Astrobites@Long Beach: Monday Afternoon Sessions

Astrobites is again liveblogging AAS! In order to avoid inundating our readers’ RSS feeds, we’ll be updating this post with short paragraphs about the talks we’ve heard and posters we’ve seen. So keep checking back throughout Monday morning!

-The Astrobites Team

Monday Morning Posts

The eXtreme Deep Field. Credit: Credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team

12:45 pm Press Release: The Hubble Ultra Deep Field Gets Deeper

Richard Ellis (Caltech) began the session with a nice overview of the early Universe, discussing the cosmic dark ages through the cosmic dawn – where UV photons from the earliest stars had the energy to ionize hydrogen. The Hubble Space Telescope penetrates this time period, and asks three important questions concerning reionization: 1) when exactly was this time period? 2) was this a gradual or relatively quick process? 3) are we sure it was light that caused this process? While, the Hubble Ultra Deep Field, an image I’m sure most of us can recollect in our minds, has existed for some time now, this new image is unique because it is deeper (i.e. can reach a higher magnitude of approximately 30), uses more filters (which allow us to note the color and therefore redshift of the galaxy), and has better precision.

Alexander Rogers (University of Edinburgh) concluded that the most distant galaxies we can observe and analyze show mature stellar populations.  These distant galaxies have high metal contents and have therefore evolved quickly. Matthew Schenker (Caltech) then went on to discuss the number of bright and faint galaxies (the galaxy luminosity function) at high redshifts.  Given our current observations, we find that the number of ionizing photons cannot account for the reionization of the Universe.  But fear not! If we take the number of bright galaxies, and extrapolate to fainter galaxies, estimating how many faint galaxies existed in the early Universe (which we cannot observe due to the limiting magnitude of HST), we can see that these faint galaxies may account for reionization.  Brant Robertson (University of Arizona), the theorist on board, helped to draw conclusions from the data.  To reiterate: faint galaxies can reionize the Universe! It is likely to have occurred throughout a gradual time period, from a redshift of 15 (or even 20) to 6.  Lastly, the James Webb Space Telescope (JWST) will help shed light on the first light in the Universe.

2:00 PM: Scientific Opportunities with the James Webb Space Telescope
In this session, six invited speakers provided an overview of the scientific capabilities of Hubble’s predecessor: the The James Webb Space Telescope (JWST). JWST will be an all purpose observatory, with science goals ranging from galaxy assembly to observations of nearby planetary systems. The telescope, which has unprecedented sensitivity and infrared wavelength coverage, is scheduled to launch in 2018. In the words of Margaret Meixner, “NOW is the time to develop appropriate target lists”. A quick summary of each of the six talks is below.

  • Mark Dickinson (NOAO) – JWST and deep field studies of galaxy evolution at high redshift. This talk focused on the high redshift Universe (z >> 4), where we are currently limited to measuring the average properties of galaxies, rather than the detailed physics on the assembly and growth of galaxies. As the speaker highlighted, we don’t currently have secure spectroscopy at z > 7.3, and we are limited to small samples of galaxies even well below this redshift. With JWST, we will be able to obtain spectra for these objects with a few to tens of hours of observing time.
  • Jessica Lu (IfA) – The Galactic Center Seen Through the Precise, Multiplexed Eye of JWST. This talk highlighted how JWST will help us to study the center of our own Galaxy with unprecedented spatial resolution over large fields of view. These studies will help astronomers answer questions about how the supermassive black hole at the center of the Milky Way formed and has grown over time. Additionally, JWST will help us uncover how stars form in these extreme star forming regions.
  • Daniela Calzetti (UMASS) – Studies of Nearby Galaxies in the Era of JWST. This talk highlighted how JWST will help us to study relatively nearby galaxies. New observations in an unexplored wavelength regime and JWST spatial resolution will help uncover long standing questions about the detailed physics of galaxies in the local Universe. These questions range from star formation to the mass-energy-chemical cycle of galaxies (how do galaxies deal with dust) to the interaction between supermassive black holes and their host galaxies.
  • Tommaso Treu (UCSB) – Strong Lensing, dark matter, and dark energy with the James Webb Space Telescope. This talk highlighted how JWST will even help us understand matter it can’t directly see! JWST will help us uncover the nature of dark matter by helping us to measure the magnification, astrometry, and time-delays of lensed systems which in turn help us measure dark matter substructure, if it exists. Lensed quasars will also help us measure differences between an objects redshift and geometric distance, helping us uncover the nature of dark energy.
  • Margaret Meixner (STScI) – The potential of JWST for studies of the Magellanic Clouds and beyond. This talk highlighted how JWST will help us understand the chemistry of the local Universe in unprecedented detail. In particular, JWST will help us detect the presence of chemical elements at low metallicity. Additionally, JWST may help astronomers trace the life cycle of baryonic matter as it is created in stars, thrust into the interstellar region of galaxies, and then reformed into stars.
  • David Lafreniere (UofM) – The science potential of JWST for exoplanet studies. This talk covered how JWST will help uncover new, and currently undetectable, exoplanets. The speaker highlighed two detection methods: (1) transit spectroscopy and (2) direct planet imaging. Transit spectroscopy with JWST will reveal new details about the atmospheres of exoplanets while direct planet imaging with JWST will compliment the set of new planets expected to be found via direct imaging using the newest generation of extreme adaptive optics instruments coming online in the near future.

