Search

We present VLT/SINFONI observations of 35 quasars at 2.1 < z < 3.2, the majority of which were selected from the Clusters Around Radio-Loud AGN (CARLA) survey. CARLA quasars have large CIV-based black hole (BH) masses (M(BH) > 10^9 Msun) and powerful radio emission (P(500MHz) > 27.5 W/Hz). We estimate Ha-based M(BH), finding a scatter of 0.35 dex compared to CIV. We evaluate several recipes for correcting CIV-based masses, which reduce the scatter to 0.24 dex. The radio power of the radio-loud quasars is at most weakly correlated with the interconnected quantities Ha-width, L(5100A) and M(BH), suggesting that it is governed by different physical processes. However, we do find a strong inverse correlation between CIV blueshift and radio power linked to higher Eddington ratios and L(5100A). Under standard assumptions, the BH growth time is longer than the cosmic age for many CARLA quasars, suggesting that they must have experienced more efficient growth in the past. If these BHs were growing from seeds since the epoch of reionization, it is possible that they grew at the Eddington limit like the quasars at z ~ 6-7, and then continued to grow at the reduced rates observed until z ~ 2-3. Finally, we study the relation between M(BH) and environment, finding a weak positive correlation between M(BH) and galaxy density measured by CARLA., Comment: MNRAS, accepted (28 pages, 22 figures)

We present the "SINS/zC-SINF AO survey" of 35 star-forming galaxies, the largest sample with deep adaptive optics-assisted (AO) near-infrared integral field spectroscopy at z~2. The observations, taken with SINFONI at the Very Large Telescope, resolve the Ha and [NII] line emission and kinematics on scales of ~1.5 kpc. In stellar mass, star formation rate, rest-optical colors and size, the AO sample is representative of its parent seeing-limited sample and probes the massive (M* ~ 2x10^9 - 3x10^11 Msun), actively star-forming (SFR ~ 10-600 Msun/yr) part of the z~2 galaxy population over a wide range in colors ((U-V)_rest ~ 0.15-1.5 mag) and half-light radii (R_e,H ~ 1-8.5 kpc). The sample overlaps largely with the "main sequence" of star-forming galaxies in the same redshift range to a similar K_AB = 23 magnitude limit; it has ~0.3 dex higher median specific SFR, ~0.1 mag bluer median (U-V)_rest color, and ~10% larger median rest-optical size. We describe the observations, data reduction, and extraction of basic flux and kinematic properties. With typically 3-4 times higher resolution and 4-5 times longer integrations (up to 23hr) than the seeing-limited datasets of the same objects, the AO data reveal much more detail in morphology and kinematics. The now complete AO observations confirm the majority of kinematically-classified disks and the typically elevated disk velocity dispersions previously reported based on subsets of the data. We derive typically flat or slightly negative radial [NII]/Ha gradients, with no significant trend with global galaxy properties, kinematic nature, or the presence of an AGN. Azimuthal variations in [NII]/Ha are seen in several sources and are associated with ionized gas outflows, and possible more metal-poor star-forming clumps or small companions. [Abridged], Comment: Submitted to the Astrophysical Journal Supplement Series. 64 pages, 36 figures. The reduced data sets will be made available once the paper is accepted for publication. A version with full resolution Figures is available at http://www.mpe.mpg.de/~forster/FS18_AOsurvey_ApJSsubm.html

It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 hours of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, M_mol=2.0+-0.2x10^11 M_sun, extended, ~40 kpc, CO(1-0)-emitting disk in the protocluster surrounding the radio galaxy, MRC1138-262. The galaxy, at z_CO=2.1478, is a clumpy, massive disk galaxy, M_star~5x10^11 M_sun, which lies 250 kpc in projection from MRC1138-262 and is a known H-alpha emitter, HAE229. HAE229 has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO(1-0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z>0.4 that are detected in low-order CO transitions with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and FWHM are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Not finding any environmental dependence in the "star-formation efficiency" or the molecular gas content, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping are not operating efficiently in (proto)clusters. (abridged), Comment: Accepted by A&A. 15 pages, 8 figures and 4 tables

