Physics and Astronomy

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9949

This is the collection for the University of Waterloo's Department of Physics and Astronomy.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 8 of 8

Constraining the quenching mechanisms of galaxy clusters through the evolution of stellar mass functions within GOGREEN and GCLASS
(University of Waterloo, 2024-08-21) Hewitt, Guillaume; Balogh, Michael
We present an analysis of the stellar mass functions (SMFs) of 17 rich galaxy clusters within the GOGREEN and GCLASS surveys in the redshift range of 0.8 < z < 1.5, down to a stellar mass limit of log(M/M⊙) = 9.5. We fit all the data simultaneously with a model that allows the Schechter function parameters of the quiescent and star-forming populations to vary smoothly with radius and redshift. The model also fits for the concentration parameter of each population, and the quenched fraction is modeled as a smooth function of redshift and velocity dispersion. We fit the data in a Bayesian manner, using MCMC. We find no significant dependence of the shape of the star-forming SMF on radius nor redshift, and find it to be consistent with the field. We confirm previous results of a radial dependence on the quenched fraction. We find a moderately significant radial dependence on the α and M* parameters of the quiescent population SMF. The cluster core has a highly elevated quenched fraction, yet the core quiescent SMF is more similar in shape to the quiescent field. The cluster non-core has an moderately elevated quenched fraction, and its quiescent SMF is more similar to the shape of the star-forming field. We explore the contributions of ‘early mass quenching’ and mass-independent ‘environmental quenching’ models in each of these radial regimes. We find the core to be described primarily by early mass quenching, which we interpret as accelerated quenching of massive galaxies in protoclusters, possibly through merger-driven AGN feedback, and the non-core to be described by environmental-quenching, signifying the increase of mass-independent quenching mechanisms that dominate low redshift clusters.
The Dependence of Halo Mass on Galaxy Size at Fixed Stellar Mass Using Weak Lensing
(University of Waterloo, 2017-04-24) Charlton, Paul; Hudson, Michael; Balogh, Michael
Stellar mass has been shown to correlate with halo mass, but with significant scatter. The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy sizes for a fixed stellar mass. Investigating potential links between dark matter halo mass and properties of the baryons, like size, allows us to develop physical explanations for the observed variation in terms of how the baryons and dark matter interact. Galaxy-galaxy lensing allows us to probe the dark matter halos for stacked samples of galaxies, giving us an observational tool for finding halo masses. We extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single S\'{e}rsic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing us to determine halo masses for lenses according to their size. Comparing our halo masses and sizes to baselines for that stellar mass allows us to do a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as: $M_{h}(M_{*}) \propto r_{\mathrm{eff}}^{\eta}(M_{*})$, and compare $\eta$($M_{*}$) over the mass range of our sample. We find that on average, our lens galaxies have an $\eta = 0.42\pm0.12$, i.e. larger galaxies live in more massive dark matter haloes. The trend is weakest for low mass blue galaxies and strongest for high mass large red galaxies (LRGs). This suggests that different processes are responsible for the strength of the observed trend over our range of stellar mass bins. Investigation of this relationship in hydrodynamical simulations suggests that this effect is strongest in satellite galaxies, and that the trend we observe in our data should be driven primarily by the fraction of satellite galaxies.
Hunting for the Primordial Quenched Population in 2 < z < 2.5 COSMOS Protoclusters
(University of Waterloo, 2024-01-17) Edward, Adit Harin; Balogh, Michael
We present an analysis of the galaxy stellar mass function (SMF) of 14 known protoclusters between 2.0 < z < 2.5 in the COSMOS field, down to a mass limit of 10⁹ᐧ⁵ M⊙. We use existing photometric redshifts with a statistical background subtraction, and consider star−forming and quiescent galaxies identified from (NUV−r) and (r−J) colours separately. Our fiducial sample includes galaxies within 1 Mpc of the cluster centres. The shape of the protocluster SMF of star−forming galaxies is indistinguishable from that of the general field at this redshift. Quiescent galaxies, however, show a flatter SMF than in the field, with an upturn at low mass, though this is only significant at ∼2σ. There is no strong evidence for a dominant population of quiescent galaxies at any mass, with a fraction <15% at 1σ confidence for galaxies with łog(M⋆/M⊙)<10.5. We compare our results with a sample of galaxy groups at 1 10¹⁰ᐧ⁵ M⊙) quiescent galaxies by a factor ≳ 2. However, we find that at lower masses (M⋆ < 10¹⁰ᐧ⁵ M⊙), no additional environmental quenching is required.
