Average Luminosity Research Articles

Gamma-Ray and X-Ray Observations of the Periodic-repeater FRB 180916 during Active Phases

Abstract FRB 180916 is a most intriguing source capable of producing repeating fast radio bursts with a periodic 16.3 day temporal pattern. The source is well positioned in a star-forming region in the outskirts of a nearby galaxy at 150 Mpc distance. In this Letter we report on the X-ray and γ-ray observations of FRB 180916 obtained by AGILE and Swift. We focused especially on the recurrent 5 day time intervals of enhanced radio bursting. In particular, we report on the results obtained in the time intervals 2020 February 3–8, 2020 February 25, 2020 March 5–10, and 2020 March 22–28 during a multiwavelength campaign involving high-energy and radio observations of FRB 180916. We also searched for temporal coincidences at millisecond timescales between the 32 known radio bursts of FRB 180916 and X-ray and MeV events detectable by AGILE. We do not detect any simultaneous event or any extended X-ray and γ-ray emission on timescales of hours/days/weeks. Our cumulative X-ray (0.3–10 keV) flux upper limit of 5 × 10−14 erg cm−2 s−1 (obtained during 5 day active intervals from several 1–2 ks integrations) translates into an isotropic luminosity upper limit of L X,UL ∼ 1.5 × 1041 erg s−1. Deep γ-ray observations above 100 MeV over a many-year timescale provide an average luminosity upper limit one order of magnitude larger. These results provide the so-far most stringent upper limits on high-energy emission from the FRB 180916 source. Our results constrain the dissipation of magnetic energy from a magnetar-like source of radius R m , internal magnetic field B m , and dissipation timescale τ d to satisfy the relation , where R m,6 is R m in units of 106 cm, B m,16 is B m in units of 1016 G, and τ d,8 in units of 108 s.

1SWASP J034439.97+030425.5: a short-period eclipsing binary system with a close-in stellar companion

First multi-wavelength photometric light curves (LCs) of the short-period eclipsing binary (EB) 1SWASP J034439.97+030425.5 (hereafter J0344) are presented and analyzed by using the 2013 version of the Wilson-Devinney (W-D) code. To explain the asymmetric LCs of J0344, a cool star-spot on the less massive component was employed. The photometric solutions suggest that J0344 is a W-subtype shallow contact EB with a contact degree of f = 4.9% ± 3.0% and a mass ratio of q = 2.456 ± 0.013. Moreover, an obvious third light was detected in our analysis. We calculated the average luminosity contribution of the third light to the total light, and that value reaches up to 49.78%. Based on the O − C method, the variations of the orbital period were studied for the first time. Our O − C diagram reveals a secular decrease superimposed on a cyclic oscillation. The orbital period decreases at a rate of dP/dt = −6.07 × 10−7 d yr−1, which can be explained by the mass transfer from the more massive component to the less massive one. Besides, its O − C diagram also shows a cyclic oscillation with an amplitude of 0.0030 d and a period about 7.08 yr, which can be explained by the presence of a third body with a minimum mass of M3min = 0.15 ± 0.02 M⊙. The third component may play an important role in the formation and evolution of J0344 by drawing angular momentum from the central system.

AGILE Observations of Two Repeating Fast Radio Bursts with Low Intrinsic Dispersion Measures

Abstract We focus on two repeating fast radio bursts (FRBs) recently detected by the CHIME/FRB experiment in 2018–2019 (Source 1: 180916.J0158+65, and Source 2: 181030.J1054+73). These sources have low excess dispersion measures ( and , respectively), implying relatively small maximal distances. They were repeatedly observed by AGILE in the MeV–GeV energy range. We do not detect prompt emission simultaneously with these repeating events. This search is particularly significant for the submillisecond and millisecond integrations obtainable by AGILE. The sources are constrained to emit a MeV-fluence in the millisecond range below corresponding to an isotropic energy near erg for a distance of 150 Mpc (applicable to Source 1). We also searched for γ-ray emission for time intervals up to 100 days, obtaining 3σ upper limits (ULs) for the average isotropic luminosity above 50 MeV, (5–10) . For a source distance near 100 kpc (possibly applicable to Source 2), our ULs imply , and 2 . Our results are significant in constraining the high-energy emission of underlying sources such as magnetars, or other phenomena related to extragalactic compact objects, and show the prompt emission to be lower than the peak of the 2004 magnetar outburst of SGR 1806-20 for source distances less than about 100 Mpc.

