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We report the identification of an extremely rare and peculiar set of irregular radio sources, termed "STROMERSs" (STRange and Odd Morphology Extragalactic Radio Sources).ingThe irregular radio sources with very anomalous morphologies that make them exceptionally different from all the known classes and subclasses of irregular radio sources are detected as STROMERSs. A thorough search for this class of sources from the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) gave a total of nine such candidates. We checked the corresponding morphology of the identified sources in other frequency surveys. We found a detectable radio emission for all of the nine sources in the NRAO VLA Sky Survey (NVSS) at 1.4 GHz and in the TIFR GMRT Sky Survey (TGSS) at 150 MHz, while the same was found for only three sources in the Westerbork Northern Sky Survey (WENSS) at 625 MHz. However, the strange morphology was not found in all of those other survey images. We also characterized the sources with their corresponding physical parameters like optical counterpart, size, spectral index, and radio luminosity. ingThe estimated spectral values of the sources indicated that the STROMERSs were most likely radio galaxies. The presence of any nearby galaxy clusters for the STROMERSs was also checked. [ABSTRACT FROM AUTHOR]

The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multislit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kiloparsecs above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N ii ]/H α line ratio. A rough examination of the pressure balance between different circumgalactic medium phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 kpc from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position–velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of ∼150 km s−1. [ABSTRACT FROM AUTHOR]

We conduct an in-depth spectral analysis of ∼1 Ms XMM-Newton data of the narrow line Seyfert 1 galaxy RE J1034+396. The long exposure ensures high spectral quality and provides us with a detailed look at the intrinsic absorption and emission features toward this target. Two warm-absorber (WA) components with different ionization states ( log (ξ / erg cm s − 1) ∼ 4 and log (ξ / erg cm s − 1) ∼ 2.5 – 3 ) are required to explain the intrinsic absorption features in the Reflection Grating Spectrometer spectra. The estimated outflow velocities are around −1400 km s−1 and −(100–300) km s−1 for the high- and low-ionization WA components, respectively. Both absorbers are located beyond the broad-line region and cannot significantly affect the host environment. We analyze the warm absorbers in different flux states. We also examine the 2007 May observation in the low and high phases of quasiperiodic oscillation (QPO). In contrast to previous analyses showing a negative correlation between the high-ionization WA and the QPO phase, we have found no such variation in this WA component. We discover a broad emission bump in the spectral range of ∼12–18 Å, covering the primary features of the high-ionization WA. This emission bump shows a dramatic change in different source states, and its intensity may positively correlate with the QPO phase. The absence of this emission bump in previous work may contribute to the suggested WA–QPO connection. [ABSTRACT FROM AUTHOR]

Highly ionized, z=0 metal absorption lines detected in the X-ray spectra ofbackground active galactic nuclei (AGNs) provide an effective method to probethe hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way.We present an all-sky survey of the $K_{\alpha}$ transition of the local O VIIabsorption lines obtained by Voigt-profile fitting archival XMM-Newtonobservations. A total of 43 AGNs were selected, among which 12 are BL Lac-typeAGNs, and the rest are Seyfert 1 galaxies. At above the $3\sigma$ level thelocal O VII absorption lines were detected in 21 AGNs, among which 7 were newlydiscovered in this work. The sky covering fraction, defined as the ratiobetween the number of detections and the sample size, increases from at about40% for all targets to 100% for the brightest targets, suggesting a uniformdistribution of the O VII absorbers. We correlate the line equivalent widthwith the Galactic coordinates and do not find any strong correlations betweenthese quantities. Some AGNs have warm absorbers that may complicate theanalysis of the local X-ray absorber since the recession velocity can becompensated by the outflow velocity, especially for the nearby targets. Wediscuss the potential impact of the warm absorbers on our analysis. Acomprehensive theoretical modelling of the X-ray absorbers will be presented ina later paper.

