JWST reveals a possible z∼11z \sim 11 galaxy merger in triply-lensed MACS0647−-JD

MACS0647$-$JD is a triply-lensed $z\sim11$ galaxy originally discovered with the Hubble Space Telescope. Here we report new JWST imaging, which clearly resolves MACS0647$-$JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. Both are very small, with stellar masses $\sim10^8\,M_\odot$ and radii $r<100\,\rm pc$. The brighter larger component "A" is intrinsically very blue ($\beta\sim-2.6$), likely due to very recent star formation and no dust, and is spatially extended with an effective radius $\sim70\,\rm pc$. The smaller component "B" appears redder ($\beta\sim-2$), likely because it is older ($100-200\,\rm Myr$) with mild dust extinction ($A_V\sim0.1\,\rm mag$), and a smaller radius $\sim20\,\rm pc$. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. With an estimated stellar mass ratio of roughly 2:1 and physical projected separation $\sim400\,\rm pc$, we may be witnessing a galaxy merger 400 million years after the Big Bang. We also identify a candidate companion galaxy C $\sim3\,{\rm kpc}$ away, likely destined to merge with galaxies A and B. The combined light from galaxies A+B is magnified by factors of $\sim$8, 5, and 2 in three lensed images JD1, 2, and 3 with F356W fluxes $\sim322$, $203$, $86\,\rm nJy$ (AB mag 25.1, 25.6, 26.6). MACS0647$-$JD is significantly brighter than other galaxies recently discovered at similar redshifts with JWST. Without magnification, it would have AB mag 27.3 ($M_{UV}=-20.4$). With a high confidence level, we obtain a photometric redshift of $z=10.6\pm0.3$ based on photometry measured in 6 NIRCam filters spanning $1-5\rm\mu m$, out to $4300\,\r{A}$ rest-frame. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647$-$JD.Comment: 27 pages, 14 figures, submitted to Natur

The Who, What, When of Cosmic Reionization: Constraints on the Timeline and Responsible Sources

The \textit{Epoch of Reionization} marks the period following the Dark Ages, the era beginning 400,000 years after the Big Bang in which neutral hydrogen permeated the Universe. Reionization is defined as the period of cosmic history in which this hydrogen went from being neutral to ionized, ending at around redshift $z \sim 6$, or about 1 billion years after the Big Bang. This period marks the last major phase change of hydrogen in the intergalactic medium. It was also a time of significant galaxy and structure formation, when the first sources of light emerged. These nascent galaxies were likely major contributors to reionization, emitting large amounts of high energy photons which escaped into the intergalactic medium and began to ionize the vast sea of neutral hydrogen. However, beyond these facts, there are still many open questions surrounding the Epoch of Reionization. Some of the remaining uncertainties concern how quickly the transition occurred, what the key drivers were in the process, and what their physical properties are. This dissertation aims to address some of these lingering questions. In this work, I use a large sample of characteristically faint, gravitationally lensed, high-redshift galaxies in order to constrain both the timeline of reionization and the physical properties of the ionizing sources. The galaxies used in this sample have deep photometric data in multiple bands from the \textit{Hubble Space Telescope} and \textit{Spitzer Space Telescope}, as well as followup spectroscopy from the \textit{Keck Observatory}. The high quality of photometric data provides good constraints on the redshift and physical properties of galaxies in our sample, even if they lack spectroscopic confirmation. The sample is comprised of $\sim$ 250 Lyman Break galaxy candidates within the redshift range 5 < z < 8.2, spanning the heart and tail ends of the reionization era. Galaxy candidates for spectroscopic follow-up were chosen after multiband photometric observations were completed. These were selected via the Lyman Break technique and using constraints on the redshift probability distribution created from each galaxy's photometry. Follow-up spectroscopic observations resulted in 38 spectroscopically confirmed galaxies via detection of the Lyman-$\alpha$ (Ly$\alpha$, 1216\AA) line, and constraints on Ly$\alpha$ strength for the rest of the sample. For all analyses done in this dissertation, I use these $\sim$ 250 galaxies lying in the redshift range 5 < z < 8.2 in order to constrain both the timeline of reionization and the stellar and UV properties of galaxies in this epoch. I begin in Chapter 2 with a study on the timeline of reionization using Ly$\alpha$ emission properties from galaxies during and directly after the process was complete. In this work, I compare the prevalence and strength of Ly$\alpha$ emission from galaxies within the Epoch of Reionization ($z\sim 6.7$ and $z\sim 7.6$) and when reionization was mostly, if not entirely, complete ($z\sim 6$). I compare the UV luminosities and $\beta$ slopes of the samples at the different redshifts and show that the distributions are similar for both properties. As the galaxies all have similar UV properties, and therefore are likely at similar states of interstellar medium evolution, we attribute any difference in the Ly$\alpha$ equivalent width distributions to the evolving opacity of hydrogen in the intergalactic medium. The results of this study, which are consistent with other works, suggest a rapid and fairly late reionization scenario. This work is published in the \textit{Monthly Notices of the Royal Astronomical Society}, \citep{bolan_inferring_2022}. In Chapter 3, I present an analysis of the physical properties of the galaxy sample as well as the results of a search for CIII] emission in confirmed Ly$\alpha$ emitters, which can provide systemic redshifts as well as a basis on which to infer metallicities and ionization parameters. For each of the galaxies, I calculate UV luminosity and $\beta$ slope, the slope in the UV spectrum of a galaxy redward of Ly$\alpha$ emission, from photometry as well as estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age via spectral energy density fitting. For galaxies with Ly$\alpha$ emission, I look at the equivalent width (EW) of the emission line as a function of all of these properties to see if there are any correlations. I also compare the distributions of each of these properties for Ly$\alpha$ emitters against nonemitters to see if there are significant physical differences between these groups of galaxies. I find no statistically significant relationships between Ly$\alpha$ EW and any physical properties, nor any significant difference between the sample of Ly$\alpha$ emitters and nonemitters. In Chapter 4, I provide a summary. Using a sample of gravitationally lensed, intrinsically faint, high-redshift galaxies, I infer a timeline of cosmic reionziation and characterize the physical properties of typical galaxies from the era. These analyses are especially important as we enter an era of massive space and ground based observatories, such as the \textit{James Webb Space Telescope}, the \textit{European Extremely Large Telescope}, the \textit{Thirty Meter Telescope}, and the \textit{Giant Magellan Telescope}. The work done in this dissertation improves the of knowledge on high-redshift galaxies to guide future observations and surveys. With deep data on large samples of early galaxies from these observatories, a detailed timeline of reionization can be even further constrained, as well as the properties of the main drivers of the process

