Publications (52)33.59 Total impact
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Article: A SINFONI view of flies in the Spiderweb: a galaxy cluster in the making
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ABSTRACT: 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 Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) integral field spectroscopy 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 with respect to the larger scale environment. This implies a galaxy overdensity in the core of δg∼ 200 and a matter overdensity of δm∼ 70; the latter is similar to that of the outskirts of local galaxy clusters. The velocity distribution of the confirmed satellite galaxies shows a broad, double-peaked velocity structure with σ= 1360 ± 206 km s−1. 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−1 is found. We show that the protocluster has likely decoupled from the Hubble flow and is a dynamically evolved structure. A comparison to the Millennium 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 the merger of two subclusters can result in an increase in star formation and active galactic nucleus activity in the protocluster core, therefore possibly being an important stage in the evolution of massive cD galaxies.Monthly Notices of the Royal Astronomical Society 08/2011; 415(3):2245 - 2256. · 4.90 Impact Factor -
Article: Discovery of a high-z protocluster with tunable filters: the case of 6C0140+326 at z=4.4
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ABSTRACT: 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.06/2011; -
Article: H-alpha emitters in z~2 proto-clusters: evidence for faster evolution in dense environments
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ABSTRACT: 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.03/2011; -
Article: Galaxy protocluster candidates around z ~ 2.4 radio galaxies
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ABSTRACT: 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 MNRAS08/2010; -
Article: A galaxy populations study of a radio‐selected protocluster at z∼ 3.1
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ABSTRACT: We present a population study of several types of galaxies within the protocluster surrounding the radio galaxy MRC 0316−257 at z∼ 3.1. In addition to the known population of Lyα emitters and [O iii] 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 ± 0.3 times larger than found for comparable blank fields. This surface overdensity corresponds to an LBG volume overdensity of ∼8 ± 4. 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 spectral energy distribution 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 MRC 0316−257 is still in the early stages of formation.Monthly Notices of the Royal Astronomical Society 06/2010; 405(2):969 - 986. · 4.90 Impact Factor -
Article: Dynamical Masses of Early-Type Galaxies at z ~ 2: Are they Truly Superdense?
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ABSTRACT: We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M 1011 M ☉) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 z 2.0. The σ are based on individual spectra for two galaxies at z 1.4 and on a stacked spectrum for seven galaxies with 1.6 < z < 2.0, with 202 hr of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), point-spread function, and slit effects into account. Our dynamical masses M Jeans agree within 30% with virial estimates M vir = 5 × Reσ2/G, although the latter tend to be smaller. Our M Jeans also agrees within a factor 2 with the M pop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L) U in the very age-sensitive rest-frame U band are consistent with passive evolution in the past ~1 Gyr (formation redshift zf ~ 3). A "bottom-light" stellar initial mass function appears to be required to ensure close agreement between M Jeans and M pop at z ~ 2, as it does at z ~ 0. The GMASS ETGs are on average more dense than their local counterpart. However, a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ50 inside R e.The Astrophysical Journal 09/2009; 704(1):L34. · 6.02 Impact Factor -
Article: GMASS ultradeep spectroscopy of galaxies at z ~ 2. IV. The variety of dust populations
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ABSTRACT: 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<z<2.5. These objects complement a previously investigated sample of 108 UV-luminous galaxies at similar redshifts, selected from the FDF spectroscopic survey, the K20 survey, and the GDDS. The shape of the UV extinction curve is constrained by a parametric description of the rest-frame UV continuum. The UV bump is further characterised by fitting Lorentzian-like profiles. Spectra exhibit a significant 2175A feature in at least 30% of the cases. If attenuation is dominated by dust ejected from the galaxy main body via superwinds, UV extinction curves in-between those of the SMC and LMC characterise the sample galaxies. The fraction of galaxies with extinction curves differing from the SMC one increases, if more dust resides in the galactic plane or dust attenuation depends on stellar age. On average, the width of the manifested UV bumps is about 60% of the values typical of the LMC and Milky Way. This suggests the presence of dust similar to that found in the LMC2 supershell close to 30Dor. The presence of the carriers of the UV bump at 1<z<2.5 argues for outflows from AGB stars being copious then. Consistent with their higher SFRs, the GMASS galaxies with a manifested UV bump are more luminous at rest-frame 8mum, where the emission is dominated by PAHs (also products of AGB stars). In addition, they exhibit stronger UV absorption features, mostly of interstellar origin, which indicates overall more evolved stellar populations. We conclude that diversification of the small-size dust component has already started in the most evolved star-forming systems at 1<z<2.5.04/2009; -
Article: The growth and assembly of a massive galaxy at z ~ 2
