arXiv subjects

Ping Zhou

Publications and source records attributed to Ping Zhou.

At least 37 records · Page 2Linked to original sources

arXiv2025

CO in MASsive Spirals (CO-MASS): an IRAM 30m CO emission line survey of the CGM-MASS sample

There exist extremely massive spiral galaxies in isolated environments, with stellar masses several times that of the Milky Way, yet their star formation rates (SFRs) are comparable to or even lower than that of the Milky Way. In this paper, we investigate the molecular gas properties of such galaxies to better understand the origin of their low SFRs. We present IRAM 30m CO observations of five extremely massive spirals from the CGM-MASS sample. We compare their star formation efficiencies (SFEs) with the Kennicutt-Schmidt relation and find that these massive spirals generally exhibit low efficiency in converting molecular gas into stars. We further compare their molecular gas masses with their atomic gas and stellar masses, and also include the CHANG-ES sample galaxies observed with the IRAM 30m telescope in a similar manner for comparison. Our sample galaxies show low efficiency in converting atomic to molecular gas and have lower molecular gas fractions, suggesting that their suppressed star formation stems from both limited gas supply and inefficient star formation. Considering potential cold gas sources in massive spirals, we argue that their current reservoirs likely originate from past starburst or merger events rather than ongoing accretion in present isolated environments. Finally, we examine the location of these galaxies on the baryonic Tully-Fisher relation, finding them baryon-deficient and deviating from the trend of lower-mass galaxies. This suggests either a significant undetected baryonic component or a flattening/turnover of the relation at the high-mass end, consistent with the stellar mass-halo mass relation.

astro-ph.GA↗

arXiv2025

Serendipitous Discovery of an Optically-Dark Ultra-Luminous Infrared Galaxy at $z$ = 3.4

Dusty, submillimeter-selected galaxies without optical counterparts contribute a non-negligible fraction of the star formation in the early universe. However, such a population is difficult to detect through classical optical/UV-based surveys. We report the serendipitous discovery of such an optically dark galaxy, behind the quadruply-lensed $z=2.56$ quasar, H1413+117, offset to the north by 6\arcsec. From $^{12}$CO $J=4$--3, $J=6$--5, and part of the $J=13$--12 transitions, which all spatially coincide with a compact submillimeter continuum emission, we determine an unambiguous spectroscopic redshift, $z=3.386\pm 0.005$. This galaxy has a molecular mass $M_{\rm mol} \sim 10^{11}$ M$_\odot$ and a black hole mass $M_{\rm BH} \sim 10^{8}$ M$_\odot$, estimated from $^{12}$CO $J=4$--3 and archival {\it Chandra} X-ray data ($L_{\rm 2-10,keV} \sim 4 \times 10^{44}$\,erg\,s$^{-1}$), respectively. We also estimate a total infrared luminosity of $L_{\rm FIR} = (2.8\pm{2.3}) \times 10^{12}$ L$_\odot$ and a stellar mass of $M_* \lesssim 10^{11}$ M$_{\odot}$, from spectral energy distribution fitting. According to these simple mass estimations, this gas-rich and X-ray bright galaxy might be in a transition phase from starburst to quasar offering a unique case for studying galaxy-black hole co-evolution under extremely dusty conditions.

astro-ph.GA↗

arXiv2025

Absence of Radio Emission Reveals an Exceptionally Weak Explosion of the Putative Historical Supernova Pa 30

