We present new MUSE observations of a galaxy group probed by a background quasar. The quasar sightline passes between multiple $z=0.28$ galaxies, whilst showing at the same redshift low ionised metal line species, including Ca II, Mg I, Mg II and Fe II. Based on the galaxy redshifts measured from the MUSE data, we estimate the galaxies to be part of a small galaxy group with a halo mass of $\approx6\times10^{12}$ M$_{\odot}$. We use the MUSE data to reveal the two dimensional dynamical properties of the gas and stars in the group galaxies, and relate these to the absorber kinematics. With these data we consider a number of scenarios for the nature of the gas probed by the sightline absorbers: a co-rotating gas halo associated with a single galaxy within the group; outflowing material from a single group member powered by recent star-formation; and cool dense gas associated with an intra-group medium. We find that the dynamics, galaxy impact parameters, star-formation rates, and the absorber strength suggest the cool gas can not be clearly associated with any single galaxy within the group. Instead we find that the observations are consistent with a superposition of cool gas clouds originating with the observed galaxies as they fall into the group potential, and are now likely in the process of forming the intra-group medium.
We examine the heating of the intra-cluster medium (ICM) of cooling flow clusters of galaxies by jet-inflated bubbles and conclude that mixing of hot bubble gas with the ICM is more important than turbulent heating and shock heating. We use the PLUTO hydrodynamical code in full 3D to properly account for the inflation of the bubbles and to the multiple vortices induced by the jets and bubbles. The vortices mix some hot shocked jet gas with the ICM. For the parameters used by us the mixing process accounts for about four times as much heating as that by the kinetic energy in the ICM, namely, tu…
We present the results of the COS Intragroup Medium (COS-IGrM) Survey that used the Cosmic Origins Spectrograph on the Hubble Space Telescope to observe a sample of 18 UV bright quasars, each probing the intragroup medium (IGrM) of a galaxy group. We detect Ly$α$, C II, N V, Si II, Si III, and O VI in multiple sightlines. The highest ionization species detected in our data is O VI, which was detected in 8 out of 18 quasar sightlines. The wide range of ionization states observed provide evidence that the IGrM is patchy and multiphase. We find that the O VI detections generally align with radiat…
We present Hubble Space Telescope Cosmic Origin Spectrograph (COS) UV line spectroscopy and integral-field unit (IFU) observations of the intra-group medium in Stephan's Quintet (SQ). SQ hosts a 30 kpc long shocked ridge triggered by a galaxy collision at a relative velocity of 1000 km/s, where large amounts of molecular gas coexist with a hot, X-ray emitting, plasma. COS spectroscopy at five positions sampling the diverse environments of the SQ intra-group medium reveals very broad (2000 km/s) Ly$α$ line emission with complex line shapes. The Ly$α$ line profiles are similar to or much broader…
We use recent X-ray observations of the intracluster medium (ICM) of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM properties. We argue that the ICM of the cooling flow galaxy group NGC 5813 is more likely to be heated by mixing of post-shock jets' gas residing in hot bubbles with the ICM, than by shocks or turbulent-heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor…
Probing viscosity of the intracluster medium using ram-pressure stripping
National Tsing Hua University（国立清华大学）；National Center for Theoretical Sciences（国家理论科学中心）；Purdue University Fort Wayne（普渡大学韦恩堡分校）；University of Michigan（密歇根大学）
Gravitational microlensing has become a mature technique for discovering small gravitational lenses in the Universe which are otherwise beyond our detection limits. Similarly, plasma microlensing can help us explore cosmic plasma lenses. Both pulsar scintillation and extreme scattering events of compact radio sources suggest the existence of $\sim$ AU scale plasma lenses in the ionized interstellar medium (IISM), whose astrophysical correspondence remains a mystery. We demonstrate that plasma microlensing events by these plasma lenses recorded in the form of wide-band dynamic spectra are a pow…
A measurable fraction ($\sim8$ per cent) of recently discovered arcmin-size circular diffuse radio sources termed as Odd Radio Circles or ORCs can be supernovae remnants in the intragroup medium, within the local group and its immediate neighbour groups of galaxies. This estimate is based on the optical detection rate of the intragroup supernovae events in the nearby ($z \sim 0.1-0.2$) galaxy groups. A rate of about 5400 intragroup supernovae per million year is expected within the local and its immediate neighbour groups of galaxies. For a radio detectability period of about $10^{4}$ years, o…
Most of the baryonic mass in the circumgalactic medium (CGM) of a spiral galaxy is believed to be warm-hot, with temperature around $10^6$K. The narrow OVI absorption lines probe a somewhat cooler component at $\log \rm T(K)= 5.5$, but broad OVI absorbers have the potential to probe the hotter CGM. Here we present 376 ks Chandra LETG observations of a carefully selected galaxy in which the presence of broad OVI together with the non-detection of Lya was indicative of warm-hot gas. The strongest line expected to be present at $\approx 10^6$K is OVII $λ21.602$. There is a hint of an absorption l…
The power spectrum of HI intensity fluctuation of the interstellar medium carries information of the turbulence dynamics therein. We present a method to estimate the power spectrum of HI intensity fluctuation using radio interferometric observations. The method involves correlating the visibilities in the u-v plane at different baselines. This method is particularly use full for evaluating the power spectrum for the faint dwarf galaxies. We apply this method to 3 spiral galaxies and 5 dwarf galaxies. The measured power spectrum seem to follow a power law P_HI(U) = A U^α, suggesting turbulence …
We present the first mid-infrared (MIR) detections of HNC and H13CN in the interstellar medium, and numerous, resolved HCN rovibrational transitions. Our observations span 12.8 to 22.9 micron towards the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Exceptional, ~5 km/s, resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the H13CN R branch. This allows direct measurement of the species' excitation temperatures, column densities, and relative a…
We present an overview of the theory of high-redshift star and X-ray source formation, and how they affect the 21-cm background. Primary focus is given to Lyman alpha pumping and X-ray heating mechanisms at cosmic dawn, opening a new observational window for high-redshift astrophysics by generating sizable fluctuations in the 21-cm background. We describe observational prospects for power spectrum analysis and 3D tomography (imaging) of the signature of these early astrophysical sources by SKA1-LOW and SKA2.