We present APEX LABOCA 870 micron observations of the field around the high-redshift radio galaxy MRC1138-262 at z=2.16. We detect 16 submillimeter galaxies in this ~140 square arcmin bolometer map with flux densities in the range 3-11 mJy. The raw number counts indicate a density of submillimeter galaxies (SMGs) that is up to four times that of blank field surveys. Based on an exquisite multiwavelength database, including VLA 1.4 GHz radio and infrared observations, we investigate whether these sources are members of the protocluster structure at z=2.2. Using Herschel PACS+SPIRE and Spitzer MIPS photometry, we derive reliable far-infrared photometric redshifts for all sources. Follow-up VLT ISAAC and SINFONI near-infrared spectra confirm that four of these SMGs have redshifts of z=2.2. We also present evidence that another SMG in this field, detected earlier at 850 micron, has a counterpart that exhibits Halpha and CO(1-0) emission at z=2.15. Including the radio galaxy and two SMGs with far-IR photometric redshifts at z=2.2, we conclude that at least eight submm sources are part of the protocluster at z=2.16 associated with the radio galaxy MRC1138-262. We measure a star formation rate density SFRD ~1500 Msun yr^-1 Mpc^-3, four magnitudes higher than the global SFRD of blank fields at this redshift. Strikingly, these eight sources are concentrated within a region of 2 Mpc (the typical size of clusters in the local universe) and are distributed within the filaments traced by the Halpha emitters at z=2.2. This concentration of massive, dusty starbursts is not centered on the submillimeter-bright radio galaxy which could support the infalling of these sources into the cluster center. Approximately half (6/11) of the SMGs that are covered by the Halpha imaging data are associated with Halpha emitters, demonstrating the potential of tracing SMG counterparts with this population (abridged)., Comment: Accepted by A&A. ESO Press Release on 15 October 2014. 19 pages, 9 figures and 4 tables

Distant powerful radio-loud active galactic nuclei (RLAGN) tend to reside in dense environments and are commonly found in proto-clusters at z > 1.3. We examine whether this occurs because RLAGN are hosted by massive galaxies, which preferentially reside in rich environments. We compare the environments of powerful RLAGN at 1.3 < z < 3.2 from the CARLA survey to a sample of radio-quiet galaxies matched in mass and redshift. We find the environments of RLAGN are significantly denser than those of radio-quiet galaxies, implying that not more than 50% of massive galaxies in this epoch can host powerful radio-loud jets. This is not an observational selection effect as we find no evidence to suggest it is easier to observe the radio emission when the galaxy resides in a dense environment. We therefore suggest that the dense Mpc-scale environment fosters the formation of a radio-jet from an AGN. We show that the number density of potential RLAGN host galaxies is consistent with every > 10^14 solar mass cluster having experienced powerful radio-loud feedback of duration ~60 Myr during 1.3 < z < 3.2. This feedback could heat the intracluster medium to the extent of 0.5-1 keV per gas particle, which could limit the amount of gas available for further star formation in the proto-cluster galaxies., Comment: Accepted for publication in MNRAS

We present results from a narrow-band survey of the field around the high redshift radio galaxy MRC 2104-242. We have selected Halpha emitters in a 7sq.arcmin field and compared the measured number density with that of a field sample at similar redshift. We find that MRC 2104-242 lies in an overdensity of galaxies that is 8.0 +/- 0.8 times the average density of a blank field, suggesting it resides in a large-scale structure that may eventually collapse to form a massive cluster. We find that there is more dust obscured star formation in the protocluster galaxies than in similarly selected control field galaxies and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average we do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z~2.5 is governed predominantly by galaxy mass and not the host environment. We also find that the stellar mass distribution of the protocluster galaxies is skewed towards higher masses and there is a significant lack of galaxies at M < 10^10Msun within our small field of view. Based on the level of overdensity we expect to find ~22 star forming galaxies below 10^10Msun in the protocluster and do not detect any. This lack of low mass galaxies affects the level of overdensity which we detect. If we only consider high mass (M > 10^10.5Msun) galaxies, the density of the protocluster field increases to ~55 times the control field density., Comment: 14 pages, accepted for publication in MNRAS

We report the detection of ubiquitous powerful nuclear outflows in massive (> 10^11 Msun) z~2 star-forming galaxies (SFGs), which are plausibly driven by an Active Galactic Nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics (AO) assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Halpha and forbidden [NII] and [SII] line emission, with typical velocity FWHM ~ 1500 km/s, [NII]/Halpha ratio ~ 0.6, and intrinsic extent of 2 - 3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~ 60 Msun/yr and mass loading of ~ 3. At larger radii, a weaker broad component is detected but with lower FWHM ~ 485 km/s and [NII]/Halpha ~ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles, and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial to confirm the importance and energetics of the nuclear outflow phenomenon, and its connection to AGN activity and bulge growth., Comment: 18 pages, 5 figures, revised version, accepted for publication in the Astrophysical Journal

