The Ionizing Photon Production Efficiency (ξion\xi_{ion}) Of Lensed Dwarf Galaxies At z∼2z \sim 2

We measure the ionizing photon production efficiency ($\xi_{ion}$) of low-mass galaxies ($10^{7.8}$-$10^{9.8}$ $M_{\odot}$) at $1.4<z<2.7$, allowing us to better understand the contribution of dwarf galaxies to the ionizing background and cosmic reionization. We target galaxies that are magnified by the strong lensing galaxy clusters Abell 1689, MACS J0717, and MACS J1149. We utilize Keck/MOSFIRE spectra to measure optical nebular emission line fluxes and HST imaging to measure the rest-UV and rest-optical photometry. We present two methods of stacking. First, we take the average of the log(L$_{H\alpha}$ /L$_{UV}$) of galaxies in our sample to determine the typical log($\xi_{ion}$). Second, we take the logarithm of the total L$_{H\alpha}$ over the total L$_{UV}$. We prefer the latter as it provides the total ionizing UV luminosity density of galaxies when multiplied by the non-ionizing UV luminosity density from the UV luminosity function. log($\xi_{ion}$) calculated from the second method is $\sim$ 0.2 dex higher than the first method. We do not find any strong dependence between log($\xi_{ion}$) and stellar mass, M$_{UV}$ or UV spectral slope ($\beta$). We report a value of log($\xi_{ion}$) $\sim25.47\pm 0.09$ for our UV-complete sample ($-22<M_{UV}<-17.3$) and $\sim25.37\pm0.11$ for our mass-complete sample ($7.8<\log(M_*)<9.8)$. These values are consistent with measurements of more massive, more luminous galaxies in other high-redshift studies that use the same stacking technique. Our log($\xi_{ion}$) is $0.2-0.3$ dex higher than low-redshift galaxies of similar mass, indicating an evolution in the stellar properties, possibly due to metallicity, age, or the prevalence of binary stars. We also find a correlation between log($\xi_{ion}$) and the equivalent widths of H$\alpha$ and [OIII]$\lambda$5007 fluxes, confirming that these equivalent widths can be used to estimate $\xi_{ion}$.Comment: 16 pages, 6 figures, 1 table, Accepted in Ap

SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-Forming Galaxy IC 2163

SPIRITS---SPitzer InfraRed Intensive Transients Survey---is an ongoing survey of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We present the discovery and follow-up observations of one of our most luminous ($M_{[4.5]} = -17.1\pm0.4$ mag, Vega) and red ($[3.6] - [4.5] = 3.0 \pm 0.2$ mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm of IC 2163 ($D\approx35.5$ Mpc). Pre-discovery ground-based imaging revealed an associated, shorter-duration transient in the optical and near-IR (NIR). NIR spectroscopy showed a broad ($\approx 8400$ km s$^{-1}$), double-peaked emission line of He I at $1.083 \mu$m, indicating an explosive origin. The NIR spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase of $\approx 200$ days. Assuming $A_V = 2.2$ mag of extinction in SPIRITS 15c provides a good match between their optical light curves. The IR light curves and the extreme $[3.6]-[4.5]$ color cannot be explained using only a standard extinction law. Another luminous ($M_{4.5} = -16.1\pm0.4$ mag) event, SPIRITS 14buu, was serendipitously discovered in the same galaxy. The source displays an optical plateau lasting $\gtrsim 80$ days, and we suggest a scenario similar to the low-luminosity Type IIP SN 2005cs obscured by $A_V \approx 1.5$ mag. Other classes of IR-luminous transients can likely be ruled out in both cases. If both events are indeed SNe, this may suggest $\gtrsim 18\%$ of nearby core-collapse SNe are missed by currently operating optical surveys.Comment: 19 pages, 7 Figures, 4 Table

The Detection of [O III] λ4363 in a Lensed, Dwarf Galaxy at z = 2.59: Testing Metallicity Indicators and Scaling Relations at High Redshift and Low Mass

