- generate draft of research proposal by end of today.
- intro about SFR vs. redshift
- observable proxies for SFR (emission line EW)
- why study this in high mass clusters, previous work.
- Why is SPT sample special?
- highest-mass clusters across wide range of redshifts
- existing spectroscopic data that includes some emission line galaxies
- independent x-ray mass estimates for many of these clusters.
- we can therefore explore the redshift dependence of SFR in the most extreme cluster environments, across 0.2<z<1.
In this project we plan to study the star formation rate (SFR) in high-mass galaxy clusters as a function of redshift.
One of the main problems in modern astrophysics is galaxy formation over cosmic time. The SFR is one of the key observables to understand this evolution. By answering questions such as when star formation was triggered/quenched in cluster galaxies and how it evolved with redshift, we may gain more insight into the process of cluster formation. It has been found consistently that the commoving cosmic SFR increases by more than a factor of 10 over the past 8 Gyr, peaks around z ~ 2 to 3 and then declines roughly linearly to even higher redshifts (e.g. Dickinson et al. 2003)
SFR in galaxy clusters can be measured using a number of proxies, including dust emission (MIR to FIR) and direct emission from stars (emission line equivalent width or UV continuum). In this project we plan to make use of the Hα emission. In star forming galaxies, Hα emission comes from the HII regions ionized by young hot stars. Kennicutt (1998) gives the conversion between Hα emission and SFR. The advantage of using Hα is twofold. Firstly, the ionizing Lyman continuum radiation comes from massive stars with a relatively short life time, so that the Hα reconbination emission serves as a better measure of the instantaneous SFR. Secondly, the Hα emission falls in the red part of the optical spectrum (and will be even more redshifted along its way of travel to us) so is less affected by dust attenuation effects.
The SFR of galaxy clusters depend on both redshift and cluster mass (higher SFR at higher redshift and lower galaxy density; e.g. Finn et al. 2004). However, it is still being investigated how to distinguish between these two factors since higher redshift clusters typicaly have lower masses as they are at an earlier evolutionary stage. Also, the quenching of star formation is expected to be more manifest in dense environmenets. Therefore, it is of great value to focus on SFR in high mass clusters over some redshift range to better characterize SFR evolutionary properties.
The galaxy cluster sample we plan to use is selected from South Pole Telescope (SPT; Carlstrom et al. 2011) observation exploiting the Sunyaev-Zeldovich effect. The sample consists of high-mass clusters across a wide range of redshift (0.2 < z < 1.3), of which most also have spectroscopic data (from Magellan, Dressler et al., 2006 or Gemini, Hook et al., 2004) with emission line measurements. Furthermore, independent mass estimates from hot gas X-ray emission are also available for many of these clusters. Using these data (and perhaps more if follow-up observations are possible), we will be able to explore the redshift dependence of SFR in the highest-mass clusters.
Some references to start back-tracking through the literature in galaxy evolution in the cluster environment:
http://adsabs.harvard.edu/abs/2013arXiv1303.4272D
http://adsabs.harvard.edu/abs/2013arXiv1303.4148A
http://adsabs.harvard.edu/abs/2013arXiv1303.3917G
http://adsabs.harvard.edu/abs/2013arXiv1303.3916O
http://adsabs.harvard.edu/abs/2013arXiv1303.3915O
- Go through and learn the spectroscopy reduction process using raw data files provided by Jonathan
- discuss with Chris about the project. How about Matt's suggestion of "SPIRE image of SPT clusters"?
- write quick summary of key papers, including a clip out of key plots.