arXiv subjects

Xiang-Ping Wu

Publications and source records attributed to Xiang-Ping Wu.

At least 37 records · Page 2Linked to original sources

arXiv2009

A Chandra Study of Temperature Substructures in Intermediate-Redshift Galaxy Clusters

By analyzing the gas temperature maps created from the Chandra archive data, we reveal the prevailing existence of temperature substructures on ~100 kpc scales in the central regions of nine intermediate-redshift (z~0.1) galaxy clusters, which resemble those found in the Virgo and Coma Clusters. Each substructure contains a clump of hot plasma whose temperature is about 2-3 keV higher than the environment, corresponding to an excess thermal energy of ~1E58-1E60 erg per clump. Since if there were no significant non-gravitational heating sources, these substructures would have perished in 1E8-1E9 yrs due to thermal conduction and turbulent flows, whose velocity is found to range from about 200 to 400 km/s, we conclude that the substructures cannot be created and sustained by inhomogeneous radiative cooling. We also eliminate the possibilities that the temperature substructures are caused by supernova explosions, or by the non-thermal X-ray emission due to the inverse-Comptonization of the CMB photons. By calculating the rising time of AGN-induced buoyant bubbles, we speculate that the intermittent AGN outbursts (~ 1E60 erg per burst) may have played a crucial role in the forming of the high temperature substructures. Our results are supported by recent study of McNamara & Nulsen (2007), posing a tight observational constraint on future theoretical and numerical studies.

astro-ph.HE↗

arXiv2009

A Search for X-Ray Reionization Signatures from Cross-Correlation of Wmap and ROSAT Rass Data

We present an observational search for the possible correlation between cosmic microwave background (CMB) polarization map and soft X-ray background (SXRB) based on the ROSAT All-sky Survey (RASS) archive and WMAP five-year observations. This is motivated by the fact that some of the CMB polarization may arise from the scattering of CMB photons due to the free electrons generated by X-ray heating sources in the epoch of reionization. Detection of such a correlation allows one to study the role of X-ray heating in the process of reionization. However, the cross angular power spectrum of the CMB polarization and SXRB maps constructed from ROSAT RASS and WMAP five-year maps is consistent with no correlation. We attribute this negative detection to both the extremely weak signals and large instrumental noises. While a future search is needed with high sensitivity instruments for both CMB polarization and soft X-ray photons, our current results can still be used as a useful constraint on the effect of X-ray heating in the epoch of reionization.

astro-ph.CO↗

arXiv2009

Development of a radio-detection method array for the observation of ultra-high energy neutrino induced showers

The recent demonstration by the CODALEMA Collaboration of the ability of the radio-detection technique for the characterization of UHE cosmic-rays calls for the use of this powerful method for the observation of UHE neutrinos. For this purpose, an adaptation of the existing 21CM Array (China) is presently under achievment. In an exceptionally low electromagnetic noise level, 10160 log-periodic 50-200 MHz antennas sit along two high valleys, surrounded by mountain chains. This lay-out results in 30-60 km effective rock thicnesses for neutrino interactions with low incidence trajectories along the direction of two 4-6 km baselines. We will present first in-situ radio measurements demonstrating that this environment shows particularly favourable conditions for the observation of electromagnetic decay signals of taus originating from the interaction of 10^17-20 eV tau neutrinos.

astro-ph.IM↗

arXiv2008

Signatures of the Baryon Acoustic Oscillations on 21cm Emission Background

The baryon acoustic oscillations (BAO) prior to recombination should be imprinted onto the 21cm emission background from the epoch of reionization through the underlying density perturbations. Using an analytical approach for both matter power spectrum (CDM+baryons) and reionization process, we demonstrate the BAO induced signatures on the power spectrum of 21cm emission fluctuations. Future low-frequency radio telescopes such as LOFAR and MWA should be able to detect these weak BAO wiggles with an integration time of $\sim1$ year. A combination of the BAO measurements at different redshifts $z\approx1000$ (CMB), $z\approx10$ (epoch of reionization) and $z\approx0$ (clustering of galaxies) may allow one to set more robust constraints on the determinations of cosmological parameters including dark energy and its equation of state.

astro-ph↗

arXiv2007

A High-Abundance Arc in the Compact Group of Galaxies HCG 62: An AGN- or Merger-Induced Metal Outflow?

