Abstract
We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant ...process of environmental quenching in 0.2 <
z
< 0.8 groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20 k group catalog. Limiting our analysis to a complete sample of log (
M
*
/
M
⊙
) > 10.56 group galaxies, we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (∼Gyr) timescales. We find a quenching time of approximately
4.91
−
1.47
+
0.91
Gyr, consistent with the slow processes of strangulation and delayed-then-rapid quenching although more data are needed to confirm this result.
BACKGROUND: Cost-effective production of lignocellulosic biofuels remains a major financial and technical challenge at the industrial scale. A critical tool in biofuels process development is the ...techno-economic (TE) model, which calculates biofuel production costs using a process model and an economic model. The process model solves mass and energy balances for each unit, and the economic model estimates capital and operating costs from the process model based on economic assumptions. The process model inputs include experimental data on the feedstock composition and intermediate product yields for each unit. These experimental yield data are calculated from primary measurements. Uncertainty in these primary measurements is propagated to the calculated yields, to the process model, and ultimately to the economic model. Thus, outputs of the TE model have a minimum uncertainty associated with the uncertainty in the primary measurements. RESULTS: We calculate the uncertainty in the Minimum Ethanol Selling Price (MESP) estimate for lignocellulosic ethanol production via a biochemical conversion process: dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis and co-fermentation of the resulting sugars to ethanol. We perform a sensitivity analysis on the TE model and identify the feedstock composition and conversion yields from three unit operations (xylose from pretreatment, glucose from enzymatic hydrolysis, and ethanol from fermentation) as the most important variables. The uncertainty in the pretreatment xylose yield arises from multiple measurements, whereas the glucose and ethanol yields from enzymatic hydrolysis and fermentation, respectively, are dominated by a single measurement: the fraction of insoluble solids (fIS) in the biomass slurries. CONCLUSIONS: We calculate a $0.15/gal uncertainty in MESP from the TE model due to uncertainties in primary measurements. This result sets a lower bound on the error bars of the TE model predictions. This analysis highlights the primary measurements that merit further development to reduce the uncertainty associated with their use in TE models. While we develop and apply this mathematical framework to a specific biorefinery scenario here, this analysis can be readily adapted to other types of biorefining processes and provides a general framework for propagating uncertainty due to analytical measurements through a TE model.
BACKGROUND: The rapid determination of the release of structural sugars from biomass feedstocks is an important enabling technology for the development of cellulosic biofuels. An assay that is used ...to determine sugar release for large numbers of samples must be robust, rapid, and easy to perform, and must use modest amounts of the samples to be tested. In this work we present a laboratory-scale combined pretreatment and saccharification assay that can be used as a biomass feedstock screening tool. The assay uses a commercially available automated solvent extraction system for pretreatment followed by a small-scale enzymatic hydrolysis step. The assay allows multiple samples to be screened simultaneously, and uses only ~3 g of biomass per sample. If the composition of the biomass sample is known, the results of the assay can be expressed as reactivity (fraction of structural carbohydrate present in the biomass sample released as monomeric sugars). RESULTS: We first present pretreatment and enzymatic hydrolysis experiments on a set of representative biomass feedstock samples (corn stover, poplar, sorghum, switchgrass) in order to put the assay in context, and then show the results of the assay applied to approximately 150 different feedstock samples covering 5 different materials. From the compositional analysis data we identify a positive correlation between lignin and structural carbohydrates, and from the reactivity data we identify a negative correlation between both carbohydrate and lignin content and total reactivity. The negative correlation between lignin content and total reactivity suggests that lignin may interfere with sugar release, or that more mature samples (with higher structural sugars) may have more recalcitrant lignin. CONCLUSIONS: The assay presented in this work provides a robust and straightforward method to measure the sugar release after pretreatment and saccharification that can be used as a biomass feedstock screening tool. We demonstrated the utility of the assay by identifying correlations between feedstock composition and reactivity in a population of 150 samples.
