Galaxies Science Collaboration Projects
Members of the LSST Galaxies Science Collaboration research a wide range of topics related to galaxy formation and evolution. Here, we present a few scientific projects LSSTGSC members will conduct with the LSST data. Some of these projects were originally presented in the LSST Science Book, where more of our projects are described.
One of the major recent advances in astronomy has been the discovery of ubiquitous tidal streams of disrupted dwarf galaxies surrounding the Milky Way and other nearby galaxies. The existence of such streams fits well into the hierarchical picture of galaxy formation, and has caused a re-assessment of traditional views about the formation and evolution of the halo, bulge, and disk of our Galaxy.
Galaxies must grow with time through both discrete galaxy mergers and smooth gas accretion. When and how this growth occurs remains an outstanding observational question. The smooth accretion of gas and dark matter onto distant galaxies is extremely challenging to observe, and complex baryonic physics makes it difficult to infer a galaxy’s past assembly history. In contrast, counting galaxy mergers is relatively straightforward.
It is useful for many purposes to divide galaxies into different classes based on morphological or physical characteristics. The boundaries between these classes are often fuzzy, and part of the challenge of interpreting data is ensuring that the classes are defined sensibly so that selection effects do not produce artificial evolutionary trends. Increasingly realistic simulations can help to define the selection criteria to avoid such problems. Here we briefly discuss the detectability of several classes of galaxies of interest for LSST.
Deep, narrow surveys with space-borne telescopes have identified new populations of high-redshift galaxies at redshifts z > 5 through photometric dropout techniques. While these observational efforts have revolutionized our view of the high-redshift Universe, the small fields of such surveys severely limit their constraining power for understanding the bright end of the high-redshift galaxy luminosity function and for identifying other rare objects, including the most massive, oldest, and dustiest galaxies at each epoch.
The excellent image quality that LSST will deliver will allow us to obtain morphological information for all the extended objects with sufficient signal-to-noise ratio, using parametric model fitting and non-parametric estimation of various morphology indices. The parametric models, when the PSF is properly accounted for, will produce measurements of the galaxy axial ratio, position angle and size. Possible models are a general Sersic model and more classical bulge and disk decomposition.