Witnessing the Hierarchical Assembly of the Brightest Cluster Galaxy in a Cluster at [CLC][ITAL]z[/ITAL][/CLC] = 1.26

Yamada, Tōru; Koyama, Yoshihiro; Nakata, Fumiaki; Kajisawa, Masaru; Tanaka, Ichi; Kodama, Tadayuki; Okamura, S.; Propris, Roberto De

doi:10.1086/344400

Cited by 20 publications

(27 citation statements)

References 34 publications

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“…As already pointed out by van Dokkum et al (2001) and Yamada et al (2002) in their analyses of HST WFPC2 images of these clusters, two luminous red mergers are observed. The first one, in the very center of Lynx E, is composed of two ellipticals and one S0 that lie on the cluster CMR.…”

Section: Discussionsupporting

confidence: 67%

“…Within a theoretical scenario that predicts hierarchical structure formation, at these redshifts galaxy clusters are still in the process of assembling, and the Lynx Clusters might be in the process of merging into a more massive structure. While Lynx E presents a more compact galaxy distribution, with a central bright galaxy merger (Yamada et al 2002), eventually leading to a central cD (cluster dominant) galaxy, the galaxies in Lynx W are more sparsely distributed in a filamentary structure and do not present an obvious central bright cD galaxy (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Evolution of the Color‐Magnitude Relation in High‐Redshift Clusters: Early‐Type Galaxies in the Lynx Supercluster atz∼ 1.26

Mei

Holden

Blakeslee

et al. 2006

ApJ

102

108

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Color-magnitude relations (CMRs) have been derived in two high-redshift clusters, RX J0849+4452 and RX J0848+4453 (with redshifts of z ¼ 1:26 and 1.27, respectively), that lie in the highest redshift cluster superstructure known today, the Lynx Supercluster. The CMR was determined from ACS imaging in the WFC F775W (i 775 ) and F850LP (z 850 ) filters combined with ground-based spectroscopy. Early-type cluster candidates have been identified according to the Postman et al. morphological classification. In both clusters the bright red early-type population defines a tight CMR very similar in color, although the two clusters present different X-ray luminosities and shapes. The elliptical galaxy CMRs in RX J0849+4452 and RX J0848+4453 show an intrinsic (i 775 À z 850 ) color scatter of 0:026 AE 0:012 and 0:024 AE 0:015 mag, respectively, within 2 0 ($1 Mpc at z ¼ 1:26) from the cluster X-ray emission centers. Simple modeling of the scatters using stellar population models from Bruzual and Charlot gives a mean luminosity-weighted age t > 2:5 Gyr (z f > 2:75) and t > 2:6 Gyr (z f > 2:8) for ellipticals in RX J0849+4452 and RX J0848+4453, respectively. S0 galaxies follow the elliptical CMR; they show larger scatters about the CMR. The intrinsic scatter decreases and the CMR slopes are steeper at smaller radii, within both clusters. Within 1 0 from the cluster X-ray emission centers, elliptical CMR scatters imply a mean luminosity-weighted age t > 3:2 Gyr (z f > 3:7). We conclude that old stellar populations in cluster elliptical galaxies are already in place at z ¼ 1:26, both in the more evolved cluster RX J0849+4452 and in its less evolved companion RX J0848+4453. Even at a look-back time of 9 Gyr, in the early merging and buildup of massive clusters, the bulk of the stellar content of the bright elliptical galaxy population was in place-apparently formed some 2.5 Gyr earlier at z $ 3.

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Section: Discussionsupporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Evolution of the Color‐Magnitude Relation in High‐Redshift Clusters: Early‐Type Galaxies in the Lynx Supercluster atz∼ 1.26

Mei

Holden

Blakeslee

et al. 2006

ApJ

102

108

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“…Numerical simulations of cluster formation often show frequent mergers of small galaxies with a larger, central galaxy (e.g., Dubinski 1998). Supporting this view, many central cluster galaxies contain multiple components, and some cluster galaxies at high redshift are apparently merging pairs (Lauer 1988;van Dokkum et al 1999;Yamada et al 2002;Tran et al 2005). One bright galaxy (the "Spiderweb") in a protocluster at is apparently undergoing several minor z p 2.16 mergers (Miley et al 2006).…”