We present multicolour Hubble Space Telescope images of the powerful z=2.4 radio galaxy MRC 0406-244 and model its complex morphology with several components including a host galaxy, a point source, and extended nebular and continuum emission. We suggest that the main progenitor of this radio galaxy was a normal, albeit massive (M ~10^{11} solar masses), star-forming galaxy. The optical stellar disc of the host galaxy is smooth and well described by a S\'ersic profile, which argues against a recent major merger, however there is also a point-source component which may be the remnant of a minor merger. The half-light radius of the optical disc is constrained to lie in the range 3.5 to 8.2kpc, which is of similar size to coeval star forming galaxies. Biconical shells of nebular emission and UV-bright continuum extend out from the host galaxy along the radio jet axis, which is also the minor axis of the host galaxy. The origin of the continuum emission is uncertain, but it is most likely to be young stars or dust-scattered light from the AGN, and it is possible that stars are forming from this material at a rate of 200^{+1420}_{-110} solar masses per year., Comment: Accepted for publication in MNRAS

We present the first results obtained using a tunable narrowband filter in the search for high-z protoclusters. Using the recently commissioned red tunable filter on the Gran Telescopio Canarias we have searched for Lya emitters in a 75 arcmin^2 field centered on the z=4.413 radio galaxy 6C0140+326. With three different wavelength tunings we find a total of 27 unique candidate Lya emitters. The availability of three different wavelength tunings allows us to make estimates of the redshifts for each of the objects. It also allows us to separate a possible protocluster from structure in the immediate foreground. This division shows that the foreground region contains significantly fewer Lya emitters. Also, the spatial distribution of the objects in the protocluster field deviates from a random distribution at the 2.5 sigma level. The observed redshift distribution of the emitters is different from the expected distribution of a blank field at the ~3 sigma level, with the Lya emitters concentrated near the radio galaxy at z>4.38. The 6C0140+326 field is denser by a factor of 9+/-5 than a blank field, and the number density of Lya emitters close to the radio galaxy is similar to that of the z~4.1 protocluster around TNJ1338-1942. We thus conclude that there is an overdensity of Lya emitters around the radio galaxy 6C0140+326. This is one of few known overdensities at such a high redshift., Comment: 10 pages, 6 figures, accepted for publication in MNRAS

The environment of the high-z radio galaxy PKS 1138-262 at z~2.2 is a prime example of a forming galaxy cluster. We use deep SINFONI data to perform a detailed study of the kinematics of the galaxies within 60 kpc of the radio core and we link this to the kinematics of the protocluster on the megaparsec scale. Identification of optical emission lines shows that 11 galaxies are at the redshift of the protocluster. The density of line emitters is more than an order of magnitude higher in the core of the protocluster than the larger scale environment. This implies a matter overdensity in the core of delta_m~70 which is similar to the outskirts of local galaxy clusters. The velocity distribution of the confirmed satellite galaxies shows a broad, double-peaked velocity structure with sigma=1360+/-206 km/s. A similar broad, double-peaked distribution was found in a previous study targeting the large scale protocluster structure, indicating that a common process is acting on both small and large scales. Including all spectroscopically confirmed protocluster galaxies, a velocity dispersion of 1013+/-87 km/s is found. We show that the protocluster has likely decoupled from the Hubble flow and is a dynamically evolved structure. Comparison to the Millenium simulation indicates that the protocluster velocity distribution is consistent with that of the most massive haloes at z~2, but we rule out that the protocluster is a fully virialized structure based on dynamical arguments and its X-ray luminosity. Comparison to merging haloes in the Millennium simulation shows that the structure as observed in and around the Spiderweb galaxy is best interpreted as being the result of a merger between two massive haloes. We propose that this merger can result in an increase in star formation and AGN activity in the protocluster core and is possibly an important stage in the evolution of massive cD galaxies., Comment: 12 pages, 7 figures. Accepted for publication in MNRAS

This is a study of H-alpha emitters in two dense galaxy proto-clusters surrounding radio galaxies at z~2. We show that the proto-cluster surrounding MRC 1138-262 contains 14+/-2 times more H-alpha candidates than the average field (9 sigma significance), and the z=2.35 radio galaxy 4C+10.48 is surrounded by 12+/-2 times more emitters than the field (5 sigma), so it is also likely to reside in a dense proto-cluster environment. We compared these H-alpha emitters, situated in dense environments, to a control field sample selected from 3 separate fields forming a total area of 172 arcmin^2. We constructed and compared H-alpha and rest-frame R continuum luminosity functions of the emitters in both environments. The star formation density is on average 13 times greater in the proto-clusters than the field at z~2, so the total star formation rate within the central 1.5Mpc of the proto-clusters exceeds 3000Msun/yr. However, we found no significant difference in the shape of the H-alpha luminosity functions, implying that environment does not substantially affect the strength of the H-alpha line from strongly star forming galaxies. The proto-cluster emitters are typically 0.8mag brighter in rest-frame R continuum than field emitters, implying they are twice as massive as their field counterparts at the same redshift. We also show the proto-cluster galaxies have lower specific star formation rates than field galaxies, meaning the emitters in the dense environments formed more of their stars earlier than the field galaxies. We conclude that galaxy growth in the early Universe was accelerated in dense environments, and that cluster galaxies differed from field galaxies even before the cluster had fully formed., Comment: Accepted for publication in MNRAS

We study the environments of 6 radio galaxies at 2.2 < z < 2.6 using wide-field near-infrared images. We use colour cuts to identify galaxies in this redshift range, and find that three of the radio galaxies are surrounded by significant surface overdensities of such galaxies. The excess galaxies that comprise these overdensities are strongly clustered, suggesting they are physically associated. The colour distribution of the galaxies responsible for the overdensity are consistent with those of galaxies that lie within a narrow redshift range at z ~ 2.4. Thus the excess galaxies are consistent with being companions of the radio galaxies. The overdensities have estimated masses in excess of 10^14 solar masses, and are dense enough to collapse into virizalised structures by the present day: these structures may evolve into groups or clusters of galaxies. A flux-limited sample of protocluster galaxies with K < 20.6 mag is derived by statistically subtracting the fore- and background galaxies. The colour distribution of the protocluster galaxies is bimodal, consisting of a dominant blue sequence, comprising 77 +/- 10% of the galaxies, and a poorly populated red sequence. The blue protocluster galaxies have similar colours to local star-forming irregular galaxies (U -V ~ 0.6), suggesting most protocluster galaxies are still forming stars at the observed epoch. The blue colours and lack of a dominant protocluster red sequence implies that these cluster galaxies form the bulk of their stars at z < 3., Comment: Accepted for publication in MNRAS

We present a population study of several types of galaxies within the protocluster surrounding the radio galaxy MRC0316-257 at z~3.1. In addition to the known population of Ly_alpha emitters (LAEs) and [OIII] emitters, we use colour selection techniques to identify protocluster candidates that are Lyman break galaxies (LBG) and Balmer break galaxies (BBGs). The radio galaxy field contains an excess of LBG candidates, with a surface density 1.6\pm0.3 times larger than found for comparable blank fields. This surface overdensity corresponds to an LBG volume overdensity of ~8\pm4. The BBG photometric redshift distribution peaks at the protocluster's redshift, but we detect no significant surface overdensity of BBG. This is not surprising because a volume overdensity similar to the LBGs would have resulted in a surface density of ~1.2 that found in the blank field. This could not have been detected in our sample. Masses and star formation rates of the candidate protocluster galaxies are determined using SED fitting. These properties are not significantly different from those of field galaxies. The galaxies with the highest masses and star formation rates are located near the radio galaxy, indicating that the protocluster environment influences galaxy evolution at z~3. We conclude that the protocluster around MRC0316-257 is still in the early stages of formation., Comment: 19 pages, 20 figures, accepted for publication in MNRAS

We present sensitive near--infrared VLT ISAAC spectroscopic observations of the z=6.08 quasar SDSS J030331.40-001912.9. This QSO is more than a magnitude fainter than other QSOs at z~6 for which NIR spectroscopy has been obtained to date and is therefore presumably more representative of the QSO population at the end of Cosmic Reionization. Combining rest--frame UV continuum luminosity with the width measurements of the Mg II and C IV lines, we derive a black hole mass of 2(+1.0/-0.5) x 10^8 solar masses, the lowest mass observed for z~6 QSOs to date, and derive an Eddington ratio of 1.6(+0.4/-0.6), amongst the highest value derived for QSOs at any redshift. The Spitzer 24 micron non--detection of this QSO does not leave space for a significant hot dust component in its optical/near--infrared SED, in common with one other faint QSO at z=6, but in contrast to more than twenty more z=6 QSOs and all known lower redshift QSOs with sufficiently deep multi-wavelength photometry. We conclude that we have found evidence for differences in the intrinsic properties of at least one z~6 QSO as compared to the lower--redshift population., Comment: Accepted by ApJ on July 1, 2009; 5 pages, 2 figures

