arXiv subjects

Tadayuki Kodama

Publications and source records attributed to Tadayuki Kodama.

At least 127 records · Page 7Linked to original sources

arXiv2014

The environments of Ly$α$ blobs I: Wide-field Ly$α$ imaging of TN J1338-1942, a powerful radio galaxy at $z\simeq 4.1$ associated with a giant Ly$α$ nebula

We exploit wide-field Ly$alpha$ imaging with Subaru to probe the environment around TN J1338-1942, a powerful radio galaxy with a >100 kpc Ly$α$ halo at z=4.11. We used a sample of Ly$α$ emitters (LAEs) down to $\log(L_{\rm Lyα} [erg\, s^{-1}])\sim 42.8$ to measure the galaxy density around TNJ1338, compared to a control sample from a blank field taken with the same instrument. We found that TNJ1338 resides in a region with a peak overdensity of $δ_{\rm LAE}=2.8\pm 0.5$ on scales of $8\, h^{-1}\rm Mpc$ (on the sky) and $112\, h^{-1}\rm Mpc$ (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TNJ1338 are very rare, with a number density of $6.4\times 10^{-8}\rm Mpc^{-3}$ (comoving), corresponding to the densest < 0.4 percentile at $z\simeq 4.1$. We also found that the Ly$α$ luminosity function in the TNJ1338 field differs from that in the blank field: the number of bright LAEs ($\log(L_{\rm Lyα}[erg\,s^{-1}]) \gtrsim 43.3$) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly$α$ nebulae reside in extreme overdensities on $\sim 3$--$6\, \rm Mpc$ scales, where star-formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.

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arXiv2014

Discovery of nine extended ionized gas clouds in a z=0.4 cluster

From deep H-alpha imaging data of Suprime-Cam/Subaru, we discovered nine extended ionized gas clouds (EIG) around galaxies in Abell 851 cluster (A851) at z=0.4. We surveyed 30 x 25 arcmin region, and the EIGs were found only near the cluster center (<2.3 arcmin ~ 750 kpc). The parent galaxies of the EIGs are star-forming or post-starburst galaxies, all of which are spectroscopically confirmed members of the cluster. Four out of the nine parent galaxies show distortion of stellar distribution in the disk, which can be a sign of recent interaction, and the interaction may have made EIGs. On the other hand, six parent galaxies (one overlaps those exhibiting distortion) show H-alpha emission without stars, which implies a ram pressure stripping.The spe ctrum of the brightest parent galaxy shows a post-starburst signature, and resembles the H-alpha stripped galaxies found in the Coma cluster. Meanwhile, two brightest parent galaxies in A851 are more massive than the EIG parent galaxies in the Coma cluster. This is consistent with "downsizing" of star-forming galaxies, though it is still in a statistical fluctuation. We also analyzed Suprime-Cam data of another z=0.39 cluster, CL0024+17, but found no EIGs. The key difference between A851 and CL0024+17 would be the existence of a subcluster colliding with the main body of A851, in which six or seven out of the nine parent galaxies in A851 exist, and the fraction of EIGs in the subcluster is significantly higher than the main subcluster of A851 and CL0024+17.

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arXiv2014

Evidence for a gas-rich major merger in a proto-cluster at z=2.5

Gas-rich major mergers in high-redshift proto-clusters are important events, perhaps leading to the creation of the slowly rotating remnants seen in the cores of clusters in the present day. Here, we present a deep Jansky Very Large Array observation of CO J = 1-0 emission line in a proto-cluster at z = 2.5, USS1558-003. The target field is an extremely dense region, where 20 H-alpha emitters (HAEs) are clustering. We have successfully detected the CO emission line from three HAEs and discovered a close pair of red and blue CO-emitting HAEs. Given their close proximity (~30 kpc), small velocity offset (~300 km/s), and similar stellar masses, they could be in the early phase of a gas-rich major merger. For the red HAE, we derive a total infrared luminosity of L(IR)=5.1e12 Lsun using MIPS 24 um and radio continuum images. The L(IR)/L'(CO) ratio is significantly enhanced compared to local spirals and high-redshift disks with a similar CO luminosity, which is indicative of a starburst mode. We find the gas depletion timescale is shorter than that of normal star-forming galaxies regardless of adopted CO-H2 conversion factors. The identification of such a rare event suggests that gas-rich major mergers frequently take place in proto-clusters at z > 2 and may involve the formation processes of slow rotators seen in local massive clusters.

