arXiv subjects

Z. S. Yuan

Publications and source records attributed to Z. S. Yuan.

13 recordsLinked to original sources

arXiv2026

A Sample of 459 Galaxy Groups Identified from the FAST All Sky HI Survey DR2

Groups of HI-rich galaxies are key laboratories for understanding galaxy evolution and environmental effects, constructing samples of such groups is fundamental for relevant studies. Using the FAST All Sky HI Survey (FASHI) Data Release 2 (DR2), currently the largest and deepest HI catalog available, we identify galaxy groups directly from HI signals, without relying on optical pre-selection. A group-finding algorithm with a density contrast criterion and a minimum membership of five yields a catalog of 459 galaxy groups containing 3015 HI sources. Using archival spectroscopic data, we identify optical counterparts and derive total stellar masses of member galaxies as a proxy for the group total mass. The group redshift distribution peaks at z ~ 0.02, and the total HI mass peaks at ~ 10^{10} M_{\odot}. We find a significant positive correlation between total HI mass and total stellar mass, consistent with the increase in HI mass with halo mass reported in previous stacking studies. The ratio of total HI mass to total stellar mass decreases significantly with increasing total stellar mass, indicating gradual HI depletion in groups. Our sample provides rich targets for future studies of galaxy evolution and large-scale structure in the local Universe.

astro-ph.GA↗

arXiv2026

Solitary dwarf galaxy groups as tracers of dark matter halos in the local Universe

In $Λ$CDM cosmology, galaxies and clusters form within dark matter halos and merge in the hierarchical assembly paradigm to form massive systems. Using the released optical survey data, we searched for groups composed solely of dwarf galaxies, each with a stellar mass $M_*<10^{9.5}~M_{\odot}$. We identified 14 dwarf galaxy groups with at least 5 dwarf galaxies, all located within a projected radius of 200 kpc and with a line-of-sight velocity of $\pm$300 km s$^{-1}$. We checked photometric and imaging data and found that these 14 dwarf galaxy groups are solitary, with no neighboring massive galaxies with $M_*>10^{10}~M_{\odot}$ within 500 kpc and within $\pm$1200 km s$^{-1}$. These dwarf galaxies are gravitationally bound within halos with a dynamical mass of around $M_{\rm dyn} \sim 10^{12}~M_{\odot}$ and a virial radius of less than 400 kpc. The stellar mass fractions of these dwarf galaxy groups with $M_{\rm dyn}>10^{12}~M_{\odot}$ are one magnitude lower than predicted by the canonical stellar mass and halo mass relation. These dwarf galaxy groups, therefore, are indications of dark matter halos in the local Universe that host only a few newly formed dwarf galaxies.

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arXiv2026

A rare sextuple-merging brightest cluster galaxy system in a disturbed galaxy cluster observed with the Einstein Probe Follow-up X-ray Telescope

The evolutionary processes of galaxy clusters influence the properties of their member galaxies. We present a joint X-ray--optical analysis of the galaxy cluster WHY J050106.2+013714 at $z_{\rm c}=0.151$. X-ray observations with the Einstein Probe Follow-up X-ray Telescope indicate that the cluster is dynamically young. The cluster displays an average X-ray temperature of $2.8^{+0.4}_{-0.3}$ keV and a total luminosity of 9.4$\pm0.3\times10^{43}$ erg s$^{-1}$, consistent with the scaling relation of typical disturbed clusters. Remarkably, the cluster hosts a multi-merging brightest cluster galaxy (BCG) system composed of six massive galaxies, with a total stellar mass of $1.16\times10^{12}M_{\odot}$. We detected a well-defined intracluster light component extending to a size of 310 kpc. A systematic search for merging BCGs in the DESI Legacy Surveys reveals that this sextuple-merging BCG is extremely rare in the local Universe. Additionally, other merging BCGs are also likely to form in moderately disturbed clusters, which provides valuable insights into the formation of BCGs.

astro-ph.CO↗

arXiv2025

A sample of 3403 galaxy clusters identified in XMM-Newton X-ray images

Currently, the number of galaxy clusters identified using galaxy data has far exceeded the number derived from intracluster medium data. In this study, we used positional information from large optical cluster catalogues to search for previously unrecognized X-ray galaxy clusters in archival XMM-Newton data. We successfully identified 1490 galaxy clusters in X-ray images for the first time. By incorporating 1913 previously known X-ray clusters, we constructed a sample of 3403 galaxy clusters observed by XMM-Newton. Our cluster mass estimates show broad consistency with previous measurements. Comparative analyses between the known and newly identified subsamples revealed that new X-ray clusters exhibit systematically higher redshifts, lower masses, and smaller X-ray-to-optical mass ratios, but show no systematic differences in dynamical properties. The newly identified X-ray clusters are a valuable addition to previous X-ray samples and are important for future statistical studies.

