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Cake Talk: Laia Barrufet and Andrea Weibel (U. of Geneva)
Aug 11 @ 14:00 – 15:00
Laia Barrufet (University of Geneva) – Unveiling the Nature of Infrared Bright, Optically Dark Galaxies with Early JWST Data
Abstract: Over the last few years, both ALMA and Spitzer/IRAC observations have revealed a population of likely massive galaxies at z>3. However, due to the very limited photometry for individual galaxies, the true nature of these so-called HST-dark galaxies has remained elusive. In this talk, I will present the results of 33 HST-dark sources selected based on their red colours across 1.6 to 4.4 micron with NIRCam imaging from the Early Release Science Program CEERS. These galaxies are generally heavily dust-obscured, massive, star-forming sources at z~2-8. Our analysis shows the unique power of JWST to reveal this previously missing galaxy population and to provide a complete census of galaxies at z=2-8 based on rest-frame optical imaging.
Andrea Weibel (University of Geneva) – Is There Spectroscopic Evidence for Ongoing Quenching in SDSS Green Valley Galaxies?
DAWN-IRES presentations @ Room 01.2.I.158
Aug 16 @ 14:00 – 15:15
  • 2:00-2:15: Lauren
    • [CII] as a Tracer of HI Gas in High-z Galaxies
  • 2:15-2:30: Eric
    • [CII] as a tracer of molecular and atomic gas
  • 2:30-2:45: Allan
    • Analyzing ALESS73.1 in CO and [CI]
  • 2:45-3:00: Rebeca
    • Star Formation Efficiency with FLARES
  • 3:00-3:15: Hanga
    • Searching through MOSFIRE Archival Data
Cake talk: Christian Kragh Jespersen
Aug 18 @ 14:00 – 15:00

Learning Galaxy Properties from Merger Trees with Mangrove

Efficiently mapping between baryonic properties and dark matter is a major challenge in astrophysics.
Although semi-analytic models (SAMs) and hydrodynamical simulations have made impressive advances in reproducing galaxy observables across cosmologically significant volumes, both still require significant computation times, and are hard to succinctly analyze, representing a barrier to many applications. Graph Neural Networks (GNNs) have recently proven to be the natural choice for learning physical relations. Among the most inherently graph-like structures found in astrophysics are the dark matter merger trees that encode the evolution of dark matter halos. In this cake talk I will introduce a new, graph-based emulator framework, Mangrove, and show that it emulates the galactic stellar mass, cold gas mass and metallicity, instantaneous and time-averaged star formation rate, and black hole mass with scatters two times lower than other methods across a simulation box of side length 75 Mpc/h in 40 seconds, 4 orders of magnitude faster than a SAM and 9 orders of magnitude faster than a hydro simulation. I’ll also show how Mangrove allows for quantification of the dependence of galaxy properties on merger history, making it possible to learn about the simulations on a new level. I will also compare Mangrove results to the current state of the art in emulating the dark matter – galaxy connection and show significant improvements for all target properties.

Mangrove is publicly available at https://github.com/astrockragh/Mangrove.

Cake talk: The formation and quenching of the first massive galaxies
Aug 23 @ 15:30 – 16:30

Kate: The formation and quenching of the first massive galaxies (status seminar)

In this talk I will summarise the work achieved so far in my PhD and discuss plans for the rest of the PhD. I will summarise two projects nearing completion that explore the formation and quenching of the first massive galaxies in COSMOS2020. The first, entitled “COSMOS2020: Explore the epoch of quenching at z>3 with a new colour diagram” presents a new colour diagram to find massive quenched galaxies in photometric data, and presents the results of this applied to the latest COSMOS catalog. The second, entitled ” COSMOS2020: Star formation histories of massive quiescent galaxies at 3<z<5 imply early mass assembly followed by rapid quenching” explores the use of non-parametric methods to reconstruct the stellar assembly of the first massive galaxies and answer the questions: when did they form, when did the quench, and possibly – how did they quench? The final part of the talk details my plans for exploring quenching with JWST, specifically using data from the Canadian NIRISS Unbiased Cluster Survey (CANUCS).

Cake talks: Adele Basturk and Riley Tam
Aug 24 @ 14:00 – 15:00


Adele: Probing CDM interactions in high-z galaxy clustering with the BUFFALO HST survey

Analyzing the clustering behavior of galaxies across a wide redshift range allows us to model the gravitational assembly of such structures over cosmic time. We achieve this by measuring the 2-point correlation of galaxies at 0.01 < z < 8.5, gravitationally lensed by the foreground cluster Abell370 in BUFFALO. With this understanding, we can probe our current model of Cold Dark Matter (CDM), specifically the assumption that it interacts solely through gravitation. More importantly, studying galaxies at high redshift gives us a more complete picture of clustering at various snapshots in time. In this talk, I will summarize how the correlation function informs us about galaxy clustering behavior, my results from running correlation functions in both the COSMOS 2020 and BUFFALO surveys, and share how predictive clustering calculations at different redshift and mass bins compare to measured correlations.

Riely: Evidence for Inside-Out Growth in Galaxy Simulations

Recent observations have found a correlation for galaxies between their gas temperatures in star-forming clouds and specific Star Formation Rate (sSFR). The resulting model has led to several new predictions, such as inside out galaxy growth, compact galaxies at high redshifts and distinct morphological phases of galactic evolution. We employ GIDGET, a one-dimensional semi-analytical radius dependent galaxy evolution model, to explore these observational results. We find broadly similar behaviour of inside out galaxy growth and changing morphology. Additionally, we present new predictions for the nature of galaxy evolution with implications for their behaviour right after formation and for the extrapolation of the star-forming main sequence to lower masses.

