1em CHRISTOPHER BRADSHAW THESIS PROGRESS REPORT INTRODUCTION The goal of this thesis is to compare the stellar mass growth rate vs mass at various redshift of local group dwarf galaxies with distant galaxies. This work was started in the fall, but was registered with the astronomy department. As this is the first term registered in the Physics department, this progress report will cover work done since the fall. DATA The early part of the project was spent familiarizing myself with the data that would be used, and the techniques used to gather that data. The data used for distant galaxies was presented by Tomczak et al . This paper contains a table of mass vs number density (number of galaxies per unit volume) for 0.2 < z < 3 which we use to construct the stellar mass function (SMF) which shows the frequency of galaxies at different masses and redshifts. However, while we plotted this data and various subsets of it (only star forming or quiescent galaxies) we do not use the raw data. Instead, we use a fitting function - a paramaterised double Schechter function - from Leja et al which smooths the data and ensures the number density at each mass is monotonically increasing as z → 0. With this done, graphs showing the mass over 0.2 < z < 3 for various start masses were constructed. The local group dwarf galaxy data was taken from Weiza et al . This paper determines the mass of a subset of the known dwarf galaxies between 0 < z < 2.6. It does this by constructing a color magnitude diagram and determining, using know properties of stars, when star formation occurred. This is the star formation history (SFH). As with the distant galaxies, graphs showing the percentage of mass over time for various groups of the galaxies (grouped by galaxy shape or location) were plotted to better understand the data. A second distant galaxy data set was introduced later in the project. This data, taken from Whitaker et al was used to confirm that the comparison between the two main data sets were reasonable and conformed to other data. Again, a parameterization rather than raw data was used. ANALYSIS A number of corrections must be applied to these data sets before they can be compared. The first correction is for mergers. The local group data is based on galaxies that have not undergone mergers, while some of the distant galaxies will have. This has the effect of reducing the total number of galaxies in the sample over time, reducing the overall number density. We make the merger correction to the SMF using the method shown in Gomez et al . Supporting material such as plots of expected merger rates at various mass ratios and redshifts were also constructed to ensure that we were applying this correction correctly. We also apply a correction for mass loss to both the local group and data. As these both determine mass by integrating the star formation rate over time, the data shows the total stellar mass formed by a certain time, rather than the total stellar mass present at that time. Much of this mass loss is caused by the death of high mass, short lifespan (<100Myr) stars and so can be approximated as instantaneous using a multiplicative factor. The Tomczak et al data is the instantaneous mass and not calculated from the SFH and so this correction is not applied. Finally, a environmental correction was applied to the local group data. We expect that galaxies in different places in the Local Group (satellites of the Milky Way, satellites of M31 (Andromeda) and galaxies attached to neither of the main galaxies) would have different growth rates. However, the Weisz et al data contains only a subset of approximately half of all known local group galaxies and does not sample evenly from these three environments (for observational reasons). To correct for this, we weight galaxies to ensure that at each mass and redshift the different environments are correctly weighted. A significant analysis was also performed on the errors on the local group data reported by Weisz et al . These errors were calculated using methods defined in Dolphin; (systematic) and (random) but are considered extremely conservative. A method to determine a more reasonable set of uncertainties was not found and so we adopt the literature convention established by Weisz et al and simply apply a 50% fractional uncertainty to all masses. This method is also considered conservative but significantly improves on the original. COMPARISON Having made the corrections discussed above, we compare the data sets. We find that the Tomczak et al data broadly agrees with the Whitaker et al data, but that both show higher growth rates than the local group data. If this continues to hold as the final corrections are applied and the work is checked, this is an interesting result as it would should galaxy strangulation; a process by which stellar mass growth rates are slowed in the presence of large gravitational fields. CONCLUSION While we have preliminarily done most of the corrections needed to compare these data sets, there is still work to do. In particular, the merger correction is not perfectly understood and may be the source of some of the discrepancy between the two distant galaxy data sets. Tests to show that the code used for analysis is performing correctly also need to be written. Finally, this work also needs to be written up and presented.