The X-ray and radio activity of typical and luminous Ly α emitters from z ∼ 2 to z ∼ 6: evidence for a diverse, evolving population

ABSTRACT Despite recent progress in understanding Ly α emitters (LAEs), relatively little is known regarding their typical black hole activity across cosmic time. Here, we study the X-ray and radio properties of ∼4000 LAEs at 2.2 < $z$ < 6 from the SC4K survey in the COSMOS field. We detect 254 ($6.8{\rm{ per\ cent}} \pm 0.4{\rm{ per\ cent}}$) LAEs individually in the X-rays (S/N > 3) with an average luminosity of $\rm 10^{44.31\pm 0.01}\, erg\, s^{-1}$ and average black hole accretion rate (BHAR) of $\rm 0.72 \pm 0.01$ M⊙ yr−1, consistent with moderate to high accreting active galactic neuclei (AGNs). We detect 120 sources in deep radio data (radio AGN fraction of $3.2{\rm{ per\ cent}} \pm 0.3{\rm{ per\ cent}}$). The global AGN fraction ($\rm 8.6{\rm{ per\ cent}} \pm 0.4{\rm{ per\ cent}}$) rises with Ly α luminosity and declines with increasing redshift. For X-ray-detected LAEs, Ly α luminosities correlate with the BHARs, suggesting that Ly α luminosity becomes a BHAR indicator. Most LAEs ($93.1{\rm{ per\ cent}} \pm 0.6{\rm{ per\ cent}}$) at 2 < $z$ < 6 have no detectable X-ray emission (BHARs < 0.017 M⊙ yr−1). The median star formation rate (SFR) of star-forming LAEs from Ly α and radio luminosities is $7.6^{+6.6}_{-2.8}$ M⊙ yr−1. The black hole to galaxy growth ratio (BHAR/SFR) for LAEs is <0.0022, consistent with typical star-forming galaxies and the local BHAR/SFR relation. We conclude that LAEs at 2 < $z$ < 6 include two different populations: an AGN population, where Ly α luminosity traces BHAR, and another with low SFRs which remain undetected in even the deepest X-ray stacks but is detected in the radio stacks.

Radio and X-ray monitoring of the accreting millisecond X-ray pulsar IGR J17591−2342 in outburst

ABSTRACT IGR J17591−2342 is a new accreting millisecond X-ray pulsar that was recently discovered in outburst in 2018. Early observations revealed that the source’s radio emission is brighter than that of any other known neutron star low-mass X-ray binary (NS–LMXB) at comparable X-ray luminosity, and assuming its likely ≳6 kpc distance. It is comparably radio bright to black hole LMXBs at similar X-ray luminosities. In this work, we present the results of our extensive radio and X-ray monitoring campaign of the 2018 outburst of IGR J17591−2342. In total, we collected 10 quasi-simultaneous radio (VLA, ATCA) and X-ray (Swift–XRT) observations, which make IGR J17591−2342 one of the best-sampled NS–LMXBs. We use these to fit a power-law correlation index $\beta = 0.37^{+0.42}_{-0.40}$ between observed radio and X-ray luminosities (LR ∝ LXβ). However, our monitoring revealed a large scatter in IGR J17591−2342’s radio luminosity (at a similar X-ray luminosity, LX ∼1036 erg s−1, and spectral state), with LR ∼ 4 × 1029 erg s−1 during the first three reported observations, and up to a factor of 4 lower LR during later radio observations. None the less, the average radio luminosity of IGR J17591−2342 is still one of the highest among NS–LMXBs, and we discuss possible reasons for the wide range of radio luminosities observed in such systems during outburst. We found no evidence for radio pulsations from IGR J17591−2342 in our Green Bank Telescope observations performed shortly after the source returned to quiescence. None the less, we cannot rule out that IGR J17591−2342 becomes a radio millisecond pulsar during quiescence.

