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Wil van Breugel

Publications and source records attributed to Wil van Breugel.

At least 37 records · Page 2Linked to original sources
arXiv2003

SCUBA Observations of High Redshift Radio Galaxies

High redshift radio galaxies (HzRGs) are key targets for studies of the formation and evolution of massive galaxies. The role of dust in these processes is uncertain. We have therefore observed the dust continuum emission from a sample of z > 3 radio galaxies with the SCUBA bolometer array. We confirm and strengthen earlier results, that HzRGs are massive starforming systems and that submillimeter detection rate appears to be primarily a strong function of redshift. We also observed HzRG-candidates which have sofar eluded spectroscopic redshift determination. Four of these have been detected, and provide evidence that they may be extremely obscured radio galaxies, possibly in an early stage of their evolution.

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arXiv2003

An Obscured Radio Galaxy at High Redshift

Perhaps as many as 10% of high redshift radio galaxy (HzRG; z > 2) candidates that are selected using an Ultra Steep radio Spectrum (USS) criterion fail to show optical emission (continuum, lines) in deep Keck exposures. Their parent objects are only detected in the near-IR and are probably heavily obscured and/or at very high redshift. To search for signatures of dust and help constrain the nature and redshifts of these ``no-z'' radio galaxies, we have conducted a program of submillimeter and millimeter observations. Here we report the first results of a detailed study of one of these objects, WN J0305+3525. WN J0305+3525 appears associated with a small group of K ~ 21 - 22 objects and is strongly detected at both 850 micron and 1.25 mm. On the basis of its faint K-band magnitude, spectral energy distribution (SED) and other evidence we estimate that the radio galaxy is probably at a redshift z = 3 +/- 1. This would make WN J0305+3525 a radio-loud Hyper Luminous Infrared Galaxy (LFIR ~ 10^13 Lsun) similar to, but more obscured than, other dusty radio galaxies in this redshift range. This, together with the absence of Lya emission and compact (theta < 1.9") radio structure, suggests that WN J0305+3525 is embedded in a very dense, dusty medium and is probably at an early stage of its formation.

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arXiv2003

CO emission and associated HI absorption from a massive gas reservoir surrounding the z=3 radio galaxy B3 J2330+3927

We present results of a comprehensive multi-frequency study of the radio galaxy B3 J2330+3927. The 1.9" wide radio source, consisting of 3 components, is bracketed by 2 objects in our Keck K-band image. Optical and near-IR Keck spectroscopy of these two objects yield z=3.087+-0.004. The brightest (K=18.8) object has a standard type II AGN spectrum, and is the most likely location of the AGN, which implies a one-sided jet radio morphology. Deep 113 GHz observations with the IRAM Plateau de Bure Interferometer reveal CO J=4-3 emission, which peaks at the position of the AGN. The CO line is offset by 500 km/s from the systemic redshift of the AGN, but corresponds very closely to the velocity shift of an associated HI absorber seen in Lya. This strongly suggests that both originate from the same gas reservoir surrounding the AGN host galaxy. Simultaneous 230 GHz interferometer observations find a ~3x lower integrated flux density when compared to single dish 250 GHz observations with MAMBO at the IRAM 30m telescope. This can be interpreted as spatially resolved thermal dust emission at scales of 0.5" to 6". Finally, we present a tau <1.3% limit to the HI 21 cm absorption against the radio source, which represents the seventh non-detection out of 8 z>2 radio galaxies observed to date with the WSRT. We present mass estimates for the atomic, neutral, and ionized hydrogen, and for the dust, ranging from M(HI)=2x10^7 M_Sun derived from the associated HI absorber in Lya up to M(H_2)=7x10^{10} M_Sun derived from the CO emission. This indicates that the host galaxy is surrounded by a massive reservoir of gas and dust. The K-band companion objects may be concentrations within this reservoir, which will eventually merge with the central galaxy hosting the AGN.

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arXiv2002

A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey

The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the observations, the survey has a much lower resolution in declination than in right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS shows that the positional accuracy is less constrained in declination than in right ascension, but there is no significant systematic error. We present a source list containing 73570 sources. We correlate this WISH catalogue with the NVSS to construct a sample of faint Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies with large optical telescopes in the southern hemisphere. This sample is aimed at increasing the number of known high redshift radio galaxies to allow detailed follow-up studies of these massive galaxies and their environments in the early Universe.

