Physically Motivated Fit to Mass Surface Density Profiles Observed in Galaxies

Sánchez Almeida, Jorge; Trujillo, Ignacio; Plastino, Angel R.
Bibliographical reference

The Astrophysical Journal

Advertised on:
Number of authors
IAC number of authors
Refereed citations
Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ~750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ( $7\lt {\rm{log}}[{M}_{\star }/{{\rm{M}}}_{\odot }]\lt 12$ ). The propol fits are systematically better than Sérsic profiles when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\lesssim 9$ and systematically worse when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\gtrsim 10$ . Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies.
Related projects
Project Image
Starbursts in Galaxies GEFE
Starsbursts play a key role in the cosmic evolution of galaxies, and thus in the star formation (SF) history of the universe, the production of metals, and the feedback coupling galaxies with the cosmic web. Extreme SF conditions prevail early on during the formation of the first stars and galaxies, therefore, the starburst phenomenon constitutes a
Muñoz Tuñón
Group members
Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology
We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.
Martín Navarro