Chandra X-ray Data

Chandra X-ray image of the core of the cooling-flow cluster Abell 2052.

The Chandra X-ray Observatory, launched in late 1999, has been instrumental in advancing our understanding of cooling flows. Chandra's high spacial resolution (~ 0.5 acrsec) has given researchers an unprecedented view of the cores of clusters. Its images immediately revealed cavities in the ICM of numerous cooling flows. When the positions of the cavities were compared with those of the radio lobes of the central AGN, it was clear that the AGN was responsible for pushing out the cavities. Chandra X-ray data provide all the information necessary to derive estimates of the power required to create the cavities: the images allow us to measure the sizes of the cavities and the spectra allow us to derive the temperature, density, and pressure of the surrounding ICM. Together, these data give us the work required to create the cavity (W = pV, where p is the pressure and V the cavity volume) and the time, t, required for it to rise to its present position (e.g., the buoyancy time). The power is then simply P = E / t.

     As part of my thesis research, I have reduced and analyzed Chandra data for 33 systems with cavities and calculated their AGN powers. When these powers are plotted against the cooling luminosity of the cluster (see Figure 6, Rafferty et al. 2006), an interesting trend emerges: systems with larger cooling luminosities also have larger AGN powers. Such a trend is expected in simple feedback models.

     The cavity powers also give us a means of estimating the mass accretion rates onto the central suppermassive black holes. Assuming that the AGN is powered by accretion, the energy released for a given accreted mass m is E = e m c^2, where e is the efficiency of conversion of rest mass to outburst energy. Knowing E from the cavities, we can solve for m. A plot of these accretion rates versus the star formation rates of the cDs' bulges (Figure 2 of Rafferty et al. 2006) reveals that most of the systems are growing their black holes and bulges at rates consistent with the slope of the Magorrian relation: M_BH = 0.0014 M_bulge (Haring & Rix 2004).

Properties of Cooling Flows

Chandra X-ray data also allows us to derive a number of properties of the ICM. These include central temperatures, densities, abundances, pressures, entropies, and cooling times. These properties are useful clues in our investigation of feedback. For example, if active star formation is fueled by the cooling flow, one would expect some relation between the presence and strength of star formation and the central cooling time: if cooling times are long, there should be little active star formation.

    I am currently constructing a catalog of the X-ray properties of a sample of clusters with a wide range of central cooling times to investigate possible links between the cooling ICM and the central galaxy.