74 research outputs found
Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu
We report the results from spectroscopic observations of the multiple images of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with ground based telescopes and the Hubble Space Telescope (HST). From a single epoch of slitless spectroscopy with HST, we can resolve spectra of individual lensed supernova images for the first time. This allows us to perform an independent measurement of the time-delay between the two brightest images, Ît=1.4±5.0 days, which is consistent with the time-delay measured from the light-curves.
We also present measurements of narrow emission and absorption lines characterizing the interstellar medium in the host galaxy at z = 0.4087, as well as in the foreground lensing galaxy at z = 0.2163. We detect strong Na ID absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass of SNe Ia displaying "anomalously" large Na ID column densities in comparison to the amount of dust extinction derived from their light curves. For the deflecting galaxy, we refine the measurement of the velocity dispersion, Ï = 129 ± 4 km sâ»Âč, which significantly constrains the lens model.
Since the time-delay between the SN images is negligible, we can use unresolved ground based spectroscopy, boosted by a factor ~70 from lensing magnification, to study the properties of a high-z SN Ia with unprecedented signal-to-noise ratio. The spectral properties of the supernova, such as pseudo-Equivalent widths of several absorption features and velocities of the Si II-line indicate that iPTF16geu, besides being lensed, is a normal SN Ia, indistinguishable from well-studied ones in the local universe, providing support for the use of SNe Ia in precision cosmology. We do not detect any significant deviations of the SN spectral energy distribution from microlensing of the SN photosphere by stars and compact objects in the lensing galaxy
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Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu
We report the results from spectroscopic observations of the multiple images of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with ground-based telescopes and the Hubble Space Telescope (HST). From a single epoch of slitless spectroscopy with HST, we resolve spectra of individual lensed supernova images for the first time. This allows us to perform an independent measurement of the time-delay between the two brightest images, Ît = 1.4 ± 5.0 d, which is consistent with the time-delay measured from the light curves. We also present measurements of narrow emission and absorption lines characterizing the interstellar medium in the SN Ia host galaxy at z = 0.4087, as well as in the foreground lensing galaxy at z = 0.2163. We detect strong NaâID absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass of SNe Ia displaying âanomalouslyâ large NaâID column densities compared to dust extinction derived from light curves. For the lens galaxy, we refine the measurement of the velocity dispersion, Ï = 129 ± 4 kmâsâ»Âč, which significantly constrains the lens model. We use ground-based spectroscopy, boosted by a factor âŒ70 from lensing magnification, to study the properties of a high-z SN Ia with unprecedented signal-to-noise ratio. The spectral properties of the supernova, such as pseudo-Equivalent widths of several absorption features and velocities of the SiâII-line, indicate that iPTF16geu is a normal SN Ia. We do not detect any significant deviations of the SN spectral energy distribution from microlensing of the SN photosphere by stars and compact objects in the lensing galaxy
Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu
We report the results from spectroscopic observations of the multiple images
of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with
ground based telescopes and the Hubble Space Telescope (HST). From a single
epoch of slitless spectroscopy with HST, we can resolve spectra of individual
lensed supernova images for the first time. This allows us to perform an
independent measurement of the time-delay between the two brightest images,
days, which is consistent with the time-delay measured
from the light-curves.
We also present measurements of narrow emission and absorption lines
characterizing the interstellar medium in the host galaxy at z=0.4087, as well
as in the foreground lensing galaxy at z=0.2163. We detect strong Na ID
absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass
of SNe Ia displaying "anomalously" large Na ID column densities in comparison
to the amount of dust extinction derived from their light curves. For the
deflecting galaxy, we refine the measurement of the velocity dispersion,
km/s, which significantly constrains the lens model.