We present the first deep radio continuum observations of Pa 30, a nebula hosting a unique optical source driven by an ultrafast outflow with a velocity of 16,000 km s$^{-1}$. The nebula was proposed to be the remnant of a white dwarf merger that occurred in 1181CE. We report no detection of the radio diffuse emission from Pa 30 or radio emission from the central source, setting $3σ$ upper limit flux densities of $0.84\,\rm mJy$ and $0.29\,\rm mJy$ at 1.5 GHz and 6 GHz, respectively, for Pa 30. The radio surface brightness of Pa 30 is $\sim 3$ orders of magnitude smaller than that of typical supernova remnants (SNRs) with comparable angular size. If Pa 30 is an SNR, our observations show it to be the faintest known in the radio band. Considering that 10\% of the supernova (SN) kinetic energy is transferred to cosmic rays (CRs), the absence of radio synchrotron emission suggests that the SN kinetic energy $\lesssim3\times 10^{47}(B/10 μ\rm G)^{-1.65}$ erg, which is 3 to 4 orders of magnitude lower than that of typical SNRs and the lowest measured among Galactic SNRs. There is also an indication of inefficient CR acceleration for this source. The low SN kinetic energy either implies the potential existence of many more radio-faint, sub-energetic SNRs in our Galaxy or challenges the SNR interpretation of Pa 30.

astro-ph.HE↗

arXiv2025

Observatory Science with eXTP

Scheduled for launch in 2030, the enhanced X-ray Timing and Polarization (eXTP) telescope is a Chinese space-based mission aimed at studying extreme conditions and phenomena in astrophysics. eXTP will feature three main payloads: Spectroscopy Focusing Arrays (SFAs), Polarimetry Focusing Arrays (PFAs), and a Wide-field Camera (W2C). This white paper outlines observatory science, incorporating key scientific advances and instrumental changes since the publication of the previous white paper [1]. We will discuss perspectives of eXTP on the research domains of flare stars, supernova remnants, pulsar wind nebulae, cataclysmic variables, X-ray binaries, ultraluminous X-ray sources, AGN, and pulsar-based positioning and timekeeping.

astro-ph.IM↗

arXiv2025

A Target Search for Fast Radio Bursts Associated with Two Fast Blue Optical Transients: AT2018cow and CSS161010

Fast blue optical transients (FBOTs) are luminous, rapidly evolving events with blue spectra, possibly powered by newborn magnetars and linked to fast radio bursts (FRBs). Given this potential connection, we conducted deep radio observations of two nearby FBOTs (AT2018cow and CSS161010) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), but detected no FRB-like signals. Our observations establish the most stringent upper limits on millisecond radio transients from FBOTs, reaching $\sim$10 mJy flux density. Assuming a log-normal luminosity function analogous to the repeating FRB 121102, we constrain the burst rate from potential magnetars in FBOTs to $<0.01$ hr$^{-1}$. The short ejecta escape timescale ($\sim$2.6 yr) compared to our observation epochs (4$-$6 years post-explosion) suggests that nondetection may not be attributed to FBOT's ejecta absorption. These findings impose useful constraints on the FRB activity emanating from newborn magnetars within FBOTs. They indicate that if there is a burst phase, it is either characterized by weaker bursts, occurs less frequently compared to those in known repeating FRB sources, or takes place beyond the time frame of our current observations. To gain deeper insights into the birth-related activity of magnetars, it is of importance to conduct timely and sustained FRB searches in FBOTs that emerge in the future.

astro-ph.HE↗

arXiv2025

RRAT J2325-0530: A Rotating Radio Transient with an Atypical Waiting-time Distribution

We present 1.25 GHz observations of the rotating radio transient (RRAT) J2325-0530, conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Approximately 60% of detected single pulses occur in clusters of 2 to 5 consecutive bursts. Consequently, the waiting-time distribution between successive single pulses exhibits a pronounced excess at one rotation period, deviating from the exponential distribution expected for a Poisson process. After grouping consecutive bursts into single emission events, the recalculated waiting-time distribution is well described by a Weibull distribution with a shape parameter $k \gtrsim 1$. Monte Carlo simulations incorporating both intrinsic burst on-windows and rotational modulation successfully reproduce the observed one-rotation excess. These results suggest that RRAT J2325-0530 emits through a quasi-random process with on-windows slightly longer than its spin period, modulated by the the rotation of emission beam. Additionally, the polarization position angle shows complex behavior that cannot be fully described by the standard rotating vector model, and several pulses exhibit quasi-periodic micro-structures. Taken together, these features indicate complex magnetospheric dynamics underlying the sporadic emission behavior of RRAT J2325-0530.

