Rest-frame ultra-violet spectra of massive galaxies at z=3: evidence of high-velocity outflows

Galaxy formation models invoke the presence of strong feedback mechanisms that regulate the growth of massive galaxies at high redshifts. In this paper we aim to: (1) confirm spectroscopically the redshifts of a sample of massive galaxies selected with photometric redshifts z > 2.5; (2) investigate the properties of their stellar and interstellar media; (3) detect the presence of outflows, and measure their velocities. To achieve this, we analysed deep, high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We also serendipitously found two mask fillers at redshift z > 2.5, which originally were assigned photometric redshifts 2.0 < z < 2.5. In the four highest-quality spectra we derived outflow velocities by fitting the absorption line profiles with models including multiple dynamical components. We found strongly asymmetric, high-ionisation lines, from which we derived outflow velocities ranging from 480 to 1518 km/s. The two galaxies with highest velocity show signs of AGN. We revised the spectral energy distribution fitting U-band through 8 micron photometry, including the analysis of a power-law component subtraction to identify the possible presence of active galactic nuclei (AGN). The revised stellar masses of all but one of our targets are >1e10 Msun, with four having stellar masses > 5e10 Msun. Three galaxies have a significant power-law component in their spectral energy distributions, which indicates that they host AGN. We conclude that massive galaxies are characterised by significantly higher velocity outflows than the typical Lyman break galaxies at z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also much higher than among massive galaxies at z < 1, which is consistent with the powerful star formation and nuclear activity that most massive galaxies display at z > 2.Comment: 17 pages, 14 figures, Accepted for publication in A&

Exploring transmission Kikuchi diffraction using a Timepix detector

Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70° to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2,3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4,5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods

Frequency modulated few-cycle optical pulse trains induced controllable ultrafast coherent population oscillations in three-level atomic systems

We report a study on the ultrafast coherent population oscillations (UCPO) in two level atoms induced by the frequency modulated few-cycle optical pulse train. The phenomenon of UCPO is investigated by numerically solving the optical Bloch equations beyond the rotating wave approximation. We demonstrate that the quantum state of the atoms and the frequency of UCPO may be controlled by controlling the number of pulses in the pulse trains and the pulse repetition time respectively. Moreover, the robustness of the population inversion against the variation of the laser pulse parameters is also investigated. The proposed scheme may be useful for the creation of atoms in selected quantum state for desired time duration and may have potential applications in ultrafast optical switching

Synchronous Evolution of Galaxies in Groups: NGC 524 Group

By means of panoramic spectroscopy at the SAO RAS BTA telescope, we investigated the properties of stellar populations in the central regions of five early-type galaxies -- the NGC 524 group members. The evolution of the central regions of galaxies looks synchronized: the average age of stars in the bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr ago. The only galaxy, in which the ages of stellar population in the nucleus and in the bulge coincide (i.e. the nuclear burst of star formation did not take place) is NGC 502, the farthest from the center of the group of all the galaxies studied.Comment: Slightly edited version of the paper to appear in the Astrophysical Bulletin, 67(3); 24 pages including 8 figure

Stellar populations of Virgo cluster early-type dwarf galaxies with and without discs: a dichotomy in age?

[Abridged] Using VLT/FORS2 spectroscopy, we have studied the properties of the central stellar populations of a sample of 38 nucleated early-type dwarf (dE) galaxies in the Virgo Cluster. We find that these galaxies do not exhibit the same average stellar population characteristics for different morphological subclasses. The nucleated galaxies without discs are older and more metal poor than the dEs with discs . The alpha-element abundance ratio appears consistent with the solar value for both morphological types. Besides a well-defined relation of metallicity and luminosity, we also find a clear anti-correlation between age and luminosity. More specifically, there appears to be a bimodality: brighter galaxies, including the discy ones, exhibit significantly younger ages than fainter dEs. Therefore, it appears less likely that fainter and brighter dEs have experienced the same evolutionary history, as the well-established trend of decreasing average stellar age when going from the most luminous ellipticals towards low-luminosity Es and bright dEs is broken here. The older and more metal-poor dEs could have had an early termination of star formation activity, possibly being "primordial" galaxies in the sense that they have formed along with the protocluster or experienced very early infall. By contrast, the younger and relatively metal-rich brighter dEs, most of which have discs, might have undergone structural transformation of infalling disc galaxies.Comment: Accepted by MNRAS; 22 pages, 20 figure

The stellar population histories of early-type galaxies. III. The Coma Cluster

We present stellar population parameters of twelve early-type galaxies (ETGs) in the Coma Cluster based on spectra obtained using the Low Resolution Imaging Spectrograph on the Keck II Telescope. Our data allow us to examine in detail the zero-point and scatter in their stellar population properties. Our ETGs have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with the oldest galaxies having ages of ~10 Gyr old. This average age is identical to the mean age of field ETGs. Our ETGs span a large range in velocity dispersion but are consistent with being drawn from a population with a single age. Specifically, ten of the twelve ETGs are consistent within their formal errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in mass. We therefore find no evidence for downsizing of the stellar populations of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may have formed the majority of their mass at high redshifts but suffered small but detectable star formation events at z~0.1-0.3. Previous detections of 'downsizing' from stellar populations of local ETGs may not reflect the same downsizing seen in lookback studies of RSGs, as the young ages of the local ETGs represent only a small fraction of their total masses. (abridged)Comment: 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version with full resolution of Fig. 1 see http://www.astro.rug.nl/~sctrager/coma.pdf; for Table 2, see http://www.astro.rug.nl/~sctrager/coma_table2.pdf; for Table B3, see http://www.astro.rug.nl/~sctrager/coma_tableB3.pd

