arXiv subjects

Craig L. Sarazin

Publications and source records attributed to Craig L. Sarazin.

At least 55 records · Page 3Linked to original sources

arXiv2010

The Impact of Non-Equipartition on Cosmological Parameter Estimation from Sunyaev-Zel'dovich Surveys

The collisionless accretion shock at the outer boundary of a galaxy cluster should primarily heat the ions instead of electrons since they carry most of the kinetic energy of the infalling gas. Near the accretion shock, the density of the intracluster medium is very low and the Coulomb collisional timescale is longer than the accretion timescale. Electrons and ions may not achieve equipartition in these regions. Numerical simulations have shown that the Sunyaev-Zel'dovich observables (e.g., the integrated Comptonization parameter Y) for relaxed clusters can be biased by a few percent. The Y-mass relation can be biased if non-equipartition effects are not properly taken into account. Using a set of hydrodynamical simulations, we have calculated three potential systematic biases in the Y-mass relations introduced by non-equipartition effects during the cross-calibration or self-calibration when using the galaxy cluster abundance technique to constraint cosmological parameters. We then use a semi-analytic technique to estimate the non-equipartition effects on the distribution functions of Y (Y functions) determined from the extended Press-Schechter theory. Depending on the calibration method, we find that non-equipartition effects can induce systematic biases on the Y functions, and the values of the cosmological parameters Omega_8, sigma_8, and the dark energy equation of state parameter w can be biased by a few percent. In particular, non-equipartition effects can introduce an apparent evolution in w of a few percent in all of the systematic cases we considered. Techniques are suggested to take into account the non-equipartition effect empirically when using the cluster abundance technique to study precision cosmology. We conclude that systematic uncertainties in the Y-mass relation of even a few percent can introduce a comparable level of biases in cosmological parameter measurements.

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arXiv2010

Active galactic nucleus feedback in clusters of galaxies

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves.

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arXiv2010

The 400d Galaxy Cluster Survey Weak Lensing Programme: I: MMT/Megacam Analysis of CL0030+2618 at z=0.50

The mass function of galaxy clusters at high redshifts is a particularly useful probe to learn about the history of structure formation and constrain cosmological parameters. We aim at deriving reliable masses for a high-redshift, high-luminosity sample of clusters of galaxies selected from the 400d survey of X-ray selected clusters. Here, we will focus on a particular object, CL0030+2618 at z=0.50 Using deep imaging in three passbands with the MEGACAM instrument at MMT, we show that MEGACAM is well-suited for measuring gravitational shear. We detect the weak lensing signal of CL0030+2618 at 5.8 sigma significance, using the aperture mass technique. Furthermore, we find significant tangential alignment of galaxies out to ~10 arcmin or >2r_200 distance from the cluster centre. The weak lensing centre of CL0030+2618 agrees with several X-ray measurements and the position of the brightest cluster galaxy. Finally, we infer a weak lensing virial mass of M_200=7.5 10^{14} M_sun for CL0030+2618. Despite complications by a tentative foreground galaxy group in the line of sight, the X-ray and weak lensing estimates for CL0030+2618 are in remarkable agreement. This study paves the way for the largest weak lensing survey of high-redshift galaxy clusters to date.

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arXiv2009

What is a Cool-Core Cluster? A Detailed Analysis of the Cores of the X-ray Flux-Limited HIFLUGCS Cluster Sample

We use the largest complete sample of 64 galaxy clusters (HIghest X-ray FLUx Galaxy Cluster Sample) with available high-quality X-ray data from Chandra, and apply 16 cool-core diagnostics to them, some of them new. We also correlate optical properties of brightest cluster galaxies (BCGs) with X-ray properties. To segregate cool core and non-cool-core clusters, we find that central cooling time, t_cool, is the best parameter for low redshift clusters with high quality data, and that cuspiness is the best parameter for high redshift clusters. 72% of clusters in our sample have a cool core (t_cool < 7.7 h_{71}^{-1/2} Gyr) and 44% have strong cool cores (t_cool <1.0 h_{71}^{-1/2} Gyr). For the first time we show quantitatively that the discrepancy in classical and spectroscopic mass deposition rates can not be explained with a recent formation of the cool cores, demonstrating the need for a heating mechanism to explain the cooling flow problem. [Abridged]

