118712522
EXPLORING THE COSMIC REIONIZATION EPOCH IN FREQUENCY SPACE: AN IMPROVED APPROACH TO REMOVE THE FOREGROUND IN 21 cm TOMOGRAPHY
With the intent of correctly restoring the redshifted 21 cm signals emitted by neutral hydrogen during the cosmic reionization processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space in order to investigate whether they work satisfactorily with complex foreground by quantitatively evaluating the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterize both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias b and average ionization fraction x(e) of the reionization processes, at z = 8 and the noise level of 60 mK we find that although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of the Mpc-scale components of the 21 cm signals (75% for greater than or similar to 6 h(-1) Mpc scales and 34% for greater than or similar to 1 h(-1) Mpc scales) is lost because it tends to be misidentified as part of the foreground when the single-narrow-segment separation approach is applied. The best restoration of the 21 cm signals and the tightest determination of b and xe can be obtained with the three-narrow-segment fitting technique as proposed in this paper. Similar results can be obtained at other redshifts.
119241598
Central gas entropy excess as direct evidence for AGN feedback in galaxy groups and clusters
By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central ( R ≤10 h -1 71 kpc) gas entropy excess (∆ K 0 ), which corresponds to ≃ 0.1 - 0.5 keV per gas particle, beyond the power-law model that best fits the radial entropy profile of the outer regions. We also find a distinct correlation between the central entropy excess ∆ K 0 and K-band luminosity LK of the central dominating galaxies (CDGs), which is scaled as ∆ K 0 ∝ L 1.6±0.4 K , where L K is tightly associated with the mass of the supermassive black hole hosted in the CDG. In fact, if an effective mass-to-energy conversion- efficiency of 0.02 is assumed for the accretion process, the cumulative AGN feedback E AGN feedback ≃ ηM BH c 2 yields an extra heating of ≃0.5 - 17.0 keV per particle, which is sufficient to explain the central entropy excess. In most cases, the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius ( ≃0.002 - 2.2 keV per particle), and apparently exceeds the energy required to cause the scaling relations to deviate from the self-similar predictions ( ≃0.2 - 1.0 keV per particle). In contrast to the AGN feedback, the extra heating provided by supernova explosions accounts for ≃0.01 - 0.08 keV per particle in groups and is almost negligible in clusters. Therefore, the observed correlation between ∆ K 0 and L K can be considered as direct evidence for AGN feedback in galaxy groups and clusters.
16270452
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 h –1 70 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 ~1058-1060 erg per clump. If there were no significant nongravitational heating sources, these substructures would have perished in 108-109 yr due to thermal conduction and turbulent flows, whose velocity is found to range from about 200 to 400 km s–1, 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 nonthermal X-ray emission due to the inverse-Comptonization of the cosmic microwave background photons. By calculating the rising time of active galactic nucleus (AGN)-induced buoyant bubbles, we speculate that the intermittent AGN outbursts (≥1060 erg per burst) may have played a crucial role in the formation of the high-temperature substructures. Our results are supported by the recent study of McNamara and Nulsen, posing a tight observational constraint on future theoretical and numerical studies.
118410675
A joint Chandra and XMM-Newton view of Abell 3158: a massive off-centre cool gas clump as a robust diagnostic of a merger stage
In previous works, the nearby galaxy cluster Abell 3158 was reported to possess a relatively regular, relaxed morphology in the X-ray band. By analysing the Chandra and XMM-Newton archived data of Abell 3158, we have identified a bow-edge-shaped discontinuity in the X-ray surface brightness distribution about 120 h -1 71 kpc west of the X-ray peak. This feature is found to be associated with a massive, off-centre cool gas clump, and actually forms the west boundary of the cool clump. By calculating the thermal gas pressures in the cool clump and in the free-stream region, we determine that the cool gas clump is moving at a subsonic velocity of 700 +140 -340 km s -1 (M = 0.6 +0.1 -0.3 ) towards west on the sky plane. We exclude the possibility that this cool clump was formed by local inhomogeneous radiative cooling in the intracluster medium, because of the effectiveness of the thermal conduction on the time-scale of ∼.3 Gyr. As no evidence for central active galactic nucleus activity has been found in Abell 3158, and this cool clump bears many similarities to the off-centre cool gas clumps detected in other merging clusters in terms of their mass, size, location and thermal properties (e.g. lower temperature and higher abundance as compared with the environment), we speculate that the cool clump in Abell 3158 was caused by a merger event, and is the remnant of the original central cool-core of the main cluster or the infalling subcluster. This idea is supported not only by the study of the line-of-sight velocity distribution of the cluster member galaxies, but also by the study of the gas entropy-temperature correlation. This example shows that the appearance of such massive, off-centre cool gas clumps can be used to diagnose the dynamical state of a cluster, especially when prominent shocks and cold fronts are absent.
