Browsing by Author "Congiu, E."

Filter results by typing the first few letters
Now showing 1 - 16 of 16
  • Absorbed relativistic jets in radio-quiet narrow-line Seyfert 1 galaxies
    (2020-04-17) Berton, Marco; Järvelä, Emilia; Crepaldi, L.; Lähteenmäki, Anne; Tornikoski, Merja; Congiu, E.; Kharb, P.; Terreran, G.; Vietri, A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Narrow-line Seyfert 1 (NLS1) galaxies are peculiar active galactic nuclei. Most of them do not show strong radio emission, but seven radio-quiet (or radio-silent) NLS1s have recently been detected flaring multiple times at 37 GHz by the Metsahovi Radio Telescope, indicating relativistic jets in these peculiar sources. We observed them with the Karl G. Jansky Very Large Array (JVLA) in A configuration at 1.6, 5.2, and 9.0 GHz. Our results show that these sources are either extremely faint or not detected in the JVLA bands. At these frequencies, the radio emission from their relativistic jet must be absorbed, either through synchrotron self-absorption as it occurs in gigahertz-peaked sources, or more likely, through free-free absorption by a screen of ionized gas associated with starburst activity or shocks. Our findings cast new shadows on the radio-loudness criterion, which seems to be increasingly frequently a misleading parameter. New high-frequency and high-resolution radio observations are essential to test our hypotheses.
  • A catalog of narrow-line Seyfert 1 galaxies in the southern hemisphere
    (2018-01-01) Chen, S.; Berton, M.; la Mura, G.; Congiu, E.; Cracco, V.; Foschini, L.; Fan, J. H.; Ciroi, S.; Rafanelli, P.; Bastieri, D.
     A4 Artikkeli konferenssijulkaisussa
    We present a new accurate sample of narrow-line Seyfert 1 galaxies (NLS1s) in the southern hemisphere from the Six-degree Field Galaxy Survey (6dFGS). Based on the optical spectral features, 167 sources were classified as NLS1s. We derived flux-calibrated spectra in the sample for the first time. Strong luminosity correlations between the continuum and the emission lines were found. We estimated their central black hole masses and Eddington ratios, which are lying in a typical range of NLS1s. In the sample, 23 NLS1s were detected at radio frequencies and 12 of them are radio-loud. We publish the X-ray data analysis of a campaign of observations carried out by the Swift X-ray Telescope.
  • The flat-spectrum radio quasar 3C 345 from the high to the low emission state
    (2018-06-01) Berton, M.; Liao, N. H.; La Mura, G.; Järvelä, E.; Congiu, E.; Foschini, L.; Frezzato, M.; Ramakrishnan, V.; Fan, X. L.; Lähteenmäki, A.; Pursimo, T.; Abate, V.; Bai, J. M.; Calcidese, P.; Ciroi, S.; Chen, Liang; Cracco, V.; Li, S. K.; Tornikoski, M.; Rafanelli, P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report simultaneous observations at different energy bands in radio, optical, UV, X-rays and γ rays of the flat-spectrum radio-quasar 3C 345. We built the light curve of the source at different frequencies from 2008, the beginning of the Fermi all-sky survey, to 2016, using new data and public archives. In particular we obtained several optical spectra, to study the behavior of emission lines and the continuum in different activity states and to derive the black hole mass. 3C 345 showed two flaring episodes in 2009, which occurred simultaneously in γ ray, optical/UV and X-rays, and were later followed in radio. The source shows an inverse Compton dominated spectral energy distribution, which moved from higher to lower frequencies from the high to the low state. The reverberation of emission lines during one outburst event allowed us to constrain the location of production of γ rays very close to the broad-line region, and possibly in the jet-base. We report the observation of an increased accretion after the outburst, possibly induced by the decrease of magnetic field intensity with respect to the low state.
