Primordial fluctuations and non-Gaussianities in multi-field DBI inflation

We study Dirac-Born-Infeld (DBI) inflation models with multiple scalar fields. We show that the adiabatic and entropy modes propagate with a common effective sound speed and are thus amplified at the sound horizon crossing. In the small sound speed limit, we find that the amplitude of the entropy modes is much higher than that of the adiabatic modes. We show that this could strongly affect the observable curvature power spectrum as well as the amplitude of non-Gaussianities, although their shape remains as in the single-field DBI case.Comment: 4 page

Star formation in the cluster CLG0218.3-0510 at z=1.62 and its large-scale environment: the infrared perspective

The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy clusters known, with a rich muti-wavelength data set that confirms a mature galaxy population already in place. Using very deep, wide area (20x20 Mpc) imaging by Spitzer/MIPS at 24um, in conjunction with Herschel 5-band imaging from 100-500um, we investigate the dust-obscured, star-formation properties in the cluster and its associated large scale environment. Our galaxy sample of 693 galaxies at z=1.62 detected at 24um (10 spectroscopic and 683 photo-z) includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The star-formation rates (SFRs) derived from the measured infrared luminosity range from 18 to 2500 Ms/yr, with a median of 55 Ms/yr, over the entire radial range (10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy system, is vigorously forming stars at a rate of 256$\pm$70 Ms/yr, and the total cluster SFR enclosed in a circle of 1 Mpc is 1161$\pm$96 Ms/yr. We estimate a dust extinction of about 3 magnitudes by comparing the SFRs derived from [OII] luminosity with the ones computed from the 24um fluxes. We find that the in-falling region (1-3 Mpc) is special: there is a significant decrement (3.5x) of passive relative to star-forming galaxies in this region, and the total SFR of the galaxies located in this region is lower (130 Ms/yr/Mpc2) than anywhere in the cluster or field, regardless of their stellar mass. In a complementary approach we compute the local galaxy density, Sigma5, and find no trend between SFR and Sigma5. However, we measure an excess of star-forming galaxies in the cluster relative to the field by a factor 1.7, that lends support to a reversal of the SF-density relation in CLG0218.Comment: accepted for publication in MNRAS. v2: minor correction

A31N-03: Lower-Tropospheric CO2 from Near-Infrared ACOS-GOSAT Observations

We present two new products from near-infrared GOSAT observations: lower tropospheric (LMT, from 0-2.5 km) and upper tropospheric/stratospheric (U, above 2.5 km) carbon dioxide partial columns. We compare these new products to aircraft profiles and remote surface flask measurements and find that the seasonal and year-to-year variations in the new partial columns significantly improve over the ACOS-GOSAT initial guess/a priori, with distinct patterns in the LMT and U seasonal cycles which match validation data. For land monthly averages, we find errors of 1.9, 0.7, and 0.8 ppm for retrieved GOSAT LMT, U, and XCO2; for ocean monthly averages, we find errors of 0.7, 0.5, and 0.5 ppm for retrieved GOSAT LMT, U, and XCO2. In the southern hemisphere biomass burning season, the new partial columns show similar patterns to MODIS fire maps and MOPITT multispectral CO for both vertical levels, despite a flat ACOS-GOSAT prior, and CO/CO2 emission factor consistent with published values. The difference of LMT and U, useful for evaluation of model transport error, has also been validated with monthly average error of 0.8 (1.4) ppm for ocean (land). The new LMT partial column is more locally influenced than the U partial column, meaning that local fluxes can now be separated from CO2 transported from far away

Comparing serial X-ray crystallography and microcrystal electron diffraction (MicroED) as methods for routine structure determination from small macromolecular crystals.

