arXiv subjects

C. Carignan

Publications and source records attributed to C. Carignan.

At least 37 records · Page 2Linked to original sources

arXiv2016

HI Observations of two New Dwarf Galaxies: Pisces A & B with the SKA Pathfinder KAT-7

Context. Pisces A & 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. Derive the HI content and kinematics of Pisces A & B. Methods. Aperture synthesis HI observations using 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 small rotation velocities detected of ~5 km/sec and ~10 km/sec in Pisces A & 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/sec 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 sub-halo candidates. Systems such as Pisces A & B are more likely to be found at a few Mpc.s from MW-type galaxies.

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arXiv2015

HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7

We present HI observations of the Sculptor Group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the SKA precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large scale, low surface brightness emission. The KAT-7 observations detected 33% more flux than previous VLA observations, mainly in the outer parts and in the halo for a total HI mass of $2.1 \pm 0.1$ $\times 10^{9}$ M$_{\odot}$. HI can be found at large distances perpendicular to the plane out to projected distances of ~9-10 kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel technique, based on interactive profile fitting, was used to separate the main disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the HI disk confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed extra planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate (SFR) is compatible with the starburst nature of NGC 253.

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arXiv2013

Bar pattern speed and position of the circumnuclear ring in NGC 1097

We present the first galactic-scale model of the gas dynamics of the prototype barred Seyfert 1 galaxy NGC1097. We use large scale FaNTOmM Fabry-Perot interferometric data covering the entire galactic disc and combine the distribution and kinematics maps with high resolution two-dimensional spectroscopy from the Gemini telescope. We build a dynamical model for the gravitational potential by applying the analytic solution to the equations of motion, within the epicyclic approximation. Our model reproduces all the significant kinematic and structural signatures of this galaxy. We find that the primary bar is 7.9+/-0.6 kpc long and has a pattern speed of 36 +/- 2 km s^-1 kpc^-1. This places the corotation radius at 8.6 +/-0.5 kpc, the outer Lindblad resonance at 14.9+/-0.9 kpc and two inner Lindblad resonances at 60+/-5 pc and 2.9+/-0.1 kpc. These derivations lead to a ratio of the corotation radius over bar length of 1.0--1.2, which is in agreement with the predictions of simulations for fast galaxy bars. Our model presents evidence that the circumnuclear ring in this galaxy is not located near any of the resonance radii in this galaxy. The ring might have once formed at the outer inner Lindblad resonance radius, and it has been migrating inward, toward the centre of the galactic gravitational potential.

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arXiv2013

KAT-7 Science Verification: Using HI Observations of NGC 3109 to Understand its Kinematics and Mass Distribution

HI observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to what is obtained using VLA data. KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32', doubling the angular extent of existing measurements. A total HI mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA observations. The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce very well the observed rotation curve but the cosmologically motivated NFW DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass-to-light ratios for the stellar disk and/or very large values for the MOND universal constant a0. Different distances or HI contents cannot reconcile MOND with the observed kinematics, in view of the small errors on those two quantities. As for many slowly rotating gas-rich galaxies studied recently, the present result for NGC 3109 continues to pose a serious challenge to the MOND theory.

astro-ph.CO↗

arXiv2011

Deep Fabry-Perot Halpha observations of two Sculptor group galaxies, NGC 247 and NGC 300

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. 1997). 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 Halpha kinematical analysis of two Sculptor group galaxies, NGC 247 and NGC 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 0.1 cm^-6 pc are reached. For NGC 247, emission extending up to a radius comparable with that of the HI disc (r~13') 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 (r_max~14'), 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 Halpha 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.

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arXiv2010

Deep Hα Observations of NGC 253: a Very Extended and Possibly Declining Rotation Curve?

This study presents a deep Hα kinematical analysis of the Sculptor Group galaxy NGC253. The Fabry-Perot data were taken with the 36-cm Marseille Telescope in La Silla, Chile, using an EMCCD detector. Typical emission measures of ~0.1 cm^-6 pc are reached. The observations allow the detection of the Diffuse Ionized Gas component through [N II] emission at very large radii of 11.5', 12.8' and 19.0', on the receding side of the galaxy. No Hα emission is observed at radii larger than the neutral component (11.5'). The very extended rotation curve confirms previous results and shows signs of a significant decline, on the order of 30 per cent vmax . Using the rotation data, mass models are constructed with and without the outer [N II] data points, and similar results are found. The declining part of the rotation curve is very well modeled, and seems to be truly declining.