Abstract
We describe the Gems of the Galaxy Zoos (Zoo Gems) project, a gap-filler project using short windows in the Hubble Space Telescope's schedule. As with previous snapshot programs, targets are ...taken from a pool based on position; we combine objects selected by volunteers in both the Galaxy Zoo and Radio Galaxy Zoo citizen-science projects. Zoo Gems uses exposures with the Advanced Camera for Surveys to address a broad range of topics in galaxy morphology, interstellar-medium content, host galaxies of active galactic nuclei, and galaxy evolution. Science cases include studying galaxy interactions, backlit dust in galaxies, post-starburst systems, rings and peculiar spiral patterns, outliers from the usual color–morphology relation, Green Pea compact starburst systems, double radio sources with spiral host galaxies, and extended emission-line regions around active galactic nuclei. For many of these science categories, final selection of targets from a larger list used public input via a voting process. Highlights to date include the prevalence of tightly wound spiral structure in blue, apparently early-type galaxies, a nearly complete Einstein ring from a group lens, redder components at lower surface brightness surrounding compact Green Pea starbursts, and high-probability examples of spiral galaxies hosting large double radio sources.
High-resolution imaging of galaxies in rest-frame UV has revealed the
existence of giant star-forming clumps prevalent in high redshift galaxies.
Studying these sub-structures provides important ...information about their
formation and evolution and informs theoretical galaxy evolution models. We
present a new method to identify clumps in galaxies' high-resolution rest-frame
UV images. Using imaging data from CANDELS and UVCANDELS, we identify
star-forming clumps in an HST/F160W$\leq 25$ AB mag sample of 6767 galaxies at
$0.5\leq z\leq 3$ in four fields, GOODS-N, GOODS-S, EGS, and COSMOS. We use a
low-pass band filter in Fourier space to reconstruct the background image of a
galaxy and detect small-scale features (clumps) on the background-subtracted
image. Clumpy galaxies are defined as those having at least one off-center
clump that contributes a minimum of 10$\%$ of the galaxy's total rest-frame UV
flux. We measure the fraction of clumpy galaxies ($\rm f_{clumpy}$) as a
function of stellar mass, redshift, and galaxy environment. Our results
indicate that $\rm f_{clumpy}$ increases with redshift, reaching $\sim 65\%$ at
$z\sim 1.5$. We also find that $\rm f_{clumpy}$ in low-mass galaxies ($\rm
9.5\leq log(M_*/M_\odot)\leq 10$) is 10$\%$ higher compared to that of their
high-mass counterparts ($\rm log(M_*/M_\odot)>10.5$). Moreover, we find no
evidence of significant environmental dependence of $\rm f_{clumpy}$ for
galaxies at the redshift range of this study. Our results suggest that the
fragmentation of gas clouds under violent disk instability remains the primary
driving mechanism for clump formation, and incidents common in dense
environments, such as mergers, are not the dominant processes.
We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant process of ...environmental quenching in \(0.2 < z < 0.8\) groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20k Group Catalog. Limiting our analysis to a complete sample of log\((M_*/M_{\odot})>10.56\) group galaxies we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (\(\sim\)Gyr) timescales. We find a quenching time of approximately \(4.91^{+0.91}_{-1.47} \)Gyrs, consistent with the slow processes of strangulation (Larson et al. 1980) and delayed-then-rapid quenching (Wetzel et al. 2013 arXiv:1206.3571v2 astro-ph.CO), although more data are needed to confirm this result.
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep
Extragalactic Legacy Survey Fields (UVCANDELS) program provides HST/UVIS F275W
imaging for four CANDELS fields. We combine this UV ...imaging with existing
HST/near-IR grism spectroscopy from 3D-HST$+$AGHAST to directly compare the
resolved rest-frame UV and H$\alpha$ emission for a sample of 979 galaxies at
$0.7<z<1.5$ spanning a range in stellar mass of $10^{8-11.5}$ M$_\odot$. Using
a stacking analysis, we perform a resolved comparison between homogenized maps
of rest-UV and H$\alpha$ to compute the average UV-to-H$\alpha$ luminosity
ratio (an indicator of burstiness in star-formation) as a function of
galactocentric radius. We find that galaxies below stellar mass of
$\sim$10$^{9.5}$ M$_\odot$, at all radii, have a UV-to-H$\alpha$ ratio higher
than the equilibrium value expected from constant star-formation, indicating a
significant contribution from bursty star-formation. Even for galaxies with
stellar mass $\gtrsim$10$^{9.5}$ M$_\odot$, the UV-to-H$\alpha$ ratio is
elevated towards in their outskirts ($R/R_{eff}>1.5$), suggesting that bursty
star-formation is likely prevalent in the outskirts of even the most massive
galaxies but is likely over-shadowed by their brighter cores. Furthermore, we
present the UV-to-H$\alpha$ ratio as a function of galaxy surface brightness, a
proxy for stellar mass surface density, and find that regions below
$\sim$10$^{7.5}$ M$_\odot$ kpc$^{-2}$ are consistent with bursty
star-formation, regardless of their galaxy stellar mass, potentially suggesting
that local star-formation is independent of global galaxy properties at the
smallest scales. Lastly, we find galaxies at $z>1.1$ to have bursty
star-formation regardless of radius or surface brightness.
