North Carolina Astronomers' Meeting (NCAM)

Plenary Lecture: Rogier Windhorst, Arizona State University

Chasing the Reionizers of the Universe: Lyman Continuum Radiation with Hubble and the potential of Webb

Abstract: The hydrogen in the intergalactic medium (IGM) has been reionized since redshifts of about z~6-7. Yet, the reionizing Lyman Continuum (LyC) radiation has been remarkably hard to find due to ambient hydrogen gas surrounding the reionizing sources. We know those sources exist in the form of hot stars including binaries, and accretion disks around supermassive black holes in Active Galactic Nuclei (AGN). Estimates of the LyC escape fraction (f_esc) have been made from deep ground based spectroscopy above the atmospheric cutoff for objects at z>3, and from space based UV imaging with GALEX and HST, as well as HST spectroscopy, for objects at lower redshifts.

In this talk I will start reviewing the LyC work done with HST in the vacuum UV with WFC3 and COS. At redshifts z~2.3-3, LyC radiation only visibly escapes from a small subset of the objects (i.e., either for a short fraction of their spectral energy distribution (SED) life-times, or through a few holes in the ISM), and appears on average somewhat stronger for weak AGN than for faint galaxies, with LyC escape fractions generally <10-30%. Stacked LyC profiles over many objects are also remarkably spotty and non-Sersic like, suggesting isolated lucky paths in the ISM where enough gas has been cleared for the LyC radiation to escape.

At redshifts z>3.5, the IGM is opaque enough that direct detection of LyC radiation becomes prohibitive. However, accurate SEDs of galaxies and weak AGN at higher redshifts can be used to indirectly predict the amount of ionizing radiation that must be present in these objects. Here is where the promise of JWST imaging and spectroscopy comes in to identify such sources of potential ionizing radiation. These include high redshift radio galaxies and AGN (z>4) with evidence for outflows and hot young stellar populations, as well as highly gravitationally lensed star-forming clumps at very high redshifts (z>6) that show evidence for outflows, and young high redshift galaxies with SEDs hot enough to produce LyC and outflow rates high enough to let some LyC escape.

While their LyC radiation cannot be observed directly through the IGM, JWST has the potential to provide a plethora of smoking guns that have both the hot SEDs to produce LyC radiation AND the ability to remove their surrounding gas sufficiently to let some LyC escape.

Rogier Windhorst is Regents' and Foundation Professor at Arizona State University and Interdisciplinary Scientist for the James Webb Space Telescope (JWST). His research is in astronomy, cosmology, galaxy formation and evolution, the cosmic dark ages and the epoch of First Light, and astronomical instrumentation. Since the early 1990's, his group at ASU has contributed significantly to unraveling the formation and evolution of distant galaxies with the Hubble Space Telescope, and the role that supermassive black holes and Active Galactic Nuclei have played in the process of galaxy assembly. His group at ASU plans to use JWST to map the epoch of First Light in detail.

See this JWST team profile of Dr. Windhorst

Meeting registration

There is no registration fee for the NCA meeting. We will have a sign-in table in the Koury Building on GTCC’s Jamestown campus.

We would like to get a reasonably accurate head count for the meeting, so that we can let the site committee know how much food/drink to order for break refreshments. Please let us know beforehand by registering through the online registration form if you are planning on coming. Registrations for presentations should be completed by Tuesday, Sept. 19.

If you plan to come but NOT to present, we would still like for you to register beforehand – you can do this up until Thursday, Sept. 21.

Directions and maps

The meeting is held in the Koury Hospitality Careers Building on the Jamestown campus of GTCC. Koury is building 19 on the Jamestown campus map. Park in Lot F. Use the interactive map below to find the best route from where you are.

Local lodging

There are plenty of hotels around the area. Use the Greensboro Convention and Visitors Bureau website to find accommodations if you plan to stay overnight.

Abstract submission

If you would like to present an oral or display presentation at the NCAM meeting, you will be able to do so soon through an online form. The submission deadline is Tuesday, 19 September.

Display presentations

This year we will return to in-person display posters. There will be display panel space available for 15-20 posters.

Oral presentations

The proposed plan is for standard oral presentations to be 10 minutes including Q&A, though this could change, depending on the number of submissions.

After you submit the registration form, you should receive confirmation of receipt within a day of submission; if not, call or e-mail Tom English at (336) 334-4822, ext. 50023 or trenglish@gtcc.edu, to verify.

Special sessions

• NCAM has been the host for the annual business meeting of the North Carolina Section of the International Dark-Sky Association, but NC chapter ("Dark Sky North Carolina") is now meeting monthly via Zoom, so there will be no formal meeting this year. If you are interested in participating, contact Dan Caton (Appalachian State University Dark Sky Observatory), and see our display at the meeting.
• NCAM acts as an annual site for a Regional ASTRO101 Teaching Exchange – a discussion/presentation session will be held during the afternoon. Anyone who currently teaches introductory college astronomy, or who expects to teach in the future, is encouraged to attend. (If you have ideas for the discussion, contact Tom English at GTCC.)