Black hole astrophysics: from the dawn of the universe to today

How the massive black holes in the centers of most galaxies first formed, grew, and interacted with their host galaxies are among the key outstanding questions in astrophysics. I will outline how the latest ground and space telescopes get us closer to the first black hole seeds and discuss a new framework for how the galaxy-black hole system as a whole operates. Building on the last decade of discovery in galaxy evolution, we are now able to ask the right questions that will ultimately lead us to the physics of how growing black holes -- quasars -- regulate and shut down the star formation in galaxies. I will outline how current and near-future facilities such as Keck, ALMA and JWST will answer these questions. I will also consider how citizen scientists, members of the public, can contribute to discovery and understanding, and how we are on the cusp of merging the collective intelligence of humans with that of machines.

Connections Between Galaxies and the Gaseous Cosmic Web

Most galaxies grow predominantly through the accretion of gas from the intergalactic medium (IGM). In addition, they transform their environment, emitting ionizing radiation and expelling metal-enriched gas. These fundamental processes are thought to be crucial ingredients in determining the metallicity and ionization state of the IGM, the morphology of galaxies, their mass-metallicity relation, the shape of the luminosity function, the abundance of satellite galaxies etc. However, because of their diffuse nature and the lack of internal energy sources these in- and outflows have remained poorly constrained observationally.

I will report on deep, spectroscopic efforts to detect diffuse gas flows in emission at redshift ~3 that we have performed over the past several years. We are exploiting the fact that galaxies that feed and produce feedback tend to light up their immediate environment temporarily. Detectable quantities of HI Lyman alpha, two-photon continuum and metal resonance line emission allow us to take snapshots of the distribution and properties of the gas surrounding them. Our observations have uncovered a large diversity of interactions between galaxies and the IGM, some of which are seen for the first time, including stripping of satellite galaxies in individual galaxy halos; an observation of the elusive escape of ionizing radiation from a galaxy; filamentary accretion of gas onto a galaxy; and MgII emission from metal-enriched outflows.

First Measurement of the Small Scale Structure of the Intergalactic Medium

There is no such thing as empty space. Indeed, the most barren regions of the universe are the vast expanses between the galaxies, known as the intergalactic medium (IGM). Averaging just one lonely atom per cubic meter, this primordial gas left over from the Big Bang encodes fundamental information about our universe's history. About half a million years after the Big Bang, the plasma of primordial baryons recombined to form the first neutral atoms, releasing the cosmic microwave background and initiating the cosmic 'dark ages'. During this period primordial gas expanded and cooled to very low temperatures T ~ 20 K, until the stars and black holes in the first galaxies emitted enough ionizing photons to reionize and reheat the universe. The thermal state of gas in the IGM is a relic of these reionization phase transitions, which can be measured via optical observations of bright distant quasars at cosmological lookback times of a few gigayears. On Mpc length scales, gas in the intergalactic medium traces density fluctuations in the underlying and gravitationally dominant dark matter, but on smaller scales of hundreds of kpc, fluctuations are suppressed because the ~10⁴ Kelvin gas is pressure supported against gravity, analogous to the classical Jeans argument. This Jeans pressure smoothing scale thus quantifies the small scale structure of the IGM and provides a record of cosmic reionization and thermal evolution. Recently we have shown that it is possible to directly measure this pressure smoothing scale by characterizing the coherence of correlated intergalactic absorption lines in the spectra of pairs of quasars, at small angular separation on the sky. I will describe a statistical method which quantifies correlated absorption in quasar spectra, which is highly sensitive to the pressure smoothing scale, and present its first-ever measurement with data collected from the Keck telescopes. Our preliminary results suggest that the filtering scale is smaller than expected from the standard models of reionization and the thermal evolution of the IGM.

The Progenitors of the Milky Way Stellar Halo

The cannibalistic nature of the Milky Way galaxy leads to the continuous capture and destruction of lower mass dwarf galaxies. The remains of destroyed dwarfs are splayed out in a diffuse stellar halo, while the "survivors" comprise the satellite population that orbits the Milky Way. These halo populations provide a unique opportunity to decipher the accretion history of the Milky Way with a level of detail that cannot be achieved in any other galaxy. I will discuss current and future projects that aim to decipher the nature of the halo's building blocks. At present, we have very little understanding of what these building blocks actually are; is the halo built up from many smaller mass dwarfs, or from one massive dwarf? An ongoing project utilizing multi-epoch HST photometry and Keck spectroscopy will help disentangle these two scenarios using distant halo stars viewed in "7-dimensions". I will also describe several future Galactic surveys that will allow us to finally pin down the assembly history of the Milky Way halo.

