The SAMI Galaxy Survey: the cluster redshift survey, target selection and cluster properties

Abstract

We describe the selection of galaxies targeted in eight low redshift clusters (APMCC0917, A168, A4038, EDCC442, A3880, A2399, A119 and A85; 0.029 < z < 0.058) as part of the Sydney-AAO Multi-Object integral field Spectrograph Galaxy Survey (SAMI-GS). We have conducted a redshift survey of these clusters using the AAOmega multi-object spectrograph on the 3.9m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterise the dynamical properties of the clusters. In combination with existing data, the survey resulted in 21,257 reliable redshift measurements and 2899 confirmed cluster member galaxies. Our redshift catalogue has a high spectroscopic completeness (∼ 94%) for r petro ≤ 19.4 and clustercentric distances R < 2R 200 . We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, R 200 , virial and caustic masses, as well as cluster structure. The clusters have virial masses 14.25 ≤ log(M 200 /M ⊙ ) ≤ 15.19. The cluster sample exhibits a range of dynamical states, from relatively relaxed-appearing systems, to clusters with strong indications of merger-related substructure. Aperture-and PSF-matched photometry are derived from SDSS and VST/ATLAS imaging and used to estimate stellar masses. These estimates, in combination with the redshifts, are used to define the input target catalogue for the cluster portion of the SAMI-GS. The primary SAMI-GS cluster targets have R <R 200 , velocities |v pec | < 3.5σ 200 and stellar masses 9.5 ≤ log(M * approx /M ⊙ )≤ 12. Finally, we give an update on the SAMI-GS progress for the cluster regions.

Galaxy Cluster Mass Reconstruction Project – III. The impact of dynamical substructure on cluster mass estimates

“…There have been numerous studies since the 1980s probing the frequency of dynamical substructure in cluster samples (e.g., (Geller & Beers 1982;Dressler & Shectman 1988;Rhee et al 1991;Bird 1994;Escalera et al 1994;West et al 1995;Solanes et al 1999;Burgett et al 2004;Owers et al 2009;Aguerri & Sánchez-Janssen 2010, Ziparo et al 2012Einasto et al 2012;Hou et al 2012;Cohn 2012, Owers et al 2017). Many of these works also explored whether measured global properties of clusters differ for clusters in their samples with significant substructure compared to more relaxed clusters.…”

Cluster Cosmology with the Velocity Distribution Function of the HeCS-SZ Sample

“…Differences are found between the velocity dispersions of red galaxies versus the velocity dispersions of all galaxies in a cluster sample, with velocity dispersions of a color-selected sample mildly biased compared to than that of a stellarmass-selected sample (e.g. Biviano et al 2002;Goto 2005;Biviano et al 2006;Gifford et al 2013;Owers et al 2017;Farahi et al 2018;Bilton & Pimbblet 2018). To test for a bias stemming from differences in galaxy selection, we select galaxies from the mock catalog with specific star formation rate (sSFR) ≤ 10 −2 Gyr −1 (as in, e.g., Schaye et al 2015).…”

“…This results in constraints preferring a slightly larger S 8 , though still within 1 2 σ of the standard method. This can be understood in the context of velocity segregation (Biviano et al 2002;Owers et al 2017;Farahi et al 2018), with red or quiescent galaxies having a velocity dispersion that may be ≈ 5% smaller than that of the full cluster sample (Goto 2005;Biviano et al 2006;Gifford et al 2013;Bilton & Pimbblet 2018), and can be attributed to the fact that blue galaxies are typically infalling and, therefore, have higher velocities. However, it should be noted that the effect becomes smaller with well-sampled clusters (Saro et al 2013) and recent simulations find a stellar-massselected sample to be relatively unbiased (< 5% in Armitage et al (2018)), and both of these may contribute to the fact that the Quiescent Velocities constraints are not as extreme as the Biased Velocities constraints.…”

The SAMI Galaxy Survey: rules of behaviour for spin-ellipticity radial tracks in galaxies

“…We use Sydney AAO Multi-object Integral Field (SAMI; Croom et al 2012) spectrograph data obtained as part of the SAMI Galaxy Survey (Bryant et al 2015;Owers et al 2017). The SAMI instrument boasts 13 integral field unit (IFU) hexabundles, enabling the aquisition of spatiallyresolved spectroscopy for 13 objects simultaneously (Bland-Hawthorn et al 2011;Bryant et al 2014).…”

“…The final SAMI Galaxy Survey sample contains ∼ 3000 low redshift (0.004 ≤ z ≤ 0.095) galaxies with a step-wise redshift-dependent stellar mass selection. The details of the SAMI target selection for the Galaxy And Mass Assembly (GAMA, Driver et al (2011)) fields and the cluster samples are discussed by Bryant et al (2015) and Owers et al (2017), respectively. The early, first and second public data releases are described in Allen et al (2015), Green et al (2018) and Scott et al (2018), respectively.…”