Search

A growing number of supernovae (SNe) are now known to exhibit evidence for significant interaction with a dense, pre-existing, circumstellar medium (CSM). SNe Ibn comprise one such class that can be characterized by both rapidly evolving light curves and persistent narrow He  i lines. The origin of such a dense CSM in these systems remains a pressing question, specifically concerning the progenitor system and mass-loss mechanism. In this paper, we present multiwavelength data of the Type Ibn SN 2020nxt, including HST /STIS ultraviolet spectra. We fit the data with recently updated CMFGEN models designed to handle configurations for SNe Ibn. The UV coverage yields strong constraints on the energetics and, when combined with the CMFGEN models, offer new insight on potential progenitor systems. We find the most successful model is a ≲4 M⊙ helium star that lost its |$\sim 1\, {\rm M}_\odot$| He-rich envelope in the years preceding core collapse. We also consider viable alternatives, such as a He white dwarf merger. Ultimately, we conclude at least some SNe Ibn do not arise from single, massive (>30 M⊙) Wolf–Rayet-like stars. [ABSTRACT FROM AUTHOR]

The Type IIn supernova (SN IIn) 2005ip is one of the most well-studied and long-lasting examples of an SN interacting with its circumstellar environment. The optical light curve plateaued at a nearly constant level for more than five years, suggesting ongoing shock interaction with an extended and clumpy circumstellar medium (CSM). Here, we present continued observations of the SN from ∼1000 to 5000 d post-explosion at all wavelengths, including X-ray, ultraviolet, near-infrared (NIR), and mid-infrared. The UV spectra probe the pre-explosion mass loss and show evidence for CNO processing. From the bolometric light curve, we find that the total radiated energy is in excess of 1050 erg, the progenitor star's pre-explosion mass-loss rate was |${\gtrsim}1 \times 10^{-2}\, {\rm M_{\odot }~ yr}^{-1}$|⁠ , and the total mass lost shortly before explosion was |${\gtrsim}1\, {\rm M_\odot }$|⁠ , though the mass lost could have been considerably larger depending on the efficiency for the conversion of kinetic energy to radiation. The ultraviolet through NIR spectrum is characterized by two high-density components, one with narrow high-ionization lines, and one with broader low-ionization H  i , He  i , [O  i ], Mg  ii , and Fe  ii lines. The rich Fe  ii spectrum is strongly affected by Lyα fluorescence, consistent with spectral modelling. Both the Balmer and He  i lines indicate a decreasing CSM density during the late interaction period. We find similarities to SN 1988Z, which shows a comparable change in spectrum at around the same time during its very slow decline. These results suggest that, at long last, the shock interaction in SN 2005ip may finally be on the decline. [ABSTRACT FROM AUTHOR]

Using photometric redshifts we determine the galaxy population of the clusters of galaxies Cl0016+16 at , Cl1600+41 at , Cl1601+42 at and MS1008–1224 at . Comparing the clusters, we find no evidence for a universal shape of the total luminosity function (LF) at these redshifts. When dividing the LFs into spectral types, we find that the LF of the early-type galaxies alone can be described by a Gaussian, while the LF of the late-type galaxies is well fitted by a Schechter function, suggesting that the separate LFs for different populations may be universal. The difference in the total LFs can mainly be attributed to the varying relative normalization of these populations, implying that clusters with an abundant population of late-type galaxies also have steeper faint-end slopes. In MS1008–1224 we detect a faint blue population that dominates over a population with colours consistent with dwarf ellipticals, opposite to clusters at lower redshift. Compared to low-redshift clusters, we find that a general fading of the late-type population by ∼2 mag and the early-type population by ∼1 mag describes the evolution from to well. As a consequence of the different early-type and late-type LFs and their dependence on cluster radius, the fraction of blue cluster galaxies, as measured by the Butcher–Oemler effect, differs between the clusters and depends on limiting magnitude and radius. We find a correlation between the dwarf-to-giant ratio and the surface density, indicating that the high-density environment in the cluster cores is hostile to dwarf galaxies. [ABSTRACT FROM AUTHOR]

Photometric redshifts are used to determine the rest-frame luminosity function (LF) of both early- and late-type galaxies to M ∼ -17.6 for the cluster C1 1601+42 at z = 0.54. The total LF shows a steep faint-end slope α ∼ -1.4, indicating the existence of a population of numerous dwarf galaxies. Luminous galaxies, with M ≤-19.5 are mostly red, early-type galaxies, with a LF best described by a Gaussian. Faint galaxies are predominantly blue, late-type galaxies, well fitted by a Schechter function with α ∼ -1.7. Compared with clusters at lower redshift, the steepening of the faint end starts at brighter magnitudes for C1 1601+42, which may indicate a brightening of the present-day dwarf population relative to the giant population with increasing redshift. Early-type galaxies are centrally concentrated, and dominate the core region, implying that the radial gradient of early-type galaxies seen in local clusters is already established at z ∼ 0.5. Bright, late-type galaxies are rare, consistent with a decrease in star formation in field galaxies as they are accreted on to the cluster, while faint, blue galaxies are evenly distributed across the cluster, except for a depletion in the core region. The blue fraction is f ∼ 0.15, which is somewhat lower than the Butcher -- Oemler average at z ∼ 0.5. The value of is found to increase with limiting magnitude and with radius from the centre. [ABSTRACT FROM AUTHOR]