Innovative new crystallographic methods are facilitating structural studies from ever smaller crystals of biological macromolecules. In particular, serial X-ray crystallography and microcrystal electron diffraction (MicroED) have emerged as useful methods for obtaining structural information from crystals on the nanometre to micrometre scale. Despite the utility of these methods, their implementation can often be difficult, as they present many challenges that are not encountered in traditional macromolecular crystallography experiments. Here, XFEL serial crystallography experiments and MicroED experiments using batch-grown microcrystals of the enzyme cyclophilin A are described. The results provide a roadmap for researchers hoping to design macromolecular microcrystallography experiments, and they highlight the strengths and weaknesses of the two methods. Specifically, we focus on how the different physical conditions imposed by the sample-preparation and delivery methods required for each type of experiment affect the crystal structure of the enzyme

Average Metallicity and Star Formation Rate of Lya Emitters Probed by a Triple Narrow-Band Survey

We present the average metallicity and star-formation rate of Lya emitters (LAEs) measured from our large-area survey with three narrow-band (NB) filters covering the Lya, [OII]3727, and Ha+[NII] lines of LAEs at z=2.2. We select 919 z=2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted [OII] and Ha nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by narrow-band imaging or deep spectroscopy. The stacked object has an Ha luminosity of 1.7x10^{42} erg s^{-1} corresponding to a star formation rate (SFR) of 14 M_{sun} yr^{-1}. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z>~0.09 Z_{sun} (2sigma) based on the [OII]/(Ha+[NII]) index together with photo-ionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z~2, are extremely metal poor (Z<2x10^{-2} Z_{sun}) young galaxies at the 4sigma level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z~2 UV-selected galaxies toward lower masses (5x10^{8} M_{sun}), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The Ha and Lya luminosities of our NB-selected LAEs indicate that the escape fraction of Lya photons is ~12-30 %, much higher than the values derived for other galaxy populations at z~2.Comment: 21 pages, 15 figures, 8 tables. Accepted for publication in Ap

Towards the prediction of molecular parameters from astronomical emission lines using Neural Networks

Molecular astronomy is a field that is blooming in the era of large observatories such as the Atacama Large Millimeter/Submillimeter Array (ALMA). With modern, sensitive, and high spectral resolution radio telescopes like ALMA and the Square Kilometer Array, the size of the data cubes is rapidly escalating, generating a need for powerful automatic analysis tools. This work introduces MolPred, a pilot study to perform predictions of molecular parameters such as excitation temperature (T) and column density (log(N)) from input spectra by the use of neural networks. We used as test cases the spectra of CO, HCO, SiO and CHCN between 80 and 400 GHz. Training spectra were generated with MADCUBA, a state-of-the-art spectral analysis tool. Our algorithm was designed to allow the generation of predictions for multiple molecules in parallel. Using neural networks, we can predict the column density and excitation temperature of these molecules with a mean absolute error of 8.5% for CO, 4.1% for HCO, 1.5% for SiO and 1.6% for CHCN. The prediction accuracy depends on the noise level, line saturation, and number of transitions. We performed predictions upon real ALMA data. The values predicted by our neural network for this real data differ by 13% from the MADCUBA values on average. Current limitations of our tool include not considering linewidth, source size, multiple velocity components, and line blending.A.B. wishes to thank Dr. Diego Mardones for his contribution to the early stages of this work. Also, to acknowledge support from the Federico Santa María Technical University General Directorate for Research and Postgraduate Studies (DGIP). JH and SV are funded by the European Research Council (ERC) Advanced Grant MOPPEX 833460. V.M.R. acknowledges support from the Comunidad de Madrid through the Atracción de Talento Investigador Modalidad 1 (Doctores con experiencia) Grant (COOL: Cosmic Origins Of Life; 2019-T1/TIC-15379; PI: V.M. Rivilla)