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arXiv2002

Multiband VLA Observations of the Faint Radio Core of 3CR 68.1

The large, powerful Fanaroff-Riley class II radio source 3CR 68.1 is an optically red quasar with strong evidence for dust reddening, intrinsic ultraviolet line absorption, and X-ray absorption. In the context of its large, extended radio structure and the evidence for intrinsic material along the line of sight, it is a good candidate for a quasar seen through the edge of an obscuring torus proposed by unified schemes. The compact radio core coincident with the optical position of the quasar is extremely weak compared to the very bright and luminous radio lobes, suggesting that the radio core might also suffer absorption. We observed 3CR 68.1 at six frequencies and show that the radio core has a flat spectrum with no evidence for free-free absorption or other strong absorption mechanisms. This result helps establish an empirical intrinsic lower range for core-to-lobe radio flux in the most powerful radio sources.

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arXiv2002

Hubble Space Telescope Imaging of the Post-Starburst Quasar UN 1025-0040: Evidence for Recent Star Formation

We present new Hubble Space Telescope (HST) WFPC2 images of the post-starburst quasar UN J1025-0040, which contains both an active galactic nucleus (AGN) and a 400-Myr-old nuclear starburst of similar bolometric luminosity (10^{11.6} solar luminosities). The F450W and F814W images resolve the AGN from the starburst and show that the bulk of the star light (6 x 10^{10} solar masses) is contained within a central radius of about 600 parsecs, and lacks clear morphological structures at this scale. Equating the point-source light in each image with the AGN contribution, we determined the ratio of AGN-to-starburst light. This ratio is 69% in the red F814W image, consistent with our previous spectral analysis, but about 50% in the blue F450W image whereas we had predicted 76%. The HST images are consistent with previous photometry, ruling out variability (a fading AGN) as a cause for this result. We can explain the new data if there is a previously unknown young stellar population present, 40 Myr or younger, with as much as 10% of the mass of the dominant 400-Myr-old population. This younger starburst may represent the trigger for the current nuclear activity. The multiple starburst ages seen in UN J1025-0040 and its companion galaxy indicate a complex interaction and star-formation history.

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arXiv2002

A Galactic Wind at z = 5.190

We report the serendipitous detection in high-resolution optical spectroscopy of a strong, asymmetric Ly-alpha emission line at z = 5.190. The detection was made in a 2.25 hour exposure with the Echelle Spectrograph and Imager on the Keck II telescope through a spectroscopic slit of dimensions 1" x 20". The progenitor of the emission line, J123649.2+621539 (hereafter ES1), lies in the Hubble Deep Field North West Flanking Field where it appears faint and compact, subtending just 0.3" (FWHM) with I(AB) = 25.4. The ES1 Ly-alpha line flux of 3.0 x 10^(-17) ergs/cm^2/s corresponds to a luminosity of 9.0 x 10^(42) ergs/s, and the line profile shows the sharp blue cut-off and broad red wing commonly observed in star-forming systems and expected for radiative transfer in an expanding envelope. We find that the Ly-alpha profile is consistent with a galaxy-scale outflow with a velocity of v > 300 km/s. This value is consistent with wind speeds observed in powerful local starbursts (typically 10^2 to 10^3 km/s), and compares favorably to simulations of the late-stage evolution of Ly-alpha emission in star-forming systems. We discuss the implications of this high-redshift galactic wind for the early history of the evolution of galaxies and the intergalactic medium, and for the origin of the UV background at z > 3.

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arXiv2001

Radio AGN Surveys

We present a short overview of radio surveys for AGN, including the `complete' flux limited surveys and `filtered' surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z=5.19) and the most luminous z<2 radio galaxy known.

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arXiv2001

The X-ray -- radio alignment in the z = 2.2 radio galaxy PKS 1138--262

We present high resolution X-ray observations of the narrow line radio galaxy PKS 1138-262 at z = 2.156 with the ACIS-S detector on the Chandra observatory. These observations show that the X-ray emission from 1138-262 is dominated by emission from the AGN with a (rest frame) 2 to 10 keV luminosity of 4x10^{45} erg/s. The relative X-ray and radio properties of the AGN in 1138-262 are similar to those seen for the AGN in the archetype powerful radio galaxy Cygnus A. Between 10% and 25% (depending on energy) of the X-ray emission from 1138--262 is spatially extended on scales of 10'' to 20''. The extended X-ray emission is elongated, with a major axis aligned with that of the radio source. While the X-ray and radio emissions are elongated on similar scales and position angles, there is no one-to-one correspondence between the radio and X-ray features in the source. The most likely origin for the extended X-ray emission in 1138-262 is thermal emission from shocked gas, although we cannot rule-out a contribution from inverse Compton emission. If the emission is from hot gas, the gas density is 0.05 cm^{-3} and the gas mass is 2.5x10^{12} M_solar. The pressure in this hot gas is adequate to confine the radio emitting plasma and the optical line emitting gas. We set an upper limit of 1.5x10^{44} erg/s to the 2 to 10 keV luminosity of any normal cluster atmosphere associated with 1138-262. No emission was detected from any of the Ly alpha emitting galaxies in the (proto-) cluster around 1138-262, outside of the Ly alpha halo of 1138-262 itself, to a 2 to 10keV luminosity limit of 1.2x10^{43}erg/s.