We measured stellar velocity dispersions sigma and dynamical masses of 9 massive (M~10^11 Msun) early-type galaxies (ETG) from the GMASS sample at redshift 1.4

The properties of dust attenuation at rest-frame UV wavelengths are inferred from very high-quality FORS2 spectra of 78 galaxies from the GMASS survey at 1

We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z = 0, increasing its stellar mass by up to a factor of ~ 2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores., Comment: 12 pages, accepted for publication in MNRAS

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., Comment: 11 pages, 6 figures. Accepted for publication in MNRAS

We present detailed images of diffuse UV intergalactic light (IGL), situated in a 60kpc halo that surrounds the radio galaxy MRC 1138-262 at z=2. We discuss the nature of the IGL and rule out faint cluster galaxies, nebular continuum emission, synchrotron, inverse Compton emission and scattering of galactic stellar light as possible sources of the IGL. Dust scattered quasar light is an unlikely possibility that cannot be ruled out entirely. We conclude that the source of the IGL is most likely to be a young stellar population distributed in a halo encompassing the radio and satellite galaxies, undergoing star formation at a rate greater than 57 Msun/yr. Within 70kpc of the radio core, approximately 44% of the star formation that is traced by UV light occurs in this diffuse mode. The average UV colour of the IGL is bluer than the average galaxy colour, and there is a trend for the IGL to become bluer with increasing radius from the radio galaxy. Both the galaxies and the IGL show a UV colour--surface brightness relation which can be obtained by variations in either stellar population age or extinction. These observations show a different, but potentially important mode of star formation, that is diffuse in nature. Star formation, as traced by UV light, occurs in two modes in the high redshift universe: one in the usual Lyman break galaxy clump-like mode on kpc scales, and the other in a diffuse mode over a large region surrounding massive growing galaxies. Such a mode of star formation can easily be missed by high angular resolution observations that are well suited for detecting high surface brightness compact galaxies. Extrapolating from these results, it is possible that a significant amount of star formation occurs in large extended regions within the halos of the most massive galaxies forming at high redshift., Comment: Accepted for publication in MNRAS, 14 pages, 9 figures

We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z = 2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST/ACS image is reminiscent of a spider's web. More than 10 individual clumpy features are observed, apparently star-forming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a 50 times 40 kpc region at a rate of more than 100 M_sun/yr. A striking feature of the newly named ``Spiderweb galaxy'' is the presence of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centres of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies., Comment: 5 pages, 2 figures (reduced to grayscale); ApJ Letters

[Abridged] We present the results of a large program conducted with the Very Large Telescope and Keck telescope to search for forming clusters of galaxies near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and broad-band images of nine radio galaxies and their surroundings. The imaging was used to select candidate Lyman alpha emitting galaxies in ~3x3 Mpc^2 areas near the radio galaxies. A total of 337 candidate emitters were found with a rest-frame Lyman alpha equivalent width of EW_0 > 15 A and Sigma = EW_0/Delta EW_0 > 3. Follow-up spectroscopy confirmed 168 Lyman alpha emitters near eight radio galaxies. The success rate of our selection procedure is 91%. At least six of our eight fields are overdense in Lyman alpha emitters by a factor 3-5. Also, the emitters show significant clustering in velocity space. In the overdense fields, the width of the velocity distributions of the emitters is a factor 2-5 smaller than the width of the narrow-band filters. Taken together, we conclude that we have discovered six forming clusters of galaxies (protoclusters). We estimate that roughly 75% of powerful (L_2.7GHz > 10^33 erg/s/Hz/sr) high redshift radio galaxies reside in a protocluster, with a sizes of at least 1.75 Mpc. We estimate that the protoclusters have masses in the range 2-9 x 10^14 Msun and they are likely to be progenitors of present-day (massive) clusters of galaxies. For the first time, we have been able to estimate the velocity dispersion of cluster progenitors from z~5 to ~2. The velocity dispersion of the emitters increases with cosmic time, in agreement with the dark matter velocity dispersion in numerical simulations of forming massive clusters., Comment: 30 pages, 20 figures. Published in A&A. The article with high resolution figures is available at http://www.ast.cam.ac.uk/~venemans/research/datapaper/index.html

We present broad-band imaging with the Subaru Telescope of a 25'x25' field surrounding the radio galaxy TN J1338-1942 at redshift z=4.1. The field contains excesses of Lyman-alpha emitters (LAEs) and Lyman break galaxies (LBGs) identified with a protocluster surrounding the radio galaxy. Our new wide-field images provide information about the boundary of the protocluster and its surroundings. There are 874 candidate LBGs within our field, having redshifts in the range z=3.5-4.5. An examination of the brightest of these (with i'< 25.0) shows that the most prominent concentration coincides with the previously discovered protocluster. The diameter of this galaxy overdensity corresponds to ~2 Mpc at z=4, consistent with the previous estimation using LAEs. Several other concentrations of LBGs are observed in the field, some of which may well be physically connected with the z=4.1 protocluster. The observed structure in the smoothed LBG distribution can be explained as the projection of large-scale structure, within the redshift range z=3.5-4.5, comprising compact overdensities and prominent larger voids. If the 5-8 observed compact overdensities are associated with protoclusters, the observed protocluster volume density is ~5x10^-6 Mpc^-3, similar to the volume density of rich clusters in the local Universe., Comment: 5 pages, 4 figures. Accepted for publication in A&A. Full resolution version available at http://www.strw.leidenuniv.nl/~intema/files/AA_2006_4812.zip

One of the main questions of galaxy formation is how and when galaxies assembled their mass. Observations suggest that most mass assembly and star formation occured at 1 < z < 3. However, in the same redshift range, fully assembled old and massive galaxies co-exist with star-bursting systems still in their assembling stage. In order to explore galaxy evolution in this critical redshift range, we started a project called GMASS (Galaxy Mass Assembly ultra-deep Spectroscopic Survey) based on an 145 hours ESO Large Program and aimed at doing ultradeep spectroscopy with the VLT of a sample of high redshift galaxies slected with IRAC/Spitzer m(4.5mu) < 23, z(phot) > 1.4) from the GOODS-South/HUDF region. The selection at 4.5 micron is crucial to select high redshift galaxies based on the stellar mass or objects affected by strong dust extinction. The spectroscopic deep integration times (15 - 50 hours) are needed to identify unambiguously the redshift and nature of these galaxies, which redshifts are mostly in the "desert" where spectroscopy is traditionally difficult due to the absence of strong emission lines at optical wavelengths. The survey is almost complete and some preliminary results are presented here., Comment: 6 pages, 3 figures, to appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

We present deep HST/ACS observations in g,r,i,z towards the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Lya emitters (LAEs). We select 66 g-band dropouts to z=27, 6 of which are also a LAE. Although our color-color selection results in a relatively broad redshift range centered on z=4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma) in the projected pair counts at separations of <10" is interpreted as being due to physical pairs. The LAEs are young (a few x 10^7 yr), small ( = 0.13") galaxies, and we derive a mean stellar mass of ~10^8-9 Msun based on a stacked K-band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g-dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present, or are washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity and the sub-clustering at the approximate redshift of TN J1338-1942 suggest the assemblage of a >10^14 Msun structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z>4., Comment: Accepted for publication in ApJ (33 pages, 19 figures, emulateapj). v3 includes updated methods, discussion and referencing

Observations of the radio galaxy MRC 0316-257 at z=3.13 and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Ly-alpha emitters with a rest-frame equivalent width of > 15 A were selected in a ~7'x7' field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Ly-alpha emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be [OII] emitters. The Ly-alpha profiles have widths (FWHM) in the range of 120-800 km/s, with a median of 260 km/s. Where the signal-to-noise was large enough, the Ly-alpha profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an HI mass of at least 2x10^2 - 5x10^4 M_sun. The properties of the Ly-alpha galaxies (faint, blue and small) are consistent with young star forming galaxies which are still nearly dust free. The volume density of Ly-alpha emitting galaxies in the field around MRC 0316-257 is a factor of 3.3+0.5-0.4 larger compared with the density of field Ly-alpha emitters at that redshift. The velocity distribution of the spectroscopically confirmed emitters has a FWHM of 1510 km/s, which is substantially smaller than the width of the narrow-band filter (FWHM ~ 3500 km/s). The peak of the velocity distribution is located within 200 km/s of the redshift of the radio galaxy. We conclude that the confirmed Ly-alpha emitters are members of a protocluster of galaxies at z~3.13. The size of the protocluster is larger than 3.3x3.3 Mpc^2. The mass of this structure is estimated to be > 3-6x10^14 M_sun and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster. (Abridged), Comment: 23 Pages, including 20 PostScript figures. Publiced in Astronomy & Astrophysics. v2: typo fixed and Journal reference added

