Velocity Dispersions and X-Ray Temperatures of Galaxy Clusters

Girardi, M.; Fadda, D.; Giuricin, G.; Mardirossian, F.; Mezzetti, M.; Biviano, A.

doi:10.1086/176711

Cited by 181 publications

(276 citation statements)

References 43 publications

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“…Employing the least-square fit of a power-law to the data of Fig.1 yields (σ gal /km s −1 ) = 10 2.57±0.13 (kT /keV) 0.59±0.14 . Regardless of its large error bars, this relationship is essentially identical with the one for the nearby clusters (Girardi et al 1996 and references therein), and is also consistent with the isothermal hydrostatic scenario of σ gal ∼ T 0.5 . Based on the σ gal −T relationship alone, we may conclude that no significant dynamical and cosmic evolution has been detected for those massive lensing clusters within intermediate redshift z d ≈ 0.3.…”

Section: Samplesupporting

confidence: 82%

A comparison of different cluster mass estimates: consistency or discrepancy?

Chiueh

Fang

et al. 1998

Monthly Notices of the Royal Astronomical Society

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Rich and massive clusters of galaxies at intermediate redshift are capable of magnifying and distorting the images of background galaxies. A comparison of different mass estimators among these clusters can provide useful information about the distribution and composition of cluster matter and their dynamical evolution. Using a hitherto largest sample of lensing clusters drawn from literature, we compare the gravitating masses of clusters derived from the strong/weak gravitational lensing phenomena, from the X-ray measurements based on the assumption of hydrostatic equilibrium, and from the conventional isothermal sphere model for the dark matter profile characterized by the velocity dispersion and core radius of galaxy distributions in clusters. While there is an excellent agreement between the weak lensing, X-ray and isothermal sphere model determined cluster masses, these methods are likely to underestimate the gravitating masses enclosed within the central cores of clusters by a factor of 2-4 as compared with the strong lensing results. Such a mass discrepancy has probably arisen from the inappropriate applications of the weak lensing technique and the hydrostatic equilibrium hypothesis to the central regions of clusters as well as an unreasonably large core radius for both luminous and dark matter profiles. Nevertheless, it is pointed out that these cluster mass estimators may be safely applied on scales greater than the core sizes. Namely, the overall clusters of galaxies at intermediate redshift can still be regarded as the dynamically relaxed systems, in which the velocity dispersion of galaxies and the temperature of X-ray emitting gas are good indicators of the underlying gravitational potentials of clusters.

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Section: Samplesupporting

confidence: 82%

A comparison of different cluster mass estimates: consistency or discrepancy?

Chiueh

Fang

et al. 1998

Monthly Notices of the Royal Astronomical Society

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“…The corresponding members were then identified using the distance-velocity diagram (Fig. 6), which consists in the so-called "shifting gapper" method Girardi et al 1996). This procedure rejects galaxies within a fixed distance bin that are too far in velocity from the main body of the system.…”

Section: System Membershipmentioning

confidence: 99%

Fossil group origins

Zarattini¹,

Barrena²,

Girardi³

et al. 2014

A&A

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Context. Virialized halos grow by the accretion of smaller ones in the cold dark matter scenario. The rate of accretion depends on the different properties of the host halo. Those halos for which this accretion rate was very fast and efficient resulted in systems dominated by a central galaxy surrounded by smaller galaxies that were at least two magnitudes fainter. These galaxy systems are called fossil systems, and they can be the fossil relics of ancient galaxy structures. Aims. We started an extensive observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Methods. Deep r-band images were obtained with the 2.5-m Isaac Newton Telescope and Nordic Optic Telescope. Optical spectroscopic observations were performed at the 3.5-m Telescopio Nazionale Galileo for ∼1200 galaxies. This new dataset was completed with Sloan Digital Sky Survey Data Release 7 archival data to obtain robust cluster membership and global properties of each fossil group candidate. For each system, we recomputed the magnitude gaps between the two brightest galaxies (Δm 12 ) and the first and fourth ranked galaxies (Δm 14 ) within 0.5 R 200 . We consider fossil systems to be those with Δm 12 ≥ 2 mag or Δm 14 ≥ 2.5 mag within the errors. Results. We find that 15 candidates turned out to be fossil systems. Their observational properties agree with those of non-fossil systems. Both follow the same correlations, but the fossil systems are always extreme cases. In particular, they host the brightest central galaxies, and the fraction of total galaxy light enclosed in the brightest group galaxy is larger in fossil than in non-fossil systems. Finally, we confirm the existence of genuine fossil clusters. Conclusions. Combining our results with others in the literature, we favor the merging scenario in which fossil systems formed from mergers of L * galaxies. The large magnitude gap is a consequence of the extreme merger ratio within fossil systems and therefore it is an evolutionary effect. Moreover, we suggest that at least one fossil group candidate in our sample could represent a transitional fossil stage. This system could have been a fossil in the past, but not now owing to the recent accretion of another group of galaxies.

