Disk Of NGC Research Articles

XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Protoplanetary Disk

We present the first results of the eXtreme UV Environments (XUE) James Webb Space Telescope (JWST) program, which focuses on the characterization of planet-forming disks in massive star-forming regions. These regions are likely representative of the environment in which most planetary systems formed. Understanding the impact of environment on planet formation is critical in order to gain insights into the diversity of the observed exoplanet populations. XUE targets 15 disks in three areas of NGC 6357, which hosts numerous massive OB stars, including some of the most massive stars in our Galaxy. Thanks to JWST, we can, for the first time, study the effect of external irradiation on the inner (<10 au), terrestrial-planet-forming regions of protoplanetary disks. In this study, we report on the detection of abundant water, CO, 12CO2, HCN, and C2H2 in the inner few au of XUE 1, a highly irradiated disk in NGC 6357. In addition, small, partially crystalline silicate dust is present at the disk surface. The derived column densities, the oxygen-dominated gas-phase chemistry, and the presence of silicate dust are surprisingly similar to those found in inner disks located in nearby, relatively isolated low-mass star-forming regions. Our findings imply that the inner regions of highly irradiated disks can retain similar physical and chemical conditions to disks in low-mass star-forming regions, thus broadening the range of environments with similar conditions for inner disk rocky planet formation to the most extreme star-forming regions in our Galaxy.

Formation of a Massive Lenticular Galaxy Under the Tidal Interaction with a Group of Dwarf Galaxies

Based on the atomic-hydrogen (H i) observations using the Five-hundred-meter Aperture Spherical radio Telescope, we present a detailed study of the gas-rich massive S0 galaxy NGC 1023 in a nearby galaxy group. The presence of a H i extended warped disk in NGC 1023 indicates that this S0 galaxy originated from a spiral galaxy. The data also suggest that NGC 1023 is interacting with four dwarf galaxies. In particular, one of the largest dwarf galaxies has fallen into the gas disk of NGC 1023, forming a rare bright–dark galaxy pair with a large gas clump. This clump shows the signature of a galaxy but has no optical counterpart, implying that it is a newly formed starless galaxy. Our results first suggest that a massive S0 galaxy in a galaxy group can form via the morphological transformation from a spiral under the joint action of multiple tidal interactions.

The lively accretion disc in NGC 2992 – II. The 2019/2021 X-ray monitoring campaigns

ABSTRACT We report on the short- and long-term X-ray properties of the bright nearby Seyfert 2 galaxy NGC 2992, which was extensively observed with Swift, XMM–Newton, and NuSTAR. Swift targeted the source more than 100 times between 2019 and 2021 in the context of two monitoring campaigns. Both time-averaged and time-resolved analyses are performed, and we find that the short-to-long term spectral properties of NGC 2992 are dominated by a highly variable nuclear continuum. The source varied in the 2–10 keV energy band from 0.6 to 12 × 10−11 erg cm−2 s−1 during the two year long Swift monitoring. The fastest 2–10 keV flux change (by a factor of $\sim 60{{\ \rm per\ cent}}$) occurred on a time-scale of a few hours. The overall emission spectrum of the source is consistent with a power law-like continuum (Γ = 1.69 ± 0.01) absorbed by a constant line-of-sight column density NH = (7.8 ± 0.1) × 1021$\rm cm^{-2}$. The reflected emission is likely due to matter with an average column density NH = (9.6 ± 2.7) × 1022$\rm cm^{-2}$, thus NGC 2992 appears to have a globally Compton-thin circumnuclear medium. This scenario is fully supported by an independent analysis of the fractional variability and by XMM–Newton multiyear spectra.

AstroSat View of Spectral Transition in the Changing-look Active Galaxy NGC 1566 during the Declining Phase of the 2018 Outburst

Abstract NGC 1566 is a changing-look active galaxy that exhibited an outburst during 2017–2018 with a peak in 2018 June. We triggered AstroSat observations of NGC 1566 twice in 2018 August and October during its declining phase. Using the AstroSat observations, along with two XMM-Newton observations in 2015 (pre-outburst) and 2018 June (peak outburst), we found that the X-ray power law, the soft X-ray excess, and the disk components showed extreme variability during the outburst. Especially, the soft excess was negligible in 2015 before the outburst, increased to a maximum level by a factor of &gt;200 in 2018 June, and reduced dramatically by a factor of ∼7.4 in 2018 August and became undetectable in 2018 October. The Eddington fraction (L/L Edd) increased from ∼0.1% (2015) to ∼5% (2018 June) and then decreased to ∼1.5% (2018 August) and 0.3% (2018 October). Thus, NGC 1566 made a spectral transition from a high soft-excess state to a negligible soft-excess state at a few percent of the Eddington rate. The soft excess is consistent with warm Comptonization in the inner disk that appears to have developed during the outburst and disappeared toward the end of the outburst over a timescale comparable to the sound-crossing time. The multiwavelength spectral evolution of NGC 1566 during the outburst is most likely caused by the radiation pressure instability in the inner regions of the accretion disk in NGC 1566.

