LARGE-SCALE STRUCTURE AROUND A z = 2.1 CLUSTER Hung (洪肇伶), Chao-Ling; Casey, Caitlin M.; Chiang, Yi-Kuan ...
The Astrophysical journal,
08/2016, Letnik:
826, Številka:
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ABSTRACT The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with large-scale environments is less clear at . We present a search of large-scale ...structure around a galaxy cluster core at z = 2.095 using a set of spectroscopically confirmed galaxies. We find that both color-selected star-forming galaxies (SFGs) and dusty star-forming galaxies (DSFGs) show significant overdensities around the z = 2.095 cluster. A total of eight DSFGs (including three X-ray luminous active galactic nuclei, AGNs) and 34 SFGs are found within a 10′ radius (corresponds to ∼15 cMpc at ) from the cluster center and within a redshift range of , which leads to galaxy overdensities of and . The cluster core and the extended DSFG- and SFG-rich structures together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large-scale structure while the more mature core may begin to virialize. Our finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare sources indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 m images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.
We map the radial and azimuthal distribution of Mg II gas within ~ 200 kpc (physical) of ~ 4000 galaxies at redshifts 0.5 < z < 0.9 using co-added spectra of more than 5000 background galaxies at z > ...1. We investigate the variation of Mg II rest-frame equivalent width (EW) as a function of the radial impact parameter for different subsets of foreground galaxies selected in terms of their rest-frame colors and masses. Blue galaxies have a significantly higher average Mg II EW at close galactocentric radii as compared to the red galaxies. Among the blue galaxies, there is a correlation between Mg II EW and galactic stellar mass of the host galaxy. We also find that the distribution of Mg II absorption around group galaxies is more extended than that for non-group galaxies, and that groups as a whole have more extended radial profiles than individual galaxies. Interestingly, these effects can be satisfactorily modeled by a simple superposition of the absorption profiles of individual member galaxies, assuming that these are the same as those of non-group galaxies, suggesting that the group environment may not significantly enhance or diminish the Mg II absorption of individual galaxies. We show that there is a strong azimuthal dependence of the Mg II absorption within 50 kpc of inclined disk-dominated galaxies, indicating the presence of a strongly bipolar outflow aligned along the disk rotation axis. There is no significant dependence of Mg II absorption on the apparent inclination angle of disk-dominated galaxies.
A blind H i survey in the Canes Venatici region Kovač, K.; Oosterloo, T. A.; Van Der Hulst, J. M.
Monthly notices of the Royal Astronomical Society,
December 2009, Letnik:
400, Številka:
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We have carried out a blind H i survey using the Westerbork Synthesis Radio Telescope to make an inventory of objects with small H i masses (between 106 and 108 M⊙) and to constrain the low-mass end ...of the H i mass function. The survey has been conducted in a part of the volume containing the nearby Canes Venatici groups of galaxies. The surveyed region covers an area on the sky of about 86 deg2 and a range in velocity from about −450 to about 1330 km s−1. We find 70 sources in the survey by applying an automated searching algorithm. Two of the detections have not been catalogued previously, but they can be assigned an optical counterpart, based on visual inspection of the second-generation Digital Sky Survey images. Only one of the H i detections is without an optical counterpart. This object is detected in the vicinity of NGC 4822, and it has been already detected in previous H i studies. 19 of the objects have been detected for the first time in the 21-cm emission line in this survey. The distribution of the H i properties of our detections confirms our ability to find low-mass objects. 86 per cent of the detections have profile widths less than 130 km s−1, and they can be considered dwarf galaxy candidates. The H i fluxes measured imply that this survey goes about 10 times deeper than any previous blind H i survey. The H i mass function and the optical properties of the detected sources will be discussed in future papers.
We present new improved constraints on the Hubble parameter H(z) in the red-shift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of ...redshift. We provide 8 new measurements of H(z) (see table 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z ~ 1.1; for the first time, we place a constraint on H(z) at z not = to 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z ~ 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z ~ 2.
