Structural analysis of massive galaxies using HST deep imaging at z < 0.5

Abstract

Context. The most massive (M stellar ≥ 10 11 M ) galaxies in the local Universe are characterized by having a bulge-dominated morphology and old stellar populations, in addition to be confined to a tight mass-size relation. Identifying their main components can provide insights into their formation mechanisms and subsequent mass assembly. Aims. Taking advantage of Hubble Space Telescope (HST) CANDELS data, we analyze the lowest redshift (z < 0.5) massive galaxies in the H and I-band in order to disentangle their structural constituents and study possible faint non-axis-symmetric features. Methods. Our final sample consists of 17 massive galaxies. Due to the excellent HST spatial resolution for intermediate redshift objects, they are hard to model by purely automatic parametric fitting algorithms. We performed careful single and double (bulge-disk decompositions) Sérsic fits to their galaxy surface brightness profiles. We also compare the model color profiles with the observed ones and also derive multi-component global effective radii attempting to obtain a better interpretation of the mass-size relation. Additionally, we test the robustness of our measured structural parameters via simulations. Results. We find that the Sérsic index does not offer a good proxy for the visual morphological type for our sample of massive galaxies. Our derived multi-component effective radii give a better description of the size of our sample galaxies than those inferred from single Sérsic models with GALFIT. Our galaxy population lays on the scatter of the local mass-size relation, indicating that these massive galaxies do not experience a significant growth in size since z ∼ 0.5. Interestingly the few outliers are late-type galaxies, indicating that spheroids must reach the local mass-size relation earlier. For most of our sample galaxies, both single and multi-component Sérsic models with GALFIT show substantial systematic deviations from the observed surface brightness profiles in the outskirts. These residuals may be partly due to several factors, namely a non-optimal data reduction for low surface brightness features, the existence of prominent stellar haloes for massive galaxies and could also arise from conceptual shortcomings of parametric 2D image decomposition tools. They consequently propagate into galaxy color profiles. This is a significant obstacle to the exploration of the structural evolution of galaxies that calls for a critical assessment and refinement of existing surface photometry techniques.

Machine learning technique for morphological classification of galaxies from SDSS. II. The image-based morphological catalogs of galaxies at 0.02<z<0.1

“…The early-type galaxies predominate in the central part of the cluster. They also have larger masses, less gas, higher velocity dispersion, and diverse stellar population than the late-type galaxies (see, for example, these works [5,7,17,25,32,33,52,71,76,77,79,89,91,100,106]).…”

Euclid preparation

“…As a reminder, the Sérsic function is a simplified model that does not capture the entire galaxy, but gives important information about how the intensity varies with radius. Compared to other morphological parameters retrieved from single-Sérsic model fitting, the Sérsic index is regarded as the most challenging parameter to recover (Buitrago et al 2013;dos Reis et al 2020). Because the dependence of light profiles on the Sérsic index is exponential, we always analyse log 10 (n) instead of n in the following (see e.g.…”

The Emergence of Bulges and Disks in the Universe

“…In case of a single component galaxy (pure disk or elliptical), or for low-resolution data where resolving bulge component is impossible, galaxies are fitted with a single Sérsic profile (e.g., Blanton et al 2003;Driver et al 2006;van der Wel et al 2008;Hoyos et al 2011;van der Wel et al 2012;Carollo et al 2013;van der Wel et al 2014;Straatman et al 2015;Tarsitano et al 2018). Well-resolved disk and lenticular galaxies are often fitted with a combination of two Sérsic profiles, or as an exponential disk plus a free-n Sérsic bulge (e.g., Andredakis et al 1995;Khosroshahi et al 2000;Graham 2001;Prieto et al 2001;Simard et al 2011;Kelvin et al 2012;Mendel et al 2014;Meert et al 2015;Lange et al 2016;Kennedy et al 2016;Dimauro et al 2018;Cook et al 2019;dos Reis et al 2020).…”

“…Galaxies can experience significant morphological and structural transformation over cosmic time, from clumpy high redshift star-forming disks to smooth red spheroidal systems at the present day (e.g., Trujillo et al 2007;van Dokkum et al 2010;Huertas-Company et al 2015;dos Reis et al 2020;Hashemizadeh et al 2021). However, there are still many open questions as to how galaxies build-up their stellar mass, how it is distributed to form the various structural components, and how these substructures evolve, resulting in the plethora of morphological types observed in the local Universe.…”

“…Galaxies, however, are often more complex requiring extra components such as bulge, bar, etc., to be robustly fit. For example, a two-component model consisting of a spheroidal bulge (de Vaucouleurs 1948) and an extended near exponential disk (Freeman 1970) have been used to great success in describing the light profile of galaxies (e.g., Allen et al 2006;Simard et al 2011;Mendel et al 2014;Salo et al 2015;Lange et al 2016;Dimauro et al 2018;Cook et al 2019;dos Reis et al 2020). Going further, several studies have developed kinematic structural decomposition methods using advanced IFU spectroscopy (e.g., Emsellem et al 2007;Taranu et al 2017).…”