In this paper we present deep VLT multi wavelength imaging observations of the field around the radio galaxy PKS 1138-262 aimed at detecting and studying a (potential) proto-cluster centered at this radio source. PKS 1138-262 is a massive galaxy at z=2.16, located in a dense environment as indicated by optical, X-ray and radio observations. We had already found an over-density of Ly-alpha emitting galaxies in this field, consistent with a proto-cluster structure associated with the radio galaxy. In addition, we find 40 candidate H-alpha emitters that have nominal rest frame equivalent width > 25 Angstrom within 1.8 Mpc and 2000 km/s of the radio galaxy. Furthermore, we find 44 objects with I - K > 4.3. This number of extremely red objects (EROs) is about twice the number found in blank field ERO surveys, suggesting that some EROs in this field are part of the proto-cluster. The density of H-alpha emitters and extremely red objects increases towards the radio galaxy, indicating a physical association. From comparisons with other K band, ERO, H-alpha and Ly-alpha surveys, we conclude that PKS 1138-262 is located in a density peak which will evolve into a cluster of galaxies., Comment: Accepted by A&A (19/02/2004), 25 pages, 19 figures

Radio galaxy PKS 1138-262 is a massive galaxy at z=2.16, located in a dense environment. We have found an overdensity of Ly-alpha emitting galaxies in this field, consistent with a proto-cluster structure associated with the radio galaxy. Recently, we have discovered forty candidate H-alpha emitters by their excess near infrared narrow band flux. Here, we present infrared spectroscopy of nine of the brightest candidate H-alpha emitters. All these candidates show an emission line at the expected wavelength. The identification of three of these lines with H-alpha is confirmed by accompanying [NII] emission. The spectra of the other candidates are consistent with H-alpha emission at z~2.15, one being a QSO as indicated by the broadness of its emission line. The velocity dispersion of the emitters (360 km/s) is significantly smaller than that of the narrow band filter used for their selection (1600 km/s). We therefore conclude that the emitters are associated with the radio galaxy. The star formation rates (SFRs) deduced from the H-alpha flux are in the range 6-44 M_solar/yr and the SFR density observed is 5-10 times higher than in the HDF-N at z=2.23. The properties of the narrow emission lines indicate that the emitters are powered by star formation and contain very young (< 100 Myr) stellar populations with moderately high metallicities., Comment: Accepted by A&A (07/10/2004), 5 pages, 3 figures

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., Comment: 4 pages, 1 figure, published in A&A Letters

We report the discovery of a Lyman alpha emitting galaxy at z = 6.518. The single line was found in the 43 square arcmin VLT/FORS field by slitless spectroscopy limited to the atmospheric window at 9100 A (sampling Lya at 6.4 < z < 6.6). Its counterpart is undetected in a deep I band image and the line has an asymmetric appearance in a deeper follow-up spectrum. There are no plausible line identifications except for Lya with a flux of 1.9x10^-17 erg/s/cm2 and rest frame equivalent width > 80 A. The lower limit to the star formation rate density at z = 6.5 derived from our complete sample is 5x10^-4 M_sol/year/Mpc^3, consistent with measurements in the Subaru Deep Field and Hubble Ultra Deep Field but approximately ten times higher than in the Large Area Lyman Alpha survey. This Lya emitter is among the very small sample of highest redshift galaxies known., Comment: Accepted as Letter by A&A, 5 pages, 7 figures, one typo corrected

We present results from a Chandra X-ray Observatory study of the field X-ray source population in the vicinity of the radio galaxy MRC 1138-262. Many serendipitous X-ray sources are detected in an area of 8'x8' around the radio source and 90% are identified in our deep VLT images. The space density of such sources is higher than expected on the basis of the statistics of ROSAT and Chandra deep surveys. The most likely explanation is in terms of a concentration of AGN associated with the protocluster at z=2.16 which was found around the radio galaxy in previous studies. Two sources have a confirmed spectroscopic redshift close to that of the radio galaxy, and for three more sources other observations suggest that they are associated with the protocluster. Four of these five X-ray sources form, together with the radio galaxy, a filament in the plane of the sky. The direction of the filament is similar to that of the radio source axis, the large scale distribution of the other protocluster members, the 150 kpc-sized emission-line halo and the extended X-ray emission associated with the radio galaxy. The majority of optically identified X-ray sources in this field have properties consistent with type I AGN, a few could be soft, low luminosity galaxies, one is probably an obscured (type II) AGN and one is a star. These statistics are consistent with the results of deep X-ray surveys., Comment: 8 pages, 2 figures, to appear in Astronomy and Astrophysics

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., Comment: Accepted for publication in Astrophysical Journal Letters, 14 pages, 4 figures, AASTEX