astro-ph.HE↗

arXiv2025

Negative differential conductance in triangular molecular assemblies

We report the creation and characterization of a molecular-scale negative differential conductance (NDC) device by assembling a triangular trimer of 4,5,9,10-tetrabromo-1,3,6,8-tetraazapyrene (TBTAP) molecules on a superconducting Pb(111) substrate. Using low-temperature scanning tunneling spectroscopy, we observe robust NDC behavior manifesting as a decrease in current with increasing voltage between 0.7-0.9 V arising from the interplay of Coulomb blockade and strong inter-molecular capacitive coupling within the molecular cluster. Gate-controlled charging and discharging processes are directly visualized via two-dimensional differential conductance mapping, which reveals the emergence of Coulomb rings and spatial regions of NDC. Theoretical modeling using a three-impurity Anderson model and master equation approach quantitatively reproduces the experimental observations and demonstrates that the NDC emerges purely from electron correlations, independent of the underlying superconductivity. By tuning the geometry to a hexamer structure, we further show that cluster topology provides versatile control over electronic properties at the molecular scale. These results establish a functional platform for implementing multifunctional molecular devices and highlight a strategy toward programmable and scalable nanoelectronics.

cond-mat.mes-hall↗

arXiv2025

Alien Type Ia supernovae from the Milky Way merger history and one possible candidate: Kepler's supernova

The Milky Way is a dynamic and evolving system shaped by numerous merger events throughout its history. These mergers bring stars with kinematic and dynamic properties differing from the main stellar population. However, it remains uncertain whether any of the Galactic supernova remnants can be attributed to such a merger origin. In this work, we compare the progenitor of Kepler's supernova to its nearby stars, ``alien'' stars, and in-situ Milky Way stellar populations. We uncover the abnormal kinematics and dynamics of Kepler's supernova and propose that its progenitor may have an extragalactic origin. We call the Type Ia supernovae (SNe Ia) produced by stars accreted into the Milky Way through merger events ``alien SNe Ia'' since they are cosmic immigrants. We estimate the rate of alien SNe Ia exploded recently using two methods: through galactic chemical evolution, and through a method without considering exact star formation history, introduced for the first time in this paper. We consider the past accretion of a few major satellite galaxies -- Kraken, Gaia-Enceladus-Sausage, the Helmi streams, Sequoia, Sagittarius, Wukong/LMS-1, and Cetus -- assuming these were dry mergers. The first method yields $1.5\times 10^{-5} - 5.0\times10^{-5}\rm\,yr^{-1}$, while the second method yields a comparable ${3.1}^{+1.8}_{-{1.1}}\times10^{-5}\rm\,yr^{-1}$ as the rate estimates for recent alien SNe Ia. These estimates represent lower bounds because we assumed no postmerger star formation.

astro-ph.HE↗

arXiv2025

X-ray polarization in SN 1006 southwest shows spatial variations and differences with the radio band

We report the detection of a spatial variation of X-ray polarization in the southwestern shell of SN 1006 (SN 1006 SW) using IXPE. The shell has an average X-ray polarization degree (PD) of $21.6\%\pm 4.5\%$ and polarization angle (PA) of $-48^\circ \pm 5^\circ$ in the 2--4 keV energy band, similar to those in the northeastern shell. The PD varies along SN 1006 SW, with a peak PD$= 40\%\pm 8\%$ in the south and a significantly lower PD $\lesssim 27\%$ (99\% upper limit) in the west where the shell has been proposed to be interacting with an interstellar cloud. The correlation between the PD, which reflects the magnetic orderliness, and the preshock density provides observational evidence that magnetic turbulence and amplification are environment-dependent. The high PD detected in the southern region of the shell constrains the magnetic turbulence scale of $\lesssim 0.1$~pc. Moreover, by comparing the IXPE X-ray and MeerKAT radio polarization measurements for SN 1006 SW, we found that magnetic fields traced by X-ray polarization are nearly radially distributed, whereas those traced by radio polarization tend to follow a direction parallel to the Galactic plane. This suggests that the X-ray polarization probes freshly amplified magnetic fields from small-scale structures in the immediate postshock region, while the radio traces more extended regions influenced by the pre-existing ambient magnetic fields.

