arXiv subjects

M. Sun

Publications and source records attributed to M. Sun.

At least 37 records · Page 2Linked to original sources

arXiv2024

The effect of mass loss in models of red supergiants in the Small Magellanic Cloud

The rate and mechanism of mass loss of red supergiants (RSGs) remain poorly understood, especially at low metallicities. Motivated by the new empirical prescription by Yang et al. 2023, based on the largest and most complete sample in the Small Magellanic Cloud, we investigate the impact of different popular and recent RSG mass-loss prescriptions that span a range of RSG mass-loss rates on the evolution and observable properties of single massive stars. Our results show that higher mass-loss rates result in earlier envelope stripping and shorter RSG lifetimes, particularly for the more luminous stars, leading to a steeper luminosity function and predicting hotter final positions for the SN progenitors. None of the considered mass-loss prescriptions is fully consistent with all observational constraints, highlighting ongoing uncertainties in deriving and modeling RSGs mass loss. The mass-loss rates suggested by Kee et al. predict rapid envelope stripping, inconsistent with the observed population of luminous RSGs and SN progenitor detections, while the models implementing the commonly used de Jager et al. and the recent Beasor et al. prescriptions overestimate the number of luminous RSGs. While the increased mass-loss rates for luminous RSGs predicted by Yang et al. lead to better agreement with the observed RSG luminosity function, naturally reproducing the updated Humphreys-Davidson limit, they also produce luminous yellow supergiant progenitors not detected in nearby supernovae. We also estimate that binary interactions tend to slightly increase the formation of luminous RSGs due to mass accretion or merging. Our study examines the impact of RSG mass loss during the late stages of massive stars, highlighting the significance of using comprehensive observational data, exploring the uncertainties involved, and considering the effects of binary-induced or episodic mass loss.

astro-ph.SR↗

arXiv2024

ESO 137-001 -- a jellyfish galaxy model

Ram pressure stripping of the spiral galaxy ESO 137-001 within the highly dynamical intracluster medium (ICM) of the Norma cluster lead to spectacular extraplanar CO, optical, H$α$, UV, and X-ray emission. The Halpha and X-ray tails extend up to 80 kpc from the galactic disk. Dynamical simulations of the ram pressure stripping event are presented to investigate the physics of the stripped gas and its ability to from stars, to predict HI maps, and to constrain the orbit of ESO 137-001 within the Norma cluster. Special care was taken for the stripping of the diffuse gas. In a new approach, we analytically estimate the mixing between the intracluster and interstellar media. Different temporal ram pressure profiles and the ICM-ISM mixing rate were tested. Three preferred models show most of the observed multi-wavelength characteristic of ESO 137-001. Our highest-ranked model best reproduces the CO emission distribution, velocity for distances <~ 20 kpc from the galactic disk, and the available NUV observations. The second and third preferred models reproduce best the available X-ray and Halpha observations of the gas tail including the Halpha velocity field. The angle between the direction of the galaxy's motion and the galactic disk is between 60 and 75 degrees. Ram pressure stripping thus occurs more face-on. The existence of a two-tail structures is a common feature in our models. It is due to the combined action of ram pressure and rotation together with the projection of the galaxy on the sky. Our modelling of the Halpha emission caused by ionization through thermal conduction is consistent with observations. HI emission distributions for the different models are predicted. Based on the 3D velocity vector derived from our dynamical model we derive a galaxy orbit, which is close to unbound.