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arXiv2014

The environmental impacts on the star formation main sequence: an H-alpha study of the newly discovered rich cluster at z=1.52

We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z=1.52 (4C65.22) based on our broad-band and narrow-band (H-alpha) photometry with Subaru Telescope. We find that H-alpha emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z=1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z~1.5, mostly driven by the passive red massive galaxies residing within Rc<200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ~1-Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.

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arXiv2014

Identification of the progenitors of rich clusters and member galaxies in rapid formation at z>2

We present the results of near-infrared spectroscopy of H$α$ emitters (HAEs) associated with two protoclusters around radio galaxies (PKS1138-262 at $z$=2.2 and USS1558-003 at $z$=2.5) with Multi-Object Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope. Among the HAE candidates constructed from our narrow-band imaging, we have confirmed membership of 27 and 36 HAEs for the respective protoclusters, with a success rate of 70 per cent of our observed targets. The large number of spectroscopically confirmed members per cluster has enabled us for the first time to reveal the detailed kinematical structures of the protoclusters at $z$$>$2. The clusters show prominent substructures such as clumps, filaments and velocity gradients, suggesting that they are still in the midst of rapid construction to grow to rich clusters at later times. We also estimate dynamical masses of the clusters and substructures assuming their local virialization. The inferred masses ($\sim$10$^{14}$M$_\odot$) of the protocluster cores are consistent with being typical progenitors of the present-day most massive class of galaxy clusters ($\sim$10$^{15}$M$_\odot$) if we take into account the typical mass growth history of clusters. We then calculated the integrated star formation rates of the protocluster cores normalized by the dynamical masses, and compare these with lower redshift descendants. We see a marked increase of star-forming activities in the cluster cores, by almost three orders of magnitude, as we go back in time to 11 billion years ago; this scales as (1$+$$z$)$^6$.

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arXiv2014

Mapping the large scale structure around a z=1.46 galaxy cluster in 3-D using two adjacent narrow-band filters

We present a novel method to estimate accurate redshifts of star-forming galaxies by measuring the flux ratio of the same emission line observed through two adjacent narrow-band filters. We apply this method to our NB912 and new NB921 data taken with Suprime-Cam on the Subaru Telescope of a galaxy cluster, XMMXCS J2215.9-1738, at z=1.46 and its surrounding structures. We obtain redshifts for 170 [OII] emission line galaxies at z~1.46, among which 41 galaxies are spectroscopically confirmed with MOIRCS and FMOS on the Subaru mainly, showing an accuracy of $σ$((z-z_spec})/(1+z_spec))=0.002. This allows us to reveal filamentary structures that penetrate towards the centre of the galaxy cluster and intersect with other structures, consistent with the picture of hierarchical cluster formation. We also find that the projected celestial distribution does not precisely trace the real distribution of galaxies, indicating the importance of the three dimensional view of structures to properly identify and quantify galaxy environments. We investigate the environmental dependence of galaxy properties with local density, confirming that the median colour of galaxies becomes redder in higher density region while the star-formation rate of star-forming galaxies does not depend strongly on local environment in this structure. This implies that the star-forming activity in galaxies is truncated on a relatively short time scale in the cluster centre.

