Browsing by Author "Bershady, Matthew"

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    Open Access
    Kinematics of neutral hydrogen in interacting galaxies in two groups from the MeerChoirs survey
    (2023) Sankar, Sriram; Bershady, Matthew
    It is well known that galaxies shape and are shaped by their environments, but the relative contribution of environmental and internal galactic processes remains poorly understood. HI 21 cm is the ideal tracer to study the role of environments in shaping galaxies in the local universe as the extended distribution of neutral hydrogen makes it susceptible to a wide range of environmental effects that produce peculiar HI morphologies. Moreover, HI enables the study of how galaxies obtain and lose cold gas. The HI distribution of galaxies often exhibits warps, lopsidedness, and the presence of anomalous gas (AG) such as the Extraplanar Gas (EPG). In this era of resolved, sensitive HI observations, one exciting possibility is the identification of AG associated with galaxies experiencing a wide range of environmental effects. However, the task of separating AG and the disc is non-trivial due to fundamental limitations induced by instrumental effects (e.g., spatial and spectral resolution), projection effects, and systematic effects (e.g., assumptions, methods). In this work, we demonstrate a method we developed to separate anomalous gas from the disc based on physically motivated Gaussian decomposition and kinematic tagging. We perform a comprehensive analysis of the kinematics of the neutral gas in two nearby low-mass, gas-rich, late-type dominated, and relatively isolated groups from the MeerChoirs survey. The two groups, HIPASS J1250-20 and HIPASS J1403-06, both contain interacting pairs in the centre that showcase unique HI morphologies. In the groups, we investigate the impact of two ongoing co-rotating minor mergers, an intermediate-stage counter-rotating major merger, and an intermediate-stage co-rotating major merger. Additionally, we characterize several previously known and unknown dwarfs in the groups and the extended fields. We extract the kinematics of the extended, warped, and lopsided discs of the interacting galaxies using 3D tilted ring modelling. Employing techniques we developed, we detect and examine copious amounts of anomalous gas produced in the interactions in the form of leading gas, lagging gas, extended envelopes, tails, and bridges. By combining the kinematics, deep optical images, and ancillary evidence from the literature we relate the anomalous gas to star formation in the discs and the interactions. We detect gas exchange between the interacting pairs and enhanced star formation in the galaxies experiencing inflow. Notably, we report the farthest characterised EPG to date in HIPASS J1403:06 at a distance of 40 Mpc, which is also among the most massive EPG reservoirs ever studied. Furthermore, the 150 kpc long envelope of HIPASS J1250-20:S1 with a total HI mass of log MHI ∼ 10.72 M⊙ is among the most HI-rich galaxies in the literature. We posit plausible formation scenarios for the extended envelope in HIPASS J1250-20:S1 and the ∼ 90 kpc long unidirectional transverse tails observed in HIPASS J1403-06. We suspect misaligned gas accretion from companions for the former and a combination of collisional and tidal origin for the latter. Such studies of gas kinematics and galaxy dynamics across different environments will deepen our understanding of the baryon cycle, galaxy interactions, and the impact of the environment on galaxy evolution.
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    Open Access
    Kinematics of neutral hydrogen in interacting galaxies in two groups from the MeerChoirs survey
    (2023) Sankar, Sriram; Bershady, Matthew
    It is well known that galaxies shape and are shaped by their environments, but the relative contribution of environmental and internal galactic processes remains poorly understood. HI 21 cm is the ideal tracer to study the role of environments in shaping galaxies in the local universe as the extended distribution of neutral hydrogen makes it susceptible to a wide range of environmental effects that produce peculiar HI morphologies. Moreover, HI enables the study of how galaxies obtain and lose cold gas. The HI distribution of galaxies often exhibits warps, lopsidedness, and the presence of anomalous gas (AG) such as the Extraplanar Gas (EPG). In this era of resolved, sensitive HI observations, one exciting possibility is the identification of AG associated with galaxies experiencing a wide range of environmental effects. However, the task of separating AG and the disc is non-trivial due to fundamental limitations induced by instrumental effects (e.g., spatial and spectral resolution), projection effects, and systematic effects (e.g., assumptions, methods). In this work, we demonstrate a method we developed to separate anomalous gas from the disc based on physically motivated Gaussian decomposition and kinematic tagging. We perform a comprehensive analysis of the kinematics of the neutral gas in two nearby low-mass, gas-rich, late-type dominated, and relatively isolated groups from the MeerChoirs survey. The two groups, HIPASS J1250-20 and HIPASS J1403-06, both contain interacting pairs in the centre that showcase unique HI morphologies. In the groups, we investigate the impact of two ongoing co-rotating minor mergers, an intermediate-stage counter-rotating major merger, and an intermediate-stage co-rotating major merger. Additionally, we characterize several previously known and unknown dwarfs in the groups and the extended fields. We extract the kinematics of the extended, warped, and lopsided discs of the interacting galaxies using 3D tilted ring modelling. Employing techniques we developed, we detect and examine copious amounts of anomalous gas produced in the interactions in the form of leading gas, lagging gas, extended envelopes, tails, and bridges. By combining the kinematics, deep optical images, and ancillary evidence from the literature we relate the anomalous gas to star formation in the discs and the interactions. We detect gas exchange between the interacting pairs and enhanced star formation in the galaxies experiencing inflow. Notably, we report the farthest characterised EPG to date in HIPASS J1403:06 at a distance of 40 Mpc, which is also among the most massive EPG reservoirs ever studied. Furthermore, the 150 kpc long envelope of HIPASS J1250-20:S1 with a total HI mass of log MHI ∼ 10.72 M⊙ is among the most HI-rich galaxies in the literature. We posit plausible formation scenarios for the extended envelope in HIPASS J1250-20:S1 and the ∼ 90 kpc long unidirectional transverse tails observed in HIPASS J1403-06. We suspect misaligned gas accretion from companions for the former and a combination of collisional and tidal origin for the latter. Such studies of gas kinematics and galaxy dynamics across different environments will deepen our understanding of the baryon cycle, galaxy interactions, and the impact of the environment on galaxy evolution.
