Browsing by Author "Carignan, Claude"

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    Open Access
    Analysis of SALT Fabry-Pérot medium resolution data
    (2015) Tapsoba, Wendyam Blaise; Williams, Theodore; Carignan, Claude; Lucero, Danielle M
    The Southern African Large Telescope Fabry-Pérot interferometer has been used in its medium resolution mode to observe three of 30 galaxies of the MHONGOOSE galaxy sample for which very deep HI observation (typically 200 hours/galaxy) will be obtained with MeerKAT. So optical high spatial resolution of 2 arcsec data of NGC 7361, NGC 7424 and NGC 7793 have been obtained. The major object of this thesis was to test SALT Fabry-Pérot medium resolution data in order to pursue the survey of all the MHONGOOSE sample, and to be able to compare the accuracy of the kinematic results. Through this work, some FORTRAN based routines have been improved and they allow us to compute kinematic maps with good accuracy. Indeed, the velocities measured from the profiles of the Hα emission in the data cube are accurate with the range of 1 km s⁻¹ to 10 km s⁻¹. So, we computed the kinematic maps and the rotation curves of the three galaxies using DiskFit and ROTCUR. For NGC 7361 and NGC 7424 we compared the rotation curves derived by both methods. For NGC 7793 we were also able to compare our results with previous studies.
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    Open Access
    Correcting the rotation curve of spiral galaxies for the non-circular motions induced by a bar
    (2017) Randriamampandry, Toky Herimandimby; Carignan, Claude
    The mass distribution of disk galaxies is usually determined through the use of rotation curves. This determination relies on two key assumptions; that the gas moves on circular orbits and that this motion traces the underlying gravitational potential. In the case of barred spiral galaxies the first assumption is false as the bar induces non-circular streaming motions in the gas. Therefore, the rotation curves of barred galaxies need to be corrected for the non-circular motions before being used for mass model analysis. In this dissertation, we use numerical simulations to quantify and correct for the non-circular flows induced by a bar. The aim is to investigate and quantify the effect of the bar properties on the amplitude of the non-circular motions. This is done by comparing the observational data such as rotation curves and bar properties with the kinematics and bar properties obtained from mocked galaxies. In chapter III, we examine the performance of ROTCUR and DISKFIT for deriving rotation curves from velocity maps of barred spiral galaxies using mock observations. Our results confirm that ROTCUR under-/overestimates measured rotation curves if the bar is aligned with one of the symmetry axes. The DISKFIT algorithm, which is specifically designed for barred galaxies only works for galaxies of intermediate bar orientations. In chapter IV, we quantify the magnitude of the non-circular flows and constraint the range of bar orientation angles where DiskFit fails by using Tree-SPH simulations from the GalMer database by Chilingarian et al . (2010 ). We found that the rotation curve obtained from ROTCUR was 40% smaller/larger than the expected velocities calculated from the gravitational potential when the bar is aligned with the major/minor axis. For the DISKFIT analysis, we found that DiskFit produces unrealistic values for all the models when the bar is within ten degrees of the symmetry axes. New hydrodynamic simulations of three disc galaxies (NGC 1300 , NGC 1530 and NGC 3621 ) are presented in chapter IV. Our objective is to create more realistic simulated galaxies that replicate the bar properties and velocity elds of the galaxies of our sample. The initial conditions for our simulations are determined through a Bayesian analysis of the azimuthally averaged rotation curve, the stellar surface brightness, and the gas surface density. The parameters posterior distribution functions (PDFs) combine with the disc stability parameters PDFs are used as criterion to select the model parameters. The velocities of the gas particles are transformed into velocity maps and compared with the observed galaxies. We are able to reproduce the bar properties and kinematics of the three galaxies in our sample. These findings imply that a tailored simulation is an effective way of investigating non-circular flows in disc galaxies especially when the bar orientation is close to the minor or major kinematical axis of the galaxy.