astro-ph.GA↗

arXiv2023

Radio-continuum spectra of ram pressure stripped galaxies in the Coma Cluster

$Aims:$ We used the nearby Coma Cluster as a laboratory in order to probe the impact of ram pressure on star formation as well as to constrain the characteristic timescales and velocities for the stripping of the non-thermal ISM. $Methods:$ We used high-resolution ($6.5'' \approx 3\,\mathrm{kpc}$), multi-frequency ($144\,\mathrm{MHz} - 1.5\,\mathrm{GHz}$) radio continuum imaging of the Coma Cluster to resolve the low-frequency radio spectrum across the discs and tails of 25 ram pressure stripped galaxies. With resolved spectral index maps across these galaxy discs, we constrained the impact of ram pressure perturbations on galaxy star formation. We measured multi-frequency flux-density profiles along each of the ram pressure stripped tails in our sample. We then fit the resulting radio continuum spectra with a simple synchrotron aging model. $Results:$ We showed that ram pressure stripped tails in Coma have steep ($-2 \lesssim α\lesssim -1$) spectral indices. The discs of galaxies undergoing ram pressure stripping have integrated spectral indices within the expected range for shock acceleration from supernovae ($-0.8 \lesssim α\lesssim -0.5$), though there is a tail towards flatter values. In a resolved sense, there are gradients in spectral index across the discs of ram pressure stripped galaxies in Coma. These gradients are aligned with the direction of the observed radio tails, with the flattest spectral indices being found on the `leading half'. From best-fit break frequencies we estimated the projected plasma velocities along the tail to be on the order of hundreds of kilometers per second, with the precise magnitude depending on the assumed magnetic field strength.

astro-ph.GA↗

arXiv2023

Discrepant Approaches to Modeling Stellar Tides, and the Blurring of Pseudosynchronization

We examine the reasons for discrepancies between two alternative approaches to modeling small-amplitude tides in binary systems. The 'direct solution' (DS) approach solves the governing differential equations and boundary conditions directly, while the 'modal decomposition' (MD) approach relies on a normal-mode expansion. Applied to a model for the primary star in the heartbeat system KOI-54, the two approaches predict quite different behavior of the secular tidal torque. The MD approach exhibits the pseudosynchronization phenomenon, where the torque due to the equilibrium tide changes sign at a single, well-defined and theoretically predicted stellar rotation rate. The DS approach instead shows 'blurred' pseudosynchronization, where positive and negative torques intermingle over a range of rotation rates. We trace a major source of these differences to an incorrect damping coefficient in the profile functions describing the frequency dependence of the MD expansion coefficients. With this error corrected some differences between the approaches remain; however, both are in agreement that pseudosynchronization is blurred in the KOI-54 system. Our findings generalize to any type of star for which the tidal damping depends explicitly or implicitly on the forcing frequency.

astro-ph.SR↗

arXiv2023

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XV. The Halpha luminosity function of the Virgo cluster

We use a complete set of deep narrow-band imaging data for 384 galaxies gathered during the VESTIGE survey to derive the first Halpha luminosity function (LF) of the Virgo cluster within R200. The data allow us to cover the whole dynamic range of the Halpha LF (10^36 10^14 Mo. The comparison with the IllustrisTNG cosmological hydrodynamical simulations shows a more pronounced decrease at the faint end of the distribution. If Virgo is representative of typical nearby clusters of similar mass, this difference suggests that the stripping process in simulated galaxies in these environments is more efficient than observed.

astro-ph.GA↗

arXiv2022

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XIV. The main sequence relation in a rich environment down to M_star ~ 10^6 Mo

Using a compilation of Halpha fluxes for 384 star forming galaxies detected during the VESTIGE survey, we study several important scaling relations for a complete sample of galaxies in a rich environment. The extraordinary sensitivity of the data allows us to sample the whole dynamic range of the Halpha luminosity function, from massive (M*~10^11 Mo) to dwarf systems (M*~10^6 Mo). This extends previous works to a dynamic range in stellar mass and star formation rate (10^-4<SFR<10 Mo yr^-1) never explored so far. The main sequence (MS) relation derived for all star forming galaxies within one virial radius of the Virgo cluster has a slope comparable to that observed in other nearby samples of isolated objects, but has a dispersion ~3 times larger. The dispersion is tightly connected to the available amount of HI gas, with gas-poor systems located far below objects of similar stellar mass but with a normal HI content. When measured on unperturbed galaxies with a normal HI gas content, the relation has a slope a=0.92, an intercept b=-1.57, and a scatter ~0.40. We compare these observational results to the prediction of models. The observed scatter in the MS relation can be reproduced only after a violent and active stripping process such as ram-pressure that removes gas from the disc and quenches star formation on short (<1 Gyr) timescales. This rules out milder processes such as starvation. This interpretation is also consistent with the position of galaxies of different star formation activity and gas content within the phase-space diagram. We also show that the star forming regions formed in the stripped material outside perturbed galaxies are located well above the MS relation drawn by unperturbed systems. These HII regions, which might be at the origin of compact sources typical in rich environments, are living a starburst phase lasting only <50 Myr, later becoming quiescent systems.

