Abstract A numerical detection of the τ -driven transition of galaxy spins is presented, where τ is the degree of misalignment between the initial tidal field and protogalaxy inertia tensors. ...Analyzing the data from the IllustrisTNG300-1 simulations, we first measure the values of τ at the protogalactic sites found by tracing the constituents of the galactic halos in the mass range of 10.5 ≤ log M h / ( h − 1 M ⊙ ) ≤ 13 back to the initial stage, z i = 127. The probability density functions of τ are shown to be well modeled by the Γ-distributions, whose shape and scale parameters turn out to have universal values on a certain critical scale. Then, we investigate how the strength and tendency of the galaxy spin alignments with the principal axes of the local tidal fields depend on the initial condition, τ . It is found that on a scale lower than the critical one, the galaxy spin transition occurs at two different thresholds from the major to intermediate and from the intermediate to minor principal axes of the local tidal fields, respectively. Noting that the τ -dependent spin transition supersedes the strength of the previously found mass-dependent, morphology-dependent, and radius-dependent counterparts, we suggest that τ should be the key driver of all types of galaxy spin transitions and that the present galaxy spins are indeed excellent fossil records of their origin.
Abstract
A numerical detection of the radius-dependent spin transition of dark matter halos is reported. Analyzing the data from the IllustrisTNG simulations, we measure the halo spin vectors at ...several inner radii within the virial boundaries and investigate their orientations in the principal frames of the tidal and velocity shear fields, called the Tweb and Vweb, respectively. The halo spin vectors in the high-mass section exhibit a transition from the Tweb intermediate to major principal axes as they are measured at more inner radii, which holds for both the dark matter and baryonic components. The radius threshold at which the transition occurs depends on the smoothing scale,
R
f
, becoming larger as
R
f
decreases. For the case of the Vweb, the occurrence of the radius-dependent spin transition is witnessed only when
R
f
≥ 1
h
−1
Mpc. Repeating the same analysis but with the vorticity vectors, we reveal a critical difference from the spins. The vorticity vectors are always perpendicular to the Tweb (Vweb) major principal axes, regardless of
R
f
, which indicates that the halo inner spins are not strongly affected by the generation of vorticity. It is also shown that the halo spins, as well as the Tweb (Vweb) principal axes, have more directional coherence over a wide range of radial distances in the regions where the vorticity vectors have higher magnitudes. The physical interpretations and implications of our results are discussed.
Abstract
Galaxy spins are believed to retain the initially acquired tendency of being aligned with the intermediate principal axis of the linear tidal field, which disseminates the prospect of using ...them as a probe of early universe physics. This roseate prospect, however, is contingent upon the key assumption that the observable stellar spins of present galaxies measured at inner radii have the same alignment tendency toward the initial tidal field as their dark matter counterparts measured at virial limits. We test this assumption directly against a high-resolution hydrodynamical simulation by tracing the galaxy component particles back to the protogalactic stage. It is discovered that the galaxy stellar spins at
z
= 0 have strong but reoriented memory for the early universe, exhibiting a significant signal of cross-correlation with the major principal axis of the initial tidal field at
z
= 127. An analytic single-parameter model for this reorientation of the present galaxy stellar spins relative to the initial tidal field is devised and shown to be in good accord with the numerical results.
Abstract
We develop a new model within which the radius-dependent transition of the subhalo inner spins with respect to the cosmic web and the variation of the transition threshold radius (
r
th
) ...with subhalo mass (
M
vir
), smoothing scale (
r
f
), and redshift (
z
) can be coherently explained. The key tenet of this model is that the competition between the pressure effect of the inner mass and the compression effect of the local tidal field determines which principal direction of the tidal field the inner spins are aligned with. If the former predominates, then only the tidal torques turn on, resulting in the alignments of the inner spins with the intermediate principal axes of the tidal field. Otherwise, the subhalo spins acquire a tendency to be aligned with the shortest axes of the subhalo shapes, which is in the major principal directions of the tidal field. Quantifying the two effects in terms of the densities, we make a purely analytical prediction for
r
th
(
M
vir
,
z
,
r
f
). Testing this model against the numerical results from a high-resolution dark-matter-only
N
-body simulation in the redshift range of 0 ≤
z
≤ 3 on the galactic mass scale of
11.8
≤
log
M
vir
/
(
h
−
1
M
⊙
)
≤
12.6
for two different cases of
r
f
/(h
-1
Mpc)
= 0.5 and 1, we find excellent agreements of the model predictions with the numerical results. It is also shown that this model naturally predicts the alignments between the inner spins of the present subhalos with the principal axes of the high-
z
tidal field at the progenitors’ locations.