Effect of thalidomide combined with tamoxifen on hormone levels and vascular-related growth factors in breast cancer-bearing mice

Objective To investigate the effects of thalidomide combined with tamoxifen on hormone levels and vascular-related growth factors in breast cancer-bearing mice. Methods MCF-7 cells were used to establish a tumor-bearing mouse model of breast cancer. 48 mice were randomly divided into control group, tamoxifen group (25 mg/kg), thalidomide group (50 mg/kg), thalidomide combined with tamoxifen group for 12 mice in each group. Continuous gavage for 2 weeks, once per day. The tumor weight, tumor inhibition rate, hormone level, and blood vessel-related growth factors were compared. Results (1) Tumor weight and tumor inhibition rate: The tumor weight of the model control group, tamoxifen group, thalidomide group, thalidomide combined with tamoxifen group breast cancer tumor-bearing mice were (2.52±0.45), (2.07±0.40), (2.12±0.43), (1.15±0.35) g, the tumor inhibition rates of the tamoxifen group, thalidomide group, thalidomide and tamoxifen group were (17.86±3.12)%, (15.87±2.54)%, and (54.37±6.24)%. The tumor weight of thalidomide combined with tamoxifen breast cancer-bearing mice was significantly lower than that of tamoxifen group and thalidomide group, and the tumor inhibition rate was significantly higher than that of tamoxifen group and thalidomide group (t=5.996, 18.129, 6.061, 19.796, P<0.05, P<0.01). (2) Hormone levels: The mean luminosity values of estrogen receptor-α (ER-α) in the model control group, tamoxifen group, thalidomide group, thalidomide combined with tamoxifen group were 0.712±0.015, 0.421±0.010, 0.385±0.012, 0.212±0.007, the mean photometric values of estrogen receptor-β (ER-β) were 0.105±0.005, 0.192±0.007, 0.178±0.006, and 0.245±0.008, respectively. The average luminosity value of ER-α in thalidomide combined with tamoxifen group was significantly lower than that in tamoxifen group and thalidomide group, the average luminosity value of ER-β was significantly higher than that of tamoxifen group and thalidomide group (t=38.366, 17.271, 40.160, 23.209, P<0.01). (3) Vascular growth-related growth factor: serum vascular endothelial growth factor (VEGF) levels in model control group, tamoxifen group, thalidomide group, thalidomide combined with tamoxifen group were (125.12±22.34), (96.36±13.25), (84.42±11.35), (72.12±9.45) ng/L, the basic fibroblast growth factor (bEGF) content was (18.32±3.24), (14.21±2.35), (12.12±2.10), (10.32±1.45) ng/L, the levels of endostatin (ES) were (12.32±1.45), (14.65±1.62), (16.12±2.02), and (18.32±2.42) μg/L. The serum levels of VEGF and bEGF in thalidomide combined with tamoxifen group were significantly lower than those in tamoxifen group and thalidomide group, the ES content was significantly higher than that of the tamoxifen group and the thalidomide group (t=5.160, 4.880, 4.366, 2.885, 2.443, 2.418, P<0.05). Conclusion Thalidomide combined with tamoxifen may inhibit the growth of breast cancer in bearing mice. Key words: Breast cancer; Thalidomide; Tamoxifen; Estrogen; Vascular growth factor

Progression Features of Dart Leaders in Natural Negative Cloud‐to‐Ground Lightning Flashes

AbstractWe have analyzed the propagation process of nine dart leaders in four natural negative lightning flashes observed by a high speed optical system LAPOS 5. The propagation speeds range from 0.6 to 3.7×107 m/s with an average value of 1.5×107 m/s. The leader luminosity peaks at the front part of the leader head and decreases gradually backward within the head. The leader channel behind the leader head has a relatively low and constant luminosity. The average luminosity of the leader head is about 1.3 times brighter than that of the leader channel behind. The head lengths of seven dart leaders were estimated to range from 21 to 88 m. Our results show that as the ground is approached, the dart leader propagates faster with its leader head growing brighter and longer. For different strokes within an individual lightning flash, it was found that the larger change ratio of leader head brightness relates with the larger change ratio of propagation speed and the larger change ratio of leader head length.

