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Register a new userDES15E2mlf: A Spectroscopically Confirmed Superluminous Supernova that Exploded 3.5 Gyr After the Big Bang
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We present the Dark Energy Survey (DES) discovery of DES15E2mlf, the most distant superluminous supernova (SLSN) spectroscopically confirmed to date. The light curves and Gemini spectroscopy of DES15E2mlf indicate that it is a Type I superluminous supernova (SLSN-I) at z = 1.861 (a lookback time of ~10 Gyr) and peaking at M_AB = -22.3 +/- 0.1 mag. Given the high redshift, our data probe the rest-frame ultraviolet (1400-3500 A) properties of the SN, finding velocity of the C III feature changes by ~5600 km/s over 14 days around maximum light. We find the host galaxy of DES15E2mlf has a stellar mass of 3.5^+3.6_-2.4 x 10^9 M_sun, which is more massive than the typical SLSN-I host galaxy.
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Two decades of effort have been poured into both single-dish and interferometric millimeter-wave surveys of the sky to infer the volume density of dusty star-forming galaxies (DSFGs, with SFR>100M$_odot$ yr$^{-1}$) over cosmic time. Though obscured galaxies dominate cosmic star-formation near its peak at $zsim2$, the contribution of such heavily obscured galaxies to cosmic star-formation is unknown beyond $zsim2.5$ in contrast to the well-studied population of Lyman-break galaxies (LBGs) studied through deep, space- and ground-based pencil beam surveys in the near-infrared. Unlocking the volume density of DSFGs beyond $z>3$, particularly within the first 1 Gyr after the Big Bang is critical to resolving key open questions about early Universe galaxy formation: (1) What is the integrated star-formation rate density of the Universe in the first few Gyr and how is it distributed among low-mass galaxies (e.g. Lyman-break galaxies) and high-mass galaxies (e.g. DSFGs and quasar host galaxies)? (2) How and where do the first massive galaxies assemble? (3) What can the most extreme DSFGs teach us about the mechanisms of dust production (e.g. supernovae, AGB stars, grain growth in the ISM) <1 Gyr after the Big Bang? We summarize the types of observations needed in the next decade to address these questions.
We discovered Bowen emission arising from a strongly lensed (i.e., with magnification factor $mu$>20) source hosted in the Sunburst arc at z=2.37. We claim this source is plausibly a transient stellar object and study the unique ultraviolet lines emerging from it. In particular, narrow ($sigma$_v ~ 40 km/s) ionisation lines of Fe fluoresce after being exposed to Lya radiation that pumps selectively their atomic levels. Data from VLT/MUSE, X-Shooter and ESPRESSO observations (the latter placed at the focus of the four UTs) at increasing spectral resolution of R=2500, 11400 and R=70000, respectively, confirm such fluorescent lines are present since at least 3.3 years (~ 1 year rest-frame). Additional Fe forbidden lines have been detected, while C and Si doublets probe an electron density n_e >~ $10^6$ cm$^{-3}$. Similarities with the spectral features observed in the circum-stellar Weigelt blobs of Eta-Carinae probing the circum-stellar dense gas condensations in radiation-rich conditions are observed. We discuss the physical origin of the transient event, which remains unclear. We expect such transient events (including also supernova or impostors) will be easily recognised with ELTs thanks to high angular resolution provided by adaptive optics and large collecting area, especially in modest ($mu < 3$) magnification regime.
A recent arXiv manuscript, arXiv:1801.03278, claims that a cosmic background radiation with a black body temperature of $T_{rm BB}$ ~ 500 K (440 F) was just barely visible to human eyes, thus fixing the onset of the Dark Ages at about 5 million years post recombination. This claim presents an insurmountable biophysical challenge, since even hotter bodies, such as 450 F pizzas, do not seem to be glowing in the dark. As volunteer referees we show that this claim is the result of employing an incorrect assumption. Via a corrected analysis we find that the Dark Ages must have had a significantly earlier start. A second, more descriptive claim, that a cosmic background radiation with $T_{rm BB}$ of 1545 K was as blinding to humans as is our own Sun, is based on the same assumption and may have to be revised.
Primordial or Big Bang nucleosynthesis (BBN) is one of the three historical strong evidences for the Big-Bang model together with the expansion of the Universe and the Cosmic Microwave Background radiation (CMB). The recent results by the Planck mission have slightly changed the estimate of the baryonic density Omega_b, compared to the previous WMAP value. This article updates the BBN predictions for the light elements using the new value of Omega_b determined by Planck, as well as an improvement of the nuclear network and new spectroscopic observations. While there is no major modification, the error bars of the primordial D/H abundance (2.67+/-0.09) x 10^{-5} are narrower and there is a slight lowering of the primordial Li/H abundance (4.89^+0.41_-0.39) x 10^{-10}. However, this last value is still ~3 times larger than its observed spectroscopic abundance in halo stars of the Galaxy. Primordial Helium abundance is now determined to be Y_p = 0.2463+/-0.0003.
Evolution in the measured rest frame ultraviolet spectral slope and ultraviolet to optical flux ratios indicate a rapid evolution in the dust obscuration of galaxies during the first 3 billion years of cosmic time (z>4). This evolution implies a change in the average interstellar medium properties, but the measurements are systematically uncertain due to untested assumptions, and the inability to measure heavily obscured regions of the galaxies. Previous attempts to directly measure the interstellar medium in normal galaxies at these redshifts have failed for a number of reasons with one notable exception. Here we report measurements of the [CII] gas and dust emission in 9 typical (~1-4L*) star-forming galaxies ~1 billon years after the big bang (z~5-6). We find these galaxies have >12x less thermal emission compared with similar systems ~2 billion years later, and enhanced [CII] emission relative to the far-infrared continuum, confirming a strong evolution in the interstellar medium properties in the early universe. The gas is distributed over scales of 1-8 kpc, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z<3 and being comparable to local low-metallicity systems.
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