Discovery and Follow-up Observations of the Young Type Ia Supernova 2016coj

The Type~Ia supernova (SN~Ia) 2016coj in NGC 4125 (redshift $z=0.004523$) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before $B$-band maximum). Our first detection (pre-discovery) is merely $0.6\pm0.5$ day after the FFLT, making SN 2016coj one of the earliest known detections of a SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but with a high velocity of \ion{Si}{2} $\lambda$6355 ($\sim 12,600$\,\kms\ around peak brightness). The \ion{Si}{2} $\lambda$6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity ($M_B \approx -18.9 \pm 0.2$ mag), and it reaches a $B$-band maximum \about16.0~d after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na~I~D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the \ion{Si}{2} line polarization is quite strong ($\sim 0.9\% \pm 0.1\%$) at peak brightness.Comment: Submitte

Searching for the Lowest Metallicity Galaxies in our Local Universe

Observational determinations of the primordial light element abundances produced during Big Bang Nucleosynthesis (BBN) provide an important test on our current understanding of the Universe and the Standard Model due to their sensitivities to two parameters at the time of BBN: the baryon density and the expansion rate of the Universe. The primordial helium-4 abundance is particularly sensitive to the latter, which is partly driven by the number of effective neutrino species. In this thesis, I present a new observational survey to discover near-pristine environments in our local Universe whose properties can be used to determine the latest value of the primordial \fourHe\ abundance.I first describe the details of our observational survey, which uses photometry from the Sloan Digital Sky Survey (SDSS) to identify candidate metal-poor galaxies. We use the Kast spectrograph on the Shane 3m telescope at Lick Observatory to obtain confirmation spectroscopy and follow up on a subset of these systems using LRIS and NIRSPEC/NIRES at Keck Observatory, which we name the Primordial Helium Legacy Experiment with Keck (PHLEK) survey. The high S/N optical and near-infrared (NIR) spectroscopy of the PHLEK sample enable a direct measurement of the electron temperature for the oxygen abundance and the detection of a suite of HeI lines for the helium abundance.Our survey results include the discovery of the Little Cub, one of the lowest-metallicity star-forming galaxies currently known. The Little Cub has a gas phase oxygen abundance about a twentieth solar metallicity and is a testament to the success in picking out metal-poor systems from photometry alone.Finally, I describe our code yMCMC, which uses the Markov Chain Monte Carlo (MCMC) technique to explore an 8-dimensional parameter space and solve for the parameters that best describe our observations. We supplement our PHLEK sample with SDSS spectroscopy and existing low-metallicity systems in the literature. Using systems well-modelled by yMCMC, we make an extrapolation to the primordial helium number abundance ratio, finding y_P=0.0805+/-0.0017. When combined with the existing primordial deuterium abundance, this places constraints on the baryon-to-photon ratio and effective number of neutrino species in agreement with the Standard Model

Searching for the Lowest Metallicity Galaxies in our Local Universe

Observational determinations of the primordial light element abundances produced during Big Bang Nucleosynthesis (BBN) provide an important test on our current understanding of the Universe and the Standard Model due to their sensitivities to two parameters at the time of BBN: the baryon density and the expansion rate of the Universe. The primordial helium-4 abundance is particularly sensitive to the latter, which is partly driven by the number of effective neutrino species. In this thesis, I present a new observational survey to discover near-pristine environments in our local Universe whose properties can be used to determine the latest value of the primordial \fourHe\ abundance.I first describe the details of our observational survey, which uses photometry from the Sloan Digital Sky Survey (SDSS) to identify candidate metal-poor galaxies. We use the Kast spectrograph on the Shane 3m telescope at Lick Observatory to obtain confirmation spectroscopy and follow up on a subset of these systems using LRIS and NIRSPEC/NIRES at Keck Observatory, which we name the Primordial Helium Legacy Experiment with Keck (PHLEK) survey. The high S/N optical and near-infrared (NIR) spectroscopy of the PHLEK sample enable a direct measurement of the electron temperature for the oxygen abundance and the detection of a suite of HeI lines for the helium abundance.Our survey results include the discovery of the Little Cub, one of the lowest-metallicity star-forming galaxies currently known. The Little Cub has a gas phase oxygen abundance about a twentieth solar metallicity and is a testament to the success in picking out metal-poor systems from photometry alone.Finally, I describe our code yMCMC, which uses the Markov Chain Monte Carlo (MCMC) technique to explore an 8-dimensional parameter space and solve for the parameters that best describe our observations. We supplement our PHLEK sample with SDSS spectroscopy and existing low-metallicity systems in the literature. Using systems well-modelled by yMCMC, we make an extrapolation to the primordial helium number abundance ratio, finding y_P=0.0805+/-0.0017. When combined with the existing primordial deuterium abundance, this places constraints on the baryon-to-photon ratio and effective number of neutrino species in agreement with the Standard Model

