Distribution of baryonic and dark matter in spiral and irregular nearby galaxies

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

Disk galaxies are self-similar: the universality of the HI-to-Halo mass ratio for isolated disks

Observed scaling relations in galaxies between baryons and dark matter global properties are key to shed light on the process of galaxy formation and on the nature of dark matter. Here, we study the scaling relation between the neutral hydrogen (HI) and dark matter mass in isolated rotationally-supported disk galaxies at low redshift. We first show that state-of-the-art galaxy formation simulations predict that the HI-to-dark halo mass ratio decreases with stellar mass for the most massive disk galaxies. We then infer dark matter halo masses from high-quality rotation curve data for isolated disk galaxies in the local Universe, and report on the actual universality of the HI-to-dark halo mass ratio for these observed galaxies. This scaling relation holds for disks spanning a range of 4 orders of magnitude in stellar mass and 3 orders of magnitude in surface brightness. Accounting for the diversity of rotation curve shapes in our observational fits decreases the scatter of the HI-to-dark halo mass ratio while keeping it constant. This finding extends the previously reported discrepancy for the stellar-to-halo mass relation of massive disk galaxies within galaxy formation simulations to the realm of neutral atomic gas. Our result reveals that isolated galaxies with regularly rotating extended HI disks are surprisingly self-similar up to high masses, which hints at mass-independent self-regulation mechanisms that have yet to be fully understood.Comment: 14 pages, 4 figures. Accepted for publication in ApJ

MIGHTEE-\HI: Possible interactions with the galaxy NGC~895

The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (\HI) is an excellent way to trace these interactions. Here, we present \HI\ observations of the spiral galaxy NGC~895, which was previously thought to be isolated. High-sensitivity \HI\ observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms, and the two newly discovered \HI\ companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH$\_$J022138.1-052631 which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC~895 is an actively star-forming galaxy with a SFR of $\mathrm{1.75 \pm 0.09 [M_{\odot}/yr]}$, a value typical for high stellar mass galaxies on the star forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC~895 and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both \HI\ and optical to reveal a more complete picture of galaxy environments.Comment: 14 pages, 10 figures. Accepted for publication in MNRA

Distribution de la matière baryonique et noire dans les galaxies spirales et irrégulières

Ma thèse porte sur la distribution de la matière noire et ordinaire dans les galaxies spirales et irrégulières. Pour ce faire, j’ai modélisé la distribution de masse dans les galaxies en composantes multiples, baryoniques (disque et bulbe) et non baryonique (halo de matière noire). Dans la première partie, j’étudie la distribution de masse de 121 galaxies spirales et irrégulières en utilisant des courbes de rotation Hα à haute résolution et des données photométriques dans l’infrarouge moyen W1 et W2 (3.4 et 4.6 μm) de WISE. Pour construire les modèles de masse, j’utilise le profil de densité pseudo-isotherme, uniforme dans le centre du halo des galaxies et le profil de densité cuspide Navarro-Frenk-White. Je permets aux rapports masse-sur-luminosité du disque et le cas échéant du bulbe de varier et je les fixe par la couleur (W1-W2). J’explore aussi l’hypothèse du disque maximal pour le modèle pseudo-isotherme. Je trouve que les relations entre les paramètres du halo de matière noire et la luminosité des galaxies dépendent de la présence de bulbe ou non dans les galaxies. Dans la seconde partie, une étude similaire est réalisée sur 100 galaxies utilisant des courbes de rotation Hα et la photométrie en bande visible Rc. Le rapport masse-sur-luminosité est maintenant fixé par la couleur (B - V). J’ai comparé les résultats obtenus avec ceux de la photométrie W1 et trouvé des résultats similaires. Cependant, la dispersion dans les paramètres est plus petite, donc, la photométrie infrarouge devrait être préférée à l’optique. Dans la troisième partie, j’ai déterminé les modèles de masse de 31 galaxies en combinant les courbes de rotation Hα et HI.My PhD research is focused on the dark and luminous matter distribution in spiral and irregular galaxies. To do this, I modeled the mass distribution in galaxies in multiple component, baryonics (disc and bulge) and non-baryonic (dark matter halo). In the first part, I study the mass distribution of 121 spirales and irregular galaxies using high quality Hα rotation curves and the mid-infrared W1 and W2 (3.4 and 4.6 μm) of WISE photometry. To construct the mass models, I use the pseudo-isothermal core density profile and the Navarro-Frenk-White cuspy density profile. I allow the mass-to-light ratios of the disc and if necessary the bulge to vary and I keep them fixed by the colour (W1-W2). I also explore the maximum disc for the pseudo-isothermal model. I find that the relations between the dark matter parameters and the luminosity of galaxies depend on the presence of bulge or not in galaxies. In the second part, a similar study is made on 100 galaxies using Hα rotation curves and the optical Rc-band photometry. The mass-to light ratios are now fixed by the (B - V) colour. I compared the results obtained with those using W1 photometry and found similar results. However the dispersion in the parameters is smaller, the infrared photometry should be preferred, when possible, to the optical one. In the third part, I determined the mass models of 31 galaxies by combining Hα and HI rotation curves

