- ID:
- ivo://CDS.VizieR/J/AJ/146/78
- Title:
- Long-term Swift monitoring of WPVS 007
- Short Name:
- J/AJ/146/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on multi-wavelength observations of the X-ray transient Narrow Line Seyfert 1 (NLS1) galaxy WPVS007. The galaxy was monitored with Swift between 2005 October and 2013 July, after it had previously undergone a dramatic drop in its X-ray flux. For the first time, we are able to repeatedly detect this NLS1 in X-rays again. This increased number of detections in the last couple of years may suggest that the strong absorber that has been found in this active galactic nucleus (AGN) is starting to become leaky and may eventually disappear. The X-ray spectra obtained for WPVS007 are all consistent with a partial covering absorber model. A spectrum based on the data during the extreme low X-ray flux states shows that the absorption column density is of the order of 4x10^23^/cm2 with a covering fraction of 95%. WPVS007 also displays one of the strongest UV variabilities seen in NLS1s. The UV continuum variability anti-correlates with the optical/UV slope {alpha}_UV_, which suggests that the variability may be primarily due to reddening. The UV variability timescales are consistent with moving dust "clouds" located beyond the dust sublimation radius of R_sub_{approx}20lt-days. We present for the first time near-infrared JHK data of WPVS007, which reveal a rich emission-line spectrum. Recent optical spectroscopy does not indicate significant variability in the broad permitted and FeII emission lines, implying that the ionizing continuum seen by those gas clouds has not significantly changed over the last decades. All X-ray and UV observations are consistent with a scenario in which an evolving broad absorption line (BAL) flow obscures the continuum emission. As such, WPVS007 is an important target for our understanding of BAL flows in low-mass AGNs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/563/A57
- Title:
- Long-term variability of AGN at hard X-rays
- Short Name:
- J/A+A/563/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variability at all observed wavelengths is a distinctive property of active galactic nuclei (AGN). Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by absorption along the line of sight. Characterizing the intrinsic hard X-ray variability of a large AGN sample and comparing it to the results obtained at lower X-ray energies can significantly contribute to our understanding of the mechanisms underlying the high-energy radiation. Swift/BAT provides us with the unique opportunity to follow, on time scales of days to years and with regular sampling, the 14-195keV emission of the largest AGN sample available up to date for this kind of investigation. As a continuation of an early work using the first 9 months of BAT data, we study the amplitude of the variations and their dependence on subclass and on energy, for a sample of 110 radio quiet and radio loud AGN selected from the BAT 58-month survey.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A23
- Title:
- LoTSS compact groups of galaxies
- Short Name:
- J/A+A/622/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the LOFAR Two-metre Sky Survey (LoTSS) Data Release I to identify the groups of galaxies (and individual galaxies) from the Hickson compact groups (HCG) and magnitude-limited compact groups (MLCG) samples that emit at the frequency of 150MHz, characterise their radio emission (extended or limited to the galaxies), and compare new results to earlier observations and theoretical predictions. The detection of 73 systems (and 7 more - probably) out of 120, of which as many as 17 show the presence of extended radio structures, confirms the previous hypothesis of the common character of the magnetic field inside galaxy groups and its detectability. In order to investigate the future potential of low-frequency radio studies of galaxy groups, we also present a more detailed insight into four radio-emitting systems, for which the strength of the magnetic field inside their intergalactic medium (IGM) is calculated. The estimated values are comparable to that found inside star-forming galaxies, suggesting a dynamical and evolutionary importance of the magnetic field in galaxy groups.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A4
- Title:
- LoTSS Deep Fields DR1 photometric redshifts
- Short Name:
- J/A+A/648/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168MHz survey split across multiple tiers over the northern sky. The first LoTSS Deep Fields data release consists of deep radio continuum imaging at 150 MHz of the Bootes, European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1), and Lockman Hole fields, down to rms sensitivities of ~32, 20, and 22 muJy/beam, respectively. In this paper we present consistent photometric redshift (photo-z) estimates for the optical source catalogues in all three fields - totalling over 7 million sources (~5 million after limiting to regions with the best photometric coverage). Our photo-z estimation uses a hybrid methodology that combines template fitting and machine learning and is optimised to produce the best possible performance for the radio continuum selected sources and the wider optical source population. Comparing our results with spectroscopic redshift samples, we find a robust scatter ranging from 1.6 to 2% for galaxies and 6.4 to 7% for identified optical, infrared, or X-ray selected active galactic nuclei (AGN). Our estimated outlier fractions (|z_phot-z_spec|/(1+z_spec)>0.15) for the corresponding subsets range from 1.5 to 1.8% and 18 to 22%, respectively. Replicating trends seen in analyses of previous wide-area radio surveys, we find no strong trend in photo-$z$ quality as a function of radio luminosity for a fixed redshift. We exploit the broad wavelength coverage available within each field to produce galaxy stellar mass estimates for all optical sources at z<1.5. Stellar mass functions derived for each field are used to validate our mass estimates, with the resulting estimates in good agreement between each field and with published results from the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A5
- Title:
- LoTSS giant radio galaxies. I.
