Excess Luminosity Research Articles

From Neutrino- to Photon-cooled in Three Years: Can Fallback Accretion Explain the X-Ray Excess in GW170817?

Abstract Excess X-ray emission from the neutron star merger GW170817 above the predicted afterglow was recently detected t ≈ 3.4 yr post-merger. One possible origin is accretion onto the newly unshrouded black hole (BH) remnant. While fallback of bound dynamical ejecta is insufficient to generate the excess luminosity, L X ∼ 5 × 1038 erg s−1, fallback from the disk wind ejecta—due to their larger mass and lower velocity—remains a possibility. We present hydrodynamic α-viscosity simulations of the post-merger disk evolution that extend to timescales t ≈ 35 s post-merger, necessary to capture the asymptotic evolution into the radiatively inefficient regime. Due to inefficient neutrino cooling, the BH accretion rate decays rapidly at late times ( M ̇ bh ∝ t − β bh , where β bh ≈ 2.4–2.8), which is incompatible with the late-time excess. However, matter falls back to the inner disk from the equatorial region more gradually, M ̇ fb ∝ t − β fb with β fb ≈ 1.43 in our α ≈ 0.03 simulations. By the present epoch t ≈ 3.4 yr, the fallback rate has become sub-Eddington and the disk can again accrete efficiently, i.e., M ̇ bh ≈ M ̇ fb , this time due to photon instead of neutrino cooling. The predicted present-day X-ray accretion luminosity, L X ≈ 0.1 M ̇ bh c 2 ≈ ( 2 – 70 ) × 10 38 erg s−1 for β fb ≈ 1.43–1.66, thus supports (with caveats) an accretion-powered origin for the X-ray excess in GW170817. The suppressed BH accretion rate prior to the sub-Eddington transition, weeks to months after the merger, is key to avoid overproducing the kilonova luminosity via reprocessing.

Evidence of hydrogen-helium immiscibility at Jupiter-interior conditions.

The phase behaviour of warm dense hydrogen-helium (H-He) mixtures affects our understanding of the evolution of Jupiter and Saturn and their interior structures1,2. For example, precipitation of He from a H-He atmosphere at about 1-10 megabar and a few thousand kelvin has been invoked to explain both the excess luminosity of Saturn1,3, and the depletion of He and neon (Ne) in Jupiter's atmosphere as observed by the Galileo probe4,5. But despite its importance, H-He phase behaviour under relevant planetary conditions remains poorly constrained because it is challenging to determine computationally and because the extremes of temperature and pressure are difficult to reach experimentally. Here we report that appropriate temperatures and pressures can be reached through laser-driven shock compression of H2-He samples that have been pre-compressed in diamond-anvil cells. This allows us to probe the properties of H-He mixtures under Jovian interior conditions, revealing a region of immiscibility along the Hugoniot. A clear discontinuous change in sample reflectivity indicates that this region ends above 150 gigapascals at 10,200 kelvin and that a more subtle reflectivity change occurs above 93 gigapascals at 4,700 kelvin. Considering pressure-temperature profiles for Jupiter, these experimental immiscibility constraints for a near-protosolar mixture suggest that H-He phase separation affects a large fraction-we estimate about 15 per cent of the radius-of Jupiter's interior. This finding provides microphysical support for Jupiter models that invoke a layered interior to explain Juno and Galileo spacecraft observations1,4,6-8.

Multimessenger Signals from Black Hole–Neutron Star Mergers without Significant Tidal Disruption

Abstract We study the multimessenger signals from the merger of a black hole with a magnetized neutron star using resistive magnetohydrodynamics simulations coupled to full general relativity. We focus on a case with a 5:1 mass ratio, where only a small amount of the neutron star matter remains post-merger, but we nevertheless find that significant electromagnetic radiation can be powered by the interaction of the neutron star’s magnetosphere with the black hole. In the lead-up to merger, strong twisting of magnetic field lines from the inspiral leads to plasmoid emission and results in a luminosity in excess of that expected from unipolar induction. We find that the strongest emission occurs shortly after merger during a transitory period in which magnetic loops form and escape the central region. The remaining magnetic field collimates around the spin axis of the remnant black hole before dissipating, an indication that, in more favorable scenarios (higher black hole spin/lower mass ratio) with larger accretion disks, a jet would form.