This session was a great overview of the future of astronomy with JWST. There will also be a “JWST town hall” to cover upcoming integration and test plan for the telescope on Wednesday. If you are interested, you can catch it via webcast here.

2:00 PM: HEAD II: New Revelations from the Transient Sky

This session covered new discoveries in the field of transient astronomy, particularly in high-energy astronomy. There were five speakers:

  • Discovery and Followup of High Energy Transients with Swift, Neil Gehrels: This talk covered some of the high energy science being done with the Swift satellite, both using its X-ray capabilities and its UV/optical telescope. Gehrels mentioned some of the interesting events that Swift has provided multiwavelength coverage for, such as GRBs with no host galaxy, tidal disruption events, and shock breakout. Swift provides a good model for transient observatories because of its rapid response, rapid data uplink/downlink, and multiwavelength capabilities.
  • Tidal Disruption Events: New Transient Probes of Accretion, Jet Physics, and Black Hole Demographics, Suvi Gezari: There is quite a bit of evidence for the presence of supermassive black holes at the center of most galaxies, but how do we probe the ones that aren’t actively accreting? Tidal disruption events – when a star passes close to a black hole and is pulled apart, creating a brief flare as material forms an accretion disk – offer a chance to probe the low-mass SMBH population. The observed properties of a tidal disruption event can provide information about black hole mass and spin, plus the structure of the disrupted star. Tidal disruption events are rare, but can be scientifically rich.
  • Electromagnetic Counterparts of Advanced LIGO Gravitational Wave Sources, Eliot Quataert: When the merger events expected to produce gravity waves occur, they can also leave an electromagnetic signature. Searching for the EM counterparts to gravitational wave sources can tell us about the host galaxies and constrain models for the merger scenario, as well as better localizing the source on the sky. Detecting the EM signal before the gravity wave can also help LIGO find the gravity wave signal in its own data, effectively lowering the S/N threshold. Knowing the amount of material ejected from a neutron star-neutron star merger – a gravity wave candidate – would also help in determining if such mergers are the site of r-process nucleosynthesis.
  • The Palomar Transient Factory View of the Transient and Variable Sky, Thomas Prince: Thomas Prince gave a brief overview of the Palomar Transient Factory and the research it’s been doing. Lots of PTF research is being presented here at AAS by many collaboration members. PTF has a hierarchical system of telescopes for time domain astronomy: a discovery telescope, a classification engine, and a bigger instrument for followup spectroscopy. It observes supernovae, novae, and many types of variable stars and flaring binaries. The new Zwicky Transient Facility upgrade is expected to give PTF higher cadence, larger coverage, and faster discovery.
  • Superluminous Supernovae, Avishay Gal-Yam: This talk covered the mysterious events known as superluminous supernovae, defined as a transient above magnitude -21. The discovery rate of such events has been increasing with non-targeted surveys. These events have been classified into three groups: SLSN-I (hydrogen lines); SLSN-II (no hydrogen lines); and SLSN-R (radioactively powered). The models for causing such events are still a matter of debate, but pair instability and stars enshrouded in optically thick layers are possible candidates.
4:30 pm: “From Gas to Stars over Cosmic Time” – Mordecai-Mark Mac Low

Classic "Madau plot" of star formation rate per unit volume as a function of redshift. Modern versions of this plot have many more data points, smaller error bars, and go back to z~10. From Madau et al. 1998.

This plenary talk addressed nothing less than the history of star formation since the time of the first galaxies. Observations of what is known as the “cosmic star formation rate”, which is the mass of stars formed per year per volume in cubic megaparsecs, have shown that star formation was about an order of magnitude higher at z=2 than it is today, and that it steadily declined towards higher redshifts (see the plot at right). The talk addressed progress towards understanding many of the important details that feed into understanding this evolution of star formation across time. There were four primary conclusions discussed:
  • Turbulence, or random motions within molecular clouds driven by external sources of energy such as supernovae, works against gravity to suppress star formation.
  • Molecular gas surface density correlates very well with star formation rate surface density, but does not directly cause star formation. (See this astrobite for more on this point).
  • Dust in molecular clouds absorbs interstellar ultraviolet radiation that would otherwise break up the clouds and prevent star formation.
  • Gravitational instability drives star formation on galaxy-wide scales as well as in molecular clouds.

The talk concluded with a look at the future: groundbreaking facilities like JWST, LSST, and the thirty meter-class telescopes will provide the resolution and sensitivity to enable more accurate measurements of star formation in the very early Universe. ALMA was enthusiastically added to the list on the suggestion of an audience member.

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