We present a Chandra study of the metal distribution in the X-ray bright compact group of galaxies HCG 62. We find that the diffuse X-ray emission is peaked at the core of the central galaxy NGC 4778, and is dominated by the contribution of the hot gas. The diffuse emission is roughly symmetric within \simeq0.25^{\prime}, which is straddled by double-sided X-ray cavities aligned in the northeast-southwest direction. By mapping the emission hardness ratio distributions and by performing the 2-dimensional spectral analysis, we identify a remarkable high-abundance arc region at about 2^{\prime} (33.6h_{70}^{-1} kpc) from the X-ray peak that spans over a vast region from south to northwest, a part of which roughly coinciding with the outer edge of the southwest X-ray cavity. The measured average abundance in this arc is higher than that in its neighboring regions by a factor of about 2, and the abundance ratios therein are nicely consistent with the dominance of the SN Ia yields. We estimate that the mass of iron contained in the arc is >3\times 10^{6}h_{70}^{-2.5} solar mass, which accounts for >3% of the iron synthesized in the galaxy. The high-abundance arc could have been formed by the AGN activities. However, it is also possible that the arc was formed in a recent merger as is implied by the recent optical kinematic study (Spavone et al. 2006), which implies that mergers may be as important as AGN activities in metal redistributions in early-type galaxies and their associated groups or clusters.

astro-ph↗

arXiv2006

Probing the Mass Distributions in NGC 1407 and Its Associated Group with the X-ray Imaging Spectroscopic and Optical Photometric and Line-strength Indices Data

We present a study of the mass distributions in the bright E0 galaxy NGC 1407 and its associated group by analyzing the high quality Chandra and ROSAT X-ray spectroscopic data. In order to probe the stellar mass distribution we calculated the B-band mass-to-light ratio profile by comparing the observed line-strength indices and multi-color photometric data with different stellar synthesis model predictions. We find that the gas is single-phase with a temperature of ~0.7 keV within 1Re. Outside 1Re the gas temperature increases quickly outwards to >1 keV, indicating its group origin. We reveal that the X-ray surface brightness profile shows a central excess in the innermost region, and on both the total mass and dark matter profiles there is a flattened feature at about <1Re, which coincides with the gas temperature transition from the galactic level to the group level. The total mass and dark matter distributions within 0.85Re are cuspy and can be approximated by power-law profiles with indices of ~2, which are marginally consistent with the generalized NFW profiles with zeta=2. The mass in outer regions can be well fitted by a single NFW profile, with the derived concentration parameter c=18.6\pm1.5. We find that the NGC 1407 group has a baryon-dominated core, while the mass in the >1Re is dominated by dark matter. At the virial radius r200=572\pm118 kpc, the inferred mass and mass-to-light ratio are M200=2.20\pm0.42E13 solarM and Mvir/LB=311\pm60 solarM/solarL,respectively, showing that the NGC 1407 group is an extremely dark system even comparable to many clusters of galaxies. Since the obtained total mass is lower than those given in the earlier galaxy kinematic works, we speculate that NGC 1400 is not a virialized member in the group's gravitational potential well.

astro-ph↗

arXiv2005

Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at z=0.194: the Central Excess Iron and SN Ia Enrichment

We present the Chandra study of the intermediately distant cluster of galaxies MS 0839.9+2938. By performing both the projected and deprojected spectral analyses, we find that the gas temperature is approximately constant at about 4 keV in 130-444h_70^-1 kpc. In the inner regions, the gas temperature descends towards the center, reaching <~ 3 keV in the central 37h_70^-1 kpc. This infers that the lower and upper limits of the mass deposit rate are 9-34 M_sun yr^-1 and 96-126 M_sun yr^-1, respectively within 74h_70^-1 kpc where the gas is significantly colder. Along with the temperature drop, we detect a significant inward iron abundance increase from about 0.4 solar in the outer regions to about 1 solar within the central 37h_70^-1 kpc. Thus MS 0839.9+2938 is the cluster showing the most significant central iron excess at z>~ 0.2. We argue that most of the excess iron should have been contributed by SNe Ia. By utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr, which is similar to those found for the nearby clusters. Coinciding with the optical extension of the cD galaxy (up to about 30h_70^-1 kpc), the observed X-ray surface brightness profile exhibits an excess beyond the distribution expected by either the beta model or the NFW model, and can be well fitted with an empirical two-beta model that leads to a relatively flatter mass profile in the innermost region.