118515683
CHANDRA OBSERVATION OF A WEAK SHOCK IN THE GALAXY CLUSTER A2556
Based on a 21.5 ks Chandra observation of A2556, we identify an edge on the surface brightness profile at about 160 h(71)(-1) kpc northeast of the cluster center, and it corresponds to a shock front whose Mach number M is calculated to be 1.25(-0.03)(+0.02). No prominent substructure, such as sub-cluster, is found in either the optical or X-ray band that can be associated with the edge, suggesting that the conventional supersonic motion mechanism may not work in this case. As an alternative solution, we propose that the nonlinear steepening of an acoustic wave, which is induced by the turbulence of the intracluster medium at the core of the cluster, can be used to explain the origin of the shock front. Although nonlinear steepening weak shock is expected to occur frequently in clusters, why it is rarely observed still remains a question that requires further investigation, including both deeper X-ray observation and extensive theoretical studies.
118463495
A Method to Extract the Angular Power Spectrum of the Epoch of Reionization from Low-Frequency Radio Interferometers
The redshifted 21 cm signal of neutral hydrogen from the epoch of reionization (EoR) is extremely weak and its first detection is therefore expected to be statistical with first-generation low-frequency radio interferometers. In this Letter, we propose a method to extract the angular power spectrum of the EoR from the visibility correlation coefficients p{sub ij} (u, v), instead of the visibilities V{sub ij} (u, v) measured directly by radio interferometers in conventional algorithm. The visibility correlation coefficients are defined as p{sub ij}(u,v)=V{sub ij}(u,v)/{radical}(|V{sub ii}||V{sub jj}|) by introducing the autocorrelation terms V{sub ii} and V{sub jj} such that the angular power spectrum C{sub l} can be obtained through C{sub l} = T {sup 2}{sub 0}(|p{sub ij} (u, v)|{sup 2}), independently of the primary beams of antennas. This also partially removes the influence of receiver gains in the measurement of C{sub l} because the amplitudes of the gains cancel each other out in the statistical average operation of (|p{sub ij} (u, v)|{sup 2}). We use the average system temperature T{sub 0} as a calibrator of C{sub l}, which is dominated by the Milky Way and extragalactic sources in the frequency range that we are interested in, below 200 MHz. Finally, we demonstratemore » the feasibility of this novel method using the simulated sky maps as targets and the 21 CentiMeter Array (21CMA) as interferometer.« less
55864619
Vertex and Track Reconstruction and Luminosity Monitoring at LHCb
116773682
A Luminosity Function of Lyman-alpha Emitting Galaxies at Redshift 4.5
We present a catalog of 59 -->z ? 4.5 Ly?-emitting galaxies spectroscopically confirmed in a campaign of Keck DEIMOS follow-up observations to candidates selected in the Large Area Ly? (LALA) narrowband imaging survey. We targeted 97 candidates for spectroscopic follow-up; by accounting for the variety of conditions under which we performed spectroscopy, we estimate a selection reliability of ~76%. Together with our previous sample of Keck LRIS confirmations, the 59 sources confirmed herein bring the total catalog to 73 spectroscopically confirmed -->z ? 4.5 Ly?-emitting galaxies in the 0.7 deg2 covered by the LALA imaging. As with the Keck LRIS sample, we find that a nonnegligible fraction of the confirmed Ly? lines have rest-frame equivalent widths ( -->W?rest) that exceed the maximum predicted for normal stellar populations: 17%-31% (93% confidence) of the detected galaxies show -->W?rest > 190 ?, and 12%-27% (90% confidence) show -->W?rest > 240 ?. We construct a luminosity function of -->z ? 4.5 Ly? emission lines for comparison to Ly? luminosity functions spanning -->3.1 z ? 3 to -->z ? 6. This result supports the conclusion that the intergalactic medium remains largely reionized from the local universe out to -->z ? 6.5. It is somewhat at odds with the pronounced drop in the cosmic star formation rate density recently measured between -->z ~ 3 and -->z ~ 6 in continuum-selected Lyman-break galaxies, and therefore potentially sheds light on the relationship between the two populations.
