- PI name and contact information
Massimo Stiavelli (admin PI; mstiavel@stsci.edu)
Takahiro Morishita (science PI; tmorishita@stsci.edu) - Project duration
- 1yr rotation with potential for thesis project
- Thesis project
for one student.
- Project abstract
The formation of supermassive black holes (SMBHs) has been a long-standing subject of astronomy. Hundreds of QSOs have been discovered up to z~7 from ground-based large surveys. Many of them are known to have black hole masses of almost 10^9 Msun already. The formation mechanism of such high-z SMBHs, however, is still under active debate, and observational constrains at higher redshift are required. One of key approaches is to study the shape of luminosity functions (LFs) as a function of cosmic time - the redshift evolution of the shape can be attributed to different modes of the QSO activity.
In this project, we aim to constrain for the first time the QSO LF at z~8 and beyond, by using data taken in the HST legacy survey (CANDELS) and on-going pure-parallel survey (BoRG). In a previous work with a similar data set of HST, we found a few QSO candidates and followup observations from the ground-based facilities are on-going. By applying a similar selection technique to these data sets, we expect to constrain the number density of QSOs down to <10^-5Mpc^-3 at Muv~-24 to -18mag, a dramatic improvement from current models. The inferred number density will reveal the contribution to cosmic reionization by low-luminosity QSOs. Identified candidates will be ideal follow-up targets with ground-based spectrographs and future JWST to directly investigate cosmic reionization, the origin of SMBHs, and the host properties of the highest redshift QSOs.
Figure1: Luminosity function of QSOs at z~8. While galaxy LFs have been studied intensively so far to this redshift, ones for QSOs have not, due to their rare nature at high redshift. Because of this, the current constraint on theoretical models is very poor, spanning by >3 orders of magnitude (red/gray hatched regions). The number density/upper limit derived in this project (blue hatched region and red points) will be an immediate constraint on those theoretical models. Furthermore, studying individual QSOs found in this project will provide a unique opportunity to understand the formation of the first blackholes and reionization of the universe. - The work you imagine having the graduate student do
The project is related to our recently approved HST observing programs (GO 15702 and AR 15804). The main tasks are two-fold:
1. To find QSO candidates at high-redshift by means of color selection/photometric redshift analysis and spectral energy distribution (SED) analysis, and
2. to estimate the number density of QSOs at z~8.
The CANDELS data and catalogs are already published, and there is no need of initial reduction. For BoRG data, the student will use our custom-developed pipeline python code and learn how to reduce HST/WFC3IR and UVIS imaging data. Computing resources provided at STScI (including laptops) are available.
- Will they be leading the paper after creating the result?
Yes. We expect the student to lead the work, write journal papers, and present at domestic/international conferences, with support by the PI and CoIs at the institute (see below). The admin PI can mentor the student for a thesis project too.
- Is there any opportunity to observe?
Yes. There are possibilities for the student to join/lead observations at 8-10m telescopes (Gemini/Keck/Subaru/Magellan) to followups identified QSO candidates.
- Potential internal/external collaboration?
The project involves collaboration with CoIs at STScI/JHU/UCLA/CfA/U of Melbourne, and possibly more upon the progress of the project.
The CoIs of the original HST programs are;
- Harry Ferguson (Space Telescope Science Institute)
- Colin Norman (The Johns Hopkins University)
- Tommaso Treu (University of California)
- Charlotte Mason (Smithsonian Institution Astrophysical Observatory)
- Michele Trenti (University of Melbourne)
