Publicação
Who is who? FADO and galaxy classification
| Resumo: | From the spectra of galaxies, we are able to extract many physical properties: star-formation rate, stellar mass and metallicity, for example. To calculate them, we must first classify galaxies according to their main mechanism of emission: star-formation (SF) or Active Galactive Nuclei (AGNs). The BPT diagrams, named after their creators, are a classification method that does exactly this, through emission line flux ratios. To extract the emission line flux of these galaxies, one uses models such as stellar population synthesis. Most of these models do not add the nebular contribution, only considering the stellar component. FADO was developed to tackle this issue in SED modelling. The purpose of this work is to compare the analysis of the Sloan Digital Sky Survey Data Release 7 galaxies (with a median z ≈ 0.116) of MPA-JHU and FADO, to understand if the nebular contribution affects galaxy classification through the standardised BPT diagrams. We have found that the self-consistent addition of nebular emission does not significantly affect galaxy classification through emission line ratio diagrams. The same is true of the galaxies in the Main Sequence, where the galaxies in FADO and MPA-JHU fall in the same regions of the parameter space. Furthermore, we found that the BPT diagram may possess a bias towards low stellar and sub-solar metallicity galaxies, as they are more likely to be misclassified by other emission line ratio diagrams. Finally, we have also found that comparing the equivalent width of Balmer lines (Hα or Hβ) with the ratio of the equivalent widths of [OIII]λ5007 and Hβ gives us a new classification diagram that separates galaxy in two types: SF and AGN. This simple classification could be used in future large spectroscopic surveys, such as MOONRISE, where at high redshifts some important emission lines for the BPT diagram are unable to be detected. |
|---|---|
| Autores principais: | Santos, Duarte Muñoz |
| Assunto: | códigos de síntese espetral classificação de galáxias evolução de galáxias AGNs Teses de mestrado - 2023 |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | From the spectra of galaxies, we are able to extract many physical properties: star-formation rate, stellar mass and metallicity, for example. To calculate them, we must first classify galaxies according to their main mechanism of emission: star-formation (SF) or Active Galactive Nuclei (AGNs). The BPT diagrams, named after their creators, are a classification method that does exactly this, through emission line flux ratios. To extract the emission line flux of these galaxies, one uses models such as stellar population synthesis. Most of these models do not add the nebular contribution, only considering the stellar component. FADO was developed to tackle this issue in SED modelling. The purpose of this work is to compare the analysis of the Sloan Digital Sky Survey Data Release 7 galaxies (with a median z ≈ 0.116) of MPA-JHU and FADO, to understand if the nebular contribution affects galaxy classification through the standardised BPT diagrams. We have found that the self-consistent addition of nebular emission does not significantly affect galaxy classification through emission line ratio diagrams. The same is true of the galaxies in the Main Sequence, where the galaxies in FADO and MPA-JHU fall in the same regions of the parameter space. Furthermore, we found that the BPT diagram may possess a bias towards low stellar and sub-solar metallicity galaxies, as they are more likely to be misclassified by other emission line ratio diagrams. Finally, we have also found that comparing the equivalent width of Balmer lines (Hα or Hβ) with the ratio of the equivalent widths of [OIII]λ5007 and Hβ gives us a new classification diagram that separates galaxy in two types: SF and AGN. This simple classification could be used in future large spectroscopic surveys, such as MOONRISE, where at high redshifts some important emission lines for the BPT diagram are unable to be detected. |
|---|