Rubin-LSST

Abstract:

Abstract The upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will enable astronomers to discover rare and distant astrophysical transients. Host-galaxy association is crucial for selecting the most scientifically interesting transients for follow-up. LSST deep drilling field (DDF) observations will detect distant transients occurring in galaxies below the detection limits of most all-sky catalogs. Here, we investigate the use of preexisting, field-specific catalogs for host identification in the DDFs and a ranking of their usefulness. We have compiled a database of 70 deep catalogs that overlap with the Rubin DDFs and constructed thin catalogs to be homogenized and combined for transient-host matching. A systematic ranking of their utility is discussed and applied based on the inclusion of information such as spectroscopic redshifts and morphological information. Utilizing this data against a Dark Energy Survey sample of supernovae with pre-identified hosts in the XMM-Large Scale Structure and the Extended Chandra Deep Field-South fields, we evaluate different methods for transient-host association in terms of both accuracy and processing speed. We also apply light data-cleaning techniques to identify and remove contaminants within our associations, such as diffraction spikes and blended galaxies where the correct host cannot be determined with confidence. We use a lightweight machine learning approach in the form of extreme gradient boosting to generate confidence scores in our contaminant selections and associated metrics. Finally, we discuss the computational expense of implementation within the LSST transient alert brokers, which will require efficient, fast-paced processing to handle the large stream of survey data.

Abstract:

Abstract A key question in extragalactic astronomy is how the star-formation rate density (SFRD) evolves over cosmic time. A powerful way of addressing this question is using radio-continuum observations, where the radio waves are unaffected by dust and are able to reach sufficient resolution to resolve individual galaxies. We present an investigation of the 1.4 GHz radio luminosity functions (RLFs) of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) using deep radio continuum observations in the COSMOS and XMM–LSS fields, covering a combined area of ∼4 deg2. These data enable the most accurate measurement of the evolution in the SFRD from mid-frequency radio continuum observations. We model the total RLF as the sum of evolving SFG and AGN components, negating the need for individual source classification. We find that the SFGs have systematically higher space densities at fixed luminosity than found in previous radio studies, but consistent with more recent studies with MeerKAT. We attribute this to the excellent low-surface brightness sensitivity of MeerKAT. We then determine the evolution of the SFRD. Adopting the far-infrared – radio correlation results in a significantly higher SFRD at z > 1, compared to combined UV and far-infrared measurements. However, using more recent relations for the correlation between star-formation rate and radio luminosity, based on full spectral energy distribution modelling, can resolve this apparent discrepancy. Thus radio observations provide a powerful method of determining the total SFRD, in the absence of dust-sensitive far-infrared data.

Abstract:

Skew spectra allow us to extract non-Gaussian information by taking the square of a map and finding the power spectrum of this new map with the original map. This allows us to use much of the infrastructure of power spectra and avoid the intricacies of estimating three point statistics. In this paper we present the first extension of skew spectra to arbitrary spin- s fields, as a means to extract non-Gaussian information efficiently from cosmological datasets like cosmic shear or cosmic microwave background polarization. We apply the formalism to weak lensing in the context of large scale structure, and discuss different ways of combining fields to build skew spectra, all while avoiding the problems associated with mass mapping. We provide plots of these new statistics for Λ cold dark matter and vary cosmological parameters.

Abstract:

Abstract We present a quadratic estimator that detects and reconstructs spatially-varying multiplicative (m −) bias in weak lensing shear measurements, by exploiting the EB mode coupling that it generates. The method combines E and B modes with inverse-variance weights, to yield an unbiased reconstruction of $m(\boldsymbol{\theta })$ to first order. We study the ability of future Stage IV surveys to obtain an unbiased reconstruction of the m-bias in differing scenarios, considering differing bias morphologies, and characteristic scales, as well as differing metrics to quantify the signal-to-noise ratio of the reconstructed map. We consider an m pattern repeating on ~1○ × 1○ sky patches, as might be the case for an m field caused by focal-plane systematics. With a Euclid-like redshift distribution, we find that ~5 % rms variations in m-bias may be detected at the 20σ level, after stacking between ~400 and ~1000 patches (rising to between ~2800 and ~7600 for 1 % rms variations, data volumes that are becoming available with upcoming surveys), depending on the morphology of the m pattern. We show that these results are robust against the cosmological model assumed in the reconstruction, as well as the presence of intrinsic alignments or baryonic effects, and that the method shows no spurious response to additive (c −) bias. These results demonstrate that percent-level, spatially-varying m −bias can be detected at high significance, enabling diagnosis and mitigation in the Stage IV weak lensing era.

Abstract:

Measuring galaxy rotation curves is critical for inferring the properties of dark-matter haloes in the Lambda Cold Dark Matter (ΛCDM) paradigm. We present H i rotation curves and mass models for 20 galaxies from the MIGHTEE survey. Using extended H i kinematics, we construct resolved mass models that include stellar, gaseous, and dark-matter components. Stellar masses are derived using 3.6 μm imaging under fixed mass-to-light ratio (ϒ* = M/L) assumptions and are complemented, for the first time for a H I-selected sample, by spatially resolved M/L, obtained from multi-wavelength SED fitting. We examine the ratio of baryonic to observed rotation velocity (Vbar/Vobs) at the characteristic radius R2.2. Adopting a fixed ϒ⋆ = 0.5 M⊙/L⊙ yields a clear dependence of V2.2/Vobs on galaxy luminosity, while adopting ϒ⋆ = 0.2 M⊙/L⊙ substantially weakens this trend. In contrast, the resolved M/L analysis preserves the luminosity dependence while modifying the stellar contribution on a galaxy-by-galaxy basis, providing a more accurate representation of the underlying relation. We model the dark-matter haloes using Navarro–Frenk–White profiles and find that the different assumptions for a fixed a M/L systematically shift galaxies relative to the theoretical stellar-to-halo mass and baryonic-to-halo mass relations, while the spatially varying M/L yields the closest agreement with theoretical benchmarks within ΛCDM. We therefore demonstrate that future investigations of the dark matter properties of galaxies using rotation curves need to account for varying M/L across individual galaxy profiles and between galaxies in order to obtain accurate measurements of the dark matter, and therefore test ΛCDM.