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arXiv2013

Star formation in the cluster CLG0218.3-0510 at z=1.62 and its large-scale environment: the infrared perspective

The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy clusters known, with a rich muti-wavelength data set that confirms a mature galaxy population already in place. Using very deep, wide area (20x20 Mpc) imaging by Spitzer/MIPS at 24um, in conjunction with Herschel 5-band imaging from 100-500um, we investigate the dust-obscured, star-formation properties in the cluster and its associated large scale environment. Our galaxy sample of 693 galaxies at z=1.62 detected at 24um (10 spectroscopic and 683 photo-z) includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The star-formation rates (SFRs) derived from the measured infrared luminosity range from 18 to 2500 Ms/yr, with a median of 55 Ms/yr, over the entire radial range (10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy system, is vigorously forming stars at a rate of 256$\pm$70 Ms/yr, and the total cluster SFR enclosed in a circle of 1 Mpc is 1161$\pm$96 Ms/yr. We estimate a dust extinction of about 3 magnitudes by comparing the SFRs derived from [OII] luminosity with the ones computed from the 24um fluxes. We find that the in-falling region (1-3 Mpc) is special: there is a significant decrement (3.5x) of passive relative to star-forming galaxies in this region, and the total SFR of the galaxies located in this region is lower (130 Ms/yr/Mpc2) than anywhere in the cluster or field, regardless of their stellar mass. In a complementary approach we compute the local galaxy density, Sigma5, and find no trend between SFR and Sigma5. However, we measure an excess of star-forming galaxies in the cluster relative to the field by a factor 1.7, that lends support to a reversal of the SF-density relation in CLG0218.

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arXiv2013

Nature of H-alpha selected galaxies at z>2. I. Main sequence and dusty star-forming galaxies

We present the results from our narrow-band imaging surveys of HAEs at z=2.2 and z=2.5 in the Subaru/XMM-Newton Deep survey Field with near-infrared camera MOIRCS on Subaru Telescope. We have constructed a clean sample of 63 star-forming galaxies at z=2.2 and 46 at z=2.5. For 12 (or ~92%) out of 13 Hαemitters (HAEs) at z=2.2, their Hαemission lines have been successfully detected by the spectroscopy. While about 42% of the red, massive HAEs with M_*>10^{10.8} M_\odot contain AGNs, most of the blue, less massive ones are likely to be star-forming galaxies. This suggests that the AGN may play an important role in galaxy evolution at the late stage of truncation. For the HAEs excluding possible AGNs, we estimate the gas-phase metallicities on the basis of [N~{\sc ii}]/Hαratios, and find that the metallicities of the Hαselected galaxies at z=2.2 are lower than those of local star-forming galaxies at fixed stellar mass, as shown by previous studies. Moreover, we present and discuss the so-called "main sequence" of star-forming galaxies at z>2 based on our unique sample of HAEs. By correlating the level of dust extinction with the location on the main sequence, we find that there are two kinds/modes of dusty star-forming galaxies: star-bursting galaxies and metal-rich normal star-forming galaxies.

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arXiv2013

Nature of H-alpha selected galaxies at z>2. II. Clumpy galaxies and compact star-forming galaxies

We present the morphological properties of 109 Hα-selected galaxies at z>2 in SXDF-UDS-CANDELS field. With high-resolution optical/near-infrared images obtained by Hubble Space Telescope, we identify giant clumps within the Hαemitters (HAEs). We find that at least 41% of our sample show clumpy structures in the underlying disks. The color gradient of clumps is commonly seen in the sense that the clumps near the galactic center tend to be redder than those in the outer regions. The mid-infrared detection in galaxies with red clumps and the spatial distribution of Hαemission suggest that dusty star-formation activity is probably occurring in the nuclear red clumps. A gas supply to a bulge component through the clump migration is one of the most potent physical processes to produce such dusty star-forming clumps and form massive bulges in local early-type galaxies. They would become large quiescent galaxies at later times just by consumption or blowout of remaining gas. Also, while most of the HAEs have extended disks, we observe two massive, compact HAEs, whose stellar surface densities are significantly higher. They are likely to be the direct progenitors of massive, compact quiescent galaxies at z=1.5-2.0. Two evolutionary paths to massive quiescent galaxies are devised to account for both the size growth of quiescent galaxies and their increased number density from z~2 to z=0.

