Post-starburst galaxies and AGN quenching
Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
Some galaxies experience a very high rate of star formation during a short period compared to their lifetime. These galaxies are known as Starburst galaxies. After some time, this high rate of star formation abruptly stops after which the galaxies enter the Post-starburst phase. This quick shutting down of star formation is known as the quenching scenario. Although a number of mechanisms have been proposed to explain this quenching, the process is not very well understood.
Accumulation of infalling matter towards a central supermassive black hole can ignite an intense radiation field in the centre. Such a region is called an Active Galactic Nucleus (AGN). There are strong indications that AGNs which have sufficient power can blow out the gas and heat the environment so that the gas can not be accumulated to form stars. In this project, I have tested the hypothesis of starburst quenching by AGN activity.
Method: In order to investigate evolutionary properties of a galaxy, one can use available galaxy spectral evolutionary libraries, based on theoretical models. Such a library contains artificial spectra which may be compared to the observed spectrum. From the best fit we can obtain information about e.g. age and mass of the starburst. I used STARLIGHT software package and a home written Uppsala code to find these best fits to each individual spectrum.
- I found that the duration of the burst for almost all the galaxies is less than 700 Myr (Million year). For most of the post-starburst sample the duration is 100-500 Myr.
- In addition, I could see that AGN activity appears with a time delay of few hundred Myr after the starburst phase.
- The main aim of the project was to answer the question: Is AGN activity quenching the star formation in starburst galaxies? I could conclude that AGN activity may be one of the factors blowing gas out of the galaxy, but that it can not be the only effective factor to quench the star formation in starburst galaxies.
There are strong indications that high redshifts quasars have sufficient power to blow out the gas, heat the environment and cause star formation quenching. In this project we have tested the hypothesis of starburst quenching by AGN activity. During this project I focused on an analysis of spectra of massive and luminous galaxies with post-starburst signatures, some of them containing indications of AGN activity. The spectra were downloaded directly from the Sloan Digital Sky Survey data DR7 data. In order to investigate evolutionary properties of galaxy, I used the STARLIGHT software package and a home written Uppsala code to find the best fit to each individual spectrum. I found that the duration of the burst for almost all the galaxies is less than 700 Myr, and for most of the post-starburst sample it takes 100-500 Myr. In addition, I could see that AGN activity appears with a time delay of few hundred Myr after the starburst phase. According to the evidence I found during this project AGN activity may be one of the factors causing star formation quenching but that it can not be the only effective factor.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:uu:diva-195508OAI: oai:DiVA.org:uu-195508DiVA: diva2:607840
Master Programme in Physics
2013-01-09, 14:00 (English)
UppsokPhysics, Chemistry, Mathematics