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arXiv2010

The kinematics of the quadrupolar nebula M1-75 and the identification of its central star

The link between the shaping of bipolar planetary nebulae and their central stars is still poorly understood. The kinematics and shaping of the multipolar nebula M 1-75 are hereby investigated, and the location and nature of its central star are briefly discussed. Fabry-Perot data from GHaFAS on the WHT sampling the Doppler shift of the [N II] 658.3 nm line are used to study the dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, and from ACAM on the WHT, allowed us to constrain the parameters of the central star. The two pairs of lobes, angularly separated by ~22 degrees, were ejected simultaneously approx. ~3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point symmetry. The shaping of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star which engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star which is likely the nebular progenitor. Its estimated V-I colour allows us to derive a rough estimate of the parameters and nature of the central star.

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arXiv2010

Kinematics of galaxies in Compact Groups. Studying the B-band Tully-Fisher relation

We obtained new Fabry-Perot data cubes and derived velocity fields, monochromatic and velocity dispersion maps for 28 galaxies in the Hickson compact groups 37, 40, 47, 49, 54, 56, 68, 79 and 93. We find that one third of the non-barred compact group galaxies have position angle misalignments between the stellar and gaseous components. This and the asymmetric rotation curves are clear signatures of kinematic perturbations, probably due to interactions among compact group galaxies. A comparison between the B-band Tully-Fisher relation for compact group galaxies and that for the GHASP field-galaxy sample shows that, despite the high fraction of compact group galaxies with asymmetric rotation curves, these lie on the Tully-Fisher relation defined by galaxies in less dense environments, although with more scatter. This is in agreement with previous results, but now confirmed for a larger sample of 41 galaxies. We confirm the tendency for compact group galaxies at the low-mass end of the Tully-Fisher relation (HCG 49b, 89d, 96c, 96d and 100c) to have either a magnitude that is too bright for its mass (suggesting brightening by star formation) and/or a low maximum rotational velocity for its luminosity (suggesting tidal stripping). These galaxies are outside the Tully Fisher relation, at the 1 sigma level, even when the minimum acceptable values of inclinations are used to compute their maximum velocities. The inclusion of such galaxies with v<100 km/s in the determination of the zero point and slope of the compact group B-band Tully-Fisher relation would strongly change the fit, making it different from the relation for field galaxies, a fact that has to be kept in mind when studying scaling relations of interacting galaxies, specially at high redshifts.

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arXiv2008

GHASP : An Halpha kinematic survey of spiral and irregular galaxies - VI. New Halpha data cubes for 108 galaxies

We present the Fabry-Perot observations obtained for a new set of 108 galaxies that completes the GHASP survey (Gassendi HAlpha survey of SPirals). The GHASP survey consists of 3D Ha data cubes for 203 spiral and irregular galaxies, covering a large range in morphological types and absolute magnitudes, for kinematics analysis. The GHASP sample is by now the largest sample of Fabry-Perot data ever published. We have derived Ha data cubes from which are computed Ha maps, radial velocity fields as well as residual velocity fields, position-velocity diagrams, rotation curves and the kinematical parameters for almost all galaxies. Original improvements in the determination of the kinematical parameters, rotation curves and their uncertainties have been implemented in the reduction procedure. This new method is based on the whole 2D velocity field and on the power spectrum of the residual velocity fieldrather than the classical method using successive crowns in the velocity field. Among the results, we point out that morphological position angles have systematically higher uncertainties than kinematical ones, especially for galaxies with low inclination. Morphological inclination of galaxies having no robust determination of their morphological position angle cannot be constrained correctly. Galaxies with high inclination show a better agreement between their kinematical inclination and their morphological inclination computed assuming a thin disk. The consistency of the velocity amplitude of our rotation curves have been checked using the Tully-Fisher relationship. Our data are in good agreement with previous determinations found in the literature. Nevertheless, galaxies with low inclination have statistically higher velocities than expected and fast rotators are less luminous than expected.

