Structure and kinematics of edge-on galaxy discs -- V. The dynamics of the stellar discs

In earlier papers in this series we determined the intrinsic stellar disc kinematics of fifteen intermediate to late type edge-on spiral galaxies using a dynamical modeling technique. From the photometry we find that intrinsically more flattened discs tend to have a lower face-on central surface brightness and a larger dynamica mass-to-light ratio. This observation suggests that at a constant maximum rotational velocity lower surface brightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from the dynamical modeling that at least twelve discs are submaximal. The average disc contributes 53$\pm$4 percent to the observed rotation at 2.2 disc scalelengths, with a 1$\sigma$ scatter of 15 percent. This percentage becomes somewhat lower when effects of finite disc flattening and gravity by the dark halo and the gas are taken into account. Since boxy and peanut-shaped bulges are probably associated with bars, the result suggests that at 2.2$h_{\rm R}$ the submaximal nature of discs is independent of barredness. The possibility remains that very high surface brightness discs are maximal.We confirm that the radial stellar disc velocity dispersion is related to the galaxy maximum rotational velocity. The scatter in this $\sigma-v_{\rm max}$ relation appears to correlate with the disc flattening, face-on central surface brightness and dynamical mass-to-light ratio. Low surface brightness discs tend to be more flattened and have smaller stellar velocity dispersions. The findings are consistent with the observed correlation between disc flattening and dynamical mass-to-light ratio.Comment: Accepted for publication by Mon. Not. R.A.

The dark matter halo shape of edge-on disk galaxies - II. Modelling the HI observations: methods

This is the second paper of a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. For this purpose, we observe the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. To calculate the force fields, we need to analyse the observed XV diagrams to accurately measure all three functions that describe the planar kinematics and distribution of a galaxy: the radial HI surface density, the rotation curve and the HI velocity dispersion. In this paper, we discuss the improvements and limitations of the methods previously used to measure these HI properties. We extend the constant velocity dispersion method to include determination of the HI velocity dispersion as a function of galactocentric radius and perform extensive tests on the quality of the fits. We will apply this 'radial decomposition XV modelling method' to our HI observations of 8 HI-rich, late-type, edge-on galaxies in the third paper of this series.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher resolution version see http://www.astro.rug.nl/~vdkruit/jea3/homepage/12566.pd

Very Luminous Carbon Stars in the Outer Disk of the Triangulum Spiral Galaxy

Stars with masses in the range from about 1.3 to 3.5 Mo pass through an evolutionary stage where they become carbon stars. In this stage, which lasts a few Myr, these stars are extremely luminous pulsating giants. They are so luminous in the near-infrared that just a few of them can double the integrated luminosity of intermediate-age (0.6 to 2 Gyr) Magellanic Cloud clusters at 2.2 microns. Astronomers routinely use such near-infrared observations to minimize the effects of dust extinction, but it is precisely in this band that carbon stars can contribute hugely. The actual contribution of carbon stars to the outer disk light of evolving spiral galaxies has not previously been morphologically investigated. Here we report new and very deep near-IR images of the Triangulum spiral galaxy M33=NGC 598, delineating spectacular arcs of carbon stars in its outer regions. It is these arcs which dominate the near-infrared m=2 Fourier spectra of M33. We present near-infrared photometry with the Hale 5-m reflector, and propose that the arcs are the signature of accretion of low metallicity gas in the outer disk of M33.Comment: 4 pages, 4 figures. Revised version submitted to A&A Letter

Structure and kinematics of edge-on galaxy discs - I. Observations of the stellar kinematics

We present deep optical long-slit spectra of 17 edge-on spiral galaxies of intermediate to late morphological type, mostly parallel to their major axes and in a few cases parallel to the minor axes.The line-of-sight stellar kinematics are obtained from the stellar absorption lines using the improvedc ross-correlation technique. In general, the stellar kinematics are regular and can be traced well into the disc-dominated region. The mean stellar velocity curves are far from solid-body, indicating that the effect of dust extinction is not large. The line-of-sight stellar disc velocity dispersion correlates with the galaxy maximum rotational velocity, but detailed modeling is necessary to establish whether this represents a physical relation. In four spirals with a boxy- or peanut-shaped bulge we are able to detect asymmetric velocity distributions, having a common signature with projected radius in the mean line-of-sight velocity and the $h_{3}$ and $h_{4}$ curves. In two cases this kinematic asymmetry probably represents the `figure-of-eight' pattern synonymous of a barred potential. We emphasize, however, that the signatures seen in the $h_{3}$ and $h_{4}$ curves may also be due to the disc seen in projection.Comment: Accepted for publication by Mon. Not. R.A.