Single-shot 3D imaging of hydroxyl radicals in the vicinity of a gliding arc discharge

Plasma-related studies in gas phase are challenging to carry out due to plasma’s transient and unpredictable behavior, excessive luminosity emission, 3D complexity and aggressive chemistry and physiochemical interactions that are easily affected by external probing. Laser-induced fluorescence is a robust technique for non-intrusive investigations of plasma-produced species. In this letter, we present 3D distributions of ground state hydroxyl radicals (OH) radicals in the vicinity of a glow-type gliding arc plasma. Such radical distributions are captured instantaneously in one single camera acquisition by combining structured laser illumination and a lock-in based imaging analysis method called FRAME. The interference of plasma emission is automatically subtracted by the FRAME technique. In addition, the orientation of the plasma discharge can be reconstructed from the 3D data matrix, which can then be used to calculate 2D distributions of ground state OH radicals in a plane perpendicular to the orientation of the plasma channel. Our results indicate that OH distributions around a gliding arc are strongly affected by gas dynamics. We believe that the ability to instantaneously capture 3D transient molecular distributions in a plasma discharge, with minimal plasma emission interference, will have a strong impact on the plasma community for in situ investigations of plasma-induced chemistry and physics.

A Multiwavelength Analysis of the Faint Radio Sky (COSMOS-XS): the Nature of the Ultra-faint Radio Population

Abstract Ultra-deep radio surveys are an invaluable probe of dust-obscured star formation, but require a clear understanding of the relative contribution from radio active galactic nuclei (AGNs) to be used to their fullest potential. We study the composition of the μJy radio population detected in the Karl G. Jansky Very Large Array COSMOS-XS survey based on a sample of 1540 sources detected at 3 GHz over an area of ∼350 arcmin2. This ultra-deep survey consists of a single pointing in the well-studied COSMOS field at both 3 and 10 GHz and reaches rms sensitivities of 0.53 and 0.41 μJy beam−1, respectively. We find multiwavelength counterparts for 97% of radio sources, based on a combination of near-UV/optical to sub-millimeter data, and through a stacking analysis at optical/near-IR wavelengths we further show that the sources lacking such counterparts are likely to be high-redshift in nature (typical z ∼ 4−5). Utilizing the multiwavelength data over COSMOS, we identify AGNs through a variety of diagnostics and find these to make up 23.2 ± 1.3% of our sample, with the remainder constituting uncontaminated star-forming galaxies. However, more than half of the AGNs exhibit radio emission consistent with originating from star formation, with only 8.8 ± 0.8% of radio sources showing a clear excess in radio luminosity. At flux densities of ∼30 μJy at 3 GHz, the fraction of star formation-powered sources reaches ∼90%, and this fraction is consistent with unity at even lower flux densities. Overall, our findings imply that ultra-deep radio surveys such as COSMOS-XS constitute a highly effective means of obtaining clean samples of star formation-powered radio sources.

