Context. Current and future blind surveys for HI generate large catalogs of spectral lines for which automated characterization would be convenient. Aims. A 6-parameter mathematical model for HI galactic spectral lines is described. The aim of the
paper is to show that this model is indeed a useful way to characterize such lines. Methods. The model is fitted to spectral lines extracted for the 34 spiral galaxies of the recent high-definition THINGS survey. Three scenarios with different instrumental characteristics are compared. Quantities obtained from the model fits, most importantly line width and total flux, are compared with analog quantities measured in more standard, non-parametric ways. Results. The model is shown to be a good fit to nearly all the THINGS profiles. When extra noise is added to the test spectra, the fits remain consistent; the model-fitting approach is also shown to return superior estimates of linewidth and flux under such conditions.
We derive the projected surface mass distribution Sigma_M for spherically symmetric mass distributions having an arbitrary rotation curve. For a galaxy with a flat rotation curve and an ISM disk having a constant Toomre stability parameter, Q, the IS
M surface mass density Sigma_g as well as Sigma_M both fall off as 1/R. We use published data on a sample of 20 well studied galaxies to show that ISM disks do maintain a constant Q over radii usually encompassing more than 50% of the HI mass. The power law slope in Sigma_g covers a range of exponents and is well correlated with the slope in the epicyclic frequency. This implies that the ISM disk is responding to the potential, and hence that secular evolution is important for setting the structure of ISM disks. We show that the gas to total mass ratio should be anti-correlated with the maximum rotational velocity, and that the sample falls on the expected relationship. A very steep fall off in Sigma_g is required at the outermost radii to keep the mass and angular momentum content finite for typical rotation curve shapes, and is observed. The observation that HI traces dark matter over a significant range of radii in galaxies is thus due to the disks stabilising themselves in a normal dark matter dominated potential. This explanation is consistent with the cold dark matter paradigm.
(Abridged) The analysis of the rotation curves (RCs) of spiral galaxies provides an efficient diagnostic for studying the properties of dark matter halos and their relations with the baryonic material. We have modeled the RCs of galaxies from The HI
Nearby Galaxy Survey (THINGS) with the Einasto halo model, which has emerged as the best-fitting model of the halos arising in dissipationless cosmological N-body simulations. We find that the RCs are significantly better fit with the Einasto halo than with either a pseudo-isothermal sphere (Iso) or Navarro-Frenk-White (NFW) halo models. In our best-fit models, the radius of density slope -2 and the density at this radius are highly correlated. The Einasto index, which controls the overall shape of the density profile, is near unity on average for intermediate and low mass halos. This is not in agreement with the predictions from LCDM simulations. The indices of the most massive halos are in rough agreement with those of cosmological simulations and appear correlated with the halo virial mass. We find that a typical Einasto density profile declines more strongly in its outermost parts than any of the Iso or NFW models whereas it is relatively shallow in its innermost regions. The core nature of those regions of halos thus extends the cusp-core controversy found for the NFW model with low surface density galaxies to the Einasto halo with more massive galaxies like those of THINGS. We thus find that the Einasto halo model provides, so far, the best match to the observed RCs, and can therefore be considered as a new standard model for dark matter halos.
We present the analysis of 12 high-resolution galactic rotation curves from The HI Nearby Galaxy Survey (THINGS) in the context of modified Newtonian dynamics (MOND). These rotation curves were selected to be the most reliable for mass modelling, and
they are the highest quality rotation curves currently available for a sample of galaxies spanning a wide range of luminosities. We fit the rotation curves with the simple and standard interpolating functions of MOND, and we find that the simple function yields better results. We also redetermine the value of a0, and find a median value very close to the one determined in previous studies, a0 = (1.22 +- 0.33) x 10^{-8} cm/s^2. Leaving the distance as a free parameter within the uncertainty of its best independently determined value leads to excellent quality fits for 75% of the sample. Among the three exceptions, two are also known to give relatively poor fits also in Newtonian dynamics plus dark matter. The remaining case (NGC 3198), presents some tension between the observations and the MOND fit, which might however be explained by the presence of non-circular motions, by a small distance, or by a value of a0 at the lower end of our best-fit interval, 0.9 x 10^{-8} cm/s^2. The best-fit stellar M/L ratios are generally in remarkable agreement with the predictions of stellar population synthesis models. We also show that the narrow range of gravitational accelerations found to be generated by dark matter in galaxies is consistent with the narrow range of additional gravity predicted by MOND.
A practical evaluation of the Multi-Scale CLEAN algorithm is presented. The data used in the comparisons are taken from The HI Nearby Galaxy Survey (THINGS). The implementation of Multi-Scale CLEAN in the CASA software package is used, although compa
risons are made against the very similar Multi-Resolution CLEAN algorithm implemented in AIPS. Both are compared against the classical CLEAN algorithm (as implemented in AIPS). The results of this comparison show that several of the well-known characteristics and issues of using classical CLEAN are significantly lessened (or eliminated completely) when using the Multi-Scale CLEAN algorithm. Importantly, Multi-Scale CLEAN reduces significantly the effects of the clean `bowl caused by missing short-spacings, and the `pedestal of low-level un-cleaned flux (which affects flux scales and resolution). Multi-Scale CLEAN can clean down to the noise level without the divergence suffered by classical CLEAN. We discuss practical applications of the added contrast provided by Multi-Scale CLEAN using two selected astronomical examples: HI holes in the interstellar medium and anomalous gas structures outside the main galactic disk.
