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Register a new userEvidence for Rapid Redshift Evolution of Strong Cluster Cooling Flows
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R. Samuele
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We present equivalent widths of the [OII] and Ha nebular emission lines for 77 brightest cluster galaxies (BCGs) selected from the 160 Square Degree $ROSAT$ X-ray survey. We find no [OII] or Ha emission stronger than -15 angstroms or -5 angstroms, respectively, in any BCG. The corresponding emission line luminosities lie below 6E40 erg/s, which is a factor of 30 below that of NGC1275 in the Perseus cluster. A comparison to the detection frequency of nebular emission in BCGs lying at redshifts above z = 0.35 drawn from the Brightest Cluster Survey (Crawford et al. 1999) indicates that we should have detected roughly one dozen emission-line galaxies, assuming the two surveys are selecting similar clusters in the X-ray luminosity range 10E42 erg/s to 10E45 erg/s. The absence of luminous nebular emission (ie., Perseus-like systems) in our sample is consistent with an increase in the number density of {it strong} cooling flow (cooling core) clusters between $rm z=0.5$ and today. The decline in their numbers at higher redshift could be due to cluster mergers and AGN heating.
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We study the evolution of Super Star Cluster (SSC) winds driven by stellar winds and supernova (SN) explosions. Time-dependent rates at which mass and energy are deposited into the cluster volume, as well as the time-dependent chemical composition of the re-inserted gas, are obtained from the population synthesis code Starburst99. These results are used as input for a semi-analytic code which determines the hydrodynamic properties of the cluster wind as a function of cluster age. Two types of winds are detected in the calculations. For the quasi-adiabatic solution, all of the inserted gas leaves the cluster in the form of a stationary wind. For the bimodal solution, some of the inserted gas becomes thermally unstable and forms dense warm clumps which accumulate inside the cluster. We calculate the evolution of the wind velocity and energy flux and integrate the amount of accumulated mass for clusters of different mass, radius and initial metallicity. We consider also conditions with low heating efficiency of the re-inserted gas or mass loading of the hot thermalized plasma with the gas left over from star formation. We find that the bimodal regime and the related mass accumulation occur if at least one of the two conditions above is fulfilled.
The process by which the mass density profile of certain galaxy clusters becomes centrally concentrated enough to produce high strong lensing (SL) cross-sections is not well understood. It has been suggested that the baryonic condensation of the intra-cluster medium (ICM) due to cooling may drag dark matter to the cores and thus steepen the profile. In this work, we search for evidence of ongoing ICM cooling in the first large, well-defined sample of strong lensing selected galaxy clusters in the range 0.1 < z < 0.6. Based on known correlations between the ICM cooling rate and both optical emission line luminosity and star formation, we measure, for a sample of 89 strong lensing clusters, the fraction of clusters that have [OII]3727 emission in their brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs is constant as a function of redshift for z > 0.2 and shows no statistically significant deviation from the total cluster population. Specific star formation rates, as traced by the strength of the 4000 angstrom break, D_4000, are also consistent with the general cluster population. Finally, we use optical imaging of the SL clusters to measure the angular separation, R_arc, between the arc and the center of mass of each lensing cluster in our sample and test for evidence of changing [OII] emission and D_4000 as a function of R_arc, a proxy observable for SL cross-sections. D_4000 is constant with all values of R_arc, and the [OII] emission fractions show no dependence on R_arc for R_arc > 10 and only very marginal evidence of increased weak [OII] emission for systems with R_arc < 10. These results argue against the ability of baryonic cooling associated with cool core activity in the cores of galaxy clusters to strongly modify the underlying dark matter potential, leading to an increase in strong lensing cross-sections.
Abell 383 is a famous rich cluster (z = 0.1887) imaged extensively as a basis for intensive strong and weak lensing studies. Nonetheless there are few spectroscopic observations. We enable dynamical analyses by measuring 2360 new redshifts for galaxies with r$_{petro} leq 20.5$ and within 50$^prime$ of the BCG (Brightest Cluster Galaxy: R.A.$_{2000} = 42.014125^circ$, Decl$_{2000} = -03.529228^circ$). We apply the caustic technique to identify 275 cluster members within 7$h^{-1}$ Mpc of the hierarchical cluster center. The BCG lies within $-11 pm 110$ km s$^{-1}$ and 21 $pm 56 h^{-1}$ kpc of the hierarchical cluster center; the velocity dispersion profile of the BCG appears to be an extension of the velocity dispersion profile based on cluster members. The distribution of cluster members on the sky corresponds impressively with the weak lensing contours of Okabe et al. (2010) especially when the impact of foreground and background structure is included. The values of R$_{200}$ = $1.22pm 0.01 h^{-1}$ Mpc and M$_{200}$ = $(5.07 pm 0.09)times 10^{14} h^{-1}$ M$_odot$ obtained by application of the caustic technique agree well with recent completely independent lensing measures. The caustic estimate extends direct measurement of the cluster mass profile to a radius of $sim 5 h^{-1}$ Mpc.
The mean free path of ionizing photons, $lambda_{rm mfp}$, is a key factor in the photoionization of the intergalactic medium (IGM). At $z gtrsim 5$, however, $lambda_{rm mfp}$ may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of $lambda_{rm mfp}$ that address this bias and extend up to $z sim 6$ for the first time. Our measurements at $z sim 5$ are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At $z sim 6$ we use QSO spectra from Keck ESI and VLT X-Shooter. We measure $lambda_{rm mfp} = 9.09^{+1.62}_{-1.28}$ proper Mpc and $0.75^{+0.65}_{-0.45}$ proper Mpc (68% confidence) at $z = 5.1$ and 6.0, respectively. The results at $z = 5.1$ are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At $z = 6.0$, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at $z = 6.0$ falls well below extrapolations from lower redshifts, indicating rapid evolution in $lambda_{rm mfp}$ over $5 < z < 6$. This evolution disfavors models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by $z = 6$, but is qualitatively consistent with models wherein reionization completed at $z = 6$ or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20% neutral at $z=6$, although our measurement at $z = 6.0$ is even lower than these models prefer.
[Abridged] Due to their large distances, high-z galaxies are observed at a very low spatial resolution. In order to disentangle the evolution of galaxy kinematics from low resolution effects, we have used Fabry-Perot 3D Ha data-cubes of 153 nearby isolated galaxies from the GHASP survey to simulate data-cubes of galaxies at z=1.7. We show that the inner velocity gradient is lowered and is responsible for a peak in the velocity dispersion map. Toy-models of rotating disks have been built to recover the parameters from low resolution data. The poor resolution makes the kinematical inclination uncertain and the center difficult to recover. The major axis is retrieved with an accuracy higher than 5deg for 70% of the sample. Toy-models also enable to retrieve statistically the maximum velocity and the mean velocity dispersion of galaxies with a satisfying accuracy. This validates the use of the Tully-Fisher relation for high-z galaxies but the loss of resolution induces a lower slope at high-z. We conclude that the main kinematic parameters are better constrained for galaxies with an optical radius larger than three times the seeing. The simulated data have been compared to actual high-z galaxies data in the redshift range 3>z>0.4. For rotation-dominated galaxies, we find that the use of the velocity dispersion central peak as a signature of rotating disks may misclassify slow and solid body rotators (~30% of our sample). We show that the projected data cannot reproduce the high velocity dispersion observed in high-z galaxies except when no beam smearing correction is applied. This unambiguously means that, at the opposite of local evolved galaxies, there exists at high redshift at least a population of disk galaxies for which a large fraction of the dynamical support is due to random motions.
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