Highly ionized, z=0 metal absorption lines detected in the X-ray spectra ofbackground active galactic nuclei (AGNs) provide an effective method to probethe hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way.We present an all-sky survey of the $K_{\alpha}$ transition of the local O VIIabsorption lines obtained by Voigt-profile fitting archival XMM-Newtonobservations. A total of 43 AGNs were selected, among which 12 are BL Lac-typeAGNs, and the rest are Seyfert 1 galaxies. At above the $3\sigma$ level thelocal O VII absorption lines were detected in 21 AGNs, among which 7 were newlydiscovered in this work. The sky covering fraction, defined as the ratiobetween the number of detections and the sample size, increases from at about40% for all targets to 100% for the brightest targets, suggesting a uniformdistribution of the O VII absorbers. We correlate the line equivalent widthwith the Galactic coordinates and do not find any strong correlations betweenthese quantities. Some AGNs have warm absorbers that may complicate theanalysis of the local X-ray absorber since the recession velocity can becompensated by the outflow velocity, especially for the nearby targets. Wediscuss the potential impact of the warm absorbers on our analysis. Acomprehensive theoretical modelling of the X-ray absorbers will be presented ina later paper.

Weak spectral features in BL Lacertae objects (BL Lacs) often provide a unique opportunity to probe the inner region of this rare type of active galactic nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph observation of the BL Lac H 2356-309. A weak Lyα emission line was detected. This is the fourth detection of a weak Lyα emission feature in the ultraviolet (UV) band in the so-called high-energy peaked BL Lacs, after Stocke et al. Assuming the line-emitting gas is located in the broad line region (BLR) and the ionizing source is the off-axis jet emission, we constrain the Lorentz factor (Γ) of the relativistic jet to be ≥8.1 with a maximum viewing angle of 3.°6. The derived Γ is somewhat larger than previous measurements of Γ ≈ 3-5, implying a covering factor of ∼3% of the line-emitting gas. Alternatively, the BLR clouds could be optically thin, in which case we constrain the BLR warm gas to be ∼10-5 M⊙. We also detected two H I and one O VI absorption lines that are within |Δv| < 150 km s-1 of the BL Lac object. The O VI and one of the H I absorbers likely coexist due to their nearly identical velocities. We discuss several ionization models and find a photoionization model where the ionizing photon source is the BL Lac object that can fit the observed ion column densities with reasonable physical parameters. This absorber can either be located in the interstellar medium of the host galaxy or in the BLR.

"Missing baryons," in the form of warm-hot intergalactic medium (WHIM), are expected to reside in cosmic filamentary structures that can be traced by signposts such as large-scale galaxy superstructures. The clear detection of an X-ray absorption line in the Sculptor Wall demonstrated the success of using galaxy superstructures as a signpost to search for the WHIM. Here we present an XMM -Newton Reflection Grating Spectrometer observation of the blazar Mkn 501, located in the Hercules Supercluster. We detected an O VII Kα absorption line at the 98.7% level (2.5σ) at the redshift of the foreground Hercules Supercluster. The derived properties of the absorber are consistent with theoretical expectations of the WHIM. We discuss the implication of our detection for the search for the "missing baryons." While this detection shows again that using signposts is a very effective strategy to search for the WHIM, follow-up observations are crucial both to strengthen the statistical significance of the detection and to rule out other interpretations. A local, z ∼ 0 O VII Kα absorption line was also clearly detected at the 4σ level, and we discuss its implications for our understanding of the hot gas content of our Galaxy. © 2014. The American Astronomical Society. All rights reserved.

Polycyclic aromatic hydrocarbon (PAH) molecules have long been suggested to be present in the interstellar medium (ISM). Nevertheless, despite their expected ubiquity and sustained searching efforts, identifying specific interstellar PAH molecules from their infrared (IR) spectroscopy has so far been unsuccessful. However, due to its unprecedented sensitivity, the advent of the JWST may change this. Meanwhile, recent years have witnessed breakthroughs in detecting specific PAH molecules (e.g. indene, cyanoindene, and cyanonaphthalene) through their rotational lines in the radio frequencies. As JWST holds great promise for identifying specific PAH molecules in the ISM based on their vibrational spectra in the IR, in this work, we model the vibrational excitation of indene, a molecule composed of a six-membered benzene ring fused with a five-membered cyclopentene ring, and calculate its IR emission spectra for a number of representative astrophysical regions. This will facilitate JWST to search for and identify indene in space through its vibrational bands and to quantitatively determine or place an upper limit on its abundance. [ABSTRACT FROM AUTHOR]

