We present a survey of X-ray point sources in a 91 ksec Chandra ACIS-S observation of the z=0.83 cluster MS1054-0321. We detect 47 X-ray sources within the 8.3 arcmin by 8.3 arcmin field, of which two are immediately confirmed from pre-existing spectroscopy to be at the redshift of the cluster. At fluxes brighter than S_(0.5 - 8 keV) = 5 x 10^{-15} erg s^{-1} cm^{-2} we find a ~ 2 sigma excess compared to predictions from field surveys, consistent with an excess of approximately 6 AGN. If these sources are associated with the cluster, they too are AGN with luminosities of order L_(0.5 - 8 keV) ~ 10^{43} erg s^{-1}. Combined with the identification of 7 cluster AGN from deep radio observations (Best et al. 2002), these observations suggest significantly enhanced AGN activity in MS1054-03 compared to local galaxy clusters. Interestingly, the excess of X-ray detected AGN is found at radial distances of between 1 and 2 Mpc, suggesting they may be associated with infalling galaxies. The radio AGN are seen within the inner Mpc of the cluster and are largely undetected in the X-ray, suggesting they are either intrinsically less luminous and/or heavily obscured.
An analysis of the kinematics and ionization state of the emission-line gas of a sample of 14 3CR radio galaxies with redshifts z|1 is carried out. The data used for these studies, deep long-slit spectroscopic exposures from the William Herschel Telescope, are presented in an accompanying paper. It is found that radio sources with small linear sizes (≲150 kpc) have lower ionization states, higher emission-line fluxes and broader line widths than larger radio sources. An analysis of the low-redshift sample of Baum et al. demonstrates that radio galaxies at low redshift show similar evolution in their velocity structures and emission-line ratios from small to large radio sources. The emission-line ratios of small radio sources are in agreement with theoretical shock ionization predictions, and their velocity profiles are distorted. Together with the other emission-line properties, this indicates that shocks associated with the radio source dominate the kinematics and ionization of the emission-line gas during the period that the radio source is expanding through the interstellar medium. Gas clouds are accelerated by the shocks, giving rise to the irregular velocity structures observed, whilst shock compression of emission-line gas clouds and the presence of the ionizing photons associated with the shocks combine to lower the ionization state of the emission-line gas. By contrast, in larger sources the shock fronts have passed well beyond the emission-line regions; the emission-line gas of these larger radio sources has much more settled kinematical properties, indicative of rotation, and emission-line ratios consistent with the dominant source of ionizing photons being the active galactic nucleus. This strong evolution with radio size of the emission-line gas properties of powerful radio galaxies mirrors the radio size evolution seen in the nature of the optical—ultraviolet continuum emission of these sources, implying that the continuum alignment effect is likely to be related to the same radio source shocks.
We report the detection of a strong jet-cloud interaction at a distance of 120 kpc from the nucleus of the radio galaxy 3C 34, which has redshift z = 0.69. Hubble Space Telescope images of the radio galaxy show a long narrow region of blue emission orientated along the radio axis and directed towards a radio hotspot. The William Herschel Telescope has been used to provide long-slit spectroscopic data of this object, and infrared observations made with the United Kingdom InfraRed Telescope have enabled its spectral energy distribution to be modelled. We propose that the aligned emission is associated with a region of massive star formation, induced by the passage of the radio jet through a galaxy within the cluster surrounding 3C 34. A star formation rate of about 100 M⊙ yr−1 is required, similar to the values necessary to produce the alignment effect in high-redshift radio galaxies. The consequences of this result for models of star formation in distant radio galaxies are discussed.
We present the final 6arcsec resolution data release of the ELAIS-N1 field from the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey Deep Fields project (LoTSS Deep). The 144,MHz images are the most sensitive achieved to date at this frequency and were created from 290,TB of data obtained from 505,hrs on-source observations taken over 7.5 years. The data were processed following the strategies developed for previous LoTSS and LoTSS Deep data releases. The resulting images span 24.53 square degrees, and using a refined source detection approach, we identified 154,952 radio sources formed from 182,184 Gaussian components within this area. The maps reach a noise level of 10.7,μJy beam^-1 at 6arcsec resolution, where approximately half of the noise is due to source confusion. In about 7.4% of the image, our limited dynamic range around bright sources results in a further $>5%$ increase in the noise. The images have a flux density scale accuracy of about 9%, and the standard deviation of offsets between our source positions and those from Pan-STARRS is 0.2arcsec in RA and Dec for high significance detections. We searched individual epoch images for variable sources, identifying 39 objects with considerable variation. We also searched for circularly polarised sources, achieving three detections of previously known emitters (two stars and one pulsar) whilst constraining the typical polarisation fraction plus leakage to be less than 0.045%.
Faint undetected sources of radio-frequency interference (RFI) might become visible in long radio observations when they are consistently present over time.Thereby, they might obstruct the detection of the weak astronomical signals of interest.This issue is especially important for Epoch of Reionization (EoR) projects that try to detect the faint redshifted H I signals from the time of the earliest structures in the Universe.We explore the RFI situation at 30-163 MHz by studying brightness histograms of visibility data observed with Low-Frequency Array (LOFAR), similar to radio-source-count analyses that are used in cosmology.An empirical RFI distribution model is derived that allows the simulation of RFI in radio observations.The brightness histograms show an RFI distribution that follows a power-law distribution with an estimated exponent around -1.5.With several assumptions, this can be explained with a uniform distribution of terrestrial radio sources whose radiation follows existing propagation models.Extrapolation of the power law implies that the current LOFAR EoR observations should be severely RFI limited if the strength of RFI sources remains strong after time integration.This is in contrast with actual observations, which almost reach the thermal noise and are thought not to be limited by RFI.Therefore, we conclude that it is unlikely that there are undetected RFI sources that will become visible in long observations.Consequently, there is no indication that RFI will prevent an EoR detection with LOFAR.
