Abstracts
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"Galaxy Formation and Evolution through Metals"
Chemical abundances in galaxies provide a fossil record of previous generations of star formation, modulated by galactic-scale gas flows. I will present the latest results from our investigation into the chemical evolution of galaxies, both locally, and at high redshift. Theory predicts that as a merger progresses, galaxy disks become disrupted by tidal effects, causing large radial gas flows toward the central regions where kpc-scale starbursts and AGN may be fueled. Isolated disk galaxies have strong chemical abundance gradients that may become disrupted during a merger. We have conducted the first investigation into chemical abundance gradients across the merger sequence. We show that abundance gradients evolve dramatically with merger progress, providing a smoking gun for galactic-scale gas flows in merging galaxies. Moving out in redshift, I present recent results from our investigation into the cosmic chemical history of galaxies. We have measured the chemical abundances for an unprecedented number of galaxies to z ~ 1, finding little evolution between z ~ 1 and the present day. At higher redshift, we exploit the power of gravitational lensing to investigate the chemical evolution in galaxies between 1 < z < 3. We have measured the first metallicity gradient in a normal spiral galaxy at z ~ 2, showing a steeper gradient than observed in local spiral galaxies. I will discuss the implications of this result and the future of this field with the next generation of telescopes. |
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"Galaxy Mergers through Cosmic Time"
Galaxies grow with time through both discrete galaxy mergers and smooth gas accretion. When and how this growth occurs, and the role of mergers in defining the properties of today's galaxies, remain outstanding observational questions. Observational estimates of the galaxy
merger rate and its evolution can vary by factors of 10, depending upon the method and assumptions used to count mergers. Using physical-motivated timescales from a large suite of galaxy merger simulations, I am able to reconcile the discrepancies between different measurements of the galaxy merger rate at z < 1. The frequency of gas-rich mergers has increased strongly from z ~ 0 to z ~ 1, while the global galaxy merger rate evolved more modestly. Finally, I will discuss the prospects for identifying galaxy mergers at z ~ 2 and beyond with the Cosmic Assembly Near-infrared Extragalactic Legacy Survey. |
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"Observing the Growth of the Most Massive Black Holes at High Redshifts"
There is ample evidence that the most significant growth epoch of the majority of super-massive black holes (SMBHs) must have occurred at z > 1-2. I will present our team's efforts to measure black hole masses and accretion rates in several high-redshift samples of AGNs, based on extensive NIR spectroscopic campaigns. I will particularly focus on a large sample of z ~ 5 AGNs, which were observed in a combined VLT-Gemini campaign. This sample probes the most massive BHs at this epoch, but shows lower masses and higher accretion rates than those of z ~ 2-3.5 sources. When combining these samples together, a clear evolutionary sequence is evident: the z ~ 5 BHs grow through Eddington-limited accretion from a broad range of seed masses; their subsequent growth, at duty cycles of ~10-20%, forms the most massive BHs observed at z ~ 2. I will also mention a few follow-up campaigns which aim at understanding the co-evolution of these BHs with their host galaxies. |
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"Signatures of Supermassive Black Hole Mergers: Before and After"
Supermassive black hole (SMBH) pairs are expected to form in major
galaxy mergers. However, until recently, only a few such objects were
known, and even less is known empirically about their subsequent
evolution to a BH merger and gravitational-wave recoil kick. I will
review the remarkable recent progress in identifying candidate SMBH
pairs, as well as recent identifications of candidate recoiling SMBHs.
I will then describe our efforts to interpret these findings and make
predictions for future observations using hydrodynamic simulations of
galaxy mergers that include SMBHs. Because many candidate SMBH pairs
have been identified as double-peaked narrow-line (NL) AGN, which may
be associated with BH motion on kiloparsec scales, we have made a
first attempt to model the NL region in galaxy merger simulations. In
general, we find that double-peaked NL AGN are a short-lived but
generic phase in gaseous major mergers, and that they arise from a
varied combination of BH motion and gas kinematics. I will discuss the
implications of our findings for follow-up confirmation of SMBH pair
candidates. Additionally, I will summarize the results of our large
study of recoiling SMBHs in galaxy merger simulations. I will describe
the dynamics of recoil in gas-rich versus gas-poor mergers, as well as
the possible effects of recoil on star formation and the BH-bulge
relations. Recoiling SMBHs may be observed as kinematically- or
spatially-offset AGN with lifetimes of up to tens of Myr; I will
conclude by describing efforts to model a candidate recoiling SMBH
that displays both types of offset. |
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"The Ionised Gas of Early-Type Galaxies"
Once considered as simple and rather dull stellar systems, early-type galaxies have
recently received a lot of attention as new data have uncovered a rather more complex
picture for their stellar structure and dynamics, their star-formation history and their
gas content. In my talk I will focus on this last aspect, and show how the SAURON
integral-field data have added to our understanding of the origin, the fate and the
source of ionization of the gas in early-type galaxies. |
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"How Dust Affects Our View of the Distant Universe"
Dust obscuration has a profound influence on our view of
distant galaxies, and can shed light on star formation processes at
high redshift. I will review recent efforts to examine the dust
attenuation and bolometric star formation rates of typical (L*)
star-forming galaxies at redshifts z~2, incorporating UV, H-alpha,
Spitzer, and Herschel observations. I will discuss the trend of dust
obscuration with bolometric luminosity and redshift, and the
implications for the metallicity evolution of galaxies. I will
conclude by showing how these multi-wavelength indicators of star
formation can be used to constrain the star formation histories of
high-redshift galaxies, and will discuss the implications of these
results for the commonly held assumptions in modeling the stellar
population of high-redshift galaxies. |
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"Growing and Observing Galaxies in a Computer"
Galaxy formation simulations are one of the main tools to understand the
physics that drives the formation and evolution of galactic systems.
Especially for high-z systems, observations are very difficult and the
interpretation leaves a lot of freedom and degeneracy. I will present
results on the physical properties of galaxies from the OverWhelmingly
Large Simulations (OWLS) project. In simulations one relies on the
treatment of astrophysical processes below the resolution limit, that also
leaves considerable freedom and limits the predictive power of these
simulations. I will show how combined data from different observational
facilities can help constrain some of these models (and how some remain
arbitrary). Next I will show how to predict observables for instruments
like HST and JWST from hydrodynamical simulations. The mass and spatial
resolution of such simulations are usually not adequate to realistically
predict observable galaxies, even if the simulated galaxy population seems
in agreement with observations. Therefore, comparison between observations
and cosmological simulations are very indirect, and should be taken with a
grain of salt. |
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