astro-ph.HE↗

arXiv2025

Ultrafast Electronic Structure Engineering in 1$T$-TaS$_2$: Role of Doping and Amplitude Mode Dynamics

In strongly correlated transition metal dichalcogenides, an intricate interplay of polaronic distortions, stacking arrangement, and electronic correlations determines the nature of the insulating state. Here, we study the response of the electronic structure to optical excitations to reveal the effect of chemical electron doping on this complex interplay. Transient changes in pristine and electron-doped 1$T$ -TaS$_2$ are measured by femtosecond time-resolved photoelectron spectroscopy and compared to theoretical modeling based on non-equilibrium dynamical mean-field theory and density functional theory. The fine changes in the oscillatory signal of the charge density wave amplitude mode indicate phase-dependent modifications in the Coulomb interaction and the hopping. Furthermore, we find an enhanced fraction of monolayers in the doped system. Our work demonstrates how the combination of time-resolved spectroscopy and advanced theoretical modeling provides insights into the physics of correlated transition metal dichalcogenides.

cond-mat.str-el↗

arXiv2025

Unusual X-ray Oxygen Line Ratios of SN 1987A Arising From the Absorption of Galactic Hot Interstellar Medium

Recent high-resolution X-ray spectroscopic studies have revealed unusual oxygen line ratios, such as the high O VII forbidden-to-resonance ratio, in several supernova remnants. While the physical origin is still under debate, for most of them, it has been suggested that this phenomenon arises from either charge exchange (CX) or resonant scattering (RS). In this work, we report the high O VII G-ratio ($\gtrsim1$) and high O VIII Ly$β$/Ly$α$ ratio ($\gtrsim0.2$) found in multiepoch XMM-Newton RGS observations of SN 1987A. The line ratios cannot be fully explained by non-equilibrium ionization effects, CX, or RS. We suggest the absorption of foreground hot gas as the most likely origin, which plays the major role in modifying line fluxes and line ratios. Based on this scenario, we introduced two Gaussian absorption components at the O VII resonance line and the O VIII Ly$α$ line and constrained the optical depth of the two lines as $τ_{\rm OVII}\sim0.6$ and $τ_{\rm OVIII}\sim0.2$. We estimated the temperature as $kT_{\rm e}\sim0.15$ keV and the oxygen column density as $N_{\rm O}\sim0.5\times10^{16}$ cm$^{-2}$ for the absorbing gas, which is consistent with the hot interstellar medium in the Galactic halo. Neglecting this absorption component may lead to an underestimation of the O abundance. We revised the O abundance of SN 1987A, which is increased by $\sim20\%$ compared with previous results. The N/O ratio by number of atoms is revised to be $\sim1.2$.

astro-ph.HE↗

arXiv2025

ASKAP observations of the radio shell in the composite supernova remnant G310.6-1.6

We report the observations of the radio shell of the supernova remnant (SNR) G310.6-1.6 at 943 MHz from the Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe's Magnetism (POSSUM) surveys by using the Australian Square Kilometre Array Pathfinder (ASKAP). We detect polarized emission from the central pulsar wind nebula (PWN) with rotation measures varying from -696 rad m$^{-2}$ to -601 rad m$^{-2}$. We measure the integrated flux density of the shell to be 36.4 +/- 2.2 mJy at 943 MHz and derive a spectral index of -0.4 +/- 0.1 for the PWN and -0.7 +/- 0.3 for the SNR shell. From the combined radio and X-ray observations, the object can be identified as a supernova explosion of about 2500 yr ago with energy of about 1.3 x 10$^{50}$ erg, suggesting an ejected mass of about 10 M_sun. The circular radio shell outside the circular hard X-ray shell is unique among Galactic SNRs. We discuss several possible scenarios, including blast wave, reverse shock, and pulsar-fed emission, but find that none of them can fully explain the observed characteristics of the shell. This poses a challenge for understanding the evolution of SNRs. The results of this paper demonstrate the potential of the ASKAP EMU and POSSUM surveys in discovering more objects of small angular size and low surface brightness.

