Uppskattning av stjärnbildningstakt hos galaxer i det unga universum

University essay from Chalmers tekniska högskola/Institutionen för rymd- och geovetenskap

Abstract: Galaxies in the local universe are almost as old as the universe itself, manyof the stars in these galaxies were formed billions of years ago. To get a morecomplete understanding of the formation and evolution of galaxies, we also needto study younger galaxies in distant regions.This bachelor's thesis uses existing methods in order to study distant galaxiesfrom the time around 3 billion years after the Big Bang, when the star formationrate density is measured to have been at its highest. The aim is to determine thestar formation rate and stellar mass of a sample of star-forming galaxies.We study a selection of galaxies of the type sBzK, which are star-forminggalaxies at z 1:5 2:5. Interstellar dust is present in these star-forming galaxies,and the dust grains are heated by ultra-violet and optical light from youngstars. The dust then re-emits the energy at far-infrared and submillimeter wavelengths.This thermal dust emission can therefore be used to estimate the starformation rate for these galaxies. Data, collected at submillimeter wavelengths,by the interferometric observatory ALMA is analysed and processed to extractthe aforementioned properties of the sBzK galaxies.This sample of galaxies are generally too faint to be individually detectedat millimeter wavelengths. Therefore two types of stacking methods, image anduv-stacking, are used to estimate their average properties. The results from thedifferent stacking methods are compared with each other. Monte Carlo stackingwith both methods is also performed in order to evaluate the results from thestacking processes.With the stacked ALMA data we were able to detect the sBzK sample. Theobtained results using uv-stacking was a SFR of 212:3M=yr, when assuming= 1:6, T = 30K and a Chabrier initial mass function. Using image stackingwe derive a similar star formation rate of 18 2:4M=yr. Based on simpleassumptions we obtain an estimate for the stellar mass of 4;6 1010M. It isalso found that the image stacked result gives a lower ux than the uv-stackedresult, leading to higher star formation rates for the uv-stacked sources. This starformation rate can be compared to our current knowledge of our own galaxy.

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