1,721,023 research outputs found
Ancient Light From Young Cosmic Cities: Physical And Observational Signatures Of Galaxy Proto-Clusters
Full text linkA growing number of galaxy clusters at z = 1-2 is being discovered as part of deep optical, IR, X-ray, and Sunyaev-Zel'dovich effect surveys. For a complete picture of cluster formation, however, it is important that we also start probing the much earlier epoch, between redshifts of about 2 and 7, during which these clusters and their galaxies first began to form. Because the study of these so-called proto-clusters is currently quite limited by small number statistics, widely varying selection techniques, and many assumptions, we have performed a large systematic study of cluster formation utilizing cosmological simulations. We use the Millennium Simulations to track the evolution of dark matter and galaxies in about 3000 clusters from the earliest times to z = 0. We define an effective radius R-e for proto-clusters and characterize their growth in size and mass with cosmic time. We show that the progenitor regions of galaxy clusters (ranging in mass from similar to 10(14) to a few times 10(15) M-circle dot) can already be identified in galaxy surveys at very early times (at least up to z similar to 5), provided that the galaxy overdensities are measured on a sufficiently large scale (R-e similar to 5-10 Mpc comoving) and with sufficient statistics. We present the overdensities in matter, dark matter halos, and galaxies as functions of present-day cluster mass, redshift, bias, and window size that can be used to interpret the wide range of structures found in real surveys. We also derive the probability that a structure having a galaxy overdensity delta(gal), defined by a set of observational selection criteria, is indeed a proto-cluster, and we show how their z = 0 masses can already be estimated long before virialization. We present overdensity profiles as a function of radius, and we further show how the projected surface overdensities of proto-clusters decrease as the uncertainties in redshift measurements increase. We provide a table of proto-cluster candidates selected from the literature and discuss their properties in light of our simulation predictions. This paper provides the general framework that will allow us to extend the study of cluster formation out to much higher redshifts using the large number of proto-clusters that are expected to be discovered in, e. g., the upcoming HETDEX and Hyper Suprime-Cam surveys.NASAJPL/CaltechAstronom
Recommended from our members
The Galaxy Environment Of A QSO At Z Similar To 5.7
No full textHigh-redshift quasars are believed to reside in massive halos in the early universe and should therefore be located in fields with overdensities of galaxies, which are thought to evolve into galaxy clusters seen in the local universe. However, despite many efforts, the relationship between galaxy overdensities and z similar to 6 quasars is ambiguous. This can possibly be attributed to the difficulty of finding galaxies with accurate redshifts in the vicinity of z similar to 6 quasars. So far, overdensity searches around z similar to 6 quasars have been based on studies of Lyman break galaxies (LBGs), which probe a redshift range of Delta z approximate to 1. This range is large enough to select galaxies that may not be physically related to the quasar. We use deep narrow- and broadband imaging to study the environment of the z = 5.72 quasar ULAS J0203+0012. The redshift range probed by our narrow- band selection of Lyman alpha emitters (LAEs) is Delta z approximate to 0.1, which is significantly narrower than the LBG searches. This is the first time that LAEs were searched for near a z similar to 6 quasar, in an effort to provide clues about the environments of quasars at the end of the epoch of reionization. We find no enhancement of LAEs in the surroundings of ULAS J0203+0012 in comparison with blank fields. We explore different explanations and interpretations for this non-detection of a galaxy overdensity, including that (1) the strong ionization from the quasar may prevent galaxy formation in its immediate vicinity and (2) high-redshift quasars may not reside in the center of the most massive dark matter halos.ESO Telescopes at the La Silla Paranal Observatory 385.A-0030(A)Astronom
Recommended from our members
Resolving The Optical Emission Lines Of Ly Alpha Blob "B1" At Z=2.38: Another Hidden Quasar