High-resolution imaging of galaxies in rest-frame UV has revealed the existence of giant star-forming clumps prevalent in high redshift galaxies. Studying these sub-structures provides important ...information about their formation and evolution and informs theoretical galaxy evolution models. We present a new method to identify clumps in galaxies' high-resolution rest-frame UV images. Using imaging data from CANDELS and UVCANDELS, we identify star-forming clumps in an HST/F160W\(\leq 25\) AB mag sample of 6767 galaxies at \(0.5\leq z\leq 3\) in four fields, GOODS-N, GOODS-S, EGS, and COSMOS. We use a low-pass band filter in Fourier space to reconstruct the background image of a galaxy and detect small-scale features (clumps) on the background-subtracted image. Clumpy galaxies are defined as those having at least one off-center clump that contributes a minimum of 10\(\%\) of the galaxy's total rest-frame UV flux. We measure the fraction of clumpy galaxies (\(\rm f_{clumpy}\)) as a function of stellar mass, redshift, and galaxy environment. Our results indicate that \(\rm f_{clumpy}\) increases with redshift, reaching \(\sim 65\%\) at \(z\sim 1.5\). We also find that \(\rm f_{clumpy}\) in low-mass galaxies (\(\rm 9.5\leq log(M_*/M_\odot)\leq 10\)) is 10\(\%\) higher compared to that of their high-mass counterparts (\(\rm log(M_*/M_\odot)>10.5\)). Moreover, we find no evidence of significant environmental dependence of \(\rm f_{clumpy}\) for galaxies at the redshift range of this study. Our results suggest that the fragmentation of gas clouds under violent disk instability remains the primary driving mechanism for clump formation, and incidents common in dense environments, such as mergers, are not the dominant processes.
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides HST/UVIS F275W imaging for four CANDELS fields. We combine this UV ...imaging with existing HST/near-IR grism spectroscopy from 3D-HST\(+\)AGHAST to directly compare the resolved rest-frame UV and H\(\alpha\) emission for a sample of 979 galaxies at \(0.7<z<1.5\) spanning a range in stellar mass of \(10^{8-11.5}\) M\(_\odot\). Using a stacking analysis, we perform a resolved comparison between homogenized maps of rest-UV and H\(\alpha\) to compute the average UV-to-H\(\alpha\) luminosity ratio (an indicator of burstiness in star-formation) as a function of galactocentric radius. We find that galaxies below stellar mass of \(\sim\)10\(^{9.5}\) M\(_\odot\), at all radii, have a UV-to-H\(\alpha\) ratio higher than the equilibrium value expected from constant star-formation, indicating a significant contribution from bursty star-formation. Even for galaxies with stellar mass \(\gtrsim\)10\(^{9.5}\) M\(_\odot\), the UV-to-H\(\alpha\) ratio is elevated towards in their outskirts (\(R/R_{eff}>1.5\)), suggesting that bursty star-formation is likely prevalent in the outskirts of even the most massive galaxies but is likely over-shadowed by their brighter cores. Furthermore, we present the UV-to-H\(\alpha\) ratio as a function of galaxy surface brightness, a proxy for stellar mass surface density, and find that regions below \(\sim\)10\(^{7.5}\) M\(_\odot\) kpc\(^{-2}\) are consistent with bursty star-formation, regardless of their galaxy stellar mass, potentially suggesting that local star-formation is independent of global galaxy properties at the smallest scales. Lastly, we find galaxies at \(z>1.1\) to have bursty star-formation regardless of radius or surface brightness.
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