Abstract
In linear theory, the galaxy angular momentum vectors that originate from initial tidal interactions with surrounding matter distribution intrinsically develop perpendicular alignments with ...the directions of maximum matter compression, regardless of galaxy mass. In simulations, however, galaxy spins exhibit parallel alignments in the mass range lower than a certain threshold, which depends on redshift, web type, and background cosmology. We show that the observed three-dimensional spins of the spiral galaxies located on the void surfaces from the Sloan Digital Sky Survey indeed transit from perpendicular to parallel alignments with the directions toward the nearest void centers at the threshold zone,
9.51
≤
log
M
th
,
⋆
/
(
h
−
1
M
⊙
)
≤
10.03
. This study presents the first direct observational evidence for the occurrence of mass-dependent spin transition of real galaxies with respect to non-filamentary structures of the cosmic web, opening a way to constrain the initial conditions of the early universe by measuring the spin transition threshold.
Gut microbiota play an important part in the pathogenesis of mucosal inflammation, such as inflammatory bowel disease (IBD). However, owing to the complexity of the gut microbiota, our understanding ...of the roles of commensal and pathogenic bacteria in the maintenance of immune homeostasis in the gut is evolving only slowly. Here, we evaluated the role of gut microbiota and their secreting extracellular vesicles (EV) in the development of mucosal inflammation in the gut. Experimental IBD model was established by oral application of dextran sulfate sodium (DSS) to C57BL/6 mice. The composition of gut microbiota and bacteria-derived EV in stools was evaluated by metagenome sequencing using bacterial common primer of 16S rDNA. Metagenomics in the IBD mouse model showed that the change in stool EV composition was more drastic, compared to the change of bacterial composition. Oral DSS application decreased the composition of EV from Akkermansia muciniphila and Bacteroides acidifaciens in stools, whereas increased EV from TM7 phylum, especially from species DQ777900_s and AJ400239_s. In vitro pretreatment of A. muciniphila-derived EV ameliorated the production of a pro-inflammatory cytokine IL-6 from colon epithelial cells induced by Escherichia coli EV. Additionally, oral application of A. muciniphila EV also protected DSS-induced IBD phenotypes, such as body weight loss, colon length, and inflammatory cell infiltration of colon wall. Our data provides insight into the role of gut microbiota-derived EV in regulation of intestinal immunity and homeostasis, and A. muciniphila-derived EV have protective effects in the development of DSS-induced colitis.
Abstract
We present a numerical evidence supporting the scenario that the peculiar alignments of the galaxy stellar spins with the major principal axes of the local tidal tensors are produced during ...the quiescent evolution period when the galaxies experience no recent merger events. Analyzing the merger tree from the TNG300-1 simulation of the IllustrisTNG project, we find the latest merger epochs,
a
(
z
m
), of the galaxies, and create four
a
(
z
m
)-selected samples that are controlled to share the identical mass and density distributions. For each sample, we determine the spin and shape vectors of the galaxy stellar, cold and hot gas, and dark matter components separately, and compute the average strengths of their alignments with the principal directions of the local tidal fields as well as their mutual alignment tendencies. It is found that the stellar (cold gas) spin axes of the galaxies whose latest merger events occur at earlier epochs are more strongly aligned (weakly antialigned) with the major principal axes of the tidal fields. It is also shown that, although the mass-dependent transition of the galaxy DM spins have little connection with the merger events, the morphologies, spin–shape, and shape-shear alignment strengths of the four components of the galaxies sensitively depend on
a
(
z
m
). Noting that the stellar components of the galaxies that undergo long quiescent evolution have distinctively oblate shapes and very strong spin–shape alignments, we suggest that the local tidal field might be traced by using the stellar shapes of galaxies without signatures of mergers as a proxy of their stellar spins.
