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Register a new userJHK Spectra of the z=2.39 Radio Galaxy 53W002
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We present low-resolution, near-IR JHK spectra of the weak z=2.39 radio galaxy 53W002, obtained with the OH-airglow Suppressor spectrograph (OHS) and Cooled Infrared Spectrograph and Camera for OHS (CISCO) on the Subaru Telescope. They cover rest-frame wavelengths of 3400-7200 A, and the emission lines of [O II]3727, Hb, [O III]4959, 5007, Ha, [N II]6548, 6583 and [S II]6716, 6731 were detected. Using the Ha/Hb line ratio, we find an extinction of E(B-V)=0.14. The emission-line ratios are reproduced by a cloud of electron density n_e=1x10^{3-4}(/cm3) with solar metallicity, ionized by an alpha=-0.7 power-law continuum with ionizing parameter U=1x10^-3. In addition to these emission lines, we make the first spectroscopic confirmation of the Balmer discontinuity in a high-z radio galaxy. Together with rest-frame UV photometry from the literature, we show that at least 1/3 of the present stellar mass was formed in the current starburst. The stellar mass was estimated to be (1-1.4)x10^11 M_sol by one-component model fitting, which is smaller than that of typical z~1 B2/6C radio galaxies. We suggest that 53W002 is currently assembling a large part of its stellar mass through merger events with the surrounding sub-galactic clumps, some of which can be identified with the Lya emitters detected in narrow-band imaging. After a few such events over the next few Gyr, 53W002 will evolve into a massive elliptical galaxy.
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We searched massive galaxy population in the known large-scale high-density structure of Lyman$~alpha$ emitters (LAEs) at $z=2.39$ near the radio galaxy 53W002 by using $B,~V,~i^prime,~J,~H,$ and $~K_s$-bands imaging data taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their $JHK_s$-band colors and photometric redshift analysis ($JHK_s$-selected galaxies) in our survey field of $70.2~{rm{arcmin}}^{2}$, and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the $JHK_s$-selected galaxies in the 53W002 field at $K_s<22.25,~J-K_s>2,$ or $V-K_s>4$. In particular the number density of the $JHK_s$-selected galaxies with $K_s<22.25$ and $J-K_s>2$ in the 53W002 field is eight times higher than the comparison sample. Most of those with $K_s<22.25$ and $J-K_s>2$ are massive galaxies with $M_s>10^{11}~M_odot$, and their sSFRs of $10^{-11}$--$10^{-10}~rm{yr^{-1}}$ suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with $M_s=5times10^{10}$--$10^{11}~M_odot$ and ${rm{sSFR}}<10^{-11}~rm{yr^{-1}}$ as well as that of low-mass galaxies with $M_s=10^{9.75}$--$10^{10}~M_odot$ and various sSFRs. The massive galaxies with $M_s>10^{11}~M_odot$ are not located at the density peaks of LAEs, but they show a wide distribution along the similar direction with the structure of LAEs over $sim15$--$20$ comoving Mpc. On the other hand, the quiescent galaxies with ${rm{sSFR}}<10^{-11}~rm{yr^{-1}}$ clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activity depends on location in the protocluster.
High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) evolution, test cosmological models, and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multi-frequency Giant Metrewave Radio Telescope (GMRT) observations of eight z>4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z>4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z>4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultra-steep spectra (USS). Recently a new method has been proposed to identify these objects based on their megahertz-peaked spectra (MPS). Neither method would have identified more than 18% of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.
The z~1 radio galaxy 3C280 has a striking rest-frame UV morphology, with multiple line and continuum components precisely aligned with the radio structure, including an obvious semi-circular arc. We explore the nature of these various components by bringing together HST and ground-based imaging, ground-based spectroscopy, and radio mapping. From plausible decompositions of the spectra, we show that the continuum of the nuclear component is likely dominated by a combination of nebular thermal continuum, quasar light, and light from old stars. A component that falls directly on the probable path of the radio jet shows mostly nebular thermal continuum and includes contributions from a relatively young stellar population with an age around 100 Myr. The arc appears to be completely dominated by line emission and nebular thermal continuum, with no evidence for a significant stellar contribution. Though much of the aligned light is in UV components, the underlying old elliptical is also well-aligned with the radio axis. The elliptical is well-fit by a de Vaucouleurs profile, probably has a moderately old stellar population (~3 Gyr), and is a massive system with a velocity dispersion of sigma ~ 270 km/s that implies it contains a supermassive black hole. Although the arc and the extended emission surrounding the eastern lobe suggest that interactions between the radio lobe and jet must have been important in creating the UV morphology, the ionization and kinematic properties in these componentsare more consistent with photoionization than shock excitation. 3C280 may be a transition object between the compact steep-spectrum radio galaxies which seem to be shock-dominated, and the extended radio sources which may have evolved past this phase and rarely show shock signatures.
With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J,H,K spectra of the atmospheres of objects estimated to have very low substellar masses of sim5-20 MJup and young ages of sim1-50 Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the sample youth, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models. This analysis represents the first systematic model comparison with infrared spectra of young brown dwarfs. The fits to the full JHK spectra of each object result in a range of best fit effective temperatures of +/-150-300K whether or not the full model grid or a subset restricted to lower log(g) values is used. This effective temperature range is significantly larger than the uncertainty typically assigned when using a single model grid. Fits to a single wavelength band can vary by up to 1000K using the different models. Since the overall shape of these spectra is governed more by the temperature than surface gravity, unconstrained model fits did not find matches with low surface gravity or a trend in log(g) with age. This suggests that empirical comparison with spectra of unambiguously young objects targets (such as these SINFONI data) may be the most reliable method to search for indications of low surface gravity and youth. For two targets, the SINFONI data are a second epoch and the data show no variations in morphology over time. The analysis of two other targets, AB Pic B and CT Cha B, suggests that these objects may have lower temperatures, and consequently lower masses, than previously estimated.
In this letter we report the discovery of a z=4.88 radio galaxy discovered with a new technique which does not rely on pre-selection of a sample based on radio properties such as steep-spectral index or small angular size. This radio galaxy was discovered in the Elais-N2 field and has a spectral index of alpha = 0.75, i.e. not ultra-steep spectrum. It also has a luminosity consistent with being drawn from the break of the radio luminosity function and can therefore be considered as a typical radio galaxy. Using the Spitzer-SWIRE data over this field we find that the host galaxy is consistent with being similarly massive to the lower redshift powerful radio galaxies (~1-3L*). We note however, that at z=4.88 the H-alpha line is redshifted into the IRAC 3.6micron filter and some of the flux in this band may be due to this rather than stellar continuum emission. The discovery of such a distant radio source from our initial spectroscopic observations demonstrate the promise of our survey for finding the most distant radio sources.
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