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arXiv2013

A fundamental metallicity relation for galaxies at z = 0.84 - 1.47 from HiZELS

We obtained Subaru FMOS observations of Halpha emitting galaxies selected from the HiZELS narrow-band survey, to investigate the relationship between stellar mass, metallicity and star-formation rate at z = 0.84 - 1.47, for comparison with the Fundamental Metallicity Relation seen at low redshift. Our findings demonstrate, for the first time with a homogeneously selected sample, that a relationship exists for typical star-forming galaxies at z = 1 - 1.5 and that it is surprisingly similar to that seen locally. Therefore, star-forming galaxies at z = 1 - 1.5 are no less metal abundant than galaxies of similar mass and star formation rate (SFR) at z = 0.1, contrary to claims from some earlier studies. We conclude that the bulk of the metal enrichment for this star-forming galaxy population takes place in the 4 Gyr before z = 1.5. We fit a new mass-metallicity-SFR plane to our data which is consistent with other high redshift studies. However, there is some evidence that the mass-metallicity component of this high redshift plane is flattened, at all SFR, compared with z = 0.1, suggesting that processes such as star-formation driven winds, thought to remove enriched gas from low mass halos, are yet to have as large an impact at this early epoch. The negative slope of the SFR-metallicity relation from this new plane is consistent with the picture that the elevation in the SFR of typical galaxies at z > 1 is fuelled by the inflow of metal-poor gas and not major merging.

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arXiv2013

On the formation time scale of massive cluster ellipticals based on deep near-IR spectroscopy at z~2

We present improved constraints on the formation time scale of massive cluster galaxies based on rest-frame optical spectra of galaxies in a forming cluster located at z=2.16. The spectra are obtained with MOIRCS on the Subaru telescope with an integration time of ~7 hours. We achieve accurate redshift measurements by fitting SEDs using the spectra and broad-band photometry simultaneously, allowing us to identify probable cluster members. Clusters at low redshifts are dominated by quiescent galaxies, but we find that quiescent galaxies and star forming galaxies co-exist in this z=2 system. Interestingly, the quiescent galaxies form a weak red sequence in the process of forming. By stacking the spectra of star forming galaxies, we observe strong emission lines such as [OII] and [OIII] and we obtain a tentative hint of AGN activities in these galaxies. On the other hand, the stacked spectrum of the quiescent galaxies reveals a clear 4000A break with a possible CaII H+K absorption feature and strong emission lines such as [OII] are absent in the spectrum, confirming the quiescent nature of these galaxies. We then perform detailed spectral analyses of the stacked spectrum, which suggest that these massive quiescent galaxies formed at redshifts between 3 and 4 on a time scale of <~0.5 Gyr. This short formation time scale is not reproduced in recent numerical simulations. We discuss possible mechanisms for how these galaxies form 10^11 Msun stellar mass on a short time scale and become red and quiescent by z=2.

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arXiv2013

On the evolution and environmental dependence of the star formation rate versus stellar mass relation since z~2

This paper discusses the evolution of the correlation between galaxy star formation rates (SFRs) and stellar mass (M*) over the last ~10 Gyrs, particularly focusing on its environmental dependence. We first present the mid-infrared (MIR) properties of the H-alpha-selected galaxies in a rich cluster Cl0939+4713 at z=0.4. With a MIR stacking analysis, we find that the median SFR of H-alpha emitters is higher in higher-density environment at z=0.4. We also find that star-forming galaxies in high-density environment tend to have higher specific SFR (SSFR), although the trend is much less significant compared to that of SFR. This increase of SSFR in high-density environment is not visible when we consider the SFR derived from H-alpha alone, suggesting that the dust attenuation in galaxies depends on environment; galaxies in high-density environment tend to be dustier (by up to ~0.5 mag). We then discuss the environmental dependence of the SFR-M* relation for star-forming galaxies since z~2, by compiling our comparable, narrow-band selected, large H-alpha emitter samples in both distant cluster environments (from MAHALO-Subaru) and field environments (from HiZELS). We find that the SSFR of H-alpha-selected galaxies (at the fixed mass of log(M*/Msun)=10) rapidly evolves as (1+z)^3, but the SFR-M* relation is independent of the environment since z~2, as far as we rely on the H-alpha-based SFRs (with M*-dependent extinction correction). Even if we consider the possible environmental variation in the dust attenuation, we conclude that the difference in the SFR-M* relation between cluster and field star-forming galaxies is always small (~<0.2dex level) at any time in the history of the Universe since z~2. [abridged]

