ORCID Profile
0000-0002-9994-505X
Current Organisation
University of St Andrews
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Astronomical Society
Date: 20-12-2016
Publisher: American Astronomical Society
Date: 09-10-2015
Publisher: EDP Sciences
Date: 03-2023
DOI: 10.1051/0004-6361/202244205
Abstract: The study of the properties of galaxies in the first billion years after the Big Bang is one of the major topics of current astrophysics. Optical and near-infrared spectroscopy of the afterglows of long gamma-ray bursts (GRBs) provides a powerful diagnostic tool to probe the interstellar medium (ISM) of their host galaxies and foreground absorbers, even up to the highest redshifts. We analyze the VLT/X-shooter afterglow spectrum of GRB 210905A, triggered by the Neil Gehrels Swift Observatory, and detect neutral hydrogen, low-ionization, high-ionization, and fine-structure absorption lines from a complex system at z = 6.3118, which we associate with the GRB host galaxy. We use them to study the ISM properties of the host system, revealing the metallicity, kinematics, and chemical abundance pattern of its gas along the GRB line of sight. We also detect absorption lines from at least two foreground absorbers at z = 5.7390 and z = 2.8296. The total metallicity of the z ∼ 6.3 system is [M/H] tot = −1.72 ± 0.13, after correcting for dust depletion and taking α -element enhancement into account, as suggested by our analysis. This is consistent with the values found for the other two GRBs at z ∼ 6 with spectroscopic data showing metal absorption lines (GRB 050904 and GRB 130606A), and it is at the higher end of the metallicity distribution of quasar d ed Lyman- α systems (QSO-DLAs) extrapolated to such a high redshift. In addition, we determine the overall amount of dust and dust-to-metal mass ratio (DTM) ([Zn/Fe] fit = 0.33 ± 0.09 and DTM = 0.18 ± 0.03). We find indications of nucleosynthesis due to massive stars and, for some of the components of the gas clouds, we find evidence of peculiar nucleosynthesis, with an overabundance of aluminum (as also found for GRB 130606A). From the analysis of fine-structure lines, we determine distances of several kiloparsecs for the low-ionization gas clouds closest to the GRB. Those are farther distances than usually found for GRB host absorption systems, possibly due to the very high number of ionizing photons produced by the GRB that could ionize the line of sight up to several hundreds of parsecs. Using the HST/ F 140 W image of the GRB field, we show the GRB host galaxy (with a possible afterglow contamination) as well as multiple objects within 2″ from the GRB position. We discuss the galaxy structure and kinematics that could explain our observations, also taking into account a tentative detection of Lyman- α emission at z = 6.3449 (∼1200 km s −1 from the GRB redshift in velocity space), and the observational properties of Lyman- α emitters at very high redshift. This study shows the amazing potential of GRBs to access detailed information on the properties (metal enrichment, gas kinematic, dust content, nucleosynthesis...) of very high-redshift galaxies, independently of the galaxy luminosity. Deep spectroscopic observations with VLT/MUSE and JWST will offer the unique possibility of combining the information presented in this paper with the properties of the ionized gas, with the goal of better understanding how galaxies in the reionization era form and evolve.
Publisher: American Astronomical Society
Date: 03-09-2015
Publisher: EDP Sciences
Date: 09-2010
Publisher: American Astronomical Society
Date: 23-03-2018
Publisher: Oxford University Press (OUP)
Date: 10-04-2019
Publisher: Oxford University Press (OUP)
Date: 19-11-2019
Abstract: The Transiting Exoplanet Survey Satellite (TESS) produces a large number of single-transit event candidates, since the mission monitors most stars for only ∼27 days. Such candidates correspond to long-period planets or eclipsing binaries. Using the TESS Sector 1 full-frame images, we identified a 7750 ppm single-transit event with a duration of 7 hours around the moderately evolved F-dwarf star TIC-238855958 (Tmag=10.23, Teff=6280±85 K). Using archival WASP photometry we constrained the true orbital period to one of three possible values. We detected a subsequent transit-event with NGTS, which revealed the orbital period to be 38.20 d. Radial velocity measurements from the CORALIE Spectrograph show the secondary object has a mass of M2= 0.148 ± 0.003 M⊙, indicating this system is an F-M eclipsing binary. The radius of the M-dwarf companion is R2 = 0.171 ± 0.003 R⊙, making this one of the most well characterised stars in this mass regime. We find that its radius is 2.3-σ lower than expected from stellar evolution models.