Cake talks: Ethan Garcia and Thomas Cleveland
Sep 1 @ 14:00 – 15:00

Ethan: Unlocking Star Formation in Galactic Photometry

Understanding star-formation conditions and its associated Initial Mass Function (IMF) is critical to deriving galactic properties and their evolution in the universe. Although the IMF has traditionally been inconclusive beyond the local universe, recent research at DAWN parameterized the IMF in the EAZY photometric fitting code. Here, we employ the same IMF parameterization in LePhare, a fundamentally different method of fitting photometry. Results from fitting thousands of galaxies in extensive catalogs suggest systematic variations in the IMF over time that are similarly consistent with EAZY, further verifying that most galaxies exhibit top-heavier stellar populations than in the Milky Way. In addition, LePhare extracts relationships of the variable IMF with properties of star-forming and quenched populations, yielding a more complete and accurate picture of galactic evolution.

Thomas: Constraints and Predictions on Alternatives to Dark Energy
Recent studies find that measurements of the Hubble constant (H0) determined from the Cosmic Microwave Background are ~9% lower than measurements of H0 from much lower-redshift supernova observations.   Several possible modifications to the standard ΛCDM cosmological model have been proposed to explain this discrepancy.  A re-analysis of the supernova dataset finds that there are actually two discrepancies: one in H0 but another in the composition of the Universe as well.  We show that the models designed to fix this “Hubble Tension” are incapable of correcting each simultaneously.  And in a different, simple class of dark energy models, we show these quantities are not only preserved, but meet other observations including Ωmh2.  These models predict drastic differences for the future of the Universe than those under ΛCDM—possibly even in the present.


Cake talk: Kei Ito
Sep 8 @ 14:00 – 15:00

Title: AGN Activity and Environment of Massive Quiescent Galaxies at High Redshift
Recent multi-band observations have found that galaxies with suppressed star formation activity exist even in the high redshift universe. The state-of-art spectrograph has now confirmed them up to z~4. On the other hand, it is not well understood why they get quenched at such a high redshift and where they live. Here, I will introduce our two recent works for quiescent galaxies in the COSMOS field, (1) X-ray (Chandra) and radio (VLA) stacking analysis to explore their AGN activity and its connection to quenching and (2) the discovery of an overdense structure of quiescent galaxies at z=2.77 which are likely to be a new type of protocluster with the Keck/MOSFIRE observation.

Cake Talks: Meghana Killi and Antonello Calabrò
Sep 15 @ 14:00 – 15:00
Meghana Killi: PhD status seminar – Morphology and Spectroscopy of High-redshift Galaxies
I will give an overview of my research over the last two years and a brief outline of my plans for the last year of my PhD program. I have 3 ongoing projects: The first is a gas-phase metallicity measurement using far infrared emission lines from a normal galaxy in the reionisation epoch at z~7. The second is a statistical study of spatial offsets between stars and the interstellar medium in main-sequence star-forming galaxies at z~4-6. The third is an analysis of a sample of bright, compact Lyman alpha emitters found in archival Hubble data also around z~4-6. I will explain the motivation behind each work, highlight the most important results (so far), and attempt to place the findings in larger astrophysical context.

Antonello Calabrò: ISM kinematics and outflows in star-forming galaxies at z ~ 3
Gaseous flows inside and outside galaxies are key to understanding galaxy evolution, as they regulate their star-formation activity and chemical enrichment across cosmic time. In this talk, I will present a study on the ISM kinematics of a sample of ~ 300 CIII] and HeII emitters at redshift 2 < z < 5 selected from the VANDELS survey and representative of the star-forming Main Sequence in the stellar mass range 9<log(M*/Msun)<11. Outflow and inflow velocities, which are derived as the velocity shift of low and high-ionization far-UV absorption lines (i.e., SiII, CII, AlIII, SiIV, AlIII) from the systemic redshift, are then compared to other galaxy properties in order to investigate their physical drivers. I will also derive the mass outflow rate, and finally explore the fate of the outflows by comparing their velocities to the typical escape velocity estimated from a subset of our sample with MOSFIRE follow-up.
Cake talk: Marshall Perrin
Sep 20 @ 15:30 – 16:30

JWST: from First Photons to First Science

After decades of development by a globe-spanning international team, JWST is now providing an unprecedented view of the cosmos. In this talk I will describe our experience thus far operating this new great observatory: from mission design history and development, to prelaunch preparations, to launch and commissioning, and now into the first of many years of mission operations at the Earth-Sun L2 point.  I will provide a first-hand look at the processes and teamwork we used to deploy the observatory and align its segmented mirror system, and discuss some of the surprises (both challenges and good news) encountered during commissioning.  Even early during telescope commissioning, this observatory’s tremendous power and sensitivity were already apparent with spectacular images and spectra. Now during science operations, we continue to learn more about observatory hardware performance; this is still early days in our adventure with JWST. I will close with a look at (a small fraction of) some of the early science results with JWST, with particular attention to our early observations of nearby exoplanetary systems.

Cake talk: Michele Ginolfi
Sep 22 @ 14:00 – 15:00
Michele Ginolfi: A swarm of galaxies revealed around a hot dust-obscured hyper-luminous galaxy
The phase transition between galaxies and quasars is often identified with the rare population of hyper-luminous, hot dust-obscured galaxies. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. Here we report the detection of several galaxies emitting Lyman-alpha emission on projected physical scales of about 400 kpc around the hyper-luminous hot dust-obscured galaxy W0410, at redshift z = 3.6, using MUSE observations. While this indicates that W0410 evolves in a very dense environment, we do not find clear signs of mergers that could sustain its growth. Data suggest that if mergers occurred, as models expect, these would involve less massive satellites, with only a moderate impact on the internal interstellar medium of W0410, which is sustained by a rotationally-supported fast-rotating molecular disk, as ALMA observations suggest.