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We study the relationship between the H{sc i} specific angular momentum (j$_{rm g}$) and the H{sc i} mass (M$_{rm g}$) for a sample of galaxies with well measured H{sc i} rotation curves. We find that the relation is well described by an unbroken power law jg $propto$ mg$^{alpha}$ over the entire mass range (10$^{7}$-10$^{10.5}$ M$_{odot}$), with $alpha = 0.89 pm 0.05$ (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H{sc i} disks in a marginally stable state. The slope we observe is also significantly different from both the $j propto M^{2/3}$ relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disk galaxies. Our sample includes two H{sc i}-bearing ultra diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H{sc i} disks which are found to have significantly higher angular momentum than expected from the power law relation. The H{sc i} disks of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar disks, consistent with the gas being recently accreted. We speculate that late stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations.
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We study the empirical relation between an astronomical objects angular momentum $J$ and mass $M$, $J=beta M^alpha$, the $J-M$ relation, using N-body simulations. In particular, we investigate the time evolution of the $J-M$ relation to study how the initial power spectrum and cosmological model affect this relation, and to test two popular models of its origin - mechanical equilibrium and tidal torque theory. We find that in the $Lambda$CDM model, $alpha$ starts with a value of $sim 1.5$ at high redshift $z$, increases monotonically, and finally reaches $5/3$ near $z=0$, whereas $beta$ evolves linearly with time in the beginning, reaches a maximum and decreases, and stabilizes finally. A three-regime scheme is proposed to understand this newly observed picture. We show that the tidal torque theory accounts for this time evolution behaviour in the linear regime, whereas $alpha=5/3$ comes from the virial equilibrium of haloes. The $J-M$ relation in the linear regime contains the information of the power spectrum and cosmological model. The $J-M$ relations for haloes in different environments and with different merging histories are also investigated to study the effects of a halos non-linear evolution. An updated and more complete understanding of the $J-M$ relation is thus obtained.
In a $Lambda$CDM Universe, the specific stellar angular momentum ($j_ast$) and stellar mass ($M_ast$) of a galaxy are correlated as a consequence of the scaling existing for dark matter haloes ($j_{rm h}propto M_{rm h}^{2/3}$). The shape of this law is crucial to test galaxy formation models, which are currently discrepant especially at the lowest masses, allowing to constrain fundamental parameters, e.g. the retained fraction of angular momentum. In this study, we accurately determine the empirical $j_ast-M_ast$ relation (Fall relation) for 92 nearby spiral galaxies (from S0 to Irr) selected from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample in the unprecedented mass range $7 lesssim log M_ast/M_odot lesssim 11.5$. We significantly improve all previous estimates of the Fall relation by determining $j_ast$ profiles homogeneously for all galaxies, using extended HI rotation curves, and selecting only galaxies for which a robust $j_ast$ could be measured (converged $j_ast(<R)$ radial profile). We find the relation to be well described by a single, unbroken power-law $j_astpropto M_ast^alpha$ over the entire mass range, with $alpha=0.55pm 0.02$ and orthogonal intrinsic scatter of $0.17pm 0.01$ dex. We finally discuss some implications for galaxy formation models of this fundamental scaling law and, in particular, the fact that it excludes models in which discs of all masses retain the same fraction of the halo angular momentum.
We present the relation between stellar specific angular momentum $j_*$, stellar mass $M_*$, and bulge-to-total light ratio $beta$ for THINGS, CALIFA and Romanowsky & Fall datasets, exploring the existence of a fundamental plane between these parameters as first suggested by Obreschkow & Glazebrook. Our best-fit $M_*-j_*$ relation yields a slope of $alpha = 1.03 pm 0.11$ with a trivariate fit including $beta$. When ignoring the effect of $beta$, the exponent $alpha = 0.56 pm 0.06$ is consistent with $alpha = 2/3$ predicted for dark matter halos. There is a linear $beta - j_*/M_*$ relation for $beta lesssim 0.4$, exhibiting a general trend of increasing $beta$ with decreasing $j_*/M_*$. Galaxies with $beta gtrsim 0.4$ have higher $j_*$ than predicted by the relation. Pseudobulge galaxies have preferentially lower $beta$ for a given $j_*/M_*$ than galaxies that contain classical bulges. Pseudobulge galaxies follow a well-defined track in $beta - j_*/M_*$ space, consistent with Obreschkow & Glazebrook, while galaxies with classical bulges do not. These results are consistent with the hypothesis that while growth in either bulge type is linked to a decrease in $j_*/M_*$, the mechanisms that build pseudobulges seem to be less efficient at increasing bulge mass per decrease in specific angular momentum than those that build classical bulges.
We use high-resolution HI data from the WHISP survey to study the HI and angular momentum properties of a sample of 114 late-type galaxies. We explore the specific baryonic angular momentum -- baryonic mass ($j_b - M_b$) relation, and find that an unbroken power law of the form $j_b propto M_b^{0.55 pm 0.02}$ fits the data well, with an intrinsic scatter of $sim 0.13 pm 0.01$ dex. We revisit the relation between the atomic gas fraction, $f_{atm}$, and the integrated atomic stability parameter $q$ (the $f_{atm} - q$ relation), originally introduced by Obreschkow et al., and probe this parameter space by populating it with galaxies from different environments, in order to study the influence of the environment on their $j_b$, $f_{atm}$ and $q$ values. We find evidence that galaxies with close neighbours show a larger intrinsic scatter about the $f_{atm} - q$ relation compared to galaxies without close-neighbours. We also find enhanced SFR among the deviating galaxies with close neighbours. In addition, we use the bulge-to-total (B/T) ratio as a morphology proxy, and find a general trend of decreasing B/T values with increasing disc stability and HI fraction in the $f_{atm} - q$ plane, indicating a fundamental link between mass, specific angular momentum, gas fraction and morphology of galaxies.
We derive the stellar-to-halo specific angular momentum relation (SHSAMR) of galaxies at $z=0$ by combining i) the standard $Lambda$CDM tidal torque theory ii) the observed relation between stellar mass and specific angular momentum (Fall relation) and iii) various determinations of the stellar-to-halo mass relation (SHMR). We find that the ratio $f_j = j_ast/j_{rm h}$ of the specific angular momentum of stars to that of the dark matter i) varies with mass as a double power-law, ii) it always has a peak in the mass range explored and iii) it is $3-5$ times larger for spirals than for ellipticals. The results have some dependence on the adopted SHMR and we provide fitting formulae in each case. For any choice of the SHMR, the peak of $f_j$ occurs at the same mass where the stellar-to-halo mass ratio $f_ast = M_ast/M_{rm h}$ has a maximum. This is mostly driven by the straightness and tightness of the Fall relation, which requires $f_j$ and $f_ast$ to be correlated with each other roughly as $f_jpropto f_ast^{2/3}$, as expected if the outer and more angular momentum rich parts of a halo failed to accrete onto the central galaxy and form stars (biased collapse). We also confirm that the difference in the angular momentum of spirals and ellipticals at a given mass is too large to be ascribed only to different spins of the parent dark-matter haloes (spin bias).
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