Pristine Gas Research Articles

Star formation histories of dwarf and giant galaxies with different supernovae-driven outflows: NGC 2403, NGC 628

The star formation histories and chemical evolution of a dwarf spiral galaxy NGC 2403 and a massive spiral galaxy NGC 628 are studied in this work through a simple chemical evolutionary model under the influence of several supernovae-driven galactic outflows. The galactic disk of each galaxy is considered as a collection of some concentric rings each of which evolves independently without exchanging matters among themselves. The disk is formed through continuous accretion of pristine gas from halo. A classical Kennicutt–Schmidt star formation law is taken into account with an exponential gas accretion rate. In order to analyze the impact of outflow, we have taken into account two separate types of supernovae-driven gas outflow, namely supernovae momentum-driven outflow and supernovae energy-driven outflow, both of which depend on the circular velocity of the disk. By comparing our model’s anticipated result with observational data, the most viable models are chosen. For the dwarf galaxy NGC 2403, the supernovae energy-driven outflow model yields a better result which indicates that the supernovae energy-driven outflow mechanism plays a major role in driving the outflows in low mass galaxies. However, for NGC 628, both the outflow models adequately account for the observed features, suggesting that both momentum-driven and energy-driven outflows contribute equally to the outflows of the massive galaxy NGC 628. Furthermore, we contrasted the evolution of radial and global properties of these galaxies.

Facet-Controlled Synthesis of CeO2 Nanoparticles for High-Performance CeO2 Nanoparticle/SnO2 Nanosheet Hybrid Gas Sensors

CeO2 nanocubes with metastable {100} facets and CeO2 nanooctahedrons with the most stable {111} facets are herein fabricated by controlling the morphology and facets of CeO2 nanoparticles. SnO2 nanosheet-based assembled films coated with these CeO2 nanocubes or CeO2 nanooctahedrons yield {100} CeO2 nanocubes/SnO2 nanosheets and {111} CeO2 nanooctahedron/SnO2 nanosheet hybrid gas sensors, respectively. The hybrid sensors with CeO2 nanoparticles exhibited enhanced sensing responses to numerous chemical species relative to a pristine SnO2 nanosheet gas sensor, including acetone, hydrogen, ethanol, ammonia, acetaldehyde, and allyl mercaptan. In particular, the responses of {100} CeO2 nanocubes/SnO2 nanosheets and {111} CeO2 nanooctahedron/SnO2 nanosheet gas sensors to acetone or allyl mercaptan were 6.8 and 10.3 times higher, respectively, than that of the pristine SnO2 nanosheet gas sensor. Furthermore, the sensor response to ammonia was 2.5 times higher than that of a commercial volatile organic compound (VOC) gas sensor (TGS2602, Figaro Engineering Inc.). The CeO2 nanocube-based sensor with exposed metastable {100} facets promotes the adsorption and oxidation of VOCs owing to the higher surface energy of the metastable {100} facets and therefore exhibits a higher sensing performance than the CeO2 nanooctahedron-based sensor with an exposed {111} facet. The developed sensors show excellent potential for the detection of gas markers in human breath and perspiration for disease diagnosis.

Globular cluster formation with multiple stellar populations: a single-binary composite scenario

ABSTRACT We discuss a GC formation scenario in which the first generation (1G) of single asymptotic giant branch (AGB) stars and intermediate-mass close binaries (IMCBs) eject gas, from which the second generation (2G) of stars can be formed. The two key parameters in the scenario are the fractions of binary stars (fb) and the slopes (α) of the stellar initial mass functions (IMFs) for 1G stars. Principle results derived by analytic and one-zone models of GC formation are as follows. The mass fraction of 2G stars (f2g) can be higher than ≈0.4 for α < 1.8 and is not so dependent on fb. The ratio of the initial mass of a GC to the present-day mass (Mgc) ranges from 2 to 7 depending on α for 0.5 ≤ fb ≤ 0.9. The differences in [Na/Fe] between 1G and 2G stars can be as large as 0.7 for a wide range of model parameters. The Li abundances of 2G stars can be as high as those of 1G even if the pristine gas from IMCBs is assumed to be Li-free. Formation histories of 2G stars show at least two peaks owing to two peaks in the total ejection rate of gas from IMCB populations. The observed correlation between f2g and Mgc can be due to α depending on Mgc. The hypothetical long duration of 2G formation (≈108 yr) is possible, because massive star formation can be suppressed through frequent dynamical interaction between 1G stars and gas clouds.

