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- 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
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.
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).
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.
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.
Title: AGN Activity and Environment of Massive Quiescent Galaxies at High Redshift
Abstract: 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.
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.
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.
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.
Title: The connections between mergers and SMBHs: comprehensive understanding from spectroscopy and photometry
Abstract: In this presentation, I will introduce two projects that I am working on related to the connections between galaxy mergers and SMBHs. In the first project, motivated by testing the hypothesis that mergers build up the BH-host mass relation., we look for physically-associated dual quasars with separation < 4″ in Subaru HSC/SSP footprint. Our published work has reported 6 such systems. Dual quasars are a special phase in the lifetime of a galaxy-galaxy merger when both of the SMBHs are activated. Spectroscopic observations of these systems will allow us to estimate the BH masses of both galaxies using the viral method. And the stellar mass of host galaxies can be measured with SED fitting using HSC photometry and 2D decomposition methods. Therefore, we are able to compare the BH-host scaling relation in mergers with those in single galaxies in the local universe (Kormendy & Ho 2013). We find that mergers typically bring such systems above the local relation, thus, making the BHs over massive. We also found our observational results are inconsistent with Horizon-AGN simulation.
In the second project, we study the non-parametric asymmetry (A, Conselice 2000) of the host galaxies of all single SDSS quasars in the HSC footprint at 0.2<z<0.8 based on all five bands of photometry grizy. After some quality checks, the final sample size is 2424. Different from the first project, which focuses on the BH-host mass relation. In this project, we explore the correlation between SMBH and host galaxies in a broader way, i.e., the correlations between A and BH mass, Eddington ratio, bolometric luminosity, stellar mass, rest frame U-V color, and redshift. As a result, we find the strongest correlation exists between asymmetry and Lbol (spearman correlation ~0.37). And interestingly, we find this correlation has band dependence, which is stronger in bluer bands (g,r,i), while weaker in redder bands (z,y). The merger ratios of quasar hosts based on criteria A>0.35 also show a similar tendency, which ranges from 16% in bluer bands to 8% in redder bands. We found this may explain the discrepancies in previous works that argued whether quasar hosts have larger merger ratios than inactive galaxies. We also studies the correlations between the merger ratios of quasar hosts and Lbol and z, we found similar results as Treister et al. 2012 that when the quasars are brighter, they are more likely to be mergers, while the ratio shows no evolution with redshift.