies (and in particular, of S0s).…”

MASSIV: Mass Assembly Survey with SINFONI in VVDS

“…However, at z 0.8 only one third of the evolution can be accounted by these mergers, f wet (0, 0.8) ∼ 40%. That supports the idea that gas-rich major merging is the main process involved in the assembly of the red sequence at z 1 (e.g., Ilbert et al 2010;López-Sanjuan et al 2010b;Eliche-Moral et al 2010;Prieto et al 2013).…”

Galaxy and Mass Assembly (GAMA): Exploring the WISE Web in G12

“…A second external comparison uses small-area, yet deep, Kband (2.2 μm) galaxy counts from the Minezaki et al (1998) survey of the South Galactic Pole (SGP), and the Prieto et al (2013) near-infrared study of a field in the Groth Strip (GS). The SGP galaxy counts reached a limiting K magnitude of 19.0 in the 181 arcmin 2 field, and similarly, the GS observations reached 19.5 mag (90%) in a 155 arcmin 2 area.…”