Deeply Buried Nuclei in the Infrared-luminous Galaxies NGC 4418 and Arp 220. II. Line Forests at λ = 1.4–0.4 mm and Circumnuclear Gas Observed with ALMA

Abstract We present the line observations in our Atacama Millimeter-Submillimeter Array imaging spectral scan toward three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in f rest = 215–697 GHz at about 0.″2 (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of ∼100 pc in size. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, most of the major lines and many 13C isotopologues show absorption against even brighter continuum cores of the nuclei. The lines with higher upper-level energies, including those from vibrationally excited molecules, tend to arise from smaller areas, indicating radially varying conditions in these nuclei. The outflows from the two Arp 220 nuclei cause blueshifted line absorption below the continuum level. The absorption mostly has small spatial offsets from the continuum peaks to indicate the outflow orientations. The bipolar outflow from the western nucleus is also imaged in multiple emission lines, showing the extent of ∼1″ (400 pc). Redshifted line absorption against the nucleus of NGC 4418 indicates either an inward gas motion or a small collimated outflow slanted to the nuclear disk. We also resolved some previous confusions due to line blending and misidentification.

Black Holes and the Supermassive Compact Object at the Galactic Center: Multi-arts of Thought and Nature

Black Holes and the Supermassive Compact Object at the Galactic Center: Multi-arts of Thought and Nature

The lively accretion disc in NGC 2992 – I. Transient iron K emission lines in the high-flux state

ABSTRACT We report on one of the brightest flux levels of the Seyfert 2 galaxy NGC 2992 ever observed in X-rays, on 2019 May. The source has been monitored every few days from 2019 March 26 to 2019 December 14 by Swift-X-Ray Telescope (XRT), and simultaneous XMM–Newton (250 ks) and NuSTAR (120 ks) observations were triggered on 2019 May 6. The high count rate of the source (its 2–10 keV flux ranged between 0.7 and 1.0 × 10−10 erg cm−2 s−1) allows us to perform a time-resolved spectroscopy, probing spatial scales of tens of gravitational radii from the central black hole. By constructing a map of the excess emission over the primary continuum, we find several emission structures in the 5.0–7.2 keV energy band. From fitting the 50 European Photon Imaging Camera (EPIC)-pn spectral slices of ∼5 ks duration, we interpret them as a constant narrow iron Kα line and three variable components in the iron K complex. When a self-consistent model accounting for the accretion disc emission is considered (KYNrline), two of these features (in the 5.0–5.8 and 6.8–7.2 keV bands) can be ascribed to a flaring region of the accretion disc located at rin ≃ 15–40rg from the black hole. The third one (6.5–6.8 keV) is likely produced at much larger radii (rin &amp;gt; 50rg). The inner radius and the azimuthal extension retrieved from the co-added spectra of the flaring states are rin = 15 ± 3rg and ϕ = 165°–330°, suggesting that the emitting region responsible for the broad iron K component is a relatively compact annular sector within the disc. Our findings support a physical scenario in which the accretion disc in NGC 2992 becomes more active at high accretion rates ($L_{\rm bol}/L_{\rm Edd}\ge 4$ per cent).

A comparison of star formation history between NGC 300 and M33

AbstractNGC 300 is a near-optical twin of the Local Group galaxy M33, which are benchmarks for understanding late-type spiral galaxies. They are two bulgeless and low-mass spiral galaxies in different environments. In order to explore the common properties and differences between the two nearby low-mass systems, we first use the simple chemical evolution model to explore the star formation history (SFH) of NGC300 and M33, and then compare the feasible model predicted SFH of NGC 300 with that of M33. Through comparing the SFHs between them, it can be found that the mean stellar age of NGC 300 is older than that of M33, there is a recent lack of primordial gas infall onto the disk of NGC 300, recent star formation along the disk of NGC 300 is less active than that of M33, and the local environment may play a key role in the secular evolution of a galaxy.

