A more local and more recent interaction may help to put all the pieces of this galactic puzzle together. 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. 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. 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 youngest stars (age ≲ 100 Myr) trace a flocculent spiral pattern extending out to ≳8 kpc from the centre of the galaxy. 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. 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. Pontecorvo 3, 56127 Pisa, ItalyĮuropean Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, ItalyĮ-mail: di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti93/2, 40129 Bologna, Italyĭipartimento di Fisica, Università of Pisa, Largo B. Astronomical objects: linking to databases.Including author names using non-Roman alphabets.Suggested resources for more tips on language editing in the sciences Punctuation and style concerns regarding equations, figures, tables, and footnotes Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. Illustration of the Milky Way's spirals by NASA/JPL-Caltech/ESO/R. Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. They have not been around for very long in terms of the life time of the universe.Īdditional images via Wikimedia Commons. Astronomers use these facts to determine that spirals are typically young galaxies. The gas and dust are used to make new stars, and these baby stars glow very brightly. You can see the dust in the dark spots of the spiral arms. Spiral galaxies are made up of young stars, gas, and dust. When this happens with galaxies, astronomers say the galaxy is ‘edge-on’ when we can see it from the side and ‘face-on’ when you can see it from the top. If you look from the side, you can’t tell if there’s a hole in the center or what kind of sprinkles are on top. Think of looking at a donut if you look from above you can see all the sprinkles and the hole in the center. Sometimes, though, you can’t see the center or the arms of the galaxy very well. Galaxies with bar-like centers are known as barred-spirals. The center of the galaxy can either look like a bright sphere or a long glowing bar. Some spiral galaxies are described by what the center looks like. Typically these galaxies have two arms, but there have been some observed to have four, five, or even six arms. There are very obvious swirls of stars and dust coming off of the center. So what makes a spiral galaxy? These galaxies are mostly known for the fact that they look like a spiral. Our home galaxy, the Milky Way, is classified as a spiral galaxy.
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