arXiv subjects

R. Sancisi

Publications and source records attributed to R. Sancisi.

22 records · Page 2Linked to original sources

arXiv2000

On the apparent coupling of neutral hydrogen and dark matter in spiral galaxies

We have studied a mass model for spiral galaxies in which the dark matter surface density is a scaled version of the observed HI surface density. Applying this mass model to a sample of 24 spiral galaxies with reliable rotation curves one obtains good fits for most galaxies. The scaling factors cluster around 7, after correction for the presence of primordial helium. But for several cases different, often larger, values are found. For galaxies that can not be fitted well the discrepancy occurs at large radii and results from a fairly rapid decline of the HI surface density in the outermost regions. Because of such imperfections and in view of possible selection effects it is not possible to conclude here that there is a real coupling between HI and dark matter in spiral galaxies.

astro-ph↗

arXiv2000

The vertical extent and kinematics of the HI in NGC 2403

The neutral hydrogen line profiles along the major axis of the nearby spiral galaxy NGC 2403 show a wing towards the sytemic velocity. This asymmetry can be explained with the presence of an abnormally thick HI disk (FWHM ~ 5 kpc) or with a two-component structure: a thin disk and a slowly rotating, thicker (1-3 kpc) HI layer. The latter model gives a better representation of the observations. These results throw a new light on the disk-halo connection. In particular, the decrease of rotational velocity with height above the plane may be the result of a galactic fountain flow. A vertically extended, slowly rotating HI layer may be common among spiral galaxies with high levels of star formation.

astro-ph↗

arXiv1998

Kinematically Lopsided Spiral Galaxies

Asymmetries in the distribution of light and neutral hydrogen are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in their kinematics. Two examples of kinematically lopsided galaxies are presented and discussed. The shape of the rotation curve --rising more steeply on one side of the galaxy than on the other-- is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Probably at least half of all spiral galaxies are lopsided.

astro-ph↗

arXiv1997

The HI Halo of NGC 891

Neutral hydrogen observations of the nearby, edge-on spiral galaxy NGC 891 reveal the presence of an HI halo extending up to at least 5 kpc from the plane. This halo gas appears to rotate 25 to 100 km/s more slowly than the gas in the plane. If this velocity difference is due to the gradient in the gravitational potential, then it may serve to discriminate between disk and spheroidal mass models. The classic picture of a large outer flare in the HI layer of NGC 891 may no longer be valid. A correlation is seen between the distributions of HI, Halpha and radio continuum emission, which supports, in accordance with galactic fountain models, the picture of a substantial disk-halo circulation related to the star formation activity in the disk of NGC 891. There is now also clear evidence for the presence of a rapidly rotating (v_rot ~ 230 km/s) disk or ring of HI in the central part of NGC 891.

astro-ph↗