astro-ph↗

arXiv2005

Chandra Study of X-Ray Point Sources in the Early-Type Galaxy NGC 4552 (M89)

We present a Chandra ACIS study of the early-type galaxy NGC 4552. We detect 47 X-ray point sources, most of which are likely LMXBs, within 4 R_e. The brightest X-ray source coincides with the optical/UV/radio center of the galaxy, and shows variability on >1 hr timescales, indicating the possible existence of a LLAGN. The 46 off-center sources and the unresolved point sources contribute about 29% and 20% to the total luminosity of the galaxy, respectively. The corrected cumulative XLF of the off-center sources is best fit by a broken power-law model with a break at L_b=4.4+2.0-1.4 e38 ergs/s. We identified 210 GCs candidates in a HST WFPC2 optical image of the galaxy's central region. Of the 25 off-center LMXBs that fall within the WFPC2 FOV, 10 sources are coincident with a GC. Thus the fraction of the GCs hosting bright LMXBs and the fraction of the LMXBs associated with GCs are 4.8% and 40%, respectively. In the V and I bands, the GCs hosting bright LMXBs are typically 1-2 magnitudes brighter than the GCs with no detected LMXBs. There are about 1.9+-0.4 times as many LMXBs in the red, metal-rich GCs as there are in the blue, metal-poor ones. We find no obvious difference between the luminosity distributions of LMXBs in GCs and in field, but the cumulative spectrum of the LMXBs in GCs tends to be softer than that of the LMXBs in field. We detected 3 X-ray sources that have isotropic luminosities larger than 1e39 erg/s. The one located in the joint Chandra-HST field is found to be associated with a GC. By studying the ACIS spectra we infer that the this may be a candidate black hole system with a mass of 15-135 M_sun. One of the other sources with a luminosity brighter than 1e39 ergs/s reveals temporal variations in brightness on timescales greater than an hour.

astro-ph↗

arXiv2005

Searching for Early Ionization with the Primeval Structure Telescope

The Primeval Structure Telescope (PaST), will be used search for and study the era the of the first luminous objects, the epoch of reionization. The first stars ionized the gas around them producing a pattern of ionization that reflects the large scale density structure present at the time. The PaST array will be used in an attempt to sense and study this ionization, by mapping the brightness of 21-cm neutral hydrogen emission at redshifts from 6 to 25. This emission disappears on ionization, allowing the study of large scale structure and of star formation at this very early epoch. The 10,000 antenna PaST array will be used to image ionized structures by creating 1 million pixel images of the sky. The angular scales of the images to be produced span from 5 arc-minutes to 10 degrees. The array is currently under construction and over 2000 antennas have been installed.

astro-ph↗

arXiv2004

A halo approach to the evaluation of the cross-correlation between the SZ sky and galaxy survey

Using a purely analytic approach to gaseous and dark matter halos, we study the cross-correlation between the Sunyaev-Zel'dovich (SZ) sky and galaxy survey under flat sky approximation, in an attempt to acquire the redshift information of the SZ map. The problem can be greatly simplified when it is noticed that the signals of the SZ-galaxy correlation arise only from hot gas and galaxies inside the same massive halos (i.e. clusters), and field galaxies make almost no contribution to the cross-correlation. Under the assumption that both the hot gas and galaxies trace the common gravitational potential of dark halos, we calculate the expected cross SZ-galaxy power spectra for the WMAP/Planck SZ maps and the SDSS galaxy sample at small scales $100 400$ with the WMAP/Planck experiments. Future SZ observations with better angular resolutions and sufficiently wide sky coverages will be needed if this technique is applied for the statistical measurement of redshift distribution of the SZ sources.