In a previous paper we reported a 3-sigma detection of an absorption linefrom the Warm-Hot Intergalactic Medium (WHIM) using the Chandra and XMM X-raygrating spectra of the blazar H2356-309, the sight-line of which intercepts theSculptor Wall, a large-scale superstructure of galaxies at z ~ 0.03. To verifyour initial detection, we obtained a deep (500 ks), follow-up exposure ofH2356-309 as part of the Cycle-10 Chandra Large Project Program. From a jointanalysis of the Cycle-10 and previous (Cycle-8) Chandra grating data we detectthe redshifted OVII WHIM line at a significance level of 3.4-sigma, asubstantial improvement over the 1.7-sigma level reported previously when usingonly the Cycle-8 data. The significance increases to 4.0-sigma when theexisting XMM grating data are included in the analysis, thus confirming athigher significance the existence of the line at the redshift of the SculptorWall with an equivalent width of 28.5+/-10.5 mA (90% confidence). We obtain a90% lower limit on the OVII column density of 0.8 10^16 cm^-2 and a 90% upperlimit on the Doppler-b parameter of 460 km/s. Assuming the absorber isuniformly distributed throughout the ~ 15 Mpc portion of the blazar'ssight-line that intercepts the Sculptor Wall, that the OVII column density is ~2 10^16 cm^-2 (corresponding to b > 150 km/s where the inferred column densityis only weakly dependent on b), and that the oxygen abundance is 0.1 solar, weestimate a baryon over-density of ~ 30 for the WHIM, which is consistent withthe peak of the WHIM mass fraction predicted by cosmological simulations. Theclear detection of OVII absorption in the Sculptor Wall demonstrates theviability of using current observatories to study WHIM in the X-ray absorptionspectra of blazars behind known large-scale structures.

Milky Way-type galaxies are surrounded by a warm-hot gaseous halo containing a considerable amount of baryons and metals. The kinematics and spatial distribution of highly ionized ion species such as O vi can be significantly affected by supernova (SN) explosions and early (pre-SN) stellar feedback (e.g., stellar winds, radiation pressure). Here we investigate effects of stellar feedback on O vi absorptions in Milky Way−like galaxies by analyzing the suites of high-resolution hydrodynamical simulations under the framework of SMUGGLE, a physically motivated subgrid interstellar medium and stellar feedback model for the moving-mesh code Arepo. We find that the fiducial run with the full suite of stellar feedback and moderate star formation activities can reasonably reproduce Galactic O vi absorptions observed by space telescopes such as the Far-Ultraviolet Spectroscopic Explorer, including the scale height of low-velocity (∣ v LSR∣ < 100 km s−1) O vi, the column density–line width relation for high-velocity (100 km s−1 ≤ ∣ v LSR∣ < 400 km s−1) O vi, and the cumulative O vi column densities. In contrast, model variations with more intense star formation activities deviate from observations further. Additionally, we find that the run considering only SN feedback is in broad agreement with the observations, whereas in runs without SN feedback this agreement is absent, which indicates a dominant role of SN feedback in heating and accelerating interstellar O vi. This is consistent with the current picture that interstellar O vi is predominantly produced by collisional ionization where mechanical feedback can play a central role. In contrast, photoionization is negligible for O vi production owing to the lack of high-energy (≳114 eV) photons required. [ABSTRACT FROM AUTHOR]

The Hot Universe Baryon Surveyor (HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view, the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, diffuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope. [ABSTRACT FROM AUTHOR]

To study the role of H i content in galaxy interactions, we select galaxy pairs and control galaxies from the SDSS-IV MaNGA IFU survey, adopting kinematic asymmetry as a new effective indicator to describe the merger stage. With archival data from the HI-MaNGA survey and new observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we investigate the differences in H i gas fraction (f H i), star formation rate (SFR), and H i star formation efficiency (SFEH i) between pairs and controls. Our results suggest that on average the H i gas fraction of major-merger pairs is marginally decreased by ∼ 15% relative to isolated galaxies, and paired galaxies during pericentric passage show weakly decreased f H i (−0.10 ± 0.05 dex), significantly enhanced SFR (0.42 ± 0.11 dex), and SFEH i (0.48 ± 0.12 dex). We propose the marginally detected H i depletion may originate from the gas consumption in fueling the enhanced H2 reservoir of galaxy pairs. [ABSTRACT FROM AUTHOR]

Keywords: errata; addenda; (galaxies:) quasars: absorption lines; Galaxies; (galaxies:) quasars: emission lines EN errata addenda (galaxies:) quasars: absorption lines Galaxies (galaxies:) quasars: emission lines 1975 1984 10 12/12/22 20230115 NES 230115 In Yu et al. ([4]), we missed the heliocentric and air-to-vacuum wavelength correction for the observed quasar spectrum. Addenda, (galaxies:) quasars: absorption lines, errata, Galaxies, (galaxies:) quasars: emission lines. [Extracted from the article]