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    Deep HI observations of nearby late-type galaxies
    (2019) Sorgho, Amidou; Carignan, Claude
    This thesis makes use of sensitive Hi observations to map the distribution and kinematics of the low column density neutral hydrogen in late-type nearby mostly isolated galaxies and in the nearby M81 group. Using the KAT-7, GBT and MeerKAT AR1 telescopes, we present in the second chapter a survey of the Hi in a sample of twenty nearby, mostly isolated galaxies down to low column density levels. This provided a new Hi view of some of these galaxies, which allowed to derive their kinematics out to unprecedented extents. Despite the short spacings of KAT-7 and MeerKAT AR1, and the large size of the single-dish GBT that make these telescopes ideal for detecting faint structures, the observations revealed no clear detection of low column density Hi clouds down to a typical sensitivity of ∼2.2 × 1018 cm−2 that could be associated to gas accretion in the observed galaxies. However, we do not discard the existence of such structures that, we note, could be in the form of discrete clouds smaller than the beam size of the telescopes. In the third chapter, we use the DRAO telescope to perform a sensitive survey of the Hi in a 5 ◦ × 5 ◦ area of the M81 group. Similarly to previous observations, we find that the three major and interacting galaxies of the group – M81, M82 and NGC 3077 – are connected through Hi bridges and intergalactic Hi clouds. One of the major findings of the survey is the more complete map of the western Hi arm connecting the three galaxies to the dwarf galaxy NGC 2976. These observations offer enough resolution to map the structure of the arm, and reveal a complex of small clouds filling the space between the arm and the Hi forming “main body” of the interacting galaxies. Using a tilted-ring model, we also construct a large-scale rotation curve of the system formed by the interacting galaxies. Consistently with the large-scale velocity field, we observe a flat trend for the rotation velocity of the system from 20 kpc out to 80 kpc, well beyond the outskirts of the M81 disk, although with asymmetries like a wiggle at the vicinity of M82. The fourth chapter focuses on a subset of the M81 survey containing the dwarf galaxy IC 2574 and the Hi complex HIJASS J1021+68. In this chapter we perform a thorough analysis of the distribution and kinematics of the Hi in the two systems, and thanks to the high sensitivity we are able to detect a substantially large amount of low column density Hi around IC 2574, in the form of an Hi envelope, and in two large concentrations around the galaxy. We find evidence that HIJASS J1021+68 – which is found to be connected to IC 2574 through a filament of discrete clouds – is not a dark galaxy as previously suggested, but is instead a complex of clouds either stripped from, or falling onto the primordial Hi envelope of IC 2574. The kinematical analysis of IC 2574 using a 3D tilted-ring model brings us to derive its rotation curve out to a larger extent than previous works and allows us to constrain its Dark Matter halo parameters, which we find consistent with the literature. Overall, the different results presented in this work prove that the Hi content of local galaxies is higher than what current observations reveal, and new sensitive telescopes such as MeerKAT and the upcoming SKA will unveil a new Hi view of galaxies.
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    Open Access
    Deep HI observations of nearby late-type galaxies
    (2019) Sorgho, Amidou; Carignan, Claude
    This thesis makes use of sensitive Hi observations to map the distribution and kinematics of the low column density neutral hydrogen in late-type nearby mostly isolated galaxies and in the nearby M81 group. Using the KAT-7, GBT and MeerKAT AR1 telescopes, we present in the second chapter a survey of the Hi in a sample of twenty nearby, mostly isolated galaxies down to low column density levels. This provided a new Hi view of some of these galaxies, which allowed to derive their kinematics out to unprecedented extents. Despite the short spacings of KAT-7 and MeerKAT AR1, and the large size of the single-dish GBT that make these telescopes ideal for detecting faint structures, the observations revealed no clear detection of low column density Hi clouds down to a typical sensitivity of ∼2.2 × 1018 cm−2 that could be associated to gas accretion in the observed galaxies. However, we do not discard the existence of such structures that, we note, could be in the form of discrete clouds smaller than the beam size of the telescopes. In the third chapter, we use the DRAO telescope to perform a sensitive survey of the Hi in a 5 ◦ × 5 ◦ area of the M81 group. Similarly to previous observations, we find that the three major and interacting galaxies of the group – M81, M82 and NGC 3077 – are connected through Hi bridges and intergalactic Hi clouds. One of the major findings of the survey is the more complete map of the western Hi arm connecting the three galaxies to the dwarf galaxy NGC 2976. These observations offer enough resolution to map the structure of the arm, and reveal a complex of small clouds filling the space between the arm and the Hi forming “main body” of the interacting galaxies. Using a tilted-ring model, we also construct a large-scale rotation curve of the system formed by the interacting galaxies. Consistently with the large-scale velocity field, we observe a flat trend for the rotation velocity of the system from 20 kpc out to 80 kpc, well beyond the outskirts of the M81 disk, although with asymmetries like a wiggle at the vicinity of M82. The fourth chapter focuses on a subset of the M81 survey containing