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    Open Access
    Kinematics of neutral hydrogen in interacting galaxies in two groups from the MeerChoirs survey
    (2023) Sankar, Sriram; Bershady, Matthew
    It is well known that galaxies shape and are shaped by their environments, but the relative contribution of environmental and internal galactic processes remains poorly understood. HI 21 cm is the ideal tracer to study the role of environments in shaping galaxies in the local universe as the extended distribution of neutral hydrogen makes it susceptible to a wide range of environmental effects that produce peculiar HI morphologies. Moreover, HI enables the study of how galaxies obtain and lose cold gas. The HI distribution of galaxies often exhibits warps, lopsidedness, and the presence of anomalous gas (AG) such as the Extraplanar Gas (EPG). In this era of resolved, sensitive HI observations, one exciting possibility is the identification of AG associated with galaxies experiencing a wide range of environmental effects. However, the task of separating AG and the disc is non-trivial due to fundamental limitations induced by instrumental effects (e.g., spatial and spectral resolution), projection effects, and systematic effects (e.g., assumptions, methods). In this work, we demonstrate a method we developed to separate anomalous gas from the disc based on physically motivated Gaussian decomposition and kinematic tagging. We perform a comprehensive analysis of the kinematics of the neutral gas in two nearby low-mass, gas-rich, late-type dominated, and relatively isolated groups from the MeerChoirs survey. The two groups, HIPASS J1250-20 and HIPASS J1403-06, both contain interacting pairs in the centre that showcase unique HI morphologies. In the groups, we investigate the impact of two ongoing co-rotating minor mergers, an intermediate-stage counter-rotating major merger, and an intermediate-stage co-rotating major merger. Additionally, we characterize several previously known and unknown dwarfs in the groups and the extended fields. We extract the kinematics of the extended, warped, and lopsided discs of the interacting galaxies using 3D tilted ring modelling. Employing techniques we developed, we detect and examine copious amounts of anomalous gas produced in the interactions in the form of leading gas, lagging gas, extended envelopes, tails, and bridges. By combining the kinematics, deep optical images, and ancillary evidence from the literature we relate the anomalous gas to star formation in the discs and the interactions. We detect gas exchange between the interacting pairs and enhanced star formation in the galaxies experiencing inflow. Notably, we report the farthest characterised EPG to date in HIPASS J1403:06 at a distance of 40 Mpc, which is also among the most massive EPG reservoirs ever studied. Furthermore, the 150 kpc long envelope of HIPASS J1250-20:S1 with a total HI mass of log MHI ∼ 10.72 M⊙ is among the most HI-rich galaxies in the literature. We posit plausible formation scenarios for the extended envelope in HIPASS J1250-20:S1 and the ∼ 90 kpc long unidirectional transverse tails observed in HIPASS J1403-06. We suspect misaligned gas accretion from companions for the former and a combination of collisional and tidal origin for the latter. Such studies of gas kinematics and galaxy dynamics across different environments will deepen our understanding of the baryon cycle, galaxy interactions, and the impact of the environment on galaxy evolution.
