Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpecific Angular Momentum of Disc Merger Remnants and the $lambda_R$-Parameter
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the $lambda_R$-parameter, which is a luminosity weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early type galaxies in so called fast $lambda_R > 0.1$ and slow rotators $lambda_R < 0.1$. Tests on merger remnants reveal that $lambda_R$ is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of $lambda_R$ values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in creating a slow or a fast rotator in a single binary merger, the former being created mostly in an equal mass merger. Slow rotators have a $lambda_R$ which does not vary with projection. The confusion rate with face-on fast rotators is very small. Merger with low gas fractions form slow rotators with smaller ellipticities and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of $lambda_R$ as high as our progenitor disc galaxies.
rate research
Read More
The main features of the gravitational dynamics of binary neutron star systems are now well established. While the inspiral can be precisely described in the post-Newtonian approximation, fully relativistic magneto-hydrodynamical simulations are required to model the evolution of the merger and post-merger phase. However, the interpretation of the numerical results can often be non-trivial, so that toy models become a very powerful tool. Not only do they simplify the interpretation of the post-merger dynamics, but also allow to gain insights into the physics behind it. In this work, we construct a simple toy model that is capable of reproducing the whole angular momentum evolution of the post-merger remnant, from the merger to the collapse. We validate the model against several fully general-relativistic numerical simulations employing a genetic algorithm, and against additional constraints derived from the spectral properties of the gravitational radiation. As a result, from the remarkably close overlap between the model predictions and the reference simulations within the first milliseconds after the merger, we are able to systematically shed light on the currently open debate regarding the source of the low-frequency peaks of the gravitational wave power spectral density. Additionally, we also present two original relations connecting the angular momentum of the post-merger remnant at merger and collapse to initial properties of the system.
Throughout the Hubble time, gas makes its way from the intergalactic medium into galaxies fuelling their star formation and promoting their growth. One of the key properties of the accreting gas is its angular momentum, which has profound implications for the evolution of, in particular, disc galaxies. Here, we discuss how to infer the angular momentum of the accreting gas using observations of present-day galaxy discs. We first summarize evidence for ongoing inside-out growth of star forming discs. We then focus on the chemistry of the discs and show how the observed metallicity gradients can be explained if gas accretes onto a disc rotating with a velocity 20-30% lower than the local circular speed. We also show that these gradients are incompatible with accretion occurring at the edge of the discs and flowing radially inward. Finally, we investigate gas accretion from a hot corona with a cosmological angular momentum distribution and describe how simple models of rotating coronae guarantee the inside-out growth of disc galaxies.
We investigate the relation between stellar mass and specific stellar angular momentum, or `Fall relation, for a sample of 17 isolated, regularly rotating disc galaxies at z=1. All galaxies have a) rotation curves determined from Halpha emission-line data; b) HST imaging in optical and infrared filters; c) robust determinations of their stellar masses. We use HST images in f814w and f160w filters, roughly corresponding to rest-frames B and I bands, to extract surface brightness profiles for our systems. We robustly bracket the specific angular momentum by assuming that rotation curves beyond the outermost Halpha rotation point stay either flat or follow a Keplerian fall-off. By comparing our measurements with those determined for disc galaxies in the local Universe, we find no evolution in the Fall relation in the redshift range 0<z<1, regardless of the band used and despite the uncertainties in the stellar rotation curves at large radii. This result holds unless stellar masses at z=1 are systematically underestimated by more than 50%. Our findings are compatible with expectations based on a LCDM cosmological framework and support a scenario where both the stellar Tully-Fisher and mass-size relations for spirals do not evolve significantly in this redshift range.
The relations between the specific angular momenta ($j$) and masses ($M$) of galaxies are often used as a benchmark in analytic models and hydrodynamical simulations as they are considered to be amongst the most fundamental scaling relations. Using accurate measurements of the stellar ($j_ast$), gas ($j_{rm gas}$), and baryonic ($j_{rm bar}$) specific angular momenta for a large sample of disc galaxies, we report the discovery of tight correlations between $j$, $M$, and the cold gas fraction of the interstellar medium ($f_{rm gas}$). At fixed $f_{rm gas}$, galaxies follow parallel power laws in 2D $(j,M)$ spaces, with gas-rich galaxies having a larger $j_ast$ and $j_{rm bar}$ (but a lower $j_{rm gas}$) than gas-poor ones. The slopes of the relations have a value around 0.7. These new relations are amongst the tightest known scaling laws for galaxies. In particular, the baryonic relation ($j_{rm bar}-M_{rm bar}-f_{rm gas}$), arguably the most fundamental of the three, is followed not only by typical discs but also by galaxies with extreme properties, such as size and gas content, and by galaxies previously claimed to be outliers of the standard 2D $j-M$ relations. The stellar relation ($j_{ast}-M_{ast}-f_{rm gas}$) may be connected to the known $j_ast-M_ast-$bulge fraction relation; however, we argue that the $j_{rm bar}-M_{rm bar}-f_{rm gas}$ relation can originate from the radial variation in the star formation efficiency in galaxies, although it is not explained by current disc instability models.
A primary goal of integral field spectroscopic (IFS) surveys is to provide a statistical census of galaxies classified by their internal kinematics. As a result, the observational spin parameter, $lambda_R$, has become one of the most popular methods of quantifying the relative importance of velocity dispersion and rotation in supporting a galaxys inner structure. The goal of this paper is to examine the relationship between the observationally deduced $lambda_R$ and one of the most commonly used theoretical spin parameters in the literature, the Bullock et al. (2001) $lambda$. Using a set of $N$-body realisations of galaxies from which we construct mock IFS observations, we measure $lambda_R$ as an observer would, incorporating the effects of beam smearing and seeing conditions. Assuming parameters typical of current IFS surveys, we confirm that there are strong positive correlations between $lambda_R$ and measurement radius, and strong negative correlations between $lambda_R$ and size of the PSF, for late-type galaxies; these biases can be reduced using a recently proposed empirical correction. Once observational biases are corrected for, we find that $lambda_R$ provides a good approximation to $sim sqrt{3}/2 ; lambda(rm R_{rm eff})$, where $lambda$ is evaluated for the galactic stellar component within 1 R$_{rm eff}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