Aims. We present a study of a large filamentary structure at z ~ 0.73 in the field of the COSMOS survey, the so-called COSMOS Wall. This structure encompasses a comprehensive range of environments ...from a dense cluster and a number of galaxy groups to filaments, less dense regions, and adjacent voids. It thus provides a valuable laboratory for the accurate mapping of environmental effects on galaxy evolution at a look-back time of ~6.5 Gyr, when the Universe was roughly half its present age. Methods. We performed deep spectroscopic observations with VIMOS at VLT of a K-band selected sample of galaxies in this complex structure, building a sample of galaxies complete in galaxy stellar mass down to a lower limit of log(ℳ∗/ℳ⊙) ~ 9.8, which is significantly deeper than previously available data. Thanks to its location within the COSMOS survey, each galaxy benefits from a wealth of ancillary information: HST-ACS data with I-band exposures down to IAB ~ 28 complemented by extensive multiwavelength ground- and space-based observations spanning the entire electromagnetic spectrum. Results. In this paper we detail the survey strategy and weighting scheme adopted to account for the biases introduced by the photometric preselection of our targets. We present our galaxy stellar mass and rest-frame magnitudes estimates together with a group catalog obtained with our new data and their member galaxies color/mass distribution. Conclusions. Owing to our new sample we can perform a detailed, high definition mapping of the complex COSMOS Wall structure. The sharp environmental information, coupled with high quality spectroscopic information and rich ancillary data available in the COSMOS field, enables a detailed study of galaxy properties as a function of local environment in a redshift slice where environmental effects are important, and in a stellar mass range where mass and environment driven effects are both at work.
Context. Galaxies migrate along filaments of the cosmic web from small groups to clusters, which creates the appearance that the evolution of their properties speeds up as environments get denser. ...Aims. We introduce the M USE gAlaxy Groups in C OSMOS (MAGIC) survey, which was built to study the impact of environment on galaxy evolution down to low stellar masses over the last 8 Gyr. Methods. The MAGIC survey consists of 17 Multi-Unit Spectrocopic Exporer (MUSE) fields targeting 14 massive, known structures at intermediate redshift (0.3 < z < 0.8) in the COSMOS area, with a total on-source exposure of 67 h. We securely measured the redshifts for 1419 sources and identified 76 galaxy pairs and 67 groups of at least three members using a friends-of-friends algorithm. The environment of galaxies is quantified from group properties, as well as from global and local density estimators. Results. The MAGIC survey has increased the number of objects with a secure spectroscopic redshift over its footprint by a factor of about 5 compared to previous extensive spectroscopic campaigns on the COSMOS field. Most of the new redshifts have apparent magnitudes in the z ++ band z app ++ > 21.5. The spectroscopic redshift completeness is high: in the redshift range of O II emitters (0.25 ≤ z < 1.5), where most of the groups are found, it globally reaches a maximum of 80% down to z app ++ = 25.9, and locally decreases from ∼100% to ∼50% in magnitude bins from z app ++ = 23−24 to z app ++ = 25.5. We find that the fraction of quiescent galaxies increases with local density and with the time spent in groups. A morphological dichotomy is also found between bulge-dominated quiescent and disk-dominated star-forming galaxies. As environment gets denser, the peak of the stellar mass distribution shifts towards M ⋆ > 10 10 M ⊙ , and the fraction of galaxies with M ⋆ < 10 9 M ⊙ decreases significantly, even for star-forming galaxies. We also highlight peculiar features such as close groups, extended nebulae, and a gravitational arc. Conclusions. Our results suggest that galaxies are preprocessed in groups of increasing mass before entering rich groups and clusters. We publicly release two catalogs containing the properties of galaxies and groups, respectively.
Void galaxies, residing within the deepest underdensities of the Cosmic Web, present an ideal population for the study of galaxy formation and evolution in an environment undisturbed by the complex ...processes modifying galaxies in clusters and groups, as well as provide an observational test for theories of cosmological structure formation. We have completed a pilot survey for the H I imaging aspects of a new Void Galaxy Survey (VGS), imaging 15 void galaxies in H I in local (d < 100 Mpc) voids. H I masses range from 3.5 X 108 to 3.8 X 109 M , with one nondetection with an upper limit of 2.1 X 108 M . Our galaxies were selected using a structural and geometric technique to produce a sample that is purely environmentally selected and uniformly represents the void galaxy population. In addition, we use a powerful new backend of the Westerbork Synthesis Radio Telescope that allows us to probe a large volume around each targeted galaxy, simultaneously providing an environmentally constrained sample of fore- and background control samples of galaxies while still resolving individual galaxy kinematics and detecting faint companions in H I. This small sample makes up a surprisingly interesting collection of perturbed and interacting galaxies, all with small stellar disks. Four galaxies have significantly perturbed H I disks, five have previously unidentified companions at distances ranging from 50 to 200 kpc, two are in interacting systems, and one was found to have a polar H I disk. Our initial findings suggest void galaxies are a gas-rich, dynamic population which present evidence of ongoing gas accretion, major and minor interactions, and filamentary alignment despite the surrounding underdense environment.
We estimate the two-point correlation function in redshift space of the recently compiled H i Parkes All-Sky Survey neutral hydrogen (H i) sources catalogue, which if modelled as a power law, ξ(r) = ...(r0/r)γ, the best-fitting parameters for the H i selected galaxies are found to be r0= 3.3 ± 0.3 h−1 Mpc with γ= 1.38 ± 0.24. Fixing the slope to its universal value γ= 1.8, we obtain r0= 3.2 ± 0.2 h−1 Mpc. Comparing the measured two-point correlation function with the predictions of the concordance cosmological model (ΩΛ= 0.74), we find that at the present epoch the H i selected galaxies are antibiased with respect to the underlying matter fluctuation field with their bias value being b0≃ 0.68. Furthermore, dividing the H i galaxies into two richness subsamples we find that the low-mass H i galaxies have a very low present bias factor (b0≃ 0.48), while the high-mass H i galaxies trace the underlying matter distribution as the optical galaxies (b0≃ 1). Using our derived present-day H i galaxy bias we estimate their redshift-space distortion parameter, and correct accordingly the correlation function for peculiar motions. The resulting real-space correlation length is rre0= 1.8 ± 0.2 h−1 Mpc and rre0= 3.9 ± 0.6 h−1 Mpc for the low- and high-mass H i galaxies, respectively. The low-mass H i galaxies appear to have the lowest correlation length among all extragalactic populations studied to date. In order to corroborate these results we have correlated the IRAS–Point Source Catalogue for Redshift (PSCz) reconstructed density field, smoothed over scales of 5 h−1 Mpc, with the positions of the H i galaxies, to find that indeed the H i galaxies are typically found in negative overdensity regions (δρ/ρPSCz≲ 0), even more so the low-mass H i galaxies. Finally, we also study the redshift evolution of the H i galaxy linear bias factor and find that the H i-galaxy population is antibiased up to z∼ 1.3. While at large redshifts z∼ 3, we predict that the H i galaxies are strongly biased. Our bias evolution predictions are consistent with the observational bias results of Lyα galaxies.
We explore the role of environment in the evolution of galaxies over 0.1 < z < 0.7 using the final zCOSMOS-bright data set. Using the red fraction of galaxies as a proxy for the quenched population, ...we find that the fraction of red galaxies increases with the environmental overdensity δ and with the stellar mass M
*, consistent with previous works. As at lower redshift, the red fraction appears to be separable in mass and environment, suggesting the action of two processes: mass m(M
*) and environmental ρ(δ) quenching. The parameters describing these appear to be essentially the same at z ∼ 0.7 as locally. We explore the relation between red fraction, mass and environment also for the central and satellite galaxies separately, paying close attention to the effects of impurities in the central-satellite classification and using carefully constructed samples well matched in stellar mass. There is little evidence for a dependence of the red fraction of centrals on overdensity. Satellites are consistently redder at all overdensities, and the satellite quenching efficiency, sat(δ, M
*), increases with overdensity at 0.1 < z < 0.4. This is less marked at higher redshift, but both are nevertheless consistent with the equivalent local measurements. At a given stellar mass, the fraction of galaxies that are satellites, f
sat(δ, M
*), also increases with overdensity. The obtained ρ(δ)/f
sat(δ, M
*) agrees well with sat(δ, M
*), demonstrating that the environmental quenching in the overall population is consistent with being entirely produced by a satellite quenching process at least up to z = 0.7. However, despite the unprecedented size of our high-redshift samples, the associated statistical uncertainties are still significant and our statements should be understood as approximations to physical reality, rather than physically exact formulae.
We investigate full quantum mechanical evolution of two electrons nonlinearly coupled to quantum phonons and simulate the dynamical response of the system subject to a short spatially uniform optical ...pulse that couples to dipole-active vibrational modes. Nonlinear electron-phonon coupling can either soften or stiffen the phonon frequency in the presence of electron density. In the former case, an external optical pulse tuned just below the phonon frequency generates attraction between electrons and leads to a long-lived bound state even after the optical pulse is switched off. It originates from a dynamical modification of the self-trapping potential that induces a metastable state. By increasing the pulse frequency, the attractive electron-electron interaction changes to repulsive. Two sequential optical pulses with different frequencies can switch between attractive and repulsive interaction. Finally, we show that the pulse-induced binding of electrons is shown to be efficient also for weakly dispersive optical phonons, in the presence anharmonic phonon spectrum and in two dimensions.
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