The Accretion History of AGN: A Newly Defined Population of Cold Quasars

Abstract Quasars are the most luminous of active galactic nuclei, and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg2 of the Stripe 82 field, of which the 15.6 deg2 covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multiwavelength counterparts, and 30% of these are unobscured quasars, with L X > 1044 erg s−1 and M B < −23. We define a new population of quasars that are unobscured, have X-ray luminosities in excess of 1044 erg s−1, have broad emission lines, and yet are also bright in the far-infrared, with a 250 μm flux density of S 250 > 30 mJy. We refer to these Herschel-detected, unobscured quasars as “cold quasars.” A mere 4% (21) of the X-ray- and optically selected unobscured quasars in Stripe 82X are detected at 250 μm. These cold quasars lie at z ∼ 1–3, have L IR > 1012 L ⊙, and have star formation rates (SFRs) of ∼200–1400 M ⊙ yr−1. Cold quasars are bluer in the mid-IR than the full quasar population, and 72% of our cold quasars have WISE W3 < 11.5 [Vega], while only 19% of the full quasar sample meets this criteria. Crucially, cold quasars have on average ∼nine times as much star formation as the main sequence of star-forming galaxies at similar redshifts. Although dust-rich, unobscured quasars have occasionally been noted in the literature before, we argue that they should be considered as a separate class of quasars due to their high SFRs. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold quasars are type-1 blue quasars that reside in starburst galaxies.

NS 1987A in SN 1987A

Abstract The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact object’s predicted position. The infrared excess could be due to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spin down of a pulsar, or to thermal emission from an embedded, cooling neutron star (NS 1987A). It is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. Not only are there indications that the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 yr old neutron star. Furthermore, models of cooling neutron stars within the minimal cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1S0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations do not overlap, then pulsar spin down or accretion might be more likely, but the pulsar’s period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope.

Sub-galactic scaling relations between X-ray luminosity, star formation rate, and stellar mass

ABSTRACT X-ray luminosity (LX) originating from high-mass X-ray binaries (HMXBs) is tightly correlated with the host galaxy’s star formation rate (SFR). We explore this connection at sub-galactic scales spanning ∼7 dex in SFR and ∼8 dex in specific SFR (sSFR). There is good agreement with established relations down to SFR ≃ 10−3 M$_{\odot }\, \rm {yr^{-1}}$, below which an excess of X-ray luminosity emerges. This excess likely arises from low-mass X-ray binaries. The intrinsic scatter of the LX–SFR relation is constant, not correlated with SFR. Different star formation indicators scale with LX in different ways, and we attribute the differences to the effect of star formation history. The SFR derived from H α shows the tightest correlation with X-ray luminosity because H α emission probes stellar populations with ages similar to HMXB formation time-scales, but the H α-based SFR is reliable only for $\rm sSFR{\gt }10^{-12}$ M$_{\odot }\, \rm {yr^{-1}}$/M⊙.

The HSC-SSP Transient Survey: Implications from Early Photometry and Rise Time of Normal Type Ia Supernovae

Abstract With a booming number of Type Ia supernovae (SNe Ia) discovered within a few days of their explosions, a fraction of SNe Ia that show luminosity excess in the early phase (early-excess SNe Ia) have been confirmed. In this article, we report early-phase observations of seven photometrically normal SNe Ia (six early detections and one deep non detection limit) at the COSMOS field through a half-year transient survey as a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In particular, a blue light-curve excess was discovered for HSC17bmhk, a normal SN Ia with rise time longer than 18.8 days, during the first four days after the discovery. The blue early excess in optical wavelength can be explained not only by interactions with a nondegenerate companion or surrounding dense circumstellar matter but also radiation powered by radioactive decays of 56Ni at the surface of the SN ejecta. Given the growing evidence of the early-excess discoveries in normal SNe Ia that have longer rise times than the average, and a similarity in the nature of the blue excess to a luminous SN Ia subclass, we infer that early excess discovered in HSC17bmhk and other normal SNe Ia are most likely attributed to radioactive 56Ni decay at the surface of the SN ejecta. In order to successfully identify normal SNe Ia with early excess similar to that of HSC17bmhk, early UV photometries or high-cadence blue-band surveys are necessary.

Thai national telescope studies of ultraluminous X-ray sources

Ultraluminous X-ray sources (ULXs) are extra-galactic, non-nuclear sources with X-ray luminosity in excess of 1039 erg s–1. It has been thought that the majority of ULX populations are stellar-mass objects accreting matter at a super-Eddington rate. Although ULX studies are often focused in the X-ray regime, this work studied the ULXs in the optical regime, identified as the ULX counterparts (CTPs). The optical variability of nine CTPs were observed using the 2.4-m Thai National Telescope. Out of the nine ULXs, we detected three ULXs exhibiting strong variability up to ∼1 magnitude, suggesting that the CTP light does not come from the donor star’s emission. The paper discusses the physical origins of the variability which potentially explain the observed light curves.