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“…First, we performed the 1D adaptive-kernel method (hereafter DEDICA, Pisani 1993Pisani , 1996; see also Fadda et al 1996;Girardi et al 1996). We searched for significant peaks in the velocity distribution at >99% c.l.…”

Section: Member Selectionmentioning

confidence: 99%

Internal dynamics of Abell 1240: a galaxy cluster with symmetric double radio relics

Barrena¹,

Girardi

Boschin

et al. 2009

A&A

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Context. The mechanisms giving rise to diffuse radio emission in galaxy clusters, and in particular their connection with cluster mergers, are still debated. Aims. We aim to obtain new insights into the internal dynamics of the cluster Abell 1240, which appears to contain two roughly symmetric radio relics, separated by ∼2 h −1 70 Mpc. Methods. Our analysis is based mainly on redshift data for 145 galaxies mostly acquired at the Telescopio Nazionale Galileo and on new photometric data acquired at the Isaac Newton Telescope. We also use X-ray data from the Chandra archive and photometric data from the Sloan Digital Sky Survey (Data Release 7). We combine galaxy velocities and positions to select 89 cluster galaxies and analyze the internal dynamics of the Abell 1237 + Abell 1240 cluster complex, Abell 1237 being a close companion of Abell 1240 in its southern direction. Results. We estimate similar redshifts for Abell 1237 and Abell 1240, z = 0.1935 and z = 0.1948, respectively. For Abell 1237, we estimate a line-of-sight (LOS) velocity dispersion of σ V ∼ 740 km s −1 and a mass of M ∼ 6 × 10 14 h −1 70 M . For Abell 1240, we estimate a LOS σ V ∼ 870 km s −1 and a mass in the range M ∼ 0.9−1.9 × 10 15 h −1 70 M , which takes account of its complex dynamics. Abell 1240 is shown to have a bimodal structure with two galaxy clumps roughly aligned along its N-S direction, the same as defined by the elongation of its X-ray surface brightness and the axis of symmetry of the relics. The two brightest galaxies of Abell 1240, associated with the northern and southern clumps, are separated by a LOS rest-frame velocity difference V rf ∼ 400 km s −1 and a projected distance D ∼ 1.2 h −1 70 Mpc. The two-body model agrees with the hypothesis that we are looking at a cluster merger that occurred largely in the plane of the sky, the two galaxy clumps being separated by a rest-frame velocity difference V rf ∼ 2000 km s −1 at a time of 0.3 Gyr after the crossing core, while Abell 1237 is still infalling onto Abell 1240. Chandra archive data confirm the complex structure of Abell 1240 and allow us to estimate a global X-ray temperature of T X = 6.0 ± 0.5 keV. Conclusions. In agreement with the findings from radio data, our results for Abell 1240 strongly support the "outgoing merger shocks" model to explain the presence of the relics.

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Velocity Dispersions and X-Ray Temperatures of Galaxy Clusters

Cited by 181 publications

References 43 publications

A comparison of different cluster mass estimates: consistency or discrepancy?

A comparison of different cluster mass estimates: consistency or discrepancy?

Fossil group origins

Internal dynamics of Abell 1240: a galaxy cluster with symmetric double radio relics

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