A 3D view of the Dark Universe: illuminating intergalactic gas at high redshift with fluorescent Lyman-alpha emission

Gravitational collapse during the Universe's first billion years transformed a nearly homogeneous matter distribution into a network of filaments - the Cosmic Web - where galaxies form and evolve. Because most of this material is too diffuse to form stars, its study has been limited so far to absorption probes against background sources. In this talk, I will present the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external "source of illuminations¹¹. In particular, I will show results from ultra-deep narrow-band imaging and recent integral-field-spectroscopy as a part of the MUSE Guaranteed Time of Observation program that revealed numerous ³dark galaxies² and giant Lyman-alpha emitting filaments around quasars. Finally, I will discuss how the unexpectedly high luminosities of the giant Lyman-alpha filaments, together with the constraints from Helium and metal extended emission, present a serious challenge for our current understanding of the Intergalactic and Circumgalactic media based on hydrodynamical cosmological simulations.

Extrasolar Planetary Magnetic Fields

Planetary-scale magnetic fields are a window to a planet's interior and provide shielding of the planet's atmosphere, and may be essential for life on the surface. The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal dynamo currents that generate planetary-scale magnetic fields. These internal dynamo currents arise from differential rotation, convection, compositional dynamics, or a combination of these in a planet's interior. Extrapolated to extrasolar planets, knowledge of a planet's magnetic field places constraints on the thermal state, composition, and dynamics of its interior-all of which will be difficult, if not impossible, to determine by other means-as well as potentially crucial information about the extent to which the surface of a terrestrial planet is shielded from cosmic rays and potentially habitable.

In this talk, I shall review efforts to detect and measure extrasolar planetary magnetic fields. There are potentially numerous observational signatures of planetary magnetic fields, though the most promising appears to be the radio emission generated by an interaction between the planet's magnetosphere and the host star's stellar wind. I summarize recent efforts to detect extrasolar planetary magnetic fields, with an emphasis on on-going efforts at radio wavelengths.

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. I acknowledge ideas and advice from the participants in the "Planetary Magnetic Fields: Planetary Interiors and Habitability" workshop organized by the W. M. Keck Institute for Space Studies.

Discovering and Characterizing Exoplanets with High-Contrast Spectroscopy

Advances in adaptive optics and infrared instrumentation now enable us to see young exoplanets millions of times fainter than their host stars. By collecting photons emitted by these worlds, imaging allows us to measure the chemistry and physical states of their atmospheres. Now, a new generation of experiments is combining upgraded adaptive optics with integral-field spectrographs (IFSs) to discover and characterize fainter worlds closer to their host stars. I will present the results of recent high-contrast surveys and the scientific promise of this new generation of instruments, with a particular focus on the CHARIS IFS for the Subaru telescope. CHARIS will be the only instrument of its class in the northern hemisphere and will have the broadest spectral coverage of any high-contrast IFS; it will provide unique sensitivity to close-in exoplanets and present new data analysis challenges. CHARIS is now being built and will begin operations this summer. It will commence its first two year, 20 night survey in early 2017, taking spectra of giant exoplanets and searching about 100 stars for new companions.

Finding the first metals in near-pristine environments

The birth of the first stars arguably marks one of the most important physical and chemical transformations of the Universe; these stars kick started reionization and synthesised the first metals. However, despite their importance, we still know very little about them. Although no primordial star has yet been identified, we can begin to understand their properties by studying the relative abundances of the chemical elements they created during their lives. In this talk, I will present the results from a suite of model calculations that follow the chemical enrichment of the first stars. These minihalo models predict the chemical signature that is borne into the second generation of stars, and provide a new perspective on the formation of carbon-enhanced metal-poor stars. I will also present the latest results from my survey to discover the most metal-poor damped Lyman-alpha galaxies (1/1000 of solar metallicity) at redshift z~3. Such near-pristine environments allow us to understand the early phases of dwarf galaxy evolution, probe the chemical signatures of the first stars, and study the primordial abundances of the light elements. I show that some of these systems may have been enriched solely by the first generation of stars.