Local Hubble Flow Research Articles

The local Hubble flow: is it a manifestation of dark energy?

ABSTRACT To study the local Hubble flow, we have run constrained dark matter (DM) simula-tions of the Local Group (LG) in the concordance ΛCDM and OCDM cosmologies,with identical cosmological parameters apart from the Λ term. The simulations wereperformed within a computational box of 64h −1 Mpc centred on the LG. The initialconditions were constrained by the observed peculiar velocities of galaxies and posi-tions of X-ray nearby clusters of galaxies. The simulations faithfully reproduce thenearby large scale structure, and in particular the Local Supercluster and the Virgocluster. LG-like objects have been selected from the DM halos so as to closely resemblethe dynamical properties of the LG. Both the ΛCDM and OCDM simulations showvery similar local Hubble flow around the LG-like objects. It follows that, contrary torecent statements, the dark energy (DE) does not manifest itself in the local dynamics.Key words: galaxies: Local Group – cosmology: dark matter – methods: N-bodysimulations

The very local Hubble flow: simulating the transition from chaos to order

The physical nature of the very local (<3 Mpc) Hubble flow is studied on the basis of the recent high-precision observations in the Local Volume. A model including both analytical treatment and computer simulations describes the flow’s dynamical evolution from a chaotic Little Bang initial state to the present-day state of a quasi-regular expansion. The dynamical effect of the uniform cosmic vacuum (time-independent dark energy or the cosmological constant) is taken into account.

The Hubble Flow around the Centaurus A/M83 Galaxy Complex

We present Hubble Space Telescope ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities VLG < 550 km s-1. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 ± 0.05 Mpc, a velocity dispersion of 136 km s-1, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4-8.1) × 1012 M⊙. This elliptical-dominated group is found to have a relatively high mass-to-light ratio: M/LB = 125 M⊙/L⊙. For the M83 group we derived a mean distance of 4.79 ± 0.10 Mpc, a velocity dispersion of 61 km s-1, a mean harmonic radius of 89 kpc, and an estimated orbital/virial mass of (0.8-0.9) × 1012 M⊙. This spiral-dominated group is found to have a relatively low M/LB = 34 M⊙/L⊙. The radius of the zero-velocity surface around Cen A lies at R0 = 1.40 ± 0.11 Mpc, implying a total mass within R0 of MT = (6.0 ± 1.4) × 1012 M⊙. This value is in good agreement with the Cen A orbital/virial mass estimates and provides confirmation of the relatively high M/LB of this elliptical-dominated group. The centroids of both groups, as well as surrounding field galaxies, have very small peculiar velocities, <25 km s-1, with respect to the local Hubble flow with H0 = 68 km s-1 Mpc-1.

Non-Friedmann cosmology for the Local Universe, significance of the universal Hubble constant, and short-distance indicators of dark energy

Based on the increasing evidence of the cosmological relevance of the local Hubble flow, we consider a simple analytical cosmological model for the Local Universe. This is a non-Friedmann model with a non-uniform static space-time. The major dynamical factor controlling the local expansion is the antigravity produced by the omnipresent and permanent dark energy of the cosmic vacuum (or the cosmological constant). The antigravity dominates at larger distances than 1-2 Mpc from the center of the Local group. The model gives a natural explanation of the two key quantitative characteristics of the local expansion flow, which are the local Hubble and the velocity dispersion of the flow. The observed kinematical similarity of the local and global flows of expansion is clarified by the model. We analytically demonstrate the efficiency of the vacuum cooling mechanism that allows one to see the Hubble law this close to the Local group. The universal Hubble constant H V (≈60 km s -1 Mpc -1 ), depending only on the vacuum density, has special significance locally and globally. The model makes a number of verifiable predictions. It also unexpectedly shows that the dwarf galaxies of the local flow with the shortest distances and lowest redshifts may be the most sensitive indicators of dark energy in our neighborhood.

The quiescent Hubble flow, local dark energy tests, and pairwise velocity dispersion in a $ \mathsf{\Omega} = {\mathsf 1}$ universe

We review the increasing evidence for the cosmological relevance of the cold local Hubble flow. New observations, N-body simulations and other theoretical arguments are discussed, supporting our previous suggestion that the cosmological vacuum or uniform dark energy can have locally observable consequencies, especially a lower velocity scatter in DE dominated regions. The apparent contradiction between the slight dependence of the growth factor on ΩΛ and the significant influence of dark energy in realistic N-body calculations is clarified. An interesting new result is that in the standard A cosmology, gravitation dominates around a typical matter fluctuation up to about the correlation length r 0 , and we tentatively link this with the high pairwise velocity dispersion on scales up to several Mpc. as measured from galaxy redshift-space correlations. Locally, the smooth Hubble flow on similar scales is consistent with N-body simulations including ΩΛ 0.7 and a low density contrast in the Local Volume, which make it generally vacuum-dominated beyond 1-2 Mpc from galaxies and groups. We introduce a useful way to view the Hubble flow in terms of zero gravity spheres around galaxies: e.g., a set of non-intersecting spheres, observed to be expanding, actually participates in accelerating expansion. The observed insensitiveness of the local velocity dispersion to galaxy mass is explained as an effect of the vacuum, too.

Gravitational Binding, Virialization, and the Peculiar Velocity Distribution of the Galaxies

We examine the peculiar velocity distribution function of galaxies in cosmological many-body gravitational clustering. Our statistical mechanical approach derives a previous basic assumption and generalizes earlier results to galaxies with haloes. Comparison with the observed peculiar velocity distributions indicates that individual massive galaxies are usually surrounded by their own haloes, rather than being embedded in common haloes. We then derive the density of energy states, giving the probability that a randomly chosen configuration of N galaxies in space is bound and virialized. Gravitational clustering is very efficient. The results agree well with the observed probabilities for finding nearby groups containing N galaxies. A consequence is that our local relatively low mass group is quite typical, and the observed small departures from the local Hubble flow beyond our group are highly probable.

The very local Hubble flow: Computer simulations of dynamical history

The phenomenon of the very local ( ≤ 3 Mpc) Hubble flow is studied on the basis of the data of recent precision observations. A set of computer simulations is performed to trace the trajectories of the flow galaxies back in time to the epoch of the formation of the Local Group. It is found that the “initial conditions” of the flow are drastically different from the linear velocity-distance relation. The simulations enable one also to recognize the major trends of the flow evolution and identify the dynamical role of universal antigravity produced by the cosmic vacuum.

The Cepheid Distance to NGC 5236 (M83) with the ESO Very Large Telescope

Cepheids have been observed in NGC 5236 (M83) using the Antu (Unit Telescope 1) 8.2 m telescope of the ESO Very Large Telescope with the Focal Reducer/Low Dispersion Spectrograph 1. Repeated imaging observations have been made between 2000 January and 2001 July. Images were obtained in 34 epochs in the V band and in six epochs in the I band. The photometry was made with the ROMAFOT reduction package and checked independently with DoPHOT and a modified version of HSTPHOT. Twelve Cepheid candidates have periods ranging between 12 and 55 days. The dereddened distance modulus is adopted to be (m - M)0 = 28.25 ± 0.15, which corresponds to a distance of 4.5 ± 0.3 Mpc. The Cepheid distance of NGC 5253 has been rediscussed and strengthened by its SN 1972E. The mean distance of (m - M)0 = 28.01 ± 0.15 (based on SN 1972E) shows the galaxy to be a close neighbor of M83, suggesting that the two galaxies may have interacted in the past and thus possibly explaining the amorphous morphology of NGC 5253. The distance difference between M83 and NGC 5253 is only 0.5 ± 0.4 Mpc. The projected distance is only ~ 0.15 Mpc. M83 is the principal member of the nearby M83 group containing also, besides NGC 5253, several dwarf members, for five of which tip of the red giant branch distances are available. The adopted group distance of (m - M)0 = 28.28 ± 0.10 (4.5 ± 0.2 Mpc), together with its mean recession velocity of vLG = 249 ± 42 km s-1, shows again the extreme quietness of the local (1-10 Mpc) expansion field. M83 fits onto the local mean Hubble flow line of the velocity-distance relation (with H0~ 60) with no significant deviation, supporting the earlier conclusion that the local velocity expansion field is remarkably cold on a scale of 10 Mpc, contrary to the predictions of the simplest cold dark matter model for large-scale structure. The role of a cosmological constant has been invoked as a possible solution in providing a nearly uniform force field everywhere in the presence of a lumpy galaxy distribution.

Is the Redshift Clustering of Long-Duration Gamma-Ray Bursts Significant?