The role of H i content in galaxy interactions is still under debate. To study the H i content of galaxy pairs at different merging stages, we compile a sample of 66 major-merger galaxy pairs and 433 control galaxies from the Sloan Digital Sky Survey IV (SDSS-IV) MaNGA IFU survey. In this study, we adopt kinematic asymmetry as a new effective indicator to describe the merging stage of galaxy pairs. With archival data from the HI-MaNGA survey and new observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we investigate the differences in H i gas fraction (f H I), star formation rate (SFR), and H i star formation efficiency (SFEH I) between the pair and control samples. Our results suggest that the H i gas fraction of major-merger pairs on average is marginally decreased by ∼15% relative to isolated galaxies, implying mild H i depletion during galaxy interactions. Compared to isolated galaxies, pre-passage paired galaxies have similar f H I, SFR, and SFEH I, while pairs during the pericentric passage have weakly decreased f H I (âˆ'0.10 ± 0.05 dex), significantly enhanced SFR (0.42 ± 0.11 dex), and SFEH I (0.48 ± 0.12 dex). When approaching the apocenter, paired galaxies show marginally decreased f H I (âˆ'0.05 ± 0.04 dex), comparable SFR (0.04 ± 0.06 dex), and SFEH I (0.08 ± 0.08 dex). We propose that the marginally detected H i depletion may originate from the gas consumption in fueling the enhanced H2 reservoir of galaxy pairs. In addition, new FAST observations also reveal a H i absorber (N H I ∼ 4.7 Ă— 1021 cmâˆ'2), which may suggest gas infalling and the triggering of active galactic nuclei activity. [ABSTRACT FROM AUTHOR]

Author(s): Fabrizio Nicastro (corresponding author) [1]; Smita Mathur [2]; Martin Elvis [1]; Jeremy Drake [1]; Taotao Fang [3]; Antonella Fruscione [1]; Yair Krongold [1, 4]; Herman Marshall [5]; Rik Williams [...]

The location of nearly half of the ordinary matter in the Universe is unknown. X-ray observations suggest that this elusive 'baryonic' matter is hidden in the filamentary structure of the cosmic web. The location of nearly half of the ordinary matter in the Universe is unknown. X-ray observations suggest that this elusive 'baryonic' matter is hidden in the filamentary structure of the cosmic web., Author(s): Taotao FangAuthor Affiliations:Missing matter found in the cosmic web Why have the missing baryons been so difficult to detect? One reason is that the density of the baryonic matter [...]

Outflows from supermassive black holes (SMBHs) play an important role in the co-evolution of themselves, their host galaxies, and the larger scale environments. Such outflows are often characterized by emission and absorption lines in various bands and in a wide velocity range blueshifted from the systematic redshift of the host quasar. In this paper, we report a strong broad line region (BLR) outflow from the z  ≈ 4.7 quasar BR 1202-0725 based on the high-resolution optical spectrum taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph installed on the 6.5 m Magellan/Clay telescope, obtained from the 'Probing the He  ii re-Ionization ERa via Absorbing C  iv Historical Yield' (HIERACHY) project. This rest-frame ultraviolet (UV) spectrum is characterized by a few significantly blueshifted broad emission lines from high ions; the most significant one is the C  iv line at a velocity of |$\sim -6500$|  km s−1 relative to the H α emission line, which is among the highest velocity BLR outflows in observed quasars at z  > 4. The measured properties of UV emission lines from different ions, except for O  i and Ly α, also follow a clear trend that higher ions tend to be broader and outflow at higher average velocities. There are multiple C  iv and Si  iv absorbing components identified on the blue wings of the corresponding emission lines, which may be produced by either the outflow or the intervening absorbers. [ABSTRACT FROM AUTHOR]