Chemical abundances in the dwarf galaxy NGC 4163 based on the nebular and auroral emission lines

AbstractWe constructed an oxygen abundance map and N/O ratio map of the unusually low excitation dwarf irregular galaxy NGC 4163 based on publicly available spectroscopy obtained by the MaNGA survey. We detected auroral emission line [O II]7320,7330 which allows us to measure chemical abundance by direct method. We found that the scatter of the oxygen abundance derived by the strong line method is large. The oxygen abundances 12 + log(O/H) derived by strong line method vary from to with a mean value of . The oxygen abundances derived in two apertures of 2 arcseconds by the direct method using our measurements of the auroral line is about 7.8 dex. The nitrogen‐to‐oxygen ratio of about −1.5 is typical value for a low metallicity galaxy, maybe slightly shifted towards higher N/O ratios with respect to the N/O values in the H II regions in nearby galaxies. An unusual negative trend between (N/O) and oxygen abundance is detected. NGC 4163 is a gas‐poor galaxy with a neutral atomic gas mass fraction of around 0.25. The oxygen abundance in the galaxy is only around 0.1 of the oxygen abundance potentially attainable in a galaxy with such a gas mass fraction. The low metallicity coupled with the low gas mass fraction implies that either the metallicity of the interstellar medium of the galaxy was reduced by pristine gas infall in the recent epoch or the evolution of this galaxy was accompanied by strong galactic winds.

Morpho-kinematics of MACS J0416.1-2403 low-mass galaxies

We use optical integral field spectroscopy from VLT/MUSE, as well as photometric observations from Hubble Space Telescope and VLT/HAWK-I, to study the morpho-kinematics of 17 low-mass (log(M/M⊙) < 9.5) MACS J0416.1-2403 cluster galaxies at R200 and five field galaxies with a redshift of z ∼ 0.4. By measuring fluxes of strong emission lines from the MUSE data, we have recovered the star formation rates, gas-phase metallicities, and spatially resolved gas kinematics, and we have also investigated the ionising mechanisms. We have analysed the structure and morphology of the galaxies from the optical and infrared photometric data, performing a multi-component decomposition into a bulge and a disk. The spatially resolved gas velocity fields of the cluster members and field galaxies were modelled using a 3D approach, which allowed us to retrieve their intrinsic gas kinematics, including the maximum rotation velocity and velocity dispersion. This enabled us to study scaling relations such as the Tully–Fisher and the stellar mass–S0.5 relation for low-mass galaxies in different environments and to search for signatures of cluster-specific processes using disturbed gas velocity fields as tracers. Most galaxies from our sample fall in the star-forming and composite region in the diagnostic diagram, which allows for the ionising sources in a galaxy to be disentangled. The cluster and field population can be classified as star-forming main-sequence galaxies, with only a sub-sample of four quenched systems. We observe significant scatter for the cluster galaxies in the mass-metallicity plane, and the lowest-mass systems deviate from the predictions of the fundamental metallicity relation, showing higher metallicities, whereas the higher-mass ones are in accordance with the model predictions. This might hint at the cutoff of pristine gas inflow and/or the removal of the hot halo gas as the mechanisms driving these offsets. Our morpho-kinematic analysis reveals a sub-sample of dwarfs with maximum velocities vmax < 50 km s−1 and vmax, gas/σgas < 1, which depart from the Tully–Fisher relation. This might indicate that their interstellar medium is affected by external environmental processes, such as ram pressure stripping. However, ∼30% of the cluster galaxies have rotation-dominated gas disks and follow the Tully–Fisher relation within 1σ. Using the S0.5 parameter, which links the dynamical support of ordered motions with that of random motions, we can differentiate between galaxies affected by gravitational processes and systems affected by hydrodynamical ones. In the stellar mass–S0.5 plane, both cluster and field galaxies follow a tight sequence, with only a sub-population of five galaxies strongly departing (> 4σ) from this relation, showing high σgas values. Both the morphology and kinematics of the outlier galaxies hint at a combination of pre-processing and cluster-specific interactions affecting their stellar and gas disks.

