Thesis proposal

Christopher Bradshaw
Phys 472 Thesis Proposal

The overall goal will be to compare the rate of stellar mass increase in galaxies vs their current mass at various redshifts for three data sets. One of these data sets is obtained using the star formation histories (SFH) for local group dwarfs, while the other two are from observations of the stellar mass function (SMF) at various redshifts (z). Comparing these data will allow us to determine whether the star formation history of local group dwarfs is typical.

The first of the data sets used is the FourStar Galaxy evolution survey (ZFOURGE). This is the deepest measurement of the SMF currently available, with data between \(0.2 < z < 3\). The galaxies in this data set are fairly large, with stellar masses of between \(8 < log(M/M_{\odot}) < 11\).25 at recent times, and \(9.5 < log(M/M_{\odot}) < 11.5\) at \(z = 2.5\). The second data set used is the SFH of 40 local group dwarf galaxies. This data was composed by analyzing the color-magnitude diagram (similar to the HR diagram) of these galaxies. This data set covers a similar period of time as the ZFOURGE data (\(0 < z < 2.6\)) but a very different mass range (\(5 < log(M/M_{\odot}) < 8\)). Finally, data from 3D-HST and CANDELS will be used as an additional constraint on the mass growth histories of galaxies.

The ZFOURGE data will not be used directly. Instead, we will use a parameterized Schechter function that models the data. This requires very little processing or error analysis. Similarly, the 3D-HST and CANDELS data can also be parameterized. On the other hand, the Local Group SFH data has significant sources of error that need to be analyzed. We will also need to normalize some aspects of these data sets (whether they take into account mergers, various constants used).

Work Plan
We first need to justify our extrapolation of the ZFOURGE data to the mass range of the local group dwarfs. Having done that, much of the rest of the work will be in quantifying the error on the local group data, and correcting for various disparities between the data sets. We will correct for effect of galactic mergers in the ZFOURGE SMF data, as the local group galaxies have not experienced mergers. We will also correct the average growth rates obtained from the local group SFH to reflect the morphology distribution of the sample. Finally, we will need a comprehensive understanding of the local group SFH error bars, which are substantial and have correlated x-y errors. A substantial amount of these errors may come from choices of constants, which can be normalized between data sets and then the errors can be ignored.

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