CC SNe Research Articles

The GALEX-PTF Experiment. II. Supernova Progenitor Radius and Energetics via Shock-cooling Modeling

The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early ultraviolet (UV) observations of core-collapse supernovae (CC SNe). We present the results from a simultaneous Galaxy Evolution Explorer (GALEX) and Palomar Transient Factory (PTF) search for early UV emission from SNe. We analyze five CC SNe for which we obtained near-UV (NUV) measurements before the first ground-based R-band detection. We introduce SOPRANOS, a new maximum likelihood fitting tool for models with variable temporal validity windows, and use it to fit the Sapir & Waxman shock-cooling model to the data. We report four Type II SNe with progenitor radii in the range of R * ≈ 600–1100 R ⊙ and a shock velocity parameter in the range of v s* ≈ 2700–6000 km s−1 (E/M ≈ 2–8 × 1050 erg/M ⊙) and one Type IIb SN with R * ≈ 210 R ⊙ and v s* ≈ 11,000 km s−1 (E/M ≈ 1.8 × 1051 erg/M ⊙). Our pilot GALEX/PTF project thus suggests that a dedicated, systematic SN survey in the NUV band, such as the wide-field UV explorer ULTRASAT mission, is a compelling method to study the properties of SN progenitors and SN energetics.

Spatially resolved properties of supernova host galaxies in SDSS-IV MaNGA

We crossmatch galaxies from Mapping Nearby Galaxies at Apache Point Observatory with the Open Supernova Catalog, obtaining a total of 132 SNe within MaNGA bundle. These 132 SNe can be classified into 67 Type Ia and 65 Type CC. We study the global and local properties of supernova host galaxies statistically. Type Ia SNe are distributed in both star-forming galaxies and quiescent galaxies, while Type CC SNe are all distributed along the star-forming main sequence. As the stellar mass increases, the Type Ia/CC number ratio increases. We find: (1) there is no obvious difference in the interaction possibilities and environments between Type Ia SN hosts and a control sample of galaxies with similar stellar mass and SFR distributions, except that Type Ia SNe tend to appear in galaxies which are more bulge-dominated than their controls. For Type CC SNe, there is no difference between their hosts and the control galaxies in galaxy morphology, interaction possibilities as well as environments; (2) compared to galaxy centers, the SN locations have smaller velocity dispersion, lower metallicity, and younger stellar population. This is a natural result of radius gradients for all these parameters. The SN location and its symmetrical position relative to the galaxy center, as well as regions with similar effective radii have very similar [Mg/Fe], gas-phase metallicity, gas velocity dispersion and stellar population age.

The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z = 0.27

Abstract We present ZTF18abvkwla (the “Koala”), a fast blue optical transient discovered in the Zwicky Transient Facility (ZTF) One-Day Cadence (1DC) Survey. ZTF18abvkwla has a number of features in common with the groundbreaking transient AT 2018cow: blue colors at peak ( mag), a short rise time from half-max of under two days, a decay time to half-max of only three days, a high optical luminosity ( mag), a hot (≳40,000 K) featureless spectrum at peak light, and a luminous radio counterpart. At late times ( ), the radio luminosity of ZTF18abvkwla ( at 10 , observer-frame) is most similar to that of long-duration gamma-ray bursts (GRBs). The host galaxy is a dwarf starburst galaxy ( , ) that is moderately metal-enriched ( ), similar to the hosts of GRBs and superluminous supernovae. As in AT2018cow, the radio and optical emission in ZTF18abvkwla likely arise from two separate components: the radio from fast-moving ejecta ( ) and the optical from shock-interaction with confined dense material (<0.07 M ⊙ in ). Compiling transients in the literature with and mag, we find that a significant number are engine-powered, and suggest that the high peak optical luminosity is directly related to the presence of this engine. From 18 months of the 1DC survey, we find that transients in this rise-luminosity phase space are at least two to three orders of magnitude less common than CC SNe. Finally, we discuss strategies for identifying such events with future facilities like the Large Synoptic Survey Telescope, as well as prospects for detecting accompanying X-ray and radio emission.