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arXiv2013

Probing of the Interactions Between the Hot Plasmas and Galaxies in Clusters from z=0.1 to 0.9

Based on optical and X-ray data for a sample of 34 relaxed rich clusters of galaxies with redshifts of 0.1-0.9, we studied relative spatial distributions of the two major baryon contents, the cluster galaxies and the hot plasmas. Using multi-band photometric data taken with the UH88 telescope, we determined the integrated (two dimensional) radial light profiles of member galaxies in each cluster using two independent approaches, i.e., the background subtraction and the color-magnitude filtering. The ICM mass profile of each cluster in our sample, also integrated in two dimensions, was derived from a spatially-resolved spectral analysis using XMM-Newton and Chandra data. Then, the radially-integrated light profile of each cluster was divided by its ICM mass profile, to obtain a profile of "galaxy light vs. ICM mass ratio". The ratio profiles over the central 0.65 R500 regions were found to steepen from the higher- to lower- redshift subsamples, meaning that the galaxies become more concentrated in the ICM sphere towards lower redshifts. The evolution is also seen in galaxy number vs. ICM mass ratio profiles. A range of systematic uncertainties in the galaxy light measurements, as well as many radius-/redshift- dependent biases to the galaxy vs. ICM profiles have been assessed, but none of them is significant against the observed evolution. Besides, the galaxy light vs. total mass ratio profiles also exhibit gradual concentration towards lower redshift. We interpret in the context that the galaxies, the ICM, and the dark matter components followed a similar spatial distribution in the early phase (z>0.5), while the galaxies have fallen towards the center relative to the others at a later phase.

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arXiv2013

Re-evaluating Hot Jupiter WASP-12b: An Update

The hot Jupiter WASP-12b is one of the largest, hottest, and best-studied extrasolar planets. We revisit our recent analysis of WASP-12b's emission spectrum in light of near-infrared spectroscopic measurements which have been claimed to support either a hydride-dominated or carbon-rich atmospheric composition. We show that this new spectrum is still consistent with a featureless blackbody, indicating a nearly isothermal photosphere on the planet's day side. Thus the ensemble of occultation measurements for WASP-12b is still insufficient to constrain the planet's atmospheric composition.

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arXiv2012

Calibrating [OII] star-formation rates at z>1 from dual Hα-[OII] imaging from HiZELS

We investigate the relationship between Hα and [OII](λ3727) emission in faint star-forming galaxies at z=1.47 with dust uncorrected star formation rates (SFRs) down to 1.4 Msun/yr, using data in two narrow-bands from WFCAM/UKIRT and Suprime-Cam/Subaru. A stacking analysis allows us to investigate Hα emission flux from bright [OII] emitters as well as faint ones for which Hα is not individually detected, and to compare them with a large sample of local galaxies. We find that there is a clear, positive correlation between the average Hα and [OII] luminosities for [OII] emitters at z=1.47, with its slope being consistent with the local relation. [OII] emitters at z=1.47 have lower mean observed ratios of Hα/[OII] suggesting a small but systematic offset (at 2.8σ significance) towards lower values of dust attenuation, A(Hα)~0.35, than local galaxies. This confirms that [OII] selection tends to pick up galaxies which are significantly less dusty on average than Hα selected ones, with the difference being higher at z=1.47 than at z=0. The discrepancy of the observed line ratios between [OII] emitters at z=1.47 and the local galaxies may in part be due to the samples having different metallicities. However, we demonstrate that metallicity is unlikely to be the main cause. Therefore, it is important to take into account that the relations for the dust correction which are derived using Hα emitter samples, and frequently used in many studies of high-z galaxies, may overestimate the intrinsic SFRs of [OII]-selected galaxies, and that surveys of [OII] emission galaxies are likely to miss dusty populations.