Using our measurements of the Hα emission line flux originating in the cool (T ∼ 104 K) gas that populates the halos of galaxies, we build a joint model to describe the mass of the cool circumgalactic medium (CGM) as a function of galactic stellar mass () and environment. Because the Hα emission correlates with the main cooling channel for this gas, we are able to estimate the rate at which the CGM cools and becomes fuel for star formation in the central galaxy. We describe this calculation, which uses our observations, previous measurements of some critical CGM properties, and modeling of the cooling mechanism using the C loudy modeling suite. We find that the mass cooling rate is larger than the star formation rates of the central galaxies by a factor of ∼4–90, empirically confirming that there is sufficient fuel to resolve the gas consumption problem and that feedback is needed to avoid collecting too much cold gas in galaxies. We find excellent agreement between our estimates of both the mass cooling rates and mass loading factors and the predictions of independent theoretical studies. The convergence in results that we find from several completely different treatments of the problem, particularly at the lower end of the galactic mass range, is a strong indication that we have a relatively robust understanding of the quantitative effects of feedback across this mass range. [ABSTRACT FROM AUTHOR]

We present a multiwavelength study of galaxies around D4UD01, a spectroscopically confirmed protocluster at z = 3.24, to investigate environmental trends. 450 galaxies are selected based on KS band detection with photometric redshifts (photo-z) at 3.0 < z < 3.4, among which ∼12% are classified as quiescent galaxies. The quiescent galaxies are among the most massive and reddest ones in the entire sample. We identify a large photo-z galaxy overdensity in the field, which lies close to the previously spectroscopically confirmed sources of the protocluster. We find that the quiescent galaxies are largely concentrated in the overdense protocluster region with a higher quiescent fraction, showing a sign of environmental quenching. Galaxies in the protocluster are forming faster than their field counterparts as seen in the stellar mass function, suggesting early and accelerated mass assembly in the overdense regions. Although weak evidence of suppressed star formation is found in the protocluster, the statistics are not significant enough to draw a definite conclusion. Our work sheds light on how the formation of massive galaxies is affected in the dense region of a protocluster when the universe was only 2 Gyr old. [ABSTRACT FROM AUTHOR]

We present a detailed study of near-IR selected galaxies in a protocluster field at z = 3.13. Protocluster galaxies are selected using the available mutliwavelength data with the photometric redshifts (photo-z) at 2.9 < z < 3.3, reaching a mass completeness of. Diverse types of galaxies have been found in the field, including normal star-forming galaxies, quiescent galaxies, and dusty star-forming galaxies. The photo-z galaxies form two large overdense structures in the field, largely overlapping with the previously identified galaxy overdensities traced by Lyα emitters (LAEs) and Lyman break galaxies, respectively. The northern overdensity consists of a large fraction of old and/or dusty galaxy populations, while the southern one is mainly composed of normal star-forming galaxies that are spatially correlated with the LAEs. This agrees with our previous study arguing the spatial offset of different galaxy overdensities may be due to halo assembly bias. Given the large end-to-end sizes of the two overdensities, one possibility is that they will form into a supercluster by the present day. We also find strong evidence that the star formation activities of the galaxies in the overdense protocluster regions are enhanced in comparison to their field counterparts, which suggests an accelerated mass assembly in this protocluster. [ABSTRACT FROM AUTHOR]

The spin distribution of massive black holes (MBHs) contains rich information on their assembly history. However, only limited information can be extracted from currently available spin measurements of MBHs owing to the small sample size and large measurement uncertainties. Upcoming X-ray telescopes with improved spectral resolution and larger effective area are expected to provide new insights into the growth history of MBHs. Here we investigate, at a proof of concept level, how stringent constraints can be placed on the accretion history of MBHs by the spin measurements from future X-ray missions. We assume a toy model consisting of a two-phase accretion history composed of an initial coherent phase with a constant disk orientation, followed by a chaotic phase with random disk orientations in each accretion episode. By utilizing mock spin data generated from such models and performing Bayesian Markov Chain Monte Carlo simulations, we find that most accretion models of MBHs can be reconstructed provided that MBH spins are measured with an accuracy of. We also quantify the precision of the reconstructed parameters by adopting various combinations of sample sizes and spin accuracies, and find that the sample size is more crucial to model reconstruction once the spin accuracy reaches ∼0.1. To some extent, a better spin accuracy will compensate for a small sample size and vice versa. Future X-ray missions such as the Advanced Telescope for High Energy Astrophysics and the enhanced X-ray Timing and Polarimetry mission, may provide spin measurements of ≳100 MBHs with an uncertainty of ∼0.04–0.1 and will thus put strong constraints on the MBH growth history. [ABSTRACT FROM AUTHOR]

