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

Abstract

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.

The near-infrared luminosity function of cluster galaxies beyond redshift one

“…9 the K band M/L ratio for the three clusters is compared to previous determinations at lower redshifts (Carlberg et al 1997;Cirimele et al 1997;Girardi et al 2000;Hradecky et al 2000;Rines et al 2001;Hoekstra et al 2002;Kneib et al 2003;Lin et al 2003;Sanderson & Ponman 2003;Andernach et al 2004;Gavazzi et al 2004;Rines et al 2004).…”

“…Keeping in mind these issues that complicate the comparison of inhomogeneous samples, as well as possible systematic differences in the masses estimated by different means (see for instance Sanderson & Ponman 2003;Andernach et al 2004), we can compare the M/L ratio of the clusters studied in this work with estimates at lower redshift. A comparison of the cluster M/L ratios in the B band, out to redshift z 0.8, was presented for instance by Hoekstra et al (2002), who found that the evolution of the M/L ratio is consistent with the luminosity evolution of galaxies as derived from the fundamental plane in distant clusters (see their Fig.…”

“…The empty symbols show the K band M/L ratio derived from published M/L estimates in other passbands, i.e. B/B j band (circle) from Girardi et al (2000), Hoekstra et al (2002), Sanderson & Ponman (2003), Gavazzi et al (2004), R/r band (square) from Carlberg et al (1997) and Andernach et al (2004), and V band from Cirimele et al (1997) and Hradecky et al (2000) (see text). Crossed and circled points have masses determined from galaxy kinematics or strong/weak lensing respectively, at a difference with X-ray masses used in this work.…”

“…To avoid excessive confusion in the plot, some points do not represent a single cluster but are based on different samples: 32 groups and clusters from Sanderson & Ponman (2003), 8 groups and clusters from Hradecky et al (2000), 16 clusters from Carlberg et al (1997) grouped in 4 redshift bins, 105 clusters from Girardi et al (2000), 12 clusters from Cirimele et al (1997), 13 clusters from Lin et al (2003), 180 clusters from Andernach et al (2004), and 9 clusters from Rines et al (2004). In such cases, the weighted average (and corresponding error) of the sample is plotted in Fig.…”

M/L of X-ray luminous clusters from weak lensing

“…In Figure 1 The halo-mass dependence of M/L is still not a fully resolved issue: While some dynamical studies indicate that mass increases faster than luminosity (Girardi et al 2002), such a trend is not seen from a recent X-ray based study (Sanderson & Ponman 2003). We note that since our clusters only cover a modest range in mass, our results must be combined with other data sets probing less massive systems to be able to address this issue.…”