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| 2. |
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| 3. |
- Bakx, Tom, 1990, et al.
(författare)
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A dusty protocluster surrounding the binary galaxy HerBS-70 at z = 2.3
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 530:4, s. 4578-4596
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Tidskriftsartikel (refereegranskat)abstract
- We report on deep SCUBA-2 observations at 850 μm and NOrthern Extended Millimetre Array (NOEMA) spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive (M∗ ≈ 2 × 1011 M☉) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at z = 2.3, with the east component (HerBS-70E) hosting an active galactic nucleus. The SCUBA-2 observations detected, in addition to the binary system, 21 sources at >3.5σ over an area of ∼25 square comoving Mpc with a sensitivity of 1σ850 = 0.75 mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4–3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times (80−500 Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around 5 × 1013 M☉, with a projected current-day mass of 1015 M☉, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.
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| 4. |
- Berta, S., et al.
(författare)
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z -GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies: III. Physical properties
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- The z-GAL survey observed 137 bright Herschel-selected targets with the IRAM Northern Extended Millimeter Array, with the aim to measure their redshift and study their properties. Several of them have been resolved into multiple sources. Consequently, robust spectroscopic redshifts have been measured for 165 individual galaxies in the range 0.8., <., z., <., 6.5. In this paper we analyse the millimetre spectra of the z-GAL sources, using both their continuum and line emission to derive their physical properties. At least two spectral lines are detected for each source, including transitions of 12CO, [CI], and H2O. The observed 12CO line ratios and spectral line energy distributions of individual sources resemble those of local starbursts. In seven sources the para-H2O (211-202) transition is detected and follows the IR versus H2O luminosity relation of sub-millimetre galaxies. The molecular gas mass of the z-GAL sources is derived from their 12CO, [CI], and sub-millimetre dust continuum emission. The three tracers lead to consistent results, with the dust continuum showing the largest scatter when compared to 12CO. The gas-to-dust mass ratio of these sources was computed by combining the information derived from 12CO and the dust continuum and has a median value of 107, similar to star-forming galaxies of near-solar metallicity. The same combined analysis leads to depletion timescales in the range between 0.1 and 1.0 Gyr, which place the z-GAL sources between the main sequence' of star formation and the locus of starbursts. Finally, we derived a first estimate of stellar masses "modulo possible gravitational magnification "by inverting known gas scaling relations: the z-GAL sample is confirmed to be mostly composed by starbursts, whereas ∼25% of its members lie on the main sequence of star-forming galaxies (within ±0.5 dex).
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| 5. |
- Cox, P., et al.
(författare)
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z-GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies: I. Overview
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- Using the IRAM NOrthern Extended Millimetre Array (NOEMA), we conducted a Large Programme (z-GAL) to measure redshifts for 126 bright galaxies detected in the Herschel Astrophysical Large Area Survey (H-ATLAS), the HerMES Large Mode Survey (HeLMS), and the Herschel Stripe 82 (HerS) Survey. We report reliable spectroscopic redshifts for a total of 124 of the Herschel-selected galaxies. The redshifts are estimated from scans of the 3 and 2-mm bands (and, for one source, the 1-mm band), covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. Together with the Pilot Programme, where 11 sources had their spectroscopic redshifts measured, our survey has derived precise redshifts for 135 bright Herschel-selected galaxies, making it the largest sample of high-z galaxies with robust redshifts to date. Most emission lines detected are from 12CO (mainly from J = 2 1 to 5 4), with some sources seen in [CI] and H2O emission lines. The spectroscopic redshifts are in the range 0.8
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| 6. |
- Ismail, D., et al.