Real-time, Value-driven Data Augmentation in the Era of LSST

Abstract The deluge of data from time-domain surveys is rendering traditional human-guided data collection and inference techniques impractical. We propose a novel approach for conducting data collection for science inference in the era of massive large-scale surveys that uses value-based metrics to autonomously strategize and coordinate follow-up in real time. We demonstrate the underlying principles in the Recommender Engine For Intelligent Transient Tracking (REFITT) that ingests live alerts from surveys and value-added inputs from data brokers to predict the future behavior of transients and design optimal data augmentation strategies given a set of scientific objectives. The prototype presented in this paper is tested to work given simulated Rubin Observatory Legacy Survey of Space and Time (LSST) core-collapse supernova (CC SN) light curves from the Photometric LSST Astronomical Time-series Classification Challenge data set. CC SNe were selected for the initial development phase as they are known to be difficult to classify, with the expectation that any learning techniques for them should be at least as effective for other transients. We demonstrate the behavior of REFITT on a random LSST night given ∼32,000 live CC SNe of interest. The system makes good predictions for the photometric behavior of the events and uses them to plan follow-up using a simple data-driven metric. We argue that machine-directed follow-up maximizes the scientific potential of surveys and follow-up resources by reducing downtime and bias in data collection.

A DECam Search for Explosive Optical Transients Associated with IceCube Neutrino Alerts

In this work, we investigate the likelihood of association between realtime, TeV-PeV energy neutrino alerts from IceCube and optical counterparts in the form of core-collapse supernovae (CC SNe). The optical follow-up of IceCube alerts requires two main instrumental capabilities: (1) deep imaging, since 73\% of neutrinos would come from CC SNe at redshifts $z > 0.3$, and (2) a large field of view (FoV), since typical IceCube muon neutrino pointing accuracy is on the order of $\sim1$~deg. With Blanco/DECam ($gri$ to 24th magnitude and $2.2$~deg diameter FoV), we performed a triggered optical follow-up observation of two IceCube alerts, IC170922A and IC171106A on $\sim6$~nights during the $\sim3$~weeks following each alert. For the IC170922A (IC171106A) follow-up observations, we expect that 12.1\% (9.5\%) of coincident CC SNe at $z \lesssim 0.3$ are detectable, and that on average, 0.23 (0.07) unassociated SNe in the neutrino 90\% containment regions also pass our selection criteria. We find two candidate CC SNe that are temporally coincident with the neutrino alerts in the FoV, but none in the 90\% containment regions, which is statistically consistent with expected rates of background CC SNe for these observations. If CC SNe are the dominant source of TeV-PeV neutrinos, we would expect an excess of coincident CC SNe to be detectable at the $3\sigma$ confidence level using DECam observations similar to those of this work for $\sim60$ ($\sim200$) neutrino alerts with (without) redshift information for all candidates.

A meta-analysis of core-collapse supernova56Ni masses

Context.A fundamental property determining the transient behaviour of core-collapse supernovae (CC SNe) is the amount of radioactive56Ni synthesised in the explosion. Using established methods, this is a relatively easy parameter to extract from observations.Aims.I provide a meta-analysis of all published56Ni masses for CC SNe.Methods.Collating a total of 258 literature56Ni masses, I compared distributions of the main CC SN types: SNe II, SNe IIb, SNe Ib, SNe Ic, and SNe IcBL.Results.Using these published values, I calculated a median56Ni mass of 0.032M⊙for SNe II (N = 115), 0.102M⊙for SNe IIb (N = 27), 0.163M⊙for SNe Ib (N = 33), 0.155M⊙for SNe Ic (N = 48), and 0.369M⊙for SNe IcBL (N = 32). On average, stripped-enevelope SNe (SE-SNe: IIb, Ib, Ic, and Ic-BL) have much higher values than SNe II. These observed distributions are compared to those predicted from neutrino-driven explosion models. While the SN II distribution follows model predictions, the SE-SNe have a significant fraction of events with56Ni masses much higher than predicted.Conclusions.If the majority of published56Ni masses are to be believed, these results imply significant differences in the progenitor structures and/or explosion properties between SNe II and SE-SNe. However, such distinct progenitor and explosion properties are not currently favoured in the literature. Alternatively, the popular methods used to estimate56Ni masses for SE-SNe may not be accurate. Possible issues with these methods are discussed, as are the implications of true56Ni mass differences on progenitor properties of different CC SNe.