Ionizing feedback effects on star formation in globular clusters with multiple stellar populations

ABSTRACT Using 3D radiation-hydrodynamical simulations, we study the effects of ionizing radiation on the formation of second-generation (SG) stars in globular clusters (GCs) with multiple stellar populations. In particular, we focus on massive ($10^7 \, \mathrm{M}_{\odot }$) and young (40-Myr old) GCs. We consider stellar winds from asymptotic giant branch (AGB) stars, ram pressure, gas accretion on to the cluster, and photo-ionization feedback of binary stars. We find that the stellar luminosity is strong enough to warm and ionize the intracluster medium, but it does not lead to a significant gas expulsion. The cluster can thus retain the ejecta of AGB stars and the accreted pristine gas. In addition, efficient cooling occurs in the central region of the cluster within $50\, \mathrm{Myr}$ from the formation of first generation stars, leading to the formation of SG stars. Our results indicate that the inclusion of photo-ionization does not suppress SG formation, but rather delays it by about $\sim 10\, \mathrm{Myr}$. The time delay depends on the density of the pristine gas, so that a denser medium exhibits a shorter delay in star formation. Moreover, photo-ionization leads to a modest decrease in the total SG mass, compared to a model without it.

Room-Temperature Detection of Perfluoroisobutyronitrile with SnO2/Ti3C2Tx Gas Sensors.

Ti3C2Tx MXene is an emerging two-dimensional transition-metal carbide/nitride with excellent properties of large specific surface and high carrier mobility for room-temperature gas sensing. However, achieving high sensitivity and long-term stability of pristine Ti3C2Tx-based gas sensors remains challenging. SnO2 is a typical semiconductor metal oxide with high reaction activity and stable chemical properties ideal for a dopant that can comprehensively improve sensing performance. Ti3C2Tx and SnO2 are investigated for the first time in this study as functional materials for hybridization and room-temperature detection of the gas insulating medium fluorinated nitrile (C4F7N) with microtoxicity. A Ti3C2Tx-SnO2 nanocomposite sensor exhibits superior sensitivity, high selectivity, strong anti-interference ability, and excellent long-term stability. The enhanced sensing mechanism is ascribed to the synergistic effect between SnO2 and Ti3C2Tx and the strong adsorption ability of SnO2 to C4F7N similar to bait for fish. We also established an actual leakage scene and demonstrated the feasibility of the Ti3C2Tx-SnO2 sensor to provide distribution rules with high sensing efficiency for actual engineering applications. The results of this work can expand the gas sensing application of Ti3C2Tx MXene and provide a reference for maintaining C4F7N-based eco-friendly gas-insulated equipment.

Accelerated Growth of Seed Black Holes by Dust in the Early Universe

We explore the effect of dust on the growth of seed black holes (BHs) in the early universe. Previous 1D radiation-hydrodynamic (RHD) simulations show that increased radiation pressure on dust further suppresses the accretion rate than the case for the chemically pristine gas. Using the Enzo+Moray code, we perform a suite of 3D RHD simulations of accreting BHs in a dusty interstellar medium (ISM). We use the modified Grackle cooling library to consider dust physics in its nonequilibrium chemistry. The BH goes through an early evolutionary phase, where ionizing BH radiation creates an oscillating H ii region as it cycles between accretion and feedback. As the simulations proceed, dense cold gas accumulates outside the ionized region where inflow from the neutral medium meets the outflow driven by radiation pressure. In the late phase, high-density gas streams develop and break the quasi-spherical symmetry of the ionized region, rapidly boosting the accretion rate. The late phase is characterized by the coexistence of strong ionized outflows and fueling high-density gas inflows. The mean accretion rate increases with metallicity reaching a peak at Z ∼ 0.01–0.1 Z ☉, one order of magnitude higher than the one for pristine gas. However, as the metallicity approaches the solar abundance, the mean accretion rate drops as the radiation pressure becomes strong enough to drive out the high-density gas. Our results indicate that a dusty metal-poor ISM can accelerate the growth rate of BHs in the early universe, but can also stun its growth as the ISM is further enriched toward the solar abundance.