GHASP: an H α kinematical survey of spiral galaxies – XI. Distribution of luminous and dark matter in spiral and irregular nearby galaxies using WISE photometry

23 pages, 18 figures, accepted for publication on MNRAS. Online data are found on the journal websiteInternational audienceWe present the mass distribution of a sample of 121 nearby galaxies with high quality optical velocity fields and available infra-red $\it{WISE}$ 3.4 $\mu$m data. Contrary to previous studies, this sample covers all morphological types and is not biased toward late-type galaxies. These galaxies are part of the Fabry-Perot kinematical $\it{GHASP}$ survey of spirals and irregular nearby galaxies. Combining the kinematical data to the $\it{WISE}$ surface brightness data probing the emission from the old stellar population, we derive mass models allowing us to compare the luminous to the dark matter halo mass distribution in the optical regions of those galaxies. Dark matter (DM) models are constructed using the isothermal core profile and the Navarro-Frenk-White cuspy profile. We allow the M/L of the baryonic disc to vary or we keep it fixed, constrained by stellar evolutionary models (WISE W$_1$-W$_2$ color) and we carry out best fit (BFM) and pseudo-isothermal maximum disc (MDM) models. We found that the MDM provides M/L values four times higher than the BFM, suggesting that disc components, on average, tend to be maximal. The main results are: (i) the rotation curves of most galaxies are better fitted with core rather than cuspy profiles; (ii) the relation between the parameters of the DM and of the luminous matter components mostly depends on morphological types. More precisely, the distribution of the DM inside galaxies depends on whether or not the galaxy has a bulge

Looking at the distant universe with the MeerKAT array: discovery of a luminous OH megamaser at z > 0.5

In the local universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (H i), radio surveys to probe the cosmic evolution of H i in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep H i survey, we report the first untargeted detection of an OHM at z > 0.5, LADUMA J033046.20-275518.1 (nicknamed "Nkalakatha"). The host system, WISEA J033046.26-275518.3, is an infrared-luminous radio galaxy whose optical redshift z ≈ 0.52 confirms the MeerKAT emission-line detection as OH at a redshift z OH = 0.5225 ± 0.0001 rather than H i at lower redshift. The detected spectral line has 18.4σ peak significance, a width of 459 ± 59 km s-1, and an integrated luminosity of (6.31 ± 0.18 [statistical] ± 0.31 [systematic]) × 103 L ⊙, placing it among the most luminous OHMs known. The galaxy's far-infrared luminosity L FIR = (1.576 ±0.013) × 1012 L ⊙ marks it as an ultraluminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step toward a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts

Looking at the Distant Universe with the MeerKAT Array: Discovery of a luminous OH megamaser at z>0.5z > 0.5

In the local Universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (HI), radio surveys to probe the cosmic evolution of HI in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep HI survey, we report the first untargeted detection of an OHM at $z > 0.5$, LADUMA J033046.20$-$275518.1 (nicknamed "Nkalakatha"). The host system, WISEA J033046.26$-$275518.3, is an infrared-luminous radio galaxy whose optical redshift $z \approx 0.52$ confirms the MeerKAT emission line detection as OH at a redshift $z_{\rm OH} = 0.5225 \pm 0.0001$ rather than HI at lower redshift. The detected spectral line has 18.4$\sigma$ peak significance, a width of $459 \pm 59\,{\rm km\,s^{-1}}$, and an integrated luminosity of $(6.31 \pm 0.18\,{\rm [statistical]}\,\pm 0.31\,{\rm [systematic]}) \times 10^3\,L_\odot$, placing it among the most luminous OHMs known. The galaxy's far-infrared luminosity $L_{\rm FIR} = (1.576 \pm 0.013) \times 10^{12}\,L_\odot$ marks it as an ultra-luminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step towards a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts