The dipole anisotropy of the 2 Micron All‐Sky Redshift Survey

Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.23). 05/2006; 368(4):1515 - 1526. DOI: 10.1111/j.1365-2966.2006.10243.x
Source: OAI

ABSTRACT We estimate the acceleration on the Local Group (LG) from the 2 Micron All-Sky Redshift Survey (2MRS). The sample used includes about 23 200 galaxies with extinction-corrected magnitudes brighter than Ks= 11.25 and it allows us to calculate the flux-weighted dipole. The near-infrared flux-weighted dipoles are very robust because they closely approximate a mass-weighted dipole, bypassing the effects of redshift distortions and require no preferred reference frame. This is combined with the redshift information to determine the change in dipole with distance. The misalignment angle between the LG and the cosmic microwave background (CMB) dipole drops to 12°± 7° at around 50 h−1 Mpc, but then increases at larger distances, reaching 21°± 8° at around 130 h−1 Mpc. Exclusion of the galaxies Maffei 1, Maffei 2, Dwingeloo 1, IC342 and M87 brings the resultant flux dipole to 14°± 7° away from the CMB velocity dipole. In both cases, the dipole seemingly converges by 60 h−1 Mpc. Assuming convergence, the comparison of the 2MRS flux dipole and the CMB dipole provides a value for the combination of the mass density and luminosity bias parameters Ω0.6m/bL= 0.40 ± 0.09.


Available from: Quentin A. Parker, Jun 10, 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dust extinction and stellar confusion by the Milky Way reduce the efficiency of detecting galaxies at low Galactic latitudes, creating the so-called Zone of Avoidance. This stands as a stumbling block in charting the distribution of galaxies and cosmic flow fields, and therewith our understanding of the local dynamics in the Universe (CMB dipole, convergence radius of bulk flows). For instance, ZoA galaxies are generally excluded from the whole-sky Tully-Fisher Surveys ($|b| \leq 5^\circ$) even if catalogued. We show here that by fine-tuning the near-infrared TF relation, there is no reason not to extend peculiar velocity surveys deeper into the ZoA. Accurate axial ratios ($b/a$) are crucial to both the TF sample selection and the resulting TF distances. We simulate the effect of dust extinction on the geometrical properties of galaxies. As expected, galaxies appear rounder with increasing obscuration level, even affecting existing TF samples. We derive correction models and demonstrate that we can reliably reproduce the intrinsic axial ratio from the observed value up to extinction level of about $A_J\simeq3$ mag ($A_V\sim11$ mag), we also recover a fair fraction of galaxies that otherwise would fall out of an uncorrected inclination limited galaxy sample. We present a re-calibration of the 2MTF relation in the NIR $J$, $H$, and $K_s$-bands for isophotal rather than total magnitudes, using their same calibration sample. Both TF relations exhibit similar scatter at high Galactic latitudes. However, the isophotal TF relation results in a significant improvement in the scatter for galaxies in the ZoA, and low surface brightness galaxies in general, because isophotal apertures are more robust in the face of significant stellar confusion.
    Monthly Notices of the Royal Astronomical Society 11/2014; 447(2). DOI:10.1093/mnras/stu2496 · 5.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We test the isotropy of the local distribution of galaxies using the 2MASS extended source catalogue. By decomposing the full sky survey into distinct patches and using photometric redshift data, we use a combination of parametric and non-parametric statistical methods to obtain the shape and normalisation of the luminosity function in each patch. By making various magnitude and density cuts to the data, we reconstruct the luminosity density as a function of median redshift of the sample. We find evidence that the local Universe is locally underdense, with the luminosity density rising by $\sim 40\%$ between mean survey redshifts of $\bar{z} \simeq 0.03$ and $\bar{z} \simeq 0.09$. Specifically, the luminosity function normalisation rises from $\phi^{\ast} = 0.0106 \pm 0.0014 h^{3} {\rm Mpc}^{-3}$ at mean survey redshift $\bar{z} \sim 0.045$ to $\phi^{\ast} = 0.0126 \pm 0.0008 h^{3} {\rm Mpc}^{-3}$ at $\bar{z} \sim 0.09$. The data suggests that the shape of the local $K$-band luminosity function is anisotropic, exhibiting hemispherical asymmetry in the North and South Galactic plane. The inferred total luminosity density increases with survey redshift but is consistent with the assumption of isotropy over the whole sky.
    Journal of Cosmology and Astroparticle Physics 05/2014; 2014(10). DOI:10.1088/1475-7516/2014/10/070 · 5.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present, for the first time, a characterization of the Local Universe (LU) using high precision constrained $N$-body simulations based on self-consistent phase-space reconstructions of the large-scale structure. Our study relies on the Two-Micron All-Sky Galaxy Redshift Survey. The first question we want to address is whether we live in a special cosmic web environment. We assess this problem by estimating cosmic variance from a set of unconstrained $\Lambda$CDM simulations as a function of distance to random observers. By computing volume and mass filling fractions for voids, sheets, filaments and knots, we find that the LU displays a typical scatter of about $1\sigma$ at scales $r\gtrsim15\,h^{-1}\,$Mpc, in agreement with $\Lambda$CDM, converging to a fair unbiased sample when considering spheres of about $60\,h^{-1}\,$Mpc radius. Additionally, we compute the matter density profile of the LU and found a reasonable agreement with the estimates of Karachentsev (2012) only when considering the contribution of dark haloes. This indicates that the observational estimates may be biased towards low density values. As a first application of our reconstructed cosmic web, we investigate the likelihood of different galaxy morphological types to inhabit certain cosmic web environments. In particular we find, that irrespective of the method used to define the web, either based on the density or on the peculiar velocity field, elliptical galaxies show a clear tendency to preferentially reside in clusters as opposed to voids (up to a level of $5.3\sigma$ and $9.8\sigma$ respectively) and the opposite happens to spiral galaxies (up to a level of $5.6\sigma$ and $5.4\sigma$ respectively). These findings are compatible with previous works, however providing results at higher confidence levels.
    Monthly Notices of the Royal Astronomical Society 06/2014; 445(1). DOI:10.1093/mnras/stu1746 · 5.23 Impact Factor