astro-ph↗

arXiv2003

Weak lensing of the Sunyaev-Zel'dovich sky

We address the question of whether the angular power spectrum of the thermal Sunyaev-Zel'dovich (SZ) sky is further distorted by weak gravitational lensing of foreground large-scale structures. Using an analytic approach to both gaseous and dark halo models, we show that the contamination of weak lensing in the measurement of SZ power power is negligibly small, and relatively corrections |ΔC_l|/C_l are less than 3% up to l=10^5. This arises from both the weaker gravitational potentials of low-redshift matter inhomogeneities that can act as lenses for SZ sources (clusters) and the shallower shape of intrinsic SZ power spectrum at large l, in contrast to the cosmic microwave background which can be significantly affected by weak lensing because of the distant location and significant damping of its intrinsic power spectrum at small angular scales.

astro-ph↗

arXiv2003

Cross-correlation between the soft X-ray background and SZ Sky

While both X-ray emission and Sunyaev-Zel'dovich (SZ) temperature fluctuations are generated by the warm-hot gas in dark matter halos, the two observables have different dependence on the underlying physical properties, including the gas distribution. A cross-correlation between the soft X-ray background (SXRB) and the SZ sky may allow an additional probe on the distribution of warm-hot gas at intermediate angular scales and redshifts complementing studies involving clustering within SXRB and SZ separately. Using a halo approach, we investigate this cross-correlation analytically. The two contributions are correlated mildly with a correlation coefficient of $\sim0.3$, and this relatively low correlation presents a significant challenge for its detection. The correlation, at small angular scales, is affected by the presence of radiative cooling or preheating and provides a probe on the thermal history of the hot gas in dark halos. While the correlation remains undetectable with CMB data from the WMAP satellite and X-ray background data from existing catalogs, upcoming observations with CMB missions such as Planck, for the SZ side, and an improved X-ray map of the large scale structure, such as the one planned with DUET mission, may provide a first opportunity for a reliable detection of this cross-correlation.

astro-ph↗

arXiv2003

Contamination of Cluster Radio Sources in the Measurement of the Thermal Sunyaev-Zel'dovich Angular Power Spectrum

We present a quantitative estimate of the confusion of cluster radio halos and galaxies in the measurement of the angular power spectrum of the thermal Sunyaev-Zel'dovich (SZ) effect. To achieve the goal, we use a purely analytic approach to both radio sources and dark matter of clusters by incorporating empirical models and observational facts together with some theoretical considerations. It is shown that the correction of cluster radio halos and galaxies to the measurement of the thermal SZ angular power spectrum is no more than 20% at $l>2000$ for observing frequencies $ν>30$ GHz. This eliminates the concern that the SZ measurement may be seriously contaminated by the existence of cluster radio sources.

astro-ph↗

arXiv2003

Autocorrelation function of the soft X-ray background produced by warm-hot gas in dark halos

We calculate the angular two-point autocorrelation function (ACF) of the soft X-ray background (SXRB) produced by the warm-hot intergalactic medium (WHIM) associated with dark halos, motivated primarily by searching for missing baryons and distinguishing different physical processes of the WHIM in dark halos. We employ a purely analytic model for the halo population which is completely determined by the universal density profile and the Press-Schechter mass function. We then adopt a phenomenological approach to nongravitational processes of the WHIM such as preheating and radiative cooling. It shows that the power spectra of the SXRB predicted by three WHIM models, namely, the self-similar model, preheating model and cooling model demonstrate remarkably different signatures in both amplitude and shape, with the peak locations moving from 4X10^4 for the self-similar model to a smaller value of (3-5)X10^3 when nongravitational processes are taken into account. The corresponding ACFs for preheating and cooling models become shallower too as compared with the prediction of the self-similar model. This may permit an effective probe of the physical processes of the WHIM in massive halos in conjunction with the observationally determined power spectrum or ACF of the SXRB from diffuse WHIM. However, a direct comparison of our theoretical predictions with existing data (e.g. the ACF determined from ROSAT observations) is still difficult because of the dominant contribution of AGNs in the soft X-ray sky. We discuss briefly the implication of our results for resolving the missing baryon problem in the local universe.

astro-ph↗

arXiv2002

Can radiative cooling and nongravitational heating explain simultaneously the global X-ray properties of clusters and the unresolved cosmic X-ray background ?