Section: Lmentioning

confidence: 97%

An Extremely Massive Dry Galaxy Merger in a Moderate Redshift Cluster

Rines

Finn

Vikhlinin

2007

ApJ

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We have identified perhaps the largest major galaxy merger ever seen. While analysing Spitzer IRAC images of CL0958+4702, an X-ray selected cluster at z=0.39, we discovered an unusual plume of stars extending $\gtrsim$110 kpc outward from the bright central galaxy (BCG). Three galaxies 1-1.5 mag fainter than the BCG lie within 17 kpc (projected) of the BCG and are probably participating in the merger. The plume is detected in all four IRAC channels and at optical wavelengths in images from the WIYN telescope; the surface brightness is remarkably high ($\mu_r\approx$24.8 mag arcsec$^{-2}$ at 50 kpc). The optical and infrared colors are consistent with those of other BCGs, suggesting that the plume is composed of old stars and negligible recent star formation (hence a "dry merger"). The luminosity in the plume is at least equivalent to a 4L^* galaxy. A diffuse halo extending 110 kpc from the BCG in one IRAC image suggests the total amount of diffuse light is L_r\sim 1.3x10^{11}h^{-2} L_sun. A Chandra observation shows an X-ray image and spectrum typical of moderate-mass clusters. We use MMT/Hectospec to measure 905 redshifts in a 1 deg^2 region around the cluster. The velocities of two of the BCG companions indicate a merger timescale for the companion galaxies of $\sim$110 Myr and $\sim$0.5-1 Gyr for the plume. We conclude that the BCG and intracluster light of CL0958 is formed by major mergers at moderate redshifts. After the major merger is complete, CL0958 will likely become a fossil cluster.Comment: 5 pages, 2 figures, to appear in ApJ

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“…2. The k-correction is well understood over the wavelength range appropriate to our sample (0.9 − 2.2 µm) introducing an uncertainty of about 10% in the rest-frame The cluster X-ray luminosities are bolometric estimates taken from the literature and the cluster The photometry for J1252 and J0849 were sourced from the literature 14,21 and for these galaxies the total K s magnitudes and J − K s colours were measured in similar aperture sizes. All data have been analysed in an identical manner for direct comparison (see Supplementary Information).…”

mentioning

confidence: 99%

Early assembly of the most massive galaxies

Collins

Stott

Hilton

et al. 2009

Nature

166

175

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The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging 1 . Stars begin to form relatively quickly in sub-galactic sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate 2, 3 . Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4 − 5 Gyrs after the Big Bang, having 2 grown to more than 90% of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models 4, 5 based on the largest simulations of dark matter halo development 1 . These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22% of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.Brightest cluster galaxies (BCGs) are located at the centres of galaxy clusters. They constitute a separate population from bright elliptical galaxies 6 and both their homogeneity and extreme luminosity have motivated their use as standard candles for cosmology 7-9 .Our investigation focuses on BCGs in the most distant X-ray emitting galaxy clusters at redshifts z = 1.2 −1.5, where (1 + z) is the expansion factor of the Universe relative to the present. It has been shown that X-ray cluster selection is currently the optimum strategy for an unbiased investigation of BCG evolution 10 . Properties of our BCGs and their host clusters are listed in Table 1. All five clusters were discovered serendipitously in X-rays and they are the most distant clusters discovered in their respective X-ray surveys 11-15 .The cluster J2215 was discovered as part of the XMM Cluster Survey (XCS 16,17 ) and has the highest redshift of any spectroscopically confirmed cluster 12,18 . 3The stellar mass of a BCG depends upon the hierarchical build up of its host dark matter halo and its stellar evolution history, along with the baryonic physics of the galaxy.We base our study of BCGs on photometry in the infrared wavebands J (1.26 µm) and K s (2.14 µm). Infrared imaging is essential at these large redshifts to compensate for the redshifting of the early-type galaxy spectra. Also, these wavebands are less sensitive than optical light to the presence of young stars and are a more accurate tracer of the underlying old stellar population and, hence, of the stellar mass of the systems. Fig. 1 shows an infrared image of the cluster J2235 from our sample (see also Supplementary Fig. 1).We start by examining the ages of the stars themselves in these galaxies using the run of J − K s colour evolution with redshift as shown in Fig. 2. For BCGs at ...

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Witnessing the Hierarchical Assembly of the Brightest Cluster Galaxy in a Cluster at [CLC][ITAL]z[/ITAL][/CLC] = 1.26

Cited by 20 publications

References 34 publications

Evolution of the Color‐Magnitude Relation in High‐Redshift Clusters: Early‐Type Galaxies in the Lynx Supercluster atz∼ 1.26

Evolution of the Color‐Magnitude Relation in High‐Redshift Clusters: Early‐Type Galaxies in the Lynx Supercluster atz∼ 1.26

An Extremely Massive Dry Galaxy Merger in a Moderate Redshift Cluster

Early assembly of the most massive galaxies

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