No full textWe have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (L-Ly alpha approximate to 10(44) erg s(-1)) and nearest (z approximate to 2.38) of all Ly alpha blobs (LABs). The target, known in the literature as object "B1", lies at a redshift where the main optical emission lines are accessible in the observed near-infrared. We detect luminous [OIII]lambda lambda 4959,5007 and H alpha emission with a spatial extent of at least 32 x 40 kpc (4 '' x 5 ''). The dominant optical emission line component shows relatively broad lines (600-800 km s(-1), FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. The new evidence for AGN photoionization, combined with previously detected CIV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [OII] is relatively weak compared with [OIII] (extinction-corrected [OIII]/[OII] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the extinction-corrected [OIII] luminosity we infer a bolometric AGN luminosity of similar to 3x10(46) erg s(-1), and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow-line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Ly alpha, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Ly alpha in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment.Astronom
A large-scale galaxy structure at z = 2.02 associated with the radio galaxy MRC 0156-252
Full text linkWe present the spectroscopic confirmation of a structure of galaxies surrounding the radio galaxy MRC 0156-252 at z = 2.02. The structure was initially discovered as an overdensity of both near-infrared selected z > 1.6 and mid-infrared selected z > 1.2 galaxy candidates. We used the VLT/FORS2 multi-object spectrograph to target ~80 high-redshift galaxy candidates, and obtain robust spectroscopic redshifts for more than half the targets. The majority of the confirmed sources are star-forming galaxies at z > 1.5. In addition to the radio galaxy, two of its close-by companions (<6″) also show AGN signatures. Ten sources, including the radio galaxy, lie within | z − 2.020 | <0.015 (i.e., velocity offsets <1500 km s-1) and within projected 2 Mpc comoving of the radio galaxy. Additional evidence suggests not only that the galaxy structure associated with MRC 0156-252 is a forming galaxy cluster but also that this structure is most probably embedded in a larger-scale structure
Recommended from our members
The Spectrally Resolved Lyman-Alpha Emission Of Three Lyman-Alpha-Selected Field Galaxies At Z Similar To 2.4 From The HETDEX Pilot Survey
No full textWe present new results on the spectrally resolved Ly alpha emission of three Ly alpha-emitting field galaxies at z similar to 2.4 with high Lya equivalent width (> 100 angstrom) and Lya luminosity (similar to 10(43) erg s(-1)). At 120 km s(-1) (FWHM) spectral resolution, the prominent double-peaked Lya profile straddles the systemic velocity, where the velocity zero point is determined from spectroscopy of the galaxies' rest-frame optical nebular emission lines. The average velocity offset from systemic of the stronger redshifted emission component for our sample is 176 km s(-1) while the average total separation between the redshifted and main blueshifted emission components is 380 km s(-1). These measurements are a factor of similar to 2 smaller than for UV-continuum-selected galaxies that show Lya in emission with lower Lya equivalent widths. We compare our Lya spectra to the predicted line profiles of a spherical "expanding shell" Ly alpha radiative transfer grid that models large-scale galaxy outflows. Specifically, blueward of the systemic velocity where two galaxies show a weak, highly blueshifted (by similar to 1000 km s(-1)) tertiary emission peak, the model line profiles are a relatively poor representation of the observed spectra. Since the neutral gas column density has a dominant influence over the shape of the Lya line profile, we caution against equating the observed Lya velocity offset with a physical outflow velocity, especially at lower spectral resolution where the unresolved Lya velocity offset is a convoluted function of several degenerate parameters. Referring to rest-frame ultraviolet and optical Hubble Space Telescope imaging, we find that galaxy-galaxy interactions may play an important role in inducing a starburst that results in copious Lya emission as well as perturbing the gas distribution and velocity field, both of which have strong influence over the Lya emission line profile.National Science Foundation AST-0926815Texas Norman Hackerman Advanced Research Program 003658-0295-2007Astronom
Taking snapshots of the jet-ISM interplay with ALMA
Full text linkWe present an update of our ongoing project to characterise the impact of radio jets on the interstellar medium (ISM). This is done by tracing the distribution, kinematics and excitation of the molecular gas at high spatial resolution using ALMA. The radio active galactic nuclei (AGN) studied are in the interesting phase of having a recently born radio jet. In this stage, the plasma jets can have the largest impact on the ISM, as also predicted by state-of-the-art simulations. The two targets we present have quite different ages, allowing us to get snapshots of the effects of radio jets as they grow and evolve. Interestingly, both also host powerful quasar emission, making them ideal for studying the full impact of AGN. The largest mass outflow rate of molecular gas is found in a radio galaxy () hosting a newly born radio jet still in the early phase of emerging from an obscuring cocoon of gas and dust. Although the molecular mass outflow rate is high (few hundred), the outflow is limited to the inner few hundred pc region. In a second object (), the jet is larger (a few kpc) and is in a more advanced evolutionary phase. In this object, the distribution of the molecular gas is reminiscent of what is seen, on larger scales, in cool-core clusters hosting radio galaxies. Interestingly, gas deviating from quiescent kinematics (possibly indicating an outflow) is not very prominent, limited only to the very inner region, and has a low mass outflow rate. Instead, on kpc scales, the radio lobes appear associated with depressions in the distribution of the molecular gas. This suggests that the lobes have broken out from the dense nuclear region. However, the AGN does not appear to be able, at present, to stop the star formation observed in this galaxy. These results support the idea that the effects of the radio source start in the very first phases by producing outflows which, however, tend to be limited to the kpc region. After that, the effects turn into producing large-scale bubbles which could, in the long term, prevent the surrounding gas from cooling. Thus, our results provide a way to characterise the effect of radio jets in different phases of their evolution and in different environments, bridging the studies done for radio galaxies in clusters
Constraining the physics of carbon crystallization through pulsations of a massive DAV BPM37093
Full text linkWe are trying to reduce the largest uncertainties in using white dwarf stars as Galactic chronometers by understanding the details of carbon crystalliazation that currently result in a 1–2 Gyr uncertainty in the ages of the oldest white dwarf stars. We expect the coolest white dwarf stars to have crystallized interiors, but theory also predicts hotter white dwarf stars, if they are massive enough, will also have some core crystallization. BPM 37093 is the first discovered of only a handful of known massive white dwarf stars that are also pulsating DAV, or ZZ Ceti, variables. Our approach is to use the pulsations to constrain the core composition and amount of crystallization. Here we report our analysis of 4 hours of continuous time series spectroscopy of BPM 37093 with Gemini South combined with simultaneous time-series photometry from Mt. John (New Zealand), SAAO, PROMPT, and Complejo Astronomico El Leoncito (CASLEO, Argentina).Fil: Nitta, Atsuko. Gemini Observatory; Estados UnidosFil: Kepler, S. O.. Universidade Federal do Rio Grande do Sul; BrasilFil: Chené, André Nicolás. Gemini Observatory; Estados UnidosFil: Koester, D.. Universitat Kiel; AlemaniaFil: Provencal, J. L.. University of Delaware; Estados UnidosFil: Kleinmani, S. J.. Gemini Observatory; Estados UnidosFil: Sullivan, D. J.. Victoria University of Wellington; Nueva ZelandaFil: Chote, Paul. University of Warwick; Reino UnidoFil: Sefako, Ramotholo. South African Astronomical Observatory; SudáfricaFil: Kanann, Antonio. Universidade Federal de Santa Catarina; BrasilFil: Romero, Alejandra D.. Universidade Federal do Rio Grande do Sul; BrasilFil: Corti, Mariela Alejandra. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Kilic, Mukremin. University of Oklahoma; Estados UnidosFil: Montgomery, M. H.. University of Texas at Austin; Estados UnidosFil: Winget, D.. University of Texas at Austin; Estados UnidosXXIX IAU General AssemblyHonoluluEstados UnidosInternational Astronomical Unio
Emergence of cosmic structures around distant radio galaxies and quasars
Full text linkThis thesis presents observational evidence for the formation of galaxy clusters associated with distant radio galaxies and quasars.Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UBL - phd migration 201
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