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arXiv2009

A Suzaku Search for Non-thermal Emission at Hard X-ray Energies in the Coma Cluster

The brightest cluster radio halo known resides in the Coma cluster of galaxies. The relativistic electrons producing this diffuse synchrotron emission should also produce inverse Compton emission that becomes competitive with thermal emission from the ICM at hard X-ray energies. Thus far, claimed detections of this emission in Coma are controversial (Fusco-Femiano et al. 2004; Rossetti & Molendi 2004). We present a Suzaku HXD-PIN observation of the Coma cluster in order to nail down its non-thermal hard X-ray content. The contribution of thermal emission to the HXD-PIN spectrum is constrained by simultaneously fitting thermal and non-thermal models to it and a spatially equivalent spectrum derived from an XMM-Newton mosaic of the Coma field (Schuecker et al. 2004). We fail to find statistically significant evidence for non-thermal emission in the spectra, which are better described by only a single or multi-temperature model for the ICM. Including systematic uncertainties, we derive a 90% upper limit on the flux of non-thermal emission of 6.0x10^-12 erg/s/cm^2 (20-80 keV, for photon index of 2.0), which implies a lower limit on the cluster-averaged magnetic field of B>0.15 microG. Our flux upper limit is 2.5x lower than the detected non-thermal flux from RXTE (Rephaeli & Gruber 2002) and BeppoSAX (Fusco-Femiano et al. 2004). However, if the non-thermal hard X-ray emission in Coma is more spatially extended than the observed radio halo, the Suzaku HXD-PIN may miss some fraction of the emission. A detailed investigation indicates that ~50-67% of the emission might go undetected, which could make our limit consistent with these detections. The thermal interpretation of the hard Coma spectrum is consistent with recent analyses of INTEGRAL (Eckert et al. 2007) and Swift (Ajello et al. 2009) data.

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arXiv2008

Hard X-ray Properties of the Merging Cluster Abell 3667 as Observed with Suzaku

Wide-band Suzaku data on the merging cluster Abell 3667 were examined for hard X-ray emission in excess to the known thermal component. Suzaku detected X-ray signals in the wide energy band from 0.5 to 40 keV. The hard X-ray (> 10 keV) flux observed by the HXD around the cluster center cannot be explained by a simple extension of the thermal emission with average temperature of ~7 keV. The emission is most likely an emission from a very hot (kT > 13.2 keV) thermal component around the cluster center, produced via a strong heating process in the merger. In the north-west radio relic, no signature of non-thermal emission was observed. Using the HXD, the overall upper-limit flux within a 34'x34' field-of-view around the relic is derived to be 5.3e-12 erg s-1 cm-2 in the 10-40 keV band, after subtracting the ICM contribution estimated using the XIS or the XMM-Newton spectra. Directly on the relic region, the upper limit is further tightened by the XIS data to be less than 7.3e-13 erg s-1 cm-2, when converted into the 10--40 keV band. The latter value suggest that the average magnetic field within the relic is higher than 1.6 uG. The non-thermal pressure due to magnetic fields and relativistic electrons may be as large as ~20% of the thermal pressure in the region.

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arXiv2008

Suzaku Observation of the Ophiuchus Galaxy Cluster: One of the Hottest Cool Core Clusters

We present the analysis of a Suzaku observation of the Ophiuchus galaxy cluster. We confirmed that the cluster has a cool core. While the temperature of the intracluster medium (ICM) decreases toward the center, the metal abundance increases. Except for the core (r<~50 kpc), the cluster is hot (~9-10 keV) and is almost isothermal for r<~1 Mpc; the latter contradicts a previous study. We do not detect the variation of the redshift of the ICM in the cluster; the upper limit of the velocity difference is 3000 km s^-1. The iron line ratios in X-ray spectra indicate that the ICM has reached the ionization equilibrium state. From these results, we conclude that the Ophiuchus cluster is not a major merger cluster but one of the hottest clusters with a cool core. We obtain the upper limit of non-thermal emission from the cluster, which is consistent with both the recent claimed detection with INTEGRAL and the recent upper limits with the Swift/BAT. If the cluster has bright non-thermal emission as suggested by the INTEGRAL measurement, it is probably not due to a recent major cluster merger.

