Type Ia Supernovae

Type Ia Supernovae are in many aspects still enigmatic objects. Recent years have witnessed a bonanza of supernova observations. The increased samples from dedicated searches have allowed the statistical investigation of Type Ia Supernovae as a class. The observational data on Type Ia Supernovae are very rich, and the uniform picture of a decade ago has been replaced by several correlations which connect the maximum luminosity with light curve shape, color evolution, spectral appearance, and host galaxy morphology. These correlations hold across almost the complete spectrum of Type Ia Supernovae, with a number of notable exceptions. After 150 days past maximum, however, all observed objects show the same decline rate and spectrum. Bolometric light curves are a handy tool to investigate the overall appearance of Type Ia Supernovae. The nickel masses derived this way show large variations, which combined with the dynamics from line widths, indicate that the brighter events are also coming from more massive objects. The lack of accurate distances and the uncertainty in the correction for absorption are hampering further progress. Improvements in these areas are vital for the detailed comparison of luminosities and the determination of nickel masses.Comment: 33 pages with 4 embedded figures; To appear in Astronomy and Astrophysics Revie

Emission within a Damped Lyman Alpha Absorption Trough: the Complex Sight Line Towards Q2059-360

We present new spectroscopic observations of the quasar Q2059-360, confirming the existence of an emission feature within the Damped Lyman Alpha (DLA) absorption trough. By observing also at slit positions offset from the quasar, we show that the emission is spatially extended by at least a few arcseconds, and hence confirm that the feature seen must be due to emission rather than unusual absorption characteristics. We find that the DLA trough is very close in redshift to the broad Lyman~$\alpha$ emission line of the QSO, with the result that the DLA absorption removes much of the peak region of that line. Despite the similarity of the redshifts of the DLA and the QSO, the lack of high-ionization lines of the DLA system and the unresolved widths of the corresponding metal lines indicate that the DLA cloud is not an associated system. The emission feature has a large velocity offset of +490 km/s with respect to the DLA system, and is resolved in velocity, comprising two components with a separation of ~ 300 km/s. We consider three possibilities: (1) Both emission and absorption occur within an object similar to the high redshift Lyman-break galaxies; (2) The emission feature arises from an object distinct from both the DLA absorber and the QSO, perhaps a young star-forming galaxy or a proto-galactic clump. It could be associated with the DLA absorber and perhaps the QSO in a compact group or cluster; (3) The redshifts are such that the emission feature could be due to Narrow Line Region filaments of the QSO, if the DLA absorption covers a sufficiently small angular size to allow the filaments to be seen beyond the edge of the DLA cloud.Comment: 10 pages, 6 figures. Accepted for publication in MNRA

Measuring the Hubble constant with Type Ia supernovae as near-infrared standard candles

The most precise local measurements of $H_0$ rely on observations of Type Ia supernovae (SNe Ia) coupled with Cepheid distances to SN Ia host galaxies. Recent results have shown tension comparing $H_0$ to the value inferred from CMB observations assuming $\Lambda$CDM, making it important to check for potential systematic uncertainties in either approach. To date, precise local $H_0$ measurements have used SN Ia distances based on optical photometry, with corrections for light curve shape and colour. Here, we analyse SNe Ia as standard candles in the near-infrared (NIR), where intrinsic variations in the supernovae and extinction by dust are both reduced relative to the optical. From a combined fit to 9 nearby calibrator SNe with host Cepheid distances from Riess et al. (2016) and 27 SNe in the Hubble flow, we estimate the absolute peak $J$ magnitude $M_J = -18.524\;\pm\;0.041$ mag and $H_0 = 72.8\;\pm\;1.6$ (statistical) $\pm$ 2.7 (systematic) km s$^{-1}$ Mpc$^{-1}$. The 2.2 $\%$ statistical uncertainty demonstrates that the NIR provides a compelling avenue to measuring SN Ia distances, and for our sample the intrinsic (unmodeled) peak $J$ magnitude scatter is just $\sim$0.10 mag, even without light curve shape or colour corrections. Our results do not vary significantly with different sample selection criteria, though photometric calibration in the NIR may be a dominant systematic uncertainty. Our findings suggest that tension in the competing $H_0$ distance ladders is likely not a result of supernova systematics that could be expected to vary between optical and NIR wavelengths, like dust extinction. We anticipate further improvements in $H_0$ with a larger calibrator sample of SNe Ia with Cepheid distances, more Hubble flow SNe Ia with NIR light curves, and better use of the full NIR photometric data set beyond simply the peak $J$-band magnitude.Comment: 13 pages, replaced to match published version in A&A, code available at https://github.com/sdhawan21/irh

The Rise Times and Bolometric Light Curve of SN 1994D: Constraints on Models of Type Ia Supernovae

Using the published photometry and an empirical model of the temporal evolution of the apparent magnitudes in the UBVRI passbands, we have constructed a continuous optical bolometric, or ``quasi-bolometric'', light curve of the well-observed Type Ia supernova SN 1994D. The optical bolometric light curve is found to have a maximum luminosity of about $8.8\times 10^{42} \times (\frac{D}{13.7 Mpc})^2$ erg/s, which is reached $\sim 18$ days after the explosion. In addition, the optical bolometric light curve exhibits an inflection, or ``shoulder'', about $25$ days after maximum. This inflection corresponds to the secondary maximum observed in all filter light curves redder than $B$. The individual filter curves have rise times similar to that of the optical bolometric light curve; other Type Ia supernovae are found to have similar rise times. Our fits indicate that the peak bolometric luminosity and the maxima in the B, V, and R light curves all occur within a day of one another. These results can be used to place constraints on theoretical models of Type Ia events. For example, all current theoretical models predict rise times to peak luminosity which are significantly shorter than that estimated for SN 1994D.Comment: 12 pages, 1 color PostScript figure, special style file (aaspp4) included. Accepted for publication in Astrophysical Journal Letters. A PostScript version with embedded figure is available at http://www.ifa.hawaii.edu/~vacc