(abridged) We present a clustering analysis of 370 high-confidence H-alpha emitters (HAEs) at z=2.23. The HAEs are detected in the Hi-Z Emission Line Survey (HiZELS), a large-area blank field 2.121um narrowband survey using the United Kingdom Infrared Telescope (UKIRT) Wide Field Camera (WFCAM). Averaging the two-point correlation function of HAEs in two ~1 degree scale fields (United Kingdom Infrared Deep Sky Survey/Ultra Deep Survey [UDS] and Cosmological Evolution Survey [COSMOS] fields) we find a clustering amplitude equivalent to a correlation length of r_0=3.7+/-0.3 Mpc/h for galaxies with star formation rates of >7 M_sun/yr. The data are well-fitted by the expected correlation function of Cold Dark Matter, scaled by a bias factor: omega_HAE=b^2 omega_DM where b=2.4^{+0.1}_{-0.2}. The corresponding 'characteristic' mass for the halos hosting HAEs is log(M_h/[M_sun/h])=11.7+/-0.1. Comparing to the latest semi-analytic GALFORM predictions for the evolution of HAEs in a LCDM cosmology, we find broad agreement with the observations, with GALFORM predicting a HAE correlation length of ~4 Mpc/h. Motivated by this agreement, we exploit the simulations to construct a parametric model of the halo occupation distribution (HOD) of HAEs, and use this to fit the observed clustering. Our best-fitting HOD can adequately reproduce the observed angular clustering of HAEs, yielding an effective halo mass and bias in agreement with that derived from the scaled omega_DM fit, but with the relatively small sample size the current data provide a poor constraint on the HOD. Our results support the broad picture that 'typical' (~L*) star-forming galaxies have been hosted by dark matter haloes with M_h<10^12 M_sun/h since z~2, but with a broad occupation distribution and clustering that is likely to be a strong function of luminosity.
We present a detailed multiwavelength study (from rest-frame ultraviolet to far-infrared) of narrow-band selected, star-forming (SF) Hα emitters (HAEs) at z ∼ 2.23 taken from the High-Redshift(Z) Emission Line Survey (HiZELS). We find that HAEs have similar properties and colours derived from spectral energy distributions as sBzK galaxies, and probe a well-defined portion of the SF population at z ∼ 2. This is not true for Lyα emitters (LAEs), which are strongly biased towards blue, less massive galaxies (missing a significant percentage of the SF population). Combining our Hα observations with matched, existing Lyα data, we determine that the Lyα escape fraction (fesc) is low (only ∼4.5 per cent of HAEs show Lyα emission) and decreases with increasing dust attenuation, ultraviolet continuum slope, stellar mass and star formation rate (SFR). This suggests that Lyα preferentially escapes from blue galaxies with low dust attenuation. However, a small population of red and massive LAEs is also present, in agreement with previous works and indicating that dust and Lyα are not mutually exclusive. Using different and completely independent measures of the total SFR, we show that the Hα emission is an excellent tracer of star formation at z ∼ 2 with deviations typically lower than 0.3 dex for individual galaxies. We find that the slope and zero-point of the HAE main sequence at z ∼ 2 strongly depend on the dust-correction method used to recover the SFR, although they are consistent with previous works when similar assumptions are made.
The Combined EIS-NVSS Survey of Radio Sources (CENSORS) is a 1.4-GHz radio survey selected from the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS) and complete to a flux density of 7.2 mJy. It targets the European Southern Observatory (ESO) Imaging Survey (EIS) Patch D, which is a 3 × 2-deg2 field centred on right ascension 09h51m36s•0 and declination −21°00′ 00∳ (J2000). This paper presents K-band imaging of 142 of the 150 CENSORS sources. The primary motivation for beginning infrared imaging of the sample was to identify the host galaxies of ∼30 per cent of sources for which the EIS I-band imaging failed to produce a likely candidate. In addition, K-band magnitudes allow photometric redshift estimation and I-K colours aid the identification of host galaxies (which are typically old, red ellipticals). Of the sources observed in the I and K bands, four remain undetected, possibly indicating high redshifts for the host galaxies, and eight involve complicated radio structures, or several candidate host galaxies, which have yet to be resolved. Thus, the host galaxy identifications are brought to 92 per cent completeness. In conjunction with spectroscopic observations, the K-band magnitudes have been aperture corrected and used to establish a K-z relation for the CENSORS radio galaxies. This relation is of interest because of its variation, at z > 1, between radio surveys of different flux-density limit. Establishing this relation for CENSORS may shed light on the origin of this variation and will allow an appropriate K-z redshift estimator for any CENSORS source which remains without a spectroscopic redshift. It is shown that whilst the K-z relation for CENSORS is fainter than that of 3CRR at all redshifts, it agrees well with that of 7C over all redshifts studied.
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