The effects of varying colour–luminosity relations on Type Ia supernova science (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2021
Using Zwicky Transient Facility (ZTF) observations, we identify a pair of ‘sibling’ Type Ia supernovae (SNe Ia), i.e. hosted by the same galaxy at z = 0.0541. They exploded within 200 d from each other at a separation of 0.6,mathrmarcsec0.6\,\mathrm{ arcsec}0.6,mathrmarcsec corresponding to a projected distance of only 0.6 kpc. Performing salt2 light-curve fits to the gri ZTF photometry, we show that for these equally distant ‘standardizable candles’, there is a difference of 2 mag in their rest-frame B-band peaks, and the fainter supernova (SN) has a significantly red salt2 colour c = 0.57 ± 0.04, while the stretch values x1 of the two SNe are similar, suggesting that the fainter SN is attenuated by dust in the interstellar medium of the host galaxy. We use these measurements to infer the salt2 colour standardization parameter, β = 3.5 ± 0.3, independent of the underlying cosmology and Malmquist bias. Assuming the colour excess is entirely due to dust, the result differs by 2σ from the average Milky Way total-t...
COLOR DISPERSION AND MILKY-WAY-LIKE REDDENING AMONG TYPE Ia SUPERNOVAE
The Astrophysical Journal, 2014
Past analyses of Type Ia Supernovae (SNe Ia) have identified an irreducible scatter of 5 − 10% in distance widely attributed to an intrinsic dispersion in luminosity. Another, equally valid, source of this scatter is intrinsic dispersion in color. Misidentification of the true source of this scatter can bias both the retrieved color-luminosity relation and cosmological parameter measurements. The size of this bias depends on the magnitude of the intrinsic color dispersion relative to the distribution of colors that correlate with distance. We produce a realistic simulation of a misattribution of intrinsic scatter, and find a negative bias in the recovered color-luminosity relation, β, of ∆β ≈ −1.0 (∼ 33%) and a positive bias in the equation of state parameter, w, of ∆w ≈ +0.04 (∼ 4%). We re-analyze current published data sets with the assumptions that the distance scatter is predominantly the result of color. Unlike previous analyses, we find that the data are consistent with a Milky Way reddening law (R V = 3.1), and that a Milky Way dust model better predicts the asymmetric color-luminosity trends than the conventional luminosity scatter hypothesis. We also determine that accounting for color variation reduces the correlation between various Host galaxy properties and Hubble residuals by ∼ 20%.
The Astrophysical Journal, 2017
Conventional Type Ia supernova (SN Ia) cosmology analyses currently use a simplistic linear regression of magnitude versus color and light curve shape, which does not model intrinsic SN Ia variations and host galaxy dust as physically distinct effects, resulting in low color-magnitude slopes. We construct a probabilistic generative model for the dusty distribution of extinguished absolute magnitudes and apparent colors as the convolution of a intrinsic SN Ia color-magnitude distribution and a host galaxy dust reddening-extinction distribution. If the intrinsic color-magnitude (M B vs. B − V) slope β int differs from the host galaxy dust law R B , this convolution results in a specific curve of mean extinguished absolute magnitude vs. apparent color. The derivative of this curve smoothly transitions from β int in the blue tail to R B in the red tail of the apparent color distribution. The conventional linear fit approximates this effective curve near the average apparent color, resulting in an apparent slope β app between β int and R B. We incorporate these effects into a hierarchical Bayesian statistical model for SN Ia light curve measurements, and analyze a dataset of SALT2 optical light curve fits of 248 nearby SN Ia at z < 0.10. The conventional linear fit obtains β app ≈ 3. Our model finds a β int = 2.3 ± 0.3 and a distinct dust law of R B = 3.8 ± 0.3, consistent with the average for Milky Way dust, while correcting a systematic distance bias of ∼ 0.10 mag in the tails of the apparent color distribution. Finally, we extend our model to examine the SN Ia luminosity-host mass dependence in terms of intrinsic and dust components.
A galaxy-driven model of type Ia supernova luminosity variations
Monthly Notices of the Royal Astronomical Society
Type Ia supernovae (SNe Ia) are used as standardizable candles to measure cosmological distances, but differences remain in their corrected luminosities which display a magnitude step as a function of host galaxy properties such as stellar mass and rest-frame U−R colour. Identifying the cause of these steps is key to cosmological analyses and provides insight into SN physics. Here we investigate the effects of SN progenitor ages on their light-curve properties using a galaxy-based forward model that we compare to the Dark Energy Survey 5-yr SN Ia sample. We trace SN Ia progenitors through time and draw their light-curve width parameters from a bimodal distribution according to their age. We find that an intrinsic luminosity difference between SNe of different ages cannot explain the observed trend between step size and SN colour. The data split by stellar mass are better reproduced by following recent work implementing a step in total-to-selective dust extinction ratio (RV) between ...
The Astrophysical Journal, 2020
We present optical and near-infrared (ugriY JH) photometry of host galaxies of Type Ia supernovae (SN Ia) observed by the Carnegie Supernova Project-I. We determine host galaxy stellar masses and, for the first time, study their correlation with SN Ia standardized luminosity across optical and nearinfrared (uBgV riY JH) bands. In the individual bands, we find that SNe Ia are more luminous in more massive hosts with luminosity offsets ranging between −0.07±0.03 mag to −0.15±0.04 mag after lightcurve standardization. The slope of the SN Ia Hubble residual-host mass relation is negative across all uBgV riY JH bands with values ranging between −0.036±0.025 mag/dex to −0.097±0.027 mag/deximplying that SNe Ia in more massive galaxies are brighter than expected. The near-constant observed correlations across optical and near-infrared bands indicate that dust may not play a significant role in the observed luminosity offset-host mass correlation. We measure projected separations between SNe Ia and their host centers, and find that SNe Ia that explode beyond a projected 10 kpc have a 30% to 50% reduction of the dispersion in Hubble residuals across all bands-making them a more uniform subset of SNe Ia. Dust in host galaxies, peculiar velocities of nearby SN Ia, or a combination of both may drive this result as the color excesses of SNe Ia beyond 10 kpc are found to be generally lower than those interior, but there is also a diminishing trend of the dispersion as we exclude nearby events. We do not find that SN Ia average luminosity varies significantly when they are grouped in various host morphological types. Host galaxy data from this work will be useful, in conjunction with future high-redshift samples, in constraining cosmological parameters.