Short-term variabilities in X-ray/Optical/UV emission from Seyfert 1 galaxy NGC 4593

We present results obtained from a detailed multi-band analysis of the Seyfert 1 galaxy NGC 4593. Publicly available Swift monitoring observations in optical, ultraviolet and X-ray bands were used in the present work. A total of 185 pointings over a duration of about a month were used to understand the variabilities in emission in optical, ultraviolet, soft and hard X-ray bands. It was found that the source emission in the hard X-ray band (1.5-10 keV range) was highly variable compared to that at longer wavelengths. The variability amplitude decreased gradually from hard X-ray to optical bands. A cross-correlation analysis between light curves in different bands inferred that the observed variation in ultraviolet and optical bands is strongly correlated with the hard X-ray emission. Observed time lag for changes in emission in longer wavelength bands with respect to the hard X-ray emission suggests X-ray reprocessing as the cause of variation. Though the observed lag spectrum follows a 4/3rd power of wavelength, as predicted by the standard disk model, the estimated lags are found to be larger than the lags predicted from the standard disk model. This suggests that the actual disk in NGC 4593 is possibly larger than the standard thin disk. Though similar findings have been reported in NGC 5548 and Fairall 9, simultaneous near-infrared, ultraviolet, soft X-ray and hard X-ray band observations of a sample of AGNs with the 1.2 m telescope of Physical Research Laboratory at Mount Abu, India and first space-based multiwavelength observatory of India - AstroSat will provide significant information on the actual and model predicted sizes of the accretion disk.

Search for gas accretion imprints in voids – I. Sample selection and results for NGC 428

We present the first results of a project aimed at searching for gas accretion events and interactions between late-type galaxies in the void environment. The project is based on long-slit spectroscopic and scanning Fabry-Perot interferometer observations performed with the SCORPIO and SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as archival multiwavelength photometric data. In the first paper of the series we describe the project and present a sample of 18 void galaxies with oxygen abundances that fall below the reference `metallicity-luminosity' relation, or with possible signs of recent external accretion in their optical morphology. To demonstrate our approach, we considered the brightest sample galaxy NGC 428, a late-type barred spiral with several morphological peculiarities. We analysed the radial metallicity distribution, the ionized gas line-of-sight velocity and velocity dispersion maps together with WISE and SDSS images. Despite its very perturbed morphology, the velocity field of ionized gas in NGC 428 is well described by pure circular rotation in a thin flat disc with streaming motions in the central bar. We also found some local non-circular gas motions clearly related to stellar feedback processes. At the same time, we revealed a circumnuclear inclined disc in NGC 428 and a region with significant residual velocities that could be considered as a result of a recent (<0.5 Gyr) accretion event. The observed oxygen abundance gradient does not contradict this conclusion.

X-Ray Structure between the Innermost Disk and Optical Broad-line Region in NGC 4151

Abstract We present an analysis of the narrow Fe Kα line in Chandra/HETGS observations of the Seyfert active galactic nucleus (AGN) NGC 4151. The sensitivity and resolution afforded by the gratings reveal asymmetry in this line. Models including weak Doppler boosting, gravitational redshifts, and scattering are generally preferred over Gaussians at the 5σ level of confidence, and generally measure radii consistent with . Separate fits to “high/unobscured” and “low/obscured” phases reveal that the line originates at smaller radii in high-flux states; model-independent tests indicate that this effect is significant at the 4–5σ level. Some models and Δt ≃ 2 × 104 s variations in line flux suggest that the narrow Fe Kα line may originate at radii as small as in high-flux states. These results indicate that the narrow Fe Kα line in NGC 4151 is primarily excited in the innermost part of the optical broad line region (BLR), or X-ray BLR. Alternatively, a warp could provide the solid angle needed to enhance Fe Kα line emission from intermediate radii, and might resolve an apparent discrepancy in the inclination of the innermost and outer disk in NGC 4151. Both warps and the BLR may originate through radiation pressure, so these explanations may be linked. We discuss our results in detail, and consider the potential for future observations with Chandra, XARM, and ATHENA to measure black hole masses and to study the intermediate disk in AGNs using narrow Fe Kα emission lines.

