Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Shape of Dark Matter Haloes III. Kinematics and Structure of the HI disc
78
0
0.0
(
0
)
Added by
Pieter C. van der Kruit
Publication date
2016
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present a new strategy for fitting the structure and kinematics of the HI in edge-on galaxies using a fit to the terminal-velocity channel maps of a HI data cube. The strategy can deal with self-absorbing HI gas and the presence of warps. The method is first tested on a series of models. We demonstrate that fitting optically thin models to real galaxies will lead to an overestimation of the thickness and velocity dispersion, and to a serious underestimation of the HI face-on column densities. We subsequently fit both self-absorption and optically thin models to the HI data of six edge-on galaxies. In three of these we have also measured the velocity dispersion. On average 27 pm 6 % of the total HI mass of edge-on galaxies is hidden by self-absorption. This implies that the HI mass, thickness and velocity dispersion of galaxies is typically underestimated in the literature.
rate research
Read More
We present a new HI modelling tool called textsc{Galactus}. The program has been designed to perform automated fits of disc-galaxy models to observations. It includes a treatment for the self-absorption of the gas. The software has been released into the public domain. We describe the design philosophy and inner workings of the program. After this, we model the face-on galaxy NGC2403, using both self-absorption and optically thin models, showing that self-absorption occurs even in face-on galaxies. It is shown that the maximum surface brightness plateaus seen in Paper I of this series are indeed signs of self-absorption. The apparent HI mass of an edge-on galaxy can be drastically lower compared to that same galaxy seen face-on. The Tully-Fisher relation is found to be relatively free from self-absorption issues.
In the previous papers in this series, we have measured the stellar and hi content in a sample of edge-on galaxies. In the present paper, we perform a simultaneous rotation curve and vertical force field gradient decomposition for five of these edge-on galaxies. The rotation curve decomposition provides a measure of the radial dark matter potential, while the vertical force field gradient provide a measure of the vertical dark matter potential. We fit dark matter halo models to these potentials. Using our hi self-absorption results, we find that a typical dark matter halo has a less dense core ($0.094pm0.230$,M$_odot$/pc$^3$) compared to an optically thin hi model ($0.150pm0.124$,M$_odot$/pc$^3$). The HI self-absorption dark matter halo has a longer scale length $R_c$ of $1.42pm 3.48$,kpc, versus $1.10pm 1.81$,kpc for the optically thin HI model. The median halo shape is spherical, at $q=1.0pm0.6$ (self-absorbing hi), while it is prolate at $q=1.5pm0.6$ for the optically thin. Our best results were obtained for ESO,274-G001 and UGC,7321, for which we were able to measure the velocity dispersion in Paper III. These two galaxies have drastically different halo shapes, with one oblate and one strongly prolate. Overall, we find that the many assumptions required make this type of analysis susceptible to errors.
We present stellar-dynamical measurements of the central supermassive black hole (SMBH) in the S0 galaxy NGC 307, using adaptive-optics IFU data from VLT-SINFONI. We investigate the effects of including dark-matter haloes as well as multiple stellar components with different mass-to-light (M/L) ratios in the dynamical modeling. Models with no halo and a single stellar component yield a relatively poor fit with a low value for the SMBH mass ($7.0 pm 1.0 times 10^{7} M_{odot}$) and a high stellar M/L ratio (K-band M/L = $1.3 pm 0.1$). Adding a halo produces a much better fit, with a significantly larger SMBH mass ($2.0 pm 0.5 times 10^{8} M_{odot}$) and a lower M/L ratio ($1.1 pm 0.1$). A model with no halo but with separate bulge and disc components produces a similarly good fit, with a slightly larger SMBH mass ($3.0 pm 0.5 times 10^{8} M_{odot}$) and an identical M/L ratio for the bulge component, though the disc M/L ratio is biased high (disc M/L $ = 1.9 pm 0.1$). Adding a halo to the two-stellar-component model results in a much more plausible disc M/L ratio of $1.0 pm 0.1$, but has only a modest effect on the SMBH mass ($2.2 pm 0.6 times 10^{8} M_{odot}$) and leaves the bulge M/L ratio unchanged. This suggests that measuring SMBH masses in disc galaxies using just a single stellar component and no halo has the same drawbacks as it does for elliptical galaxies, but also that reasonably accurate SMBH masses and bulge M/L ratios can be recovered (without the added computational expense of modeling haloes) by using separate bulge and disc components.
The Local Group is a unique environment in which to study the astrophysics of galaxy formation. The proximity of the Milky Way and M31 causes a large fraction of the low-mass halo population to interact with more massive dark matter haloes, which increases their concentrations and strips them of gas and other material. Some low-mass haloes pass through the haloes of the Milky Way or M31 and are either ejected into the field or exchanged between the two primary hosts. We use high resolution gas-dynamical simulations to describe a new class of field halo that passed through the haloes of both the Milky Way and M31 at early times and is almost twice as concentrated as isolated field haloes. These Hermeian haloes are distributed anisotropically at greater distances from the Local Group barycentre than the primary haloes and appear to cluster close to the Milky Way and M31 in projection. We show that some Hermeian haloes can host galaxies that are promising targets for indirect dark matter searches and are competitive with signals from other dwarf galaxies. Hermeian galaxies in the Local Group should be detectable by forthcoming wide-field imaging surveys.
We use the halo occupation distribution (HOD) framework to characterise the predictions from two independent galaxy formation models for the galactic content of dark matter haloes and its evolution with redshift. Our galaxy samples correspond to a range of fixed number densities defined by stellar mass and span $0 le z le 3$. We find remarkable similarities between the model predictions. Differences arise at low galaxy number densities which are sensitive to the treatment of heating of the hot halo by active galactic nuclei. The evolution of the form of the HOD can be described in a relatively simple way, and we model each HOD parameter using its value at $z=0$ and an additional evolutionary parameter. In particular, we find that the ratio between the characteristic halo masses for hosting central and satellite galaxies can serve as a sensitive diagnostic for galaxy evolution models. Our results can be used to test and develop empirical studies of galaxy evolution and can facilitate the construction of mock galaxy catalogues for future surveys.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
