Testing the Presence of Multiple Photometric Components in Nearby Early-type Galaxies Using SDSS

Abstract

We investigate two-dimensional image decomposition of nearby, morphologically selected early-type galaxies (ETGs). We are motivated by recent observational evidence of significant size growth of quiescent galaxies and theoretical development advocating a two-phase formation scenario for ETGs. We find that a significant fraction of nearby ETGs show changes in isophotal shape that require multi-component models. The characteristic sizes of the inner and outer component are ∼ 3 and ∼ 15 kpc. The inner component lies on the mass-size relation of ETGs at z ∼ 0.25 − 0.75, while the outer component tends to be more elliptical and hints at a stochastic buildup process. We find real physical differences between the single-and double-component ETGs, with the double-component galaxies being younger and more metal-rich. The fraction of double component ETGs increases with increasing σ and decreases in denser environments. We hypothesize that double-component systems were able to accrete gas and small galaxies until later times, boosting their central densities, building up their outer parts, and lowering their typical central ages. In contrast, the oldest galaxies, perhaps due to residing in richer environments, have no remaining hints of their last accretion episode.

SDSS-IV MaNGA: Uncovering the Angular Momentum Content of Central and Satellite Early-type Galaxies

“…We will also investigate secondary trends with stellar populations and gradients therein (e.g., Greene et al 2015;Goddard et al 2017;Oh et al 2017), the spatial extent of the ionized gas, and the presence or absence of an extended stellar halo.…”

“…Some of these outliers appear round visually, suggesting that they have poorly measured ò values. A related issue is that we utilize an effective ò value, but in general these massive galaxies grow more flattened at larger radius (e.g., Huang et al 2012;Oh et al 2017), which may contribute to the scatter. However, the majority of these galaxies are quite elongated and display low levels of rotation along their major axis, with a high central dispersion (see example maps in Appendix A).…”

“…In the future, it will be interesting to investigate additional galaxy properties, such as luminosity-weighted mean age, which seems to correlate with the outer ellipticity of halos (Oh et al 2017), disky or boxy isophotes (e.g., Bender et al 1989), stellar population gradients (e.g., Greene et al 2015;Goddard et al 2017), or even cD envelope fraction, as Zhao et al (2015b) have argued that the cD envelope is an alternate tracer of merger history.…”

Individual stellar haloes of massive galaxies measured to 100 kpc at 0.3 < z < 0.5 using Hyper Suprime-Cam

“…Two-dimensional analyses have also found that the stellar distributions of massive ETGs are often better fit by multiple-component models (e.g. Huang et al 2013a;Oh et al 2017). Huang et al (2013b) further suggest a connection between the multi-component nature of massive galaxies and their two-phase assembly history.…”

A detection of the environmental dependence of the sizes and stellar haloes of massive central galaxies

“…There have been multiple observational attempts to test the two-phase formation scenario using galaxies at low redshift, by investigating surface brightness or mass density profiles (e.g., Huang et al 2013a,b;Oh et al 2017), optical colour gradients (e.g., La Barbera et al 2010Barbera et al , 2012, and stellar population gradients (e.g., Coccato et al 2010Coccato et al , 2011Greene et al 2015; Barbosa et al 2016). These observations are generally consistent with the two-phase formation scenario.…”