Article

# 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: 5.52). 05/2006; 368(4):1515 - 1526. DOI:10.1111/j.1365-2966.2006.10243.x
Source: arXiv

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.

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##### Article: The Clustering Dipole of the Local Universe from the Two Micron All Sky Survey
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ABSTRACT: The unprecedented sky coverage and photometric uniformity of the Two Micron All Sky Survey (2MASS) provides a rich resource for investigating the galaxies populating the local Universe. A full characterization of the large-scale clustering distribution is important for theoretical studies of structure formation. 2MASS offers an all-sky view of the local galaxy population at 2.15 micron, unbiased by young stellar light and minimally affected by dust. We use 2MASS to map the local distribution of galaxies, identifying the largest structures in the nearby universe. The inhomogeneity of these structures causes an acceleration on the Local Group of galaxies, which can be seen in the dipole of the Cosmic Microwave Background (CMB). We find that the direction of the 2MASS clustering dipole is 11 degrees from the CMB dipole, confirming that the local galaxy distribution accelerates the Local Group. From the magnitude of the dipole we find a value of the linear bias parameter b=1.37 +/- 0.3 in the K_s-band. The 2MASS clustering dipole is 19 degrees from the latest measurement of the dipole using galaxies detected by the Infrared Astronomical Satellite (IRAS) suggesting that bias may be non-linear in some wavebands. Comment: 7 pages, 4 figures, submitted to ApJ Letters, a version of the paper with full resolution figures can be found here http://daisy.astro.umass.edu/~ari/
The Astrophysical Journal 03/2003; · 6.73 Impact Factor
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ABSTRACT: We calculate the angular correlation function of galaxies in the Two Micron All Sky Survey. We minimize the possible contamination by stars, dust, seeing and sky brightness by studying their cross correlation with galaxy density, and limiting the galaxy sample accordingly. We measure the correlation function at scales between 1-18 arcdegs using a half million galaxies. We find a best fit power law to the correlation function has a slope of 0.76 and an amplitude of 0.11. However, there are statistically significant oscillations around this power law. The largest oscillation occurs at about 0.8 degrees, corresponding to 2.8 h^{-1} Mpc at the median redshift of our survey, as expected in halo occupation distribution descriptions of galaxy clustering. We invert the angular correlation function using Singular Value Decomposition to measure the three-dimensional power spectrum and find that it too is in good agreement with previous measurements. A dip seen in the power spectrum at small wavenumber k is statistically consistent with CDM-type power spectra. A fit of CDM-type power spectra to k < 0.2 h Mpc^{-1} give constraints of \Gamma_{eff}=0.116 and \sigma_8=0.96. This suggest a K_s-band linear bias of 1.1+/-0.2. This \Gamma_{eff} is different from the WMAP CMB derived value. On small scales the power-law shape of our power spectrum is shallower than that derived for the SDSS. These facts together imply a biasing of these different galaxies that might be nonlinear, that might be either waveband or luminosity dependent, and that might have a nonlocal origin. Comment: 14 pages, 20 figures, to be published in ApJ January 20th, revision included two new figures, version with high resolution figures can be found here http::www
The Astrophysical Journal 04/2003; · 6.73 Impact Factor
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##### Article: Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS
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The Astronomical Journal 04/2003; · 4.97 Impact Factor