Publisher: American Astronomical Society
Date: 11-06-2020
Publisher: Springer Science and Business Media LLC
Date: 25-04-2008
Publisher: Oxford University Press (OUP)
Date: 09-02-2023
Abstract: We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (∼200 mas yr−1), low metallicity ([Fe/H]≈−0.28) K-dwarf with a mass of 0.68 ± 0.05 M⊙ and a radius of 0.67 ± 0.01 R⊙. We obtain photometric follow-up observations with a variety of facilities, and we use these data sets to determine that the inner planet, TOI-836 b, is a 1.70 ± 0.07 R⊕ super-Earth in a 3.82-d orbit, placing it directly within the so-called ‘radius valley’. The outer planet, TOI-836 c, is a 2.59 ± 0.09 R⊕ mini-Neptune in an 8.60-d orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 ± 0.9 M⊕, while TOI-836 c has a mass of 9.6 ± 2.6 M⊕. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 min for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.
Publisher: Oxford University Press (OUP)
Date: 12-06-2021
Abstract: We report on the stellar content, half-light radii and star formation rates of a s le of 10 known high-redshift (z ≳ 2) galaxies selected on strong neutral hydrogen (H i) absorption ($\\log ({\\rm N_{H\\, \\rm {I}}\\: /\\: cm}^{-2})\\,\\gt\\, 19$) towards background quasars. We use observations from the Hubble Space Telescope Wide Field Camera 3 in three broad-band filters to study the spectral energy distribution (SED) of the galaxies. Using careful quasar point spread function subtraction, we study their galactic environments, and perform the first systematic morphological characterization of such absorption-selected galaxies at high redshifts. Our analysis reveals complex, irregular hosts with multiple star-forming clumps. At a spatial s ling of 0.067 arcsec per pixel (corresponding to 0.55 kpc at the median redshift of our s le), 40 per cent of our s le requires multiple Sérsic components for an accurate modelling of the observed light distributions. Placed on the mass–size relation and the ‘main sequence’ of star-forming galaxies, we find that absorption-selected galaxies at high redshift extend known relations determined from deep luminosity-selected surveys to an order of magnitude lower stellar mass, with objects primarily composed of star-forming, late-type galaxies. We measure half-light radii in the range r1/2 ∼ 0.4 to 2.6 kpc based on the reddest band (F160W) to trace the oldest stellar populations, and stellar masses in the range log (M⋆/M⊙) ∼ 8 to 10 derived from fits to the broad-band SED. Spectroscopic and SED-based star formation rates are broadly consistent, and lie in the range $\\log (\\mathrm{SFR}/{\\rm M}_{\\odot }\\, {\\rm yr}^{-1}) \\sim 0.0$ to 1.7.
Publisher: American Astronomical Society
Date: 11-09-2019
Publisher: Oxford University Press (OUP)
Date: 19-05-2014
DOI: 10.1093/MNRAS/STU728
Publisher: American Astronomical Society
Date: 18-10-2017
Publisher: Springer Science and Business Media LLC
Date: 15-08-2008
Publisher: American Astronomical Society
Date: 30-03-2016
Publisher: American Astronomical Society
Date: 15-03-2022
Abstract: Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets—such as solar data or data with known injected planetary and/or stellar signals—to better understand method performance and whether planetary signals are preserved.
Publisher: American Astronomical Society
Date: 18-09-2020
Publisher: American Astronomical Society
Date: 18-06-2018
Publisher: Oxford University Press (OUP)
Date: 14-03-2019
DOI: 10.1093/MNRAS/STZ735
Abstract: We report Giant Metrewave Radio Telescope (GMRT), Very Large Telescope (VLT), and Spitzer Space Telescope observations of ESO 184−G82, the host galaxy of GRB 980425/SN 1998bw, that yield evidence of a companion dwarf galaxy at a projected distance of 13 kpc. The companion, hereafter GALJ193510-524947, is a gas-rich, star-forming galaxy with a star formation rate of $\\rm 0.004\\, M_{\\odot }\\, yr^{-1}$, a gas mass of $10^{7.1\\pm 0.1} \\, \\mathrm{M}_{\\odot}$, and a stellar mass of $10^{7.0\\pm 0.3} \\, \\mathrm{M}_{\\odot}$. The interaction between ESO 184−G82 and GALJ193510-524947 is evident from the extended gaseous structure between the two galaxies in the GMRT H i 21 cm map. We find a ring of high column density H i gas, passing through the actively star-forming regions of ESO 184−G82 and the GRB location. This ring lends support to the picture in which ESO 184−G82 is interacting with GALJ193510-524947. The massive stars in GALJ193510-524947 have similar ages to those in star-forming regions in ESO 184−G82, also suggesting that the interaction may have triggered star formation in both galaxies. The gas and star formation properties of ESO 184−G82 favour a head-on collision with GALJ193510-524947 rather than a classical tidal interaction. We perform state-of-the-art simulations of dwarf–dwarf mergers and confirm that the observed properties of ESO 184−G82 can be reproduced by collision with a small companion galaxy. This is a very clear case of interaction in a gamma-ray burst host galaxy and of interaction-driven star formation giving rise to a gamma-ray burst in a dense environment.
Publisher: American Astronomical Society
Date: 28-08-2019
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Palle Moller.