The Astrophysical Journal, 2000
From an analysis of SNe 1972E, 1980N, 1981B, 1981D, 1983R, 1998bu, 1999cl, and 1999cp we find that the intrinsic V−K colors of Type Ia SNe of typical luminosity (i.e. with multi-color light curve shape (MLCS) parameter −0.4 ∼ < ∆ ∼ < +0.2 mag) suggest a uniform color curve. V−K colors become bluer linearly with time from roughly one week before B-band maximum until one week after maximum, after which they redden linearly until four weeks after maximum. V−H colors exhibit very similar color evolution. V−J colors exhibit slightly more complex evolution, with greater scatter. The existence of V minus near infrared color relations allows the construction of near infrared light curve templates that are an improvement on those of .
THE CARNEGIE SUPERNOVA PROJECT: INTRINSIC COLORS OF TYPE Ia SUPERNOVAE
The Astrophysical Journal, 2014
We present an updated analysis of the intrinsic colors of SNe Ia using the latest data release of the Carnegie Supernova Project. We introduce a new light-curve parameter very similar to stretch that is better suited for fast-declining events, and find that these peculiar types can be seen as extensions to the population of "normal" SNe Ia. With a larger number of objects, an updated fit to the Lira relation is presented along with evidence for a dependence on the late-time slope of the B − V lightcurves with stretch and color. Using the full wavelength range from u to H band, we place constraints on the reddening law for the sample as a whole and also for individual events/hosts based solely on the observed colors. The photometric data continue to favor low values of R V , though with large variations from event to event, indicating an intrinsic distribution. We confirm the findings of other groups that there appears to be a correlation between the derived reddening law, R V , and the color excess, E(B − V), such that larger E(B − V) tends to favor lower R V. The intrinsic u-band colors show a relatively large scatter that cannot be explained by variations in R V or by the Goobar (2008) power-law for circumstellar dust, but rather is correlated with spectroscopic features of the supernova and is therefore likely due to metallicity effects.
The Dependence of Type Ia Supernova Luminosities on Their Local Environment
We present a fully consistent catalog of the local and global properties of the host galaxies of 882 Type Ia supernovae (SNIa) spanning the redshift range 0.01 < z < 1 and corresponding to a preliminary version of the compilation sample including SNLS 5 years data, SDSS, and low redshift surveys. We measure low and moderate redshift host galaxy photometry in SDSS stacked and single-epoch images and use SED fitting techniques to derive host properties such as stellar mass and U − V rest-frame colors, the latter being an indicator of the luminosity weighted age of the stellar population in a galaxy. We combine these results with high redshift host photometry from the SNLS survey and thus obtain a consistent catalog of host stellar masses and colors across a wide redshift range. We also estimate the local observed fluxes at the supernova location within a proper distance radius of 3 kpc, and transpose them into local U − V rest-frame colors. This is the first time that local environments surrounding SNIa have been measured at redshifts spanning the entire Hubble diagram. We find that local U − V colors convey more information than the properties of the host galaxy as a whole (host stellar mass or global U − V rest-frame color). Once selection requirements are chosen, we perform cosmological fits using local color as a third standardization variable and find its significance at the level of 7σ, indicating that the remaining luminosity variations in SNIa samples can be reduced using a third variable in light-curve fitters taking the local environment into account. Moreover, Hubble diagram residuals are more correlated with local color than any other variable. We discuss the possible implications for cosmology and find that using the local color in place of the stellar mass results in a change in the measured value of the dark energy equation of state parameter of 0.6%. Standardization using local U − V color in addition to stretch and color reduces the total dispersion in the Hubble diagram from 0.15 to 0.14 mag. This will be of paramount importance for the forthcoming SNIa surveys, and in particular LSST for which w(z) will be accessible in bins of redshift with a constraining power several orders of magnitude greater than that of current surveys.
The Astrophysical Journal, 2012
We use type-Ia supernovae (SNe Ia) discovered by the SDSS-II SN Survey to search for dependencies between SN Ia properties and the projected distance to the host galaxy center, using the distance as a proxy for local galaxy properties (local star-formation rate, local metallicity, etc.). The sample consists of almost 200 spectroscopically or photometrically confirmed SNe Ia at redshifts below 0.25. The sample is split into two groups depending on the morphology of the host galaxy. We fit light-curves using both MLCS2k2 and SALT2, and determine color (A V , c) and light-curve shape (∆, x 1 ) parameters for each SN Ia, as well as its residual in the Hubble diagram. We then correlate these parameters with both the physical and the normalized distances to the center of the host galaxy and look for trends in the mean values and scatters of these parameters with increasing distance. The most significant (at the 4 σ level) finding is that the average fitted A V from MLCS2k2 and c from SALT2 decrease with the projected distance for SNe Ia in spiral galaxies. We also find indications that SNe in elliptical galaxies tend to have narrower light-curves if they explode at larger distances, although this may be due to selection effects in our sample. We do not find strong correlations between the residuals of the distance moduli with respect to the Hubble flow and the galactocentric distances, which indicates a limited correlation between SN magnitudes after standardization and local host metallicity.