We present Keck/MOSFIRE (Multi-Object Spectrometer for InfraRed Exploration) and Keck/LRIS (Low Resolution Imaging Spectrometer) spectroscopy of A1689-217, a lensed (magnification ~7.9), star-forming (SFR ~ 16 M_☉ yr⁻¹), dwarf (log(M_★/M_☉) = 8.07–8.59) Lyα emitter (EW₀ ~ 138 Å) at z = 2.5918. Dwarf galaxies similar to A1689-217 are common at high redshift and likely responsible for reionization, yet few have been studied with detailed spectroscopy. We report a 4.2σ detection of the electron-temperature-sensitive [O iii] λ4363 emission line and use this line to directly measure an oxygen abundance of 12 + log(O/H) = 8.06 ± 0.12 (~1/4 Z_☉). A1689-217 is the lowest-mass galaxy at z > 2 with an [O iii] λ4363 detection. Using the rest-optical emission lines, we measure A1689-217's other nebular conditions, including electron temperature (T e ([O iii]) ~ 14,000 K), electron density (n e ~ 220 cm⁻³), and reddening (E(B-V) ~ 0.39). We study relations between strong-line ratios and direct metallicities with A1689-217 and other galaxies with [O iii] λ4363 detections at z ~ 0–3.1, showing that the locally calibrated, oxygen-based, strong-line relations are consistent from z ~ 0 to 3.1. We also show additional evidence that the O₃₂ versus R₂₃ excitation diagram can be utilized as a redshift-invariant, direct-metallicity-based, oxygen abundance diagnostic out to z ~ 3.1. From this excitation diagram and the strong-line ratio–metallicity plots, we observe that the ionization parameter at fixed O/H is consistent with no redshift evolution. Although A1689-217 is metal-rich for its M_★ and star formation rate, we find it to be consistent within the large scatter of the low-mass end of the fundamental metallicity relation

UVUDF: UV Luminosity Functions at the Cosmic High Noon

We present the rest-1500 Å UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon—the peak of cosmic star formation rate at 1.5 < z < 3. We use deep NUV imaging data obtained as part of the Hubble Ultra-Violet Ultra Deep Field (UVUDF) program, along with existing deep optical and NIR coverage on the HUDF. We select F225W, F275W, and F336W dropout samples using the Lyman break technique, along with samples in the corresponding redshift ranges selected using photometric redshifts, and measure the rest-frame UV LF at z ~ 1.7, 2.2, 3.0, respectively, using the modified maximum likelihood estimator. We perform simulations to quantify the survey and sample incompleteness for the UVUDF samples to correct the effective volume calculations for the LF. We select galaxies down to M_(UV) = -15.9, -16.3, -16.8 and fit a faint-end slope of α = -1.20^(+0.10)_(-0.13), -1.32^(+0.10)_(-0.14), -1.39^(+0.08)_(-0.12) at 1.4 < z < 1.9, 1.8 < z < 2.6, and 2.4 < z < 3.6, respectively. We compare the star formation properties of z ~ 2 galaxies from these UV observations with results from Hα and UV+IR observations. We find a lack of high-SFR sources in the UV LF compared to the Hα and UV+IR, likely due to dusty SFGs not being properly accounted for by the generic IRX-β relation used to correct for dust. We compute a volume-averaged UV-to-Hα ratio by abundance matching the rest-frame UV LF and Hα LF. We find an increasing UV-to-Hα ratio toward low-mass galaxies (M_∗ ≾ 5 x 10^9 M_⊙). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end

XIPE: the X-ray Imaging Polarimetry Explorer

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental Astronomy http://link.springer.com/journal/1068

The Lyman Continuum Escape Fraction of Star-forming Galaxies at 2.4≲z≲3.72.4\lesssim z\lesssim3.7 from UVCANDELS

The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space Telescope (HST) Cycle-26 Treasury Program, allocated in total 164 orbits of primary Wide-Field Camera 3 Ultraviolet and Visible light F275W imaging with coordinated parallel Advanced Camera for Surveys F435W imaging, on four of the five premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. We introduce this survey by presenting a thorough search for galaxies at $z\gtrsim2.4$ that leak significant Lyman continuum (LyC) radiation, as well as a stringent constraint on the LyC escape fraction ($f_{\rm esc}$) from stacking the UV images of a population of star-forming galaxies with secure redshifts. Our extensive search for LyC emission and stacking analysis benefit from the catalogs of high-quality spectroscopic redshifts compiled from archival ground-based data and HST slitless spectroscopy, carefully vetted by dedicated visual inspection efforts. We report a sample of five galaxies as individual LyC leaker candidates, showing $f_{\rm esc}^{\rm rel}\gtrsim60\%$ estimated using detailed Monte Carlo analysis of intergalactic medium attenuation. We develop a robust stacking method to apply to five samples of in total 85 non-detection galaxies in the redshift range of $z\in[2.4,3.7]$. Most stacks give tight 2-$\sigma$ upper limits below $f_{\rm esc}^{\rm rel}<6\%$. A stack for a subset of 32 emission-line galaxies shows tentative LyC leakage detected at 2.9-$\sigma$, indicating $f_{\rm esc}^{\rm rel}=5.7\%$ at $z\sim2.65$, supporting the key role of such galaxies in contributing to the cosmic reionization and maintaining the UV ionization background. These new F275W and F435W imaging mosaics from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes.Comment: 33 pages, 21 figures, and 5 tables. Resubmitted after addressing the referee repor

The Electron-Temperature-Based Oxygen Abundance of Dwarf Galaxies at the Peak of Cosmic Star Formation