A photometric study of the short-period eclipsing binary 1SWASP J204932.94-654025.8, showing strong third light

1SWASP J204932.94-654025.8 (hereafter J2049) is a newly discovered eclipsing binary system with an orbital period of 0.2299103 days. BVRc light curves (LCs) are presented and analyzed by using the 2013 version of the Wilson–Devinney (W–D) program. Because the observed LCs are asymmetric, a hot star-spot was employed on the secondary component during our analysis. We found that J2049 is a W-subtype shallow contact eclipsing binary system with an orbit inclination of 62∘.69 ± 0∘.95 and a mass ratio of q =1.326 ± 0.056. More importantly, we found the presence of a strong third light, with an average luminosity contribution of 31.3% of the total light. Based on times of the light minima, the orbital period changes of J2049 are studied for the first time, and there is no evidence for any significant dp/dt now. Considering the presence of the third light and the short time span of the eclipse times, more observations are needed in the future.

The Nuclotron-based Ion Collider Facility Project. The Physics Programme for the Multi-Purpose Detector

The Nuclotron-based Ion Collider fAcility (NICA) is a new accelerator complex under construction at the Joint Institute for Nuclear Research (JINR), Dubna, Russia. The main goal of the planned facility is to provide accelerated particle beams for a wide range of experimental studies of the hot and dense strongly interacting QCD matter generated during collisions. The NICA project in its entirety allows for a fixed target experimental site, as well as two interaction points. The heavy ion programme includes two planned detectors: Baryonic Matter at Nuclotron (BM@N) - a fixed target experiment with extracted Nuclotron beams; and a collider-mode experiment at one of the interaction points - the MultiPurpose Detector (MPD). For the NICA collider, the accelerated beams by design will consist of particles ranging from protons and light nuclei to fully stripped gold ions. Beam energies will span with luminosity Lpp ≥ 1 × 1030 cm−2s−1, and , and average luminosity LAuAu = 1 × 1027 cm−2s−1. The second interaction point is planned to be occupied by a third experiment - Spin Physics Detector (SPD), which will focus on the investigation of nucleon spin structure and polarization phenomena through the use of polarized proton and deuteron beams. A brief overview of the Multi-Purpose Detector is presented along with the major sub-detector systems. The MPD research programme will focus on multiple observables including collective flow, particle multiplicity and spectra. Special attention will be given to strangeness production and vector mesons, event-by-event fluctuations and hadron femtoscopy measurements. Several feasibility studies are referenced.

HSC-XD 52: An X-Ray Detected AGN in a Low-mass Galaxy at z ∼ 0.56

Abstract The properties of low-mass galaxies hosting central black holes provide clues about the formation and evolution of the progenitors of supermassive black holes. In this Letter, we present HSC-XD 52, a spectroscopically confirmed low-mass active galactic nucleus (AGN) at an intermediate redshift of z ∼ 0.56. We detect this object as a very luminous X-ray source coincident with a galaxy observed by the Hyper Suprime-Cam (HSC) as part of a broader search for low-mass AGN. We constrain its stellar mass through spectral energy distribution modeling to be LMC-like at M ⋆ ≈ 3 × 109 M ⊙, placing it in the dwarf regime. We estimate a central black hole mass of M BH ∼ 106 M ⊙. With an average X-ray luminosity of , HSC-XD 52 is among the most luminous X-ray selected AGN in dwarf galaxies. The spectroscopic and photometric properties of HSC-XD 52 indicate that it is an intermediate-redshift counterpart to local low-mass AGN.