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arXiv2012

Re-Evaluating WASP-12b: Strong Emission at 2.315 micron, Deeper Occultations, and an Isothermal Atmosphere

We revisit the atmospheric properties of the extremely hot Jupiter WASP-12b in light of several new developments. First, new narrowband (2.315 micron) secondary eclipse photometry that we present here, which exhibits a planet/star flux ratio of 0.45% +/- 0.06 %, corresponding to a brightness temperature of 3640 K +/- 230 K; second, recent Spitzer/IRAC and Hubble/WFC3 observations; and third, a recently observed star only 1" from WASP-12, which has diluted previous observations and which we further characterize here. We correct past WASP-12b eclipse measurements for the presence of this object, and we revisit the interpretation of WASP-12b's dilution-corrected emission spectrum. The resulting planetary emission spectrum is well-approximated by a blackbody, and consequently our primary conclusion is that the planet's infrared photosphere is nearly isothermal. Thus secondary eclipse spectroscopy is relatively ill-suited to constrain WASP-12b's atmospheric abundances, and transmission spectroscopy may be necessary to achieve this goal.

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arXiv2012

Massive starburst galaxies in a z=2.16 proto-cluster unveiled by panoramic H-alpha mapping

We present a panoramic narrow-band study of H-alpha emitters in the field of the z=2.16 proto-cluster around PKS1138-262 using MOIRCS on the Subaru Telescope. We find 83 H-alpha emitters down to a SFR(Ha)~10Msun/yr across a ~7'x7' region centered on the radio galaxy, and identify ~10-Mpc scale filaments of emitters running across this region. By examining the properties of H-alpha emitters within the large-scale structure, we find that galaxies in the higher-density environments at z=2.16 tend to have redder colours and higher stellar masses compared to galaxies in more underdense regions. We also find a population of H-alpha emitters with red colours ((J-Ks)>1), which are much more frequent in the denser environments and which have apparently very high stellar masses with M*>~10^11Msun, implying that these cluster galaxies have already formed a large part of their stellar mass before z~2. Spitzer Space Telescope 24-micron data suggests that many of these red H-alpha emitters are bright, dusty starbursts (rather than quiescent sources). We also find that the proto-cluster galaxies follow the same correlation between SFR and M* (the "main sequence") of z~2 field star-forming galaxies, but with an excess of massive galaxies. These very massive star-forming galaxies are not seen in our similar, previous study of z~1 clusters, suggesting that their star-formation activity has been shut off at 1<~z<~2. We infer that the massive red (but active) galaxies in this rich proto-cluster are likely to be the products of environmental effects, and they represent the accelerated galaxy formation and evolution in a biased high density region in the early Universe.

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arXiv2012

A star-bursting proto-cluster in making associated to a radio galaxy at z=2.53 discovered by H_alpha imaging

We report a discovery of a proto-cluster in vigorous assembly and hosting strong star forming activities, associated to a radio galaxy USS 1558-003 at z=2.53, as traced by a wide-field narrow-band H_alpha imaging with MOIRCS on Subaru Telescope. We find 68 H_alpha emitters with dust-uncorrected SFRs down to 8.6 Msun/yr. Their spatial distribution indicates that there are three prominent clumps of H_alpha emitters, one surrounding the radio galaxy and another located at ~1.5 Mpc away to the south-west, and the other located in between the two. These contiguous three systems are very likely to merge together in the near future and may grow to a single more massive cluster at later times. Whilst most H_alpha emitters reside in the "blue cloud" on the color--magnitude diagram, some emitters have very red colors with J-Ks>1.38(AB). Interestingly, such red H_alpha emitters are located towards the faint end of the red sequence, and they tend to be located in the high density clumps. We do not see any statistically significant difference in the distributions of individual star formation rates or stellar masses of the H_alpha emitters between the dense clumps and the other regions, suggesting that this is one of the notable sites where the progenitors of massive galaxies in the present-day clusters were in their vigorous formation phase. Finally, we find that H_alpha emission of the radio galaxy is fairly extended spatially over ~4.5 arcsec. However it is not as widespread as its Lya halo, meaning that the Lya emission is indeed severely extended by resonant scattering.

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