arXiv subjects

W. van Breugel

Publications and source records attributed to W. van Breugel.

At least 19 recordsLinked to original sources

arXiv2010

Mid-Infrared Variability from the Spitzer Deep, Wide-Field Survey

We use the multi-epoch, mid-infrared Spitzer Deep, Wide-Field Survey to investigate the variability of 474,179 objects in 8.1 deg^2 of the NDWFS Bootes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 micron bands. We find that 1.1% of the studied sample meet our standard selection criteria for being classed as a variable source. We require that the 3.6 and 4.5 micron light-curves are strongly correlated (r>0.8) and that their joint variance exceeds that for all sources with the same magnitude by 2 sigma. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBootes survey, radio catalogs, 24 micron-selected AGN candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects. Most of the stellar, galaxy and unclassified sources are false positives. For our standard selection criteria, 11-12% of the mid-IR counterparts to X-ray sources, 24 micron-selected AGN candidates and spectroscopically identified AGNs show variability. Mid-IR AGN variability can be well described by a single power-law structure function with a power-law index of 0.5 at both 3.6 and 4.5 microns, and an amplitude of 0.1 mag on rest-frame time scales of 2 years. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities. (Abridged)

astro-ph.CO↗

arXiv2009

The Spitzer Deep, Wide-Field Survey

The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of ten square degrees in the Bootes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Cycle four Spitzer Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit -- for the first time -- the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z~3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS datasets will thus be especially useful for characterizing galaxy evolution beyond z~1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly-released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 x 10e5 distinct sources detected to the average 5-sigma, 4" diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 micron, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 min integration time of the SDWFS IRAC imaging, more than 50% of isolated FIRST radio sources and more than 80% of on-axis XBootes sources are detected out to 8.0 micron. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.

astro-ph.CO↗

arXiv2008

Evidence for powerful AGN winds at high redshift: Dynamics of galactic outflows in radio galaxies during the "Quasar Era"

AGN feedback now appears as an attractive mechanism to resolve some of the outstanding problems with the "standard" cosmological models, in particular those related to massive galaxies. To directly constrain how this may influence the formation of massive galaxies near the peak in the redshift distribution of powerful quasars, z~2, we present an analysis of the emission-line kinematics of 3 powerful radio galaxies at z~2-3 (HzRGs) based on rest-frame optical integral-field spectroscopy obtained with SINFONI on the VLT. HzRGs are among the most massive galaxies, so AGN feedback may have a particularly clear signature. We find evidence for bipolar outflows in all HzRGs, with kinetic energies that are equivalent to 0.2% of the rest-mass of the supermassive black hole. Velocity offsets in the outflows are ~800-1000 km s^-1 between the blueshifted and redshifted line emission, FWHMs ~1000 km s^-1 suggest strong turbulence. Ionized gas masses estimated from the Ha luminosity are of order 10^10 M_s, similar to the molecular gas content of HzRGs, underlining that these outflows may indicate a significant phase in the evolution of the host galaxy. The total energy release of ~10^60 erg during a dynamical time of ~10^7 yrs corresponds to about the binding energy of a massive galaxy. Geometry, timescales and energy injection rates of order 10% of the kinetic energy flux of the jet suggest that the outflows are most likely driven by the radio source. The global energy density release of ~10^57 erg s^-1 Mpc^-3 may also influence the subsequent evolution of the HzRG by enhancing the entropy and pressure in the surrounding halo and facilitating ram-pressure stripping of gas in satellite galaxies that may contribute to the subsequent mass assembly of the HzRG through low-dissipation "dry" mergers.

astro-ph↗

arXiv2008

[OIII] emitters in the field of the MRC 0316-257 protocluster

Venemans et al. (2005) found evidence for an overdensity of Ly-alpha emission line galaxies associated with the radio galaxy MRC 0316-257 at z=3.13 indicating the presence of a massive protocluster. Here, we present the results of a search for additional star-forming galaxies and AGN within the protocluster. Narrow-band infrared imaging was used to select candidate [O III] emitters in a 1.1 x 1.1 Mpc^2 region around the radio galaxy. Thirteen candidates have been detected. Four of these are among the previously confirmed sample of Ly-alpha galaxies, and an additional three have been confirmed through follow-up infrared spectroscopy. The three newly confirmed objects lie within a few hundred km/s of each other, but are blueshifted with respect to the radio galaxy and Ly-alpha emitters by ~2100 km/s. Although the sample is currently small, our results indicate that the radio-selected protocluster is forming at the centre of a larger, ~60 co-moving Mpc super-structure. On the basis of an HST/ACS imaging study we calculate dust-corrected star-formation rates and investigate morphologies and sizes of the [O III] candidate emitters. From a comparison of the star formation rate derived from UV-continuum and [O III] emission, we conclude that at least two of the [O III] galaxies harbour an AGN which ionized the O+ gas.

astro-ph↗

arXiv2008

The Nascent Red Sequence at z~2

We present new constraints on the evolution of the early-type galaxy color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space Telescope. This field contains a spectroscopically confirmed space-overdensity of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio galaxy MRC 1138-262. Using these NICMOS data we identify a significant surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram (when compared with deep NICMOS imaging from the HDF-N and UDF). The optical-NIR colors of these prospective red-sequence galaxies indicate the presence of on-going dust-obscured star-formation or recently formed (<~ 1.5 Gyr)stellar populations in a majority of the red galaxies. We measure the slope and intrinsic scatter of the CMR for three different red galaxy samples selected by a wide color cut, and using photometric redshifts both with and without restrictions on rest-frame optical morphology. In all three cases both the rest-frame $U-B$ slope and intrinsic color scatter are considerably higher than corresponding values for lower redshift galaxy clusters. These results suggest that while some relatively quiescent galaxies do exist in this protocluster both the majority of the galaxy population and hence the color-magnitude relation are still in the process of forming, as expected.

astro-ph↗

arXiv2007

Compact radio sources and jet-driven AGN feedback in the early Universe: Constraints from integral-field spectroscopy

To investigate the impact of radio jets during the formation epoch of their massive host galaxies, we present an analysis of two massive, log(M_stel/ M_sun)~10.6 and 11.3, compact radio galaxies at z=3.5, TNJ0205+2242 and TNJ0121+1320. Their small radio sizes (R<= 10 kpc) are most likely a sign of youth. We compare their radio properties and gas dynamics with those in well extended radio galaxies at high redshift, which show strong evidence for powerful, jet-driven outflows of significant gas masses (M 10^9-10 M_sun). Our analysis combines rest-frame optical integral-field spectroscopy with existing radio imaging, CO emission line spectra, and rest-frame UV spectroscopy. [OIII]5007 line emission is compact in both galaxies and lies within the region defined by the radio lobes. For TNJ0205+2242, the Ly-alpha profile narrows significantly outside the jet radius, indicating the presence of a quiescent halo. TNJ0121+1320 has two components separated by ~10 kpc and a velocity offset of ~300 km s^-1. If motions are gravitational, this implies a dynamical mass of 2x10^11 M_sun for the more massive, radio-loud component. The dynamical mass, molecular gas mass measured from the CO line emission, and radio luminosity of these two compact radio galaxies imply that compact radio sources may well develop large-scale, energetic outflows as observed in extended radio galaxies, with the potential of removing significant fractions of the ISM from the host galaxy. The absence of luminous emission line gas extending beyond the radio emission in these sources agrees with the observed timescales and outflow rates in extended radio galaxies, and adds further evidence that the energetic, large-scale outflows observed in extended radio sources (Nesvadba et al. 2006) are indeed the result of influence of the radio jet.

astro-ph↗

arXiv2004

Discovery of six Ly alpha emitters near a radio galaxy at z ~ 5.2

We present the results of narrow-band and broad-band imaging with the Very Large Telescope of the field surrounding the radio galaxy TN J0924-2201 at z = 5.2. Fourteen candidate Ly alpha emitters with a rest-frame equivalent width of > 20 A were detected. Spectroscopy of 8 of these objects showed that 6 have redshifts similar to that of the radio galaxy. The density of emitters at the redshift of the radio galaxy is estimated to be a factor 1.5-6.2 higher than in the field, and comparable to the density of Ly alpha emitters in radio galaxy protoclusters at z = 4.1, 3.1 and 2.2. The Ly alpha emitters near TN J0924-2201 could therefore be part of a structure that will evolve into a massive cluster. These observations confirm that substantial clustering of Ly alpha emitters occurs at z > 5 and support the idea that radio galaxies pinpoint high density regions in the early Universe.

astro-ph↗

arXiv2003

Extended X-ray emission around 4C 41.17 at z=3.8

We present sensitive, high-resolution, X-ray imaging from Chandra of the high-redshift radio galaxy 4C 41.17 (z=3.8). Our 150-ks Chandra exposure detects strong X-ray emission from a point source coincident with the nucleus of the radio galaxy. In addition we identify extended X-ray emission with a luminosity ~1e45 erg/s covering a 100kpc (15'') diameter region around the radio galaxy. The extended X-ray emission follows the general distribution of radio emission in the radio lobes of this source, and the distribution of a giant Lyman-alpha emission line halo, while the spectrum of the X-ray emission is non-thermal and has a power law index consistent with that of the radio synchrotron. We conclude that the X-ray emission is most likely Inverse-Compton scattering of far-infrared photons from a relativistic electron population probably associated with past and current activity from the central object. Assuming an equipartition magnetic field the CMB energy density at z=3.8 can only account for at most 40% of the Inverse-Compton emission. Published submillimeter maps of 4C 41.17 have detected an apparently extended and extremely luminous far-infrared emission around the radio galaxy. We demonstrate that this photon component and its spatial distribution, in combination with the CMB can reproduce the observed X-ray luminosity. We propose that photo-ionization by these Inverse-Compton X-ray photons plays a significant role in this system, and provides a new physical feedback mechanism to preferentially affect the gas within the most massive halos at high redshift. This is the highest redshift example of extended X-ray emission around a radio galaxy currently known. (Abridged)

astro-ph↗

arXiv2002

AO Observations of Three Powerful Radio Galaxies

The host galaxies of powerful radio sources are ideal laboratories to study active galactic nuclei (AGN). The galaxies themselves are among the most massive systems in the universe, and are believed to harbor supermassive black holes (SMBH). If large galaxies are formed in a hierarchical way by multiple merger events, radio galaxies at low redshift represent the end-products of this process. However, it is not clear why some of these massive ellipticals have associated radio emission, while others do not. Both are thought to contain SMBHs, with masses proportional to the total luminous mass in the bulge. It either implies every SMBH has recurrent radio-loud phases, and the radio-quiet galaxies happen to be in the "low" state, or that the radio galaxy nuclei are physically different from radio-quiet ones, i.e. by having a more massive SMBH for a given bulge mass. Here we present the first results from our adaptive optics imaging and spectroscopy pilot program on three nearby powerful radio galaxies. Initiating a larger, more systematic AO survey of radio galaxies (preferentially with Laser Guide Star equipped AO systems) has the potential of furthering our understanding of the physical properties of radio sources, their triggering, and their subsequent evolution.

astro-ph↗

arXiv2002

BRIGHT lights, BIG city: Massive galaxies, giant Ly-a nebulae, and proto--clusters

High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super--massive black holes and proto--clusters. We report on deep narrow--band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-alpha nebulae centered on the galaxies and to search for over--dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.

astro-ph↗

arXiv2002

The most distant structure of galaxies known: a protocluster at z=4.1

Imaging and spectroscopy with the Very Large Telescope have revealed 20 Lyman-alpha emitters within a projected distance of 1.3 Mpc and 600 km/s of the luminous radio galaxy TN J1338-1942 at z=4.1. Compared to the field density of Lyman-alpha emitters, this implies an overdensity on the order of 15. The structure has a projected size of at least 2.7 Mpc x 1.8 Mpc and a velocity dispersion of 325 km/s, which makes it the most distant structure known. Using the galaxy overdensity and assuming a bias parameter b = 3 - 5, the mass is estimated to be ~10^15 M_sun. The radio galaxy itself is surrounded by an uniquely asymmetric Lyman-alpha halo. Taken together with our previous data on PKS 1138-262 at z ~ 2.16, these results suggest that luminous radio sources are excellent tracers of high density regions in the early Universe, which evolve into present-day clusters. The statistics of bright radio sources and of concentrations in the Lyman break galaxy population are consistent with the picture that each of those concentrations harbours an active or passive luminous radio source.

astro-ph↗

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.

astro-ph↗

arXiv2001

A Tunable Lyot Filter at Prime Focus: a Method for Tracing Supercluster Scales at z ~ 1

Tunable narrow-band, emission-line surveys have begun to show the ease with which star forming galaxies can be identified in restricted redshift intervals to z ~ 5 with a 4m class telescope. These surveys have been carried out with imaging systems at the Cassegrain or Nasmyth focus and are therefore restricted to fields smaller than 10 arcmin. We now show that tunable narrowband imaging is possible over a 30 arcmin field with a high-performance Lyot filter placed directly in front of a CCD mosaic at the prime focus. Our design is intended for the f/3.3 prime focus of the AAT 3.9m, although similar devices can be envisaged for the Subaru 8m (f/2), Palomar 5m (f/3.4), VISTA 4m (f/6), Mayall 4m (f/2.6) or CFHT 3.6m (f/4). A modified Wynne doublet ensures sub-arcsecond performance over the field. In combination with the new Wide-Field Imaging 8K x 8K mosaic (WFI) at the AAT, the overall throughput (35%) of the system to unpolarised light is expected to be comparable to the TAURUS Tunable Filter (TTF). Unlike the TTF, the field is fully monochromatic and the instrumental profile has much better wing suppression. For targetted surveys of emission-line sources at z ~ 1, a low-resolution (R ~ 150 at 550nm) Lyot filter on a 4m telescope is expected to be comparable or superior to current instruments on 8-10m class telescopes. We demonstrate that the 30 arcmin field is well matched to superclusters at these redshifts such that large-scale structure should be directly observable.

astro-ph↗

arXiv2001

Keck Adaptive Optics Observations of the Radio Galaxy 3C294: A Merging System at z = 1.786?

We present seeing-limited and adaptive optics (AO) images of the z = 1.786 radio galaxy 3C294 in the H and K' infrared bands obtained at Keck Observatory. The infrared emission of 3C294 is dominated by two distinct components separated by ~1" (9 kpc). The eastern knot contains an unresolved core that contributes ~4% of the K'-band light; we identify this core with the active nucleus. The western component is about 2.5 times brighter. The most plausible interpretation of the near-infrared morphology is an ongoing merger event, with the active nucleus located in the less massive of the two galaxies.

astro-ph↗

arXiv2000

A search for clusters at high redshift - II. A proto cluster around a radio galaxy at z=2.16

VLT spectroscopic observations of Ly alpha--excess objects in the field of the clumpy radio galaxy 1138-262 at z=2.16 have led to the discovery of 14 galaxies and one QSO at approximately the same distance as the radio galaxy. All galaxies have redshifts in the range 2.16 \pm 0.02, centered around the redshift of the radio galaxy, and are within a projected physical distance of 1.5 Mpc from it. The velocity distribution suggests that there are two galaxy subgroups having velocity dispersions of ~500 km/s and ~300 km/s and a relative velocity of 1800 km/s. If these are virialized structures, the estimated dynamical masses for the subgroups are ~9 and ~3x10E13 solar masses respectively, implying a total mass for the structure of more than 10E14 solar masses. The new observations, together with previous results, suggest that the structure of galaxies around 1138-262 is likely to be a forming cluster.

astro-ph↗

arXiv2000

Search for clusters at high redshift - I. Candidate Lya emitters near 1138-262 at z=2.2

Radio, optical and X-ray observations of the powerful radio galaxy PKS 1138-262 at z=2.156 have suggested that this galaxy is a massive galaxy in the center of a forming cluster. We have imaged 1138-262 and the surrounding 38 square arcminute field with the Very Large Telescope in a broad band and a narrow band encompassing the redshifted Lya emission. We detect 50 objects with rest equivalent width larger than 20 A and a luminous, highly extended Lya halo around 1138-262. If the radio galaxy is at the center of a forming cluster, these objects are candidate Lya emitting cluster galaxies.

astro-ph↗

arXiv2000

Thomson Thick X-ray Absorption in a Broad Absorption Line Quasar PG0946+301

We present a deep ASCA observation of a Broad Absorption Line Quasar (BALQSO) PG0946+301. The source was clearly detected in one of the gas imaging spectrometers, but not in any other detector. If BALQSOs have intrinsic X-ray spectra similar to normal radio-quiet quasars, our observations imply that there is Thomson thick X-ray absorption (N_H >~10^{24} cm^{-2}) toward PG0946+301. This is the largest column density estimated so far toward a BALQSO. The absorber must be at least partially ionized and may be responsible for attenuation in the optical and UV. If the Thomson optical depth toward BALQSOs is close to one, as inferred here, then spectroscopy in hard X-rays with large telescopes like XMM would be feasible.

astro-ph↗

arXiv1999

NICMOS Imaging of High-Redshift Radio Galaxies

We have obtained near-infrared (1.6 micron) images of 11 powerful 3CR radio galaxies at redshifts 0.8 < z < 1.8 using NICMOS on board HST. The high angular resolution permits a detailed study of galaxy morphology in these systems at rest-frame optical wavelengths, where starlight dominates over the extended, aligned UV continuum. The NICMOS morphologies are mostly symmetric and are consistent with dynamically relaxed, elliptical host galaxies dominated by a red, mature stellar population. The aligned structures are sometimes faintly visible, and nuclear point sources may be present in a few cases which manifest the ``unveiled'' AGN that is obscured from view at optical wavelengths. Our observations are consistent with the hypothesis that the host galaxies of z ~ 1-2 radio galaxies are similar to modern-day gE galaxies. Their sizes are typical of gE galaxies but smaller than present-day cD and brightest cluster galaxies, and their surface brightnesses are higher, as expected given simple luminosity evolution.

astro-ph↗