New Constraints on the Halo Mass of Ultra-Diffuse Galaxies with UNIONS using Weak Gravitational Lensing
(University of Waterloo, 2024-08-19) Ducatel, Jordan; Balogh, Michael; Hudson, Mike
While a lot of progress has been made in detecting and measuring various properties of Ultra-diffuse Galaxies (UDGs) over the last decade, the dark matter halo mass of these extremely faint and large objects remains a mystery. A better constraint on the total halo mass of UDGs would disentangle the wide variety of proposed formation mechanisms. We detect a contaminated sample of 545 potential UDGs, of which we estimate 290 to be true UDGs, in the ongoing Ultraviolet Near Infrared Optical Northern Sky Survey (UNIONS) using the Canada-France Imaging Survey (CFIS) r-band imaging, limiting our search to within 66 galaxy clusters up to redshift z ≤ 0.1. From weak gravitational lensing measurement around our UDG sample corrected for interloper contamination, we find an excess surface density consistent with zero (no detection) and a 2σ upper limit on the average halo mass of m200 ≤ 10^12.51 M⊙. By combining our measurement with that of Sifón et al. (2018), the only other weak gravitational lensing measurement of UDGs, we are able to constrain the halo mass further with a 2σ upper limit of m200 ≤ 10^12.05 M⊙ when accounting for the potential low-biasing effect of interlopers in this combined sample. Our results do not disentangle whether UDGs tend to be, on average, more dark matter-dominated or dark matter-deficient galaxies and therefore does not allow us to put new constraints on their formation mechanism. This work on UDG detection in a wide field survey optimized for weak lensing helps pave the way for future direct halo mass measurements of UDGs in upcoming surveys such as the Euclid Wide Survey.
Testing the Extremes of Initial Mass Function Variability using Compact Stellar Systems
(University of Waterloo, 2022-07-29) Cheng, Chloe Mai Tam; Balogh, Michael
The initial mass function (IMF) is a cornerstone in star formation and galaxy evolution studies. It has traditionally been assumed to be universal, but this has been challenged by increasingly detailed observations of diverse, extragalactic stellar populations. However, this observed variability in the IMF is debated as a sufficient theoretical framework to explain it has not yet been substantiated. A major limitation is that these observations have only probed narrow regions of mass-metallicity-density parameter space (i.e. metal-rich, early-type galaxies). We present an unprecedented sample of integrated light spectroscopy of diverse objects, including "compact" stellar systems (CSSs, i.e. globular clusters and ultra-compact dwarf galaxies) and brightest cluster galaxies. Our sample covers a wide range of metallicities (-1.7 < [Fe/H] < 0.01) and velocity dispersions (7.4 km/s < σ < 275 km/s). We carefully reduce high S/N Keck LRIS spectra and measure the IMF by employing a new suite of full-spectrum stellar population synthesis models. These simultaneously fit for ages, metallicities, and detailed chemical abundances, allowing us to robustly measure the effects of the IMF. We show that CSSs do not follow trends with physical parameters that have been found for early-type galaxies (ETGs). In particular, previously established metallicity-dependent trends with the IMF may change in complex ways. We examine potential factors that could be causing the population of CSSs to contrast with the ETGs in this parameter space.
Tracing galaxy evolution through the reconstruction of their star formation histories
(University of Waterloo, 2023-05-24) Webb, Kristi; Balogh, Michael
This thesis studies the star formation histories (SFHs) of galaxies in order to understand the nature of 'quenching.' The suppression of star formation, i.e., quenching, over the history of the Universe results in a growing population of quiescent galaxies. The physical processes governing how and why galaxies are quenched remain unknown. Observations show that massive galaxies, and those in dense cluster environments, make up a great proportion of the quiescent population. A number of theories have been proposed to explain both the mass dependence and environmental dependence of this population. Through studying the ages and stellar properties of the quiescent galaxies, the predictions of these theories can be tested. The first section of this thesis concentrates on the differences between galaxies in isolated ('field') or cluster environments as part of the Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) survey. Leveraging multi-wavelength and spectroscopic observations of 331 quiescent galaxies at 1 < z < 1.5, the data is fit to model spectral energy distributions (SEDs) to infer the SFHs and properties of the individual galaxies. In looking at the age trends between galaxies of different stellar masses, it is confirmed that more massive galaxies show evidence of earlier formation times, while lower mass galaxies exhibit more diverse SFHs. This result supports the paradigm of mass-dependent galaxy evolution. The novel result of this