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arXiv2008

GH $α$ FaS : Galaxy H-alpha Fabry-Perot System for the WHT

GH$α$FaS a new Fabry-Perot system, is now available at the William Herschel Telescope. It was mounted, for the first time, at the Nasmyth focus of the 4.2 meter WHT on La Palma in July 2007. Using modern technology, with a spectral resolution of the order R$\sim$15000, and with a seeing limited spatial resolution, GH$α$FaS will provide a new look at the H$α$ -emitting gas over a 4.8 arcminutes circular field in the nearby universe. Many science programs can be done on a 4.2 metre class telescope in world class seeing conditions with a scanning Fabry-Perot. Not only galaxies but HII regions, planetary nebulae, supernova remnants and the diffuse interstellar medium are subjects for which unique data can be aquired rapidly. Astronomers from the Laboratoire d'Astrophysique Expérimentale (LAE) in Montréal, the Laboratoire d'Astrophysique de Marseille (LAM-OAMP), and the Instituto de Astrofísica de Canarias (IAC), have inaugurated GH$α$FaS by studying in detail the dynamics of some nearby spiral galaxies. A robust set of state-of-the-arts tools for reducing and analyzing the data cubes obtained with GH$α$FaS has also been developed.

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arXiv2008

GALEX observations of Low Surface Brightness Galaxies: UV color and star formation efficiency

We present GALEX UV observations of a sample of Low Surface Brightness (LSB) galaxies for which HI data are available, allowing us to estimate their star formation efficiency. We find that the UV light extends to larger radii than the optical light (some galaxies, but not all, look similar to the recently discovered XUV-disk galaxies). Using a standard calibration to convert the UV light into star formation rates, we obtain lower star formation efficiencies in LSB galaxies than in high surface brightness galaxies by about one order of magnitude. We show however that standard calibrations may not apply to these galaxies, as the FUV-NUV color obtained from the two GALEX bands (FUV and NUV; lambda_eff= 1516 and 2267 A, respectively) is redder than expected for star forming galaxies. This color can be interpreted as a result of internal extinction, modified Initial Mass Function or by star formation histories characterized by bursts followed by quiescent phases. Our analysis favors this latter hypothesis.

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arXiv2008

Deep Fabry-Perot Halpha Observations of NGC 7793: a Very Extended Halpha Disk and a Truly Declining Rotation Curve

Deep Halpha observations of the Sculptor Group galaxy NGC 7793 were obtained on the ESO 3.60m and the Marseille 36cm telescopes at La Silla, Chile. Halpha emission is detected all the way to the edge of the HI disk, making of the HII disk of NGC 7793 one of the largest ever observed in a quiet non-AGN late-type system. Even in the very outer parts, the HII ionizing sources are probably mainly internal (massive stars in the disk) with an unlikely contribution from the extragalactic ionizing background. The Halpha kinematics confirms what had already been seen with the HI observations: NGC 7793 has a truly declining rotation curve. However, the decline is not Keplerian and a dark halo is still needed to explain the rotation velocities in the outer parts.

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arXiv2008

H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II

This is the second part of an H-alpha kinematics follow-up survey of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program is to shed new light on the role of baryons and their kinematics and on the dark/luminous matter relation in the star forming regions of galaxies, in relation with studies at other wavelengths. The data for 37 galaxies are presented. The observations were made using Fabry-Perot interferometry with the photon-counting camera FaNTOmM on 4 different telescopes, namely the Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m, and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are computed using custom IDL routines designed for an optimal use of the data. The kinematical parameters and rotation curves are derived using the GIPSY software. It is shown that non-circular motions associated with galactic bars affect the kinematical parameters fitting and the velocity gradient of the rotation curves. This leads to incorrect determinations of the baryonic and dark matter distributions in the mass models derived from those rotation curves.