Supernova rates from the SUDARE VST-Omegacam search II. Rates in a galaxy sample

This is the second paper of a series in which we present measurements of the Supernova (SN) rates from the SUDARE survey. In this paper, we study the trend of the SN rates with the intrinsic colours, the star formation activity and the mass of the parent galaxies. We have considered a sample of about 130000 galaxies and a SN sample of about 50 events. We found that the SN Ia rate per unit mass is higher by a factor of six in the star-forming galaxies with respect to the passive galaxies. The SN Ia rate per unit mass is also higher in the less massive galaxies that are also younger. These results suggest a distribution of the delay times (DTD) less populated at long delay times than at short delays. The CC SN rate per unit mass is proportional to both the sSFR and the galaxy mass. The trends of the Type Ia and CC SN rates as a function of the sSFR and the galaxy mass that we observed from SUDARE data are in agreement with literature results at different redshifts. The expected number of SNe Ia is in agreement with the observed one for all four DTD models considered both in passive and star-forming galaxies so we can not discriminate between different progenitor scenarios. The expected number of CC SNe is higher than the observed one, suggesting a higher limit for the minimum progenitor mass. We also compare the expected and observed trends of the SN Ia rate with the intrinsic U - J colour of the parent galaxy, assumed as a tracer of the age distribution. While the slope of the relation between the SN Ia rate and the U - J color in star-forming galaxies can be reproduced well by all four DTD models considered, only the steepest of them is able to account for the rates and colour in star-forming and passive galaxies with the same value of the SN Ia production efficiency.

Metallicity measurements of gamma-ray burst and supernova explosion sites: lessons from H ii regions in M31

We examine how the small-scale ($<$\,kpc) variation of metallicity within a galaxy, which is found in nearby galaxies, affect the observational estimates of metallicity in the explosion sites of transient events such as core-collapse supernovae (CC SNe) and gamma-ray bursts (GRBs). Assuming the same luminosity, metallicity, and spatial distributions of \ion{H}{ii}\ regions (hereafter HIIRs) as observed in M31, we compute the apparent metallicities that we would obtain when the spectrum of a target region is blended with those of surrounding HIIRs within the length scale of typical spatial resolution. When the spatial resolution of spectroscopy is $\lesssim$ 0.5\,kpc, which is typical for the existing studies of CC SN sites, we find that the apparent metallicities reflect the metallicities of target regions, but with significant systematic uncertainties in some cases. When the spatial resolution is $\gtrsim$ 1.0 kpc, regardless of the target regions (which has a wide range of metallicity that spans $\sim$ 0.6 dex for the M31 HIIRs), we always obtain the apparent metallicities similar to the average metallicity of the M31 HIIRs. Given that the apparent metallicities measured with $\gtrsim$\,kpc scale resolution do not necessarily reflect the immediate environment of the stellar explosions, the current observational estimates of high metallicities for some of the long GRB host galaxies do {\em not} rule out the hypothesis that the long GRBs are exclusively born in a low-metallicity environment.