astro-ph.GA↗

arXiv2025

Evolution of X-ray Gas in SN 1987A from 2007 to 2021: Ring Fading and Ejecta Brightening Unveiled through Differential Emission Measure Analysis

As the nearest supernova (SN) observed since Kepler's SN of 1604, SN 1987A provides an unprecedented opportunity to study in detail the early evolution of supernova remnants (SNRs). Despite extensive studies through both observations and simulations, there is still an urgent need for a more effective approach to integrate the results from two sides. In this study, we conducted a detailed differential emission measure (DEM) analysis on the XMM-Newton observations taken in 2007 to 2021 to characterize the continuous temperature structure of SN 1987A, which can be better compared with simulations. The X-ray plasma exhibit a temperature distribution with a major peak at $\sim0.5$-$1$ keV and a high-temperature tail extending to $\gtrsim5$ keV. The emission measure (EM) of the major peak started to decline around 2014, while the EM of the tail continued increasing and appears to have formed a secondary peak at $\sim3$-$5$ keV in recent years. Our DEM results consistent well with simulations, which help to further identify the major peak as originating from the equatorial ring and the secondary peak as arising from the newly shocked ejecta. Together with the simulations, our DEM analysis reveals recent fading of the ring and brightening of the ejecta in X-rays from SN 1987A. Additionally, we observed a recent decrease in the centroid energy of Fe K line, providing further evidence of newly shocked ejecta.

astro-ph.HE↗

arXiv2025

Science objectives of the Einstein Probe mission

The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the Einstein Probe mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects/phenomena and their underlying physical processes revealed in the dynamic X-ray universe, as well as studies in other areas of X-ray astronomy.

astro-ph.HE↗

arXiv2024

Molecular chemistry induced by J-shock toward supernova remnant W51C

Shock waves from supernova remnants (SNRs) have strong influence on the physical and chemical properties of molecular clouds (MCs). Shocks propagating into magnetized MCs can be classified into "jump" J-shock and "continuous" C-shock. The molecular chemistry in the re-formed molecular gas behind J-shock is still not well understood, which will provide a comprehensive view of the chemical feedback of SNRs and the chemical effects of J-shock. We conducted a W-band (71.4-89.7 GHz) observation toward a re-formed molecular clump behind a J-shock induced by SNR W51C with the Yebes 40 m radio telescope to study the molecular chemistry in the re-formed molecular gas. Based on the local thermodynamic equilibrium (LTE) assumption, we estimate the column densities of HCO+, HCN, C2H and o-c-C3H2, and derive the maps of their abundance ratios with CO. The gas density is constrained by non-LTE analysis of the HCO+ J=1-0 line. We obtain the following abundance ratios: $N({\rm HCO^+})/N({\rm CO})\sim (1.0\text{--}4.0)\times 10^{-4}$, $N({\rm HCN})/N({\rm CO})\sim (1.8\text{--}5.3)\times 10^{-4}$, $N({\rm C_2H})/N({\rm CO})\sim (1.6\text{--}5.0)\times 10^{-3}$, and $N({o\text{-}c\text{-}{\rm C_3H_2}})/N({\rm CO})\sim (1.2\text{--}7.9)\times 10^{-4}$. The non-LTE analysis suggests that the gas density is $n_{\rm H_2}\gtrsim 10^4\rm \ cm^{-3}$. We find that the N(C2H)/N(CO) and N(o-c-C3H2)/N(CO) are higher than typical values in quiescent MCs and shocked MCs by 1-2 orders of magnitude, which can be qualitatively attributed to the abundant C+ and C at the earliest phase of molecular gas re-formation. The Paris-Durham shock code can reproduce, although not perfectly, the observed abundance ratios, especially the enhanced N(C2H)/N(CO) and N(o-c-C3H2)/N(CO), with J-shocks propagating in to both non-irradiated and irradiated molecular gas with a preshock density of $n_{\rm H}=2\times 10^3\rm \ cm^{-3}$.

