The 2M++ Galaxy Redshift Catalogue 3 SDSS 6Df
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Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 October 2018 (MN LATEX style file v2.2) The 2M++ galaxy redshift catalogue Guilhem Lavaux1,2 & Michael J. Hudson3,4,5 1 Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080 2 Department of Physics and Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218, USA 3 Institut d’Astrophysique de Paris, UMR7095 CNRS, Univ. Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris, France 4 Department of Physics & Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1 Canada 5 Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON N2L 2Y5, Canada 4 October 2018 ABSTRACT Peculiar velocities arise from gravitational instability, and thus are linked to the surrounding distribution of matter. In order to understand the motion of the Local Group with respect to the Cosmic Microwave Background, a deep all-sky map of the galaxy distribution is required. Here we present a new redshift com- pilation of 69 160 galaxies, dubbed 2M++, to map large-scale structures of the Local Universe over nearly the whole sky, and reaching depths of K ≤ 12.5, or 200h−1 Mpc. The target catalogue is based on the Two-Micron-All-Sky Extended Source Catalog (2MASS-XSC). The primary sources of redshifts are the 2MASS Redshift Survey, the 6dF galaxy redshift survey and the Sloan Digital Sky Sur- vey (DR7). We assess redshift completeness in each region and compute the weights required to correct for redshift incompleteness and apparent magnitude limits, and discuss corrections for incompleteness in the Zone of Avoidance. We present the density field for this survey, and discuss the importance of large-scale structures such as the Shapley Concentration. 1 INTRODUCTION previous full-sky galaxy redshift catalogues like PSCz (Saunders et al. 2000) or the Two-Micron-All-Sky Red- Peculiar velocities remain the only method to map shift Survey (Huchra et al. 2005; Erdo˘gdu et al. 2006a; the distribution of dark matter on very large Huchra et al. 2011, 2MRS). We present here a new cata- scales in the low redshift Universe. Recently, sev- logue called the 2M++ galaxy redshift compilation. The eral intriguing measurements (Kashlinsky et al. 2008; photometry for this compilation is based is on the Two- Watkins et al. 2009; Lavaux et al. 2010; Kashlinsky et al. Micron-All-Sky-Survey (2MASS) Extended Source Cata- 2010; Feldman et al. 2010) of the mean or “bulk” flow log (Skrutskie et al. 2006, 2MASS-XSC). We gather the −1 on scales larger than 100h Mpc suggest a high veloc- high-quality redshifts from the 2MASS redshift survey −1 ity of our local ∼ 100 h Mpc volume with respect (Huchra et al. 2005; Erdo˘gdu et al. 2006a; Huchra et al. to the Cosmic Microwave Background (CMB) frame. 2011) limited to K = 11.5, the 6dF galaxy redshift survey In the standard cosmological framework, peculiar ve- Data Release Three (6dFGRS Jones et al. 2009) and the locities are proportional to peculiar acceleration and so Sloan Digital Sky Survey Data Release Seven (SDSS-DR7 one expects the bulk flow to arise from fluctuations in Abazajian et al. 2009). the distribution of matter, and hence presumably of arXiv:1105.6107v1 [astro-ph.CO] 30 May 2011 galaxies, on very large scales. Another statistic for mea- suring such large-scale fluctuations is the convergence of the gravity dipole as a function of distance. How- A summary of this paper is as follows. In Section 2, ever, the rate of convergence has been a subject of re- we describe the steps in constructing the 2M++ red- cent debate (Kocevski & Ebeling 2006a; Erdo˘gdu et al. shift galaxy catalogue: source selection, magnitude cor- 2006a,b; Lavaux et al. 2010; Bilicki et al. 2011, and refer- rections, redshift incompleteness estimation and correc- ences therein). A closely-related topic is the gravitational tion, the luminosity function (LF) estimation and the influence of the Shapley Concentration, the largest con- final weight computation. In Section 3, we discuss the centration of galaxy clusters in the nearby Universe. It Zone of Avoidance (ZoA) in our catalogue, and how its is therefore important to have catalogues that are as full effects can be mitigated. In Section 4, we define groups sky and as deep as possible to understand whether the of galaxies and check some of their overall properties. In distribution of matter in the nearby Universe may explain Section 5, we compute and analyse the density field, pre- the above-mentioned results. senting maps of the Supergalactic plane and three cluster It is already possible with currently available data density and velocity profiles. Section 6 summarizes our to build a redshift