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Register a new userConfrontation of MOND with the rotation curves of early-type disc galaxies
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We extend the MOND analysis to a sample of 17 high surface brightness, early-type disc galaxies with rotation curves derived from a combination of 21cm HI line observations and optical spectroscopic data. A number of these galaxies have asymptotic rotation velocities between 250 and 350 km/s making them among the most massive systems (in terms of baryonic mass) considered in the context of MOND. We find that the general MOND prediction for such galaxies -- a rotation curve which gradually declines to the asymptotic value -- is confirmed, and in most cases the MOND rotation curve, determined from the mean radial light and gas distribution, agrees in detail with the observed rotation curve. In the few cases where MOND appears not to work well, the discrepancies can generally be understood in terms of various observational errors -- such as incorrect orientation angles and/or distances -- or of unmodelled physical effects -- such as non-circular motions. The implied mass-to-light ratios for the stellar disc and bulge constrain the MOND interpolating function; the form recently suggested by Zhao & Famaey (2005) yields more sensible values than the one traditionally used in MOND determinations of galaxy rotation curves.
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We investigate a sub-sample of the rotation curves consisting of 45 HSB non-bulgy spiral galaxies selected from SPARC (Spitzer Photometry and Accurate Rotation Curves) database by using two dark halo models (NFW and Burkert) and MOdified Newtonian Dynamics (MOND) theory. Among these three models, the core-dominated Burkert halo model provides a better description of the observed data ($chi_{ u}^2$ = 0.33) than Navarro, Frenk and White (NFW, $chi_{ u}^2$= 0.45) and MOND model ($chi_{ u}^2$ = 0.58). So our results show that, for dark halo models, the selected 45 HSB non-bulgy spiral galaxies prefer a cored density profile to the cuspy one (NFW); We also positively find that there is a correlation between $rho_0$ and $r_0$ in Burkert model. For MOND fits, when we take $a_0$ as a free parameter, there is no obvious correlation between $a_0$ and disk central surface brightness at 3.6 $mu m$ of these HSB spiral galaxies, which is in line with the basic assumption of MOND that $a_0$ should be a universal constant. Interestingly, our fittings gives $a_0$ an average value of $(0.74 pm 0.45) times 10^{- 8}rm {cm s^{- 2}}$ if we exclude the three highest values in the sample, which is smaller than the standard value ($1.21 times 10^{-8}rm {cm s^{- 2}}$).
We present rotation curves derived for a sample of 62 late-type dwarf galaxies that have been observed as part of the Westerbork HI Survey of Spiral and Irregular Galaxies (WHISP) project. The rotation curves were derived by interactively fitting model data cubes to the observed cubes, taking rotation curve shape, HI distribution, inclination, and the size of the beam into account. This makes it possible to correct for the effects of beam smearing. The dwarf galaxies in our sample have rotation-curve shapes that are similar to those of late-type spiral galaxies, in the sense that their rotation curves, when expressed in units of disk scale lengths, rise as steeply in the inner parts and start to flatten at two disk scale lengths. None of the galaxies in our sample have solid-body rotation curves that extend beyond three scale lengths. The logarithmic outer rotation curve slopes are similar between late-type dwarf and spiral galaxies. Thus, whether the flat part of the rotation curve is reached seems to depend more on the extent of the rotation curve than on its amplitude. We also find that the outer rotation curve shape does not strongly depend on luminosity, at least for galaxies fainter than M_R~-19. We find that in spiral galaxies and in the central regions of late-type dwarf galaxies, the shape of the central distribution of light and the inner rise of the rotation curve are related. This implies that galaxies with stronger central concentrations of light also have higher central mass densities, and it suggests that the luminous mass dominates the gravitational potential in the central regions, even in low surface brightness dwarf galaxies.
We present rotation curves for 19, mostly luminous, early-type disk galaxies. Rotation velocities are measured from a combination of HI velocity fields and long-slit optical emission line spectra along the major axis. We find that the rotation curves generally rise rapidly in the central regions and often reach rotation velocities of 200 - 300 km/s within a few hundred parsecs of the centre. The detailed shape of the central rotation curves shows a clear dependence on the concentration of the stellar light distribution and the bulge-to-disk luminosity ratio: galaxies with highly concentrated stellar light distributions reach the maximum in their rotation curves at relatively smaller radii than galaxies with small bulges and a relatively diffuse light distribution. We interpret this as a strong indication that the dynamics in the central regions are dominated by the stellar mass. At intermediate radii, many rotation curves decline. The strength of the decline is correlated with the total luminosity of the galaxies, more luminous galaxies having on average more strongly declining rotation curves. At large radii, however, all declining rotation curves flatten out, indicating that substantial amounts of dark matter must be present in these galaxies too. A comparison of our rotation curves with the Universal Rotation Curve from Persic et al. (1996) reveals large discrepancies between the observed and predicted rotation curves; we argue that rotation curves form a multi-parameter family which is too complex to describe with a simple formula depending on total luminosity only. (abridged)
A small fraction of early-type galaxies (ETGs) show prolate rotation, i.e. they rotate around their long photometric axis. In simulations, certain configurations of galaxy mergers are known to produce this type of rotation. We investigate the association of prolate rotation and signs of galaxy interactions among the observed galaxies. We collected a sample of 19 nearby ETGs with distinct prolate rotation from the literature and inspected their ground-based deep optical images for interaction signs - 18 in archival images and one in a new image obtained with the Milankovic telescope. Tidal tails, shells, asymmetric/disturbed stellar halos, or on-going interactions are present in all the 19 prolate rotators. Comparing this with the frequency of tidal disturbance among the general sample of ETGs of a roughly similar mass range and surface-brightness limit, we estimate that the chance probability of such an observation is only 0.00087. We also found a significant overabundance of prolate rotators that are hosting multiple stellar shells. The visible tidal features imply a relatively recent galaxy interaction. That agrees with the Illustris large-scale cosmological hydrodynamical simulation, where prolate rotators are predominantly formed in major mergers during the last 6 Gyr. In the appendix, we present the properties of an additional galaxy, NGC 7052, a prolate rotator for which no deep images are available, but for which an HST image revealed the presence of a prominent shell, which had not been reported before.
We present the discovery of rotation in quenched, low-mass early-type galaxies that are isolated. This finding challenges the claim that (all) rotating dwarf early-type galaxies in clusters were once spiral galaxies that have since been harassed and transformed into early-type galaxies. Our search of the Sloan Digital Sky Survey data within the Local volume ($z<0.02$) has yielded a sample of 46 galaxies with a stellar mass $M_star lesssim 5times10^9$ M$_odot$ (median $M_star sim 9.29 times 10^8$ M$_odot$), a low H$alpha$ equivalent width EW$_{{rm H}alpha}< 2$ AA, and no massive neighbour ($M_{star}gtrsim3 times 10^{10}$ M$_{odot}$) within a velocity interval of $Delta V = 500$ km s$^{-1}$ and a projected distance of $sim$1 Mpc. Nine of these galaxies were subsequently observed with Keck ESI and their radial kinematics are presented here. These extend out to the half-light radius $R_e$ in the best cases, and beyond $R_e/2$ for all. They reveal a variety of behaviours similar to those of a comparison sample of early-type dwarf galaxies in the Virgo cluster observed by Toloba et al. Both samples have similar frequencies of slow and fast rotators, as well as kinematically decoupled cores. This, and especially the finding of rotating quenched low-mass galaxies in isolation, reveals that the early-type dwarfs in galaxy clusters need not be harassed or tidally stirred spiral galaxies.
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