astro-ph.GA↗

arXiv2022

Varying Joint Patterns and Compensatory Strategies Can Lead to the Same Functional Gait Outcomes: A Case Study

This paper analyses joint-space walking mechanisms and redundancies in delivering functional gait outcomes. Multiple biomechanical measures are analysed for two healthy male adults who participated in a multi-factorial study and walked during three sessions. Both participants employed varying intra- and inter-personal compensatory strategies (e.g., vaulting, hip hiking) across walking conditions and exhibited notable gait pattern alterations while keeping task-space (functional) gait parameters invariant. They also preferred various levels of asymmetric step length but kept their symmetric step time consistent and cadence-invariant during free walking. The results demonstrate the importance of an individualised approach and the need for a paradigm shift from functional (task-space) to joint-space gait analysis in attending to (a)typical gaits and delivering human-centred human-robot interaction.

cs.RO↗

arXiv2022

Ram Pressure Stripping in High-Density Environments

Galaxies living in rich environments are suffering different perturbations able to drastically affect their evolution. Among these, ram pressure stripping, i.e. the pressure exerted by the hot and dense intracluster medium (ICM) on galaxies moving at high velocity within the cluster gravitational potential well, is a key process able to remove their interstellar medium (ISM) and quench their activity of star formation. This review is aimed at describing this physical mechanism in different environments, from rich clusters of galaxies to loose and compact groups. We summarise the effects of this perturbing process on the baryonic components of galaxies, from the different gas phases (cold atomic and molecular, ionised, hot) to magnetic fields and cosmic rays, and describe their induced effects on the different stellar populations, with a particular attention to its role in the quenching episode generally observed in high density environments. We also discuss on the possible fate of the stripped material once removed from the perturbed galaxies and mixed with the ICM, and we try to estimate its contribution to the pollution of the surrounding environment. Finally, combining the results of local and high redshift observations with the prediction of tuned models and simulations, we try to quantify the importance of this process on the evolution of galaxies of different mass, from dwarfs to giants, in various environments and at different epochs.

astro-ph.GA↗

arXiv2022

Dot products in ${\Bbb F}_q^3$ and the Vapnik-Chervonenkis dimension

Given a set $E \subset {\Bbb F}_q^3$, where ${\Bbb F}_q$ is the field with $q$ elements. Consider a set of "classifiers" ${\mathcal H}^3_t(E)=\{h_y: y \in E\}$, where $h_y(x)=1$ if $x \cdot y=t$, $x \in E$, and $0$ otherwise. We are going to prove that if $|E| \ge Cq^{\frac{11}{4}}$, with a sufficiently large constant $C>0$, then the Vapnik-Chervonenkis dimension of ${\mathcal H}^3_t(E)$ is equal to $3$. In particular, this means that for sufficiently large subsets of ${\Bbb F}_q^3$, the Vapnik-Chervonenkis dimension of ${\mathcal H}^3_t(E)$ is the same as the Vapnik-Chervonenkis dimension of ${\mathcal H}^3_t({\Bbb F}_q^3)$. In some sense the proof leads us to consider the most complicated possible configuration that can always be embedded in subsets of ${\Bbb F}_q^3$ of size $\ge Cq^{\frac{11}{4}}$.

math.CO↗

arXiv2022

Probing multiphase gas in local massive elliptical galaxies via multiwavelength observations

