Galaxy And Mass Assembly (GAMA): Structural Investigation of Galaxies via Model Analysis

Abstract

We present single‐Sérsic two‐dimensional (2D) model fits to 167 600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey imaging data available from the Galaxy And Mass Assembly (GAMA) data base. In order to facilitate this study we developed Structural Investigation of Galaxies via Model Analysis (sigma), an r wrapper around several contemporary astronomy software packages including source extractor, psf extractor and galfit 3. sigma produces realistic 2D model fits to galaxies, employing automatic adaptive background subtraction and empirical point spread function measurements on the fly for each galaxy in GAMA. Using these results, we define a common coverage area across the three GAMA regions containing 138 269 galaxies. We provide Sérsic magnitudes truncated at 10re which show good agreement with SDSS Petrosian and GAMA photometry for low Sérsic index systems (n < 4), and much improved photometry for high Sérsic index systems (n > 4), recovering as much as Δm= 0.5 mag in the r band. We employ a K‐band Sérsic index/u−r colour relation to delineate the massive (n > ∼2) early‐type galaxies (ETGs) from the late‐type galaxies (LTGs). The mean Sérsic index of these ETGs shows a smooth variation with wavelength, increasing by 30 per cent from g through K. LTGs exhibit a more extreme change in Sérsic index, increasing by 52 per cent across the same range. In addition, ETGs and LTGs exhibit a 38 and 25 per cent decrease, respectively, in half‐light radius from g through K. These trends are shown to arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxy populations.

Galaxy And Mass Assembly (GAMA): $\mathcal {M_\star }\text{--}R_{\rm e}$ relations ofz= 0 bulges, discs and spheroids

“…This is most obvious in the Sérsic index -colour plane where the single component Sd and elliptical galaxies occupy distinct peaks with composite galaxies (S0abc) scattered between and around these peaks (see e.g., Driver et al 2006;Cameron et al 2009;Kelvin et al 2012;Lange et al 2015). These components have very different characteristics with spheroids typically having a featureless appearance and being pressure supported.…”

“…A number of studies now show that the Sérsic index of discs and spheroids (be they pure or component) vary smoothly with mass and luminosity or due to dust or galaxy type (see e.g. Graham & Guzman 2003;Gadotti 2009;Kelvin et al 2012;Graham 2013;Pastrav et al 2013a,b). Hence studies where the Sérsic index of the bulge or disc components are fixed may be overly restrictive.…”

The SAMI Galaxy Survey: spatially resolving the environmental quenching of star formation in GAMA galaxies

“…To take into account the effect of this projection onto the sky, the radial profiles of Hα were constructed by averaging the dust corrected fluxes over a series of concentric elliptical annuli. These annuli were centred on the centroid of the continuum flux of each galaxy, with their ellipticities and position angles based on the GAMA photometric model fits to reanalysed SDSS DR7 r-band images (Kelvin et al 2012). Some examples of radial profiles, dust-corrected Hα maps and EW(Hα) maps are shown for galaxies with a range of stellar masses and star-forming morphologies in Figure 7.…”

The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation

“…For the simulation we use the age and metallicity of the stellar particles to produce mock rest-frame r-band luminosity, and do not consider the effects of dust on the apparent size of galaxies. For the measurements, there exist systematic differences depending on the exact band that is used, and we apply empirically-derived corrections to convert them uniformly to the rest-frame r-band (Kelvin et al 2012;Szomoru et al 2013;van der Wel et al 2014), as described below. (iv) In terms of the stellar mass assigned to each galaxy, we use the bound mass assigned by SUBFIND, while observationally it is determined using the aforementioned profile fits to the light profiles and a conversion to stellar mass using model massto-light (M/L) ratios.…”

“…Such systematics include definitions of galaxy masses and sizes (Dutton et al 2011), background subtraction (He et al 2013), light fitting procedures (Stott et al 2011;Mosleh et al 2013;Bernardi et al 2014), wavelength dependence (Kelvin et al 2012;Bond et al 2014;van der Wel et al 2014), selection effects (Law et al 2012;Mosleh et al 2013), and possibly cosmic variance. In this work we make an attempt to minimize systematics when comparing our simulation results to observations, but we stop short of full forward modeling of the simulation to match the parameters of particular observational studies.…”