Using a simple analytic approach we address the question of whether radiative cooling, nongravitational heating and cooling plus heating models can simultaneously explain the observed global X-ray properties (entropy and X-ray luminosity distributions) of groups and clusters and the residual soft X-ray background (XRB) after discrete sources are removed. Within the framework of typical cold dark matter structure formation characterized by an amplitude of matter power spectrum sigma_8=0.9, it is argued that while radiative cooling alone is able to marginally reproduce the entropy floor detected in the central regions of groups and clusters, it is insufficient to account for the steepening of the X-ray luminosity - temperature relation for groups and the unresolved soft XRB. A phenomenological preheating model, in which either an extra specific energy budget or an entropy floor is added to the hot gas in groups and clusters, fails in the recovery of at least one of the X-ray observed features. Finally, the soft XRB predicted by our combined model of cooling plus heating exceeds the observational upper limits by a factor of ~2, if the model is required to reproduce the observed entropy and X-ray luminosity - temperature relationships of groups and clusters. If the discrepancy is not a result of the oversimplification of our analytic models, this implies that either our current understanding of the physical processes of the hot gas is still incomplete, or the normalization of the present power spectrum has been systematically overestimated. For the latter, both the X-ray properties of groups and clusters and the XRB predicted by preheating model and cooling plus heating model can be reconciled with the X-ray observations if a lower value of the normalization parameter sigma_8 \approx 0.7 is assumed.

astro-ph↗

arXiv2002

The Effect of Radiative Cooling on the Sunyaev-Zel'dovich Cluster Counts and Angular Power Spectrum: Analytic Treatment

Recently, the entropy excess detected in the central cores of groups and clusters has been successfully interpreted as being due to radiative cooling of the hot intragroup/intracluster gas. In such a scenario, the entropy floors $S_{\rm floor}$ in groups/clusters at any given redshift are completely determined by the conservation of energy. In combination with the equation of hydrostatic equilibrium and the universal density profile for dark matter, this allows us to derive the remaining gas distribution of groups and clusters after the cooled material is removed. Together with the Press-Schechter mass function we are able to evaluate effectively how radiative cooling can modify the predictions of SZ cluster counts and power spectrum. It appears that our analytic results are in good agreement with those found by hydrodynamical simulations. Namely, cooling leads to a moderate decrease of the predicted SZ cluster counts and power spectrum as compared with standard scenario. However, without taking into account energy feedback from star formation which may greatly suppress cooling efficiency, it is still premature to claim that this modification is significant for the cosmological applications of cluster SZ effect.

astro-ph↗

arXiv2002

Analytic Approaches to Understanding the Distribution and Evolution of Intracluster Gas

I will briefly review various analytic approaches to understanding the contents and properties of the hot X-ray emitting gas contained in clusters and groups. Special emphases are given to the following three issues: (1)Reconstruction of the gas distribution in groups and clusters from a (joint) analysis of X-ray, SZ and gravitational lensing observations; (2)Test of the analytic density profiles of dark halos suggested by numerical simulations and empirical models with current X-ray data; And (3)the effects of preheating and radiative cooling on the X-ray properties of groups and clusters.

astro-ph↗

arXiv2002

The Effect of radiative cooling on the scale-dependence of global stellar and gas contents of groups and clusters of galaxies

It is widely believed that the global baryon content and mass-to-light ratio of groups and clusters of galaxies are a fair representative of the matter mix of the universe and therefore, can be used to reliably determine the cosmic mass density parameter Omega_M. However, this fundamental assumption is challenged by growing evidence from optical and X-ray observations that the average gas mass fraction and mass-to-light ratio increase mildly with scale from poor groups to rich clusters. Although a number of time-consuming hydrodynamical simulations combined with semi-analytic approaches have been carried out, which permit a sophisticated treatment of some complicated processes in the formation and evolution of cosmic structures, the essential physics behind the phenomenon still remains a subject of intense debate. In this Letter, using a simple analytic model, we show that radiative cooling of the hot intragroup/intracluster gas may allow one to reproduce the observed scale-dependence of the global stellar and gas mass fractions and mass-to-light ratio of groups and clusters, provided that about half of the cooled gas is converted into stars. Together with the recent success in the recovery of the entropy excess and the steepening of the X-ray luminosity-temperature relations detected in groups and clusters, radiative cooling provides a simple, unified scheme for the evolution of hot gas and the formation of stars in the largest virialized systems of the universe.

astro-ph↗