Assembly of void galaxies: Star formation and molecular gas

• Autores: Jesús Domínguez Gómez
• Directores de la Tesis: Ute Lisenfeld (dir. tes.) , Isabel Pérez Martín (dir. tes.)
• Lectura: En la Universidad de Granada ( España ) en 2023
• Idioma: español
• ISBN: 9788411954945
• Número de páginas: 197
• Tribunal Calificador de la Tesis: Jorge Iglesias Páramo (presid.) , Almudena Zurita Muñoz (secret.) , Francesca Pinna (voc.)
• Enlaces
  • Tesis en acceso abierto en: DIGIBUG
• Resumen

  • Galaxies in the Universe are distributed in a web-like structure characterised by different large-scale environments: dense clusters, elongated filaments, sheet-like walls, and under-dense regions, called voids. The low number density of galaxies in voids is expected to affect the properties of their galaxies. Void galaxies are essential to understand the physical processes that drive galaxy evolution as they are less affected by external factors than galaxies in denser environments. Previous studies have shown that galaxies in voids are on average bluer, less massive, and have later morphologies than galaxies in denser environments. However, there is no consensus about the star formation properties of void galaxies, and it has never been observationally proven that their star formation histories are significantly different from those in filaments, walls, and clusters. The Calar Alto Void Integral-field Treasury surveY (CAVITY) project was started to fill this gap by studying in detail a sample of around 300 void galaxies with integral field spectroscopy.

    In this thesis, as a preparatory study of the CAVITY project, we analyse stellar populations in the centre of void galaxies to derive the star formation history, which describes the rate at which the galaxies have assembled their stars; and the average stellar metallicity, which traces the accumulated fossil record of star formation through out the entire life of the galaxies. In addition, we also analyse the star formation rate, molecular gas mass, and star formation efficiency of void galaxies as tracers of their current and potential star formation. Comparing the star formation rate, molecular gas, star formation efficiency, star formation history, and stellar metallicity of galaxies in various environments, including voids, filaments, walls, and clusters, can provide valuable insights into how the large-scale environment impacts galaxy evolution.

    We present the first molecular gas mass survey of void galaxies, together with data for the atomic gas mass and star formation rate (SFR) from the literature. We compare with galaxies in filaments and walls in order to better understand how the molecular gas mass and SFR are related to the large-scale environment. We observed with the IRAM 30 m telescope the CO(1-0) and CO(2-1) emission of 20 void galaxies selected from the Void Galaxy Survey, with a stellar mass range from 10^(8.5) to 10^(10.3) solar masses. We detected 15 objects in at least one CO line. We compared the molecular gas mass, the star formation efficiency (SFE), the atomic gas mass, the molecular-to-atomic gas mass ratio, and the specific star formation rate (sSFR) of the void galaxies with two control samples of galaxies in filaments and walls, selected from xCOLD GASS and EDGE-CALIFA, for different stellar mass bins.

    In general, we do not find any significant difference in the molecular and SFR between void galaxies and galaxies in filaments and walls, but some tentative differences emerge for some other parameters when trends with stellar mass are studied. The SFE of void galaxies seems lower than in filament and wall galaxies for low stellar masses. In addition, it appears that there is a trend of increasing deficiency in the atomic gas content in void galaxies compared to galaxies in filaments and walls for higher stellar masses, accompanied by an increase in the molecular-to-atomic gas mass ratio. However, all trends with stellar mass are based on a low number of galaxies and need to be confirmed for a larger sample of galaxies. This study can be considered the starting point and trigger of the CO-CAVITY subproject within CAVITY, aimed at providing comprehensive information of the molecular gas content of the CAVITY galaxies.

    We also present the first stellar population comparison between galaxies in different large-scale environments for a stellar mass range from 10^(8.0) to 10^(11.5) solar masses and a redshift range of 0.01[menor que]z[menor que]0.05. We aim to better understand how the large-scale structure affects galaxy evolution by studying the star formation history and the stellar mass-metallicity relation of thousands of galaxies, which allows us to make a statistically sound comparison between galaxies in voids, filaments, walls, and clusters. We apply non-parametric full spectral fitting techniques (pPXF and STECKMAP) to 10807 spectra from the SDSS-DR7 (987 in voids, 6463 in filaments and walls, and 3357 in clusters) to obtain their stellar populations (stellar mass, age, and metallicity) and derive their SFH and mass-weighted average stellar metallicity.

    We find that void galaxies have had, on average, slower star formation histories than galaxies in denser large-scale environments. We find two main star formation history types, which are present in all the environments: `short-timescale' galaxies are not affected by their large-scale environment at early times but only later in their lives; `long-timescale' galaxies have been continuously affected by their environment and stellar mass. Both types have evolved slower in voids than in filaments, walls, and clusters. We also find that galaxies in voids have on average slightly lower stellar metallicities than galaxies in filaments and walls, and much lower than galaxies in clusters. These differences are more significant for low-mass than for high-mass galaxies, for `long-timescale' than for `short-timescale', for spiral than for elliptical, and for blue than for red galaxies.

    In this thesis, it is confirmed that the large-scale environment affects galaxy evolution slowing down the star formation history and reducing the stellar metallicity of void galaxies compared to galaxies in filaments, walls, and clusters. In addition, it seems that there are no significant differences with respect to the molecular gas, star formation rate, and star formation efficiency between galaxies in different large-scale environments. However, these last results need to be confirmed for a larger sample of void galaxies.