Substructure and Dynamics of the Fornax Cluster

By Michael Drinkwater, M. Gregg, M. C. U. O. Melbourne, Igpp, Lawrence Livermore National Laboratory, R. S. O. Astronomy, Astrophysics, The Australian National University. 2000

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We present the first dynamical analysis of a galaxy cluster to include a large fraction of dwarf galaxies. Our sample of 108 Fornax Cluster members measured with the UK Schmidt Telescope FLAIR-II spectrograph contains 55 dwarf galaxies (15.5 > bJ > 18.0 or -16 > MB > -13.5). Hα emission shows that 36% ± 8% of the dwarfs are star forming, twice the fraction implied by morphological classifications. The total sample has a mean velocity of 1493 ± 36 km s-1 and a velocity dispersion of 374 ± 26 km s-1. The dwarf galaxies form a distinct population: their velocity dispersion (429 ± 41 km s-1) is larger than that of the giants (308 ± 30 km s-1) at the 98% confidence level. This suggests that the dwarf population is dominated by infalling objects whereas the giants are virialized. The Fornax system has two components, the main Fornax Cluster centered on NGC 1399 with = 1478 km s-1 and σcz = 370 km s-1 and a subcluster centered 3° to the southwest including NGC 1316 with = 1583 km s-1 and σcz = 377 km s-1. This partition is preferred over a single cluster at the 99% confidence level. The subcluster, a site of intense star formation, is bound to Fornax and probably infalling toward the cluster core for the first time. We discuss the implications of this substructure for distance estimates of the Fornax Cluster. We determine the cluster mass profile using the method of Diaferio, which does not assume a virialized sample. The mass within a projected radius of 1.4 Mpc is (7 ± 2) × 1013 M☉, and the mass-to-light ratio is 300 ± 100 M☉/L☉. The mass is consistent with values derived from the projected mass virial estimator and X-ray measurements at smaller radii.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b06666ee15cc474c9be48732d3fc6ed82938cffe

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Citations in the corpus

• The ACS Virgo Cluster Survey. I. Introduction to the Survey (2004, background): “…degree of substructure (Geller & Beers 1982; Dressler & Schectman 1988; Fitchett & Merritt 1988; Mohr et al. 1993; Bird 1994), and there is mounting evidence that, even among nearby clusters, the process of virialization may not be fully complete (e.g., Adami et al. 1998; Drinkwater et al. 2001).”
• CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey. I. Infall Patterns and Mass Profiles (2006, background): “However, other investigators have found infall patterns around the Fornax Cluster (Drinkwater et al. 2001), the Shapley Supercluster (Reisenegger et al. 2000), an ensemble cluster comprised of poor clusters in the Two Degree Field Galaxy Redshift Survey (Biviano & Girardi 2003), and even the galaxy ”
• MEASURING THE ULTIMATE HALO MASS OF GALAXY CLUSTERS: REDSHIFTS AND MASS PROFILES FROM THE HECTOSPEC CLUSTER SURVEY (HeCS) (2012, background): “However, other investigators have found infall patterns around the Fornax Cluster (Drinkwater et al. 2001), the Shapley Supercluster (Reisenegger et al. 2000), an ensemble cluster comprised of poor clusters in the Two Degree Field Galaxy Redshift Survey (Biviano & Girardi 2003), and even the galaxy ”
• Ultra-diffuse galaxies outside clusters: clues to their formation and evolution (2016, methodology): “For the Coma cluster (Koda et al. 2015), the velocity dispersion was taken from Girardi et al. (1993), whereas for the Fornax cluster (Muñoz et al. 2015) the velocity dispersion is obtained from Drinkwater et al. (2001).”
• What is a cool-core cluster? a detailed analysis of the cores of the X-ray flux-limited HIFLUGCS cluster sample (2009, background): “Although NGC1399 shows some evidence of merging (e.g. Drinkwater et al. 2001), it appears to be just starting to merge so only the outer regions have been affected.”
• Galaxy threshing and the origin of ultra-compact dwarf galaxies in the Fornax cluster (2003, result): “The adopted set of parameters is consistent with the X-ray observations of Jones et al. (1997) and the mass estimation of the Fornax cluster derived from kinematics of the cluster galaxies by Drinkwater et al. (2001).”
• The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies (2005, background): “These objects appear to be similar to UCD3, the brightest of the compact objects in Fornax, which Drinkwater et al. (2001) have suggested is surrounded by a low surface brightness envelope.”
• WIDE-FIELD PRECISION KINEMATICS OF THE M87 GLOBULAR CLUSTER SYSTEM (2011, background): “Thus NGC 1399, like M87, shows no transition to hotter cluster kinematics (which would be ∼ 300– 400 km s−1; e.g., Drinkwater et al. 2001).”