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arXiv2008

Deep Chandra X-ray Observations of Low Mass X-ray Binary Candidates in the Early-Type Galaxy NGC 4697

Chandra X-ray observations routinely resolve tens to hundreds of low-mass X-ray binaries (LMXBs) per galaxy in nearby massive early-type galaxies. These studies have raised important issues regarding the behavior of this population of remnants of the once massive stars in early-type galaxies, namely the connection between LMXBs and globular clusters (GCs) and the nature of the LMXB luminosity function (LF). In this paper, we combine five epochs of Chandra observations and one central field Hubble Space Telescope Advance Camera for Surveys observation of NGC 4697, one of the nearest, optically luminous elliptical (E6) galaxies, to probe the GC-LMXB connection and LMXB-LF down to a detection/completeness limit of (0.6/1.4) x 10^{37} ergs/s. We detect 158 sources, present their luminosities and hardness ratios, and associate 34 LMXBs with GCs. We confirm that GCs with higher encounter rates (Γ_h) and redder colors (higher metallicity Z) are more likely to contain GCs, and find that the expected number of LMXBs per GC is proportional to Γ_h^{0.79+0.18/-0.15} Z^{0.50+0.20/-0.18}, consistent with fainter X-ray sources in Galactic GCs and LMXBs in Virgo early-type galaxies. Approximately 11+/-2% / 8 +/-2% of GCs in NGC 4697 contain an LMXB at the detection/completeness limit. We propose that the larger proportion of metal-rich GCs in NGC 4697 compared to the Milky Way explains why these fractions are much higher than those of the Milky Way at similar luminosities. We confirm that a broken power-law is the best fit to the LMXB-LF, although we cannot rule out a cutoff power-law, and argue that this raises the possibility that there is no universal form for the LMXB-LF in early-type galaxies. We find marginal evidence for different LFs of LMXBs in GCs and the field and different spectra of GC-LMXBs and Field-LMXBs.

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arXiv2008

Measurements of Variability of Low Mass X-ray Binary Candidates in the Early-Type Galaxy NGC 4697 from Multi-Epoch Chandra X-ray Observations

Multi-epoch Chandra X-ray observations of nearby massive early-type galaxies open up the study of an important regime of low-mass X-ray binary (LMXB) behavior -- long term variability. In a companion paper, we report on the detection of 158 X-ray sources down to a detection/completeness limit of 0.6/1.4 x 10^{37} ergs/s using five Chandra observations of NGC 4697, one of the nearest (11.3 Mpc), optically luminous (M_B < -20), elliptical (E6) galaxy. In this paper, we report on the variability of LMXB candidates measured on timescales from seconds to years. At timescales of seconds to hours, we detect five sources with significant variability. Approximately 7% of sources show variability between any two observations, and 16+/-4% of sources do not have a constant luminosity over all five observations. Among variable sources, we identify eleven transient candidates, with which we estimate that if all LMXBs in NGC 4697 are long-term transients then they are on for ~ 100 yr and have a 7% duty cycle. These numbers are consistent with those found for brighter LMXBs in M87 and NGC 1399, which suggests that there does not appear to be a measurable difference between the outburst durations of long-term transient neutron star LMXBs and black hole LMXBs. We discuss in detail a transient supersoft source, whose properties are not easily explained by standard explanations for supersoft sources.

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arXiv2008

An Infrared Survey of Brightest Cluster Galaxies. II: Why are Some Brightest Cluster Galaxies Forming Stars?

Quillen et al.(2007) presented an imaging survey with the {\it Spitzer Space Telescope} of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters. They found that at least half of these sources have signs of excess infrared emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star forming galaxies. The gas depletion time scale is about 1 Gyr. The physical extent of the infrared excess is consistent with that of the optical emission line nebulae. This supports the hypothesis that the star formation occurs in molecular gas associated with the emission line nebulae and with evidence that the emission line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates (${\dot M}_X$) estimated from the X-ray emission and the star formation rate estimated from the infrared luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates suggesting that the re-heating of the ICM is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.