Intermediate Luminosity Optical Transients (ILOTs) from Merging Giants

Abstract We suggest and study the formation of intermediate luminosity optical transients (ILOTs) from the merger of two cool giant stars. For the two stars to merge when both are in their giant phases, they must have close masses at their zero-age main sequence, and the orbital separation must be in the right range. After the two giants merge, the two cores spiral in toward each other within a common envelope. We study the energy sources of radiation in this process, which includes the ejection of mass that powers radiation by both recombination and by collision with previously ejected mass. This process includes no jets, unlike many other types of ILOTs, hence the event will not form a bipolar nebula. Using the stellar evolution numerical code mesa for two binary systems with stellar masses of (15M ⊙, 15.75M ⊙) and (31M ⊙, 31.5M ⊙), we find that the merger of the two cores releases gravitational energy that marginally ejects the entire common envelope. This implies that in many cases the two cores merge, i.e., a fatal common envelope evolution, leading to a somewhat more luminous ILOT. A typical ILOT from the merger of two cool giant stars lasts for several months to several years, and has a typical average luminosity of , where M CE is the ejected common envelope mass. The merger-driven massive outflow forms dust, hence leading to a very red ILOT, possibly even infrared luminous and undetectable in the visible.

Do AGN really suppress star formation?

AbstractActive galactic nuclei (AGN) are believed to regulate star formation inside their host galaxies through “AGN feedback”. We summarise our on-going study of luminous AGN (z ∼ 0.2−3; LAGN,bol 1043 erg s−1), which is designed to search for observational signatures of feedback by combining observed star-formation rate (SFR) measurements from statistical samples with cosmological model predictions. Using the EAGLE hydrodynamical cosmological simulations, in combination with our Herschel + ALMA surveys, we show that – even in the presence of AGN feedback – we do not necessarily expect to see any relationships between average galaxy-wide SFRs and instantaneous AGN luminosities. We caution that the correlation with stellar mass for both SFR and AGN luminosity can contribute to apparent observed positive trends between these two quantities. On the other hand, the EAGLE simulations, which reproduce our observations, predict that a signature of AGN feedback can be seen in the wide specific SFR distributions of all massive galaxies (not just AGN hosts). Overall, whilst we can not rule out that AGN have an immediate small-scale impact on in-situ star-formation, all of our results are consistent with a feedback model where galaxy-wide in-situ star formation is not rapidly suppressed by AGN, but where the feedback likely acts over a longer timescale than a single AGN episode.

Time-projection chamber for Multi-Purpose Detector of NICA project at JINR

Time Projection Chamber (TPC) is the main tracker of the Multi-Purpose Detector (MPD). The detector will operate at one of the beam interaction points of collider NICA (Nuclotron-based Ion Collider fAcility) [1] and it is optimized to investigate heavy-ion collisions in the energy range from 4 to 11 GeV/nuclon. At the average luminosity of 1027 cm−2⋅s−1 for gold collisions at 9 GeV/nuclon the event rate will reach up to 7 kHz. The emphasis of this paper is made on the TPC front end electronics based on novel ASIC chips, other systems of the TPC are shortly described.

Thermal evolution and quiescent emission of transiently accreting neutron stars

Aims.We study the long-term thermal evolution of neutron stars in soft X-ray transients (SXTs), taking the deep crustal heating into account consistently with the changes of the composition of the crust. We collect observational estimates of average accretion rates and thermal luminosities of such neutron stars and compare the theory with observations.Methods.We performed simulations of thermal evolution of accreting neutron stars, considering the gradual replacement of the original nonaccreted crust by the reprocessed accreted matter, the neutrino and photon energy losses, and the deep crustal heating due to nuclear reactions in the accreted crust. We also tested and compared results for different modern theoretical models. We updated a compilation of the observational estimates of the thermal luminosities in quiescence and average accretion rates in the SXTs and compared the observational estimates with the theoretical results.Results.The long-term thermal evolution of transiently accreting neutron stars is nonmonotonic. The quasi-equilibrium temperature in quiescence reaches a minimum and then increases toward the final steady state. The quasi-equilibrium thermal luminosity of a neutron star in an SXT can be substantially lower at the minimum than in the final state. This enlarges the range of possibilities for theoretical interpretation of observations of such neutron stars. The updates of the theory and observations leave the previous conclusions unchanged, namely that the direct Urca process operates in relatively cold neutron stars and that an accreted heat-blanketing envelope is likely present in relatively hot neutron stars in the SXTs in quiescence. The results of the comparison of theory with observations favor suppression of the triplet pairing type of nucleon superfluidity in the neutron-star matter.

