Interpreting the Spitzer/IRAC colours of 7 ≤ z ≤ 9 galaxies: distinguishing between line emission and starlight using ALMA

ABSTRACT Prior to the launch of JWST, Spitzer/IRAC photometry offers the only means of studying the rest-frame optical properties of z >7 galaxies. Many such high-redshift galaxies display a red [3.6]−[4.5] micron colour, often referred to as the ‘IRAC excess’, which has conventionally been interpreted as arising from intense [O iii]+H β emission within the [4.5] micron bandpass. An appealing aspect of this interpretation is similarly intense line emission seen in star-forming galaxies at lower redshift as well as the redshift-dependent behaviour of the IRAC colours beyond z ∼ 7 modelled as the various nebular lines move through the two bandpasses. In this paper, we demonstrate that, given the photometric uncertainties, established stellar populations with Balmer (4000 Å rest frame) breaks, such as those inferred at z > 9 where line emission does not contaminate the IRAC bands, can equally well explain the redshift-dependent behaviour of the IRAC colours in 7 ≲ z ≲ 9 galaxies. We discuss possible ways of distinguishing between the two hypotheses using ALMA measures of [O iii] λ88 micron and dust continuum fluxes. Prior to further studies with JWST, we show that the distinction is important in determining the assembly history of galaxies in the first 500 Myr.

MMT/MMIRS spectroscopy of z = 1.3 - 2.4 extreme [O iii] emitters: implications for galaxies in the reionization era

ABSTRACT Galaxies in the reionization era have been shown to have prominent [O iii] + H β emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at z ≳ 6. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [O iii] emitting galaxies at 1.3 < z < 2.4. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses ($10^7\!-\!10^8 \, \mathrm{M}_\odot$) and larger specific star formation rates (5–300 Gyr−1), providing a window on galaxies directly following a burst or recent upturn in star formation. The hydrogen ionizing production efficiency (ξion) is found to increase with the [O iii] equivalent width (EW), in a manner similar to that found in local galaxies. We describe how this relationship helps explain the anomalous success rate in identifying Ly α emission in z ≳ 7 galaxies with strong [O iii] + H β emission. We probe the impact of the intense radiation field on the ISM using O32 and Ne3O2, two ionization-sensitive indices. Both are found to scale with the [O iii] EW, revealing extreme ionization conditions not commonly seen in older and more massive galaxies. In the most intense line emitters, the indices have very large average values (O32 = 9.1, Ne3O2 = 0.5) that have been shown to be linked to ionizing photon escape. We discuss implications for the nature of galaxies most likely to have O32 values associated with significant LyC escape. Finally we consider the optimal strategy for JWST spectroscopic investigations of galaxies at z ≳ 10 where the strongest rest-frame optical lines are no longer visible with NIRSpec.

Small river plumes off the northeastern coast of the Black Sea under average climatic and flooding discharge conditions

This study focuses on the impact of discharges of small rivers on the delivery and fate of fluvial water and suspended matter at the northeastern part of the Black Sea under different local precipitation conditions. Several dozens of mountainous rivers flow into the sea at the study region, and most of them, except for several of the largest, have little annual runoff and affect adjacent coastal waters to a limited extent under average climatic conditions. However, the discharges of these small rivers are characterized by a quick response to precipitation events and can significantly increase during and shortly after heavy rains, which are frequent in the considered area. The delivery and fate of fluvial water and terrigenous sediments at the study region, under average climatic and rain-induced flooding conditions, were explored and compared using in situ data, satellite imagery, and numerical modeling. It was shown that the point-source spread of continental discharge dominated by several large rivers under average climatic conditions can change to the line-source discharge from numerous small rivers situated along the coast in response to heavy rains. The intense line-source runoff of water and suspended sediments forms a geostrophic alongshore current of turbid and freshened water, which induces the intense transport of suspended and dissolved constituents discharged with river waters in a northwestern direction. This process significantly influences water quality and causes active sediment load at large segments of the narrow shelf at the northeastern part of the Black Sea compared to average climatic discharge conditions.

ABOUT THERMAL STABILITY OF BISMUTH(III) IODINE ETIOPORPHYRIN II COMPLEX

For the first time, a complex of bismuth(III) with iodine and etioporphyrin II is reported. It was prepared by reacting etioporphyrin II and bismuth(III) iodide in pyridine in Ar atmosphere. The prepared compound was characterized by FT-IR, 1H-NMR, UV-VIS spectroscopy and mass spectrometry. One intense line at m/z 684.990 attributed to the complex without the iodine atom is observed in the mass spectrum. This is in agreement with the data indicating that bismuthporphyrin complexes generally have low stability. Analysis of FT-IR spectra obtained at room temperature and at 145°С is reported. Priroda15 DFT package was used for optimization of complex geometry and calculation of the IR spectrum. Calculations were done using BPE functional and L1 basis set under relativistic approximation of Dyall Modified Dirac. Assignment of the vibrational frequencies is reported. Collected data indicate that the complex of bismuth(III) with iodine and etioporphyrin II is not stable and easily hydrolyses when exposed to air forming the corresponding hydroxocomplex. This transformation does not change significantly the dynamics of the porphyrin ring.

The 1280 Cm−1 Absorption Line in Amorphous Hydrogenated Boron Carbide

We report infrared absorption measurements that provide evidence for the presence of boron carbide icosahedra in amorphous hydrogenated boron carbide thin films. The infrared absorption spectra is dominated by an intense line at 1280 cm-1 with a FWHM of ≃320 cm-1. Similar lines have been previously reported in polycrystalline boron carbide, where boron carbide icosahedra make up the unit cell. In both systems, the linewidth narrows and the peak position shifts to higher energy with increasing carbon concentrations. From annealing studies of amorphous hydrogenated boron carbide, hydrogen plays a very small role in the 1280 cm-1 line. Finally, the integrated intensity of the 1280 cm-1 line is a sublinear function of the boron concentration, providing further evidence that the carbon concentration in these icosahedra increases as the carbon concentration of the film increases.

Charge Transfer Complex of Hexakis (Alkylthio) Benzene with Tetrafluorotetracyanoquinodimethane (tEDTB)2 TCNQF4

ABSTRACTIn order to evaluate the potentiality of organic donor molecules for molecular organic ferromagnets, with in principle C3 molecular symmetry, as in the hexakis (alkylthio) benzene, we have prepared single crystals of the charge transfer complex of tris [ethylene dithio] benzene (tEDTB) with TCNQF4, which have been subsequently oxidized with bromine and arsenic pentafluoride gas. The stoichiometry of this complex is 2:1 and it crystallizes in the triclinic system, space group P1 with the following cell parameters: a=11.515, b=11.044, c=10.460 A, α=111.50°, β=122.50°, γ=93.82°. The crystal structure consists of columns of alternating donor dyads and acceptors monads (DDADDA). The degree of charge transfer is estimated to be 0.2-0.3 from the methods based on bond lengths. While (tEDTB)2- TCNQF4 does not give a significant ESR spectrum, after treatment with the bromine or AsF5 gas, a single intense line, centered around the free electron g value, appears without any evidence of either a ground or an excited triplet state.