Nearby Large-scale Structures Research Articles

The 2019 outburst of AMXP SAX J1808.4–3658 and radio follow up of MAXI J0911–655 and XTE J1701–462

ABSTRACTWe present radio coverage of the 2019 outburst of the accreting millisecond X-ray pulsar (AMXP) SAX J1808.4–3658, obtained with MeerKAT. We compare these data to contemporaneous X-ray and optical measurements in order to investigate the coupling between accretion and jet formation in this system, while the optical light curve provides greater detail of the outburst. The reflaring activity following the main outburst peak was associated with a radio re-brightening, indicating a strengthening of the jet in this phase of the outburst. We place quasi-simultaneous radio and X-ray measurements on the global radio:X-ray plane for X-ray binaries, and show they reside in the same region of luminosity space as previous outburst measurements, but significantly refine the correlation for this source. We also present upper limits on the radio emission from the AMXP MAXI J0911–655 and the transitional Z/Atoll-type transient XTE J1701–462. In the latter source, we also confirm that nearby large-scale structures reported in previous radio observations of the source are persistent over a period of ∼15 yr, and so are almost certainly background radio galaxies and not associated with the X-ray transient.

On the environments of giant radio galaxies

ABSTRACT We test the hypothesis that environments play a key role in enabling the growth of enormous radio structures spanning more than 700 kpc, an extreme population of radio galaxies called giant radio galaxies (GRGs). To achieve this, we explore (1) the relationships between the occurrence of GRGs and the surface number density of surrounding galaxies, including satellite galaxies and galaxies from neighbouring haloes, and (2) the GRG locations towards large-scale structures. The analysis is done by making use of a homogeneous sample of 110 GRGs detected from the LOFAR Two-metre Sky Survey in combination with photometric galaxies from the DESI Legacy Imaging Surveys and a large-scale filament catalogue from the Sloan Digital Sky Survey. Our results show that the properties of galaxies around GRGs are similar with that around the two control samples, consisting of galaxies with optical colours and luminosity matched to the properties of the GRG host galaxies. Additionally, the properties of surrounding galaxies depend on neither their relative positions to the radio jet/lobe structures nor the sizes of GRGs. We also find that the locations of GRGs and the control samples with respect to the nearby large-scale structures are consistent with each other. These results demonstrate that there is no correlation between the GRG properties and their environments traced by stars, indicating that external galaxy environments are not the primary cause of the large sizes of the radio structures. Finally, regarding radio feedback, we show that the fraction of blue satellites does not correlate with the GRG properties, suggesting that the current epoch of radio jets has minimal influence on the nature of their surrounding galaxies.

A Redshift Survey of the Nearby Galaxy Cluster A2107: Global Rotation of the Cluster and Its Connection to Large-scale Structures in the Universe

Abstract We study the rotational motion of the galaxy cluster A2107 at redshift z = 0.04 and its connection to nearby large-scale structures using a large amount of spectroscopic redshift data. By combining 978 new redshifts from the MMT/Hectospec observations with data in the literature, we construct a large sample of 1968 galaxies with measured redshifts at clustercentric radius R < 60′. Our sample has high (80%) and spatially uniform completeness at r-band apparent magnitude . We first apply the caustic method to the sample and identify 285 member galaxies of A2107 at R < 60′. Then the rotation amplitude and the position angle of the rotation axis are measured. We find that the member galaxies show strong global rotation at R < 20′ (v rot/σ v ∼ 0.6) with a significance of >3.8σ, which is confirmed by two independent methods. The rotation becomes weaker in outer regions. There are at least five filamentary structures that are connected to the cluster and that consist of known galaxy groups. These structures are smoothly connected to the cluster, which seem to be inducing the global rotation of the cluster through inflow of galaxies.

