Calibrating photometric redshift measurements with the Multi-channel Imager (MCI) of the China Space Station Telescope (CSST)

The China Space Station Telescope (CSST) photometric survey aims to perform a high spatial resolution (~0.15'') photometric imaging for the targets that cover a large sky area (~17,500 deg^2) and wide wavelength range (from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager (MCI), one of the five instruments of the CSST, can provide accurate photometric redshift (photo-$z$) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio (SNR) data is adopted in the estimation of photo-z. We investigate the dependency of photo-z accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photo-z measurements with accuracy sigma_z~0.017 and outlier fraction f_c~2.2%. It can effectively improve the photo-z measurements of the main CSST survey using the Survey Camera (SC) to an accuracy sigma_z~0.015 and outlier fraction f_c~1.5%. It indicates that the original MCI filters are proper for the photo-z calibration.

Modelling the M*–SFR relation at high redshift: untangling factors driving biases in the intrinsic scatter measurement

ABSTRACT We present a method to self-consistently propagate stellar-mass [$\hbox{$\hbox{${\rm M}$}_{\star }$}=\log (\hbox{${\rm M}$}/\hbox{${\rm M}_{\odot }$})$] and star-formation-rate [$\hbox{${\Psi }$}=\log (\hbox{${\psi }$}/\hbox{${\rm M}_{\odot }$}\, {\rm yr}^{-1}$)] uncertainties on to intercept (α), slope (β), and intrinsic-scatter (σ) estimates for a simple model of the main sequence of star-forming galaxies, where $\hbox{${\Psi }$}= \alpha + \beta \hbox{$\hbox{${\rm M}$}_{\star }$}+ \mathcal {N}(0,\sigma)$. To test this method and compare it with other published methods, we construct mock photometric samples of galaxies at z ∼ 5 based on idealized models combined with broad- and medium-band filters at wavelengths 0.8–5 μm. Adopting simple Ψ estimates based on dust-corrected ultraviolet luminosity can underestimate σ. We find that broad-band fluxes alone cannot constrain the contribution from emission lines, implying that strong priors on the emission-line contribution are required if no medium-band constraints are available. Therefore, at high redshifts, where emission lines contribute a higher fraction of the broad-band flux, photometric fitting is sensitive to Ψ variations on short (∼10 Myr) time-scales. Priors on age imposed with a constant (or rising) star formation history (SFH) do not allow one to investigate a possible dependence of σ on $\hbox{${\rm M}$}_{\star }$ at high redshifts. Delayed exponential SFHs have less constrained priors, but do not account for Ψ variations on short time-scales, a problem if σ increases due to stochasticity of star formation. A simple SFH with current star formation decoupled from the previous history is appropriate. We show that, for simple exposure-time calculations assuming point sources, with low levels of dust, we should be able to obtain unbiased estimates of the main sequence down to $\mathrm{ log}(\hbox{${\rm M}$}/\hbox{${\rm M}_{\odot }$})\sim 8$ at z ∼ 5 with the James Webb Space Telescope while allowing for stochasticity of star formation.

Efficient Inverted Solar Cells Using Benzotriazole-Based Small Molecule and Polymers

We synthesized medium-band-gap donor-acceptor (D-A) -type conjugated polymers (PBTZCZ-L and PBTZCZ-H) consisting of a benzotriazole building block as an acceptor and a carbazole unit as a donor. In comparison with the polymers, a small conjugated molecule (BTZCZ-2) was developed, and its structural, thermal, optical, and photovoltaic properties were investigated. The power conversion efficiency (PCE) of the BTZCZ-2-based solar cell devices was less than 0.5%, considerably lower than those of polymer-based devices with conventional device structures. However, inverted solar cell devices configured with glass/ITO/ZnO:PEIE/BTZCZ-2:PC71BM/MoO3/Ag showed a tremendously improved efficiency (PCE: 5.05%, Jsc: 9.95 mA/cm2, Voc: 0.89 V, and FF: 57.0%). We believe that this is attributed to high energy transfer and excellent film morphologies.

Probing the existence of a rich galaxy overdensity at z = 5.2

We report the results of a pilot spectroscopic program of a region at z = 5.2 in the GOODS-N field containing an overdensity of galaxies around the well-known submillimeter galaxy HDF850.1. We have selected candidate cluster members from the optical 25 medium-band photometric catalog of the project SHARDS (Survey for High-z Absorption Red and Dead Sources). 17 rest-frame UV selected galaxies (LAEs and LBGs) with 5.15<zphot<5.27, candidates to be physically associated with the overdensity, have been observed with the instrument OSIRIS at the GranTeCan telescope. 13 out of these 17 (76 per cent) sources have secure spectroscopic confirmations via the Lyα line at the redshift of the galaxy protocluster PCl−HDF850.1, demonstrating the high reliabilty of our photometric redshift method. 10 out of 13 sources are newly confirmed members. Thus, we increase the number of confirmed members in this overdensity from 13 to 23 objects. In order to fully characterize this structure we combined our dataset with the sample from the literature. Beside the SMG HDF850.1, none of the 23 spectroscopically confirmed members are bright in the far-infrared/submm wavelength regime (SFRIR < few hundred M⊙ yr−1). The clustering analysis of the whole sample of 23 confirmed members reveals four distinct components in physical space in different evolutionary states, within Δz < 0.04 from the central region hosting SMG HDF850.1. The halo mass of the whole structure at z = 5.2, estimated by a variety of methods, range between 2 − 8 × 1012M⊙. The comparison with literature suggests a large scale assembly comparable to the formation of a central Virgo-like cluster at z=0 with several satellite components which will possibly be incorporated in a single halo if the protocluster is the progenitor of a more massive Coma-like cluster (>1015M⊙).

Over 17.5% Efficiency Ternary Organic Solar Cells with Enhanced Photon Utilization via a Medium Band Gap Non-Fullerene Acceptor

The light harvesting and photocurrent generation from acceptors largely determine the photovoltaic performance of organic solar cells (OSCs). We have designed and prepared two medium band gap non-fullerene acceptors (NFAs),...