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- ItemThe Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX). III. A Red Quasar with Extremely High Equivalent Widths Showing Powerful Outflows(London : Institute of Physics Publ., 2022) Liu, Chenxu; Gebhardt, Karl; Kollatschny, Wolfram; Ciardullo, Robin; Mentuch Cooper, Erin; Davis, Dustin; Farrow, Daniel J.; Finkelstein, Steven L.; Gawiser, Eric; Gronwall, Caryl; Hill, Gary J.; House, Lindsay; Schneider, Donald P.; Urrutia, Tanya; Zeimann, Gregory R.We report an active galactic nucleus (AGN) with an extremely high equivalent width (EW), EWLyα+N V,rest ≳921 Å, in the rest frame, at z ∼ 2.24 in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX), as a representative case of the high-EW AGN population. The continuum level is a nondetection in the HETDEX spectrum; thus the measured EW is a lower limit. The source is detected with significant emission lines (>7σ) at Lyα + N v λ1241, C iv λ1549, and a moderate emission line (∼4σ) at He ii λ1640 within the wavelength coverage of HETDEX (3500-5500 Å). The r-band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit of r = 25.12 at 5σ. The Lyα emission line spans a clearly resolved region of ∼10″ (85 kpc) in diameter. The Lyα line profile is strongly double peaked. The spectral decomposed blue gas and red gas Lyα emission are separated by ∼1.″2 (10.1 kpc) with a line-of-sight velocity offset of ∼1100 km s−1. This source is probably an obscured AGN with powerful winds.
- ItemUltrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion(London : Institute of Physics Publ., 2022) Bell, Eric F.; Smercina, Adam; Price, Paul A.; D’Souza, Richard; Bailin, Jeremy; de Jong, Roelof S.; Gozman, Katya; Jang, In Sung; Monachesi, Antonela; Gnedin, Oleg Y.; Slater, Colin T.The faint and ultrafaint dwarf galaxies in the Local Group form the observational bedrock upon which our understanding of small-scale cosmology rests. In order to understand whether this insight generalizes, it is imperative to use resolved-star techniques to discover similarly faint satellites in nearby galaxy groups. We describe our search for ultrafaint galaxies in the M81 group using deep ground-based resolved-star data sets from Subaru’s Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the M81 group and identify five additional extremely low surface brightness candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to M V ∼ − 6 (similar to current limits for Andromeda satellites). These candidates’ luminosities and sizes are similar to known Local Group dwarf galaxies Tucana B, Canes Venatici I, Hercules, and Boötes I. Most of these candidates are likely to be real, based on tests of our techniques on blank fields. Intriguingly, all of these candidates are spatially clustered around NGC 3077, which is itself an M81 group satellite in an advanced state of tidal disruption. This is somewhat surprising, as M81 itself and its largest satellite M82 are both substantially more massive than NGC 3077 and, by virtue of their greater masses, would have been expected to host as many or more ultrafaint candidates. These results lend considerable support to the idea that satellites of satellites are an important contribution to the growth of satellite populations around Milky Way-mass galaxies.
- ItemDestabilization of super-rotating Taylor-Couette flows by current-free helical magnetic fields(London : Cambridge Univ. Press, 2021) Rüdiger, G.; Schultz, M.; Hollerbach, R.In an earlier paper we showed that the combination of azimuthal magnetic fields and super-rotation in Taylor–Couette flows of conducting fluids can be unstable against non-axisymmetric perturbations if the magnetic Prandtl number of the fluid is Pm≠1. Here we demonstrate that the addition of a weak axial field component allows axisymmetric perturbation patterns for Pm of order unity depending on the boundary conditions. The axisymmetric modes only occur for magnetic Mach numbers (of the azimuthal field) of order unity, while higher values are necessary for the non-axisymmetric modes. The typical growth time of the instability and the characteristic time scale of the axial migration of the axisymmetric mode are long compared with the rotation period, but short compared with the magnetic diffusion time. The modes travel in the positive or negative z direction along the rotation axis depending on the sign of BϕBz. We also demonstrate that the azimuthal components of flow and field perturbations travel in phase if |Bϕ|≫|Bz|, independent of the form of the rotation law. Within a short-wave approximation for thin gaps it is also shown (in an appendix) that for ideal fluids the considered helical magnetorotational instability only exists for rotation laws with negative shear.