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arXiv2001

Optical and Near-IR Imaging of Ultra Steep Spectrum Radio Sources - The K-z diagram of radio and optically selected galaxies

We present optical and/or near-IR images of 128 ultra steep spectrum (USS) radio sources. Roughly half of the objects are identified in the optical images (R <~ 24), while in the near-IR images, >94% are detected at K<~ 22. The mean K-magnitude is K=19.26 within a 2" diameter aperture. The distribution of R-K colors indicates that at least 1/3 of the objects observed have very red colors (R-K>5). The major axes of the identifications in K-band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter. We argue that this may be due to a dependence of K-magnitude on the radio power, with the highest radio power sources inhabiting the most massive host galaxies. We present a composite K-z diagram of radio-loud and radio-quiet galaxies, selected from the HDF-North and the Hawaii surveys. Out to z <~ 1, the radio-loud galaxies trace the bright envelope of the radio quiet galaxies, while at z >~ 1, the radio-loud galaxies are >~ 2 magnitudes brighter. We argue that this is not due to a contribution from the AGN or emission lines. This difference strongly suggests that radio galaxies pinpoint the most massive systems out to the highest known redshifts, probably due to the mutual correlation of the mass of the galaxy and the radio power on the mass of the central black hole.

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arXiv2001

HST STIS Observations of PG 0946+301: the Highest Quality UV Spectrum of a BALQSO

We describe deep (40 orbits) HST/STIS observations of the BALQSO PG 0946+301 and make them available to the community. These observations are the major part of a multi-wavelength campaign on this object aimed at determining the ionization equilibrium and abundances (IEA) in broad absorption line (BAL) QSOs. We present simple template fits to the entire data set, which yield firm identifications for more than two dozen BALs from 18 ions and give lower limits for the ionic column densities. We find that the outflow's metalicity is consistent with being solar, while the abundance ratio of phosphorus to other metals is at least ten times solar. These findings are based on diagnostics that are not sensitive to saturation and partial covering effects in the BALs, which considerably weakened previous claims for enhanced metalicity. Ample evidence for these effects is seen in the spectrum. We also discuss several options for extracting tighter IEA constraints in future analyses, and present the significant temporal changes which are detected between these spectra and those taken by the HST/FOS in 1992.

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arXiv2000

Spectroscopy of Ultra Steep Spectrum Radio Sources

We present optical spectroscopy of 62 objects selected from several samples of ultra steep spectrum (USS) radio sources. 46 of these are from our primary catalog, consisting of 669 sources with radio spectral indices alpha < -1.30 (S_nu ~ nu^alpha); this first spectroscopic sub-sample was selected on the basis of their faint optical and near-IR identifications. Most are identified as narrow-lined radio galaxies with redshifts ranging from z=0.25 to z=5.19. Ten objects are at z>3, nearly doubling the number of such sources known to date. Four of the USS radio sources are identified with quasars, of which at least three have very red spectral energy distributions. The source TN J0936-2242 is identified with an extremely red object (ERO, R-K>5); both it and a close companion are at z=1.479. The spectrum of the ERO closely resembles that of previously discovered radio galaxies at z~1.5. Five sources show continuum emission, but fail to show any clear emission or absorption features, despite integrations of ~1 h with the Keck telescope. We suggest that these objects could be (i) radio galaxies with faint emission lines in the ``redshift desert'' at 1.5 <~ z <~ 2.3, (ii) radio galaxies with an obscured AGN, which are dominated by a stellar continuum observed with insufficient S/N, or (iii) pulsars. Three radio sources identified with faint objects in the K-band images remain undetected in 50-90 min spectroscopic integrations with the Keck telescope, and are possible z>7 candidates.

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arXiv2000

Evidence Against a Redshift z>6 for the Galaxy STIS 123627+621755

The identification of galaxies at extreme distances provides our most direct information on the earliest phases of galaxy formation. The distance implied by redshifts z > 5 makes this a challenging endeavor for even the most luminous sources; interpretation of low signal-to-noise ratio observations of faint galaxies is difficult and occasional misidentifications will occur. Here we report on STIS 123627+621755, a galaxy with a suggested spectroscopic redshift of z = 6.68 and the most distant spectroscopically-identified object claimed. For the suggested redshift and reported spectral energy distribution, the galaxy should be essentially invisible shortward of 9300 Angstroms because the intervening intergalactic medium absorbs essentially all light energetic enough to ionize neutral hydrogen (lambda < (1 + z) x 912 Angstroms; the redshifted Lyman limit). The galaxy should be relatively bright in the near-infrared with f(nu) ~ 1 microJy. Here we report a detection of the galaxy at 6700 Angstroms, below the Lyman limit for z = 6.68. We also report a non-detection at 1.2 microns, implying the flux has dropped by a factor of three or more between rest 1216 Angstroms and rest 1560 Angstroms for z = 6.68. Our observations are inconsistent with the suggested extreme distance of STIS 123627+621755 and conservatively require z < 6.