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arXiv2008

XMM-Newton and Chandra Observations of Abell 2626: Interacting Radio Jets and Cooling Core with Jet Precession?

We present a detailed analysis of the XMM-Newton and Chandra observations of Abell 2626 focused on the X-ray and radio interactions. Within the region of the radio mini-halo (~70 kpc), there are substructures which are probably produced by the central radio source and the cooling core. We find that there is no obvious correlation between the radio bars and the X-ray image. The morphology of Abell 2626 is more complex than that of the standard X-ray radio bubbles seen in other cool core clusters. Thus, Abell 2626 provides a challenge to models for the cooling flow -- radio source interaction. We identified two soft X-ray (0.3--2 keV) peaks with the two central cD nuclei; one of them has an associated hard X-ray (2--10 keV) point source. We suggest that the two symmetric radio bars can be explained by two precessing jets ejected from an AGN. Beyond the central regions, we find two extended X-ray sources to the southwest and northeast of the cluster center which are apparently associated with merging subclusters. The main Abell 2626 cluster and these two subclusters are extended along the direction of the Perseus-Pegasus supercluster, and we suggest that Abell 2626 is preferentially accreting subclusters and groups from this large-scale structure filament. We also find an extended X-ray source associated with the cluster S0 galaxy IC 5337; the morphology of this source suggests that it is infalling from the west, and is not associated with the southwest subcluster, as had been previously suggested.

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arXiv2008

A Transient Black-Hole Low-Mass X-Ray Binary Candidate in Centaurus A

We report the discovery of a bright transient X-ray source, CXOU J132518.2-430304, towards Centaurus A (Cen A) using six new Chandra X-Ray Observatory observations in 2007 March--May. Between 2003 and 2007, its flux has increased by a factor of >770. The source is likely a low-mass X-ray binary in Cen A with unabsorbed 0.3-10 keV band luminosities of (2-3) x 10^{39} erg s^-1 and a transition from the steep-power law state to the thermal state during our observations. CXOU J132518.2-430304 is the most luminous X-ray source in an early-type galaxy with extensive timing information that reveals transience and a spectral state transition. Combined with its luminosity, these properties make this source one of the strongest candidates to date for containing a stellar-mass black hole in an early-type galaxy. Unless this outburst lasts many years, the rate of luminous transients in Cen A is anomalously high compared to other early-type galaxies.

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arXiv2008

The Impact of Galaxy Cluster Mergers on Cosmological Parameter Estimation from Surveys of the Sunyaev-Zel'dovich Effect

Sensitive surveys of the Cosmic Microwave Background will detect thousands of galaxy clusters via the Sunyaev-Zel'dovich (SZ) effect. Two SZ observables, the central or maximum and integrated Comptonization parameters y_max and Y, relate in a simple way to the total cluster mass, which allow the construction of mass functions (MFs) that can be used to estimate cosmological parameters such as Omega_M, sigma_8, and the dark energy parameter w. However, clusters form from the mergers of smaller structures, events that can disrupt the equilibrium of intracluster gas upon which SZ-M relations rely. From a set of N-body/hydrodynamical simulations of binary cluster mergers, we calculate the evolution of Y and y_max over the course of merger events and find that both parameters are transiently "boosted," primarily during the first core passage. We then use a semi-analytic technique developed by Randall et al. (2002) to estimate the effect of merger boosts on the distribution functions YF and yF of Y and y_max, respectively, via cluster merger histories determined from extended Press-Schechter (PS) merger trees. We find that boosts do not induce an overall systematic effect on YFs, and the values of Omega_M, sigma_8, and w were returned to within 2% of values expected from the nonboosted YFs. The boosted yFs are significantly biased, however, causing Omega_M to be underestimated by 15-45%, sigma_8 to be overestimated by 10-25%, and w to be pushed to more negative values by 25-45%. We confirm that the integrated SZ effect, Y, is far more robust to mergers than y_max, as previously reported by Motl et al. (2005) and similarly found for the X-ray equivalent Y_X, and we conclude that Y is the superior choice for constraining cosmological parameters.

