Radio AGN in Galaxy Clusters: Feedback, Merger Signatures, and Cluster Tracers
The number of spectroscopically confirmed galaxy clusters with z>1.0 is very low compared to the number of well-studied low-redshift clusters. Using bent, double-lobed radio sources as signposts we can efficiently locate high-redshift clusters. Using our Spitzer Snapshot Survey, we have identified approximately 300 new clusters with redshift z>0.7. Here I present the initial results from this survey regarding the efficiency of the method for finding new clusters. These newly identified clusters can then be used to study galaxy formation and evolution, as well as the effect that feedback from active galactic nuclei (AGN) has on galaxies and their environments. I have already explored the effects of feedback on two low-redshift clusters using deep Chandra observations. One of these clusters (A2029) is a relaxed, cool-core cluster that is home to a sloshing spiral. The other (A98) is undergoing a merger.
Powerful jets from intermediate-mass protostars
We present new spectroscopy and Hubble Space Telescope imaging of protostellar jets discovered in an Ha survey f the Carina Nebula. Near-IR [Fe II] emission from these jets traces dense gas that is self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in Ha emission from these jets. In some cases, [Fe II] emission traces the jet inside its natal dust pillar, connecting the larger Ha outflow to the embedded IR source that drives it. New proper motion measurements reveal tangential velocities similar to those typically measured in lower-luminosity sources (100-200 km/s). Combining high jet densities and fast outflow speeds leads to mass-loss rate estimates an order of magnitude higher than those derived from the Ha emission measure alone. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (~2-8 M?) protostars. For some sources, mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars others remain deeply embedded and require long-wavelength, high-resolution images confirm their luminosity. These outflows are all highly collimated, with opening angles of only a few degrees. With this new view of collimated jets from intermediate-mass protostars, we argue that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core and the material it sweeps up is irradiated and rendered observable. Thus, the jets in Carina offer strong additional evidence that stars up to ~8 M? form by the same accretion mechanisms as low-mass stars.
Rachel Paterno-Mahler, Megan Reiter