Effects of engine operating conditions on flame propagation processes in a compression ignition optical engine

This paper describes the effects of swirl flow in a diesel optical single-cylinder engine with experimental results and simulation results obtained using KIVA code. Experiments were conducted with an optical single-cylinder engine for various operating conditions such as injection timing, exhaust gas recirculation (EGR), and swirl ratio, and a numerical study was also conducted to analyze the effects of swirl flow and combustion characteristics in detail. Correlations between in-cylinder flow from numerical simulations and the flame propagation process from experiments were conducted. The optical experimental and simulation results demonstrated that retarded injection timing and high EGR rate reduced the luminosity of flame and the wall heat transfer. However, a high EGR rate simultaneously reduced the combustion efficiency. The average luminosity of the optical image was determined by the flame in the high-temperature region above 2400 K. The luminosity and volume fraction of the temperature region above 2400 K showed the same trends. Correlation results between the experiment and simulation showed that swirl flow affects the propagation process. The flame region was generated in the center of the combustion chamber due to swirl flow based on visualization and analysis results. That is, swirl flow caused separation of the flame by disrupting the continuity of the spray.

Production and Test Status of the Superconducting Magnets for the NICA Project and the SIS100 Synchrotron

NICA is an international project accelerator collider complex under construction at the Joint Institute for Nuclear Research in Dubna. The facility is aimed at providing collider experiments with heavy ions up to gold in the center of mass energy from 4 to 11 GeV/u and an average luminosity up to 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">27</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for Au <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">79+</sup> . Collision experiments with polarized deuterons and protons are also foreseen. The facility includes two injector chains, a new superconducting booster synchrotron, the existing 6 AGeV superconducting synchrotron Nuclotron, and a new superconducting collider consisting of two rings, each 503 m in circumference. The planned FAIR synchrotron SIS100 has to deliver high-intensity beams for the FAIR project at GSI, Darmstadt. This machine will use fast-cycling 4 T/s magnets with a magnetic field up to 2 T. The NICA booster synchrotron, the NICA collider, and the heavy ion synchrotron SIS100 are based on iron-dominated window frametype magnets with a hollow superconductor winding analogous to the Nuclotron magnet. Progress in the manufacturing and testing of the NICA magnets and the SIS100 superconducting magnets is presented.

Revealing the differences in the SMBH accretion rate distributions of starburst and non-starburst galaxies

We infer and compare the specific X-ray luminosity distributions for a sample of massive (i.e. $\log_{10} (M*/M\odot) > 10.5$) galaxies split according to their far-infrared-derived star-forming properties (i.e., starburst and non-starburst) and redshift. We model each distribution as a power-law with an upper and lower turnover, and adopt a maximum likelihood method to include information from non-detections in the form of upper limits. When we use our inferred distributions to calculate the ratios of high to low sLx AGN (corresponding to above and below $0.1\lambda_{\text{Edd}}$, respectively) we find that starbursts have significantly higher proportions of high sLx AGN compared to their non-starburst counterparts. These findings help explain the increase in average X-ray luminosity in bins of increasing SFR reported by previous studies.

