GAMA - Galaxy And Mass Assembly

In Hamburg I worked Prof. Joe Liske on the GAMA survey. Our aim is to examine the importance of environment on galaxy evolution by looking in which environments galaxy pairs and mergers are most commonly found. If a preferred location is found, this would point to a location where galaxies are pre-processed by mergers, before they are accreted to more dense environments following the hierarchical structure formation of the Universe.

Illustration of a small galaxy group in the GAMA survey. Image credit: GAMA survey.

The Spitzer Survey of Stellar Structure in Galaxies (S⁴G)

My PhD. studies revolved around the Spitzer Survey of Stellar Structure in Galaxies project, in which 2300 nearby (< 40 Mpc) galaxies of all morphological types were observed in 3.6 and 4.5 micron wavelengths using the Spitzer Space Telescope. Full description of the survey can be found in Sheth et al. 2011. This survey has expanded significantly since the first data release in 2015 (@ NASA/IPAC archive), and more massive early-type as well as low mass galaxies of all types are being added to the sample using Spitzer Space Telescope and various ground-based optical telescopes. I am member of the core data team of this survey, and below I introduce some of the key areas of the survey I was part of.

Disk breaks in S⁴G

The surface brightness in galaxies disks is generally assumed to follow a simple exponential decline. However, it has been found that this does not apply for most disk galaxies, and instead multiple exponential sections are found in the disks (see examples below). These changes between exponential sections are called disk breaks, and they are thought to be formed by multitude of internal processes of galaxies, as well as galaxies environmentally driven processe.

In two of my papers (Laine et al. 2014 and Laine et al. 2016) I examined these disk breaks using S⁴G data with samples of hundreds of galaxies. The main results of these two studies were the connection of disk breaks with the morphological structures of the galaxies. For example, we found a connection between ring structures and down-bending Type II breaks: the rings are formed due to bar resonances in the disks by accumulating gas at the resonance radius, and the resulting star formation eventually manifests as a change in the disk surface brightness profile.

Examples of disk breaks in two S⁴G galaxies. Image from Laine et al. 2016.

Multicomponent photometric structural decompositions

My major contribution to the data analysis pipelines of the S⁴G survey was in the two dimensional multicomponent photometric structural decomposition pipeline. In this work we made human supervised decompositions of all the 2300 galaxies of the first phase of the survey, which decompositions include, when judged appropriate, a central point source, bulge, disk, and bar components. This work is explained in detail in Salo et al. 2015, and the decomposition sample remains to be the largest galaxy sample for which such detailled decompositions have been made. Decompositions of the extended S⁴G survey sample, as well as detailed analysis of the galaxy bulge, disk, and bar parameters are underway.

Examples of a bulge-disk-bar decomposition. Image from Salo et al. 2015.

Publications