Realizing Partnership Potential: A Report on a Formal Collaboration Between a Teaching and Learning Centre and Libraries at the University of Toronto

In 2010, the University of Toronto’s Centre for Teaching Support &amp; Innovation (CTSI) and University of Toronto Libraries (UTL) jointly launched Partnering for Academic Student Success (PASS), a partnership to foster new opportunities for collaboration between academic librarians and those involved in developing excellence in university teaching. This article describes the challenge of professional education in support of the teaching mission for librarians, and a partnership designed to address this need.  The article reports on the genesis, goals, and key principles contributing to the partnership’s success, while discussing implications and recommendations for those seeking to develop similar programs of intentional collaboration that enable teaching/learning goals

Dear Delegate

increase in the type, range and quality of papers submitted for consideration for publication and we accepted 17 papers from those submitted. All papers were double blind peer-reviewed before acceptance into the conference for publication. There are several definite strands of research and interest within the subject of computer based forensics these include disk sanitisation, honeypots and discovery techniques. The papers authors are drawn from a cross section of the forensics community from practioners to academics. Conferences such as these are simply not possible without willing volunteers who follow through with the commitment they have initially made and I would like to take this opportunity to thank the conference committee for their tireless efforts in this regard. These efforts have included but not been limited to the reviewing and editing of the conference papers, helping with the planning, organisation and exEdith Cowan Universitytion of the conference. To our sponsors who have contributed both financial and moral support by their contributions and donations to the conference, who likewise conferences like this need

Inferring the intergalactic medium neutral fraction at z similar to 6-8 with low-luminosity Lyman break galaxies

ABSTRACT We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $\overline{x}_{\small HI}$, at z ∼ 6–8 using the properties of Lyman break galaxies (LBGs) during the epoch of reionization. We use large samples of LBG candidates at 5.5 ≤ z&nbsp;≤ 8.2 with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-α (Lyα) equivalent width (EW) for detections or the EW limit spectrum for non-detections to parametrize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at z ∼ 6.0, we are able to infer $\overline{x}_{\small HI}$ at two redshifts: z ∼ 6.7 and z ∼ 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at z ∼ 6.0 in order to constrain the intrinsic faint-end Lyα EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyα distribution from those of the IGM. We infer an upper limit of $\overline{x}_{\small HI}$ ≤ 0.25 (0.44) at z&nbsp;=&nbsp;6.7&nbsp;±&nbsp;0.2 and a neutral fraction of $\overline{x}_{\small HI}$&nbsp;=&nbsp;$0.83^{+0.08}_{-0.11}$ (0.83$^{+0.11}_{-0.21}$) at z =&nbsp;7.6&nbsp;±&nbsp;0.6, both within 68&nbsp;per cent (95&nbsp;per cent) uncertainty, results that favour a moderately late and fairly rapid reionization