Galaxies in pairs show enhanced star formation (SF) compared to their counterparts in isolation, which is often explained by the tidal effect of neighboring galaxies. Recent observations, however, ...reported that galaxies paired with early-type neighbors do not undergo the SF enhancement. Here we revisit the influence of neighbors using a large sample of paired galaxies from the Sloan Digital Sky Survey and a carefully constructed control sample of isolated counterparts. We find that star-forming neighbors enhance SF, and even more so for more star-forming (and closer) neighbors, which can be attributed to collisions of interstellar medium (ISM) leading to SF. We further find that, contrary to the anticipated tidal effect, quiescent neighbors quench SF, and even more so for more quiescent (and closer) neighbors. This seems to be due to removal of gas reservoirs via ram pressure stripping and gas accretion cut off by hot gas halos of quiescent neighbors, on top of their paucity of ISM to collide to form stars. Our findings, especially the intimate connection of SF to the status and strength of neighbors' SF, imply that the hydrodynamic mechanisms, along with the tidal effect, play a crucial role during the early phase of galactic interactions.
Abstract
Recent observations revealed a coherence between the spin vector of a galaxy and the orbital motion of its neighbors. We refer to the phenomenon as “the spin–orbit alignment (SOA)” and ...explore its physical origin via the IllustrisTNG simulation. This is the first study to utilize a cosmological hydrodynamic simulation to investigate the SOA of galaxy pairs. In particular, we identify paired galaxies at
z
= 0 having the nearest neighbor with mass ratios from 1/10 to 10 and calculate the spin–orbit angle for each pair. Our results are as follows. (a) There exists a clear preference for prograde orientations (i.e., SOA) for galaxy pairs, qualitatively consistent with observations. (b) The SOA is significant for both baryonic and dark matter spins, being the strongest for gas and the weakest for dark matter. (c) The SOA is stronger for less massive targets and for targets having closer neighbors. (d) The SOA strengthens for galaxies in low-density regions, and the signal is dominated by central–satellite pairs in low-mass halos. (e) There is an explicit dependence of the SOA on the duration of interaction with its current neighbor. Taken together, we propose that the SOA witnessed at
z
= 0 has been developed mainly by interactions with a neighbor for an extended period of time, rather than tidal torque from the ambient large-scale structure.
Abstract
We explore how the galaxy stellar spins acquire a peculiar tendency of being aligned with the major principal axes of the local tidal fields, in contrast to their dark matter (DM) ...counterparts, which tend to be perpendicular to them, regardless of their masses. Analyzing the halo and subhalo catalogs from IllustrisTNG 300 hydrodynamic simulations at
z
≤ 1, we determine the cosines of the alignment angles,
cos
α
, between the galaxy stellar and DM spins. Creating four
cos
α
-selected samples of the galaxies and then controlling them to share the same density and mass distributions, we determine the average strengths of the alignments between the galaxy stellar spins and the tidal tensor major axes over each sample. It is clearly shown that at
z
≤ 0.5 the more severely the galaxy stellar spin directions deviate from the DM counterparts, the stronger the peculiar tidal alignments become. Taking the ensemble averages of such galaxy properties as central black hole-to-stellar mass ratio, specific star formation rate, formation epoch, stellar-to-total mass ratio, velocity dispersions, average metallicity, and degree of the cosmic web anisotropy over each sample, we also find that all of these properties exhibit either strong correlations or anticorrelations with
cos
α
. Our results imply that the peculiar tidal alignments of the galaxy stellar spins may be caused by anisotropic occurrence of some baryonic process responsible for discharging stellar materials from the galaxies along the tidal major directions at
z
< 1.
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