Diffuse X-ray emission around an ultraluminous X-ray pulsar

Ultraluminous X-ray sources (ULXs) are extragalactic X-ray emitters located off-centre of their host galaxy and with a luminosity in excess of a few 1039 erg s−1, if emitted isotropically1,2. The discovery of periodic modulation revealed that in some ULXs the accreting compact object is a neutron star3–7, indicating luminosities substantially above their Eddington limit. The most extreme object in this respect is NGC 5907 ULX-1 (ULX1), with a peak luminosity that is 500 times its Eddington limit. During a Chandra observation to probe a low state of ULX1, we detected diffuse X-ray emission at the position of ULX1. Its diameter is 2.7 ± 1.0 arcsec and contains 25 photons, none below 0.8 keV. We interpret this extended structure as an expanding nebula powered by the wind of ULX1. Its diameter of about 200 pc, characteristic energy of ~1.9 keV and luminosity of ~2 × 1038 erg s−1 imply a mechanical power of 1.3 × 1041 erg s−1 and an age of ~7 × 104 yr. This interpretation suggests that a genuinely super-Eddington regime can be sustained for timescales much longer than the spin-up time of the neutron star powering the system. As the mechanical power from a single ULX nebula can rival the injection rate of cosmic rays of an entire galaxy8, ULX nebulae could be important cosmic ray accelerators9. Diffuse X-ray emission is detected around an ultraluminous X-ray source, interpreted as a wind-powered expanding nebula. Its energetics suggests that a super-Eddington regime can be longer than the spin-up time of the central neutron star.

Multiwavelength analysis of nearby ultraluminous x-ray sources (ULXs) and their environment

Ultraluminous X-ray sources (ULXs) are known as extragalactic point-like X-ray sources with luminosities considerably in excess of the maximum luminosity of a 10 solar mass accreting black hole. X-ray spectra of ULXs have been investigated in many previous studies. However, sparse observations render it more difficult to convincingly distinguish between two competing scenarios, i.e. sub-critical accreting intermediate-mass black hole and super-critical accreting stellar remnant black hole. Here, we report our investigation of a sample of nearby ULXs, as well as their host galaxies, in order to get a more complete understanding of their nature. Multiwavelength analysis was applied to study these ULXs. From X-ray study, we found that most ULXs in our sample do exhibit spectral variability in which higher energy X-ray predominates the spectra as the source becomes brighter. We also compiled some properties of the host galaxies, as a proxy of ULX environment. We found that ULXs in our sample can neither be exclusively associated with a certain type of morphology, nor with high nuclear activity. We also found that 12 out of 19 ULXs reside in host galaxies with star formation rate of less than 1 solar mass per year.

Layered semi-convection and tides in giant planet interiors

Context. Recent Juno observations have suggested that the heavy elements in Jupiter could be diluted throughout a large fraction of its gaseous envelope, providing a stabilising compositional gradient over an extended region of the planet. This could trigger layered semi-convection, which, in the context of giant planets more generally, may explain Saturn’s luminosity excess and play a role in causing the abnormally large radii of some hot Jupiters. In giant planet interiors, it could take the form of density staircases, which are convective layers separated by thin stably stratified interfaces. In addition, the efficiency of tidal dissipation is known to depend strongly on the planetary internal structure. Aims. We aim to study the resulting tidal dissipation when internal waves are excited in a region of layered semi-convection by tidal gravitational forcing due to other bodies (such as moons in giant planet systems, or stars in hot Jupiter systems). Methods. We adopt a local Cartesian model with a background layered density profile subjected to an imposed tidal forcing, and we compute the viscous and thermal dissipation rates numerically. We consider two sets of boundary conditions in the vertical direction: periodic boundaries and impenetrable, stress-free boundaries, with periodic conditions in the horizontal directions in each case. These models are appropriate for studying the forcing of short-wavelength tidal waves in part of a region of layered semi-convection, and in an extended envelope containing layered semi-convection, respectively. Results. We find that the rates of tidal dissipation can be enhanced in a region of layered semi-convection compared to a uniformly convective medium, where the latter corresponds with the usual assumption adopted in giant planet interior models. In particular, a region of layered semi-convection possesses a richer set of resonances, allowing enhanced dissipation for a wider range of tidal frequencies. The details of these results significantly depend on the structural properties of the layered semi-convective regions. Conclusions. Layered semi-convection could contribute towards explaining the high tidal dissipation rates observed in Jupiter and Saturn, which have not yet been fully explained by theory. Further work is required to explore the efficiency of this mechanism in global models.

