- ID:
- ivo://CDS.VizieR/J/ApJ/510/659
- Title:
- Size and Structure of AGN in NGC 5548
- Short Name:
- J/ApJ/510/659
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of 3 yr of ground-based observations of the Seyfert 1 galaxy NGC 5548, which, combined with previously reported data, yield optical continuum and broad-line H{beta} light curves for a total of 8 yr. The light curves consist of over 800 points, with a typical spacing of a few days between observations. During this 8 yr period, the nuclear continuum has varied by more than a factor of 7, and the H{beta} emission line has varied by a factor of nearly 6. The H{beta} emission line responds to continuum variations with a time delay or lag of {=~}10--20 days, the precise value varying somewhat from year to year. We find some indications that the lag varies with continuum flux in the sense that the lag is larger when the source is brighter.
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- ID:
- ivo://CDS.VizieR/J/ApJ/766/37
- Title:
- Sizes of MRC radio galaxies and QSOs
- Short Name:
- J/ApJ/766/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the currently popular orientation-based unified scheme, a radio galaxy appears as a quasar when its principal radio-axis happens to be oriented within a certain cone opening angle around the observer's line of sight. Due to geometrical projection, the observed sizes of quasars should therefore appear smaller than those of radio galaxies. We show that this simple, unambiguous prediction of the unified scheme is not borne out by the actually observed angular sizes of radio galaxies and quasars. Except in the original 3CR sample, based on which the unified scheme was proposed, in other much larger samples no statistically significant difference is apparent in the size distributions of radio galaxies and quasars. The population of low-excitation radio galaxies with apparently no hidden quasars inside, which might explain the observed excess number of radio galaxies at low redshifts, cannot account for the absence of any foreshortening of the sizes of quasars at large redshifts. On the other hand, from infrared and X-ray studies, there is evidence of a hidden quasar within a dusty torus in many radio galaxies, at z>0.5. It is difficult to reconcile this with the absence of foreshortening of quasar sizes at even these redshifts, and perhaps one has to allow that the major radio axis may not have anything to do with the optical axis of the torus. Otherwise, to resolve the dichotomy of radio galaxies and quasars, a scheme quite different from the present might be required.
- ID:
- ivo://CDS.VizieR/J/ApJS/217/12
- Title:
- S7 observations with WiFeS of active galaxies
- Short Name:
- J/ApJS/217/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we describe the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7) and present results on 64 galaxies drawn from the first data release. The S7 uses the Wide Field Spectrograph (WiFeS) mounted on the ANU 2.3m telescope located at the Siding Spring Observatory to deliver an integral field of 38x25 arcsec at a spectral resolution of R=7000 in the red (530-710nm), and R=3000 in the blue (340-560nm). From these data cubes we have extracted the narrow-line region spectra from a 4 arcsec aperture centered on the nucleus. We also determine the H{beta} and [OIII]{lambda}5007 fluxes in the narrow lines, the nuclear reddening, the reddening-corrected relative intensities of the observed emission lines, and the H{beta} and [OIII]{lambda}5007 luminosities determined from spectra for which the stellar continuum has been removed. We present a set of images of the galaxies in [OIII]{lambda}5007, [NII]{lambda}6584, and H{alpha}, which serve to delineate the spatial extent of the extended narrow-line region and also to reveal the structure and morphology of the surrounding HII regions. Finally, we provide a preliminary discussion of those Seyfert 1 and Seyfert 2 galaxies that display coronal emission lines in order to explore the origin of these lines.
- ID:
- ivo://CDS.VizieR/J/AJ/127/156
- Title:
- Soft X-Ray-Selected AGNs complete sample
- Short Name:
- J/AJ/127/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the optical spectra and simple statistical analysis for a complete sample of 110 soft X-ray-selected AGNs. About half of the sources are narrow-line Seyfert 1 galaxies (NLS1's), which have the steepest X-ray spectra, the strongest Fe II emission, and slightly weaker [O III] {lambda}5007 emission than broad-line Seyfert 1's (BLS1's). Kolmogorov-Smirnov tests show that NLS1's and BLS1's have clearly different distributions of the X-ray spectral slope {alpha}_X_, X-ray short-term variability, and Fe II equivalent widths and luminosity and Fe II/H{beta} ratios.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/129
- Title:
- Space telescope RM project. II. Swift data
- Short Name:
- J/ApJ/806/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended active galactic nucleus (AGN) UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. Approximately daily Hubble Space Telescope UV sampling was also obtained. The UV/optical light curves show strong correlations (r_max_=0.57-0.90) and the clearest measurement to date of interband lags. These lags are well-fit by a {tau}{propto}{lambda}^4/3^ wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of ~0.35+/-0.05lt-day at 1367{AA}, assuming a simple face-on model. The U band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker (r_max_<0.45) and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/128
- Title:
- Space telescope RM project. I. NGC5548
- Short Name:
- J/ApJ/806/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the first results from a six-month long reverberation-mapping experiment in the ultraviolet based on 171 observations of the Seyfert 1 galaxy NGC 5548 with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Significant correlated variability is found in the continuum and broad emission lines, with amplitudes ranging from ~30% to a factor of two in the emission lines and a factor of three in the continuum. The variations of all the strong emission lines lag behind those of the continuum, with HeII{lambda}1640 lagging behind the continuum by ~2.5 days and Ly{alpha}{lambda}1215, CIV{lambda}1550, and SiIV{lambda}1400 lagging by ~5-6 days. The relationship between the continuum and emission lines is complex. In particular, during the second half of the campaign, all emission-line lags increased by a factor of 1.3-2 and differences appear in the detailed structure of the continuum and emission-line light curves. Velocity-resolved cross-correlation analysis shows coherent structure in lag versus line of sight velocity for the emission lines; the high-velocity wings of CIV respond to continuum variations more rapidly than the line core, probably indicating higher velocity broad-line region clouds at smaller distances from the central engine. The velocity-dependent response of Ly{alpha}, however, is more complex and will require further analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/837/131
- Title:
- Space telescope RM project. V. NGC5548 sp. monitoring
- Short Name:
- J/ApJ/837/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an optical spectroscopic monitoring program targeting NGC 5548 as part of a larger multiwavelength reverberation mapping campaign. The campaign spanned 6 months and achieved an almost daily cadence with observations from five ground-based telescopes. The H{beta} and HeII{lambda}4686 broad emission-line light curves lag that of the 5100{AA} optical continuum by 4.17_-0.36_^+0.36^days and 0.79_-0.34_^+0.35^days, respectively. The H{beta} lag relative to the 1158{AA} ultraviolet continuum light curve measured by the Hubble Space Telescope is ~50% longer than that measured against the optical continuum, and the lag difference is consistent with the observed lag between the optical and ultraviolet continua. This suggests that the characteristic radius of the broad-line region is ~50% larger than the value inferred from optical data alone. We also measured velocity-resolved emission-line lags for H{beta} and found a complex velocity-lag structure with shorter lags in the line wings, indicative of a broad-line region dominated by Keplerian motion. The responses of both the H{beta} and He II emission lines to the driving continuum changed significantly halfway through the campaign, a phenomenon also observed for CIV, Ly{alpha}, HeII(+OIII]), and SiIV(+OIV]) during the same monitoring period. Finally, given the optical luminosity of NGC5548 during our campaign, the measured H{beta} lag is a factor of five shorter than the expected value implied by the R_BLR_-L_AGN_ relation based on the past behavior of NGC 5548.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/993
- Title:
- Spatial extent of (U)LIRGs in the MIR. I.
- Short Name:
- J/ApJ/723/993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5-15um low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE_{lambda}_, defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE_{lambda}_ varies from one galaxy to another, but we can identify three general types of FEE_{lambda}_: one where FEE_{lambda}_ is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7um. The mean size of the LIRG cores at 13.2um is 2.6kpc. However, once the IR luminosity of the systems reaches the threshold of L_IR_~10^11.8^L_{sun}_, slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE_13.2um_<~0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5kpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/32
- Title:
- Spatial extent of (U)LIRGs in the MIR. II.
- Short Name:
- J/ApJ/741/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the second part of our analysis of the extended mid-infrared (MIR) emission of the GOALS sample based on 5-14um low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for all galaxies in the sample, FEE_{lambda}_, defined as the fraction of the emission that originates outside of the unresolved central component of a source, and spatially separate the MIR spectrum of a galaxy into its nuclear and extended components. We find that the [NeII]12.81um emission line is as compact as the hot dust MIR continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more extended. In addition, the 6.2 and 7.7um PAH emission is more compact than that of the 11.3um PAH, which is consistent with the formers being enhanced in a more ionized medium. The presence of an active galactic nucleus (AGN) or a powerful nuclear starburst increases the compactness and the luminosity surface density of the hot dust MIR continuum, but has a negligible effect on the spatial extent of the PAH emission on kpc-scales. Furthermore, it appears that both processes, AGN and/or nuclear starburst, are indistinguishable in terms of how they modify the integrated PAH-to-continuum ratio of the FEE in (ultra)luminous infrared galaxies ((U)LIRGs). Globally, the 5-14um spectra of the extended emission component are homogeneous for all galaxies in the GOALS sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/5179
- Title:
- Spatially offset AGN cand. in CLASS survey
- Short Name:
- J/MNRAS/475/5179
- Date:
- 02 Nov 2021 11:24:39
- Publisher:
- CDS
- Description:
- Prompted by a recent claim by Barrows et al. that X-ray active galactic nuclei (AGNs) are often found significantly offset from the centres of their host galaxies, we have looked for examples of compact radio sources that are offset from the optical centroids of nearby (z<0.2) galaxies. We have selected a sample of 345 galaxies from the Sloan Digital Sky Survey (SDSS) galaxy catalogue, which have nearby compact radio sources listed in the Cosmic-Lens All Sky Survey (CLASS) catalogue. We find only three matches ~0.87 per cent of the sample) with offsets greater than 600 milliarcsec (mas), which is considerably fewer than we would have expected from the Barrows et al. X-ray survey. We fit our histogram of offsets with a Rayleigh distribution with {sigma}=60.5mas, but find that there is an excess of objects with separations greater than ~150mas. Assuming that this excess represents AGNs with real offsets, we place an upper limit of ~17 per cent on the fraction of offset AGNs in our radio-selected sample. We select 38 objects with offsets greater than 150mas, and find they have some diverse properties: Some are well known, such as Mrk 273 and Arp 220, some have dust lanes, which may have affected the optical astrometry, and a few are strong new candidates for offset AGNs.