The 26 long-duration gamma-ray bursts (GRBs) with known redshifts form a distinct cosmological set, selected differently than other cosmological probes such as quasars and galaxies. Since the progenitors are now believed to be connected with active star formation and since burst emission penetrates dust, one hope is that with a uniformly selected sample, the large-scale redshift distribution of GRBs can help constrain the star formation history of the universe. However, we show that strong observational biases in ground-based redshift discovery hamper a clean determination of the large-scale GRB rate and hence the connection of GRBs to the star formation history. We then focus on the properties of the small-scale (clustering) distribution of GRB redshifts. When corrected for heliocentric motion relative to the local Hubble flow, the observed redshifts appear to show a propensity for clustering: eight of 26 GRBs occurred within a recession velocity difference of 1000 km s-1 of another GRB. That is, four pairs of GRBs occurred within 30 h Myr in cosmic time, despite being causally separated on the sky. We investigate the significance of this clustering using a simulation that accounts for at least some of the strong observational and intrinsic biases in redshift discovery. Comparison of the numbers of close redshift pairs expected from the simulation with that observed shows no significant small-scale clustering excess in the present sample; however, the four close pairs occur in only about 20% of the simulated data sets (the precise significance of the clustering is dependent on the modeled biases). We conclude with some impetuses and suggestions for future precise GRB redshift measurements.

Local galaxy flows within 5 Mpc

We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxies as part of our snapshot survey of nearby galaxy candidates. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical accuracy of ~12%. The resulting distances are 4.26 Mpc (KKH 5), 4.74 Mpc (KK 16), 4.72 Mpc (KK 17), 4.66 Mpc (ESO 115-021), 4.43 Mpc (KKH 18), 3.98 Mpc (KK 27), 4.61 Mpc (KKH 34), 4.99 Mpc (KK 54), 4.23 Mpc (ESO 490-017), 4.90 Mpc (FG 202), 5.22 Mpc (UGC 3755), 5.18 Mpc (UGC 3974), 4.51 Mpc (KK 65), 5.49 Mpc (UGC 4115), 3.78 Mpc (NGC 2915), and 5.27 Mpc (NGC 6503). Based on distances and radial velocities of 156 nearby galaxies, we plot the local velocity-distance relation, which has a slope of km s-1 Mpc-1 and a radial velocity dispersion of 85 km s-1. When members of the M81 and Cen A groups are removed, and distance errors are taken into account, the radial velocity dispersion drops to km s-1. The local Hubble flow within 5 Mpc exhibits a significant anisotropy, with two infall peculiar velocity regions directed towards the Supergalactic poles. However, two observed regions of outflow peculiar velocity, situated on the Supergalactic equator, are far away (~50°) from the Virgo/anti-Virgo direction, which disagrees with a spherically symmetric Virgo-centric flow. About 63% of galaxies within 5 Mpc belong to known compact and loose groups. Apart from them, we found six new probable groups, consisting entirely of dwarf galaxies.

The very local Hubble flow

We present Hubble Space Telescope/WFPC2 images of eighteen galaxies situated in the vicinity of the Local Group (LG) as part of an ongoing snapshot survey of nearby galaxies. Their distances derived from the magnitude of the tip of the red giant branch are 1:92 0:10 Mpc (ESO 294-010), 3:06 0:37 (NGC 404), 3:15 0:32 (UGCA 105), 1:36 0:07 (Sex B), 1:33 0:08 (NGC 3109), 2:64 0:21 (UGC 6817), 2:86 0:14 (KDG 90), 2:27 0:19 (IC 3104), 2:54 0:17 (UGC 7577), 2:56 0:15 (UGC 8508), 3:01 0:29 (UGC 8651), 2:610:16 (KKH 86), 2:790:26 (UGC 9240), 1:110:07 (SagDIG), 0:940:04 (DDO 210), 2:070:18 (IC 5152), 2:23 0:15 (UGCA 438), and 2:45 0:13 (KKH 98). Based on the velocity-distance data for 36 nearest galaxies around the LG, we nd the radius of the zero-velocity surface of the LG to beR0 =( 0:940:10) Mpc, which yields a total mass MLG =( 1:3 0:3) 10 12 M. The galaxy distribution around the LG reveals a Local Minivoid which does not contain any galaxy brighter than MV = 11 mag within a volume of100 Mpc 3 . The local Hubble flow seems to be very cold, having a one-dimensional mean random motion of30 km s 1 . The best-t value of the local Hubble parameter is 73 15 km s 1 Mpc 1 . The luminosity function for the nearby eld galaxies is far less steep than one for members of the nearest groups.

Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator

The properties of the velocity field in the local volume (cz < 550 km s-1) have been difficult to constrain because of a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distribution of galaxies in the 1.2 Jy IRAS redshift survey predict a quadrupolar flow pattern locally with strong infall at the poles of the local supergalactic plane. We probe this velocity field and begin to establish a consistent set of galactic distances. We have obtained images of nearby galaxies in the I and V bands from the W. M. Keck Observatory and in F814W and F555W filters from the Hubble Space Telescope. Where these galaxies are well resolved into stars, we can use the tip of the red giant branch (TRGB) as a distance indicator. Using a maximum likelihood analysis to quantitatively measure the I magnitude of the TRGB, we determine precise distances to seven nearby galaxies: Leo I, Sextans B, NGC 1313, NGC 3109, UGC 3755, UGC 6456, and UGC 7577.

Dark energy and the quietness of the local Hubble flow

The linearity and quietness of the local $(&lt;10 \mathrm{Mpc})$ Hubble flow (LHF) in view of the very clumpy local universe is a long standing puzzle in standard and in open CDM (cold dark matter) cosmogony. The question addressed in this paper is whether the antigravity component of the recently discovered dark energy can cool the velocity flow enough to provide a solution to this puzzle. We calculate the growth of matter fluctuations in a flat universe containing a fraction ${\ensuremath{\Omega}}_{X}{(t}_{0})$ of dark energy obeying the time independent equation of state ${p}_{X}=w{\ensuremath{\rho}}_{X}.$ We find that dark energy can indeed cool the LHF. However the dark energy parameter values required to make the predicted velocity dispersion consistent with the observed value ${v}_{\mathrm{rms}}\ensuremath{\simeq}40 \mathrm{km}/\mathrm{s}$ have been ruled out by other observational tests constraining the dark energy parameters w and ${\ensuremath{\Omega}}_{X}.$ Therefore despite the claims of recent qualitative studies, dark energy with time independent equation of state cannot by itself explain the quietness and linearity of the local Hubble flow.

The cold local Hubble flow as a signature of dark energy

The Local Group environment at 1-10 Mpc expands linearly and smoothly, as if ruled by uniform matter, while observations show on the same scales the very lumpy local galaxy universe. This enigma in cosmology has also been demonstrated by high-resolution N-body CDM simulations. We suggest that the homogeneous dark energy component, revealed by SNIa observations, may resolve the problem of the local cold Hubble flow within the highly non-uniform environment. Linear density perturbations on a homogeneous background with the equation of state are decaying for . Exact non-linear Einstein's equations for a spherically symmetric matter concentration, show that there is a zero-mass surface where the positive mass of the local cloud is compensated by the negative dark energy mass, and beyond this surface dark energy dominates dynamically. In such regions the velocity dispersion is adiabatically cooling, and this may explain why the Hubble law starts on the outskirts of the Local Group, with the same H0 as globally and with a remarkably small velocity dispersion.

Probing small length scales in heavy-ion collisions with event-by-event correlation analysis

I consider recent proposals of fluctuation suppression for certain global event variables in heavy-ion collisions as a signature of QGP formation. I relate these proposals to possible formation of a pion lattice at chemical freezeout due to rapid traversal of the QCD phase boundary reflecting the greater symmetry of a locally equilibrated prehadronic state. I then present a method to detect this structure in the transverse phase space of heavy-ion collisions which depends on a newly-identified effect of local transverse Hubble flow on two-particle distributions and suggest that such structure may have been observed already in the transverse phase space of Pb-Pb collisions at the SPS.

A supercluster of IRAS galaxies behind the Great Attractor

THE dynamics of nearby galaxies support the existence of a large concentration of mass (the 'Great Attractor') in the Centaurus region at a redshift (z) between 0.012 and 0.015 (refs 1, 2). Scaramella et al3 have suggested that a concentration of rich clusters of galaxies at z≈0.05 in the Centaurus region may also have a significant role in perturbing the local Hubble flow. The existence of such overdense regions in the Universe would have a profound effect on ideas about the formation of large-scale structure4. At present the reality of such regions is supported by some, but not by all, studies of the streaming of distant galaxies1,2,5–9. We demonstrate here that redshifts of galaxies that are in the Infrared Astronomical Satellite (IRAS) survey show the existence of an extended supercluster at z ≈0.05 surrounding the concentration of clusters described by Scaramella et al. Its contribution to the Local Group peculiar (non-Hubble) velocity is probably minor, although it may dominate motions on the far side of the Great Attractor.