CHRISTOPHER BRADSHAW PHYS 472 THESIS PROPOSAL SUMMARY 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. DATA 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⊙)<11.25 at recent times, and 9.5 < log(M/M⊙)<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⊙)<8). Finally, data from 3D-HST and CANDELS will be used as an additional constraint on the mass growth histories of galaxies. ANALYSIS 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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INTRODUCTION Young protostars are observed to launch energetic collimated bipolar mass outflows . These protostellar outflows play a fundamental role in the star formation process on a variety of scales. On sub-pc scales they entrain and unbind core gas, thus setting the efficiency at which dense gas turns into stars . Interaction between outflows and infalling material may regulate protostellar accretion and, ultimately, terminate it . On sub-pc up to cloud scales, outflows inject substantial energy into their surroundings, potentially providing a means of sustaining cloud turbulence over multiple dynamical times. The origin of outflows is attributed to the presence of magnetic fields, and a variety of different models have been proposed to explain the launching mechanism \citep[e.g.,][]{arce07}. Of these, the “disk-wind" model , in which the gas is centrifugally accelerated from the accretion disk surface, and the “X-wind" model , in which gas is accelerated along tightly wound field lines, are most commonly invoked to explain observed outflow signatures. However, investigating the launching mechanism is challenging because launching occurs on scales of a few stellar radii and during times when the protostar is heavily extincted by its natal gas. Consequently, separating outflow gas from accreting core gas, discriminating between models, and determining fundamental outflow properties are nontrivial. Three main approaches have been applied to studying outflows. First, single-dish molecular line observations have been successful in mapping the extent of outflows and their kinematics on core to cloud scales \citep[][]{bourke97,arce10,dunham14}. However, outflow gas with velocities comparable to the cloud turbulent velocity can only be extracted with additional assumptions and modeling \citep[e.g.,][]{arce01b,dunham14}, which are difficult to apply to confused, clustered star forming environments . Second, interferometry provide a means of mapping outflows down to 1,000 AU scales scales , and the Atacama Large Millimeter/submilllimeter Antenna (ALMA) is extending these limits down to sub-AU scales . However, interferometry is not suitable for producing large high-resolution maps and it resolves out larger scale structure. Consequently, it is difficult to assemble a complete and multi-scale picture of outflow properties with these observations. Finally, numerical simulations provide a complementary approach that supplies three-dimensional predictions for launching, entrainment and energy injection . The most promising avenue for understanding outflows lies at the intersection of numerical modeling and observations. By performing synthetic observations to model molecular and atomic lines, continuum, and observational effects, simulations can be mapped into the observational domain where they can be compared directly to observations \citep[e.g.,][]{Offner11,Offner12b,Mairs13}. Such direct comparisons are important for assessing the “reality" of the simulations, to interpret observational data and to assess observational uncertainties . In addition to observational instrument limitations, chemistry and radiative transfer introduce additional uncertainties that are difficult to quantify without realistic models . Synthetic observations have previously been performed in the context of understanding outflow opening angles , observed morphology , and impact on spectral energy distributions . The immanent completion of ALMA provides further motivation for predictive synthetic observations. Although ALMA will have unprecedented sensitivity and resolution compared to existing instruments, by nature interferometry resolves out large-scale structure and different configurations will be sensitive to different scales. Atmospheric noise and total observing time may also effect the fidelity of the data. Previous synthetic observations performed by suggest that the superior resolution of full ALMA and the Atacama Compact Array (ACA) will be able to resolve core structure and fragmentation prior to binary formation. predicts that ALMA will be able to resolve complex outflow velocity structure and helical structure in molecular emission. In this paper we seek to quantify the accuracy of different ALMA configurations in recovering fundamental gas properties such as mass, line-of-sight momentum, and energy. We use the casa software package to synthetically observe protostellar outflows in the radiation-hydrodynamic simulations of . By modeling the emission at different times, inclinations, molecular lines, and observing configurations we evaluate how well physical quantities can be measured in the star formation process. In section §[Methods] we describe our methods for modeling and observing outflows. In section §[results] we evaluate the effects of different observational parameters on bulk quantities. We discuss results and summarize conclusions in §[Conclusions].