(författare)
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z-GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies: II. Dust properties
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- We present the dust properties of 125 bright Herschel galaxies selected from the z-GAL NOEMA spectroscopic redshift survey. All the galaxies have precise spectroscopic redshifts in the range 1.3 < z < 5.4. The large instantaneous bandwidth of NOEMA provides an exquisite sampling of the underlying dust continuum emission at 2 and 3 mm in the observed frame, with flux densities in at least four sidebands for each source. Together with the available Herschel 250, 350, and 500 μm and SCUBA-2 850 μm flux densities, the spectral energy distribution (SED) of each source can be analyzed from the far-infrared to the millimeter, with a fine sampling of the Rayleigh-Jeans tail. This wealth of data provides a solid basis to derive robust dust properties, in particular the dust emissivity index (β) and the dust temperature (Tdust). In order to demonstrate our ability to constrain the dust properties, we used a flux-generated mock catalog and analyzed the results under the assumption of an optically thin and optically thick modified black body emission. The robustness of the SED sampling for the z-GAL sources is highlighted by the mock analysis that showed high accuracy in estimating the continuum dust properties. These findings provided the basis for our detailed analysis of the z-GAL continuum data. We report a range of dust emissivities with β ∼1.5 -3 estimated up to high precision with relative uncertainties that vary in the range 7% 15%, and an average of 2.2 ± 0.3. We find dust temperatures varying from 20 to 50 K with an average of Tdust., ∼30 K for the optically thin case and Tdust., ∼38 K in the optically thick case. For all the sources, we estimate the dust masses and apparent infrared luminosities (based on the optically thin approach). An inverse correlation is found between Tdust and β with β Tdust-0.69, which is similar to what is seen in the local Universe. Finally, we report an increasing trend in the dust temperature as a function of redshift at a rate of 6.5 ±0.5 K/z for this 500 μm-selected sample. Based on this study, future prospects are outlined to further explore the evolution of dust temperature across cosmic time.
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| 7. |
- Buscaglia, M. T., et al.
(författare)
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Ferroelectric properties of dense nanocrystalline BaTiO3 ceramics
- 2004
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 15:9, s. 1113-1117
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Tidskriftsartikel (refereegranskat)abstract
- Dense BaTiO3 ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data show a broad ferro-para phase transition with a maximum permittivity of approximate to1100 at 390 K and 1 kHz. The local ferroelectric switching behaviour was investigated by piezoresponse force microscopy. Typical piezoelectric hysteresis loops were recorded at different positions of the sample. The present results provide experimental evidence for polarization switching at the local scale, indicating that the critical grain size for the disappearance of ferroelectric behaviour in dense, bulk BaTiO3 nanocrystalline ceramics is below 50 nm.
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| 8. |
- Buscaglia, V., et al.
(författare)
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Nanostructured barium titanate ceramics
- 2004
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 148:1, s. 24-27
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Tidskriftsartikel (refereegranskat)abstract
- Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO3) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 degreesC of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing. Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.
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| 9. |
- Zhao, Zhe, 1973-, et al.
(författare)
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Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Institute of Physics (AIP). - 1098-0121 .- 1550-235X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- A progressive reduction of tetragonal distortion, heat of transition, Curie temperature, and relative dielectric constant has been observed on dense BaTiO3 ceramics with grain size decreasing from 1200 to 50 nm. The correlations between grain size, extent of tetragonal distortion, and ferroelectric properties strongly support the existence of an intrinsic size effect. From the experimental trends the critical size for disappearance of ferroelectricity has been evaluated to be 10-30 nm. The strong depression of the relative permittivity observed for the nanocrystalline ceramics can be ascribed to the combination of the intrinsic size effect and of the size-dependent "dilution" effect of a grain boundary "dead" layer.
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| 10. |
- Buscaglia, M. T., et al.
(författare)
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High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:6
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical models for small ferroelectric particles predict a progressive decrease of the Curie temperature, spontaneous lattice strain, and polarization until the critical size corresponding to transition to the cubic phase and disappearance of ferroelectricity is reached. In contrast, the behavior of nanocrystalline BaTiO3 ceramics with a grain size of approximate to 30 nm is dominated by extrinsic effects related to the grain boundaries which mask the expected downscaling of properties. While the noncubic crystal structure, the high dielectric constant (approximate to 1600) and the variation of permittivity with temperature suggest a ferroelectric behavior, very slim, and nearly linear polarization hysteresis loops are observed. Evidence for the existence of a ferroelectric domain structure with domains extending over several grains and of polarization switching at local scale is given by piezoresponse force microscopy. The suppression of macroscopic ferroelectric hysteresis and switching originates from a frozen domain structure stable under an external field owing to the effects exerted by the grain boundaries, such as the clamping of the domain walls and the hindrance of polarization switching. Furthermore, the depolarization field originated by the low-permittivity nonferroelectric grain boundaries can cause a significant reduction of polarization. If the grain size is small enough, the ceramic is expected to undergo a "phase transition" to a polar phase with nonswitchable polarization. The BaTiO3 ceramics with grain size of 30 nm investigated in the present study are deemed to be close to this transition.
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