The local extragalactic velocity field, the local mean mass density, and biased galaxy formation

view Abstract Citations (39) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Local Extragalactic Velocity Field, the Local Mean Mass Density, and Biased Galaxy Formation Brown, M. E. ; Peebles, P. J. E. Abstract In this paper, a relationship is derived between the local mass density and the perturbation of the local Hubble flow. The local mass density is estimated by the method used in the Virgocentric flow. The infrared Tully-Fisher relation of Aaronson et al. (1982) is used to find limits on the gravitational perturbation to the local Hubble flow and bright galaxy counts (N) are used to estimate the local galaxy concentration. It is concluded that if mass is proportional to N, with no fluctuations, and the local mass per galaxy is a fair sample, then the density parameter is roughly 0.1, consistent with other dynamical estimates and inconsistent with the naive interpretation of biasing which accounts for the low apparent mass density derived from clustering dynamics by the assumption that the mass per galaxy is unusually low in the regions of high density where clustering has been studied. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/165304 Bibcode: 1987ApJ...317..588B Keywords: Galactic Clusters; Galactic Evolution; Local Group (Astronomy); Mass Distribution; Space Density; Velocity Distribution; Astronomical Models; Computational Astrophysics; Red Shift; Astrophysics; COSMOLOGY; GALAXIES: CLUSTERING; GALAXIES: FORMATION; GALAXIES: REDSHIFTS full text sources ADS | data products NED (16) SIMBAD (15)

On the Virgo supercluster and the mean mass density of the universe

Recent measurements of the anisotropy of the microwave background radiation of the local Hubble flow suggest that the local group of galaxies has a motion of 300--500 km s/sup -1/ directed toward Virgo. If this velocity is generated by the Virgo supercluster, it provides a powerful test of the cosmological parameter ..cap omega... Using a catalog of redshift data complete to m/sub b/=14.0, we have computed the mean overdensity delta-bar toward the Virgo cluster to be approx.2.0 +- 0.3. When this result is combined with a nonlinear spherically symmetric flow model around Virgo, we derive ..cap omega.. approx. = 0.4 +- 0.1. Thus the measured mass-to-light ratio of the universe continues to rise with increasing scale size of measurement.

The growth of aspherical structure in the universe - Is the Local Supercluster an unusual system

view Abstract Citations (146) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The growth of aspherical structure in the universe: Is the Local Supercluster an unusual system? White, S. D. M. ; Silk, J. Abstract The growth and subsequent collapse of homogeneous ellipsoidal perturbations in a uniform expanding background is considered as a simple model for the formation of large-scale aspherical structures in the observed universe. Numerical calculations of the evolution of such perturbations turn out to be well described by an approximate analytic solution of the equations of motion, and simple relationships are found between the initial shape of a perturbation and its shape and kinematic properties at the time of collapse. Perturbations do not change their shape significantly until they reach a density contrast of order unity. As a result, structures with the kinematic properties of the Local Supercluster should form much more commonly in a low-density universe than in a flat universe. The homogeneity of the local Hubble flow, the motion of the Milky Way with respect to the microwave background, and the flattening of the Local Supercluster can be successfully accounted for by these models, provided that the initial perturbation is sufficiently flattened. Viable models are obtained only if the ratio of the lengths of the two smaller axes of the initial perturbation is at least 3:1 in an Einstein-de Sitter universe or at least 1.8:1 in a universe for which the density parameter (Omega) is of order 0.1, when the protocluster pancakes. Publication: The Astrophysical Journal Pub Date: July 1979 DOI: 10.1086/157156 Bibcode: 1979ApJ...231....1W Keywords: Asphericity; Astronomical Models; Cosmology; Galactic Clusters; Spatial Distribution; Galactic Evolution; Numerical Analysis; Universe; Astrophysics; Clusters of Galaxies:Cosmology; Local Supercluster:Formation full text sources ADS |

Groups of Galaxies. II. The Luminosity Function

view Abstract Citations (81) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Groups of Galaxies. II. The Luminosity Function Turner, Edwin L. ; Gott, J. Richard, III Abstract The luminosity function of galaxies in small groups is determined by combining the data on 63 groups from the sample presented in paper I of this series. The data are well fitted by (L) L exp (-LIL*) with a = -1 and L* = 3.4 x 1010 L0. Although several suggestive differences are noted, no statistically significant variations between either rich-cluster and small-group or early and late morphological type luminosity functions are found. A number of useful relations based on the fitted analytic approximation are presented. Luminosity function-based distance and total luminosity estimates (derived using the Schechter and Press method) are given for all of the paper I groups. These data are used to set a weak upper limit of 200 km s ' on perturbations in the local Hubble flow. The relative merits of the luminosity-function distances and the brightest cluster-member distance indicator are examined. Subject headings: cosmology - galaxies: clusters of - luminosity function Publication: The Astrophysical Journal Pub Date: October 1976 DOI: 10.1086/154686 Bibcode: 1976ApJ...209....6T full text sources ADS |