Since the time-delay between the SN images is negligible, we can use
unresolved ground based spectroscopy, boosted by a factor ~70 from lensing
magnification, to study the properties of a high-z SN Ia with unprecedented
signal-to-noise ratio. The spectral properties of the supernova, such as
pseudo-Equivalent widths of several absorption features and velocities of the
Si II-line indicate that iPTF16geu, besides being lensed, is a normal SN Ia,
indistinguishable from well-studied ones in the local universe, providing
support for the use of SNe Ia in precision cosmology. We do not detect any
significant deviations of the SN spectral energy distribution from microlensing
of the SN photosphere by stars and compact objects in the lensing galaxy.Comment: 10 pages, 10 figures. Comments are welcome
Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS HII region observations: A pilot study of NGC 628
The ionising radiation of young and massive stars is a crucial form of
stellar feedback. Most ionising (Lyman-continuum; LyC, )
photons are absorbed close to the stars that produce them, forming compact HII
regions, but some escape into the wider galaxy. Quantifying the fraction of LyC
photons that escape is an open problem. In this work, we present a semi-novel
method to estimate the escape fraction by combining broadband photometry of
star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with HII regions
observed by the Star formation, Ionized gas, and Nebular Abundances Legacy
Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the
completeness of the combined catalogue, and find that 49\% of HII regions lack
corresponding star clusters as a result of a difference in the sensitivities of
the LEGUS and SIGNALS surveys. For HII regions that do have matching clusters,
we infer the escape fraction from the difference between the ionising power
required to produce the observed HII luminosity and the predicted ionising
photon output of their host star clusters; the latter is computed using a
combination of LEGUS photometric observations and a stochastic stellar
population synthesis code SLUG (Stochastically Lighting Up Galaxies). Overall,
we find an escape fraction of across our
sample of 42 HII regions; in particular, we find HII regions with high
are predominantly regions with low H-luminosity. We also
report possible correlation between and the emission lines [O ii]/[N
ii] and [O ii]/H.Comment: Accepted for publication at MNRA
Signals: I. Survey description
SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H II regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the CanadaâFranceâHawaii Telescope. Over 355 h (54.7 nights) have been allocated beginning in fall 2018 for eight consecutive semesters. Once completed, SIGNALS will provide a statistically reliable laboratory to investigate massive star formation, including over 50 000 resolved H II regions: the largest, most complete, and homogeneous data base of spectroscopically and spatially resolved extragalactic H II regions ever assembled. For each field observed, three datacubes covering the spectral bands of the filters SN1 (363â386 nm), SN2 (482â513 nm), and SN3 (647â685 nm) are gathered. The spectral resolution selected for each spectral band is 1000, 1000, and 5000, respectively. As defined, the project sample will facilitate the study of small-scale nebular physics and many other phenomena linked to star formation at a mean spatial resolution of âŒ20 pc. This survey also has considerable legacy value for additional topics, including planetary nebulae, diffuse ionized gas, and supernova remnants. The purpose of this paper is to present a general outlook of the survey, notably the observing strategy, galaxy sample, and science requirements
H α morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters
The morphology of H II regions around young star clusters provides insight into the time-scales and physical processes that clear a clusterâs natal gas. We study âŒ700 young clusters (â€10âMyr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H α morphology (concentrated, partially exposed, no-emission) and whether they have neighbouring clusters (which could affect the clearing time-scales). Through visual inspection of the HST images, and analysis of ages, reddenings, and stellar masses from spectral energy distributions fitting, together with the (Uâ B), (V â I) colours, we find (1) the median ages indicate a progression from concentrated (âŒ3âMyr), to partially exposed (âŒ4âMyr), to no H α emission (>5âMyr), consistent with the expected temporal evolution of H II regions and previous results. However, (2) similarities in the age distributions for clusters with concentrated and partially exposed H α morphologies imply a short time-scale for gas clearing (âČ1âMyr). Also, (3) our cluster sampleâs median mass is âŒ1000 Mâ, and a significant fraction (âŒ20 per centâ ) contain one or more bright red sources (presumably supergiants), which can mimic reddening effects. Finally, (4) the median E(B â V) values for clusters with concentrated H α and those without H α emission appear to be more similar than expected (âŒ0.18 versus âŒ0.14, respectively), but when accounting for stochastic effects, clusters without H α emission are less reddened. To mitigate stochastic effects, we experiment with synthesizing more massive clusters by stacking fluxes of clusters within each H α morphological class. Composite isolated clusters also reveal a colour and age progression for H α morphological classes, consistent with analysis of the individual clusters
Global maps of soil temperature
Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-kmÂČ resolution for 0â5 and 5â15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-kmÂČ pixels (summarized from 8500 unique temperature sensors) across all the worldâs major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications
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