Fossil group origins

Context. It is thought that fossil systems are relics of structure formation in the primitive Universe. They are galaxy aggregations that have assembled their mass at high redshift with few or no subsequent accretion. Observationally these systems are selected by large magnitude gaps between their 1st and 2nd ranked galaxies (Δm12). Nevertheless, there is still debate over whether or not this observational criterium selects dynamically evolved ancient systems. Aims. We have studied the properties of the nearby fossil group RX J075243.6+455653 in order to understand the mass assembly of this system. Methods. Deep spectroscopic observations allow us to construct the galaxy luminosity function (LF) of RX J075243.6+455653 down to Mr*+6. The analysis of the faint-end of the LF in groups and clusters provides valuable information about the mass assembly of the system. In addition, we have analyzed the nearby large-scale structure around this group. Results. We identified 26 group members within r200 ~ 0.96 Mpc. These galaxies are located at Vc = 15551 ± 65 km s-1 and have a velocity dispersion of σc = 333 ± 46 km s-1. The X-ray luminosity of the group is LX = 2.2 × 1043 h70-2 erg s-1, resulting in a mass of M = 4.2 × 1013 h70-1 within 0.5r200. The group has Δm12 = 2.1 within 0.5r200, confirming the fossil nature of this system. RX J075243.6+455653 has a central brightest group galaxy (BGG) with Mr = −22.67, one of the faintest BGGs observed in fossil systems. The LF of the group shows a flat faint-end slope (α = −1.08 ± 0.33). This low density of dwarf galaxies is confirmed by the low value of the dwarf-to-giant ratio (DGR = 0.99 ± 0.49) for this system. Both the lack of dwarf galaxies and the low luminosity of the BGG suggests that RX J075243.6+455653 still has to accrete mass from its nearby environment. This mass accretion will be achieved because it is the dominant structure of a rich environment formed by several groups of galaxies (15) within ~ 7 Mpc from the group center and with ± 1000 km s-1. Conclusions. RX J075243.6+455653 is a group of galaxies that has not yet completed the process of its mass assembly. This new mass accretion will change the fossil state of the group. This group is an example of a galaxy aggregation selected by a large magnitude gap but still in the process of the accretion of its mass.

Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

Based on the cosmological hydrodynamic simulations, we investigate the correlations between the spin, velocity shear and vorticity in dark matter halos, as well as the relationship between the baryonic matter and the dark matter. We find that (1) the difference between the vorticity of baryonic matter and that of dark matter is evident on the scales of < 0.2 h−1 Mpc; (2) the vorticity of baryonic matter exhibits a stronger correlation with the tensor of velocity shear than the vorticity of dark matter does; and (3) the spinning direction of small-mass dark matter halos tends to be parallel to the direction of their host filaments, while the spinning direction of massive dark matter halos tends to be perpendicular to the direction of their host filaments, and the intensity of this kind correlation depends on the size of simulation box, and the simulation accuracy. These factors may cause the relationship between the the spins of dark matter halos and those of galaxies to be complicated, and affect the correlation between the galaxy spins and the nearby large-scale structures.

Testing isotropy in the Two Micron All-Sky redshift survey with information entropy

We use information entropy to test the isotropy in the nearby galaxy distribution mapped by the Two Micron All-Sky redshift survey (2MRS). We find that the galaxy distribution is highly anisotropic on small scales. The radial anisotropy gradually decreases with increasing length scales and the observed anisotropy is consistent with that expected for an isotropic Poisson distribution beyond a length scale of $90 \, h^{-1}\, {\rm Mpc}$. Using mock catalogues from N-body simulations, we find that the galaxy distribution in the 2MRS exhibits a degree of anisotropy compatible with that of the $\Lambda$CDM model after accounting for the clustering bias of the 2MRS galaxies. We also quantify the polar and azimuthal anisotropies and identify two directions $(l,b)=(150^{\circ}, -15^{\circ})$, $(l,b)=(310^{\circ},-15^{\circ})$ which are significantly anisotropic compared to the other directions in the sky. We suggest that their preferential orientations on the sky may indicate a possible alignment of the Local Group with two nearby large scale structures. Despite the differences in the degree of anisotropy on small scales, we find that the galaxy distributions in both the 2MRS and the $\Lambda$CDM model are isotropic on a scale of $90 \, h^{-1}\, {\rm Mpc}$.