  • A host galaxy study of southern narrow-line Seyfert 1 galaxies
    (2023-11-01) Varglund, I.; Järvelä, E.; Ciroi, S.; Berton, M.; Congiu, E.; Lähteenmäki, A.; Di Mille, F.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We studied seven nearby narrow-line Seyfert 1 (NLS1) galaxies in J and Ks bands with redshifts varying from 0.019 to 0.092. This is the first multi-source study targeting the hosts of southern NLS1 galaxies. Our data were obtained with the FourStar instrument of the 6.5 m Magellan Baade telescope at the Las Campanas Observatory (Chile). The aim of our study is to determine the host galaxy morphologies of these sources by using GALFIT. We were able to model six out of the seven sources reliably. Our conclusion is that all of the reliably modelled sources are disk-like galaxies, either spirals or lenticulars. None of these sources present an elliptical morphology. Our findings are in agreement with the hypothesis that disk-like galaxies are the main host of jetted NLS1 galaxies. Taking advantage of observations in two bands, we also produced a J-Ks colour map of each source. Five of the six colour maps show significant dust extinction near the core of the galaxy-a feature often seen in gamma-ray-detected jetted NLS1 galaxies, and interpreted to be a consequence of a past minor merger.
  • Hunting for the nature of the enigmatic narrow-line Seyfert 1 galaxy PKS 2004-447
    (2021-10-21) Berton, M.; Peluso, G.; Marziani, P.; Komossa, S.; Foschini, L.; Ciroi, S.; Chen, S.; Congiu, E.; Gallo, L. C.; Björklund, I.; Crepaldi, L.; Di Mille, F.; Järvelä, E.; Kotilainen, J.; Kreikenbohm, A.; Morrell, N.; Romano, P.; Sani, E.; Terreran, G.; Tornikoski, M.; Vercellone, S.; Vietri, A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that, in some cases, can harbor powerful relativistic jets. One of them, PKS 2004-447, shows gamma-ray emission, and underwent its first recorded multifrequency flare in 2019. However, past studies revealed that in radio this source can be classified as a compact steep-spectrum source (CSS), suggesting that, unlike other gamma-ray sources, the relativistic jets of PKS 2004-447 have a large inclination with respect to the line of sight. We present here a set of spectroscopic observations of this object, aimed at carefully measuring its black hole mass and Eddington ratio, determining the properties of its emission lines, and characterizing its long term variability. We find that the black hole mass is (1.5 +/- 0.2)x10(7) M-circle dot, and the Eddington ratio is 0.08. Both values are within the typical range of NLS1s. The spectra also suggest that the 2019 flare was caused mainly by the relativistic jet, while the accretion disk played a minor role during the event. In conclusion, we confirm that PKS 2004-447 is one of the rare examples of gamma-ray emitting CSS/NLS1s hybrid, and that these two classes of objects are likely connected in the framework of AGN evolution.
  • The Interacting Late-type Host Galaxy of the Radio-loud Narrow-line Seyfert 1 IRAS 20181-2244
    (2019-02-01) Berton, M.; Congiu, E.; Ciroi, S.; Komossa, S.; Frezzato, M.; Mille, F. Di; Antón, S.; Antonucci, R.; Caccianiga, A.; Coppi, P.; Jarvela, E.; Kotilainen, J.; Lahteenmaki, A.; Mathur, S.; Chen, S.; Cracco, V.; Mura, G. La; Rafanelli, P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Narrow-line Seyfert 1 galaxies (NLS1s) are a class of active galactic nuclei that are known to be one of the few sources of γ-rays, which originate in a relativistic beamed jet. Because of their relatively large distance, a poorly investigated aspect of these jetted NLS1s is their environment, and in particular, their host galaxy. In this work, we present the results of a morphological analysis of the host galaxy of the jetted NLS1 IRAS 20181-2244 observed with the 6.5 m Baade Telescope of the Las Campanas Observatory. The GALFIT analysis run on the Ks image, along with additional spectroscopic observations performed with the Nordic Optical Telescope, clearly revealed the presence of an interacting system of two galaxies. The data suggest that this NLS1 is hosted by a late-type galaxy, although the result is not conclusive. This analysis, along with other results in the literature, might suggest that two populations of jetted NLS1 exist. Further morphological studies are needed to confirm or disprove this hypothesis.