We investigate the cold and warm gas content, kinematics, and spatial distribution of six local massive elliptical galaxies to probe the origin of the multiphase gas in their atmospheres. We report new observations, including SOFIA [CII], ALMA CO, MUSE H$α$+[NII] and VLA radio observations. These are complemented by a large suite of multiwavelength archival datasets, including thermodynamical properties of the hot gas and radio jets, which are leveraged to investigate the role of AGN feeding/feedback in regulating the multiphase gas content. Our galaxy sample shows a significant diversity in cool gas content, spanning filamentary and rotating structures. In our non-central galaxies, the distribution of such gas is often concentrated, at variance with the more extended features observed in central galaxies. Misalignment between the multiphase gas and stars suggest that stellar mass loss is not the primary driver. A fraction of the cool gas might be acquired via galaxy interactions, but we do not find quantitative evidence of mergers in most of our systems. Instead, key evidence supports the origin via condensation out of the diffuse halo. Comparing with Chaotic Cold Accretion (CCA) simulations, we find that our cool gas-free galaxies are likely in the overheated phase of the self-regulated AGN cycle, while for our galaxies with cool gas the k-plot and AGN power correlation corroborate the phase of CCA feeding in which the condensation rain is triggering more vigorous AGN heating. The related C-ratio further shows that central/non-central galaxies are expected to generate an extended/inner rain, consistent with our sample.

astro-ph.GA↗

arXiv2022

Relationships Between Stellar Velocity Dispersion and the Atmospheres of Early-Type Galaxies

The Voit et al. (2020) black hole feedback valve model predicts relationships between stellar velocity dispersion and atmospheric structure among massive early-type galaxies. In this work, we test that model using the Chandra archival sample of 49 early-type galaxies from Lakhchaura et al. (2018). We consider relationships between stellar velocity dispersion and entropy profile slope, multiphase gas extent, and the ratio of cooling time to freefall time. We also define subsamples based on data quality and entropy profile properties that clarify those relationships and enable more specific tests of the model predictions. We find that the atmospheric properties of early-type galaxies generally align with the predictions of the Voit et al. (2020) model, in that galaxies with greater stellar velocity dispersion tend to have radial profiles of pressure, gas density, and entropy with steeper slopes and less extended multiphase gas. Quantitative agreement with the model predictions improves when the sample is restricted to have low central entropy and stellar velocity dispersion of between 220 and 300 km/s.

astro-ph.GA↗

arXiv2021

Comparison of the material quality of AlxIn1-xN (x ~ 0-0.50) films deposited on Si (100) and (111) by reactive RF sputtering

Here, we compare the material quality of AlxIn1-xN layers deposited on Si with different crystallographic orientations, (100) and (111), via radio-frequency (RF) sputtering. To modulate their Al content, the Al RF power was varied from 0 to 225 W, whereas the In RF power and deposition temperature were fixed at 30 W and 300oC, respectively. X-ray diffraction measurements reveal a c-axis-oriented wurtzite structure with no phase separation regardless of the Al content (x = 0-0.50), which increases with the Al power supply. The surface morphology of the AlxIn1-xN layers improves with increasing Al content and it is similar for samples grown on both Si substrates (the root-mean-square roughness decreases from 12 nm to 2.5 nm). Furthermore, from TEM images we notice a similar grain-like columnar morphology and defect density on samples deposited on both Si substrates under the same conditions. Simultaneously grown AlxIn1-xN-on-sapphire samples point to a residual n-type carrier concentration in the 1020-1021 cm-3 range. The optical band gap energy of these layers evolves from 1.75 eV to 2.56 eV with increasing Al content, consistent with the blue shift of their low-temperature photoluminescence. In general, the material quality of the AlxIn1-xN films on Si is similar for both crystallographic orientations. Nonetheless, samples deposited on sapphire show an improved structural and morphological characteristic likely due to the lower difference in lattice constants between the nitride and the sapphire substrate.

cond-mat.mtrl-sci↗

arXiv2021

The XMM-SERVS survey: XMM-Newton point-source catalogs for the W-CDF-S and ELAIS-S1 fields