Radiokemian relevanssi : Tulevien radiokemistien käsityksiä

Radiokemi står inför en väldokumenterad utbildning och rekryteringskris. Äldre radiokemister går i pension och färre unga studerar radiokemi. I sin tur leder detta till brist på nyutbildade radiokemister, såväl som förlust av historisk kunskap (eftersom kunskap ofta inte förmedlas). Här analyserade vi relevansen av studien av radiokemi i högre utbildning genom framtida radiokemists uppfattningar. Vårt mål var att ge inblick i framtida radiokemisternas tänkande och ge några tydliga exempel på hur man stöder relevans. En kvalitativ studie genomfördes genom en forskningsfråga: Vilka uppfattningar om relevans upplever framtida radiokemister om radiokemistudier och radiokemi som fält? Vi använde relevansmodellen av Stuckey et al. (2013) som ram för relevans. Detta valdes eftersom det erbjuder en omfattande definition av relevans inklusive individuella, samhälleliga och yrkesmässiga dimensioner. Uppgifterna samlades in från forskarstudenter i radiokemi (magister- och doktorsexamen) genom användning av ett kvalitativt frågeformulär som utformades med den valda relevansramen. Totalt deltog 15 framtida radiokemister i studien. Uppgifterna analyserades genom teoribaserad innehållsanalys med användning av det valda relevansramverket. Enligt våra uppgifter upplever framtida radiokemister att deras universitetsstudier och kemifältet är mycket relevanta. De upplevde att ämnen för radiokemi är intressanta (individuell relevans), fältet har stor samhällseffekt genom radiofarmaceutika, energilösningar och miljöproblemlösning (samhällsrelevans) och att deras professionella framtid var tydlig, till exempel ett jobb inom kärnkraftsområdet industri (yrkesrelevans). Dessa resultat kan användas för studentrekrytering och för att utveckla radiokemiundervisning mot en mer relevant inriktning.Radiokemialla on koulutus- ja rekrytointikriisi. Vanhemmat radiokemistit siirtyvät eläkkeelle, ja yhä vähemmän nuoria valitsee radiokemiaa opiskelualakseen. Asetelman vuoksi on pulaa pätevistä radiokemisteistä, ja hiljaista tietoa häviää. Tässä tutkimuksessa selvitetään tulevien radiokemistien kokemuksia radiokemian relevanssista. Tavoitteena on selvittää, miksi radiokemiaa valinneet opiskelijat ovat alan valinneet. Tutkimus oli luonteeltaan laadullinen tutkimus. Aineisto kerättiin sähköpostikyselyillä sisältäen kaksi aineistonkeruusykliä. Ainesot analysoitiin teoriapohjaisella sisällnöanalyysillä tunnetun Stuckeyn et al. (2013) relevanssia hyödyntäen. Tutkimuksen mukaan tulevat radiokemistit kokivat alan erittäin relevanssiksi. He kokivat, että radiokemian olevan mielenkiintoista (henkilökohtainen relevanssi), radiokemian yhteiskunnallisen merkityksen olevan suuri esim. lääke- ja energiateollisuuden kautta (yhteiskunnallinen relevanssi) ja heillä oli selkeä kuva tulevaisuuden työllistymisestä (ammatillinen relevanssi). Tutkimuksen tuloksia voidaan käyttää opiskelijoiden rekrytointiin ja radiokemian opetuksen relevanssin vahvistamiseen.Radiochemistry faces a well-documented training and recruitment crisis. Older radiochemists are retiring, and fewer young people are studying radiochemistry. In turn, this is leading to a shortage in newly qualified radiochemists, as well as a loss of historical knowledge (as know-how is often not passed-on). Here, we analyzed the relevance of the study of radiochemistry in higher education through future radiochemists’ perceptions. Our objective was to provide insights into future radiochemists’ thinking and provide some clear examples on how to support relevance. A qualitative study was conducted through a research question: What perceptions of relevance do future radiochemists experience about radiochemistry studies and radiochemistry as a field? We used the relevance model of Stuckey et al. (2013) as the relevance framework. This was selected because it offers a comprehensive definition of relevance including individual, societal, and vocational dimensions. The data were gathered from postgraduate radiochemistry students (masters and Ph.D. level) through use of a qualitative questionnaire that was designed using the selected relevance framework. In total, 15 future radiochemists participated in the study. The data were analyzed through theory-based content analysis using the selected relevance framework. According to our data, future radiochemists experience their university study and the chemistry field as being highly relevant. They experienced that radiochemistry topics are interesting (individual relevance), the field has great societal impact through radiopharmaceuticals, energy solutions, and environmental problem-solving (societal relevance), and that their professional future was clear, for example, a job in the nuclear industry (vocational relevance). These results can be used in student recruitment and in developing radiochemistry teaching toward a more relevance-oriented direction.Peer reviewe

Diffractive triangulation of radiative point sources

We describe a general method to determine the location of a point source of waves relative to a twodimensional single-crystalline active pixel detector. Based on the inherent structural sensitivity of crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the location of a wave emitter. The principle described here can be applied to various types of waves, provided that the detector elements are suitably structured. As a prototypical practical application of the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of microstructural crystal orientations, strains, and phase distributions