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arXiv2007

Variable Low-Mass X-ray Binaries in Early-Type Galaxies

As the Chandra X-ray Observatory mission matures, increasing numbers of nearby galaxies are being observed multiple times, sampling the variability of extragalactic X-ray binaries on timescales extending from seconds to years. We present results on luminous low-mass X-ray binaries from several early-type galaxies. We show that instantaneous LMXB luminosity functions of early-type galaxies do not significantly change between observations; a relatively low fraction of sources are strongly variable on <~ 5 yr timescales. We discuss the implications that a relatively small number of transient LMXBs are being discovered in early-type galaxies.

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arXiv2007

Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446

Wide-angle tail (WAT) radio sources are often found in the centers of galaxy clusters where intracluster medium (ICM) ram pressure may bend the lobes into their characteristic C-shape. We examine the low redshift (z=0.1035) cluster Abell 1446, host to the WAT radio source 1159+583. The cluster exhibits possible evidence for a small-scale cluster-subcluster merger as a cause of the WAT radio source morphology. This evidence includes the presence of temperature and pressure substructure along the line that bisects the WAT as well as a possible wake of stripped interstellar material or a disrupted cool core to the southeast of the host galaxy. A filament to the north may represent cool, infalling gas that's contributing to the WAT bending while spectroscopically determined redshifts of member galaxies may indicate some component of a merger occurring along the line-of-sight. The WAT model of high flow velocity and low lobe density is examined as another scenario for the bending of 1159+583. It has been argued that such a model would allow the ram pressure due to the galaxy's slow motion through the ICM to shape the WAT source. A temperature profile shows that the cluster is isothermal (kT= 4.0 keV) in a series of annuli reaching a radius of 400 kpc. There is no evidence of an ongoing cooling flow. Temperature, abundance, pressure, density, and mass profiles, as well as two-dimensional maps of temperature and pressure are presented.

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arXiv2007

Low-Mass X-ray Binaries and Globular Clusters in Centaurus A

We present results of Hubble Space Telescope and Chandra X-ray Observatory observations of globular clusters (GCs) and low-mass X-ray binaries (LMXBs) in the central regions of Centaurus A. Out of 440 GC candidates we find that 41 host X-ray point sources that are most likely LMXBs. We fit King models to our GC candidates in order to measure their structural parameters. We find that GCs that host LMXBs are denser and more compact, and have higher encounter rates and concentrations than the GC population as a whole. We show that the higher concentrations and masses are a consequence of the dependence of LMXB incidence on central density and size plus the general trend for denser GCs to have higher masses and concentrations. We conclude that neither concentration nor mass are fundamental variables in determining the presence of LMXBs in GCs, and that the more fundamental parameters relate to central density and size.

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arXiv2007

An infrared survey of brightest cluster galaxies: Paper I

We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8 micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.

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arXiv2007

A Chandra Observation of Abell 13: Investigating the Origin of the Radio Relic

We present results from the Chandra X-ray observation of Abell 13, a galaxy cluster that contains an unusual noncentral radio source, also known as a radio relic. This is the first pointed X-ray observation of Abell 13, providing a more sensitive study of the properties of the X-ray gas. The X-ray emission from Abell 13 is extended to the northwest of the X-ray peak and shows substructure indicative of a recent merger event. The cluster X-ray emission is centered on the bright galaxy H of Slee et al. 2001. We find no evidence for a cooling flow in the cluster. A knot of excess X-ray emission is coincident with the other bright elliptical galaxy F. This knot of emission has properties similar to the enhanced emission associated with the large galaxies in the Coma cluster. With these Chandra data we are able to compare the properties of the hot X-ray gas with those of the radio relic from VLA data, to study the interaction of the X-ray gas with the radio emitting electrons. Our results suggest that the radio relic is associated with cooler gas in the cluster. We suggest two explanations for the coincidence of the cooler gas and radio source. First, the gas may have been uplifted by the radio relic from the cluster core. Alternatively, the relic and cool gas may have been displaced from the central galaxy during the cluster merger event.

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