We present the X-ray point-source catalogs in two of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields, W-CDF-S (4.6 deg$^2$) and ELAIS-S1 (3.2 deg$^2$), aiming to fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large areas. The W-CDF-S and ELAIS-S1 regions were targeted with 2.3 Ms and 1.0 Ms of XMM-Newton observations, respectively; 1.8 Ms and 0.9 Ms exposures remain after flare filtering. The survey in W-CDF-S has a flux limit of 1.0 $\times$ 10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ over 90% of its area in the 0.5-10 keV band; 4053 sources are detected in total. The survey in ELAIS-S1 has a flux limit of 1.3 $\times$ 10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ over 90% of its area in the 0.5-10 keV band; 2630 sources are detected in total. Reliable optical-to-IR multiwavelength counterpart candidates are identified for $\approx$ 89% of the sources in W-CDF-S and $\approx$ 87% of the sources in ELAIS-S1. 3186 sources in W-CDF-S and 1985 sources in ELAIS-S1 are classified as AGNs. We also provide photometric redshifts for X-ray sources; $\approx$ 84% of the 3319/2001 sources in W-CDF-S/ELAIS-S1 with optical-to-NIR forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. The completion of the XMM-Newton observations in the W-CDF-S and ELAIS-S1 fields marks the end of the XMM-SERVS survey data gathering. The $\approx$ 12,000 point-like X-ray sources detected in the whole $\approx$ 13 deg$^2$ XMM-SERVS survey will benefit future large-sample AGN studies.

astro-ph.GA↗

arXiv2021

Bose-Einstein condensate-mediated superconductivity in graphene

We propose a mechanism for robust BCS-like superconductivity in graphene placed in the vicinity of a Bose-Einstein condensate. Electrons in the graphene interact with the excitations above the condensate, called Bogoliubov quasiparticles (or bogolons). It turns out that bogolon-pair-mediated interaction allows us to surpass the long-standing problem of the vanishing density of states of particles with a linear spectrum. This results in a dramatic enhancement of the superconducting properties of graphene while keeping its relativistic dispersion. We study the behavior of the superconducting gap and calculate critical temperatures in cases with single-bogolon and bogolon-pair-mediated pairing processes, accounting for the complex band structure of graphene. We also compare the critical temperature of the superconducting transition with the BKT temperature.

cond-mat.supr-con↗

arXiv2020

Revealing the relation between black-hole growth and host-galaxy compactness among star-forming galaxies

Recent studies show that a universal relation between black-hole (BH) growth and stellar mass ($M_\bigstar$) or star formation rate (SFR) is an oversimplification of BH-galaxy co-evolution, and that morphological and structural properties of host galaxies must also be considered. Particularly, a possible connection between BH growth and host-galaxy compactness was identified among star-forming (SF) galaxies. Utilizing $\approx 6300$ massive galaxies with $I_{\rm 814W}~<~24$ at $z$ $<$ 1.2 in the COSMOS field, we perform systematic partial-correlation analyses to investigate how sample-averaged BH accretion rate ($\rm \overline{BHAR}$) depends on host-galaxy compactness among SF galaxies, when controlling for morphology and $M_\bigstar$ (or SFR). The projected central surface-mass density within 1 kpc, $Σ_{1}$, is utilized to represent host-galaxy compactness in our study. We find that the $\rm \overline{BHAR}$-$Σ_{1}$ relation is stronger than either the $\rm \overline{BHAR}$-$M_\bigstar$ or $\rm \overline{BHAR}$-SFR relation among SF galaxies, and this $\rm \overline{BHAR}$-$Σ_{1}$ relation applies to both bulge-dominated galaxies and galaxies that are not dominated by bulges. This $\rm \overline{BHAR}$-$Σ_{1}$ relation among SF galaxies suggests a link between BH growth and the central gas density of host galaxies on the kpc scale, which may further imply a common origin of the gas in the vicinity of the BH and in the central $\sim$ kpc of the galaxy. This $\rm \overline{BHAR}$-$Σ_{1}$ relation can also be interpreted as the relation between BH growth and the central velocity dispersion of host galaxies at a given gas content, indicating the role of the host-galaxy potential well in regulating accretion onto the BH.