catalogue significantly deeper than key results. c 0000 RAS 2 G. Lavaux & M. J. Hudson 2 CATALOGUE CONSTRUCTION to retain as much as possible information from the shal- lower 2MRS catalogue, we opt to follow closely the mag- In this Section, we describe the construction of the 2M++ nitude used by 2MRS for target selection. We define as galaxy redshift catalogue from the different data sources. K2M++ the magnitude of a galaxy measured in the KS First, in Section 2.1, we describe the source data sets − band, within the circular isophote at 20 mag arcsec 2, af- that form the basis of our catalogue, as well as the pri- ter various corrections as described below (Section 2.2). mary steps in the construction of the 2M++ catalogue. Several of the steps taken to build the catalogue are de- We then present the methodology used for merging these scribed in greater detail in the following Sections. We now different sources. In Section 2.2, we describe the correc- outline these steps: tions applied to apparent magnitudes to homogenize the target selection. In Section 2.3, we test and apply the red- (i) We import the redshift information for 2MASS- shift cloning procedure to our data to increase the overall XSC galaxies from the NYU-VAGC for SDSS-DR7, the redshift completeness. We then estimate redshift com- 6dF-DR3, and from the 2MASS Redshift Survey. pleteness (Section 2.4.2) and present the number counts (ii) We correct for small-scale redshift incompleteness of galaxies as a function of redshift (Section 2.5). Finally, (arising from fibre collisions) by ‘cloning’ the redshifts of we compute the LF of our sample in Section 2.6 and nearby galaxies (Section 2.3). compute the total weights to apply to each galaxy in (iii) We correct the apparent magnitudes for Galactic Section 2.7. dust extinction (Section 2.2). (iv) We use the redshift to correct for galaxy evolution- ary effects and aperture corrections (Section 2.2). We call 2.1 Source datasets and construction procedure this magnitude K2M++. At those magnitudes, we assume that the photometric completeness is one at Galactic lat- Our catalogue is based on the Two-Micron-All-Sky- ◦ Survey (Skrutskie et al. 2006, 2MASS) photometric cat- itudes higher than 10 . alogue for target selection, which has very high com- (v) We compute two sets of galaxy samples: a tar- get sample with K2M++ ≤ 11.5 in regions not covered pleteness up to KS = 13.2 (Cole et al. 2001). Here- by 6dFGRS or SDSS, and a target sample limited to after, for brevity, we use K in place of KS. As noted above, we will be using redshifts from the SDSS- K2M++ ≤ 12.5 in regions covered by SDSS or 6dFGRS. DR7, the 6dfGRS and the 2MRS. In addition to (vi) We estimate the redshift completeness as a func- these main sources, we have gathered additional red- tion of position on the sky for in each of these regions. shifts from a number of other sources (Schneider et al. (vii) We place galaxies in groups and clusters using a 1990; de Vaucouleurs et al. 1991; Binggeli et al. 1993; percolation algorithm. Huchra et al. 1995; Falco et al. 1999; Conselice et al. (viii) We compute the Schechter parameters of the LF 2001; Rines et al. 2003; Koribalski et al. 2004) through of the combined catalogue (Section 2.6). We use this LF NED queries.1 Due to the inhomogeneity of the tar- to compute the weights to apply to each of the observed get selection between the different redshift surveys, we galaxies to take into account the unobserved ones (Sec- think that it is more appropriate to define a new tar- tion 2.7). get selection rather than using existing target databases In future work we will update the estimated distances from the above surveys. We used of the NYU-VAGC for the galaxies using reconstructed velocity field and re- (Blanton et al. 2005) catalogue for matching the SDSS execute step (viii) to update the corrections. The detail of data to the 2MASS Extended Source Catalog (2MASS- this procedure will be discussed in a later paper (Lavaux XSC). The NYU-VAGC provides the SDSS survey mask & Hudson, 2011, in preparation). in MANGLE format (Hamilton & Tegmark 2004).2 We sampled the mask on a HEALPix grid at Nside = 512 (∼10 arcminutes resolution). This angular resolution cor- 2.2 Apparent magnitude corrections responds to ∼1h−1 Mpc at ∼300h−1 Mpc. Because ulti- mately we will be smoothing the density field on scales We describe in this Section the corrections that must be of ∼4h−1 Mpc, the mask has sufficient resolution for our applied to apparent magnitudes to mitigate the effects purposes. Additionally, we filter out from our target se- of cosmological surface brightness dimming, Galactic ex- lection the extended sources that are known not to be tinction and stellar evolution.