The fraction of core-collapse supernovae (CCSNe) occurring in the central regions of galaxies is not well constrained at present. This is partly because large-scale transient surveys operate at ...optical wavelengths, making it challenging to detect transient sources that occur in regions susceptible to high extinction factors. Here we present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG) NGC 3256. The first, SN 2018ec, was discovered using the ESO HAWK-I/GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of
A
V
= 2.1
−0.1
+0.3
mag. The second, AT 2018cux, was discovered during the course of follow-up observations of SN 2018ec, and is consistent with a subluminous Type IIP classification with an
A
V
= 2.1 ± 0.4 mag of host extinction. A third CCSN, PSN J10275082−4354034 in NGC 3256, was previously reported in 2014, and we recovered the source in late-time archival
Hubble
Space Telescope imaging. Based on template light curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of
A
V
= 0.3
−0.3
+0.4
mag. We also extend our study with follow-up data of the recent Type IIb SN 2019lqo and Type Ib SN 2020fkb that occurred in the LIRG system Arp 299 with host extinctions of
A
V
= 2.1
−0.3
+0.1
and
A
V
= 0.4
−0.2
+0.1
mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, that there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb/Ib/Ic/Ibn) and 15 H-rich (Type II/IIn) CCSNe have different underlying progenitor age distributions, with the H-poor progenitors being younger at 3
σ
significance. However, we note that the currently available sample sizes of CCSNe and host LIRGs are small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages.
We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of Mg = −15.46 ± ...0.15 mag and a bolometric luminosity of 5.5 × 1041 erg s−1. Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC 4490−2011OT1.
Context. Unusual stellar explosions represent an opportunity to learn about both stellar and galaxy evolution. Mapping the atomic gas in host galaxies of such transients can lead to an understanding ...of the conditions that trigger them. Aims. We provide resolved atomic gas observations of the host galaxy, CGCG137-068, of the unusual and poorly understood transient AT 2018cow, which we obtained in searching for clues to understand its nature. We test whether it is consistent with a recent inflow of atomic gas from the intergalactic medium, as suggested for host galaxies of gamma-ray bursts (GRBs) and some supernovae (SNe). Methods. We observed the HI hyperfine structure line of the AT 2018cow host with the Giant Metrewave Radio Telescope. Results. There is no unusual atomic gas concentration near the position of AT 2018cow. The gas distribution is much more regular than the distributions of GRB/SN hosts. The AT 2018cow host has an atomic gas mass lower by 0.24 dex than predicted from its star formation rate (SFR) and is at the lower edge of the galaxy main sequence. In the continuum we detected the emission of AT 2018cow and of a star-forming region in the north-eastern part of the bar (away from AT 2018cow). This region hosts a third of the galaxy’s SFR. Conclusions. The absence of atomic gas concentration close to AT 2018cow, along with a normal SFR and regular HI velocity field, sets CGCG137-068 apart from GRB/SN hosts studied in HI. The environment of AT 2018cow therefore suggests that its progenitor may not have been a massive star. Our findings are consistent with an origin of the transient that does not require a connection between its progenitor and gas concentration or inflow: an exploding low-mass star, a tidal disruption event, a merger of white dwarfs, or a merger between a neutron star and a giant star. We interpret the recently reported atomic gas ring in CGCG 137-068 as a result of internal processes connected with gravitational resonances caused by the bar.
Context. The host galaxies of gamma-ray bursts (GRBs) have been claimed to have experienced a recent inflow of gas from the intergalactic medium. This is because their atomic gas distribution is not ...centred on their optical emission and because they are deficient in molecular gas given their high star formation rates (SFRs). Similar studies have not been conducted for host galaxies of relativistic supernovae (SNe), which may have similar progenitors. Aims. The potential similarity of the powering mechanisms of relativistic SNe and GRBs allowed us to make a prediction that relativistic SNe are born in environments similar to those of GRBs, that is, ones which are rich in atomic gas. Here we embark on testing this hypothesis by analysing the properties of the host galaxy NGC 3278 of the relativistic SN 2009bb. This is the first time the atomic gas properties of a relativistic SN host are provided and the first time resolved 21 cm-hydrogen-line (H I) information is provided for a host of an SN of any type in the context of the SN position. Methods. We obtained radio observations with the Australia Telescope Compact Array (ATCA) covering the H I line, and optical integral field unit spectroscopy observations with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). Moreover, we analysed archival carbon monoxide (CO) and multi-wavelength data for this galaxy. Results. The atomic gas distribution of NGC 3278 is not centred on the optical galaxy centre, but instead around a third of atomic gas resides in the region close to the SN position. This galaxy has a few times lower atomic and molecular gas masses than predicted from its SFR. Its specific SFR (sSFR ≡ SFR/M*) is approximately two to three times higher than the main-sequence value, placing it at the higher end of the main sequence, towards starburst galaxies. SN 2009bb exploded close to the region with the highest SFR density and the lowest age, as evident from high Hα EW, corresponding to the age of the stellar population of ~5.5 Myr. Assuming this timescale was the lifetime of the progenitor star, its initial mass would have been close to ~36 M⊙. Conclusions. As for GRB hosts, the gas properties of NGC 3278 are consistent with a recent inflow of gas from the intergalactic medium, which explains the concentration of atomic gas close to the SN position and the enhanced SFR. Super-solar metallicity at the position of the SN (unlike for most GRBs) may mean that relativistic explosions signal a recent inflow of gas (and subsequent star formation), and their type (GRBs or SNe) is determined either (i) by the metallicity of the inflowing gas, so that metal-poor gas results in a GRB explosion and metal-rich gas (for example a minor merger with an evolved galaxy or re-accretion of expelled gas) results in a relativistic SN explosion without an accompanying GRB, or (ii) by the efficiency of gas mixing (efficient mixing for SN hosts leading to a quick disappearance of metal-poor regions), or (iii) by the type of the galaxy (more metal-rich galaxies would result in only a small fraction of star formation being fuelled by metal-poor gas).