Statistical Studies of Supernova Environments

AbstractMapping the diversity of SNe to progenitor properties is key to our understanding of stellar evolution and explosive stellar death. Investigations of the immediate environments of SNe allow statistical constraints to be made on progenitor properties such as mass and metallicity. Here, we review the progress that has been made in this field. Pixel statistics using tracers of e.g. star formation within galaxies show intriguing differences in the explosion sites of, in particular SNe types II and Ibc (SNe II and SNe Ibc respectively), suggesting statistical differences in population ages. Of particular interest is that SNe Ic are significantly more associated with host galaxy Hα emission than SNe Ib, implying shorter lifetimes for the former. In addition, such studies have shown (unexpectedly) that the interacting SNe IIn do not explode in regions containing the most massive stars, which suggests that at least a significant fraction of their progenitors arise from the lower end of the core-collapse SN mass range. Host H ii region spectroscopy has been obtained for a significant number of core-collapse events, however definitive conclusions on differences between distinct SN types have to-date been elusive. Single stellar evolution models predict that the relative fraction of SNe Ibc to SNe II should increase with increasing metallicity, due to the dependence of mass-loss rates on progenitor metallicity. We present a meta-analysis of all current host H ii region oxygen abundances for CC SNe. It is concluded that the SN II to SN Ibc ratio shows little variation with oxygen abundance, with only a suggestion that the ratio increases in the lowest bin. Radial distributions of different SNe are discussed, where a central excess of SNe Ibc has been observed within disturbed galaxy systems, which is difficult to ascribe to metallicity or selection effects. Environment studies are also being undertaken for SNe Ia, where constraints can be made on the shortest delay times of progenitor systems. It is shown that ‘redder’ SNe Ia are more often found within star-forming regions. Environment studies are evolving to enable studies at higher spatial resolutions than previously possible, while in addition the advent of wide-field integral field unit instruments allows galaxy-wide spectral analyses which will provide fruitful results to this field. Some example contemporary results are shown in that direction.

Probing the stellar initial mass function with high-z supernovae

The first supernovae will soon be visible at the edge of the observable universe, revealing the birthplaces of Population III stars. With upcoming near-infrared missions, a broad analysis of the detectability of high-$z$ supernovae is paramount. We combine cosmological and radiation transport simulations, instrument specifications, and survey strategies to create synthetic observations of primeval core-collapse, Type IIn and pair-instability supernovae with the James Webb Space Telescope ($JWST$). We show that a dedicated observational campaign with the $JWST$ can detect up to $\sim 15$ pair-instability explosions, $\sim 300$ core-collapse supernovae, but less than one Type IIn explosion per year, depending on the Population III star formation history. Our synthetic survey also shows that $\approx 1-2 \times10^2$ supernovae detections, depending on the accuracy of the classification, are sufficient to discriminate between a Salpeter and flat mass distribution for high redshift stars with a confidence level greater than 99.5 per cent. We discuss how the purity of the sample affects our results and how supervised learning methods may help to discriminate between CC and PI SNe.

Princicpal Component Analysis of type II supernova V band light-curves

AbstractWe present a Principal Component Analysis (PCA) of the V band light-curves of a sample of more than 100 nearby Core collapse supernovae (CC SNe) from [Anderson et al. (2014)]. We used different reference epochs in order to extract the common properties of these light-curves and searched for correlations to some physical parameters such as the burning of 56Ni, and morphological light-curve parameters such as the length of the plateau, the stretch of the light-curve, and the decrements in brightness after maximum and after the plateau. We also used these similarities to create SNe II light-curve templates that will be used in the future for standardize these objects and determine cosmological distances.