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arXiv2000

UV Spectropolarimetry of Narrow-line Radio Galaxies

We present the results of UV spectropolarimetry (2000 - 3000A) and far-UV spectroscopy (1500 - 2000A) of two low-redshift narrow-line radio galaxies (NLRGs) taken with the Faint Object Spectrograph onboard the Hubble Space Telescope (HST). Spectropolarimetry of several NLRGs has shown that, by the presence of broad permitted lines in polarized flux spectrum, they have hidden quasars seen through scattered light. Imaging polarimetry has shown that NLRGs including our targets often have large scattering regions of a few kpc to >~10 kpc scale. This has posed a problem about the nature of the scatterers in these radio galaxies. Their polarized continuum has the spectral index similar to or no bluer than that of quasars, which favors electrons as the dominant scattering particles. The large scattering region size, however, favors dust scattering, because of its higher scattering efficiency compared to electrons. In this paper, we investigate the polarized flux spectrum over a wide wavelength range, combining our UV data with previous optical/infrared polarimetry data. We infer that the scattering would be often caused by opaque dust clouds in the NLRGs and this would be a part of the reason for the apparently grey scattering. In the high-redshift radio galaxies, these opaque clouds could be the proto-galactic subunits inferred to be seen in the HST images. However, we still cannot rule out the possibility of electron scattering, which could imply the existence of a large gas mass surrounding these radio galaxies.

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arXiv2000

A Statistical Study of Emission Lines from High Redshift Radio Galaxies

We have compiled a sample of 165 radio galaxies from the literature to study the properties of the extended emission line regions and their interaction with the radio source over a large range of redshift 0<z<5.2. For each source, we have collected radio (size, lobe distance ratio and power) and spectroscopic parameters (luminosity, line width and equivalent width) for the four brightest UV lines. We also introduce a parameter A_{Ly-alpha} measuring the asymmetry of the Ly-alpha line. Using these 18 parameters, we examine the statistical significance of all 153 mutual correlations, and find the following significant correlations: (i) Ly-alpha asymmetry A_{Ly-alpha} with radio size and redshift, (ii) line luminosity with radio power, (iii) line luminosities of UV lines with each other, and (iv) equivalent widths of UV lines with each other. Using line-ratio diagnostic diagrams, we examine the ionization mechanism of the extended emission line regions in HzRGs. The high ionization lines seem to confirm previous results showing that AGN photo-ionization provides the best fit to the data, but are inconsitent with the CII/CIII ratio, which favour the highest velocity shock ionization models. We note that the CII line is 5 times more sensitive to shock ionization than the high ionization UV lines, and show that a combination of shock and photo-ionization provides a better overall fit to the integrated spectra of HzRGs. Because most HzRGs have radio sizes <~150 kpc, their integrated spectra might well contain a significant contribution from shock ionized emission. [abridged]

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arXiv2000

The Highest Redshift Radio Galaxies

At low redshifts powerful radio sources are uniquely associated with massive galaxies, and are thought to be powered by supermassive black holes. Modern 8m -- 10m telescopes may be used used to find their likely progenitors at very high redshifts to study their formation and evolution.

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arXiv2000

The FIRST Sample of Ultraluminous Infrared Galaxies at High Redshift I. Sample and Near-IR Morphologies

We present a new sample of distant ultraluminous infrared galaxies. The sample was selected from a positional cross--correlation of the IRAS Faint Source Catalog with the FIRST database. Objects from this set were selected for spectroscopy by virtue of following the well-known star-forming galaxy correlation between 1.4 GHz and 60 micron flux, and by being optically faint on the POSS. Optical identification and spectroscopy were obtained for 108 targets at the Lick Observatory 3m telescope. Most objects show spectra typical of starburst galaxies, and do not show the high ionization lines of active galactic nuclei. The redshift distribution covers 0.1 < z < 0.9, with 13 objects at z > 0.5 and an average redshift of 0.31. K-band images were obtained at the IRTF, Lick, and Keck observatories in sub-arcsec seeing of all optically identified targets. About 2/3 of the objects appear to be interacting galaxies, while the other 1/3 appear to be normal. Nearly all the identified objects have far-IR luminosities greater than 10^11 L_sun, and ~25% have L_FIR > 10^12 L_sun.

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