Constraints on neutrino masses from the study of the nearby large-scale structure and galaxy cluster counts

The high precision measurements of the cosmic microwave background by the Planck survey yielded tight constraints on cosmological parameters and the statistics of the density fluctuations at the time of recombination. This provides the means for a critical study of structure formation in the Universe by comparing the microwave background results with present epoch measurements of the cosmic large-scale structure. It can reveal subtle effects such as how different forms of Dark Matter may modify structure growth. Currently most interesting is the damping effect of structure growth by massive neutrinos. Different observations of low redshift matter density fluctuations provided evidence for a signature of massive neutrinos. Here we discuss the study of the cosmic large-scale structure with a complete sample of nearby, X-ray luminous clusters from our REFLEX cluster survey. From the observed X-ray luminosity function and its reproduction for different cosmological models, we obtain tight constraints on the cosmological parameters describing the matter density, [Formula: see text], and the density fluctuation amplitude, [Formula: see text]. A comparison of these constraints with the Planck results shows a discrepancy in the framework of a pure [Formula: see text]CDM model, but the results can be reconciled, if we allow for a neutrino mass in the range of 0.17 eV to 0.7 eV. Also some others, but not all of the observations of the nearby large-scale structure provide evidence or trends for signatures of massive neutrinos. With further improvement in the systematics and future survey projects, these indications will develop into a definitive measurement of neutrino masses.

Testing the correlations between ultrahigh energy cosmic rays and the Veron-Cetty and Veron catalogue of quasars and active galactic nuclei

We investigate several aspects of the correlations reported by the Pierre Auger Observatory between the highest energy ultra-high energy cosmic rays (UHECRs) and galaxies in the Veron-Cetty Veron (VCV) catalogue of active galactic nuclei (AGNs). First, we quantify the extent of the inhomogeneity and impurity of the VCV catalogue. Second, we determine how the correlation between the highest energy Auger UHECRs and VCV galaxies is modified when only AGNs satisfying optical spectral line ratios, i.e. a very pure sample, are used. Finally, we measure the correlation between the published Auger UHECRs and the distribution of nearby galaxies. We find that the correlation between the arrival directions of published Auger UHECRs and the VCV AGNs is much stronger than the correlation with the random sets of galaxies drawn from nearby large-scale structure. This suggests that the correlation of the UHECRs with AGNs is not solely due to AGNs tracing the large-scale distribution of matter. We also find that once we take into account the heavy oversampling of the VCV catalogue in the Virgo region, the lack of UHECRs from that region is not incompatible with UHECRs having AGN sources.

The 6dF Galaxy Survey: final redshift release (DR3) and southern large-scale structures

We report the final redshift release of the 6dF Galaxy Survey, a combined redshift and peculiar velocity survey over the southern sky (|b|>10 deg). Its 136,304 spectra have yielded 110,256 new extragalactic redshifts and a new catalogue of 125,071 galaxies making near-complete samples with (K, H, J, r_F, b_J) <= (12.65, 12.95, 13.75, 15.60, 16.75). The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online database. We describe changes to the information in the database since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10% of the sample. Here we provide redshift maps of the southern local universe with z<=0.1, showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS database is http://www-wfau.roe.ac.uk/6dFGS

The future of the local large scale structure: the roles of dark matter and darkenergy

We study the distinct effects of dark matter and dark energy on thefuture evolution of nearby large scale structures using constrainedN-body simulations. We contrast a model of cold dark matter and a cosmological constant(ΛCDM) with an open CDM (OCDM) model with the same matter densityΩm = 0.3 and the sameHubble constant h = 0.7. Already by the time the scale factor has increased by a factor of 6 (29 Gyr from now inΛCDM; 78 Gyr from now in OCDM) the comoving position of the Local Group is frozen. Well beforethat epoch the two most massive members of the Local Group, the Milky Way and Andromeda,will merge. However, as the expansion rates of the scale factor in the two models are different,the Local Group will be receding in physical coordinates from Virgo exponentially in aΛCDM model and at a roughly constant velocity in an OCDM model. More generally, in comovingcoordinates the future large scale structure will look like a sharpened image ofthe present structure: the skeleton of the cosmic web will remain the same, butclusters will be more ‘isolated’ and the filaments will become thinner. This impliesthat the long-term fate of large scale structure as seen in comoving coordinatesis determined primarily by the matter density. We conclude that although theΛCDM model is accelerating at present due to its dark energy component while the OCDM modelis non-accelerating, their large scale structures in the future will look very similar incomoving coordinates.