astro-ph.GA↗

arXiv2025

A pulsar-helium star compact binary system formed by common envelope evolution

A stellar common envelope occurs in a binary system when the atmosphere of an evolving star expands to encompass an orbiting companion object. Such systems are predicted to evolve rapidly, ejecting the stellar envelope and leaving the companion in a tighter orbit around a stripped star. We used radio timing to identify a pulsar, PSR J1928+1815, with a spin period of 10.55 ms in a compact binary system with an orbital period of 3.60 hours. The companion star has 1.0 to 1.6 solar masses, eclipses the pulsar for about 17% of the orbit, and is undetected at other wavelengths, so it is most likely a stripped helium star. We interpret this system as having recently undergone a common envelope phase, producing a compact binary.

astro-ph.HE↗

arXiv2024

A catalogue of merging clusters of galaxies: cluster partners, merging subclusters, and post-collision clusters

Clusters of galaxies are merging during the formation of large-scale structures in the Universe. Based on optical survey data, we identify a large sample of pre-mergers of galaxy clusters and merging subclusters in rich clusters. We find 39,382 partners within a velocity difference of 1500 km/s and a projected separation of 5r_{500} around 33,126 main clusters, where r_{500} is the radius of the main cluster. Based on the galaxy distribution inside rich clusters with more than 30 member galaxy candidates, we identify subclusters by modeling the smoothed optical distribution with a two-component profile, and a coupling factor is obtained for merging subclusters in 7845 clusters. In addition, we find 3446 post-collision mergers according to the deviations of brightest cluster galaxies from other member galaxies, most of which have been partially validated by using the Chandra and XMM-Newton X-ray images. Two new bullet-like clusters have been identified by using the optical and X-ray images. The large samples of merging clusters of galaxies presented here are important databases for studying the hierarchical structure formation, cluster evolution, and the physics of intergalactic medium.

astro-ph.CO↗

arXiv2023

More relaxed intracluster gas than galaxies in clusters in quasi-equilibrium

During cluster mergers, the intracluster gas and member galaxies undergo dynamic evolution, but at different timescales and reach different states. We collect 24 galaxy clusters in quasi-equilibrium state as indicated by the X-ray image, and calculate the cluster orientations and three kinds of dynamical parameters, i.e., the normalized centroid offset, the sphere index and the ellipticity, for these clusters from the distributions of member galaxies and also the intracluster gas. We find consistent alignments for the orientations estimated from the two components. However, the three kinds of dynamical parameters indicated by member galaxies are systematically larger than those derived from the gas component, suggesting that the gas component is more relaxed than member galaxies. Differences of dynamical features between the intracluster gas and member galaxies are independent of cluster mass and concentration. We conclude that the intracluster gas reaches the dynamic equilibrium state earlier than the almost collisionless member galaxies.

astro-ph.GA↗

arXiv2022

Peering into the Milky Way by FAST: IV. Identification of two new Galactic supernova remnants G203.1+6.6 and G206.7+5.9

A 5$^{\circ}$ $\times$ 7$^{\circ}$ sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.5$^{\circ}$ and 3.5$^{\circ}$ respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The FAST L-band receiver covers a frequency range of 1.0-1.5 GHz. Commissioning of the receiving system, including the measurements of the half-power beam width, gain, and main-beam efficiency is made by observing the calibrators. The multi-channel spectroscopy backend mounted to the receiver allows an in-band spectral-index determination. The brightness-temperature spectral indices of both objects are measured to be $β$ $\sim$ $-$2.6 to $-$2.7. Polarized emission is detected from the archival Effelsberg $λ$11 cm data for all the shell structures of G203.1+6.6 and G206.7+5.9. These results clearly indicate a non-thermal synchrotron emitting nature, confirming that G203.1+6.6 and G206.7+5.9 are large shell-type supernova remnants (SNRs). Based on morphological correlation between the radio continuum emission of G206.7+5.9 and the HI structures, the kinematic distance to this new SNR is estimated to be about 440 pc, placing it in the Local Arm.

astro-ph.GA↗

arXiv2022

The alignment between brightest cluster galaxies and host clusters

The alignment between brightest cluster galaxies (BCGs) and host clusters can reveal the mystery of formation and evolution for galaxy clusters. We measure cluster orientations in optical based on the projected distribution of member galaxies and in X-ray by fitting the morphology of intra-cluster medium (ICM). Cluster orientations determined in the two wavelengths are generally consistent. The orientation alignment between BCGs and host clusters is confirmed and more significant than previous works. We find that BCGs are more aligned with cluster orientations measured in X-ray than those from optical data. Clusters with a brighter BCG generally show a stronger alignment. We argue that the detected redshift evolution of the alignment is probably caused by observational bias rather than intrinsic evolution. The alignment is not related to the ellipticity of BCGs, and the richness, ellipticity and dynamical state of host clusters. The strong alignment between BCGs and morphology of ICMs may be the consequence of the co-evolution between the central massive galaxy and host clusters.

