Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (24 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2024)

Dwarf galaxies are unique probes of the nature of dark matter and baryonic processes such as stellar feedback. They are faint and less constrained in observations compared to more massive galaxies. Observations of nearby dwarf galaxies over the past two decades have revealed discrepancies with simulations based on the Lambda Cold Dark Matter (LCDM) cosmology. This thesis aims to constrain the properties of dwarf galaxies as a population through the new generation of galaxy surveys. First, I will present a study using a spectroscopic sample of star-forming dwarf galaxies observed with Keck/DEIMOS, where I compare their kinematics and star formation properties with FIRE-2 hydrodynamical simulations. Next, I will introduce a much larger medium-band imaging survey on Blanco/DECam, the Merian Survey, which aims to build a large sample of dwarf galaxies to constrain their dark matter halo properties through weak gravitational lensing. I will present the filter design of the Merian Survey and its predicted performance. Finally, I will validate the Merian Survey using Merian first-year data, demonstrating that Merian is capable of measuring the weak lensing signal around dwarf galaxies at z~0.1. With this thesis, I will show that the medium-band methodology used in Merian could significantly benefit both future broad-band imaging and spectroscopic surveys by providing additional invaluable information.

    Cover page: Characterizing dark matter and feedback in star-forming dwarf galaxies
    • Thesis
    • Peer Reviewed
    UC Santa Cruz Electronic Theses and Dissertations (2023)

    In low mass galaxies, gas outflows driven by stellar feedback can generate fluctuations in gravitational potential and lower the central density of dark matter halos, which can solve the cusp-core problem. We compare observational signals of feedback driven outflows in simulated low redshift galaxies from the Feedback in Realistic Environments (FIRE) project, as well as new baryonic zooms of galaxies from the Romulus25 run. The FIRE simulations predict a correlation between sSFR and gas velocity dispersion at low redshift, however the Romulus simulations do not. We analyze dwarf galaxies observed with Keck DEIMOS for correlations between specific star formation rates (sSFR) and H-alpha velocity dispersion at redshift below 0.35, and compare to simulation predictions. We find no correlation between sSFR and H-alpha velocity dispersion in our observed data. Our results support the scenario that if dwarf galaxies are cored by stellar feedback, the coring process is completed at intermediate redshifts.