The dark matter halo shape of edge-on disk galaxies - I. HI observations

This is the first paper of a series in which we will attempt to put constraints on the flattening of dark halos in disk galaxies. We observe for this purpose the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. In this paper, we define a sample of 8 HI-rich late-type galaxies suitable for this purpose and present the HI observations.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher resolution version see http://www.astro.rug.nl/~vdkruit/jea3/homepage/12565.pd

Kinematics and dynamics of the "superthin" edge-on disk galaxy IC 5249

We present spectroscopic observations of the stellar motions in the disk of the superthin edge-on spiral galaxy IC 5249 and re-analyse synthesis observations of the HI. We find that the HI rotation curve rises initially to about 90-100 km/s, but contrary to the conclusion of Abe et al. (1999) flattens well before the edge of the optical disk. Over most part of the optical disk we have been able to establish that the (tangential) stellar velocity dispersion is 25-30 km/s. From earlier surface photometry we adopt a value for the radial scalelength of the disk of 7 +/- 1 kpc, a vertical scaleheight of 0.65 +/- 0.05 kpc and a disk truncation radius of 17 +/- 1 kpc. The very thin appearance of IC 5249 on the sky is the result of a combination of a low (face-on) surface brightness, a long scalelength and a a sharp truncation at only about 2.5 scalelengths. From various arguments we derive the stellar velocity dispersions at a position one radial scalelength as sigma_R about 35 km/s, sigma_{theta} about 30 km/s and sigma_z about 20 km/s. This is comparable to the values for the disk of our Galaxy in the solar neighborhood.Comment: 11 pages and 8 figures. Accepted for Astronomy and Astrophysics (September 2001

Identifying the gene(s) that allow tigriopus californicus to survive under thermal stress

The copepod species, Tigriopus californicus, is one of the most thermally adaptable species in the biosphere. They have been found in tide pools from the coast of Alaska down to the coast of Southern California. However, as all other organisms have limits, the T. californicus are only able to tolerate temperatures up to 34ºC. By comparing gene expression between specimens exposed to high temperatures and those expressed to optimal temperatures, we identified the genes responsible for conferring tolerance to increasing temperatures. After testing gene expression between copepods at 20ºC and at 34ºC, we have determined that both the hsp70 gene and the toll-like receptors of the T. californicus play a role in tolerance to temperature variance.L’espèce copépode, Tigriopus californicus, est une des espèces les plus thermiquement adaptables de la biosphère. On les trouve dans les bâches depuis la côte de l’Alaska jusqu’à la côte sud de la Californie. Toutefois, comme tous les autres organ¬ismes, les Tigriopus californicus ont des limites et ne peuvent pas tolérer des températures supérieures à 34oC. En comparant l’expression génétique entre les spécimens exposés à des températures élevées et ceux exposés à des températures optimales, nous avons identifié les gènes responsables de la tolérance à des températures en hausse. Après avoir testé l’expression génétique entre les copépodes à 20oC et à 34oC, nous avons déterminé que le gène hsp70 et les récepteurs de type Toll du T. californicus jouent tous deux un rôle dans la tolérance aux variations de température

The outer disks of galaxies: "To be or not to be truncated?"

We have in recent years come to view the outer parts of galaxies as having vital clues about their formation and evolution. Here, we would like to briefly present our results from a complete sample of nearby, late-type, spiral galaxies, using data from the SDSS survey, especially focused on the stellar light distribution in the outer disk. Our study shows that only the minority of late-type galaxies show a classical, exponential Freeman Type I profile down to the noise limit, whereas the majority exhibit either downbending (stellar truncation as introduced 1979 by Piet van der Kruit) or upbending profiles.Comment: LaTeX, 6 pages. To appear in the proceedings of the "Island Universes: Structure and Evolution of Disk Galaxies" conference held in Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht

Gravitational stability and dynamical overheating of stellar disks of galaxies

We use the marginal stability condition for galactic disks and the stellar velocity dispersion data published by different authors to place upper limits on the disk local surface density at two radial scalelengths $R=2h$. Extrapolating these estimates, we constrain the total mass of the disks and compare these estimates to those based on the photometry and color of stellar populations. The comparison reveals that the stellar disks of most of spiral galaxies in our sample cannot be substantially overheated and are therefore unlikely to have experienced a significant merging event in their history. The same conclusion applies to some, but not all of the S0 galaxies we consider. However, a substantial part of the early type galaxies do show the stellar velocity dispersion well in excess of the gravitational stability threshold suggesting a major merger event in the past. We find dynamically overheated disks among both seemingly isolated galaxies and those forming pairs. The ratio of the marginal stability disk mass estimate to the total galaxy mass within four radial scalelengths remains within a range of 0.4---0.8. We see no evidence for a noticeable running of this ratio with either the morphological type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter