High-Resolution Rotation Curves and Galaxy Mass Models From Things

Abstract

We present rotation curves of 19 galaxies from THINGS, The H I Nearby Galaxy Survey. The high spatial and velocity resolution of THINGS make these the highest quality H I rotation curves available to date for a large sample of nearby galaxies, spanning a wide range of H I masses and luminosities. The high quality of the data allows us to derive the geometrical and dynamical parameters using H I data alone. We do not find any declining rotation curves unambiguously associated with a cut-off in the mass distribution out to the last measured point. The rotation curves are combined with 3.6 µm data from SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models. Our best-fit, dynamical disk masses, derived from the rotation curves, are in good agreement with photometric disk masses derived from the 3.6 µm images in combination with stellar population synthesis arguments and two different assumptions for the stellar Initial Mass Function (IMF). We test the Cold Dark Matter-motivated cusp model, and the observationally motivated central density core model and find that (independent of IMF) for massive, disk-dominated galaxies, all halo models fit apparently equally well; for low-mass galaxies, however, a core-dominated halo is clearly preferred over a cuspy halo. The empirically derived densities of the dark matter halos of the late-type galaxies in our sample are half of what is predicted by CDM simulations, again independent of the assumed IMF. Stellar mass-to-light ratio trendsAn overview of the derived Υ 3.6 ⋆ values of the main disk components of our sample galaxies is given in Fig. 59. Here we plot the photometric (fixed) and dynamical (free) values for Υ 3.6 ⋆ against the colors and luminosities of the galaxies. The left-hand panels show the fixed and free Υ 3.6 ⋆ values of the disks for both the ISO and NFW model plotted against (J − K) color. We also distinghuish between our two choices for the IMF. Also shown is the predicted relation between Υ 3.6 ⋆ and color (Eqs. 4 and 5), again for both the diet-Salpeter and the Kroupa IMFs. By definition, the photometric Υ 3.6 ⋆ values follow their respective relations. The small scatter is caused by the color gradients present in these galaxies which make the photometric Υ 3.6 ⋆ differ slightly from those with a constant Υ 3.6 ⋆ as a function of radius.In general, we see that the diet-Salpeter curve defines an approximate upper limit to the distribution of the majority of the best fit values (apart from a few obviously discrepant cases). Accepting the best fit (free) Υ 3.6 ⋆ values at face value, this would suggest that a diet-Salpeter Υ 3.6 ⋆ analysis overestimates the disk masses slightly. Indeed, the Kroupa fixed Υ 3.6 ⋆ values seem to be a better match to the free Υ 3.6 ⋆ values. Alternative explanations could be effects of star formation history, or unexpectedly large contamination by PAHs, AGBs or hot dust in the 3.6 µm maps, though it is likely that the IMF plays the dominant role. Future rigorous population synthesis modeling should shed light on s...

NIHAO – IV: core creation and destruction in dark matter density profiles across cosmic time

“…This prediction of a universal, cuspy profile for the dark matter seems to be in tension with observations of rotation curves of low mass galaxies (e.g Moore 1994, Salucci & Burkert 2000Simon et al 2005;de Blok et al 2008;Kuzio de Naray, McGaugh & de Blok 2008;Kuzio de Naray, McGaugh & Mihos 2009;Oh et al 2011a), which seem to prefer density profiles with a constant density core in the center. This cusp-core controversy suggests that either a modification of the whole CDM paradigm is required (e.g., self interacting dark matter, SIDM, Vogelsberger et al 2014), or the inadequacy of pure N-body simulations to capture the dark matter dynamics on small scales, due to the absence of dissipative phenomena connected to baryonic physics.…”

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

“…These correlations were first found by Athanassoula et al (1987, hereafter ABP), by Kormendy (1988Kormendy ( , 1990, and by Kormendy & Freeman (1996). Some of the correlations have been confirmed at least qualitatively by, e. g., Burkert (1995); Persic et al (1996Persic et al ( , 1997; Verheijen (1997); Salucci & Burkert (2000); Borriello & Salucci (2001); Begum & Chengalur (2004); Graham et al (2006); Spano et al (2008); Kuzio de Naray et al (2008);de Blok et al (2008), and Plana et al (2010). The most thorough discussion to date is by Kormendy & Freeman (2004).…”

“…Some authors have tried to "save cusps" by emphasizing systematic uncertainties like beam-smearing in the H I rotation data and non-circular motions in the higher-resolution optical rotation data; these could create the appearance of a core. Over the past decade, rotation curve data and mass modeling have improved, and cores in the DM halos of dwarf and low-surface-brightness galaxies are consistently favored (e. g., Marchesini et al 2002;de Blok & Bosma 2002;de Blok et al 2008;Weldrake et al 2003;Gentile et al 2004Gentile et al , 2009Spano et al 2008;Oh et al 2008Oh et al , 2011aDonato et al 2009;Plana et al 2010, Chen & McGaugh 2010). de Blok (2010 concludes that almost all dwarf disk galaxies that have been studied have cored halos.…”

“…As Broeils (1992) remarks, H I rotation curves are less accurate for galaxies that are nearly face-on. Similar criteria were used by, e. g., Begeman (1987) and de Blok et al (2008). Oval distortions (Bosma 1978;Kormendy 1982;Kormendy & Kennicutt 2004) can lead to incorrect estimates of inclinations for the more face-on galaxies.…”

Fitting galactic rotation curves with conformal gravity and a global quadratic potential

“…The galaxy NGC 4826 is a highly unusual galaxy in which the inner 10 of the 89 rotation curve data points reported in [10] are counter-rotating with respect to the outer 79. With the two regions being well segregated (the inner points lie within 50 ′′ of the center of the galaxy while the outer region points lie beyond 130 ′′ ), we provide a fit to the 79 outer region points alone.…”