Mechanism of NH3 gas sensing by SnO2/PANI nanocomposites: charge transport and temperature dependence study

Metal oxide-Polyaniline (PANI) nanocomposites have shown improved gas sensing characteristics that can be attributed to the formation of a p–n junction between the n-type metal oxide and the p-type PANI. The charge transport, grain boundary depletion region, and intragrain resistance are studied to understand the gas sensing mechanism of pristine metal oxide gas sensors. However, gas sensing mechanisms for metal-oxide/PANI nanocomposites have not been studied extensively. In this work, we have studied the gas sensing mechanism of SnO2/PANI nanocomposites using electrochemical impedance spectroscopy, and temperature dependent gas sensing experiments. Well-defined SnO2 nanoclusters were observed in the PANI matrix. The n-type SnO2 was covered by p-type PANI, and a depletion region was formed at the interface. The presence of the p–n junction depletion region was confirmed by impedance spectroscopy. The polarons in PANI were trapped by NH3 leading to a change in the width of the conducting path due to rearrangement of charge carriers along the depletion region. The change in the conduction path, along with the trapped polarons, enhanced the sensor response. For higher loadings of SnO2, the depletion region was deformed, and the sensor response decreased due to non-uniform boundaries. 1 wt% SnO2 with respect to aniline precursor in in situ synthesis showed the best response of 37.8% for 100 ppm NH3 at 35 °C. The response was stable for low humidity levels up to 51%RH. The response increased for higher humidity levels. The sensor response increased from 0.17 to 2.99 upon bending 1000 times at 7.8 mm diameter due to cracks in the surface. The sensor showed only 10% variation in response after 9 months.

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE

Context. While star formation on large molecular cloud scales and on small core and disk scales has been investigated intensely over the past decades, the connection of the large-scale interstellar material with the densest small-scale cores has been a largely neglected field. Aims. We wish to understand how the gas is fed from clouds down to cores. This covers dynamical accretion flows as well as the physical and chemical gas properties over a broad range of spatial scales. Methods. Using the IRAM facilities NOEMA and the IRAM 30 m telescope, we mapped large areas (640 arcmin2) of the archetypical star formation complex Cygnus X at 3.6 mm wavelengths in line and continuum emission. The data were combined and imaged together to cover all accessible spatial scales. Results. The scope and outline of The Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) as part of the Max Planck IRAM Observatory Program (MIOP) is presented. We then focus on the first observed subregion in Cygnus X, namely the DR20 star formation site, which comprises sources in a range of evolutionary stages from cold pristine gas clumps to more evolved ultracompact Hii regions. The data covering cloud to cores scales at a linear spatial resolution of <5000 au reveal several kinematic cloud components that may be part of several large-scale flows around the central cores. The temperature structure of the region is investigated by means of the HCN/HNC intensity ratio and compared to dust-derived temperatures. We find that the deuterated DCO+ emission is almost exclusively located toward regions at low temperatures below 20 K. Investigating the slopes of spatial power spectra of dense gas tracer intensity distributions (HCO+, H13CO+, and N2H+), we find comparatively flat slopes between −2.9 and −2.6, consistent with high Mach numbers and/or active star formation in DR20. Conclusions. This MIOP large program on star formation in Cygnus X provides unique new data connecting cloud with core scales. The analysis of the DR20 data presented here highlights the potential of this program to investigate in detail the different physical and chemical aspects and their interrelations from the scale of the natal molecular cloud down to the scale of accretion onto the individual protostellar cores.

SDSS-IV MaNGA: the chemical co-evolution of gas and stars in spiral galaxies

ABSTRACT We investigate archaeologically how the metallicity in both stellar and gaseous components of spiral galaxies of differing masses evolve with time, using data from the SDSS-IV MaNGA survey. For the stellar component, we can measure this evolution directly by decomposing the galaxy absorption-line spectra into populations of different ages and determining their metallicities. For the gaseous component, we can only measure the present-day metallicity directly from emission lines. However, there is a well-established relationship between gas metallicity, stellar mass, and star formation rate which does not evolve significantly with redshift; since the latter two quantities can be determined directly for any epoch from the decomposition of the absorption-line spectra, we can use this relationship to infer the variation in gas metallicity over cosmic time. Comparison of present-day values derived in this way with those obtained directly from the emission lines confirms the validity of the method. Application of this approach to a sample of 1619 spiral galaxies reveals how the metallicity of these systems has changed over the last 10 billion yr since cosmic noon. For lower-mass galaxies, both stellar and gaseous metallicity increase together, as one might expect in well-mixed fairly isolated systems. In higher-mass systems, the average stellar metallicity has not increased in step with the inferred gas metallicity, and actually decreases with time. Such disjoint behaviour is what one might expect if these more massive systems have accreted significant amounts of largely pristine gas over their lifetimes, and this material has not been well mixed into the galaxies.

