Rubin-LSST

Abstract:

Extragalactic fast X-ray transients (eFXTs) represent a rapidly growing class of high-energy phenomena, whose physical origins remain poorly understood. With its wide-field, sensitive all-sky monitoring, the Einstein Probe (EP) has greatly increased the discovery rate of eFXTs. The search for and identification of the optical counterparts of eFXTs are vital for understanding their classification and constraining their physical origin. Yet, a considerable fraction of eFXTs still lack secure classifications due to the absence of timely follow-up observations. We carry out a systematic search of publicly available optical survey data and transient databases (including the Zwicky Transient Facility and the Transient Name Server) for optical counterparts to eFXT candidates detected by EP. In this paper, we describe our ongoing program and report the first results. Specifically, we identified the eFXT EP240506a to be associated with a UV/optical counterpart, AT 2024ofs. Spectroscopy of its host galaxy with the Very Large Telescope yields a redshift of z = 0.120 ± 0.002. By combining archival survey data with early-time multiwavelength observations, we find that the luminosity and light-curve evolution of AT 2024ofs are consistent with a core-collapse supernova origin. From detectability simulations, we estimate a local event rate density ρ0=8.8−3.9+21.2yr−1Gpc−3 for EP240506a-like events, and completeness-corrected rate of about 36–78 yr−1 Gpc−3 for EP-detected X-ray transients associated with supernovae. Our results demonstrate the potential of EP to uncover prompt high-energy emission from core-collapse supernovae and underscore the critical importance of timely follow-up of future eFXT events.

Abstract:

<jats:title>Abstract</jats:title> <jats:p> We analyse the large-scale angular clustering of quasars in the <jats:italic>Gaia</jats:italic> - <jats:italic>unWISE</jats:italic> quasar catalog, <jats:italic>Quaia</jats:italic> , and their cross-correlation with maps of the lensing convergence of the Cosmic Microwave Background (CMB), to constrain the level of primordial non-Gaussianity (PNG). Specifically, we target the scale-dependent bias that would be induced by PNG on biased tracers of the matter inhomogeneities on large scales. The <jats:italic>Quaia</jats:italic> sample is particularly well suited for this analysis, given the large effective volume covered, and our ability to map out the main potential sources of systematic contamination and mitigate their impact. Using the universality relation to characterise the response of the quasar overdensity to PNG ( <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1), we report constraints on the local-type PNG parameter   <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> of <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> = -20.5 <jats:sup>+19.0</jats:sup> <jats:sub>-18.1</jats:sub> (68% C.L.) by combining the quasar auto-correlation and its cross-correlation with CMB lensing in two tomographic redshift bins (or <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> = -28.7 <jats:sup>+26.1</jats:sup> <jats:sub>-24.6</jats:sub> if assuming a lower response for quasars, <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1.6). The error on <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> can be further improved if the cross-correlation between the tomographic redshift bins is included. Using the CMB lensing cross-correlations alone, we find <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> = -13.8 <jats:sup>+26.7</jats:sup> <jats:sub>-25.0</jats:sub> and <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> = -15.6 <jats:sup>+42.3</jats:sup> <jats:sub>-34.8</jats:sub> for <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1 and <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1.6 respectively. These are the tightest constraints on <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> to date from angular clustering statistics and cross-correlations with CMB lensing. </jats:p>

Abstract:

Abstract Deep radio continuum surveys provide fundamental constraints on galaxy evolution, but source confusion limits sensitivity to the faintest sources. We present a complete framework for producing high-fidelity deblended radio catalogues from the confused MIGHTEE maps using the probabilistic deblending framework XID+ and prior positions from deep multi-wavelength data in the COSMOS field. To assess performance, we construct MIGHTEE-like simulations based on the Tiered Radio Extragalactic Continuum Simulation (T-RECS) radio source population, ensuring a realistic distribution of star-forming galaxies and active galactic nuclei (AGN) for validation. Through these simulations, we show that prior catalogue purity is the dominant factor controlling deblending accuracy: a high-purity prior, containing only sources with a high likelihood of radio detection, recovers accurate flux densities and reproduces input source counts down to ~3σ (where σ = thermal noise). On the other hand, a complete prior overestimates the source counts due to spurious detections. Our optimal strategy combines the high-purity prior with a mask that removes sources detected above 50 μJy. Applied to the ~1.3 deg2 area of the MIGHTEE-COSMOS field defined by overlapping multi-wavelength data, this procedure yields a deblended catalogue of 89,562 sources. The derived 1.4 GHz source counts agree with independent P(D) analyses and indicate that we resolve the radio background to ~4.8 μJy. We also define a recommended high-fidelity sample of 20,757 sources, based on detection significance, flux density, and goodness-of-fit, which provides reliable flux densities for individual sources in the confusion-limited regime.

Abstract:

Context . Many applications in transient science, gravitational wave follow-up, and galaxy population studies require all-sky galaxy catalogs with reliable distances, extents, and stellar masses. However, existing catalogs often lack completeness beyond ~100 Mpc, suffer from stellar contamination, or do not provide homogeneous stellar mass estimates and size information. Aims . Our goal is to build a high-purity, high-completeness, all-sky galaxy catalog out to 2000 Mpc, specifically designed to support time-domain and multi-messenger astrophysics. Methods . We combined major galaxy catalogs and deep imaging surveys – including the Legacy Surveys, Pan-STARRS, DELVE, and SDSS – and added spectroscopic, photometric, and redshift-independent distances. We cleaned the sample using the Gaia catalog to remove stars and visually inspected all ambiguous cases below 100 Mpc through a classification platform that gathered 27 000 expert votes. Stellar masses were estimated using optical and mid-infrared profile-fit photometry, and we improved the accuracy of photometric distances by combining multiple independent estimates. Results . The resulting catalog, REGALADE, includes nearly 80 million galaxies with distances under 2000 Mpc. It provides stellar masses for 88% of the sample and ellipse fits for 80%. REGALADE is more than 90% complete for galaxies contributing 50% of the total r -band luminosity out to 360 Mpc. In science tests, it recovers 60% more known supernova hosts, doubles the number of low-luminosity transient hosts, and identifies more reliable hosts for ultraluminous and hyper-luminous X-ray sources. Conclusions . REGALADE is one of the most complete and reliable all-sky galaxy catalog to date for the nearby Universe, built for real-world applications in transient and multi-messenger astrophysics. The full dataset, visual classifications, and code will be released to support broad community use.