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Carignan C.,University of Cape Town | Carignan C.,Observatoire Dastrophysique Of Luniversite Of Ouagadougou | Libert Y.,University of Cape Town | Lucero D.M.,University of Cape Town | And 6 more authors.
Astronomy and Astrophysics | Year: 2016

Pisces A and Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 Hi clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims. We derive the Hi content and kinematics of Pisces A and B. Methods. Our aperture synthesis Hi observations used the seven-dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results. The low rotation velocities of ~5 km s-1 and ~10 km s-1 in Pisces A and B, respectively, and their Hi content show that they are really dwarf irregular galaxies (dIrr). Despite that small rotation component, it is more the random motions ~9-11 km s-1 that provide most of the gravitational support, especially in the outer parts. The study of their kinematics, especially the strong gradients of random motions, suggest that those two dwarf galaxies are not yet in equilibrium. Conclusions. These Hi- rich galaxies may be indicative of a large population of dwarfs at the limit of detectability. However, such gas-rich dwarf galaxies will most likely never be within the virial radius of MW-type galaxies and become subhalo candidates. Systems such as Pisces A and B are more likely to be found at a few Mpc s from MW-type galaxies. © 2016 ESO.

De Denus-Baillargeon M.-M.,University of Montreal | Hernandez O.,University of Montreal | Boissier S.,Aix - Marseille University | Amram P.,Aix - Marseille University | And 3 more authors.
Astrophysical Journal | Year: 2013

The baryonic mass-to-light ratio (Υ) used to perform the photometry-to-mass conversion has a tremendous influence on the measurement of the baryonic content and distribution as well as on the determination of the dark halo parameters. Since numerous clues hint at an inside-out formation process for galaxies, a radius-dependant Υ is needed to physically represent the radially varying stellar population. In this article, we use chemo-spectrophotometric galactic evolution (CSPE) models to determine Υ for a wide range of masses and sizes in the scenario of an inside-out formation process by gas accretion. We apply our method to a SINGS subsample of 10 spiral and dwarf galaxies with photometric coverage ranging from the UV to the mid-IR. The CSPE models prove to be a good tool for weighting the different photometric bands in order to obtain consistent stellar disk masses regardless of the spectral band used. On the other hand, we show that the color index versus Υ relation is an imperfect tool for assigning masses to young stellar populations because of the degeneracy affecting Υ in all bands at low color index. The disks resulting from our analysis are compatible with the maximum disk hypothesis provided that an adequate bulge/disk decomposition is performed and that the correction for the presence of a bar is not neglected since bars disturb the internal disk kinematics. Disk-mass models including Υ as a free parameter as well as models using our physically motivated, radially varying Υ are presented and discussed for each galaxy. © 2013. The American Astronomical Society. All rights reserved.

Hess K.M.,University of Cape Town | Hess K.M.,University of Groningen | Hess K.M.,Netherlands Institute for Radio Astronomy | Jarrett T.H.,University of Cape Town | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

The Antlia Cluster is a nearby, dynamically young structure, and its proximity provides a valuable opportunity for detailed study of galaxy and group accretion on to clusters. We present a deep HI mosaic completed as part of spectral line commissioning of the Karoo Array Telescope (KAT-7), and identify infrared counterparts from the Widefield Infrared Survey Explorer extended source catalogue to study neutral atomic gas content and star formation within the cluster. We detect 37 cluster members out to a radius of ~0.9 Mpc with MHI > 5 × 107M⊙. Of these, 35 are new HI detections, 27 do not have previous spectroscopic redshift measurements, and one is the Compton thick Seyfert II, NGC 3281, which we detect in HI absorption. The HI galaxies lie beyond the X-ray-emitting region 200 kpc from the cluster centre and have experienced ram pressure stripping out to at least 600 kpc. At larger radii, they are distributed asymmetrically suggesting accretion from surrounding filaments. Combining HI with optical redshifts, we perform a detailed dynamical analysis of the internal substructure, identify large infalling groups, and present the first compilation of the largescale distribution of HI and star-forming galaxies within the cluster. We find that elliptical galaxy NGC 3268 is at the centre of the oldest substructure and argue that NGC 3258 and its companion population are more recent arrivals. Through the presence of HI and ongoing star formation, we rank substructures with respect to their relative time since accretion on to Antlia. © 2015 The Authors.

Hlavacek-Larrondo J.,University of Montreal | Hlavacek-Larrondo J.,Institute of Astronomy | Marcelin M.,French National Center for Scientific Research | Epinat B.,Toulouse 1 University Capitole | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

It has been suggested that diffuse ionized gas can extend all the way to the end of the Hi disc, and even beyond, such as in the case of the warped galaxy NGC 253 (Bland-Hawthorn et al.). Detecting ionized gas at these radii could carry significant implications as to the distribution of dark matter in galaxies. With the aim of detecting this gas, we carried out a deep Hα kinematical analysis of two Sculptor group galaxies, NGC 247 and 300. The Fabry-Perot data were taken at the 36-cm Marseille Telescope in La Silla, Chile, offering a large field of view. With almost 20 hours of observations for each galaxy, very faint diffuse emission is detected. Typical emission measures of 0.1cm-6pc are reached. For NGC 247, emission extending up to a radius comparable with that of the Hi disc (r~ 13arcmin) is found, but no emission is seen beyond the Hi disc. For NGC 300, we detect ionized gas on the entirety of our field of view (rmax~ 14arcmin), and find that the bright Hii regions are embedded in a diffuse background. Using the deep data, extended optical rotation curves are obtained, as well as mass models. These are the most extended optical rotation curves thus far for these galaxies. We find no evidence suggesting that NGC 247 has a warped disc, and to account for our non-detection of Hα emission beyond its Hi disc, as opposed to the warped galaxy NGC 253, our results favour the model in which, only through a warp, ionization by hot young stars in the central region of a galaxy can let photons escape and ionize the interstellar medium in the outer parts. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Kam Z.S.,University of Montreal | Kam Z.S.,Observatoire Dastrophysique Of Luniversite Of Ouagadougou | Kam Z.S.,University of Cape Town | Carignan C.,University of Montreal | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

As part of a long-term project to revisit the kinematics and dynamics of the large disc galaxies of the Local Group, we present the first deep, wide-field (~42 arcmin× 56 arcmin) 3Dspectroscopic survey of the ionized gas disc of Messier 33. Fabry-Perot interferometry has been used to map its Hα distribution and kinematics at unprecedented angular resolution (≲3 arcsec) and resolving power (~12 600), with the 1.6 m telescope at the Observatoire du Mont Mégantic. The ionized gas distribution follows a complex, large-scale spiral structure, unsurprisingly coincident with the already-known spiral structures of the neutral and molecular gas discs. The kinematical analysis of the velocity field shows that the rotation centre of the Hα disc is distant from the photometric centre by ~168 pc (sky-projected distance) and that the kinematical major-axis position angle and disc inclination are in excellent agreement with photometric values. The Hα rotation curve agrees very well with the HI rotation curves for 0 < R < 6.5 kpc, but the Hα velocities are 10-20 km s-1 higher for R > 6.5 kpc. The reason for this discrepancy is not well understood. The velocity dispersion profile is relatively flat around 16 km s-1, which is at the low end of velocity dispersions of nearby star-forming galactic discs. A strong relation is also found between the Hα velocity dispersion and the Hα intensity. Mass models were obtained using the Hα rotation curve but, as expected, the dark matter halo's parameters are not very well constrained since the optical rotation curve only extends out to 8 kpc. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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