The role of rotation on the formation of second generation stars in globular clusters

ABSTRACT By means of 3D hydrodynamic simulations, we explore the effects of rotation in the formation of second-generation (SG) stars in globular clusters (GC). Our simulations follow the SG formation in a first-generation (FG) internally rotating GC; SG stars form out of FG asymptotic giant branch (AGB) ejecta and external pristine gas accreted by the system. We have explored two different initial rotational velocity profiles for the FG cluster and two different inclinations of the rotational axis with respect to the direction of motion of the external infalling gas, whose density has also been varied. For a low (10−24 g cm−3) external gas density, a disc of SG helium-enhanced stars is formed. The SG is characterized by distinct chemo-dynamical phase space patterns: it shows a more rapid rotation than the FG with the helium-enhanced SG subsystem rotating more rapidly than the moderate helium-enhanced one. In models with high external gas density ($10^{-23}\, {\rm g\ cm^{-3}}$), the inner SG disc is disrupted by the early arrival of external gas and only a small fraction of highly enhanced helium stars preserves the rotation acquired at birth. Variations in the inclination angle between the rotation axis and the direction of the infalling gas and the velocity profile can slightly alter the extent of the stellar disc and the rotational amplitude. The results of our simulations illustrate the complex link between dynamical and chemical properties of multiple populations and provide new elements for the interpretation of observational studies and future investigations of the dynamics of multiple-population GCs.

PtO2-decorated MoS2 ultrathin nanostructures for enhanced NH3 gas sensing properties

Recently, transition metal dichalcogenides (TMDs) have attracted much attention due to their high surface-to-volume ratio, various active edge sites, and adjustable bandgaps. However, in general, TMDs still exhibit low gas response and incomplete recovery. Surface modification is an effective way to facilitate the adsorption and desorption processes, thus enhancing the TMD gas sensor's sensing performance. In this study, a PtO2-decorated MoS2 nanostructure gas sensor was fabricated using a chemical reduction process. The result showed that the as-obtained nanostructures consist of accumulated ultrathin MoS2 nanosheets decorated with spherical PtO2 nanoparticles. The gas response of the as-obtained PtO2-decorated MoS2 gas sensor toward NH3 is remarkably high, with 450% upon 500 ppm NH3, which is almost 20 times higher than that of the pristine MoS2 nanostructure gas sensor in their optimal working conditions. The enhancement in gas sensing properties was attributed to the catalytic spillover effect of PtO2 nanoparticles as well as the formation of p-p heterojunction on the MoS2 surface.

On the Probability of the Extremely Lensed z = 6.2 Earendel Source Being a Population III Star

The recent discovery of the extremely lensed Earendel object at z = 6.2 is remarkable in that it is likely a single star or stellar multiple, observed within the first billion years of cosmic history. Depending on its mass, which is still uncertain but will soon be more tightly constrained with the James Webb Space Telescope, the Earendel star might even be a member of the first generation of stars, the so-called Population III (Pop III). By combining results from detailed cosmological simulations of the assembly of the first galaxies, including the enrichment of the pristine gas with heavy chemical elements, with assumptions on key stellar parameters, we quantify the probability that Earendel indeed has a Pop III origin. We find that this probability is nonnegligible throughout the mass range inferred for Earendel, specifically ranging from a few percent at the lower-mass end to near unity for some Pop III initial mass function (IMF) models toward the high-mass end of the allowed range. For models that extend the metal-enriched IMF to 500 M ⊙, the likelihood of Earendel being a Pop III star stays at the few to 10% level. We discuss the implications of such a discovery for the overall endeavor to probe the hitherto so elusive first stars in the universe.

Room temperature NO2 sensing performance of a-C-decorated TeO2 nanowires

TeO2 is a semiconducting metal oxide that is not popular for sensing studies due to its poor sensing performance in its pristine form. To enhance its sensing performance, we deposited amorphous carbon (a-C) on its surface. We first synthesized TeO2 nanowires using a thermal evaporation method, and then we deposited an a-C layer on them by a simple procedure using a flame carbon vapor deposition technique. We showed that the a-C-decorated sensor had a lower optimized sensing temperature (26 °C) relative to the pristine TeO2 sensor (50 °C) and presented a higher sensitivity to NO2 gas. The maximum responses to NO2 (10 ppm) were 1.918 and 1.468 for a-C-decorated and pristine TeO2 nanowires, respectively. Furthermore, the a-C-decorated sensor indicated outstanding selectivity toward NO2. The high performance of a-C-decorated sensor was results of its higher surface area created by the bumpy carbon layer on the surface of TeO2 nanowires as well as the electronic sensitization due to the a-C layer. We also confirmed NO2 sensing behaviors of bare and a-C-decorated TeO2 nanowires using density functional theory (DFT) calculations, where calculated binding energies between NO2 and the sensing layer were stronger for NO2 and a-C-decorated TeO2 nanowire gas sensor relative to pristine gas sensors. The present approach for enhancing the sensing of TeO2 nanowires can be extended to other sensor systems as a simple, inexpensive strategy to improve sensor performance.

Gas Leakage From Shallow Ponding Magma and Trapdoor Faulting at Sierra Negra Volcano (Isabela Island, Galápagos)

AbstractWe report on new volcanic gas composition results acquired in October 2017 at Minas de Azufre, a persistent fumarolic field topping the resurgent Sierra Negra caldera, in the Galápagos archipelago. Our results indicate that the Minas de Azufre fumaroles are moderately hydrous (52–64 mol.% H2O) and rich in CO2 (35–46 mol.%), with total sulfur (ST) being 21–35 times less abundant than CO2. SO2, the most abundant S species, is released at an average rate of 19 ± 9 tons/day. Using a volatile saturation model that provides the composition of magmatic gases at equilibrium with western Galápagos basaltic melt (48 wt. % SiO2) in the 400–0.1 MPa pressure range, we infer that Minas de Azufre fumarolic emissions consist of a mixture of (a) magma‐derived gases coexisting with a melt at ∼50–60 MPa and (b) shallow meteoric water. We thus propose that the fumaroles are supplied by outgassing of magma stored in a ∼2 km deep sill‐like reservoir underneath the caldera floor, and that the trapdoor fault system at the western margin of the resurgent caldera block acts as a preferential pathway for magmatic gas ascent and surface discharge. Our results thus suggest that, in contrast to the majority of the volcano‐hosted hydrothermal systems worldwide, Minas de Azufre releases a relatively pristine magmatic gas.

Star-formation quenching of cluster galaxies as traced by metallicity and presence of active galactic nuclei, and galactic conformity

Aims. We strive to explore the differences in the properties and quenching processes of satellite galaxies in a sample of massive clusters with passive and star-forming (SF) brightest cluster galaxies (BCGs). One aim is to investigate galactic conformity effects, manifested in a correlation between the fraction of satellite galaxies that halted star formation and the state of star formation in the central galaxy. Methods. We explored 18 clusters from the Local Cluster Substructure Survey at 0.15 < z < 0.26, using spectra from the Arizona Cluster Redshift Survey Hectospec survey of about 1800 cluster members at R < R200 in a mass-complete sample. Nine clusters have a SF BCG and nine have a passive BCG, which enable the exploration of galactic conformity effects. We measured the fluxes of emission lines of cluster members, allowing us to derive O/H gas metallicities and to identify active galactic nuclei (AGN). We compared our cluster galaxy sample with a control field sample of about 1300 galaxies with similar masses and at similar redshifts observed with Hectospec as part of the same survey. We used the location of SF galaxies, recently quenched galaxies (RQGs) and AGN in the projected velocity versus the position phase-space (phase-space diagram) to identify objects in the inner regions of the clusters and to compare their fractions in clusters with SF and passive BCGs. Results. The metallicities of log(M/M⊙)≥10 SF cluster galaxies with R < R200 were found to be enhanced with respect to the mass-metallicity relation obtained for our sample of coeval field SF galaxies. This metallicity enhancement among SF cluster galaxies is limited to lower-mass satellites (10 < log(M/M⊙) < 10.7) of the nine clusters with a passive BCG, with no metallicity enhancement seen for SF galaxies in clusters with active BCGs. Many of the SF galaxies with enhanced metallicities are found in the core regions of the phase-space diagram expected for virialized populations. We find a higher fraction of log(M/M⊙)≥10.7 SF galaxies at R < R500 in clusters with active BCGs as compared to clusters with passive BCGs, which stands as a signal of galactic conformity. In contrast, much higher fractions at R < R500 of AGN and, particularly of RQGs, are found in clusters with passive BCGs in comparison to clusters with active BCGs. Conclusions. We deduce that strangulation is initiated in clusters with passive BCGs when SF satellite galaxies pass R200, by stopping the pristine gas inflow that would otherwise dilute the interstellar medium and would keep their metallicities at the level of values similar to those of field galaxies at similar redshifts. These satellite galaxies continue to form stars by consuming the available gas in the disk. For galaxies with massses above log(M/M⊙)∼10.7 that manage to survive and remain SF when traveling to R < R500 of clusters with passive BCGs, we assume that they suffer a rapid quenching of star formation, likely due to AGN triggered by the increasing ram pressure stripping toward the cluster center, which can compress the gas and fuel AGN. These AGN can rapidly quench and maintain quenched satellite galaxies. On the other hand, we found that surviving SF massive satellite galaxies around active BCGs are less affected by environment when they enter R < R500, since we observe R < R500 SF galaxies with masses up to M ∼ 1011 M⊙ and with metallicities typical of coeval field galaxies. This observed galactic conformity implies that active BCGs must maintain their activity over timescales of at least ∼1 Gyr.