Twelve type II-P supernovae seen with the eyes ofSpitzer

Core-collapse supernovae (CC SNe), especially those of type II-plateau (II-P), are thought to be important contributors to cosmic dust production. The most obvious indicator of the presence of newly-formed and/or pre-existing dust is the time-dependent mid-infrared (MIR) excess coming from the environment of SNe. Our goal was to collect publicly available, previously unpublished measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The temporal changes of the observed fluxes may be indicative of the underlying supernova, while spectral energy distribution (SED) fitting to the fluxes in different IRAC channels may reveal the physical parameters of the mid-IR radiation, presumably due to warm dust. IRS spectra were extracted and calibrated with SPICE, while photometric SEDs were assembled using IRAF and MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to get basic information on the dust presumed as the source of MIR radiation. We found twelve SNe satisfying the criterion above, observed at late-time epochs (typically after +300 days). In three cases we could not identify any point source at the SN position on late time IRAC images. We found two SNe, 2005ad and 2005af, which likely have newly-formed dust in their environment, while in the other seven cases the observed MIR flux may originate from pre-existing circumstellar or interstellar dust. Our results support the previous observational conclusions that warm new dust in the environment of SNe contributes only marginally to cosmic dust content.

Supernovae in the Subaru Deep Field: the rate and delay-time distribution of Type Ia supernovae out to redshift 2

The Type Ia supernova (SN Ia) rate, when compared to the cosmic star formation history (SFH), can be used to derive the delay-time distribution (DTD; the hypothetical SN Ia rate versus time following a brief burst of star formation) of SNe Ia, which can distinguish among progenitor models. We present the results of a supernova (SN) survey in the Subaru Deep Field (SDF). Over a period of 3 years, we have observed the SDF on four independent epochs with Suprime-Cam on the Subaru 8.2-m telescope, with two nights of exposure per epoch, in the R, i′and z′ bands. We have discovered 150 SNe out to redshift z≈ 2. Using 11 photometric bands from the observer-frame far-ultraviolet to the near-infrared, we derive photometric redshifts for the SN host galaxies (for 24 we also have spectroscopic redshifts). This information is combined with the SN photometry to determine the type and redshift distribution of the SN sample. Our final sample includes 28 SNe Ia in the range 1.0 < z < 1.5 and 10 in the range 1.5 < z < 2.0. As our survey is largely insensitive to core-collapse SNe (CC SNe) at z > 1, most of the events found in this range are likely SNe Ia. Our SN Ia rate measurements are consistent with those derived from the Hubble Space Telescope (HST) Great Observatories Origins Deep Survey (GOODS) sample, but the overall uncertainty of our 1.5 < z < 2.0 measurement is a factor of 2 smaller, of 35–50 per cent. Based on this sample, we find that the SN Ia rate evolution levels off at 1.0 < z < 2.0, but shows no sign of declining. Combining our SN Ia rate measurements and those from the literature, and comparing to a wide range of possible SFHs, the best-fitting DTD (with a reduced χ2= 0.7) is a power law of the form Ψ(t) ∝tβ, with index β=−1.1 ± 0.1 (statistical) ±0.17 (systematic). This result is consistent with other recent DTD measurements at various redshifts and environments, and is in agreement with a generic prediction of the double-degenerate progenitor scenario for SNe Ia. Most single-degenerate models predict different DTDs. By combining the contribution from CC SNe, based on the wide range of SFHs, with that from SNe Ia, calculated with the best-fitting DTD, we predict that the mean present-day cosmic iron abundance is in the range ZFe= (0.09–0.37) ZFe, ⊙. We further predict that the high-z SN searches now beginning with HST will discover 2–11 SNe Ia at z > 2.

Nearby supernova rates from the Lick Observatory Supernova Search - IV. A recovery method for the delay-time distribution