astro-ph.GA↗

arXiv2020

A Black-Hole Feedback Valve in Massive Galaxies

Star formation in the universe's most massive galaxies proceeds furiously early in time but then nearly ceases. Plenty of hot gas remains available but does not cool and condense into star-forming clouds. Active galactic nuclei (AGN) release enough energy to inhibit cooling of the hot gas, but energetic arguments alone do not explain why quenching of star formation is most effective in high-mass galaxies. In fact, optical observations show that quenching is more closely related to a galaxy's central stellar velocity dispersion ($σ_v$) than to any other characteristic. Here, we show that high $σ_v$ is critical to quenching because a deep central potential well maximizes the efficacy of AGN feedback. In order to remain quenched, a galaxy must continually sweep out the gas ejected from its aging stars. Supernova heating can accomplish this task as long as the AGN sufficiently reduces the gas pressure of the surrounding circumgalactic medium (CGM). We find that CGM pressure acts as the control knob on a valve that regulates AGN feedback and suggest that feedback power self-adjusts so that it suffices to lift the CGM out of the galaxy's potential well. Supernova heating then drives a galactic outflow that remains homogeneous if $σ_v \gtrsim 240 \, {\rm km \, s^{-1}}$. AGN feedback can effectively quench galaxies with a comparable velocity dispersion, but feedback in galaxies with a much lower velocity dispersion tends to result in convective circulation and accumulation of multiphase gas within the galaxy.

astro-ph.GA↗

arXiv2020

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).VI. Environmental quenching on HII region scales

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope (CFHT). We use a new set of data extracted from VESTIGE to study the impact of the hostile cluster environment on the star formation process down to the scale of HII regions (~ 50 pc). HII regions are identified and their parameters measured using the HIIphot code on a sample of 114 late-type galaxies spanning a wide range in morphological type (Sa-Sd, Im, BCD), stellar mass (10^6.5 <= M_star <= 10^11 Mo), and star formation activity (10^-3 <= SFR <= 10 Mo yr^-1). Owing to the exquisite average resolution of the VESTIGE data (0.65 arcsec), we detect 11302 HII regions with an Halpha luminosity L(Halpha) >= 10^37 erg s^-1. We show that the typical number of HII regions in gas-stripped objects is significantly lower than in healthy late-types of similar stellar mass. We also show that in these gas-stripped galaxies the number of HII regions significantly drops outside the effective radius, suggesting that the quenching process occurs outside-in, in agreement with other multifrequency observations. These new results consistently confirm that the main mechanism responsible for the decrease of the star formation activity observed in cluster galaxies is ram pressure, allowing us to discard other milder processes such as starvation or strangulation unable to reproduce the observed radially truncated profiles.

astro-ph.GA↗

arXiv2019

The X-ray Halo Scaling Relations of Supermassive Black Holes

We carry out a comprehensive Bayesian correlation analysis between hot halos and direct masses of supermassive black holes (SMBHs), by retrieving the X-ray plasma properties (temperature, luminosity, density, pressure, masses) over galactic to cluster scales for 85 diverse systems. We find new key scalings, with the tightest relation being the $M_\bullet-T_{\rm x}$, followed by $M_\bullet-L_{\rm x}$. The tighter scatter (down to 0.2 dex) and stronger correlation coefficient of all the X-ray halo scalings compared with the optical counterparts (as the $M_\bullet-σ_{\rm e}$) suggest that plasma halos play a more central role than stars in tracing and growing SMBHs (especially those that are ultramassive). Moreover, $M_\bullet$ correlates better with the gas mass than dark matter mass. We show the important role of the environment, morphology, and relic galaxies/coronae, as well as the main departures from virialization/self-similarity via the optical/X-ray fundamental planes. We test the three major channels for SMBH growth: hot/Bondi-like models have inconsistent anti-correlation with X-ray halos and too low feeding; cosmological simulations find SMBH mergers as sub-dominant over most of the cosmic time and too rare to induce a central-limit-theorem effect; the scalings are consistent with chaotic cold accretion (CCA), the rain of matter condensing out of the turbulent X-ray halos that sustains a long-term self-regulated feedback loop. The new correlations are major observational constraints for models of SMBH feeding/feedback in galaxies, groups, and clusters (e.g., to test cosmological hydrodynamical simulations), and enable the study of SMBHs not only through X-rays, but also via the Sunyaev-Zel'dovich effect (Compton parameter), lensing (total masses), and cosmology (gas fractions).

astro-ph.GA↗