14197201
Alignment between galaxies and large-scale structure
Based on the Sloan Digital Sky Survey DR6 (SDSS) and the Millennium Simulation (MS), we investigate the alignment between galaxies and large-scale structure. For this purpose, we develop two new statistical tools, namely the alignment correlation function and the cos(2θ)-statistic. The former is a two-dimensional extension of the traditional two-point correlation function and the latter is related to the ellipticity correlation function used for cosmic shear measurements. Both are based on the cross correlation between a sample of galaxies with orientations and a reference sample which represents the large-scale structure. We apply the new statistics to the SDSS galaxy catalog. The alignment correlation function reveals an overabundance of reference galaxies along the major axes of red, luminous (L ≥ L ∗ ) galaxies out to projected separations of 60 h - 1 Mpc . The signal increases with central galaxy luminosity. No alignment signal is detected for blue galaxies. The cos(2θ) -statistic yields very similar results. Starting from a MS semi-analytic galaxy catalog, we assign an orientation to each red, luminous and central galaxy, based on that of the central region of the host halo (with size similar to that of the stellar galaxy). As an alternative, we use the orientation of the host halo itself. We find a mean projected misalignment between a halo and its central region of ∼ 25°. The misalignment decreases slightly with increasing luminosity of the central galaxy. Using the orientations and luminosities of the semi-analytic galaxies, we repeat our alignment analysis on mock surveys of the MS. Agreement with the SDSS results is good if the central orientations are used. Predictions using the halo orientations as proxies for central galaxy orientations overestimate the observed alignment by more than a factor of 2. Finally, the large volume of the MS allows us to generate a two-dimensional map of the alignment correlation function, which shows the reference galaxy distribution to be flattened parallel to the orientations of red luminous galaxies with axis ratios of ∼ 0.5 and ∼ 0.75 for halo and central orientations, respectively. These ratios are almost independent of scale out to 60 h - 1 Mpc .
126069612
Implications of infalling Fe II - emitting clouds in AGN: anisotropic properties
16287451
Ultraviolet Broad Absorption Features and the Spectral Energy Distribution of the Qso Pg 1351+64; 3.1
We present a moderate-resolution (~20 km s-1) spectrum of the mini-broad absorption line quasar (QSO) PG 1351+64 between 915 and 1180 A, obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Additional low-resolution spectra at longer wavelengths were also obtained with the Hubble Space Telescope (HST) and ground-based telescopes. Broad absorption is present on the blue wings of C III λ977, Lyβ, O VI λλ1032, 1038, Lyα, N V λλ1238, 1242, Si IV λλ1393, 1402, and C IV λλ1548, 1550. The absorption profile can be fitted with five components at velocities of ~-780, -1049, -1629, -1833, and -3054 km s-1 with respect to the emission-line redshift of z = 0.088. All the absorption components cover a large fraction of the continuum source, as well as the broad-line region. The O VI emission feature is very weak, and the O VI/Lyα flux ratio is 0.08, one of the lowest among low-redshift active galaxies and QSOs. The UV continuum shows a significant change in slope near 1050 A in the rest frame. The steeper continuum shortward of the Lyman limit extrapolates well to the observed weak X-ray flux level. The absorbers' properties are similar to those of high-redshift broad absorption line QSOs. The derived total column density of the UV absorbers is on the order of 1021 cm-2, unlikely to produce significant opacity above 1 keV in the X-ray. Unless there is a separate, high-ionization X-ray absorber, the QSO's weak X-ray flux may be intrinsic. The ionization level of the absorbing components is comparable to that anticipated in the broad-line region; therefore, the absorbers may be related to broad-line clouds along the line of sight.