The supernova (SN) delay-time distribution (DTD) - the SN rate versus time that would follow a brief burst of star formation - can shed light on SN progenitors, and on chemical enrichment timescales. Previous attempts to recover the DTD have used comparisons of mean SN rates vs. redshift to cosmic star-formation history (SFH), or comparison of SN rates among galaxies of different mean ages. We present an approach to recover the SN DTD that avoids such averaging. We compare the SFHs of individual galaxies to the numbers of SNe discovered in each galaxy (generally zero, sometimes one or a few SNe). We apply the method to a subsample of 3505 galaxies, hosting 82 SNe Ia and 119 core-collapse SNe (CC SNe), from the Lick Observatory SN Search (LOSS), with SFHs reconstructed from SDSS spectra. We find a >2sigma SN Ia DTD signal in our shortest-delay, "prompt", bin at <420 Myr. Despite a systematic error, due to the limited aperture of the SDSS spectroscopic fibres, which causes some of the prompt signal to leak to the later DTD bins, the data require prompt SNe Ia at the >99% confidence. We further find, at 4sigma, SNe Ia that are "delayed" by > 2.4 Gyr. Thus, the data support the existence of both prompt and delayed SNe Ia. The time integral over the CC SN DTD is 0.010+/-0.002 SNe per Msun, as expected if all stars of mass >8 Msun lead to visible SN explosions. This argues against a minimum mass for CC SNe of >10 Msun, and against a significant fraction of massive stars that collapse without exploding. For SNe Ia, the time-integrated DTD is 0.0023+/-0.0006 SNe per Msun formed, most of them with delays < 2.4 Gyr. We show, using simulations, that application of the method to the full existing LOSS sample, but with complete and unbiased SFH estimates for the survey galaxies, could provide a detailed measurement of the SN Ia DTD.

Dust formation in the ejecta of the type II-P supernova 2004dj

Core-collapse supernovae (CC SNe), especially Type II-Plateau ones, are thought to be important contributors to cosmic dust production. SN 2004dj, one of the closest and brightest SN since 1987A, offered a good opportunity to examine dust formation processes. To find signs of newly formed dust, we analyze all available mid-infrared (MIR) archival data from the Spitzer Space Telescope. We re-reduce and analyze data from IRAC, MIPS and IRS instruments obtained between +98 and +1381 days after explosion, generating light curves and spectra for each epoch. Observed spectral energy distributions are fitted with both analytic and numerical models, using the radiative-transfer code MOCASSIN for the latter ones. We also use imaging polarimetric data obtained at +425 days by the Hubble Space Telescope. We present convincing evidence of dust formation in the ejecta of SN 2004dj from MIR light curves and spectra. Significant MIR excess flux is detected in all bands between 3.6 and 24 um. In the optical, a ~0.8% polarization is also detected at a 2-sigma level, which exceeds the interstellar polarization in that direction. Our analysis shows that the freshly-formed dust around SN 2004dj can be modeled assuming a nearly spherical shell containing amorphous carbon grains, cooling from ~700 K to ~400 K between +267 and +1246 days. Persistent excess flux has been found above 10 um, which is explained by a cold (~115 K) dust component. If this cold dust is of circumstellar origin, it is likely to be condensed in a cool, dense shell between the forward and reverse shocks. Pre-existing circumstellar dust is less likely, but cannot be ruled out. An upper limit of ~8x10^{-4} M_sun was derived for the dust mass, which is similar to previously published values for other dust-producing SNe.

CHARACTERIZING THE CONTAMINATING DISTANCE DISTRIBUTION FOR BAYESIAN SUPERNOVA COSMOLOGY

Measurements of the equation of state of dark energy from surveys of thousands of Type Ia Supernovae will be limited by spectroscopic follow-up and must therefore rely on photometric identification, increasing the chance that the sample is contaminated by core collapse supernovae (CC SNe). Bayesian methods for SN cosmology can remove contamination bias while maintaining high statistical precision but are sensitive to the choice of parameterization of the contaminating distance distribution. We use simulations to investigate the form of the contaminating distribution and its dependence on the absolute magnitudes, light curve shapes, colors, extinction, and redshifts of CC SNe. We find that the CC luminosity function (LF) dominates the distance distribution function, but its shape is increasingly distorted as the redshift increases and more CC SNe fall below the survey magnitude limit. The shapes and colors of the CC light curves generally shift the distance distribution, and their effect on the CC distances is correlated. We compare the simulated distances to the first year results of the SDSS-II SN survey and find that the SDSS distance distributions can be reproduced with simulated CC SNe that are ∼1 mag fainter than the standard Richardson et al. LFs, which do not produce a good fit. To exploit the full power of the Bayesian parameter estimation method, parameterization of the contaminating distribution should be guided by the current knowledge of the CC LFs, coupled with the effects of the survey selection and magnitude limit, and allow for systematic shifts caused by the parameters of the distance fit.

