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M. J. Jarvis

Publications and source records attributed to M. J. Jarvis.

188 records · Page 11Linked to original sources
arXiv2004

HI in the proto-cluster environment at z>2: absorbing haloes and the Lyman alpha forest

We present VLT-UVES echelle spectra of the Lyman alpha emission and absorption in five radio galaxies at redshifts z=2.55-4.1. Together with data from our pilot study, we have a sample of 7 such systems with radio source sizes ~ 1-90 kpc with which to address the origin of the absorbing gas. Echelle resolution again reveals that some systems with N_HI>1E18 cm^-2 in lower resolution data in fact consist of several weaker absorbers with N_HI<1E15 cm^-2. We identify two groups of HI absorbers: strong absorbers with N_HI=1E18-1E20 cm^-2 and weaker systems with N_HI=1E13-1E15 cm^-2. There are none at intermediate N_HI. The strong absorbers may be a by-product of massive galaxy formation or could instead represent material cooling behind the expanding bow-shock of the radio jet, as simulated by Krause. New observations are required to discriminate between these possibilities. We argue that the weaker absorbers with N_HI=1E13-1E15 cm^-2 are part of the Lyman alpha forest, as their rate of incidence is within a factor of 2-4 of that in the IGM at large. Such column densities are consistent with models of a multi-phase proto-intracluster medium at z>2.

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arXiv2003

A Deep, High-Resolution Survey at 74 MHz

We present a 74 MHz survey of a 165 square degree region located near the north galactic pole. This survey has an unprecedented combination of both resolution (25'' FWHM) and sensitivity (RMS noise as low as 24 mJy/beam). We detect 949 sources at the 5-sigma level in this region, enough to begin exploring the nature of the 74 MHz source population. We present differential source counts, spectral index measurements and the size distribution as determined from counterparts in the high resolution FIRST 1.4 GHz survey. We find a trend of steeper spectral indices for the brighter sources. Further, there is a clear correlation between spectral index and median source size, with the flat spectrum sources being much smaller on average. Ultra-steep spectrum objects (alpha < -1.2) are identified, and we present high resolution VLA follow-up observations of these sources which, identified at such a low frequency, are excellent candidates for high redshift radio galaxies.

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arXiv2003

The Black Hole Masses of High-Redshift Quasars

A reliable method for estimating the black-hole masses of high-redshift quasars would provide crucial new information for understanding the nature and cosmological evolution of quasars. In this proceedings we summarize the results of our recent paper (McLure & Jarvis 2002) which provides a virial black-hole mass estimator based on rest-frame UV observables, thereby allowing reliable black-hole mass estimates to be obtained out to redshifts of $z\sim2.5$ from optical spectra alone.

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arXiv2002

The clustering of sub-mJy radio sources in The Bootes Deep Field

We measure the angular clustering of ~2000 radio sources in The Bootes Deep Field, covering 5.3 deg^2 down to S(1.4 GHz)=0.2 mJy. With reference to work by Blake & Wall, we show that the size distribution of multi-component radio galaxies dominates the overall clustering signal, and that its amplitude extrapolates smoothly from their measurements above 5 mJy. The upper limits on any true galaxy-galaxy clustering are consistent with the clustering of the sub-mJy radio-loud AGN being effectively diluted by the more weakly-clustered IRAS-type starburst galaxies. Source count models imply that the survey contains around 400 of the latter galaxies above 0.2 mJy out to z ~ 1 to 2. Measurement of their clustering must await their identification via the optical and infrared data due on this field.

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arXiv2002

Probing the absorbing haloes around two high-redshift radio galaxies with VLT-UVES

We present VLT-UVES echelle spectroscopy of the HI and CIV absorption in the spatially-extended Lyman-alpha emission around two high-redshift radio galaxies 0200+015 (z=2.23) and 0943-242 (z=2.92). The absorbers in 0943-242 exhibit little additional structure compared with previous low-resolution spectroscopy and the main absorber is still consistent with HI column density of ~10^19 cm^-2. This is consistent with a picture in which the absorbing gas has low density and low metallicity and is distributed in a smooth absorbing shell located beyond the emission-line gas. However, the main absorbers in 0200+015 are very different. The previous single absorber fit of HI column density \~10^19 cm^-2, now splits into two ~4 x 10^14 cm^-2 absorbers which extend more than 15kpc to obscure additional Ly-alpha emission coincident with a radio lobe in these high-resolution observations. Although consistent with the shell-like distribution for the absorption systems, 0200+015 requires a much higher metal enrichment than 0943-242. The metallicity, inferred from the CIV absorption, is considerably lower in 0943-242 than in 0200+015. We explain these differences with an evolutionary scenario based on the size of the radio source. In both sources the HI absorption gas originates from either a gas-rich merger or pristine cluster gas which cools and collapses towards the centre of the dark matter halo. The higher metallicity in the larger radio source (0200+015) may be a result of a starburst driven superwind (concurrent with the triggering of the radio emission) which has engulfed the outer halo in this older source.

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arXiv2002

Measuring the black hole masses of high redshift quasars

A new technique is presented for determining the black-hole masses of high-redshift quasars from optical spectroscopy. The new method utilizes the full-width half maximum (FWHM) of the low-ionization MgII emission line and the correlation between broad-line region (BLR) radius and continuum luminosity at 3000 Angstroms. Using archival UV spectra it is found that the correlation between BLR radius and 3000 Angstrom luminosity is tighter than the established correlation with 5100 Angstrom luminosity. Furthermore, it is found that the correlation between BLR radius and 3000 Ang luminosity is consistent with a relation of the form $R_{BLR} \propto lambda L_{lambda}^{0.5}$, as expected for a constant ionization parameter. Using a sample of objects with broad-line radii determined from reverberation mapping it is shown that the FWHM of MgII and H beta are consistent with following an exact one-to-one relation, as expected if both H beta and MgII are emitted at the same radius from the central ionizing source. The resulting virial black-hole mass estimator based on rest-frame UV observables is shown to reproduce black-hole mass measurements based on reverberation mapping to within a factor of 2.5 (1 sigma). Finally, the new UV black-hole mass estimator is shown to produce identical results to the established optical (H beta) estimator when applied to 128 intermediate-redshift (0.3<z<0.9) quasars drawn from the Large Bright Quasar Survey and the radio-selected Molonglo quasar sample. We therefore conclude that the new UV virial black-hole mass estimator can be reliably used to estimate the black-hole masses of quasars from z~0.25 through to the peak epoch of quasar activity at z~2.5 via optical spectroscopy alone.

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arXiv2001

Deep Westerbork 1.4 GHz Imaging of the Bootes Field

We present the results from our deep (16x12 hour) Westerbork Synthesis Radio Telescope (WSRT) observations of the approximately 7 square degree Bootes Deep Field, centered at 14h32m05.75s, 34d16'47.5" (J2000). Our survey consists of 42 discrete pointings, with enough overlap to ensure a uniform sensitivity across the entire field, with a limiting sensitivity of 28 microJy (1 sigma rms). The catalog contains 3172 distinct sources, of which 316 are resolved by the 13"x27" beam. The Bootes field is part of the optical/near-infrared imaging and spectroscopy survey effort conducted at various institutions. The combination of these data sets, and the deep nature of the radio observations will allow unique studies of a large range of topics including the redshift evolution of the luminosity function of radio sources, the K-z relation and the clustering environment of radio galaxies, the radio / far-infrared correlation for distant starbursts, and the nature of obscured radio loud AGN.

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