The origin of large emission line widths in massive galaxies at redshifts z ∼ 3 − 4

M Martínez-Marín, K Glazebrook, T Nanayakkara, C Jacobs, I Labbé, G G Kacprzak, C Papovich, C Schreiber

The first work from my PhD candidature was the analysis of a sample of 22 massive galaxies ( log(M)> 10), in between redshifts 3<z<4 from the ZFOURGE catalogue that shows broad emission lines. In this redshift regime, the universe was about 1.5 Gyr old.

The emission lines in galaxies can be associated with either star formation or the supermassive black hole (SMBH) of the galaxy being active. Both scenarios can be differentiated from each other by different observational tests. One is the luminosity, as galaxies with an AGN component show a higher luminosity than star-forming ones. The line ratios of the [OIII]5007 and Hbeta emission lines are also higher for AGNs than star-forming galaxies, according to their stellar mass, as shown in the Juenau+14 Mass excitation diagram (MEx). Also, SED fitting codes like CIGALE can estimate the AGN component of a galaxy by applying AGN modelling to the galaxy photometry.

We measure the luminosity, emission from the [OIII]5007 and Hbeta lines, the luminosity and the fraction of AGN from CIGALE. All these tests showed that the entire sample has an AGN.

Many massive galaxies have been found recently, in this early period of the universe, that have already stopped their star formation. Scientists are using simulations to find an explanation for these, considering the role of active galactic nuclei (AGN) in the galaxies' star formation history. Also, if we put this sample in context to the rest of the massive galaxies at similar redshifts, calculating the fraction of galaxies with an AGN related to those without. In that case, we see a high fraction of galaxies with AGNs. These results can help understand the SFH of massive galaxies in this redshift regime.

You can find the entire article here in the MNRAS: https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/stae1335/7686135?utm_source=advanceaccess&utm_campaign=mnras&utm_medium=email