- ItemInterpretation of Radio Wave Scintillation Observed through LOFAR Radio Telescopes(London : Institute of Physics Publ., 2022) Forte, Biagio; Fallows, Richard A.; Bisi, Mario M.; Zhang, Jinge; Krankowski, Andrzej; Dabrowski, Bartosz; Rothkaehl, Hanna; Vocks, ChristianRadio waves propagating through a medium containing irregularities in the spatial distribution of the electron density develop fluctuations in their intensities and phases. In the case of radio waves emitted from astronomical objects, they propagate through electron density irregularities in the interstellar medium, the interplanetary medium, and Earth’s ionosphere. The LOFAR radio telescope, with stations across Europe, can measure intensity across the VHF radio band and thus intensity scintillation on the signals received from compact astronomical objects. Modeling intensity scintillation allows the estimate of various parameters of the propagation medium, for example, its drift velocity and its turbulent power spectrum. However, these estimates are based on the assumptions of ergodicity of the observed intensity fluctuations and, typically, of weak scattering. A case study of single-station LOFAR observations of the strong astronomical source Cassiopeia A in the VHF range is utilized to illustrate deviations from ergodicity, as well as the presence of both weak and strong scattering. Here it is demonstrated how these aspects can lead to misleading estimates of the propagation medium properties, for example, in the solar wind. This analysis provides a method to model errors in these estimates, which can be used in the characterization of both the interplanetary medium and Earth’s ionosphere. Although the discussion is limited to the case of the interplanetary medium and Earth’s ionosphere, its ideas are also applicable to the case of the interstellar medium.
- ItemUltracold atom interferometry in space([London] : Nature Publishing Group UK, 2021) Lachmann, Maike D.; Ahlers, Holger; Becker, Dennis; Dinkelaker, Aline N.; Grosse, Jens; Hellmig, Ortwin; Müntinga, Hauke; Schkolnik, Vladimir; Seidel, Stephan T.; Wendrich, Thijs; Wenzlawski, André; Carrick, Benjamin; Gaaloul, Naceur; Lüdtke, Daniel; Braxmaier, Claus; Ertmer, Wolfgang; Krutzik, Markus; Lämmerzahl, Claus; Peters, Achim; Schleich, Wolfgang P.; Sengstock, Klaus; Wicht, Andreas; Windpassinger, Patrick; Rasel, Ernst M.Bose-Einstein condensates (BECs) in free fall constitute a promising source for space-borne interferometry. Indeed, BECs enjoy a slowly expanding wave function, display a large spatial coherence and can be engineered and probed by optical techniques. Here we explore matter-wave fringes of multiple spinor components of a BEC released in free fall employing light-pulses to drive Bragg processes and induce phase imprinting on a sounding rocket. The prevailing microgravity played a crucial role in the observation of these interferences which not only reveal the spatial coherence of the condensates but also allow us to measure differential forces. Our work marks the beginning of matter-wave interferometry in space with future applications in fundamental physics, navigation and earth observation.
- ItemPhase-Space Correlations among Systems of Satellite Galaxies(Basel : MDPI, 2021) Pawlowski, Marcel S.Driven by the increasingly complete observational knowledge of systems of satellite galaxies, mutual spatial alignments and relations in velocities among satellites belonging to a common host have become a productive field of research. Numerous studies have investigated different types of such phase-space correlations and were met with varying degrees of attention by the community. The Planes of Satellite Galaxies issue is maybe the best-known example, with a rich field of research literature and an ongoing, controversial debate on how much of a challenge it poses to the ΛCDM model of cosmology. Another type of correlation, the apparent excess of close pairs of dwarf galaxies, has received considerably less attention despite its reported tension with ΛCDM expectations. With the fast expansion of proper motion measurements in recent years, largely driven by the Gaia mission, other peculiar phase-space correlations have been uncovered among the satellites of the Milky Way. Examples are the apparent tangential velocity excess of satellites compared to cosmological expectations, and the unexpected preference of satellites to be close to their pericenters. At the same time, other kinds of correlations have been found to be more in line with cosmological expectations—specifically, lopsided satellite galaxy systems and the accretion of groups of satellite galaxies. The latter has mostly been studied in cosmological simulations thus far, but it offers the potential to address some of the other issues by providing a way to produce correlations among the orbits of a group’s satellite galaxy members. This review is the first to provide an introduction to the highly active field of phase-space correlations among satellite galaxy systems. The emphasis is on summarizing existing, recent research and highlighting interdependencies between the different, currently almost exclusively individually considered types of correlations. Future prospects in light of upcoming observational facilities and our ever-expanding knowledge of satellite galaxy systems beyond the Local Group are also briefly discussed
- ItemType III Radio Bursts Observations on 20th August 2017 and 9th September 2017 with LOFAR Bałdy Telescope(Basel : MDPI, 2021) Dabrowski, Bartosz; Flisek, Paweł; Mikuła, Katarzyna; Froń, Adam; Vocks, Christian; Magdalenić, Jasmina; Krankowski, Andrzej; Zhang, PeiJin; Zucca, Pietro; Mann, GottfriedWe present the observations of two type III solar radio events performed with LOFAR (LOw-Frequency ARray) station in Bałdy (PL612), Poland in single mode. The first event occurred on 20th August 2017 and the second one on 9th September 2017. Solar dynamic spectra were recorded in the 10 MHz up to 90 MHz frequency band. Together with the wide frequency bandwidth LOFAR telescope (with single station used) provides also high frequency and high sensitivity observations. Additionally to LOFAR observations, the data recorded by instruments on boards of the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO) in the UV spectral range complement observations in the radio field. Unfortunately, only the radio event from 9th September 2017 was observed by both satellites. Our study shows that the LOFAR single station observations, in combination with observations at other wavelengths can be very useful for better understanding of the environment in which the type III radio events occur.