The Ultraviolet View of Supernovae

The Ultraviolet View of Supernovae

The Carbon-rich Type Ic SN 2007gr: The Photospheric Phase

The first two months of spectroscopic and photometric monitoring of the nearby type Ic SN 2007gr are presented. The very early discovery (less than 5 days after the explosion) and the relatively short distance of the host galaxy motivated an extensive observational campaign. SN 2007gr shows an average peak luminosity but unusually narrow spectral lines and an almost flat photospheric velocity profile. The detection of prominent carbon features in the spectra is shown and suggest a wide range in carbon abundance in stripped-envelope supernovae. SN 2007gr may be an important piece in the puzzle of the observed diversity of CC SNe.

How many supernovae are we missing at high redshift?

Near-infrared and radio searches for core-collapse supernovae (CC SNe) in the local universe have shown that the vast majority of the events occurring in massive starburst are missed by the current optical searches as they explode in very dusty environments. Recent infrared observations have shown that the fraction of star formation activity that takes place in very luminous dusty starbursts sharply increases with redshift and becomes the dominant star formation component at z 0.5. As a consequence, an increasing fraction of SNe are expected to be missed by high-redshift optical searches. We estimate that 5‐10 per cent of the local CC SNe are out of reach of the optical searches. The fraction of missing events rises sharply towards z = 1, when about 30 per cent of the CC SNe will be undetected. At z = 2 the missing fraction will be about 60 per cent. Correspondingly, for Type Ia SNe, our computations provide missing fractions of 15 per cent at z = 1 and 35 per cent at z = 2. Such large corrections are crucially important to compare the observed SN rate with the expectations from the evolution of the cosmic star formation history, and to design the future SN searches at high redshifts.

The metallicity dependence of the long-duration gamma-ray burst rate from host galaxy luminosities

We investigate the difference between the host galaxy properties of core-collapse supernovae (CC SNe) and long-duration gamma-ray bursts (LGRBs), and quantify a possible metallicity dependence of the efficiency of producing LGRBs. We use a sample of 16 CC SNe and 16 LGRBs from Fruchter et al. which have similar redshift distributions to eliminate galaxy evolution biases. We make a forward prediction of their host galaxy luminosity distributions from the overall cosmic metallicity distribution of star formation. The latter is based on luminosity functions, star formation rates (SFRs) and luminosity-metallicity (L-Z) relations of galaxies. This appioach is supported by the finding that LGRB hosts follow the L-Z relations of star-forming galaxies. We then compare predictions for metallicity-dependent event efficiencies with the observed host data. We find that ultraviolet-based SFR estimates predict the host distribution of CC SNe perfectly well in a metallicity-independent form. In contrast, LGRB hosts are on average fainter by one magnitude, almost as faint as the Large Magellanic Cloud. Assuming this to be a metallicity effect, the present data are insufficient to discriminate between a sharp cut-off and a soft decrease in efficiency towards higher metallicity. For a sharp cut-off, however, we find a best value for the cut-off metallicity, as reflected in the oxygen abundance, 12 + log (O/H) lim ≃ 8.7 ± 0.3 at 95 per cent confidence including systematic uncertainties, in the calibration of Asplund, Grevesse & Sauval. This value is somewhat lower than the traditionally quoted value for the Sun, but is comparable to the revised solar oxygen abundance. LGRB models that require sharp metallicity cut-offs well below approximately one-half the revised solar metallicity appear to be effectively ruled out, as they would require fainter LGRB hosts than those that are observed. We also discuss the likely implications of the still ongoing metallicity 'calibration debate'.