Laurent Chemin

THE MILKY WAY: AN EXCEPTIONALLY QUIET GALAXY; IMPLICATIONS FOR THE FORMATION OF SPIRAL GALAXIES

The Milky Way has been generally considered to be representative of the numerous spiral galaxies inhabiting the local Universe, thus providing general and perhaps the most detailed constraints on numerical models of galaxy formation. We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their locations in the planes drawn by Vf lat versus MK (the “Tully-Fisher” relation), jdisk (angular momentum) and the average Fe abundance, [Fe/H], of stars in the outskirts of the galaxy. These relations are thought to be the imprints of the dynamical, st ar-formation, and accretion history of disk galaxies. We compare the best established Tully-Fisher relations and reconcile their slopes and zero points in the plane MK-Vf lat. We then compare the properties of local spirals from a representative sample to those of the Milky Way and M31 considering how these two galaxies would appear if observed at larger distances. We find, for all relationships, that the Milky Way is systemat ically offset by � 1σ or more from the distribution of comparable local galaxies: specifically, it shows a too small stellar mass, angular momentum, disk radius and outskirts stars [Fe/H] ratio at a given Vf lat, the latter being taken as a proxy for the total mass. In contrast with the Milky Way, M31 lies well within the mean of the fundamental relationships. On the basis of their locations in the (MK, Vf lat and Rd) volume, the fraction of spirals like the Milky Way is 7±1%, while M31 appears to be a “typical” spiral. As with M31, the bulk of local spirals show evidence for a formation history shaped mainly by merging. The Milky Way appears to have had an exceptionally quiet formation history and had escaped any significant merger over the last �10 Gyrs which may explain why its angular momentum, stellar mass and [Fe/H](outskirts) are two to three times smaller than those of other local spirals. We conclude that the standard scenario of secular evolution driven by th e accretion of gas and disk instabilities is generally unable to reproduce the properties of most (if not all) spira l galaxies, which are well represented by M31. However, the relatively recent proposal explaining the evolut ion of spiral galaxies through merging (the so-called “spiral rebuilding” scenario of Hammer et al. 2005) is consistent with the properties of both distant galaxies (e.g., stellar mass assembly through episodic IR luminous burst phases driven predominately by mergers) as well as to those of their descendants ‐ the local spirals. Subject headings: Galaxy: formation, Galaxies: evolution, Galaxies: formation, Galaxies: kinematics and dynamics, angular momentum

Hα kinematics of the SINGS nearby galaxies survey — I

This is the first part of an Halpha kinematics follow-up survey of the SINGS sample. The data for 28 galaxies are presented. The observations were done on three different telescopes with FaNTOmM, an integral field photon counting spectrometer, installed in the respective focal reducer of each telescope. The data reduction was done through a newly built pipeline with the aim of producing the most homogenous data set possible. Adaptive spatial binning was applied to the data cubes in order to get a constant signal-to-noise ratio across the field of view. Radial velocity and monochromatic maps were generated using a new algorithm and the kinematical parameters were derived using tilted-ring models.

On the Relevance of the Tremaine-Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)

The relevance of the Tremaine-Weinberg (TW) method is tested to measure the bar, spiral and inner structure pattern speeds using a gaseous velocity field. The TW method is applied to various simulated barred galaxies in order to demonstrate its validity in seven different configurations, including star formation or/and dark matter halo. The reliability of the different physical processes involved and of the various observational parameters are also tested. The simulations show that the TW method could be applied to the gaseous velocity fields to get a good estimate of the bar pattern speed, under the condition that regions of shocks are avoided and measurements are confined to regions where the gaseous bar is well formed. We successfully apply the TW method to the \\ha velocity field of the Virgo Cluster Galaxy M100 (NGC 4321) and derive pattern speeds of 55+/-5 km/s/kpc for the nuclear structure, 30+/-2 km/s/kpc for the bar and 20+/-1 km/s/kpc for the spiral pattern, in full agreement with published determinations using the same method or alternative ones.

