Xiaochuan Jiang

Detecting gaseous debris disks around white dwarfs offers a unique window into the ultimate fate of planetary systems and the composition of accreted planetary material. Here we present a systematic search for such disks through the Ca II infrared triplet using the Dark Energy Spectroscopic Instrument (DESI) Early Data Release. From a parent sample of 2706 spectroscopically confirmed white dwarfs, we identify 22 candidate systems showing tentative emission-line features, which corresponds to a raw occurrence rate of 0.81%, more than ten times higher than previous estimates. The detected emission lines are predominantly weak and require confirmation by follow-up observations. Three of these candidates also exhibit infrared excess in WISE photometry, suggesting a possible coexistence of gas and dust. However, the high candidate rate indicates that most are likely false positives due to telluric residuals or unresolved binaries. This work demonstrates the potential of DESI spectra for blind searches of rare circumstellar phenomena. The recently released DESI DR1, with its substantially larger spectroscopic sample, will enable searches for more gaseous disks and provide better insights into their occurrence and nature.

The origin of the extended soft X-ray emission around nearby highly inclined disk galaxies (often called the X-ray corona) remains uncertain. The emission could arise from volume-filling hot gas and/or its interaction with cool gas. Morphological properties of the X-ray emission can provide additional information to distinguish these different origins. We define model-independent parameters H ₅₀, H ₇₅, and H ₉₅—vertical scales that enclose 50%, 75%, and 95% of the total flux of the emission, respectively. We study the correlation of these parameters with galaxy properties inferred from infrared observations of a sample of nearby highly inclined disk galaxies with high-quality Chandra data. We find weak negative correlations between H ₅₀ or H ₇₅ and the surface star formation rate (I _SFR), and no correlation for H ₉₅. However, we detect strong negative correlations of the vertical concentration of the emission, defined as H ₅₀/H ₉₅ or H ₇₅/H ₉₅, with I _SFR. Our findings suggest that the X-ray emission around disk galaxies is likely comprised of two components: the extended, weak emission, characterized by H ₉₅, is influenced by the outflowing hot gas entrained in star formation driven winds, whereas the strong emission close to the disk, which is often rich in cool gas characterized by H ₅₀ or H ₇₅, is largely impacted by cool–hot gas interaction.

We present a multi-wavelength analysis of the host galaxy of short-duration gamma-ray burst (GRB) 150101B. Follow-up optical and X-ray observations suggested that the host galaxy, 2MASX J12320498-1056010, likely harbors low-luminosity active galactic nuclei (AGNs). Our modeling of the spectral energy distribution has confirmed the nature of the AGN, making it the first reported GRB host that contains an AGN. We have also found the host galaxy is a massive elliptical galaxy with stellar population of ∼5.7 Gyr, one of the oldest among the short-duration GRB hosts. Our analysis suggests that the host galaxy can be classified as an X-ray bright, optically normal galaxy, and the central AGN is likely dominated by a radiatively inefficient accretion flow. Our work explores an interesting connection that may exist between GRB and AGN activities of the host galaxy, which can help in understanding the host environment of the GRB events and the roles of AGN feedback.

Galaxy evolution is regulated by the interplay between galactic discs and their surrounding medium. We study this interplay by examining how the galactic coronal emission efficiency of stellar feedback depends on the (surface and specific) star formation rates (SFRs) and other parameters for a sample of 52 Chandra-observed nearby highly inclined disc galaxies. We first measure the star-forming galactic disc sizes, as well as the SFRs of these galaxies, using data from the Wide-Field Infrared Survey Explorer, and then show that (1) the specific 0.5–2 keV luminosity of the coronal emission correlates with the specific SFR in a sub-linear fashion: on average, L_X/L_K∝(SFR/M_*)^Γ with Γ = 0.29 ± 0.12; (2) the efficiency of the emission L_X/SFR decreases with increasing surface SFR (I_SFR; Γ = −0.44 ± 0.12); and (3) the characteristic temperature of the X-ray-emitting plasma weakly correlates with I_SFR (Γ = 0.08 ± 0.04). These results, somewhat surprising and anti-intuitive, suggest that (i) the linear correlation between L_X and SFR, as commonly presented, is largely due to the correlation of these two parameters with galaxy mass; (ii) much of the mechanical energy from stellar feedback likely drives global outflows with little X-ray cooling and with a mass-loading efficiency decreasing fast with increasing I_SFR (Γ ≲ −0.5); (iii) these outflows heat and inflate the medium around the galactic disks of massive galaxies, reducing its radiative cooling rate, whereas for relatively low-mass galaxies, the energy in the outflows is probably dissipated in regions far away from the galactic discs.

Surface engineering of steels has been carried out using plasma inlmersion ion implantation (PI³) and related innovative techniques including plasma immersion ion beam enhanced deposition (PIIBED) of titanium and plasma immersion ion beam mixing (PIIBM) of nitrogen and titanium. Auger concentration profiles indicate that PI³ of nitrogen produces a smooth implantation profile in the surface layer of the steel. The formation of a thin layer of TiN on the surface of the specimens treated by PIIBED of titanium and by PIIBM of nitrogen and titanium was confirmed by X-ray photoelectron spectroscopy. It has been demonstrated that the surface hardness and wear resistance of all the treated specimens were greatly improved.