  • Jetted narrow-line Seyfert 1 galaxies breaking the jet paradigm: A comprehensive study of host-galaxy morphologies
    (2022-12-08) Varglund, I.; Järvelä, E.; Lähteenmäki, A.; Berton, M.; Ciroi, S.; Congiu, E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Narrow-line Seyfert 1 (NLS1) galaxies are unevolved active galactic nuclei (AGNs) that exist predominantly in spiral galaxies. However, mostly due to the small number of sources studied, it has been under debate whether also the hosts of jetted NLS1 galaxies, a particular subclass of these sources hosting a relativistic jet, are disk-like or elliptical, as the hosts of more powerful jetted AGNs. We studied the host morphologies of 14 NLS1 galaxies, 11 of which have been detected at 37 GHz, indicating that these sources harbour relativistic jets. The J- and Ks-band data used in this study were obtained with the Nordic Optical Telescope (NOT). We performed the photometric decomposition of the host galaxy using the band that gave a better fit and additionally created colour maps of all sources that had both a J- and a Ks-band observation. We were able to successfully model 12 sources, nine of which most likely have disk-like morphologies. Of the remaining sources, one source could possibly be hosted either in a disk-like or a dwarf galaxy, and in two cases the results are inconclusive. Only one of our sources shows clear signs of interaction, but the colour maps of most of our sources hint at ample dust in the nuclei, possibly indicating earlier minor mergers, which can go unnoticed due to the limited resolution of these observations. Our results further support disk-like galaxies as the predominant host type of jetted NLS1 galaxies. Most importantly, with the number of modelled hosts of jetted NLS1s now exceeding 50, with only a few elliptical hosts, it seems to be safe to conclude that also disk-like galaxies are able to launch and maintain relativistic jets, and that the traditional jet paradigm stating that only massive elliptical galaxies are capable of hosting relativistic jets is severely outdated.
  • Kiloparsec-scale emission in the narrow-line Seyfert 1 galaxy Mrk 783
    (2017-07-01) Congiu, E.; Berton, M.; Giroletti, M.; Antonucci, R.R.J.; Caccianiga, A.; Kharb, P.; Lister, M. L.; Foschini, L.; Ciroi, S.; Cracco, V.; Frezzato, M.; Järvelä, E.; La Mura, G.; Richards, J. L.; Rafanelli, P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present the first results of a radio survey of 79 narrow-line Seyfert 1 (NLS1) carried out with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A configuration aimed at studying the radio properties of these sources. We report the detection of extended emission in one object: Mrk 783. This is intriguing, since the radio-loudness parameter R of this object is close to the threshold between radio-quiet and radio-loud active galactic nuclei (AGN). The galaxy is one of the few NLS1 showing such an extended emission at z < 0.1. The radio emission is divided into a compact core component and an extended component, observed on both sides of the nucleus and extending from 14 kpc southeast to 12 kpc northwest. There is no sign of a collimated jet and the shape of the extended component is similar to those of some Seyfert galaxies. The properties of the emission are compatible with a relic produced by the intermittent activity cycle of the AGN.
  • Line shapes in narrow-line Seyfert 1 galaxies: A tracer of physical properties?
    (2020-01-01) Berton, Marco; Björklund, Irene; Lähteenmäki, Anne; Congiu, E.; Järvelä, Emilia; Terreran, G.; La Mura, G.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Line profiles can provide fundamental information on the physics of active galactic nuclei (AGN). In the case of narrow-line Seyfert 1 galaxies (NLS1s) this is of particular importance since past studies revealed how their permitted line profiles are well reproduced by a Lorentzian function instead of a Gaussian. This has been explained with different properties of the broadline region (BLR), which may present a more pronounced turbulent motions in NLS1s with respect to other AGN. We investigated the line profiles in a recent large NLS1 sample classified using SDSS, and we divided the sources into two subsamples according to their line shapes, Gaussian or Lorentzian. The line profiles clearly separate all the properties of NLS1s. Black hole mass, Eddington ratio, [O III], and Fe II strength are all very different in the Lorentzian and Gaussian samples. We interpret this in terms of evolution within the class of NLS1s. The Lorentzian sources may be the youngest objects, while Gaussian profiles may be typically associated to more evolved objects. Further detailed spectroscopic studies are needed to fully confirm our hypothesis.
  • The link between X-ray complexity and optical lines in NLS1s
    (2018-01-01) Vietri, A.; Berton, M.; Ciroi, S.; Congiu, E.; la Mura, G.; Cracco, V.; Frezzato, M.; Chen, S.; Cattapan, A.; Peruzzi, T.; Rafanelli, P.