The occurrence rates of bright X-ray flares in z  < 1 gamma-ray bursts (GRBs) with or without observed supernovae (SNe) association were compared. Our Sample I: the z  < 1 long GRBs (LGRBs) with SNe association (SN-GRBs) and with early Swift /X-Ray Telescope (XRT) observations, consists of 18 GRBs, among which only two GRBs have bright X-ray flares. Our Sample II: for comparison, all the z  < 1 LGRBs without observed SNe association and with early Swift /XRT observations, consists of 45 GRBs, among which 16 GRBs present bright X-ray flares. Thus, the study indicates a lower occurrence rate of bright X-ray flares in Sample I (11.1 per cent) than in Sample II (35.6 per cent). In addition, if dim X-ray fluctuations are included as flares, then 16.7 per cent of Sample I and 55.6 per cent of Sample II are found to have flares, again showing the discrepancy between these two samples. We examined the physical origin of these bright X-ray flares and found that most of them are probably related to the central engine reactivity. To understand the discrepancy, we propose that such a lower occurrence rate of flares in the SN-GRB sample may hint at an energy partition among the GRB, SNe, and X-ray flares under a saturated energy budget of massive star explosion. [ABSTRACT FROM AUTHOR]

Multi-wavelength flares have routinely been observed from the supermassive black hole, Sagittarius A⋆ (Sgr A⋆), at our Galactic center. The nature of these flares remains largely unclear, despite many theoretical models. We study the statistical properties of the Sgr A⋆ X-ray flares and find that they are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole. Motivated by the statistical results, we further develop a time-dependent magnetohydrodynamic (MHD) model for the multi-band flares from Sgr A⋆ by analogy with models of solar flares/coronal mass ejections (CMEs). We calculate the X-ray, infrared flare light curves, and the spectra, and find that our model can explain the main features of the flares. [ABSTRACT FROM PUBLISHER]

X-ray observations of the Galactic X-ray binaries (XRBs) revealed numerous highly ionized metal absorption lines. However, it is unclear whether such lines are produced by the hot interstellar medium (ISM) or the circumstellar medium intrinsic to the binaries. Here we present a Chandra X-ray absorption line study of 28 observations of 12 XRBs, with a focus on the Ne IX and Fe XVII lines. We report the first detections of these lines in a significant amount of observations. We do not find a significant dependence of the line equivalent width on the distance of the XRBs, but we do see a weak dependence on the source X-ray luminosity. We also find 2 out of 12 selected targets show strong temporal variation of the Ne IX absorbers. While the line ratio between the two ion species suggests a temperature consistent with the previous predictions of the ISM, comparing with two theoretical models of the ISM shows the observed column densities are significantly higher than predictions. On the other hand, photoionization by the XRBs provides a reasonably good fit to the data. Our findings suggest that a significant fraction of these X-ray absorbers may originate in the hot gas intrinsic to the XRBs, and that the ISM makes small, if not negligible, contribution. We briefly discuss the implications to the study of the Milky Way hot gas content. [ABSTRACT FROM AUTHOR]

We present a pair of high-resolution smoothed particle hydrodynamics simulations that explore the evolution and cooling behaviour of hot gas around Milky Way size galaxies. The simulations contain the same total baryonic mass and are identical other than their initial gas density distributions. The first is initialized with a low-entropy hot gas halo that traces the cuspy profile of the dark matter, and the second is initialized with a high-entropy hot halo with a cored density profile as might be expected in models with pre-heating feedback. Galaxy formation proceeds in dramatically different fashion depending on the initial setup. While the low-entropy halo cools rapidly, primarily from the central region, the high-entropy halo is quasi-stable for and eventually cools via the fragmentation and infall of clouds from ∼100 kpc distances. The low-entropy halo's X-ray surface brightness is ∼100 times brighter than current limits and the resultant disc galaxy contains more than half of the system's baryons. The high-entropy halo has an X-ray brightness that is in line with observations, an extended distribution of pressure-confined clouds reminiscent of observed populations and a final disc galaxy that has half the mass and ∼50 per cent more specific angular momentum than the disc formed in the low-entropy simulation. The final high-entropy system retains the majority of its baryons in a low-density hot halo. The hot halo harbours a trace population of cool, mostly ionized, pressure-confined clouds that contain ∼10 per cent of the halo's baryons after 10 Gyr of cooling. The covering fraction for H i and Mg ii absorption clouds in the high-entropy halo is ∼0.4 and ∼0.6, respectively, although most of the mass that fuels disc growth is ionized, and hence would be under counted in H i surveys. [ABSTRACT FROM AUTHOR]