Hintze Centre for Astrophysical Surveys

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.

Abstract:

Context. Type IIb supernovae (SNe IIb) are stellar explosions whose spectra reveal transitional features between hydrogen-rich (Type II) and helium-rich (Type Ib) SNe. Their progenitors are massive stars that were mostly stripped of their hydrogen envelope, likely through binary interaction and/or strong stellar winds. This makes such stars key tools in studies of the late stages of the evolution of massive stars. Aims. We present an extensive photometric and spectroscopic follow-up campaign of the Type IIb SN 2022ngb. Through the detailed modeling of this dataset, we aim to constrain the key physical parameters of the explosion, infer the nature of the progenitor star and its environment, and probe the dynamical properties of the ejecta. Methods. We analyzed photometric and spectroscopic data of SN 2022ngb. By constructing and modeling the bolometric light curve with semi-analytic models, we were able to estimate the primary explosion parameters. The spectroscopic data were compared with those of well-studied SNe IIb and NLTE models to constrain the properties of the progenitor and the structure of the resulting ejecta. Results. SN 2022ngb is a low-luminosity SN IIb with a peak bolometric luminosity of L Bol = 7.76 +1.15 −1.00 × 10 41 erg s −1 and a V -band rising time of 24.32 ± 0.50 days. The light curve modeling indicates an ejecta mass of ∼2.9 − 3.2 M ⊙ , an explosion energy of ∼1.4 × 10 51 erg, and a low synthesized 56 Ni mass of ∼0.045 M ⊙ . The nebular phase spectra exhibit asymmetric line profiles, pointing to a nonspherical explosion and an anisotropic distribution of radioactive material. Our analysis reveals a relatively compact stripped-envelope progenitor with a pre-SN mass of approximately 4.7 M ⊙ (corresponding to a 15–16 M ⊙ ZAMS star). Conclusions. Our analysis suggests that SN 2022ngb originated from the explosion of a moderate-mass relatively compact, stripped-envelope star in a binary system. The asymmetries inferred from the nebular phase spectral line features indicate the occurrence of a nonspherical explosion.

Abstract:

Abstract Does the environment of a galaxy directly influence the kinematics of its bar? We present observational evidence that bars in high-density environments exhibit significantly slower rotation rates than bars in low-density environments. Galactic bars are central, extended structures composed of stars, dust and gas, present in approximately 30 to 70 per cent of luminous spiral galaxies in the local Universe. Recent simulation studies have suggested that the environment can influence the bar rotation rate, $\mathcal {R}$, which is used to classify bars as either fast ($1\le \mathcal {R}\le 1.4$) or slow ($\mathcal {R}>1.4$). We use estimates of $\mathcal {R}$ obtained with the Tremaine–Weinberg method applied to Integral Field Unit spectroscopy from MaNGA and CALIFA. After cross-matching these with the projected neighbour density, log Σ, we retain 286 galaxies. The analysis reveals that bars in high-density environments are significantly slower (median $\mathcal {R} = 1.65^{+0.13}_{-0.11}$) compared to bars in low-density environments (median $\mathcal {R} =1.39^{+0.09}_{-0.08}$); Anderson–Darling p-value of pAD = 0.002 (3.1 σ). This study marks the first empirical test of the hypothesis that fast bars are formed by global instabilities in isolated galaxies, while slow bars are triggered by tidal interactions in dense environments, in agreement with predictions from numerous N-body simulations. Future studies would benefit from a larger sample of galaxies with reliable Integral Field Unit data, required to measure bar rotation rates. Specifically, more data are necessary to study the environmental influence on bar formation within dense settings (i.e. groups, clusters and filaments).

Abstract:

ABSTRACT We present photometric and spectroscopic studies of two core-collapse supernovae (SNe) 2008aq and 2019gaf in the optical wavelengths. Light curve and spectral sequence of both the SNe are similar to those of other Type IIb SNe. The pre-maximum spectrum of SN 2008aq showed prominent H $\alpha$ lines, the He lines started appearing in the near maximum spectrum. The near maximum spectrum of SN 2019gaf shows shallow H $\alpha$ absorption and He lines with almost similar strength. Both the SNe show transition from hydrogen-dominated spectra to helium-dominated spectra within a month after maximum brightness. The velocity evolution of SN 2008aq matches well with those of other well-studied Type IIb SNe, while SN 2019gaf shows higher velocities. Close to maximum light, the H $\alpha$ and He i line velocities of SN 2019gaf are $\sim$ 2000 and $\sim$ 4000 km s$^{-1}$ higher than other well-studied Type IIb SNe. Semi-analytical modelling indicates SN 2019gaf to be a more energetic explosion with a smaller ejecta mass than SN 2008aq. The zero-age main-sequence (ZAMS) mass of the progenitor estimated using the nebular spectra of SN 2008aq ranges between 13 and 20 M$_\odot$, while for SN 2019gaf, the inferred ZAMS mass is between 13 and 25 M$_\odot$. The [O i] to [Ca ii] lines flux ratio favours a less massive progenitor star in a binary system for both the SNe.