The PHLEK Survey: A New Determination of the Primordial Helium Abundance

We present Keck NIRSPEC and Keck NIRES spectroscopy of sixteen metal-poor galaxies that have pre-existing optical observations. The near-infrared (NIR) spectroscopy specifically targets the He I λ10830 Å emission line, due to its sensitivity to the physical conditions of the gas in H II regions. We use these NIR observations, combined with optical spectroscopy, to determine the helium abundance of sixteen galaxies across a metallicity range 12 log O H + 10( ) = 7.13–8.00. This data set is combined with two other samples where metallicity and helium abundance measurements can be secured: star-forming galaxies selected from the Sloan Digital Sky Survey spectroscopic database, and existing low-metallicity systems in the literature. We calculate a linear fit to these measurements, accounting for intrinsic scatter, and report a new determination of the primordial helium number abundance, = - + y 0.0805 P 0.0017 0.0017, which corresponds to a primordial helium mass fraction = - + YP 0.2436 0.0040 0.0039. Using our determination of the primordial helium abundance in combination with the latest primordial deuterium measurement, D H 10 2.527 0.030 P ´= 5 ( ) , we place a bound on the baryon density W = - + bh 0.0215 2 0.0005 0.0005 and the effective number of neutrino species = - + Neff 2.85 0.25 0.28. These values are in 1.3σ agreement with those deduced from the Planck satellite observations of the temperature fluctuations imprinted on the cosmic microwave background

Searching for the lowest metallicity galaxies in the local universe

We report a method of identifying candidate low-metallicity blue compact dwarf galaxies (BCDs) from the Sloan Digital Sky Survey (SDSS) imaging data, and present 3 m Lick Observatory and 10 m W.M. Keck Observatory optical spectroscopic observations of 94 new systems that have been discovered with this method. The candidate BCDs are selected from Data Release 12 (DR12) of SDSS on the basis of their photometric colors and morphologies. Using the Kast spectrometer on the 3 m telescope, we confirm that the candidate low-metallicity BCDs are emission-line galaxies, and we make metallicity estimates using the empirical R and S calibration methods. Follow-up observations on a subset of the lowest-metallicity systems are made at Keck using the Low Resolution Imaging Spectrometer, which allow for a direct measurement of the oxygen abundance. We determine that 45 of the reported BCDs are low-metallicity candidates with 12 + log(O/H) ≤ 7.65, including six systems which are either confirmed or projected to be among the lowest-metallicity galaxies known, at 1/30 of the solar oxygen abundance, or 12 + log(O/H) ~ 7.20

The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O III] λ4363 Å emission line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way–like galaxy

PypeIt: The Python Spectroscopic Data Reduction Pipeline

PypeIt is a Python package for semi-automated reduction of astronomical, spectroscopic data. Its algorithms build on decades-long development of previous data reduction pipelines by the developers (Bernstein, Burles, & Prochaska, 2015; Bochanski et al., 2009). The reduction procedure -- including a complete list of the input parameters and available functionality -- is provided as online documentation hosted by Read the Docs, which is regularly updated. (https://pypeit.readthedocs.io/en/latest/). Release v1.0.3 serves the following spectrographs: Gemini/GNIRS, Gemini/GMOS, Gemini/FLAMINGOS 2, Lick/Kast, Magellan/MagE, Magellan/Fire, MDM/OSMOS, Keck/DEIMOS (600ZD, 830G, 1200G), Keck/LRIS, Keck/MOSFIRE (J and Y gratings tested), Keck/NIRES, Keck/NIRSPEC (low-dispersion), LBT/Luci-I, Luci-II, LBT/MODS (beta), NOT/ALFOSC (grism4), VLT/X-Shooter (VIS, NIR), VLT/FORS2 (300I, 300V), WHT/ISIS.Comment: To be submitted to JOSS (once they return to accepting submissions). Find PypeIt at: https://github.com/pypeit/PypeI