astro-ph.GA↗

arXiv2024

Evidence for a shock-compressed magnetic field in the northwestern rim of Vela Jr. from X-ray polarimetry

Synchrotron X-ray emission has been detected from nearly a dozen young supernova remnants (SNRs). X-rays of synchrotron origin exhibit linear polarization in a regular, non-randomly oriented magnetic field. The significant polarized X-ray emission from four such SNRs has already been reported on the basis of observations with the Imaging X-ray Polarimetry Explorer (IXPE). The magnetic-field structure as derived from IXPE observations is radial for Cassiopeia A, Tycho's SNR, and SN 1006, and tangential for RX J1713.7-3946. The latter together with the recent detection of a tangential magnetic field in SNR 1E 0102.2-7219 by the Australia Telescope Compact Array in the radio band shows that tangential magnetic fields can also be present in young SNRs. Thus, the dichotomy in polarization between young and middle-aged SNRs (radial magnetic fields in young SNRs, but tangential magnetic fields in middle-aged SNRs), previously noticed in the radio band, deserves additional attention. The present analysis of IXPE observations determines, for the first time, a magnetic-field structure in the northwestern rim of Vela Jr, also known as RX J0852.0-4622, and provides a new example of a young SNR with a tangential magnetic field.

astro-ph.HE↗

arXiv2024

An X-ray Shell Reveals the Supernova Explosion for Galactic Microquasar SS 433

How black holes are formed remains an open and fundamental question in Astrophysics. Despite theoretical predictions, it lacks observations to understand whether the black hole formation experiences a supernova explosion. Here we report the discovery of an X-ray shell north of the Galactic micro-quasar SS 433 harboring a stellar-mass black hole spatially associated with radio continuum and polarization emissions, and an HI cloud. Its spectrum can be reproduced by a 1-keV under-ionized plasma, from which the shell is inferred to have been created by a supernova explosion 20-30 kyr ago and its properties constitute evidence for canonical SN explosions to create some black holes. Our analysis precludes other possible origins including heated by jets or blown by disk winds. According to the lower mass limit of the compact object in SS 433, we roughly deduced that the progenitor should be more massive than 25 M$_{\odot}$. The existence of such a young remnant in SS 433 can also lead to new insights into the supercritical accretion in young microquasars and the $γ$-ray emission of this system. The fallback ejecta may provide accretion materials within tens of thousands of years while the shock of the supernova remnant may play a crucial role in the cosmic ray (re)acceleration.

astro-ph.HE↗

arXiv2024

Probing Magnetic Fields in Young Supernova Remnants with IXPE

Synchrotron emission from the shocked regions in supernova remnants provides, through its polarization, crucial details about the magnetic field strength and orientation in these regions. This, in turn, provides information on particle acceleration in these shocks. Due to the rapid losses of the highest-energy relativistic electrons, X-ray polarization measurements allow for investigations of the magnetic field to be carried outvery close to the sites of particle acceleration. Measurements of both the geometry of the field and the levels of turbulence implied by the observed polarization degree thus provide unique insights into the conditions leading to efficient particle acceleration in fast shocks. The Imaging X-ray Polarimetry Explorer (IXPE) has carried out observations of multiple young SNRs, including Cas A, Tycho, SN 1006, and RX J1713.7-3946. In each, significant X-ray polarization detections provide measurements of magnetic field properties that show some common behavior but also considerable differences between these SNRs. Here, we provide a summary of results from IXPE studies of young SNRs, providing comparisons between the observed polarization and the physical properties of the remnants and their environments.

astro-ph.HE↗