Project Title: X-raying the Biggest Black Holes in the Universe
Faculty Sponsor: Rajib Ganguly
Project Description: Quasars are point-like objects that emit ~10^44-10^48 erg/s of energy, and are considered the most luminous sustained phenomena in the universe. They have roughly uniform energy output per decade of wavelength to within factors of ten from the radio to X-rays. The best explanation for the compact morphology and massive energy output is that of an accreting 10^7-10^10 Msun black hole.
The gross similarities in spectral features implies that all quasars have the same basic physical structure. However, the variety in the details brings up the question: What governs that structure and how? The current working paradigm holds that the accreting gas takes the form of a disk. This disk extends from a few times the black hole gravitational radius (Rg=2GM/c^2), out to 10^4-10^5 Rg. For reference, a 10^8 Msun black hole has Rg~1 AU.
A mass outflow is thought to originate from the central regions of the accretion disk. It is important to understand these outflows as they potentially offer a means for the gas in the black-hole accretion disk to shed angular momentum allowing accretion to occur. Outflows may actually regulate the accretion process. These outflows are ionized and can be seen under certain viewing angles in ultraviolet resonant absorption (e.g., CIV, NV, OVI). Generally, this happens in about 60% of quasars over several decades of luminosity, though the form of the absorption does change. The absorption profiles produced by outflows can take a variety of forms: broad absorption lines (BALs) with widths of a few 10^3 to several 10^4 km/s; narrow absorption lines (NALs) with widths of <500 km/s; and mini-BALs with velocity widths between those of BALs and NALs. The distribution of ejection velocities and velocity widths is continuous. The profiles can be smooth or discrete/clumpy and can appear at either high or low velocity with respect to the quasar redshift.
A particular puzzling element of understanding quasar outflow is the role of the X-ray. Observations indicate that the ultraviolet luminosity determines how fast an outflow *could* be driven. However, it it seems that X-rays are also involved in determining, and possibly regulating, how fast they actually go. In this project, we wish to take a very empirical approach to addressing this question. Starting with a sample of 11,000 quasars, of which nearly 40% exhibit outflows, we will explore the X-ray properties of these quasars. How bright are they in the X-ray? How does that compare to ultraviolet emission? Is there evidence for absorption of the X-rays? Is the amount of absorption related to properties of the outflow like maximum speed, or speed dispersion, or minimum speed, or outflow mass? Is the amount of X-ray absorption related to any physical parameters of the object like black hole mass, or accretion rate?
Student Tasks & Responsibilities: The student research will have several tasks in this project: (1) sorting through a list of 11,000 objects and finding archival X-ray data, (2) downloading the appropriate data sets, (3) making measurements of the X-ray flux from the data, (4) converting the X-ray flux into a luminosity, (5) assessing whether X-rays have been absorbed (and at what level), (6) searching for correlations between the X-ray luminosity/absorption with the properties of the outflow, and the physical properties of the objects.
Minimum Student Qualifications: At minimum, the student research must have experience with the UNIX or Linux operating system, and familiarity with the Perl scripting language.
Proposed Starting Date: 02/25/2013
Proposed Ending Date: 04/30/2013