ALCHEMI Finds a “Shocking” Carbon Footprint in the Starburst Galaxy NGC 253

The centers of starburst galaxies may be characterized by a specific gas and ice chemistry due to their gas dynamics and the presence of various ice desorption mechanisms. This may result in a peculiar observable composition. We analyse the abundances of CO2, a reliable tracer of ice chemistry, from data collected as part of the Atacama Large Millimeter/submillimeter Array large program ALCHEMI, a wide-frequency spectral scan toward the starburst galaxy NGC 253 with an angular resolution of 1.″6. We constrain the CO2 abundances in the gas phase using its protonated form HOCO+. The distribution of HOCO+ is similar to that of methanol, which suggests that HOCO+ is indeed produced from the protonation of CO2 sublimated from ice. The HOCO+ fractional abundances are found to be (1-2) 7 10−9 at the outer part of the central molecular zone (CMZ), while they are lower (∼10−10) near the kinematic center. This peak fractional abundance at the outer CMZ is comparable to that in the Milky Way CMZ, and orders of magnitude higher than that in Galactic disk, star-forming regions. From the range of HOCO+/CO2 ratios suggested from chemical models, the gas-phase CO2 fractional abundance is estimated to be (1-20) 7 10−7 at the outer CMZ, and orders of magnitude lower near the center. We estimate the CO2 ice fractional abundances at the outer CMZ to be (2-5) 7 10−6 from the literature. A comparison between the ice and gas CO2 abundances suggests an efficient sublimation mechanism. This sublimation is attributed to large-scale shocks at the orbital intersections of the bar and CMZ

Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of H3_3O+^+ and SO

The cosmic ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star formation regions, which impacts the physical and chemical processes which drive the formation of stars. Previous studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have found evidence for a high CRIR value; $10^3-10^6$ times the average cosmic ray ionization rate within the Milky Way. This is a broad constraint and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations towards the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H$_3$O$^+$ and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 due to emission from their transitions. We find that each of the four regions modelled has a CRIR in the range $(1-80)\times10^{-14}$ s$^{-1}$ and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays including C$_2$H, HCO$^+$, HOC$^+$, and CO. From shock and PDR/XDR models, we further find that neither UV/X-ray driven nor shock dominated chemistry are a viable single alternative as none of these processes can adequately fit the abundances of all of these species.Comment: 24 pages, 15 figures, accepted for publication in Ap

Starburst Energy Feedback Seen through HCO+/HOC+Emission in NGC 253 from ALCHEMI

Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1-0) integrated intensity shows its association with "superbubbles,"cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10-150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10-11-6 × 10-10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ⪆ 103 if the maximum visual extinction is ⪆5, or a cosmic-ray ionization rate of ζ ⪆ 10-14 s-1 (3-4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.N.H. acknowledges support from JSPS KAKENHI grant No. JP21K03634. K.S. has been supported by grants MOST 108-2112-M-001-015 and 109- 2112-M-001-020 from the Ministry of Science and Technology, Taiwan. Y.N. is supported by the NAOJ ALMA Scientific Research grant No. 2017-06B. V.M.R. and L.C. are funded by the Comunidad de Madrid through the Atracción de Talento Investigador (Doctores con experiencia) Grant (COOL: Cosmic Origins Of Life; 2019-T1/TIC-15379)

Tracing Interstellar Heating: An ALCHEMI Measurement of the HCN Isomers in NGC 253

We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using the Atacama Large Millimeter/submillimeter Array via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253\u27s dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models, which are constrained using our HCN and HNC measurements. We find that the volume density n H 2 and cosmic-ray ionization rate (CRIR) ζ are enhanced by about an order of magnitude in the galaxy’s central regions as compared to those further from the nucleus. In NGC 253\u27s central giant molecular clouds (GMCs), where observed HCN/HNC abundance ratios are the lowest, n ∼ 105.5 cm−3 and ζ ∼ 10−12 s−1 (greater than 104 times the average Galactic rate). We find a positive correlation in the association of both density and CRIR with the number of star formation-related heating sources (supernova remnants, H ii regions, and super hot cores) located in each GMC, as well as a correlation between CRIRs and supernova rates. Additionally, we see an anticorrelation between the HCN/HNC ratio and CRIR, indicating that this ratio will be lower in regions where ζ is higher. Though previous studies suggested HCN and HNC may reveal strong mechanical heating processes in NGC 253\u27s CMZ, we find cosmic-ray heating dominates the heating budget, and mechanical heating does not play a significant role in the HCN and HNC chemistry