BHαBAR: big Hα kinematical sample of barred spiral galaxies – I. Fabry–Perot observations of 21 galaxies

The Halpha gas kinematics of twenty-one representative barred spiral galaxies belonging to the BHaBAR sample is presented. The galaxies were observed with FaNTOmM, a Fabry-Perot integral-field spectrometer, on three different telescopes. The 3D data cubes were processed through a robust pipeline with the aim of providing the most homogeneous and accurate dataset possible useful for further analysis. The data cubes were spatially binned to a constant signal-to-noise ratio, typically around 7. Maps of the monochromatic Halpha emission line and of the velocity field were generated and the kinematical parameters were derived for the whole sample using tilted-ring models. The photometrical and kinematical parameters (position angle of the major axis, inclination, systemic velocity and kinematical centre) are in relative good agreement, except maybe for the later-type spirals.

A mass-velocity anisotropy relation in galactic stellar disks

The ellipsoid of stellar random motions is a fundamental ingredient of galaxy dynamics. Yet it has long been difficult to constrain this component in disks others than the Milky Way. This article presents the modeling of the azimuthal-to-radial axis ratio of the velocity ellipsoid of galactic disks from stellar dispersion maps using integral field spectroscopy data of the CALIFA survey. The measured azimuthal anisotropy is shown to be not strongly dependent on the assumed vertical-to-radial dispersion ratio of the ellipsoid. The anisotropy distribution shows a large diversity in the orbital structure of disk galaxies from tangential to radial stellar orbits. Globally, the orbits are isotropic in inner disk regions and become more radial as a function of radius, although this picture tends to depend on galaxy morphology and luminosity. The Milky Way orbital anisotropy profile measured from the Second Gaia Data Release is consistent with those of CALIFA galaxies. A new correlation is evidenced, linking the absolute magnitude or stellar mass of the disks to the azimuthal anisotropy. More luminous disks have more radial orbits and less luminous disks have isotropic and somewhat tangential orbits. This correlation is consistent with the picture in galaxy evolution in which orbits become more radial as the mass grows and is redistributed as a function of time. With the help of circular velocity curves, it is also shown that the epicycle theory fails to reproduce the diversity of the azimuthal anisotropy of stellar random motions, as it predicts only nearly radial orbits in the presence of flat curves. The origin of this conflict is yet to be identified. It also questions the validity of the vertical-to-radial axis ratio of the velocity ellipsoid derived by many studies in the framework of the epicyclic approximation.

Extended H I Rotation Curve of M31 using deep DRAO observations

Carignan et al. (2006) recently presented an extended HI rotation curve (RC) of M31, using single dish observations from the 100m Effelsberg and Green Bank telescopes. These observations were motivated by a comparison with previous HI data from Braun (1991) which presented a decreasing rotation curve as a function of radius. The single dish data were obtained along the semi-major axis of the approaching half of the M31 HI disk and showed a flat RC at large radius, extending up to ~35 kpc (using D=780 kpc). The kinematical analysis of M31 is pursued here and new deep 21cm observations obtained at the Dominion Radio Astrophysical Observatory (DRAO) are presented. A tilted-ring model is fitted to a new HI velocity field, allowing the derivation of the position angle and inclination as a function of radius. We concentrate on the approaching half of the disk. It is shown that the disk warping of M31 does not severely contaminate the kinematics of the neutral gas. As a consequence, the RC from the single dish data is in very good agreement with the newly derived RC.

Environmental Effects on the Kinematics of Virgo Cluster Galaxies

We present results from an ongoing survey dedicated to the ionized gas kinematics of Virgo cluster spiral galaxies using Fabry-Perot interferometry. Our goal is to study the environmental effects on galaxy evolution in the Virgo cluster. We report here on the Halpha distribution map and velocity field of NGC 4438, the prototype of an interacting galaxy near the centre of the cluster.

A 3D Optical Spectroscopy Study of Low Surface Brightness Galaxies

We present Halpha emission line velocity fields of two Low Surface Brightness galaxies - UGC 628 and UGC 5005 - obtained using Fabry-Perot interferometry observations at the Canada-France-Hawaii telescope. Our goal is to study the dynamics of Low Surface Brightness galaxies.