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arXiv2007

GHASP : an H alpha kinematic survey of spiral and irregular galaxies. V. Dark matter distribution in 36 nearby spiral galaxies

The results obtained from a study of the mass distribution of 36 spiral galaxies are presented. The galaxies were observed using Fabry-Perot interferometry as part of the GHASP survey. The main aim of obtaining high resolution H alpha 2D velocity fields is to define more accurately the rising part of the rotation curves which should allow to better constrain the parameters of the mass distribution. The H alpha velocities were combined with low resolution HI data from the literature, when available. Combining the kinematical data with photometric data, mass models were derived from these rotation curves using two different functional forms for the halo: an isothermal sphere and an NFW profile. For the galaxies already modeled by other authors, the results tend to agree. Our results point at the existence of a constant density core in the center of the dark matter halos rather than a cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all types the result already obtained by other authors studying dwarf and LSB galaxies but would necessitate a larger sample of galaxies to conclude more strongly. Whatever model is used (ISO or NFW), small core radius halos have higher central densities, again for all morphological types. We confirm different halo scaling laws, such as the correlations between the core radius and the central density of the halo with the absolute magnitude of a galaxy: low luminosity galaxies have small core radius and high central density. We find that the product of the central density with the core radius of the dark matter halo is nearly constant, whatever the model and whatever the absolute magnitude of the galaxy. This suggests that the halo surface density is independent from the galaxy type.

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arXiv2007

GHaFaS: Galaxy Halpha Fabry-Perot Spectrometer for the WHT

A new scanning Fabry-Perot system will soon be available at the Nasmyth focus of the 4,2m William Hershell Telescope (WHT). It has been designed by the Laboratoire d'Astrophysique Experimentale (LAE) in Montreal and is being built in collaboration with astronomers at the Instituto de Astrofisica de Canarias (IAC). The instrument will see first light at the beginning of July 2007.

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arXiv2007

An Evolutionary Sequence of Expanding Hydrogen Shells in Galaxy Discs

Large HI shells, with diameters of hundreds of pc and expansion velocities of 10-20kms-1 are well observed features of local gas rich galaxies. These shells could well be predicted as a result of the impact of OB associations on the ISM, but doubt has been cast on this scenario by the apparent absence of OB stars close to the centres of a large fraction of these shells in recent observations of the SMC. Using Fabry-Perot scanned Halpha emission line mapping of nearby galaxy discs we have detected, in all the HII regions where the observations yield sufficient angular resolution and S:N ratio, dominant Halpha shells with radii a few tens of pc, expanding at velocities of 50-100kms-1. We have applied a simple dynamically consistent framework in which we can extrapolate the properties of the observed Halpha shells to a few 10^7yr after the formation of the OB stars. The framework includes the dynamical inputs of both winds and SNe on the surrounding ISM. The results give quantitative statistical support to the hypothesis that the Halpha emitting shells are generic progenitors of the HI shells. During the time taken for an expanding shell to reach the size of a typical HI shell, the OB association may well lose its most luminous stars so the absence of such stars near the centres of many of the HI shells is well explained in this scenario.

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arXiv2006

HI studies of the Sculptor group galaxies. VIII. The background galaxies: NGC 24 and NGC 45

In order to complete our HI survey of galaxies in the Sculptor group area, VLA observations of NGC 24 and NGC 45 are presented. These two galaxies of similar magnitude M_B ~ -17.4 lie in the background of the Sculptor group and are low surface brightness galaxies, especially NGC 45. The HI distribution and kinematics are regular for NGC 24 while NGC 45 exhibits a kinematical twist of its major axis. A tilted-ring model shows that the position angle of the major axis changes by ~25 degrees. A best-fit model of their mass distribution gives mass-to-light ratios for the stellar disk of 2.5 and 5.2 for NGC 24 and NGC 45 respectively. These values are higher than the ones expected from stellar population synthesis models. Despite the large dark matter contribution, the galaxy mass is still dominated by the stellar component in their very inner regions. These high mass-to-light ratios are typical of what is seen in low surface brightness galaxies and may indicate that, in those galaxies, disks are far from the maximum disk case. The halo parameters derived from the best-fit models are thus lower limits.

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arXiv2006

Improved 3D Fabry-Perot Data Reduction Techniques

Improved data reduction techniques for 3D data cubes obtained from Fabry-Perot integral field spectroscopy are presented. They provide accurate sky emission subtraction and adaptive spatial binning and smoothing. They help avoiding the effect analogous to the beam smearing, seen in HI radio data, when strong smoothing is applied to 3D data in order to get the most extended signal coverage. The data reduction techniques presented in this paper allow one to get the best of both worlds: high spatial resolution in high signal-to-noise regions and large spatial coverage in low signal-to-noise regions.

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