Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe rotation curves shapes of late-type dwarf galaxies
302
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
Observational studies are showing that the galaxy-wide stellar initial mass function are top-heavy in galaxies with high star-formation rates (SFRs). Calculating the integrated galactic stellar initial mass function (IGIMF) as a function of the SFR of a galaxy, it follows that galaxies which have or which formed with SFRs > 10 Msol yr^-1 would have a top-heavy IGIMF in excellent consistency with the observations. Consequently and in agreement with observations, elliptical galaxies would have higher M/L ratios as a result of the overabundance of stellar remnants compared to a stellar population that formed with an invariant canonical stellar initial mass function (IMF). For the Milky Way, the IGIMF yields very good agreement with the disk- and the bulge-IMF determinations. Our conclusions are that purely stochastic descriptions of star formation on the scales of a pc and above are falsified. Instead, star formation follows the laws, stated here as axioms, which define the IGIMF theory. We also find evidence that the power-law index beta of the embedded cluster mass function decreases with increasing SFR. We propose further tests of the IGIMF theory through counting massive stars in dwarf galaxies.
Cosmological simulations of structure formation are invaluable to study the evolution of the Universe and the development of galaxies in it successfully reproducing many observations in the context of the cosmological paradigm $Lambda$CDM. However, there are remarkable discrepancies with observations that are a matter of debate. One of the most recently reported is the diversity of shapes in the rotation curves of dwarf galaxies in the local Universe which is in contrast to the apparent homogeneity of rotation curves in cosmological hydrodynamic simulations. Previous studies on similar problems have shown that sometimes can be alleviated by accounting for the impact of observational effects in the comparison. For this reason, in this work we present a set of controlled experiments to measure the impact that some systematic effects, associated with modeling the observation process in a realistic way, have on the diversity of synthetic rotation curves. Our results demonstrate that factors such as spectral power, spatial resolution and inclination angle, can naturally induce noticeable fluctuations on the shape of the rotation curves, reproducing up to $47%$ of the diversity reported in the observations. This is remarkable, especially considering that we limited the sample to highly-symmetric disks simulated in isolation. This shows that a more realistic modeling of synthetic rotation curves may alleviate the reported tension between simulations and observations, without posing a challenge to the standard cosmological model of cold dark matter.
Chameleon theories of gravity predict that the gaseous component of isolated dwarf galaxies rotates with a faster velocity than the stellar component. In this paper, we exploit this effect to obtain new constraints on the model parameters using the measured rotation curves of six low surface brightness galaxies. For $f(R)$ theories, we rule out values of $f_{R0}>10^{-6}$. For more general theories, we find that the constraints from Cepheid variable stars are currently more competitive than the bounds we obtain here but we are able to rule out self-screening parameters $chi_c>10^{-6}$ for fifth-force strengths (coupling of the scalar to matter) as low as $0.05$ the Newtonian force. This region of parameter space has hitherto been inaccessible to astrophysical probes. We discuss the future prospects for improving these bounds.
Dwarf and low surface brightness galaxies are ideal objects to test modified Newtonian dynamics (MOND), because in most of these galaxies the accelerations fall below the threshold below where MOND supposedly applies. We have selected from the literature a sample of 27 dwarf and low surface brightness galaxies. MOND is successful in explaining the general shape of the observed rotation curves for roughly three quarters of the galaxies in the sample presented here. However, for the remaining quarter, MOND does not adequately explain the observed rotation curves. Considering the uncertainties in distances and inclinations for the galaxies in our sample, a small fraction of poor MOND predictions is expected and is not necessarily a problem for MOND. We have also made fits taking the MOND acceleration constant, a_0, as a free parameter in order to identify any systematic trends. We find that there appears to be a correlation between central surface brightness and the best-fit value of a_0, in the sense that lower surface brightness galaxies tend to have lower a_0. However, this correlation depends strongly on a small number of galaxies whose rotation curves might be uncertain due to either bars or warps. Without these galaxies, there is less evidence of a trend, but the average value we find for a_0 ~ 0.7*10^-8 cm s^-2 is somewhat lower than derived from previous studies. Such lower fitted values of a_0 could occur if external gravitational fields are important.
We analyse maps of the spatially-resolved nebular emission of $approx$1500 star-forming galaxies at $zapprox0.6$-$2.2$ from deep KMOS and MUSE observations to measure the average shape of their rotation curves. We use these to test claims for declining rotation curves at large radii in galaxies at $zapprox1$-$2$ that have been interpreted as evidence for an absence of dark matter. We show that the shape of the average rotation curves, and the extent to which they decline beyond their peak velocities, depends upon the normalisation prescription used to construct the average curve. Normalising in size by the galaxy stellar disk-scale length after accounting for seeing effects ($R_{rm{d}}^{prime}$), we construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to $6R_{rm{d}}^{prime}$ ($approx$13 kpc, on average). Combining these curves with average HI rotation curves for local systems, we investigate how the shapes of galaxy rotation curves evolve over $approx$10 Gyr. The average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least $6R_{rm{d}}^{prime}$. We find a trend between the outer slopes of galaxies rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter rotation curves. Drawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies at $zapprox0$-$2.2$ are consistent with those expected from $Lambda$CDM theory and imply dark matter fractions within $6R_{rm{d}}$ of at least $approx60$ percent.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
