My Scientific Interests
Main collaborators: Mark Lacy, Eilat Glikman
My main scientific interest is the search and analysis of dust-reddened quasars. My PhD thesis focused on the discovery of the nature of these objects - back then we didn’t know if these were simply objects party obscured by a torus or part of an evolutionary scenario. While there are certainly quasars that are obscured by material close to the black hole (the so-called torus), we found that lightly obscured or dust-reddened quasars are obscured by much colder, material located in the host galaxy.
Using Hubble ACS imaging of luminous examples of these red quasars we then found much higher rates of disturbance and merger signatures in the host galaxies of these red quasars. This indicates that luminous quasars are ignited through major merger events and the red quasar phenomenon most likely has an evolutionary explanation in that we are seeing quasars that have just been born before the quasar clears out its light path and the gas and dust from the merging galaxies has settled.
With Spitzer observations it was now possible to disentangle the quasar contribution from the host star formation in order to gauge the bolometric luminosity of these systems. The quasar with the highest disturbance and largest obscuration by cold dust also appeared to be forming stars at extreme efficiencies, sometimes even above the Eddington limit. Furthermore, when we compare the high accretion rate quasar’s black hole mass to their bulge and host luminosity they lie well below the know mass-luminosity relation established for quasars. This means that stellar growth preceded black hole growth.
In the future I would like to expand my search of red quasars further. The original sample was based from the 2MASS catalog, which is quite shallow. Using UKIDSS or WISE it will be possible to find less luminous or more distant red quasars. This will not only tell us about the cosmic evolution of these objects, but also if the luminosity function of these objects is different, that is, if they are preferably found in high luminosity systems. Furthermore, we intend to do IFU Spectroscopy on these objects. Full 3D spectroscopy can tell us about feedback effects the quasar might have on the host.
Dust reddened quasars as probes of young quasars
Pic descriptions
LEFT Mask wheel of the MUSE instrument (taken November 2011)
DOWN 1 HST image of a red quasar showing merger signatures and an extremely disturbed morphology (from my 2008 paper)
DOWn 2 Simulations of galaxy mergers and the formation of elliptical galaxies (from the Springel, DiMatteo, Hernquist simulations)
DOWN 3 Mass-luminosity relation of red quasars. The objects accreting at the highest rates all lie below the local M-L relation, suggesting that star formation precedes black hole growth
DOWN 4 Spectrum of an Iron Low Ionization Broad Absorption line quasar at z~2.5. Note the extremely deep absorption troughs, several thousands of km./s wide.
DOWN 5 Cerro Paranal - site of the Very Large Telescope operated by the European Southern Observatory, where the MUSE spectrograph will be housed.
DOWN 6 A 3D view of the MUSE instrument on its VLT Nasmyth platform
Quasar Winds and their effect on the host galaxy
The MUSE Spectrograph
Main collaborator: Duncan Farrah
In the search for red quasars, an anomalously large fraction of those were broad absorption line quasars (BALQSOs), with most belonging to the extreme rare type of Iron Low Ionization BALQSOs (FeLoBALs). The absorption troughs in these quasars are evidence of winds escaping from the central engine at quite high velocities (1.000-10.000 km/s).
It has been posited that these BALQSO winds, especially the ones that show lower ionization lines, are responsible for quasar feedback - shutting off the rest of star formation in the host galaxy by expelling or heating the cold gas needed to form gas. This quasar feedback is needed to explain the mass function in galaxies in the local Universe and would also provide a logical explanation for the relations in mass, luminosity and velocity dispersion we see between the black hole and its host galaxies.
Using Spitzer data to disentangle the contributions from the AGN and from Star Formation and comparing those to the width and depth of the outflowing wind, we found an anti-correlation between the strength of the outflow and the amount of star-formation. It seems that the wind really has an effect on the host galaxy!
In the future we would like to study these FeLoBALs more, specifically with ALMA to gauge the molecular content of these quasar hosts and with Hubble to see if this anti-correlation also holds spatially.
On behalf of the entire MUSE consortium
The MUSE instrument is a giant 3D spectrograph with a 1’x1’ field of view commissioned by ESO to be put on the VLT. It consists of 24 IFUs, each slicing its field of view into 48 elements. The final datacube will have 300x300 spatial spaxels and will cover approximately the wavelength range from 4650-9300 Angstrom with a 2.4 Angstrom resolution. It is envisioned to be installed at Paranal in the summer/fall of 2013 and will begin operations a few months later. In the future AO capability will be implemented.
MUSE is, for the most part, a survey instrument. The main scientific drivers for MUSE are searches for Lyman alpha and other extragalactic emitters, the study of the intergalactic medium and characterization of stellar population in nearby galaxies and globular clusters.
My principal duties for MUSE concern the data reduction. While the final datacubes will “only” be about 3GB large, the merging and calibration of the different IFUs is a challenging process computationally. One night of typical observations (one hour per exposure) requires on the order of 10 hours for reduction at our multicore server here in the institute with one of the main issues being memory usage (>250 GB RAM).
The final user will not reduce the data his/herself. Nonetheless, the training and the spreading of the expertise on the reduction pipeline will be my main task in years to come, before gaining access to the wonderful data this instrument will produce.