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    Open Access
    Neutral hydrogen mass distributions in galaxies uncovered by three-dimensional stacking
    (2025) Firth, Andrew; Bershady, Matthew
    Atomic hydrogen (HI) serves as the raw fuel from which the star-forming molecular hydrogen forms - making it an important tracer of galaxy evolution. Due to the intrinsic faintness of the HI emission line (observed at rest at 21 cm), detecting HI emission in galaxies beyond a z = 0.1 becomes difficult, thus, many statistical techniques have since been developed in order to extend the capabilities of already rapidly improving radio observatories. HI stacking is one such technique, involving the co-addition of the HI spectra of a sample of galaxies, exploiting statistical properties of random noise to achieve a high signal-to-noise measure of their average HI content. While this technique focuses on extracted one-dimensional spectra, research extending this concept to the parent data-cube of the one-dimensional spectra is a growing area of research. Studies such as those by (Chen et al., 2021; Sinigaglia et al.,2022) focus on stacking in three-dimensions to improve the point-spread function, HI signal detectability, and hence improve HI mass measurements.We present an initial exploration of a novel approach to stacking, working at the level of imaged radio cubelets, i.e., in three dimensions (3D). Unlike previous stacking works focusing on the UV-plane, and extracts a one-dimensional profile to recover the average HI-mass of the stack, we attempt to recover fine structure within the stack. While our sample sizes prove to be the reason for the limited results, we demonstrate the potential increase in signal-to- noise by assessing the effect sigma-clipping a of stacking on galaxy surface-brightness profiles; comparing one-dimensional and three-dimensionally co-added techniques simultaneously. Using full-resolution data cubes from the Noordermeer et al. (2005) sub-sample of Wester- bork observations of neutral Hydrogen in Irregular and Spiral galaxies (WHISP) survey (van dermHulst et al., 2001), we make use of the homogeneous data reduction pipeline, well-documented global properties, and mass-distribution studies to calibrate our stacking suite. In developing this pipeline, we demonstrate the concept of aligning signal through various geometric transformations (rotation, stretching, and spectral-inversion) as a first approach to a ‘Comprehensive Unearthing of Baryons in Extended-regions using a Stacker' (Cube Stacker). Developed in Python 3.8, this pipeline bridges the gap of stacking techniques targeted at re-solved targets, preserving structure with the aim of utilising an improved SNR to uncover faint HI features. While our stacking is based on 21cm measurements of HI distributions, we ex-plore the possibility of utilising galaxy scaling-relations - incorporating the high-fidelity optical measurements of galaxies to be observed with high-sensitivty facilities such as MeerKAT. Thus, we present measures of central concentration (i.e. C80,20) for the 33 NSA-selected galaxies, and discuss the merits of an optically-based stacking-pipeline in uncovering faint HI in existing or upcoming blind surveys.
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    Open Access
    The gas content of luminous compact blue galaxies in the COSMOS field
    (2024) Arlow, Henco; Pisano, Daniel J; Bershady, Matthew
    Luminous compact blue galaxies (LCBGs) are a heterogeneous subset of starburst galaxies. Their number density drops quite significantly as we approach lower redshifts. As a set of galaxies that evolve quickly, they make excellent candidates for studying galactic evolution as a whole. In order to understand how galaxies evolve, we make use of LCBGs to study their gas content as it changes over approximately nine billion years of lookback time. We make use of HI emission line data provided by the full CHILES survey, covering a redshift range of z=0 to z=0.45 within the COSMOS f ield as well as continuum data of the same field provided by the CHILES Continuum Polarization survey. In this thesis we set out to study the properties of LCBGs in these f ields to better understand the nature of these objects as they evolve to the present day. We report on direct detections of HI found in LCBGs in CHILES.Wealsoperform acubelet stacking technique on LCBGs for which we have known spectroscopic redshifts in CHILES. From these stacks we measure average HI masses as well as upper limit values for non-detections to study how it evolves with redshift. We also measure the star formation rates of a set of LCBGs using continuum fluxes in CHILES Con Pol and compare our results to measurements made with data from CHILES's first epoch. Continuum stacking is then performed in several redshift and stellar mass bins to extract average star formation rates. We proceed to fit appropriate functions to these relations in order to quantify the dependence of LCBG sSFRs to their stellar mass and redshift.
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    Open Access
    The WiFeS Ionized Gas Kinematics of the Edge-on Galaxy J1447-17
    (2021) Mputle, Omphemetse Kelebogile; Mogotsi, Moses; Bershady, Matthew
    The presence of extraplanar diffuse ionized gas (eDIG) and galactic winds and outflows in the late Universe has been observed to be ubiquitous in nearby star-forming spiral galaxies. Optical integral field spectroscopic data from the Wide Field Spectrograph (WiFeS) on the 2.3m Australian National University Telescope is used to determine if the nearby edge-on galaxy J1447-17 from the SINGG survey hosts eDIG, winds or outflows. Tests used to detect their existence include the presence of multiple components in the Hα signal, an increased velocity dispersion in the off-plane region relative to the disk, residuals in the velocity asymmetry map and an enhanced line-ratio ([N II]λ6583/Hα) corresponding to a decrease in the Hα intensity in the case of eDIG. The absence of profiles meeting the line-ratio condition and absence of multiple Hα components compounded with strong residuals in the velocity asymmetry map are not indicative of the galaxy possessing diffuse ionized gas. Ionization cone signatures in the velocity dispersion map together with the velocity asymmetry map and greater dispersion in the off-plane regions than in the disk indicate that the galaxy hosts a galactic wind.