The strange case of the peculiar spiral galaxy NGC 5474

We present the first analysis of the stellar content of the structures and substructures identified in the peculiar star-forming galaxy NGC 5474, based on Hubble Space Telescope resolved photometry from the LEGUS survey. NGC 5474 is a satellite of the giant spiral M 101, and it is known to have a prominent bulge that is significantly off-set from the kinematic centre of the underlying H I and stellar disc. The youngest stars (age ≲ 100 Myr) trace a flocculent spiral pattern extending out to ≳8 kpc from the centre of the galaxy. On the other hand, intermediate-age (age ≳ 500 Myr) and old (age ≳ 2 Gyr) stars dominate the off-centred bulge and a large substructure residing in the south-western part of the disc (SW over-density) and they are not correlated with the spiral arms. The old age of the stars in the SW over-density suggests that this may be another signature of any dynamical interactions that have shaped this anomalous galaxy. We suggest that a fly by with M 101, generally invoked as the origin of the anomalies, may not be sufficient to explain all the observations. A more local and more recent interaction may help to put all the pieces of this galactic puzzle together.

Signal Processing Techniques Intended for Peculiar Star Detection in APOGEE Survey

Like other disciplines, Astronomy faces the era of Big Data, where the analyses and discovery of specific objects is a significant and non-trivial matter. The APOGEE survey and Gaia mission are good examples of how these kind of projects have increased the amount of data to be managed. In this context, we have developed an algorithm to search for specific features in the APOGEE database. The main purpose is to seek spectral lines both in absorption or emission, in the whole APOGEE database, in order to find chemically-peculiar stars. We propose an algorithm which has been validated using cerium lines and we have applied it to the search for other chemical compounds.