Week 5

Week 5 is our final lab session of the project, and as such was primarily focussed around finishing any remaining tasks or little odd-jobs that had yet to be done, as well as collating the data from the three sub-projects so the relationships between the different data could be investigated.

Once the data from all three sub-projects had been merged into one large catalogue, it became trivial to examine the trends and relationships between the properties of the objects, simply by plotting the data against each other and analysing the spread of the data points. We were particularly interested in the relationship between the black hole accretion rate from the AGN sub-project and properties from the other sub-projects, as how active a galaxy’s central black hole is can have a big effect on the development and structure of the galaxy, and it is intriguing to discover which properties are either affected by a high accretion rate, or in fact cause it. The property we were most keen to analyse is the stellar mass of the galaxy, as this is often one of the most important characteristics of a galaxy, and is usually an important factor in the structure and development of said galaxy. Figure 1 shows the relation between the log of the galaxies’ masses and accretion rates.

Figure 1: Log-log plot of the black hole accretion vs the stellar mass of the objects.

Unfortunately, it is rather difficult to determine any meaningful trend from this graph, and as such this area of the project may require additional investigation. The other key relationship that needs further analysis is the mass of the galaxies at each redshift, as this is perhaps the most important property of an object and determines much of its other characteristics.

The result of the week comes from the Star Formation Rate sub-project, and is essentially a culmination of their entire project, as it illustrates the relationship between the average SFR and stellar masses of the galaxies at each redshift bin ranging from z=2 to 6 (see Figure 2).

Figure 2: Log-log plots of the average star formation rate against the average stellar mass of all the galaxies at each redshift.

Figure 2 also includes data from other papers for comparison, and the last plot (bottom right) shows a side-by-side comparison of all the different redshift bins. From this last plot it is possible to deduce that the star formation rate increases both with increased mass and higher redshift, as there is generally a positive correlation between log SFR and log mass, and the SFR data from higher redshifts tends to be greater than that at lower redshifts even at roughly equal masses.

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