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ABSTRACT: 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 MNRAS01/2009; -
Article: Lyman Break Galaxies, Lyα Emitters, and a Radio Galaxy in a Protocluster at z = 4.1
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ABSTRACT: We present deep HST ACS observations in g475r625i775z850 toward the z = 4.1 radio galaxy TN J1338–1942 and its overdensity of >30 spectroscopically confirmed Lyα emitters (LAEs). We select 66 g475 band dropouts to z850,5 σ = 27, 6 of which are also LAEs. 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 σ 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 σ) in the projected pair counts at separations of θ < 10'' is interpreted as being due to physical pairs. The LAEs are young (a few times 107 yr), small ( rhl = 0.13'') galaxies, and we derive a mean stellar mass of ~108-109 M☉ based on a stacked Ks band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g475-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 washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity, and the subclustering at the approximate redshift of TN J1338–1942 suggest the assemblage of a >1014 M☉ structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z 4.The Astrophysical Journal 12/2008; 673(1):143. · 6.02 Impact Factor -
Article: [OIII] emitters in the field of the MRC 0316-257 protocluster
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ABSTRACT: 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 MNRAS07/2008; -
Article: High-Resolution Millimeter and Infrared Observations of the Hot Spots of Cygnus A
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ABSTRACT: We present high-resolution, polarimetric imaging of the radio hot spots of Cygnus A at 7 mm with the Very Large Array and derive limits to hot spot emission at 12 μm with the Infrared Space Observatory (ISO). The 7 mm images reveal the hot spot structure in total and polarized intensity in unprecedented detail, including images of the projected magnetic field morphology and the spectral index distribution between 7 mm and 3.6 cm at 025 resolution. The magnetic field distribution is consistent with "Laing cells," involving a frozen-in field plus simple kinematic dynamo effects due to bulk fluid motions. The spectral index distribution suggests that distributed particle acceleration occurs in the hot spots. The ISO limits at 12 μm require an exponential cutoff in the hot spot spectra at ≈1013 Hz. Such a cutoff is predicted by standard shock acceleration theory for relativistic electrons. The exponential cutoff observed by ISO and the high-resolution images at 7 mm are used to set a lower limit to the streaming velocity of the relativistic electrons, of 0.4c. We also find that the nuclear spectrum of Cygnus A has a peak flux density at about 30 GHz. The origin of this peak is likely to be synchrotron self-absorption in the dominant nuclear component, implying a size of 0.15 mas (= 0.15 pc), with a magnetic field strength of 0.16 G and a pressure in relativistic particles and fields of 10-3 dyn cm-2. The nuclear flux density is 1.6 ± 0.16 Jy at 7 mm, and the nucleus was not seen to vary on a timescale of 1.3 yr to ≤10%. We also have possible detections at 12 μm of three of the galaxies in the Cygnus A cluster within ±3' of Cygnus A.The Astronomical Journal 12/2007; 118(6):2581. · 4.03 Impact Factor -
Article: Diffuse UV light associated with the Spiderweb Galaxy: evidence for in-situ star formation outside galaxies
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ABSTRACT: 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 figures10/2007; -
Article: Protoclusters associated with z > 2 radio galaxies. I. Characteristics of high redshift protoclusters
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ABSTRACT: [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.html10/2006; -
Article: Large-scale structure of Lyman break galaxies around a radio galaxy protocluster at z~4
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ABSTRACT: 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.zip06/2006; -
Article: GMASS, Unveiling Distant Massive Galaxies with Spitzer
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ABSTRACT: 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.05/2006; -
Article: Lyman break galaxies, Lya emitters and a radio galaxy in a protocluster at z=4.1
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ABSTRACT: 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 referencing01/2006; -
Article: Properties of Ly-alpha emitters around the radio galaxy MRC 0316-257
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ABSTRACT: 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 added01/2005; -
Article: A search for clusters at high redshift - III. Candidate H-alpha emitters and EROs in the PKS 1138-262 proto-cluster at z=2.16
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ABSTRACT: 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 figures10/2004; -
Article: A search for clusters at high redshift - IV. Spectroscopy of H-alpha emitters in a proto-cluster at z=2.16
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ABSTRACT: 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 figures10/2004; -
Article: Discovery of six Ly alpha emitters near a radio galaxy at z ~ 5.2
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ABSTRACT: 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 Letters08/2004;
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Institutions
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2010–2011
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Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Bavaria, Germany -
CSU Mentor
Long Beach, CA, USA
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2008–2009
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Max-Planck-Institut für Astronomie
Heidelberg, Baden-Wuerttemberg, Germany
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