At $z \sim 2$, where cosmic star formation peaks, little is known about the galaxy stellar mass ($M_\ast$), star formation rate (SFR), and oxygen abundance (or gas-phase metallicity; O/H) parameter space in which typical dwarf galaxies lie ($M_\ast \leqslant 10^9\ \rm{M_\odot}$). This is due to current technological limitations as well as uncertainty about the accuracy of indirectly-measured metallicities at high-$z$. Consequently, our models and understanding of galaxy formation and evolution are largely unconstrained in this mass regime.Here we present a sample, one of the first of its kind, of 16 representative, star-forming, gravitationally-lensed dwarf galaxies at $1.7 \lesssim z \lesssim 2.6$ ($z_{\rm{mean}}=2.30$) with a median $M_\ast$ of log($M_\ast$/$\rm{M_\odot}$)$_{\rm{med}}$ = 8.29 and a median SFR of $\rm{SFR_{H\alpha}^{med} = 2.25\ M_\odot\ yr^{-1}}$. Sample spectroscopy and photometry were taken with the Keck Multi-Object Spectrometer For InfraRed Exploration and the \textit{Hubble Space Telescope}, respectively. Study of these galaxies is done largely via a composite emission-line spectrum of the sample, from which we detect the faint, electron-temperature-sensitive, auroral emission line, [O III] $\lambda$4363, with which we directly estimate metallicity. Within this sample, we also independently study the $z=2.59$ galaxy, A1689-217, which yields a rare, individual detection of [O III] $\lambda$4363 at high-$z$. In assessing indirect, locally-calibrated, strong-line metallicity relations at high-$z$, we find certain strong-line ratios are insensitive to metallicities around those we directly measure. Other indices show greater utility, but have metallicity calibrations that vary in applicability based on the high-$z$ and calibration samples considered. We do show evidence supporting the creation of a redshift-invariant, empirical metallicity relation within the $\rm{O_{32}}$ vs. $\rm{R_{23}}$ excitation diagram. Our stacked sample shows excellent agreement with the direct-method $M_\ast\,-\,$O/H relation (MZR) of Sanders et al. (2020) and disagrees with other high-$z$ MZRs displaying significantly shallower slopes. We also find excellent agreement with the MZR from the Feedback In Realistic Environments simulations after recalculating our stellar masses, which likely underestimate contributions from older stellar populations under our fiducial assumptions. Finally, we find consistency with a redshift-invariant fundamental metallicity relation (FMR), though note a large scatter in dwarf galaxy metallicities

Pu Songling, avec préface et traduction de Rainier Lanselle, Trois contes étranges : le Fou de livres, le Grand-saint égal du ciel, le Dieu grenouille, 2009

Durand-Dastès Vincent. Pu Songling, avec préface et traduction de Rainier Lanselle, Trois contes étranges : le Fou de livres, le Grand-saint égal du ciel, le Dieu grenouille, 2009. In: Études chinoises, n°29, 2010. Numéro spécial sur le pouvoir politique. pp. 354-357

The Direct-method Oxygen Abundance of Typical Dwarf Galaxies at Cosmic High Noon

We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲ z ≲ 2.6 ( z _mean = 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of $\mathrm{log}{({M}_{* }/{M}_{\odot })}_{\mathrm{med}}={8.29}_{-0.43}^{+0.51}$ and a median star formation rate of ${{\rm{S}}{\rm{F}}{\rm{R}}}_{{\rm{H}}\alpha }^{{\rm{m}}{\rm{e}}{\rm{d}}}={2.25}_{-1.26}^{+2.15}\,{M}_{\odot }\,{{\rm{y}}{\rm{r}}}^{-1}$ . We measure the faint electron-temperature-sensitive [O iii ] λ 4363 emission line at 2.5 σ (4.1 σ ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of $12+\mathrm{log}{({\rm{O}}/{\rm{H}})}_{\mathrm{direct}}={7.88}_{-0.22}^{+0.25}$ ( ${0.15}_{-0.06}^{+0.12}\ {Z}_{\odot }$ ). We investigate the applicability at high z of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixed M _* , our composite is well represented by the z ∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories $(\mathrm{log}{({M}_{* }/{M}_{\odot })}_{\mathrm{med}}={8.92}_{-0.22}^{+0.31})$ , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixed M _* and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [O ii ] λ 3729/[O ii ] λ 3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ${n}_{e}={1}_{-0}^{+215}\ {\mathrm{cm}}^{-3}$ ( ${n}_{e}={1}_{-0}^{+74}\ {\mathrm{cm}}^{-3}$ ) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies at z ∼ 2

Vie Économique : Dimensions politiques

Revue Vie Économique Sujet : La Revue Vie Économique est une initiative des Éditions vie économique (EVE), coopérative de solidarité. Lieu de débat et de réflexion sur les enjeux économiques, la revue veut aller au-delà de la pensée économique traditionnelle, trop souvent réduite aux seules transactions marchandes, en abordant les dimensions politique et sociétale des activités économiques contemporaines. Ceci inclut, évidemment, les enjeux écologiques qui imposent de changer nos manières..