      Cover page: Analyzing the Effects of Stellar Feedback on Gas Dynamics in FIRE, Romulus and Observed Low Redshift Dwarf GalaxiesCreative Commons 'BY-NC-SA' version 4.0 license
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2025)
      Homemade manure tea (HMT) is commonly used in North Africa to enhance crop yields. Yet their physicochemical and biological characteristics remain poorly understood. This study evaluated oxygen and hydrobiological profiles of three types of HMT (bovine, ovine and poultry based, respectively noted HMTb, HMTo, HMTp) and compared them to control solutions of water and water supplemented with soluble NPK fertilizer. For these three types of HMT, oxygen and hydrobiological profiles were measured daily over a 7-day incubation period in three repeated, identical experiments, each comprising randomized treatments and five repetitions per treatment. Our results show that all HMT types rapidly transitioned to hypoxic conditions in the first 24h, shifting to anoxia between day 2 and day 7 depending on HMT type. This anoxic environment promoted denitrification and led to elevated NH4+ concentrations, suggesting the presence of anammox and microaerobic processes. Particulate organic matter contents and bacterial densities were highest in HMTp, while ciliate densities were highest in HMTb. These findings underscore the bioactive potential of HMT as fertilizers, with HMTp showing a favorable nitrogen profile beneficial for agricultural applications. To maintain aerobic conditions longer and reduce nitrogen losses and greenhouse gas emissions, we recommend passive or mechanical aeration, applying HMT during cooler hours, and stabilizing the pH of HMT. This study offers valuable insights to refine HMT preparation protocols, enhancing their use as bioactive fertilizers.
        Cover page: Oxygen and hydrobiological profiles of homemade manure-based tea in North Africa.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2014)
        We perform the first fit to the anisotropic clustering of Sloan Digital Sky Survey III CMASS data release 10 galaxies on scales of ~0.8-32 h-1 Mpc.Astandard halo occupation distribution model evaluated near the best-fitting Planck ? cold dark matter (?CDM) cosmology provides a good fit to the observed anisotropic clustering, and implies a normalization for the peculiar velocity field of M~2 × 1013h-1 M haloes of fσ8(z = 0.57) = 0.450 ± 0.011. Since this constraint includes both quasi-linear and non-linear scales, it should severely constrain modified gravity models that enhance pairwise infall velocities on these scales. Though model dependent, our measurement represents a factor of 2.5 improvement in precision over the analysis of DR11 on large scales, fσ8(z = 0.57) = 0.447 ± 0.028, and is the tightest single constraint on the growth rate of cosmic structure to date. Our measurement is consistent with the Planck ?CDM prediction of 0.480 ± 0.010 at the ~1.9σ level. Assuming a halo mass function evaluated at the best-fitting Planck cosmology,we also find that 10 per cent of CMASS galaxies are satellites in haloes of mass M ~ 6 × 1013 h-1 M. While none of our tests and model generalizations indicate systematic errors due to an insufficiently detailed model of the galaxy-halo connection, the precision of these first results warrant further investigation into the modelling uncertainties and degeneracies with cosmological parameters.
          Cover page: A 2.5 per cent measurement of the growth rate from small-scale redshift space clustering of SDSS-III CMASS galaxies
          • Article
          • Peer Reviewed
          LBL Publications (2021)
          The canonical Lambda cold dark matter (ΛCDM) cosmological model makes precise predictions for the clustering and lensing properties of galaxies. It has been shown that the lensing amplitude of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) is lower than expected given their clustering properties. We present new measurements and modelling of galaxies in the BOSS LOWZ sample. We focus on the radial and stellar mass dependence of the lensing amplitude mismatch. We find an amplitude mismatch of around 35 when assuming ΛCDM with Planck Cosmological Microwave Background (CMB) constraints. This offset is independent of halo mass and radial scale in the range Mhalo ∼1013.3-1013.9h-1 M· andr=0.1-60\, h-1 Mpc (k 0.05\\20\, h\, Mpc-1). The observation that the offset is both mass and scale independent places important constraints on the degree to which astrophysical processes (baryonic effects, assembly bias) can fully explain the effect. This scale independence also suggests that the 'lensing is low' effect on small and large radial scales probably have the same physical origin. Resolutions based on new physics require a nearly uniform suppression, relative to ΛCDM predictions, of the amplitude of matter fluctuations on these scales. The possible causes of this are tightly constrained by measurements of the CMB and of the low-redshift expansion history.
            Cover page: On the halo-mass and radial scale dependence of the lensing is low effect
            • Article
            • Peer Reviewed
            LBL Publications (2022)
            Using the weak gravitational lensing data from the Hyper Suprime-Cam Subaru Strategic Program (HSC survey), we study the potential of different stellar mass estimates in tracing halo mass. We consider galaxies with log10(M∗/M⊙) > 11.5 at 0.2 < z < 0.5 with carefully measured light profiles, and clusters from the redMaPPer and CAMIRA richness-based algorithms. We devise a method (the 'Top-N test') to evaluate the scatter in the halo mass-observable relation for different tracers, and to inter-compare halo mass proxies in four number density bins using stacked galaxy-galaxy lensing profiles. This test reveals three key findings. Stellar masses based on CModel photometry and aperture luminosity within R <30 kpc are poor proxies of halo mass. In contrast, the stellar mass of the outer envelope is an excellent halo mass proxy. The stellar mass within R = [50, 100] kpc, M∗, [50, 100], has performance comparable to the state-of-the-art richness-based cluster finders at log10Mvir ⪎ 14.0 and could be a better halo mass tracer at lower halo masses. Finally, using N-body simulations, we find that the lensing profiles of massive haloes selected by M∗, [50, 100] are consistent with the expectation for a sample without projection or mis-centring effects. Richness-selected clusters, on the other hand, display an excess at R ∼1 Mpc in their lensing profiles, which may suggest a more significant impact from selection biases. These results suggest that M∗-based tracers have distinct advantages in identifying massive haloes, which could open up new avenues for cluster cosmology. The codes and data used in this work can be found here:
              Cover page: The outer stellar mass of massive galaxies: a simple tracer of halo mass with scatter comparable to richness and reduced projection effectsCreative Commons 'BY-NC' version 4.0 license
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2015)
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2016)
                We use subhalo abundance matching (SHAM) to model the stellar mass function (SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) 'CMASS' sample at z ~ 0.5. We introduce a novel method which accounts for the stellar mass incompleteness of CMASS as a function of redshift, and produce CMASS mock catalogues which include selection effects, reproduce the overall SMF, the projected two-point correlation function wp, the CMASS dn/dz, and are made publicly available. We study the effects of assembly bias above collapse mass in the context of 'age matching' and show that these effects are markedly different compared to the ones explored by Hearin et al. at lower stellar masses. We construct two models, one in which galaxy colour is stochastic ('AbM' model) as well as a model which contains assembly bias effects ('AgM' model). By confronting the redshift dependent clustering of CMASS with the predictions from our model, we argue that that galaxy colours are not a stochastic process in high-mass haloes. Our results suggest that the colours of galaxies in high-mass haloes are determined by other halo properties besides halo peak velocity and that assembly bias effects play an important role in determining the clustering properties of this sample.
                  Cover page: Connecting massive galaxies to dark matter haloes in BOSS – I. Is galaxy colour a stochastic process in high-mass haloes?
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2022)
                  We present high-fidelity cosmology results from a blinded joint analysis of galaxy-galaxy weak lensing (Δς) and projected galaxy clustering (wp) measured from the Hyper Suprime-Cam Year-1 (HSC-Y1) data and spectroscopic Sloan Digital Sky Survey (SDSS) galaxy catalogs in the redshift range 0.15
                    Cover page: Cosmological inference from an emulator based halo model. II. Joint analysis of galaxy-galaxy weak lensing and galaxy clustering from HSC-Y1 and SDSSCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2017)
                    We present high signal-to-noise galaxy-galaxy lensing measurements of the Baryon Oscillation Spectroscopic Survey constant mass (CMASS) sample using 250 deg2 of weak-lensing data from Canada-France-Hawaii Telescope Lensing Survey and Canada-France-Hawaii Telescope Stripe 82 Survey. We compare this signal with predictions from mock catalogues trained to match observables including the stellar mass function and the projected and twodimensional clustering of CMASS. We show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40 per cent larger than observed. Detailed tests show that our results are robust to a variety of systematic effects. Lowering the value of S8 = σ8 √ Ωm/0.3 compared to Planck Collaboration XIII reconciles the lensing with clustering. However, given the scale of our measurement (r < 10 h-1 Mpc), other effects may also be at play and need to be taken into consideration. We explore the impact of baryon physics, assembly bias, massive neutrinos and modifications to general relativity on ΔΣ and show that several of these effects may be non-negligible given the precision of our measurement. Disentangling cosmological effects from the details of the galaxy-halo connection, the effect of baryons, and massive neutrinos, is the next challenge facing joint lensing and clustering analyses. This is especially true in the context of large galaxy samples from Baryon Acoustic Oscillation surveys with precise measurements but complex selection functions.
                      Cover page: Lensing is low: cosmology, galaxy formation or new physics?
                      Top