Multiwavelength radio observations of a brightest cluster galaxy at z = 1.71: detection of a modest active galactic nucleus and evidence for extended star formation

ABSTRACT We present deep, multiwavelength radio observations of SpARCS104922.6 + 564032.5, a z = 1.71 galaxy cluster with a starbursting core. Observations were made with the Karl G. Jansky Very Large Array (JVLA) in three bands: 1–2 GHz, 4–8 GHz, and 8–12 GHz. We detect a radio source coincident with the brightest cluster galaxy (BCG) that has a spectral index of α = 0.44 ± 0.29 and is indicative of emission from an active galactic nucleus. The radio luminosity is consistent with the average luminosity of the lower redshift BCG sample, but the flux densities are 6σ below the predicted values of the star-forming spectral energy distribution based on far infrared data. Our new fit fails to simultaneously describe the far infrared and radio fluxes. This, coupled with the fact that no other bright source is detected in the vicinity of the BCG implies that the star formation region, traced by the infrared emission, is extended or clumpy and not located directly within the BCG. Thus, we suggest that the star-forming core might not be driven by a single major wet merger, but rather by several smaller galaxies stripped of their gas or by a displaced cooling flow, although more data are needed to confirm any of those scenarios.

Suppressed CO emission and high G/D ratios in z = 2 galaxies with sub-solar gas-phase metallicity

ABSTRACT We study a population of significantly sub-solar enrichment galaxies at z = 1.99, to investigate how molecular gas, dust, and star formation relate in low-metallicity galaxies at the peak epoch of star formation. We target our sample with several deep Atacama Large Millimeter/submillimeter Array and Very Large Array datasets, and find no individual detections of CO[4–3], CO[1–0], or dust, in stark contrast to the &amp;gt;60 per cent detection rate expected for solar-enrichment galaxies with these MS H α star formation rates (SFRs). We find that both low- and high-density molecular gas (traced by CO[1–0] and CO[4–3], respectively) are affected by the low enrichment, showing sample average (stacked) luminosity deficits &amp;gt;0.5–0.7 dex below expectations. This is particularly pertinent for the use of high-J CO emission as a proxy of instantaneous SFR. Our individual galaxy data and stacked constraints point to a strong inverse dependence ∝ Zγ of gas-to-dust ratios (G/D) and CO-to-H2 conversion factors (αCO) on metallicity at z ∼ 2, with γG/D &amp;lt;−2.2 and $\gamma _{\alpha _{\rm CO}}\lt $−0.8, respectively. We quantify the importance of comparing G/D and αCO versus metallicity trends from the literature on a common, suitably normalized metallicity scale. When accounting for systematic offsets between different metallicity scales, our z ∼ 2 constraints on these scaling relations are consistent with the corresponding relations for local galaxies. However, among those local relations, we favour those with a steep/double power-law dependence of G/D on metallicity. Finally, we discuss the implications of these findings for (a) gas mass measurements for sub-M* galaxies, and (b) efforts to identify the characteristic galaxy mass scale contributing most to the comoving molecular gas density at z = 2.

Compton-thick AGNs in the NuSTAR Era. III. A Systematic Study of the Torus Covering Factor

Abstract We present the analysis of a sample of 35 candidate Compton-thick active galactic nuclei (AGNs) selected in the nearby universe (average redshift ) with the Swift-BAT 100-month survey. All sources have available NuSTAR data, thus allowing us to constrain with unprecedented quality important spectral parameters such as the obscuring torus line-of-sight column density (N H,z), the average torus column density (N H,tor), and the torus covering factor (f c ). We compare the best-fit results obtained with the widely used MYTorus (Murphy &amp; Yaqoob 2009) model with those of the recently published borus02 model (Baloković et al. 2018) used in the same geometrical configuration of MYTorus (i.e., with f c = 0.5). We find a remarkable agreement between the two, although with increasing dispersion in N H,z moving toward higher column densities. We then use borus02 to measure f c . High-f c sources have, on average, smaller offset between N H,z and N H,tor than low-f c ones. Therefore, low f c values can be linked to a “patchy torus” scenario, where the AGN is seen through an overdense region in the torus, while high-f c objects are more likely to be obscured by a more uniform gas distribution. Finally, we find potential evidence of an inverse trend between f c and the AGN 2–10 keV luminosity, i.e., sources with higher f c values have on average lower luminosities.