work was that any age difference between cluster and field galaxies was subtle; at fixed stellar mass cluster galaxies are <0.5 Gyr older. Putting this result in the context of two simple quenching models rules out two proposed quenching scenarios: i) environmental quenching post-infall, and ii) a primordial quenched population among cluster galaxies. This is distinctly different from local clusters, for which the majority of the quiescent population is consistent with having been environmentally quenched upon infall. Our results suggest that the quiescent cluster population at z > 1 is driven by different physical processes than those at play at z = 0. The second section of this thesis focuses instead on the detailed characterization of a single galaxy, the Ultra Diffuse Galaxy (UDG) Dragonfly 44 (DF44), whose curious set of properties is inconsistent with theoretical models of UDG formation. In fitting broadband photometry with high signal-to-noise and high-resolution optical spectroscopy with SED models, the detailed stellar properties and SFH of this galaxy are investigated. The precision of the observations required a careful assessment of the SED models, where the conclusion was that DF44 formed between 7.2–12.9 Gyr ago. Regardless of whether DF44 is old or very old, the SFHs imply early formation and rapid quenching. This result in context with its large size, kinematics, stellar population properties, and its environment, challenges conventional theories of galaxy evolution. The implication is that current theoretical models are missing the true diversity of galaxy formation and evolution. The third section evaluates the assumptions of the SED fitting procedure. Modelling the SFHs of galaxies is an ill-defined problem, where the results are subject to a number of prior assumptions for what SFHs are more realistic. Modern SED fitting models make a number of these assumptions specific, which provides flexibility in studying diverse samples of galaxies. Without observational constraints to qualify such assumptions, however, the results can simply reflect the assumptions. A mock dataset of quiescent galaxies modelled after the GOGREEN sample is constructed in order to investigate the influence of the SFH prior to the results of that study. A statistical framework is used to infer the distribution of properties among a galaxy population, which in principle can mitigate unphysical assumptions made in SED-fitting. This work highlights the challenges involved in studying star formation timescales of old galaxies, and the nuances of SED-fitting procedures which can lead to spurious results.
Transition Galaxies: The Evolution of Environmental Quenching
(University of Waterloo, 2021-05-28) McNab, Karen; Balogh, Michael
We study the evolution of environmental quenching using a photometric selection of transition galaxies in GOGREEN- which encompasses clusters between 1
Ultraviolet Sizes and Morphology of Galaxies in the Coma Cluster
(University of Waterloo, 2022-08-25) Morgan, Cameron Robert; Balogh, Michael
We present a study of the Coma cluster using ultraviolet (UV) imaging obtained using the Ultraviolet Imaging Telescope. We discuss methods for measuring sizes and morphology of galaxies in the UV. Several cluster galaxies in our sample exhibit small UV sizes relative to their optical sizes, while we find that galaxies in a field sample have similar sizes in UV and optical bands. Further, we have shown that when cluster and field galaxies are matched up one-to-one based on colour and absolute i-band magnitude, the cluster galaxies tend to have smaller UV sizes than their field counterparts. We have used an NUV − i colour magnitude relation to identify a red sequence and blue cloud of galaxies in our sample. There is a trend whereby redder disk galaxies exhibit even smaller UV sizes, relative to field counterparts, than galaxies at the bluer end of the spectrum. Since this result is consistent with environmentally driven gas stripping, we have identified from our sample six known stripping candidates, and further identified one new candidate. Additionally, we find that this sample of galaxies exhibits redder UV-optical colours in the outer regions of the galaxy, a result consistent with an outside-in quenching mechanism affecting the galaxy. Beyond the blue cloud, we find a substantial population of red disks/spirals in our sample; as high as 38% of galaxies using an NUV − i = 4.0 cut to separate blue and red galaxies. This result is highly dependent on the definition of the red sequence, however. The existence of red spirals has been discussed in the literature as a possible indication of starvation lowering the rates of star formation in previously blue spirals while not disturbing the overall morphological structure of the galaxy. We have discussed these results in context as potential indicators of various environmentally driven quenching mechanisms underway in the Coma cluster, and discussed future surveys that will allow a more robust quantification of the prevalence of these mechanisms.

Browse

Browsing Physics and Astronomy by Author "Balogh, Michael"