We have analysed multiband light curves of 328 intermediate-redshift (0.05 less than or equal to z < 0.24) Type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky Survey-II Supernova Survey. ...The multiband light curves were parametrized by using the multiband stretch method, which can simply parametrize light-curve shapes and peak brightness without dust extinction models. We found that most of the SNe Ia that appeared in red host galaxies (u - r > 2.5) do not have a broad light-curve width and the SNe Ia that appeared in blue host galaxies (u - r < 2.0) have a variety of light-curve widths. The Kolmogorov-Smirnov test shows that the colour distribution of SNe Ia appearing in red/blue host galaxies is different (a significance level of 99.9 per cent). We also investigate the extinction law of host galaxy dust. As a result, we find that the value of R sub( v) derived from SNe Ia with medium light-curve widths is consistent with the standard Galactic value, whereas the value of R sub( v) derived from SNe Ia that appear in red host galaxies becomes significantly smaller. These results indicate that there may be two types of SNe Ia with different intrinsic colours, and that they are obscured by host galaxy dust with two different properties.
We investigate the polarization spectra of hydrogen-rich core-collapse supernovae (Type II SNe). The polarization signal from SNe contains two independent components: intrinsic SN polarization and ...interstellar polarization (ISP). From these components, we can study the SN explosion geometry and the dust properties in their host galaxies or in the Milky Way. In this first paper, we employ a newly improved method to investigate the properties of the ISP components of 11 well-observed Type II SNe. Our analyses revealed that 10 of these 11 SNe showed a steady ISP component with a polarization degree of ≲1.0%, while one SN was consistent with zero ISP. As for the wavelength dependence, SN 2001dh (and possibly SN 2012aw) showed a non-Milky-Way-like ISP likely originating from the interstellar dust in their respective host galaxies: their polarization maxima were located at short wavelengths (≲4000 Å). Similar results have been obtained previously for highly reddened SNe. The majority of the SNe in our sample had uncertainties in the wavelength dependence of their ISP components that were too large for further consideration. Our work demonstrates that further investigation of the ISP component of the SN polarization, by applying this method to a larger SN sample, can provide new opportunities to study interstellar dust properties in external galaxies.
We investigate the polarization spectra of hydrogen-rich core-collapse supernovae (Type II SNe). The polarization signal from SNe contains two independent components: intrinsic SN polarization and ...interstellar polarization (ISP). From these components, we can study the SN explosion geometry and the dust properties in their host galaxies or in the Milky Way. In this first paper, we employ a newly improved method to investigate the properties of the ISP components of 11 well-observed Type II SNe. Our analyses revealed that 10 of these 11 SNe showed a steady ISP component with a polarization degree of ≲1.0%, while one SN was consistent with zero ISP. As for the wavelength dependence, SN 2001dh (and possibly SN 2012aw) showed a non-Milky-Way-like ISP likely originating from the interstellar dust in their respective host galaxies: their polarization maxima were located at short wavelengths (≲4000 Å). Similar results have been obtained previously for highly reddened SNe. The majority of the SNe in our sample had uncertainties in the wavelength dependence of their ISP components that were too large for further consideration. Our work demonstrates that further investigation of the ISP component of the SN polarization, by applying this method to a larger SN sample, can provide new opportunities to study interstellar dust properties in external galaxies.
We present an extended grid of multi-epoch 1D nonlocal thermodynamic equilibrium radiative transfer calculations for nebular-phase Type Ibc supernovae (SNe) from He-star explosions. Compared to our ...previous work, which was focused on a post-explosion epoch of 200 days, here we study the spectral evolution from 100 to about 450 days. We also augment the model set with progenitors that evolved without wind mass loss. Models with the same final, pre-SN mass have similar yields and produce essentially the same emergent spectra. Hence, the uncertain progenitor mass loss history compromises the inference of the initial, main sequence mass. This shortcoming does not affect Type IIb SNe in which mass-loss has left a small residual H-rich envelope in the progenitor star at core collapse and, hence, an intact He core. However, our 1D models with a different pre-SN mass tend to yield widely different spectra, as seen through variations in the strong emission lines due to N II λλ 6548, 6583, O I λλ 6300, 6364, Ca II λλ 7291, 7323, Ni II λ 7378, and the forest of Fe II lines below 5500 Å. At the lower mass end, the ejecta are He-rich, and at 100 days, they cool through He I, N II, Ca II, and Fe II lines, with N II and Fe II dominating at 450 days. These models, associated with He giants, stand in conflict to observed SNe Ib, which typically lack strong N II emission. Instead, they may lead to SNe Ibn or, because of additional stripping by a companion star, ultra-stripped SNe Ic. In contrast, for higher pre-SN masses, the ejecta are progressively He poor and cool at 100 days through O I, Ca II, and Fe II lines, with O I and Ca II dominating at 450 days. Non-uniform, aspherical, large-scale mixing is more likely to determine the SN type at intermediate pre-SN masses, rather than any compositional differences. Variations in clumping and mixing, as well as departures from spherical symmetry would increase the spectral diversity, but also introduce additional degeneracies. More robust predictions from spectral modeling thus require that careful attention be paid to the initial conditions by incorporating the salient features of physically consistent 3D explosion models.
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