Dark Memories of the Past: Discovery of Ultra-Diffuse Objects around NGC 1068

AbstractWe have searched for a sign of the past dynamical disturbance events on NGC 1068, an archetypical Type-2 Seyfert galaxy, using deep and wide optical imaging data by the Subaru telescope. The data taken by Hyper Suprime-Cam (HSC) as well as the archived data by Suprime-Cam reveal several faint outer structures of the galaxy, most of which were never reported before. We discover three large (re = 3 -5.5 kpc), extremely diffuse objects (UDOs) within 45 kpc from the center of NGC 1068. We suggest that two of these UDOs are actually a part of a large loop-like structure surrounding NGC 1068. Such an extremely faint loop or stream is the direct evidence for a past minor merger event. The third UDO has a distorted morphology, suggesting that it is under the influence of strong tidal field. Furthermore, we have identified another ultra-diffuse but compact (μ0,r &gt; 25 mag arcsec-2, re ~ 0.8kpc) dwarf galaxy within ~140 kpc from NGC 1068. We speculate that this ultra-diffuse dwarf could be the object related to the ancient tidal disruption event (tidal dwarf) during the early mass assembly period of NGC 1068. We also detect an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are also expected to arise in a late phase (up to several billion years ago) of a minor merger, according to numerical simulations. Our findings are consistent with the idea that the AGN activity in NGC 1068 is caused by a past minor merger.

A molecular line survey toward the nearby galaxies NGC 1068, NGC 253, and IC 342 at 3 mm with the Nobeyama 45 m radio telescope: Impact of an AGN on 1 kpc scale molecular abundances

AbstractIt is important to investigate the relationships between the power sources and the chemical compositions of galaxies in order to understand the scenario of galaxy evolution. We carried out an unbiased molecular line survey towards active galactic nucleus (AGN) host galaxy NGC1068, and prototypical starburst galaxies, NGC 253 and IC 342, with the Nobeyama 45 m telescope in the 3 mm band. The advantage of this line survey is that the obtained spectra have the highest angular resolution ever obtained with single-dish telescopes. In particular, the beam size of this telescope is ∼15″–19″, which is able to separate spatially the nuclear molecular emission from that of the starburst ring (d ∼ 30″) in NGC 1068. We successfully detected approximately 23 molecular species in each galaxy, and calculated rotation temperatures and column densities. We estimate the molecular fractional abundances with respect to 13CO and CS molecules and compare them among three galaxies in order to investigate the chemical signatures of an AGN environment. As a result, we found clear trends in the abundances of molecules surrounding the AGN on a 1-kpc scale. HCN, H13CN, CN, 13CN, and HC3N are more abundant, and CH3CCH is deficient in NGC 1068 compared with the starburst galaxies. High abundances of HCN, H13CN, and HC3N suggest that the circumnuclear disk in NGC 1068 is in a high-temperature environment. The reason for the non-detection of CH3CCH is likely to be dissociation by high-energy radiation or less sublimation of a precursor of CH3CCH from grains.

Mid-infrared dust in two nearby radio galaxies, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36)

Most radio galaxies are hosted by giant gas-poor ellipticals, but some contain significant amounts of dust, which is likely to be of external origin. In order to characterize the mid-IR properties of two of the most nearby and brightest merger-remnant radio galaxies of the Southern hemisphere, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36), we used observations with the Wide-field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12 and 22 micron and Spitzer mid-infrared spectra. By applying a resolution-enhancement technique, new WISE images were produced at angular resolutions ranging from 2.6" to 5.5". Global measurements were performed in the four WISE bands, and stellar masses and star-formation rates were estimated using published scaling relations. Two methods were used to uncover the distribution of dust, one relying on two-dimensional fits to the 3.4 micron images to model the starlight, and the other one using a simple scaling and subtraction of the 3.4 micron images to estimate the stellar continuum contribution to the emission in the 12 and 22 micron bands. The two galaxies differ markedly in their mid-IR properties. The 3.4 micron brightness distribution can be well represented by the superposition of two Sersic models in NGC 1316 and by a Sersic model and an exponential disk in NGC 612. The WISE colors of NGC 1316 are typical of those of early-type galaxies; those of NGC 612 are in the range found for star-forming galaxies. From the 22 micron luminosity, we infer a star-formation rate of about 0.7 solar masses per year in NGC 1316 and about 7 solar masses per year in NGC 612. Spitzer spectroscopy shows that the 7.7-to-11.3 micron PAH line ratio is significantly lower in NGC 1316 than in NGC 612. The WISE images reveal resolved emission from dust in the central 1'-2' of the galaxies. (Abridged)

Absorption from a multi‐layer circumnuclear medium and reflection from the accretion disc in NGC 1365