- ItemThe Abundance of S-Process Elements: Temporal and Spatial Trends from Open Cluster Observations(Basel : MDPI, 2022) Magrini, Laura; Vázquez, Carlos Viscasillas; Casali, Giada; Baratella, Martina; D’Orazi, Valentina; Spina, Lorenzo; Randich, Sofia; Cristallo, Sergio; Vescovi, DiegoSpectroscopic observations of stars belonging to open clusters, with well-determined ages and distances, are a unique tool for constraining stellar evolution, nucleosynthesis, mixing processes, and, ultimately, Galactic chemical evolution. Abundances of slow (s) process neutron capture elements in stars that retain their initial surface composition open a window into the processes that generated them. In particular, they give us information on their main site of production, i.e., the low-and intermediate-mass Asymptotic Giant Branch (AGB) stars. In the present work, we review some observational results obtained during the last decade that contributed to a better understanding of the AGB phase: the growth of s-process abundances at recent epochs, i.e., in the youngest stellar populations; the different relations between age and [s/Fe] in distinct regions of the disc; and finally the use of s-process abundances combined with those of α elements, [s/α], to estimate stellar ages. We revise some implications that these observations had both on stellar and Galactic evolution, and on our ability to infer stellar ages.
- ItemThe HETDEX Instrumentation: Hobby-Eberly Telescope Wide-field Upgrade and VIRUS(London : Institute of Physics Publ., 2021) Hill, Gary J.; Lee, Hanshin; MacQueen, Phillip J.; Kelz, Andreas; Drory, Niv; Vattiat, Brian L.; Good, John M.; Ramsey, Jason; Kriel, Herman; Peterson, Trent; DePoy, D. L.; Gebhardt, Karl; Marshall, J. L.; Tuttle, Sarah E.; Bauer, Svend M.; Chonis, Taylor S.; Fabricius, Maximilian H.; Froning, Cynthia; Häuser, Marco; Indahl, Briana L.; Jahn, Thomas; Landriau, Martin; Leck, Ron; Montesano, Francesco; Prochaska, Travis; Snigula, Jan M.; Zeimann, Greg; Bryant, Randy; Damm, George; Fowler, J. R.; Janowiecki, Steven; Martin, Jerry; Mrozinski, Emily; Odewahn, Stephen; Rostopchin, Sergey; Shetrone, Matthew; Spencer, Renny; Mentuch Cooper, Erin; Armandroff, Taft; Bender, Ralf; Dalton, Gavin; Hopp, Ulrich; Komatsu, Eiichiro; Nicklas, Harald; Ramsey, Lawrence W.; Roth, Martin M.; Schneider, Donald P.; Sneden, Chris; Steinmetz, MatthiasThe Hobby-Eberly Telescope (HET) Dark Energy Experiment (HETDEX) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 deg2 of sky to identify and derive redshifts for a million Lyα-emitting galaxies in the redshift range 1.9 < z < 3.5. The ultimate goal is to measure the expansion rate of the universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. A major multiyear Wide-Field Upgrade (WFU) of the HET was completed in 2016 that substantially increased the field of view to 22′ diameter and the pupil to 10 m, by replacing the optical corrector, tracker, and Prime Focus Instrument Package and by developing a new telescope control system. The new, wide-field HET now feeds the Visible Integral-field Replicable Unit Spectrograph (VIRUS), a new low-resolution integral-field spectrograph (LRS2), and the Habitable Zone Planet Finder, a precision near-infrared radial velocity spectrograph. VIRUS consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral-field units arrayed at the focus of the upgraded HET. VIRUS operates in a bandpass of 3500-5500 Å with resolving power R ≃ 800. VIRUS is the first example of large-scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. This paper presents technical details of the HET WFU and VIRUS, as flowed down from the HETDEX science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for HETDEX.
- ItemUntangling the Sources of Abundance Dispersion in Low-metallicity Stars(London : Institute of Physics Publ., 2023) Griffith, Emily J.; Johnson, Jennifer A.; Weinberg, David H.; Ilyin, Ilya; Johnson, James W.; Rodriguez-Martinez, Romy; Strassmeier, Klaus G.We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (−2 ≲ [Fe/H] ≲ −1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (<0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ∼ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ∼6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.