- Short Name:
- J/A+A/635/A5
- Date:
- 02 Mar 2022 11:49:28
- Publisher:
- CDS
- Description:
- Giant radio galaxies (GRGs) are a subclass of radio galaxies, which have grown to megaparsec scales. GRGs are much rarer than normal-sized radio galaxies (<0.7Mpc) and the reason for their gigantic sizes is still debated. Here, we report on the biggest sample of GRGs identified to date. These objects were found in the LOFAR Two-metre Sky Survey (LoTSS) first data release images, which cover a 424 deg^2^ region. Of the 239 GRGs found, 225 are new discoveries. The GRGs in our sample have sizes ranging from 0.7Mpc to 3.5Mpc and have redshifts (z) between 0.1 and 2.3. Seven GRGs have sizes above 2Mpc and one has a size of ~3.5Mpc. The sample contains 40 GRGs hosted by spectroscopically confirmed quasars. Here, we present the search techniques employed and the resulting catalogue of the newly discovered large sample of GRGs along with their radio properties. In this paper, we also show for the first time that the spectral index of GRGs is similar to that of normal-sized radio galaxies, indicating that most of the GRG population is not dead or is not similar to a remnant-type radio galaxy. We find that 20 out of 239 GRGs in our sample are located at the centres of clusters and we present our analysis on their cluster environment and radio morphology.
- ID:
- ivo://CDS.VizieR/J/A+A/568/A74
- Title:
- Low-frequency (115-175MHz) image of M51
- Short Name:
- J/A+A/568/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarization. This observation covered the frequencies between 115MHz and 175MHz. We produced an image of total emission of M51 at the mean frequency of 151MHz with 20-arcsec resolution and 0.3mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300MHz so far. The integrated spectrum of total radio emission is well described by a power law, while flat spectral indices in the central region indicates thermal absorption. We observe the disk to extend out to 16kpc and a break in the radial profile near the optical radius of the disk. The radial scale lengths in the inner and outer disks are larger at 151MHz, and the break is smoother at 151MHz than those observed at 1.4GHz. The arm--interarm contrast is lower at 151MHz than at 1400MHz, indicating propagation of cosmic ray electrons (CRE) from spiral arms into interarm regions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/5049
- Title:
- Low-frequency study of 3C 31 with LOFAR
- Short Name:
- J/MNRAS/474/5049
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep, low-frequency radio continuum study of the nearby Fanaroff-Riley class I (FR I) radio galaxy 3C 31 using a combination of LOw Frequency ARray (LOFAR; 30-85 and 115-178MHz), Very Large Array (VLA; 290-420MHz), Westerbork Synthesis Radio Telescope (WSRT; 609MHz) and Giant Metre Radio Telescope (GMRT; 615MHz) observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/2570
- Title:
- Low ionization emission-line regions galaxies
- Short Name:
- J/MNRAS/466/2570
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using spatially resolved spectroscopy from SDSS-IV MaNGA we have demonstrated that low ionization emission-line regions (LIERs) in local galaxies result from photoionization by hot evolved stars, not active galactic nuclei, hence tracing galactic region hosting old stellar population where, despite the presence of ionized gas, star formation is no longer occurring. LIERs are ubiquitous in both quiescent galaxies and in the central regions of galaxies where star formation takes place at larger radii. We refer to these two classes of galaxies as extended LIER (eLIER) and central LIER (cLIER) galaxies, respectively. cLIERs are late-type galaxies primarily spread across the green valley, in the transition region between the star formation main sequence and quiescent galaxies. These galaxies display regular disc rotation in both stars and gas, although featuring a higher central stellar velocity dispersion than star-forming galaxies of the same mass. cLIERs are consistent with being slowly quenched inside-out; the transformation is associated with massive bulges, pointing towards the importance of bulge growth via secular evolution. eLIERs are morphologically early types and are indistinguishable from passive