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STELLAR MASS GROWTH OF SPIRAL GALAXIES IN THE COSMIC WEB


Image: An illustration of the cosmic web. Credit: NASA/NCSA University of Illinois Visualization by Frank Summers, Space Telescope Science Institute, Simulation by Martin White and Lars Hernquist, Harvard University

The distribution of galaxies in the Universe forms a vast network of interconnected filamentary structures, sheets, and clusters which are separated by immense voids. This vast foam-like structure sometimes is called the "cosmic web".
The filamentary arrangement of galaxies is a direct consequence of perturbations in the initial density field of matter shortly after the Big Bang evolving under the influence of gravity over cosmic time.

A recent paper (Alpaslan et al. 2016, MNRAS) investigates the correlated changes in stellar mass and star formation rate along filaments in the cosmic web by examining the stellar masses and UV-derived star formation rates (SFR) of 1,799 spiral galaxies that reside in filaments.


Image: Galaxies, composed of gas, stars and dark matter, collide and form filaments in the large-scale universe Credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratoy at the National Center for Supercomputing Applications

The authors find that galaxies closer to the cylindrical centre of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. In addition, these peripheral spiral galaxies have higher specific star formation rates (SSFR) at a given mass.

As expected, stellar mass of a spiral galaxy plays a dominant role in determining its star formation rate, but the authors find also that the distributions of the star formation rates vary with large-scale environment. For this reason, in addition to stellar mass as the primary discriminant, the large-scale environment is imprinted in the SFR as a second order effect.

Finally, their results suggest a model in which gas accretion from voids onto filaments is primarily in an orthogonal direction.



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