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Register a new userSpectroscopic confirmation and velocity dispersions for twenty Planck galaxy clusters at 0.16<z<0.78
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We present Gemini and Keck spectroscopic redshifts and velocity dispersions for twenty clusters detected via the Sunyaev-Zeldovich (SZ) effect by the Planck space mission, with estimated masses in the range $2.3 times 10^{14} M_{odot} < M < 9.4 times 10^{14} M_{odot}$. Cluster members were selected for spectroscopic follow-up with Palomar, Gemini and Keck optical and (in some cases) infrared imaging. Seven cluster redshifts were measured for the first time with this observing campaign, including one of the most distant Planck clusters confirmed to date, at $z=0.782pm0.010$, PSZ2 G085.95+25.23. The spectroscopic redshift catalogs of members of each confirmed cluster are included as on-line tables. We show the galaxy redshift distributions and measure the cluster velocity dispersions. The cluster velocity dispersions obtained in this paper were used in a companion paper to measure the Planck mass bias and to constrain the cluster velocity bias.
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We present spectroscopic confirmation of two new massive galaxy protoclusters at $z=2.24pm0.02$, BOSS1244 and BOSS1542, traced by groups of Coherently Strong Ly$alpha$ Absorption (CoSLA) systems imprinted in the absorption spectra of a number of quasars from the SDSS III and identified as overdensities of narrowband-selected H$alpha$ emitters (HAEs). Using MMT/MMIRS and LBT/LUCI near-infrared (NIR) spectroscopy, we confirm 46 and 36 HAEs in the BOSS1244 and BOSS1542 fields, respectively. BOSS1244 displays a South-West (SW) component at $z=2.230pm0.002$ and another North-East (NE) component at $z=2.246pm0.001$ with the line-of-sight velocity dispersions of $405pm202$ km s$^{-1}$ and $377pm99$ km s$^{-1}$, respectively. Interestingly, we find that the SW region of BOSS1244 contains two substructures in redshift space, likely merging to form a larger system. In contrast, BOSS1542 exhibits an extended filamentary structure with a low velocity dispersion of $247pm32$ km s$^{-1}$ at $z=2.241pm0.001$, providing a direct confirmation of a large-scale cosmic web in the early Universe. The galaxy overdensities $delta_{rm g}$ on the scale of 15 cMpc are $22.9pm4.9$, $10.9pm2.5$, and $20.5pm3.9$ for the BOSS1244 SW, BOSS1244 NE, and BOSS1542 filament, respectively. They are the most overdense galaxy protoclusters ($delta_{rm g}>20$) discovered to date at $z>2$. These systems are expected to become virialized at $zsim0$ with a total mass of $M_{rm SW}=(1.59pm0.20)times10^{15}$ $M_{odot}$, $M_{rm NE} =(0.83pm0.11)times10^{15}$ $M_{odot}$ and $M_{rm filament}=(1.42pm0.18)times10^{15}$ $M_{odot}$, respectively. Together with BOSS1441 described in Cai et al. (2017a), these extremely massive overdensities at $z=2-3$ exhibit different morphologies, indicating that they are in different assembly stages in the formation of early galaxy clusters.
We present the spectroscopic confirmation of a galaxy cluster at $z=2.095$ in the COSMOS field. This galaxy cluster was first reported in the ZFOURGE survey as harboring evolved massive galaxies using photometric redshifts derived with deep near-infrared (NIR) medium-band filters. We obtain medium resolution ($R sim$ 3600) NIR spectroscopy with MOSFIRE on the Keck 1 telescope and secure 180 redshifts in a $12times12$ region. We find a prominent spike of 57 galaxies at $z=2.095$ corresponding to the galaxy cluster. The cluster velocity dispersion is measured to be $sigma_{rm v1D}$ = 552 $pm$ 52 km/s. This is the first study of a galaxy cluster in this redshift range ($z gt 2.0$) with the combination of spectral resolution ($sim$26 km/s) and the number of confirmed members (${>}50$) needed to impose a meaningful constraint on the cluster velocity dispersion and map its members over a large field of view. Our $Lambda$CDM cosmological simulation suggests that this cluster will most likely evolve into a Virgo-like cluster with ${rm M_{vir}}{=}10^{14.4pm0.3} {rm M_odot}$ ($68%$ confidence) at $zsim$ 0. The theoretical expectation of finding such a cluster is $sim$ $4%$. Our results demonstrate the feasibility of studying galaxy clusters at $z > 2$ in the same detailed manner using multi-object NIR spectrographs as has been done in the optical in lower redshift clusters.
We present spectroscopic confirmation of five galaxy clusters at $1.25 < textit{z} < 1.5$, discovered in the $2500$ deg$^{2}$ South Pole Telescope Sunyaev-Zeldovich (SPT-SZ) survey. These clusters, taken from a mass-limited sample with a nearly redshift independent selection function, have multi-wavelength follow-up imaging data from the X-ray to near-infrared, and currently form the most homogeneous massive high-redshift cluster sample known. We identify $44$ member galaxies, along with $25$ field galaxies, among the five clusters, and describe the full set of observations and data products from Magellan/LDSS3 multi-object spectroscopy of these cluster fields. We briefly describe the analysis pipeline, and present ensemble analyses of cluster member galaxies that demonstrate the reliability of the measured redshifts. We report $textit{z} = 1.259, 1.288, 1.316, 1.401$ and $1.474$ for the five clusters from a combination of absorption-line (Ca II H$&$K doublet - $3968,3934$ {AA}) and emission-line ([OII] $3727,3729$ {AA}) spectral features. Moreover, the calculated velocity dispersions yield dynamical cluster masses in good agreement with SZ masses for these clusters. We discuss the velocity and spatial distributions of passive and [OII]-emitting galaxies in these clusters, showing that they are consistent with velocity segregation and biases observed in lower redshift SPT clusters. We identify modest [OII] emission and pronounced CN and H$delta$ absorption in a stacked spectrum of $28$ passive galaxies with Ca II H$&$K-derived redshifts. This work increases the number of spectroscopically-confirmed SZ-selected galaxy clusters at $textit{z} > 1.25$ from three to eight, further demonstrating the efficacy of SZ selection for the highest redshift massive clusters, and enabling detailed study of these systems.
We report the discovery of a spectroscopically-confirmed strong Lyman-$alpha$ emitter at $z=7.0281pm0.0003$, observed as part of the Reionization Cluster Lensing Survey (RELICS). This galaxy, dubbed Dichromatic Primeval Galaxy at $zsim7$ (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity ($sim0.3L^{ast}_{UV}$, where $L^{ast}_{UV}$ is the characteristic luminosity), DP7 has one of the highest observed Lyman-$alpha$ equivalent widths (EWs) among Lyman-$alpha$ emitters at $z>6$ ($>200$ Angstrom in the rest frame). The strong Lyman-$alpha$ emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope $beta$ of the galaxy as a whole is redder than typical star-forming galaxies at these redshifts, $-1.13pm 0.84$, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measure $beta$ for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyman-$alpha$ is spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyman-$alpha$ halo. Rejuvenation or merging events could explain these results. Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured Active Galactic Nucleus. DP7, with its low UV luminosity and high Lyman-$alpha$ EW, represents the typical galaxies that are thought to be the major contribution to the reionization of the Universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope.
Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sight-lines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day. Observations of the Cosmic Microwave Background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionised through a complex process that was completed about a billion years after the Big Bang, by redshift z~6. Detecting ionizing Ly-alpha photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionisation. Here we report the detection of Ly-a photons emitted less than 600 million years after the Big Bang. UDFy-38135539 is at a redshift z=8.5549+-0.0002, which is greater than those of the previously known most distant objects, at z=8.2 and z=6.97. We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby.
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