Hintze Centre for Astrophysical Surveys

Abstract:

Spectroscopic observations of the kilonova AT 2017gfo provide a unique opportunity to identify signatures from individual heavy elements freshly synthesized via the r-process, the nucleosynthetic channel responsible for producing half of all trans-iron-group elements. Limitations in the available atomic data have historically hampered comprehensive line identification studies; however, renewed interest has led to the generation of improved (more complete and accurately calibrated) line lists for r-process species. Here we demonstrate the utility of such data, by exploiting newly generated line lists for the lanthanides to model the photospheric-phase 3.4 d X-shooter spectrum of AT 2017gfo with the radiative transfer tool tardis. We find the data can only be reproduced by invoking a substantially diminished lanthanide mass fraction () than that proposed by previous studies. Specifically, our model necessitates in the line-forming region, a value lower than previously claimed. This substantial reduction in is driven by our inclusion of much more complete lanthanide line information that enables better estimation of their total contribution to the observations. We encourage future modelling works to exploit all atomic data advances, and also encourage continued efforts to generate the necessary data for the remaining r-process species of interest.

Abstract:

A central question regarding neutron star (NS) mergers is whether they are able to produce all the r-process elements, from first to third peak. We here study theoretical infrared signatures of first-peak elements with spectral synthesis modelling. By combining state-of-the-art non-local thermodynamic equilibrium physics with new radiative and collisional data for these elements, we identify several promising diagnostic lines from Ge, As, Se, Br, Kr, and Zr. The models give self-consistent line luminosities and indicate specific features that probe emission volumes at early phases (10 d), the product of ion mass and electron density in late phases (75 d), and in some cases direct ionic masses at intermediate phases. Emission by [Se i] 5.03 m + [Se iii] 4.55 m is the only candidate from the first r-process peak that could explain the Spitzer photometry of AT2017gfo. However, the models show consistently that with a Kr/Te and Se/Te ratio following the solar r-process pattern, Kr + Se emission is dominant over Te for the feature at 2.1 m observed in both AT2017gfo and AT2023vfi. The somewhat better line profile fit with [Te iii] may suggest that both AT2017gfo and AT2023vfi had a strongly subsolar production of the light r-process elements. An alternative scenario could be that Kr + Se in an asymmetric morphological distribution generates the feature. Further James Webb Space Telescope spectral observations hold promise to determine the light r-process production of kilonovae, and in particular whether the light elements are made in a slow disc outflow or in a fast proto-NS wind. We identify specific needs for further atomic data for elements.

Abstract:

We introduce a new kinematic disturbance parameter, (pronounced ‘DVSG’), which takes advantage of integral field spectroscopy (IFS) to quantify differences between a galaxy’s stellar and gas velocity maps. The motivation behind is to capture disturbances in the kinematics of a galaxy that might be missed by alternative methods, while also attempting to minimize bias towards galaxy properties or features of the IFS data. We first detail the reasons for introducing this parameter and explain how the value of a galaxy can be calculated. We then present initial results using to quantify the kinematic disturbance of obscured active galactic nuclei (AGNs) found in the MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) survey. We find that there is no statistically significant difference between the distributions of AGN and a control sample (matched in mass and redshift) of inactive galaxies. This suggests that AGN triggering may not be preferentially caused by any distinct kinematic disturbance process, or combination of processes, beyond those observed in inactive galaxies.

Abstract:

The dynamically driven double-degenerate double-detonation model has emerged as a promising progenitor candidate for Type Ia supernovae. In this scenario, the primary white dwarf ignites due to dynamical interaction with a companion white dwarf, which may also undergo a detonation. Consequently, two scenarios exist: one in which the secondary survives and another in which both white dwarfs detonate. In either case, substantial departures from spherical symmetry are imprinted on the ejecta. Here, we compute full non-local thermodynamic equilibrium nebular-phase spectra in 1D and 3D to probe the innermost asymmetries. Our simulations reveal that the multidimensional structures significantly alter the overall ionization balance, width, and velocity of features, especially when the secondary detonates. In this scenario, some element distributions may produce orientation-dependent line profiles that can be centrally peaked from some viewing angles and somewhat flat-topped from others. Comparison to observations reveals that both scenarios produce most observed features from the optical to mid-infrared. However, the current model realizations do not consistently reproduce all line shapes or relative strengths, and yield prominent optical Ar iii emission which is inconsistent with the data. When the secondary detonates, including 3D effects improves the average agreement with observations, however when compared to observations, particularly weak optical Co iii emission and the presence of optical O i and near-infrared S i challenge its viability for normal Type Ia supernovae. Thus, overall, our comparisons with normal Type Ia’s tentatively favour detonation of only the primary white dwarf but we stress that more model realizations and mid-infrared observations are needed.