Ultra-fast response and highly selectivity hydrogen gas sensor based on Pd/SnO2 nanoparticles

It is still a challenging task to achieve the rapid detection of hydrogen (H2) with the rapid development of hydrogen energy sector. In this work, the H2 sensing capabilities of pristine and Pd-modified SnO2 nanoparticles with the size of ∼7 nm were systematically evaluated. The SnO2 nanoparticles were synthesized via hydrothermal method and Pd modification was performed using impregnation route. Pd modification remarkably upgraded the H2 sensing performances compared with the pristine SnO2 gas sensor. The working temperature of SnO2 decreased from 300 °C to 125 °C after Pd loading. Among the prepared Pd/SnO2 gas sensors, 0.50 at.% Pd/SnO2 sensor exhibited the highest response magnitude of 254 toward 500 ppm H2 and rapid response/recovery time of 1/22 s at 125 °C. The enhanced H2 sensing capabilities by Pd modification may be related to the catalytic effect and the resistance modulation.

Signatures of AGN-induced Metal Loss in the Stellar Population

Abstract One way the active galactic nuclei (AGN) are expected to influence the evolution of their host galaxies is by removing metal content via outflows. In this article we present results that show that AGN can have an effect on the chemical enrichment of their host galaxies using the fossil record technique on CALIFA galaxies. We classified the chemical enrichment histories of all galaxies in our sample regarding whether they show a drop in the value of their metallicity. We find that galaxies currently hosting an AGN are more likely to show this drop in their metal content compared to the quiescent sample. Once we separate the sample by their star-forming status we find that star-forming galaxies are less likely to have a drop in metallicity but have deeper decreases when these appear. This behavior could be evidence for the influence of either pristine gas inflows or galactic outflows triggered by starbursts, both of which can produce a drop in metallicity.

Very Large Telescope Spectroscopy of Ultra-faint Dwarf Galaxies. I. Boötes I, Leo IV, and Leo V

Abstract We perform consistent reductions and measurements for three ultra-faint dwarf galaxies (UFDs): Boötes I, Leo IV, and Leo V. Using the public archival data from the GIRAFFE spectrograph on the Very Large Telescope (VLT), we locate new members and provide refined measurements of physical parameters for these dwarf galaxies. We identify nine new Leo IV members and four new Leo V members, and perform a comparative analysis of previously discovered members. Additionally, we identify one new binary star in both Leo IV and Leo V. After removing binary stars, we recalculate the velocity dispersions of Boötes I and Leo IV to be 5.1 − 0.8 + 0.7 and 3.4 − 0.9 + 1.3 km s−1, respectively; we do not resolve the Leo V velocity dispersion. We identify a weak velocity gradient in Leo V that is ∼4× smaller than the previously calculated gradient and that has a corresponding position angle that differs from the value in the literature by ∼120°. Combining the VLT data with previous values from the literature, we reanalyze the Boötes I metallicity distribution function and find that a model including infall of pristine gas, while Boötes I was forming stars’ best fits the data. Our analysis of Leo IV, Leo V, and other UFDs will enhance our understanding of these enigmatic stellar populations and contribute to future dark matter studies. This is the first in a series of papers examining 13 UDFs observed with VLT/GIRAFFE between 2009 and 2017. Similar analyses of the remaining 10 UFDs will be presented in forthcoming papers.