Angular Distribution of Gamma‐Ray Bursts and Weak Lensing

We investigate whether gamma-ray bursts (GRBs) from the current BATSE catalog have been affected by weak lensing by the nearby large-scale structure. The redshift distribution of GRBs is believed to be broad, extending to z ~ 5, so most events can be assumed to be at large redshifts and hence subject to weak lensing, which would betray itself as projected (anti)correlations between GRB events and galaxies or clusters that trace the intervening mass. Given the observed distribution of GRBs in fluence f, and statistical positional error e, we predict that most subsets drawn from the BATSE catalog will be anticorrelated with the foreground structure because of weak lensing, i.e., will show negative magnification bias. We find that GRBs are indeed anticorrelated with the Automatic Plate Measuring Facility (APM) galaxies (z ~ 0.2-0.3) in the sense that galaxy density in circles of radii 1°-15 (15-20 h-1 Mpc at z ~ 0.3) centered on e ≲ 1° GRBs is about 10% lower than expected from a random distribution; the significance of GRB-APM anticorrelations reaches 99.7%. Cross-correlation between GRBs and distant, rich Abell-Corwin-Olowin clusters is also negative. Standard cosmological models with Ωm ~ 0.3, ΩΛ ~ 0.7, and matter distribution on large scales following observed APM galaxy distribution with the biasing parameter of around 1 are not able to reproduce our GRB-APM anticorrelations. We propose a speculative model that does account for these anticorrelations, as well as positive correlations found previously, between quasi-stellar objects and APM galaxies. We briefly discuss if the proposed scheme is in conflict with observations of cosmic microwave background, galaxy surveys, cosmic velocity flows, and weak shear lensing.

Future evolution of nearby large-scale structures in a universe dominated by a cosmological constant

We simulate the future evolution of the observed inhomogeneities in the local universe assuming that the global expansion rate is dominated by a cosmological constant. We find that within two Hubble times (∼30 billion years) from the present epoch, large-scale structures will freeze in co-moving coordinates and the mass distribution of bound objects will stop evolving. The Local Group will get somewhat closer to the Virgo cluster in co-moving coordinates, but will be pulled away from the Virgo in physical coordinates due to the accelerated expansion of the Universe. In the distant future there will only be one massive galaxy within our event horizon, namely the merger product of the Andromeda and the Milky Way galaxies. All galaxies that are not gravitationally bound to the Local Group will recede away from us and eventually exit from our event horizon. More generally, we identify the critical interior overdensity above which a shell of matter around an object will remain bound to it at late times.

The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure

We present evidence to support an earlier indication that the Galaxy is embedded in an extended, highly inclined, triaxial halo outlined by the spatial distribution of companion galaxies to the Milky Way. Signatures of this spatial distribution are seen in (1) the angular variation of the radial velocity dispersion of the companion galaxies, (2) the spatial distribution of the M31 subgroup of galaxies, (3) the spatial distribution of the isolated (mainly dwarf irregular) galaxies of the Local Group, (4) the velocity anisotropy quadrupole of a subgroup of high-velocity clouds, and (5) the spatial distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M31 and surrounding galaxies on the Galaxy are not strong enough to have affected the observed structure. We conclude that this distribution is a reflection of initial conditions. A simple galaxy formation scenario is proposed that relates the results found here to those of Holmberg and Zaritsky et al. regarding the peculiar distribution of satellites around a large sample of spiral galaxies.