Evidence for a Young Stellar Population in Nearby Type 1 Active Galaxies

Abstract To understand the physical origin of the close connection between supermassive black holes (BHs) and their host galaxies, it is vital to investigate star formation properties in active galaxies. Using a large data set of nearby type 1 active galactic nuclei (AGNs) with detailed structural decomposition based on high-resolution optical images obtained with the Hubble Space Telescope, we study the correlation between BH mass and bulge luminosity and the (Kormendy) relation between bulge effective radius and surface brightness. In both relations, the bulges of type 1 AGNs tend to be more luminous than those of inactive galaxies with the same BH mass or the same bulge size. This suggests that the central regions of AGN host galaxies have characteristically lower mass-to-light ratios than inactive galaxies, most likely due to the presence of a younger stellar population in active systems. In addition, the degree of luminosity excess appears to be proportional to the accretion rate of the AGN, revealing a physical connection between stellar growth and BH growth. Adopting a simple toy model for the increase of stellar mass and BH mass, we show that the fraction of young stellar population flattens out toward high accretion rates, possibly reflecting the influence of AGN-driven feedback.

Driving the Beat: Time-resolved Spectra of the White Dwarf Pulsar AR Scorpii

Abstract We obtained high temporal resolution spectroscopy of the unusual binary system AR Scorpii (AR Sco) covering nearly an orbit. The Hα emission shows a complex line structure similar to that seen in some polars during quiescence. Such emission is thought to be due to long-lived prominences originating on the red dwarf. A difference between AR Sco and these other systems is that the white dwarf (WD) in AR Sco is rapidly spinning relative to the orbital period. “Slingshot” prominences stable at 3 to 5 stellar radii require surface magnetic fields between 100 and 500 G. This is comparable to the estimated WD magnetic field strength near the surface of the secondary. Our time-resolved spectra also show emission fluxes, line equivalent widths, and continuum color varying over the orbit and the beat/spin periods of the system. During much of the orbit, the optical spectral variations are consistent with synchrotron emission with the highest energy electrons cooling between pulses. On the timescale of the beat/spin period we detect red- and blueshifted Hα emission flashes that reach velocities of 700 km s−1. Redshifted Balmer-emission flashes are correlated with the bright phases of the continuum beat pulses while blueshifted flashes appear to prefer the time of minimum in the beat light curve. We propose that much of the energy generated in AR Sco comes from fast magnetic reconnection events occurring near the inward face of the secondary and we show that the energy generated by magnetic reconnection can account for the observed excess luminosity from the system.