AbstractNGC 1365 hosts an X‐ray obscured AGN known for both its variable absorption and its relativistic features in the reflection component. Recent simultaneous observations performed by XMM‐Newton and NuSTAR caught the source in a rare, nearly unobscured state, revealing the presence of a warm absorber and a neutral, but low column density (∼ 1022 cm–2) absorber, usually not observable due to thicker layers along the line of sight. Here I propose a multi‐layer structure of the circumnuclear medium which can explain all the observed absorption states of this source, and their variability properties. Remarkably, despite the spectral complexity due to this multi‐component absorber, the relativistic reflection component (and hence the black hole spin) can be unambiguously measured through a time resolved spectroscopic analysis. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The young nuclear stellar disc in the SB0 galaxy NGC 1023

Small kinematically-decoupled stellar discs with scalelengths of a few tens of parsec are known to reside in the centre of galaxies. Different mechanisms have been proposed to explain how they form, including gas dissipation and merging of globular clusters. Using archival Hubble Space Telescope imaging and ground-based integral-field spectroscopy, we investigated the structure and stellar populations of the nuclear stellar disc hosted in the interacting SB0 galaxy NGC 1023. The stars of the nuclear disc are remarkably younger and more metal rich with respect to the host bulge. These findings support a scenario in which the nuclear disc is the end result of star formation in metal enriched gas piled up in the galaxy centre. The gas can be of either internal or external origin, i.e. from either the main disc of NGC 1023 or the nearby satellite galaxy NGC 1023A. The dissipationless formation of the nuclear disc from already formed stars, through the migration and accretion of star clusters into the galactic centre is rejected.

Stellar content and distances to the isolated spiral galaxies NGC 6503 and NGC 6946

Based on archival Hubble Space Telescope images, we have performed stellar photometry of several fields in the isolated spiral galaxies NGC 6503 and NGC 6946 with high peculiar velocities. Based on the TRGB method, we have determined the distances to the galaxies: D = 6.30 ± 0.10 Mpc for NGC 6503 and D = 6.72 ± 0.15 Mpc for NGC 6946. The current stellar content of the galaxies does not differ from that of other similar galaxies. The metallicity for young stars in NGC 6503 is Z = 0.02 (corresponding to the solar metallicity), while the metallicity for stars in NGC 6946 reaches Z = 0.05. Very few old globular clusters have been found in NGC 6946, while they have not been found at all in NGC 6503. The number density distribution of stars with different ages in NGC 6503 does not differ from the analogous distributions in other galaxies. The large sizes of the thick disk in NGC 6503, which is clearly seen up to 6 kpc from the galactic disk plane and whose possible extension is noticeable up to 8.6 kpc from the plane, are a difference. The sizes of the region occupied by red giants of the disk in NGC 6503 are 51 × 17 kpc, which are not much larger than the sizes of this galaxy from H I radio observations.

A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1

Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M⊙, surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures.

Kinematics and excitation of the molecular hydrogen accretion disc in NGC 1275

We report the results of high spatial and spectral resolution integral-field spectroscopy of the central ~3 x 3 arcsec^2 of the active galaxy NGC 1275 (Perseus A), based on observations with the Near-infrared Integral Field Spectrograph (NIFS) and the ALTAIR adaptive-optics system on the Gemini North telescope. The circum-nuclear disc in the inner R~50 pc of NGC 1275 is seen in both the H2 and [FeII] lines. The disc is interpreted as the outer part of a collisionally-excited turbulent accretion disc. The kinematic major axis of the disc at a position angle of 68 deg is oriented perpendicular to the radio jet. A streamer-like feature to the south-west of the disc, detected in H2 but not in [FeII], is discussed as one of possibly several molecular streamers, presumably falling into the nuclear region. Indications of an ionization structure within the disc are deduced from the HeI and Br gamma emission lines, which may partially originate from the inner portions of the accretion disc. The kinematics of these two lines agrees with the signature of the circum-nuclear disc, but both lines display a larger central velocity dispersion than the H2 line. The rovibrational H2 transitions from the core of NGC 1275 are indicative of thermal excitation caused by shocks and agree with excitation temperatures of ~1360 and ~4290 K for the lower- and higher-energy H2 transitions, respectively. The data suggest X-ray heating as the dominant excitation mechanism of [FeII] emission in the core, while fast shocks are a possible alternative. The [FeII] lines indicate an electron density of ~4000 cm^{-3}. The H2 disc is modelled using simulated NIFS data cubes of H2 emission from inclined discs in Keplerian rotation around a central mass. Assuming a disc inclination of 45 deg +/- 10 deg, the best-fitting models imply a central mass of (8^{+7}_{-2}) x 10^8 Msun. (abridged)

Kinematics and stellar disk modeling of lenticular galaxies

We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ≥ 106 points. The models include three components: a “live” bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA.