Published Articles (chronological order)

November 2019

1. Lucatelli, G. and Ferrari, F. Galaxy structural analysis with the curvature of the brightness profile. Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 1, October 2019, Pages 1161–1180, doi:10.1093/mnras/stz2154.

Other Works

Master Thesis

In this work we introduce the curvature of a galaxy brightness profile to non-parametrically identify its structural subcomponents. Bulges, bars, disks, lens, rings, spiral arms and so on, are a key to understanding the formation and evolutionary paths the galaxy undertook. Their identification is also crucial for the morphological classification of galaxies. We measure and analyse in detail the curvature of $16$ galaxies with varied morphology. High (low) steepness profiles show high (low) absolute curvature measures. Transitions between components present high values of the curvature. With this new tool we identify patterns that characterise bulges (pseudo or classic), disks, bars, rings, spiral arms. The procedure can be automated in a future study to deal with large datasets and identify galaxy components automatically, or to provide a reliable starting point for traditional multi components modelling of galaxy light distribution. For a complementary study, which leaded us to introduce the curvature, we investigate the behaviour of single-Sérsic fits (e.g. single Sérsic index $n$) is and concentration index $C$ for multicomponent galaxies. We have obtained that these galaxies have systematically high values of $n$ and $C$ comparable to the ones measured in single component galaxies, thus resulting in misclassification of them.

The objective of this work is to do a photometric and morphometric analysis of simulated images of galaxies, composed by a bulge and a disk. The morphological classification of galaxies has as main objective the understanding of how these physical systems had formed and how they evolve. The way to do this, morphometry, has been widely applied in observational data, therefore, it is not an easy task to obtain information about the intrinsic parameters. In this sense it is useful apply such measurements in objects in which these quantities are known. Thus it was created mock images of galaxies with the use of the Sersic Law, combining in many ways the bulge and disk components wherein the quantities $R_b$, $I_b$, $n_b$, $R_d$, $I_d$ and the luminosity ratio $\xi_{BD} = L_B/L_T$ are changed. After the data set was created, composed by 480 mock images, an analysis was applied with the use of Morfometryka algorithm, with the aim to investigate the behavior of the morphometric indices concentration $C_1$ and $C_2$, belonging to the CASGM system ( concentration $C$, asymmetry $A$, smoothness $S$, Gini $G$ and momentum of light $M$), and the effective Sersic quantities $R_{nef}$ , $I_{nef}$, $n_{ef}$, since they are the parameters obtained from the image. The results found show that the effective Sersic index $n_{ef}$ can range a large interval and in some cases do not represent physically the “real” galaxy structure. Also, the value of nef in the transition region between the disk Sersic index and the bulge Sérsic Index can be higher for the last. Besides that, the ´ concentration index was greatly affected by the bulge+disc composition. Furthermore, it was identified that both nef and $C_1$ and $C_2$ are degenerate quantities, that is different structures can result in the same values for these quantities.