Protostellar Outflows at the EarliesT Stages (POETS)

Context. Weak and compact radio continuum and H2O masers are preferred tracers of the outflow activity nearby very young stars. Aims. We want to image the centimeter free–free continuum emission in the range 1–7 cm (26–4 GHz), which arises in the inner few 1000 au from those young stars also associated with bright H2O masers. We seek to study the radio continuum properties in combination with the H2O maser kinematics to quantify the outflow energetics powered by single young stars. Methods. We made use of the Karl G. Jansky Very Large Array (VLA) in the B configuration at K band and the A configuration at both Ku and C bands in order to image the radio continuum emission toward 25 H2O maser sites with an angular resolution and thermal rms on the order of 0.′′1 and 10 μJy beam−1, respectively. These targets add to our pilot study of 11 maser sites previously presented. The sample of H2O maser sites was selected among those regions that have accurate distance measurements, obtained through maser trigonometric parallaxes, and H2O maser luminosities in excess of 10−6 L⊙. Results. We present high-resolution radio continuum images of 33 sources belonging to 25 star-forming regions. In each region, we detect radio continuum emission within a few 1000 au of the H2O masers’ position; 50% of the radio continuum sources are associated with bolometric luminosities exceeding 5 × 103 L⊙, including W33A and G240.32 + 0.07. We provide a detailed spectral index analysis for each radio continuum source, based on the integrated fluxes at each frequency, and produce spectral index maps with the multifrequency synthesis deconvolution algorithm of CASA. The radio continuum emission traces thermal bremsstrahlung in (proto)stellar winds and jets that have flux densities at 22 GHz below 3 mJy and spectral index values between − 0.1 and 1.3. We prove a strong correlation (r > 0.8) between the radio continuum luminosity (Lrad) and the H2O maser luminosity (LH2O) of (L8 GHz∕mJy kpc2) = 103.8 × (LH2O L⊙)0.74. This power-law relation is similar to that between the radio continuum and bolometric luminosities, which confirms earlier studies. Since H2O masers are excited through shocks driven by (proto)stellar winds and jets, these results provide support to the idea that the radio continuum emission around young stars is dominated by shock ionization, and this holds over several orders of magnitude of stellar luminosites (1–105 L⊙).

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

Abstract The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from % for stars with previously detected cold dust to % for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

Stellar activity with LAMOST – II. Chromospheric activity in open clusters

We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity vary as a function of mass and rotation at different age. We measured excess equivalent widths of H$\alpha$, H$\beta$, and Ca~{\sc ii} K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities are obtained by normalizing bolometric luminosity, for more than 700 late-type stars in these open clusters. Results indicate two activity sequences in cool spot coverage and H$\alpha$ excess emission among GK dwarfs in Pleiades and M dwarfs in Praesepe and Hyades, paralleling with well known rotation sequences. A weak dependence of chromospheric emission on rotation exists among ultra fast rotators in saturated regime with Rossby number Ro$\lesssim0.1$. In the unsaturated regime, chromospheric and coronal emission show similar dependence on Ro, but with a shift toward larger Ro, indicating chromospheric emission gets easily saturated than coronal emission, and/or convective turnover time-scales based on X-ray data do not work well with chromospheric emission. More interestingly, our analysis show fully convective slow rotators obey the rotation-chromospheric activity relation similar to hotter stars, confirming the previous finding. We found correlations among H$\alpha$, H$\beta$, and Ca~{\sc ii} K emissions, in which H$\alpha$ losses are more important than Ca~{\sc ii} K for cooler and more active stars. In addition, a weak correlation is seen between chromospheric emission and photospheric activity that shows dependency on stellar spectral type and activity level, which provides some clues on how spot configuration vary as a function of mass and activity level.

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

XMM-Newton observations of the ultraluminous X-ray source NGC 1313 X-1

Ultraluminous X-ray sources (ULXs) are extra-galaxtic, non-nuclear sources with the X-ray luminosity in excess of the Eddington limit for a 10M⊙ black hole. Although some ULXs could be candidates for intermediate mass black holes accreting matter at sub-Eddington rate, it is thought that the majority population of ULXs are stellar mass black holes accreting matter at super-Eddington state. In this work, we examine the high quality X-ray spectra of the ULX NGC 1313 X-1 observed by XMM-Newton. The modeling results suggest that the data could be explained well using the super-Eddington model. Moreover, the X-ray spectral evolution of the ULX could be explained successfully in the context of accretion in the super-Eddington state.