Special Talk

• Special Talks

  Speaker: Rebecca Larson (STScI)
  Title: Advancements in Exploring the Early Universe: Unlocking the Mysteries of Galaxies During the Reionization Era
  Abstract: The history of galaxies in the early Universe remains substantially unknown. The mystery surrounding these galaxies is primarily a result of the epoch in which they existed. During the epoch of reionization (z>6), the Universe experienced its last major phase change, where the neutral gas permeating the intergalactic medium [IGM] became ionized. Light emitted from early galaxies was often blocked by this neutral gas (or "cosmic fog"), preventing restframe ultraviolet [UV] spectroscopic studies of this epoch except for faint traces of light detectable in the near-infrared [NIR] from the brightest sources. Before 2022, the high-redshift field was restricted due to limited ground- and space-based instrumentation probing NIR wavelengths and beyond. Much of what we learned spectroscopically about these galaxies during this time came from a handful of bright UV metal emission lines or far-infrared [FIR] emission (generally with only 1-2 lines detected in individual galaxies). These data only came after fighting for hours using the most massive telescopes on the ground and in space.
  Since the advent of JWST, the high-redshift field has exploded with new science probing wavelengths and redshifts previously inaccessible. Using the advanced spectroscopic NIR capabilities of the JWST, we have found increasingly distant galaxies and characterized these sources within the heart of the epoch of reionization [EoR] for the first time. In this talk, I will discuss the state of the high-redshift field before and after the launch of JWST -- highlighting our work from the Cosmic Evolution and Early Release Science [CEERS] survey, among other key early release science [ERS] & Cycle 1-3 programs. These new data have led to the discovery of an unexpected abundance of bright galaxies and active galactic nuclei [AGN] in the EoR, providing insights into the roles that the nature of these early galaxies and the nurturing from their environments played in the reionization of the Universe.

  Speaker: Pallavi Patil (JHU)​​​​​​​
  Title: Unveiling the Role of AGN in Post-Starburst Galaxies: Quenching Mechanisms at Cosmic Noon
  Abstract: One of the key problems in astrophysics is understanding how and why galaxies switch off their star formation, building the “red sequence” we observe in the local Universe. Post-starburst galaxies (PSBs), where a galaxy has recently undergone a massive starburst, are sufficiently common at z~1-2 that they may contribute significantly to the growth of the red sequence at this critical epoch. The role of active galactic nuclei (AGN) feedback in shutting star-formation in PSBs and driving the evolution from star-forming to quiescence remains a key question in galaxy evolution. Here, we present a large sample of high-z PSBs (0.5<z<3) selected using a Principal component analysis of 11-band photometry available in the UKIDSS Ultra Deep Field (UDS). We leveraged multi-wavelength datasets available to test the incidence of AGN, mainly obscured AGNs. Cross-matching of deep 1.4 GHz VLA imaging showed that only 1% of PSBs host radiatively inefficient, jetted AGNs, suggesting a low prevalence of jet-driven quenching at cosmic noon. We also present MIR imaging to check the presence of obscured AGN and study the cold gas content via dust emission during the quenching episode. Overall, our findings reveal the strong influence of stellar mass on the characteristics of PSBs, with more massive PSBs likely to reside in overdense regions and host AGNs. Finally, we discuss the implications of our study in providing robust constraints on different quenching mechanisms during a crucial epoch of cosmic time.