astro-ph.GA↗

arXiv2022

Dynamical state of galaxy clusters evaluated from X-ray images

X-ray images of galaxy clusters often show disturbed structures that are indication of cluster mergers. As a complementary to our previous work on dynamical state of 964 clusters observed by the Chandra, we process the X-ray images for 1308 clusters from XMM-Newton archival data, together with the images of 22 clusters newly released by the Chandra, and evaluate their dynamical state from these X-ray images. The concentration index $c$, the centroid shift $ω$, the power ratio $P_3/P_0$ are calculated in circular regions with a certain radius of 500 kpc, and the morphology index $δ$ is estimated within elliptical regions adaptive to the cluster size and shape. In addition, the dynamical parameters for 42 clusters previously estimated from Chandra images are upgraded based on the newly available redshifts. Good consistence is found between dynamical parameters derived from XMM-Newton and Chandra images for the overlapped sample of clusters in the two datasets. The dependence of mass scaling relations on dynamical state is shown by using data of 388 clusters.

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arXiv2020

Dynamical state for 964 galaxy clusters from Chandra X-ray images

The dynamical state of galaxy clusters describes if clusters are relaxed dynamically or in a merging process of subclusters. By using archival images from the Chandra X-ray Observatory, we derive a set of parameters to describe the dynamical state for 964 galaxy clusters. Three widely used indicators for dynamical state, the concentration index c, the centroid shift omega and the power ratio P3/P0 are calculated in the circular central region with a radius of 500 kpc. We also derive two adaptive parameters, the profile parameter kappa and the asymmetry factor alpha, in the best fitted elliptical region. The morphology index delta is then defined by combining these two adaptive parameters, which indicates the dynamical state of galaxy clusters and has good correlations to the concentration index c, the centroid shift omega, the power ratio P3/P0, and the optical relaxation factor Gamma. For a large sample of clusters, the dynamical parameters are continuously distributed from the disturbed to relaxed states with a peak in the between, rather than the bimodal distribution for the two states. We find that the newly derived morphology index delta works for the similar fundamental plane between the radio power, cluster mass and the dynamical state for clusters with diffuse radio giant-halos and mini-halos. The offset between masses estimated from the Sunyaev-Zeldovich effect and X-ray images depends on dynamical parameters. All dynamical parameters for galaxy clusters derived from the Chandra archival images are available on http://zmtt.bao.ac.cn/galaxy_clusters/dyXimages/.

astro-ph.GA↗

arXiv2016

Radio luminosity function of brightest cluster galaxies

By cross-matching the currently largest optical catalog of galaxy clusters and the NVSS radio survey database, we obtain the largest complete sample of brightest cluster galaxies (BCGs) in the redshift range of 0.05<z<0.45, which have radio emission and redshift information. We confirm that more powerful radio BCGs tend to be these optically very bight galaxies located in more relaxed clusters. We derived the radio luminosity functions of BCGs from the largest complete sample of BCGs, and find that the functions depend on the optical luminosity of BCGs and the dynamical state of galaxy clusters. However, the radio luminosity function does not show significant evolution with redshift.

astro-ph.GA↗

arXiv2015

The scaling relations and the fundamental plane for radio halos and relics of galaxy clusters

Diffuse radio emission in galaxy clusters is known to be related to cluster mass and cluster dynamical state. We collect the observed fluxes of radio halos, relics, and mini-halos for a sample of galaxy clusters from the literature, and calculate their radio powers. We then obtain the values of cluster mass or mass proxies from previous observations, and also obtain the various dynamical parameters of these galaxy clusters from optical and X-ray data. The radio powers of relics, halos, and mini-halos are correlated with the cluster masses or mass proxies, as found by previous authors, with the correlations concerning giant radio halos being, in general, the strongest ones. We found that the inclusion of dynamical parameters as the third dimension can significantly reduce the data scatter for the scaling relations, especially for radio halos. We therefore conclude that the substructures in X-ray images of galaxy clusters and the irregular distributions of optical brightness of member galaxies can be used to quantitatively characterize the shock waves and turbulence in the intracluster medium responsible for re-accelerating particles to generate the observed diffuse radio emission. The power of radio halos and relics is correlated with cluster mass proxies and dynamical parameters in the form of a fundamental plane.

astro-ph.CO↗