galaxies devoid of line emission in terms of their stellar populations, morphology and central stellar velocity dispersion. Ionized gas in eLIERs shows both disturbed and disc-like kinematics. When a large-scale flow/rotation is observed in the gas, it is often misaligned relative to the stellar component. These features indicate that eLIERs are passive galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Importantly, quiescent galaxies devoid of line emission reside in denser environments and have significantly higher satellite fraction than eLIERs. Environmental effects thus represent the likely cause for the existence of line-less galaxies on the red sequence.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A140
- Title:
- Low-luminosity type-1 QSO sample
- Short Name:
- J/A+A/561/A140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recognizing the properties of the host galaxies of quasi-stellar objects (QSOs) is essential to understand the suspected coevolution of central supermassive black holes (BHs) and their host galaxies. We selected a subsample of the Hamburg/ESO survey for bright UV-excess QSOs, containing only the 99 nearest QSOs with redshift z<=0.06, that are close enough to allow detailed structural analysis. From this "low-luminosity type-1 QSO sample", we observed 20 galaxies and performed aperture photometry and bulge-disk-bar-AGN-decomposition with BUDDA on near-infrared J, H, K band images. From the photometric decomposition of these 20 objects and visual inspection of images of another 26, we find that ~50% of the hosts are disk galaxies and most of them (86%) are barred. Stellar masses, calculated from parametric models based on inactive galaxy colors, range from 2x10^9^M_{sun}_ to 2x10^11^M_{sun}_. Black hole masses measured from single epoch spectroscopy range from 1x10^6^M_{sun}_ to 5x10^8^M_{sun}_. In comparison to higher luminosity QSO samples, LLQSOs tend to have lower stellar and BH masses. Also, in the effective radius vs. mean surface-brightness projection of the fundamental plane, they lie in the transition area between luminous QSOs and "normal" galaxies. This can be seen as further evidence that they can be pictured as a "bridge" between the local Seyfert population and luminous QSOs at higher redshift. Eleven low-luminosity QSOs for which we have reliable morphological decompositions and BH mass estimations lie below the published BH mass vs. bulge luminosity relations for inactive galaxies. This could be partially explained by bulges of active galaxies containing much younger stellar populations than bulges of inactive galaxies. Also, one could suspect that their BHs are undermassive. This might hint at the growth of the host spheroid to precede that of the BH.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A138
- Title:
- Low-luminosity type-1 QSO sample. V.
- Short Name:
- J/A+A/587/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared (NIR) H+K-band long-slit spectra of eleven galaxies that were obtained with SOFI at the NTT (ESO). The galaxies are chosen from the low-luminosity type-1 quasi-stellar object (LLQSO) sample, which comprises the 99 closest (z<=0.06) QSOs from the Hamburg/ESO survey for bright UV-excess QSOs. These objects are ideal targets to study the gap between local Seyfert galaxies and high-redshift quasars because they show much stronger AGN activity than local objects, but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [FeII] lines after carefully subtracting the continuum emission. From the broad Pa{alpha} components, we estimated black hole masses and enlarged the sample of LLQSOs that deviate from the MBH-Lbulge relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust (T~1200K) as well as stellar contribution. However, the respective fractions vary strongly among the objects. More than half of the objects show H_2_ emission lines, which indicate a large reservoir of molecular gas that is needed to feed the AGN and star formation. In the NIR diagnostic diagram all objects lie in the location of AGN-dominated objects. However, most of the objects show indications of star formation activity, suggesting that their offset location with respect to MBH-Lbulge relations of inactive galaxies may be a consequence of overluminous bulges.