the dwarf galaxy IC 2574 and the Hi complex HIJASS J1021+68. In this chapter we perform a thorough analysis of the distribution and kinematics of the Hi in the two systems, and thanks to the high sensitivity we are able to detect a substantially large amount of low column density Hi around IC 2574, in the form of an Hi envelope, and in two large concentrations around the galaxy. We find evidence that HIJASS J1021+68 – which is found to be connected to IC 2574 through a filament of discrete clouds – is not a dark galaxy as previously suggested, but is instead a complex of clouds either stripped from, or falling onto the primordial Hi envelope of IC 2574. The kinematical analysis of IC 2574 using a 3D tilted-ring model brings us to derive its rotation curve out to a larger extent than previous works and allows us to constrain its Dark Matter halo parameters, which we find consistent with the literature. Overall, the different results presented in this work prove that the Hi content of local galaxies is higher than what current observations reveal, and new sensitive telescopes such as MeerKAT and the upcoming SKA will unveil a new Hi view of galaxies.
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    Open Access
    Distribution of baryonic and dark matter in spiral and irregular nearby galaxies
    (2019) Korsaga, Marie; Amram, Philippe; Carignan, Claude; Epinat, Benoit
    My PhD research is focused on the dark matter (DM) and luminous matter distribution in spiral and irregular galaxies. Studying this matter could clearly improve our knowledge on the formation and evolution of galaxies. While the overall description of the baryon content of galaxies is now well known, we will now use the kinematics to understand the distribution of DM, especially in the inner parts of galaxies. To do this, I study the distribution of the luminous and DM in nearby galaxies. The study consists of using the GHASP (Gassendi HAlpha survey of SPirals) sample which allows me to investigate the distribution of the DM halos in the inner regions of galaxies, by connecting the kinematical data from the optical observations to the photometry data available in the literature. After summarizing the global properties of the luminous and DM of galaxies, I present the instruments based on the FabryPerot interferomter used to observe the GHASP survey. I also present the different photometry (infrared and optical bands) data, and models used to determine the distribution of luminous and DM inside galaxies. In chapter 2, we present the kinematical data and the infrared photometry data available in the literature used to construct galaxy mass models. For the kinematical data, we use rotation curves from the GHASP survey. For the photometry data, we use the luminosity profile of the mid-infrared W1 and W2 (3.4 and 4.6 µm) of WISE (Wide-field Infrared Survey Explorer), which probes the emission from the old stellar population. The radial profile is decomposed if necessary to multiple components (bulge, disc, bar, spiral arm, ect.). Combining the optical kinematical data with the infrared photometry data allows us to determine the mass distribution of the sample of 121 galaxies covering morphological types from S0 to Irr, and therefore to understand how the DM halo is distributed in early type spiral compared to late type spiral and irregular galaxies. We use two main models to describe the shape of the DM halos in galaxies: the pseudo-isothermal core density profile and the Navarro-Frenk-White cuspy density profile. We allow the mass-to-light ratios of the disc and if necessary the bulge to vary and we keep them fixed by the colour (W1- W2). We also explore the maximum disc for the pseudo-isothermal model. We find that the two profiles describe well the rotations curves while the pseudo-isothermal model gives better results. In order, to understand how the DM is distributed, we study relations between the parameters of the DM and the luminosity of galaxies. We find that the relations between the DM halo parameters and the luminosity of galaxies depend on the morphological types (presence of bulge or not in galaxies). In chapter 3, we present the mass distribution of 100 early and late type spiral and irregular galaxies by combining the kinematical data (Hα rotation curves) with the optical Rc band photometry data available in the literature. We use the same methods and descriptions given in Chapter 2. The mass-to light ratios are now fixed using the (B - V) colour. We compare the results obtained using the optical Rc band photometry to the W1 band photometry. We find similar results on the DM halo parameters but the values are higher for the mass-to-light ratios in the Rc band than in the W1. However the dispersion in the model parameters is smaller and because stellar masses are better defined, the infrared photometry should be preferred, when possible, to the optical band. The Hi rotation curves are crucial in studying the distribution of the DM in the inner and outer regions of galaxies. In chapter 4, we first construct the mass distribution of 31 galaxies using the Hα rotation curves and mid-IR photometry data used in chapter 2 with the addition of the contribution from the Hi gas component. Secondly, the mass distribution is determined with the same photometry and gas component but using hybrid (Hα and Hi) extended rotation curves. Lastly, the mass distribution is constructed using Hi kinematical data. The main goal is to understand how the luminous and DM parameters may vary when using the different kinematical data. We use the same models to construct the mass models and the fitting procedures as described in chapter 2. We find that the relation between the parameters varies from one dataset to the other.
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    HI in group interactions: HCG 44
    (2017) Hess, Kelley M; Cluver, M E; Yahya, Sahba; Leisman, Lukas; Serra, Paolo; Lucero, Danielle M; Passmoor, Sean S; Carignan, Claude
    Extending deep observations of the neutral atomic hydrogen (H I) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example, and we have combined H I data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N _{H {I}}
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    HI survey of local group dwarf galaxies
    (2019) Namumba, Brenda; Carignan, Claude
    This thesis investigates the HI properties of 3 dwarf irregular galaxies and one blue compact dwarf galaxy of the Local Group. The data set of each dwarf irregular galaxy was obtained with the Karoo Array Telescope (KAT-7) while the blue compact dwarf was observed with the Dominion Radio Astrophysical Observatory (DRAO) synthesis telescope. While the main purpose of KAT-7 was to test technical solutions for MeerKAT, its capabilities, and that of DRAO, have enabled us to produce interesting Square Kilometer Array (SKA) pathfinder science. The compact configuration of the two telescopes, coupled with low system temperatures (Ts ys) provide a unique HI dataset on nearby dwarf galaxies; sensitivity to extended HI emission while providing intermediate resolution to derive the large scale kinematics. The following properties are investigated in details: i) the HI distribution, ii) kinematics and mass distribution, iii) star formation thresholds, and iv) possible mechanisms for the chaotic HI structure and kinematics in a blue compact dwarf galaxy. The main results of our study are: from the HI distribution, the KAT-7 results have revealed even more neutral gas mass in the outer disk of NGC 6822. We detect 23% more HI mass in NGC 6822 than what was detected with the Australian Telescope Compact Array (ATCA). The KAT-7 results have been able to show an overestimate of the HI extent previously reported for Sextans A using Effelsberg observations. For IC 10, the complex HI features detected with DRAO are by a factor of ∼ 2 more extended than previous interferometric HI studies. Rotation velocities are derived for each galaxy. For NGC 6822, the rotation curve probes the gravitational potential out to 5.8 kpc, ∼ 1 kpc further than existing measurements. The rotation curves of Sextans A and B decline in the outer regions and extends out to 3.5 kpc and 4 kpc respectively. The central region of IC 10 has a regularly rotating disk, and the rotation velocities rise slowly in the inner region < 0.35 kpc. Beyond this radius the velocities are almost constant until the last point where it rises again reaching a maximum velocity of ∼ 30 km s−1 . Mass models are used to describe the distribution of dark matter. The dark matter models used are the Navarro-Frenk and White (NFW) and pseudo-isothermal (ISO) sphere. The dark matter distribution in dwarf irregular galaxies is better described by the ISO model when a mass to light ratio of 0.2 is used. This M/L value was derived for the Spitzer 3.6 µm band surface brightness profiles. The galaxies are dark matter dominated at all radii, and the stellar potential is insignificant to account for the total observed kinematics. In the case of IC 10, the kinematics of the inner disk can be described without the need of a dark matter halo. This result does not exclude the possible presence of dark matter on larger scales. Critical densities for gravitational instabilities are calculated using a one-dimensional Toomre-Q and cloud-growth based on shear criterion for the 3 dwarf irregular galaxies. In all cases, we find that in regions of star formation, the cloud growth criterion based on shear explains better the star formation. This suggests that the local shear rate could be a key player in cloud formation for irregular galaxies. Simulations are carried out to investigate if an interaction between IC 10 and M 31 can reproduce the observed HI morphology and kinematics of IC 10. The simulations are carried out using the GALACTICS code. From these simulations, it is unlikely that the HI features we see in IC 10 are caused by an interaction with M 31. The features seen in the simulations are both larger and at lower column density than what can be reached by current observations. The HI extensions with different kinematics seen south, east and west of the main core of IC 10 are more likely the result of accretion.
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    Observing galaxies in the Southern Filament of the Virgo Cluster with KAT-7 and WSRT
    (2015) Sorgho, Amidou; Carignan, Claude; Van Gorkom, Jacqueline H; Hess, Kelley M
    To date, our understanding of the formation and evolution of galaxies attributes a very important role to the neutral hydrogen (HI) gas since it constitutes the reservoir of fuel out of which galaxies form stars. In their evolution, galaxies interact with each other and with their environment, and very often these interactions leave fingerprints in the HI distribution. The extended HI envelopes of galaxies are sensitive tracers of those tidal interactions. In the present study, we map the HI distribution of galaxies in a ~1.5° X 2.5° region of the Virgo cluster using the Karoo Array Telescope (KAT-7) and the Westerbork Synthesis Radio Telescope (WSRT). With a total observing time of ~78 hours with the KAT-7 and 48 hours with the WSRT, we search for low HI column density features in the region. Despite the different observing time and beam size of the two telescopes, we reach similar column density sensitivities of NHI ~1 X 10¹⁸ atoms cm⁻² over 16.5kms⁻¹. With a new approach, we combine the two observations to map both the large and small scale structures. We detect, out to an unprecedented extent, an HI tail of ~60 kpc being stripped off NGC 4424, a peculiar spiral galaxy. The properties of the galaxy, together with the shape of the tail, suggests that NGC 4424 is a post-merger galaxy undergoing a ram pressure stripping as it falls into the centre of the Virgo Cluster along a filamentary structure. We also give the HI parameters of the galaxies detected.
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    The star formation and dynamics of nearby galaxies
    (2016) Mogotsi, Keoikantse Moses; Carignan, Claude; Meurer, G R; De Blok, W J G
    A scaling relation between the surface density of star formation and gas in the disks of galaxies has become the basis of our understanding of extragalactic star formation on scales of hundreds of parsecs and larger. This is an empirical law but star formation is a complex process - the presence of gas at sufficiently high densities to collapse and form stars depends on a wide variety of physical processes. These processes can be thought of in terms of the stability of galaxy disks, which is a balance between the gravitational force and competing forces such as the outward force due to pressure. In this study I explore how star formation is related to galaxy dynamics in the central regions of galaxies. This is done by determining the dominant contributor to the inner dynamics of galaxies and developing star formation models based on self-regulating disks that maintain a constant sub-critical stability parameter. Stability parameters for a gas-only disk and a two- uid disk containing both gas and stars are considered. These models are tested in the central regions of a sample of galaxies with a wide range of Hi masses, sizes, morphologies and stellar masses. The analysis is performed using Hα integral field spectroscopy, R-band, narrowband Hα, and near-infrared photometry to determine the star formation rates and kinematics of the galaxies. In agreement with previous studies I find that the central stellar surface density is tightly correlated with the central velocity gradient, which traces the steepness of the inner gravitational well. The baryonic fractions found in the analysis suggest that baryons dominate the central density of most galaxies in the sample, but better constraints on these are needed to make more firm conclusions. There are correlations between the star formation surface density and velocity gradient, however the observed relations do not match predictions from the models. Tests suggest that the failure of the models is due to the implied stability parameters in the galaxy centers not being constant across the galaxy sample, and that the star formation laws used in the analysis may not hold over the full parameter space of the sample.