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., Comment: aasms4.sty 25 pages. To appear in the Astrophysical journal

We have recently discovered a forming cluster around the radio galaxy MRC 1138-262 at redshift 2.2. Besides the population of Ly alpha emitting galaxies that have been confirmed spectroscopically, we have detected many candidate H alpha emitters that seem to have a different spatial distribution from the other galaxies: they are more clustered towards the center of the cluster and seem to be distributed along the same direction as the radio source. We present here the characteristics of the Ly alpha and H alpha emitters and study the nature of these populations., Comment: 4 pages, 2 figures, to appear in the proceedings of the meeting "Tracing cosmic evolution with galaxy clusters" (Sesto Pusteria 3-6 July 2001), ASP Conference Series

High redshift radio galaxies are amongst the most massive galaxies in the early Universe and have properties expected from central galaxies in forming clusters. We are carrying out an observational programme on the VLT to find and study galaxy proto clusters around radio galaxies at redshifts 2 < z < 4. First, we use narrow band imaging to select candidate galaxies which show excess Lyman alpha emission at redshifts similar to the central radio galaxy. Then, we use multi object spectroscopy to confirm the redshifts of these candidates and measure the velocity dispersion of the cluster members. Our goal is to observe a sample of about 10 targets and investigate galaxy overdensities as a function of redshift. Here, we report on the current progress of the programme and show some preliminary results which include the discovery of a structure of galaxies at redshift 4.1., Comment: 4 pages, 3 figures, Sesto conference proceeding 'Probing cosmic evolution with galaxy clusters'

The radio galaxy MRC 1138-262 at z=2.16 is most likely a brightest cluster galaxy in an early stage of evolution. Here we present observations of the luminous emission line halo and the stellar components of this radio galaxy. Optical narrow band imaging shows a very extended (about 160 kpc) and luminous Lyman alpha halo. Infrared narrow band imaging reveals a much smaller H alpha halo with a very different morphology. We advocate a model in which the inner part of the halo is photoionized by direct AGN illumination or by UV photons from young stars. Far from the nucleus (about 25 kpc), there is a region of greatly enhanced Lyman alpha emission. At this location, it is likely that shock ionization is important as indicated by a bend in the radio jet. Spectroscopy of several continuum clumps in the halo shows that, although there are striking differences between the emission and absorption features of the spectra of various regions, they have properties similar to those of Lyman-break galaxies. This is further evidence for a scenario in which massive galaxies form hierarchically from smaller building blocks., Comment: 5 pages, 5 figures, to be published in the proceedings of 'Emission Lines from Jet Flows' Nov 2001, Mexico, Eds. W. Henney, W. Steffen, L. Binette, A. Raga

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., Comment: Accepted for publication in A&A Letters, 5 pages, 3 figures

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., Comment: Accepted for publication in A&A as Letter, 4 pages, 4 figures

Observations are presented showing the doublet CIV 1550 absorption lines superimposed on the CIV emission in the radio galaxy 0943-242. Within the errors, the redshift of the absorption system that has a column density of N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha absorption trough observed by Rottgering et al. (1995). The gas seen in absorption has a resolved spatial extent of at least 13 kpc (the size of the extended emission line region). We first model the absorption and emission gas as co-spatial components with the same metallicity and degree of excitation. Using the information provided by the emission and absorption line ratios of CIV and Ly-alpha, we find that the observed quantities are incompatible with photoionization or collisional ionization of cloudlets with uniform properties. We therefore reject the possibility that the absorption and emission phases are co-spatial and favour the explanation that the absorption gas has low metallicity and is located further away from the host galaxy (than the emission line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z \~ 1% solar) and its proposed location -outer halo outside the radio cocoon- suggest that its existence preceeds the observed AGN phase and is a vestige of the initial starburst at the onset of formation of the parent galaxy., Comment: 11 pages,5 figures, A&A accepted

Observations of the powerful radio galaxy 1138-262 at z=2.2 suggest that this galaxy is a massive galaxy in the center of a forming cluster. We have imaged the field of 1138-262 with the Very Large Telescope in a narrow band encompassing the redshifted Lyman alpha emission. We detect 34 probable line emitters in the 6'x6' field. These are candidate Lyman alpha emitting galaxies in the supposed cluster. The observations also reveal that the radio galaxy is enclosed by a very extended Lyman alpha halo (160 kpc)., Comment: To appear in proceedings of conference on Clustering At High Redshift, ASP Conf. Series, ed. A. Mazuer and O.Le Fevre (Marseilles, July 1999). 2 pages, 1 figure, newpasptex