A Photometric and Kinematic Study of AWM 7

Koranyi, D.; Geller, Margaret J.; Mohr, J. J.; Wegner, Gary A.

doi:10.1086/300611

Cited by 14 publications

(23 citation statements)

References 66 publications

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“…It can be seen that one point in particular is very high on this relation: the poor cluster AWM 7 has (M/L B J ) ∼ 1600 (M/L B J ) , albeit with rather large errors. A large mass-to-light ratio was also measured for this system by Koranyi et al (1998), who found a value for the R band of (650 ± 150) h 100 (M/L) , corresponding to (830 ± 190) h 70 (M/L B J ) , consistent with our 1σ lower bound of ∼650. Exclusion of this point lowers the mean of our sample from 318 ± 52 to 276 ± 32 h 70 (M/L B J ) .…”

Section: Mass-to-light Ratiosupporting

confidence: 90%

The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

Sanderson

Ponman

2003

Monthly Notices of the Royal Astronomical Society

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We investigate the spatial distribution of the baryonic and non‐baryonic mass components in a sample of 66 virialized systems. We have used X‐ray measurements to determine the deprojected temperature and density structure of the intergalactic medium and have employed these to map the underlying gravitational potential. In addition, we have measured the deprojected spatial distribution of galaxy luminosity for a subset of this sample, spanning over two decades in mass. With this combined X‐ray/optical study, we examine the scaling properties of the baryons and address the issue of mass‐to‐light (M/L) ratio in groups and clusters of galaxies. We measure a median mass‐to‐light ratio of 249 h70(M/L)⊙ in the rest frame BJ band, in good agreement with other measurements based on X‐ray determined masses. There is no trend in M/L with X‐ray temperature and no significant trend for mass to increase faster than luminosity: M∝L1.08 ± 0.12 italicB J. This implied lack of significant variation in star formation efficiency suggests that gas cooling cannot be greatly enhanced in groups, unless it drops out to form baryonic dark matter. Correspondingly, our results indicate that non‐gravitational heating must have played a significant role in establishing the observed departure from self‐similarity in low‐mass systems. The median baryon fraction for our sample is 0.162 h−3/270, which allows us to place an upper limit on the cosmological matter density, Ωm≤ 0.27 h−170, in good agreement with the latest results from WMAP. We find evidence of a systematic trend towards higher central density concentration in the coolest haloes, indicative of an early formation epoch and consistent with hierarchical formation models.

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Section: Mass-to-light Ratiosupporting

confidence: 90%

The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

Sanderson

Ponman

2003

Monthly Notices of the Royal Astronomical Society

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“…Bright galaxies come from large haloes ( M 200 >10 13 h −1 M ⊙ , long‐dashed and short‐dashed lines). Note that these haloes show a slight bump in the luminosity function at M B −5 log h ∼−20.5 and −22, similar to the bump in the luminosity function of several real clusters (see, e.g., Molinari et al 1998, Trentham 1998 and Koranyi et al 1998) including Coma (Biviano et al 1995). In the models, this effect originates from the large merger cross‐section of the bright and massive central galaxies, which tend preferentially to accrete galaxies of somewhat lower mass.…”

Section: Groups In Real Spacesupporting

confidence: 62%

Clustering of galaxies in a hierarchical universe -- III. Mock redshift surveys

Diaferio

Kauffmann

Colberg

et al. 1999

Monthly Notices of the Royal Astronomical Society

119

144

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This is the third paper in a series which combines N‐body simulations and semi‐analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a cold dark matter model with either Ω0=1 (τCDM) or Ω0=0.3 and Λ=0.7 (ΛCDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques, and also the relation of these groups to real virialized systems. Most features of CfA2N groups are reproduced quite well by both models with no obvious dependence on Ω0. Redshift‐space correlations and pairwise velocities are also similar in the two cosmologies. The luminosity functions predicted by our galaxy formation models depend sensitively on the treatment of star formation and feedback. For the particular choices of Paper I they agree poorly with the CfA survey. To isolate the effect of this discrepancy on our mock redshift surveys, we modify galaxy luminosities in our simulations to reproduce the CfA luminosity function exactly. This adjustment improves agreement with the observed abundance of groups, which depends primarily on the galaxy luminosity density, but other statistics, connected more closely with the underlying mass distribution, remain unaffected. Regardless of the luminosity function adopted, modest differences with observation remain. These can be attributed to the presence of the ‘Great Wall’ in the CfA2N. It is unclear whether the greater coherence of the real structure is a result of cosmic variance, given the relatively small region studied, or reflects a physical deficiency of the models.

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“…Unfortunately, it is still relatively uncommon to see this correction applied (see, e.g., Koranyi et al 1998). Neglecting this correction leads to overestimate the mass of a system (see, e.g., Carlberg et al 1997a), and this can partly account for some of the claimed discrepancies between optically and X-ray derived cluster mass estimates.…”

Section: The Cluster Mass Estimatesmentioning

confidence: 99%

On the efficiency and reliability of cluster mass estimates based on member galaxies

Biviano¹,

Murante

Borgani

et al. 2006

A&A

232

353

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Aims. We study the efficiency and reliability of cluster mass estimators that are based on the projected phase-space distribution of galaxies in a cluster region. Methods. We analyse a data-set of 62 clusters extracted from a concordance ΛCDM cosmological hydrodynamical simulation. We consider both dark matter (DM) particles and simulated galaxies as tracers of the clusters gravitational potential. Two cluster mass estimators are considered: the virial mass estimator, corrected for the surface-pressure term, and a mass estimator (that we call M σ ) based entirely on the velocity dispersion estimate of the cluster. In order to simulate observations, galaxies (or DM particles) are first selected in cylinders of given radius (from 0.5 to 1.5h −1 Mpc) and 200h −1 Mpc length. Cluster members are then identified by applying a suitable interloper removal algorithm. Results. The virial mass estimator overestimates the true mass by 10% on average, for sample sizes of > ∼ 60 cluster members. For similar sample sizes, M σ underestimates the true mass by 15%, on average. For smaller sample sizes, the bias of the virial mass estimator substantially increases, while the M σ estimator becomes essentially unbiased. The dispersion of both mass estimates increases by a factor ∼2 as the number of cluster members decreases from ∼400 to ∼20. It is possible to reduce the bias in the virial mass estimates either by removing clusters with significant evidence for subclustering or by selecting early-type galaxies, which substantially reduces the interloper contamination. Early-type galaxies cannot however be used to improve the M σ estimates since their intrinsic velocity distribution is slightly biased relative to that of the DM particles. Radially-dependent incompleteness can drastically affect the virial mass estimates, but leaves the M σ estimates almost unaffected. Other observational effects, like centering and velocity errors and different observational apertures, have little effect on the mass estimates.

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A Photometric and Kinematic Study of AWM 7

Cited by 14 publications

References 66 publications

The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

Clustering of galaxies in a hierarchical universe -- III. Mock redshift surveys

On the efficiency and reliability of cluster mass estimates based on member galaxies

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