After a decade of great progress in understanding gas flow into, out of, and through the Milky Way, we are poised to merge observations with simulations to build a comprehensive picture of the multi-scale magnetized interstellar medium (ISM). These insights will also be crucial to four bold initiatives in the 2020s: detecting nanohertz gravitational waves with pulsar timing arrays (PTAs), decoding fast radio bursts (FRBs), cosmic B-mode detection, and imaging the Milky Way's black hole with the Event Horizon Telescope (EHT).
Stars in globular clusters lose mass through slow stellar winds that are retained by the stellar cluster and contribute to build up a non negligible intracluster medium over time. However, all the observations so far found only a negligible amount of gas in GCs. We propose here to test different mechanisms such as ram-pressure stripping by the motion of the GC in the galactic halo medium and the inclusion of ionising sources to explain the lack of gas in GCs. We use full 3D hydrodynamical simulations taking into account stellar winds, ionising radiation, radiative heating and radiative pressur…
We use the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) signal measured by the Planck satellite and the luminous red galaxy (LRG) samples provided by the SDSS DR7 to study the properties of galaxy cluster and intra-cluster gas. We separate the samples into three redshift bins z_1=(0.16, 0.26), z_2=(0.26, 0.36), z_3=(0.36, 0.47), and stack the Planck y-map against LRGs to derive the averaged y-profile for each redshift bin. We then fit the stacked profile with the theoretical prediction from the universal pressure profile (UPP) by using the Markov-Chain Monte-Carlo method. We f…
We present a multi-wavelength study of the radio galaxy PKS J0334-3900, which resides at the centre of Abell 3135. Using Australia Telescope Compact Array (ATCA) observations at 1.4, 2.5, 4.6 & 8.6 GHz, we performed a detailed analysis of PKS J0334-3900. The morphology and spectral indices give physical parameters that constrain the dynamical history of the galaxy, which we use to produce a simulation of PKS J0334-3900. This simulation shows that the morphology can be generated by a wind in the intracluster medium (ICM), orbital motion caused by a companion galaxy, and precession of the black …
We present a study of the mixing properties of the simulated intra cluster Medium, using tracers particles that are advected by the gas flow during the evolution of cosmic structures. Using a sample of seven galaxy clusters (with masses in the range of M=2-3 10^14Msol/h) simulated with a peak resolution of 25kpc/h up to the distance of two virial radii from their centers, we investigate the application of tracers to some important problems concerning the mixing of the ICM. The transport properties of the evolving ICM are studied through the analysis of pair dispersion statistics and mixing dis…
We describe v02 of igmspec, a database of publically available ultraviolet, optical, and near-infrared spectra that probe the intergalactic medium (IGM). This database, a child of the specdb repository in the specdb github organization, comprises 403277 unique sources and 434686 spectra obtained with the world's greatest observatories. All of these data are distributed in a single ~25 GB HDF5 file maintained at the University of California Observatories and the University of California, Santa Cruz. The specdb software package includes Python scripts and modules for searching the source catalog…
The interaction of gas-rich galaxies with the intra-cluster medium (ICM) of galaxy clusters has a remarkable impact on their evolution, mainly due to the gas loss associated with this process. In this work, we use an idealised, high-resolution simulation of a Virgo-like cluster, run with RAMSES and with dynamics reproducing that of a zoom cosmological simulation, to investigate the interaction of infalling galaxies with the ICM. We find that the tails of ram pressure stripped galaxies give rise to a population of up to more than a hundred clumps of molecular gas lurking in the cluster. The num…
The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at $\sim 65$ and $35 {\rm~ kpc}$ west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium was recently disturbed. We analyze the properties of the intracluster medium using multiple Chandra observations of Abell 2204. We find a density ratio $n_{\rm in}/n_{\rm out} = 2.05\pm0.05$ and a temperature ratio $T_{\rm out}/T_{\rm in} = 1.91\pm0.27$ (projected, or $1.87\pm0.56$ deprojected) across the western edge, and cor…