     A4 Artikkeli konferenssijulkaisussa
    Narrow-line Seyfert 1 galaxies (NLS1s) are a subclass of active galactic nuclei (AGN). It is often believed that these AGN have small black hole mass, which is responsible for the narrowness of the permitted lines. They are also characterised by a high accretion rate, typically closer to the Eddington limit. Nevertheless, narrow permitted lines might also be caused by a disk-like broad-line region (BLR) viewed pole-on. This class of objects presents strong X-ray emission, which is characterised by a very steep spectral index described by a single power law. In particular, some of them exhibit particular features around the iron K-shell energy at 6-8 keV. Recently, this different spectral behaviour was attributed to inclination. In this work we are going to analyse optical spectra to measure in different ways the width of Hβ, which is another potential inclination indicator. Our aim is to search for a correlation between the high-energy spectral complexity and FWHM of Hβ, in order to verify whether or not the broad-line region could be flattened.
  • Luminous red novae : Stellar mergers or giant eruptions?
    (2019-09-24) Pastorello, A.; Mason, E.; Taubenberger, S.; Fraser, M.; Cortini, G.; Tomasella, L.; Botticella, M. T.; Elias-Rosa, N.; Kotak, R.; Smartt, S. J.; Benetti, S.; Cappellaro, E.; Turatto, M.; Tartaglia, L.; Djorgovski, S. G.; Drake, A. J.; Berton, M.; Briganti, F.; Brimacombe, J.; Bufano, F.; Cai, Y-Z; Chen, S.; Christensen, E. J.; Ciabattari, F.; Congiu, E.; Dimai, A.; Inserra, C.; Kankare, E.; Magill, L.; Maguire, K.; Martinelli, F.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Reguitti, A.; Sollerman, J.; Spiro, S.; Terreran, G.; Wright, D. E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490-2011OT1, M 101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H alpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (similar to 6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H alpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.
  • Models of optical emission lines to investigate narrow-line Seyfert 1 galaxies in spectroscopic databases
    (2018-01-01) la Mura, G.; Bastieri, D.; Berton, M.; Chen, S.; Ciroi, S.; Congiu, E.; Cracco, V.; Fan, J. H.; Rafanelli, P.
     A4 Artikkeli konferenssijulkaisussa
    Thanks to the execution of extensive spectroscopic surveys that have covered large fractions of the sky down to magnitudes as faint as i ≈ 19, it has been possible to identify several narrow-line Seyfert 1 galaxies (NLS1s) and to investigate their properties over a large range of the electromagnetic spectrum. The interpretation of their nature, however, is still hampered by the statistical uncertainties related to the way in which NLS1 candidates are selected. In this contribution, we present a study to detect and to model emission lines in optical spectra extracted from the Sloan Digital Sky Survey (SDSS), adopting the most proper strategy to identify the source of line excitation and to produce a detailed model with measurements of several emission line parameters. We demonstrate the application of this technique to explore fundamental questions, such as the presence of gas and dust around the core of AGNs and the spectral energy distribution of their ionizing radiation. We compare the spectral properties of NLS1s with those of other type 1 active galaxies and we summarize the potential of this approach to identify NLS1s in present day and future spectroscopic surveys. We finally consider the implications of multi-frequency data analysis in the debate concerning the intrinsic nature of NLS1s.
  • The radio structure of the narrow-line Seyfert 1 Mrk 783 with VLBA and e-MERLIN
    (2020-12-01) Congiu, E.; Kharb, P.; Tarchi, A.; Berton, M.; Caccianiga, A.; Chen, S.; Crepaldi, L.; Di Mille, F.; Järvelä, E.; Jarvis, M. E.; la Mura, G.; Vietri, A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this paper, we present the analysis of new radio and optical observations of the narrow-line Seyfert 1 galaxy Mrk 783. 1.6 GHz observations performed with the e-MERLIN interferometer confirm the presence of the diffuse emission previously observed. The Very Long Baseline Array (VLBA) also detects the nuclear source both at 1.6 GHz (L band) and 5 GHz (C band). While the L-band image shows only an unresolved core, the C-band image shows the presence of a partially resolved structure at a position angle of 60◦. The brightness temperature of the emission in both bands (>106 K) suggests that it is a pc-scale jet produced by the active galactic nucleus. The relatively steep VLBA spectral index (αVLBA = 0.63 ± 0.03) is consistent with the presence of optically thin emission on milliarcsecond scales. Finally, we investigated two possible scenarios that can result in the misalignment between the kpc and pc-scale radio structure detected in the galaxy. We also analysed the optical morphology of the galaxy, which suggests that Mrk 783 underwent a merging in relatively recent times.
  • Radio-emitting narrow-line Seyfert 1 galaxies in the JVLA perspective
    (2018-06-01) Berton, M.; Congiu, E.; Järvelä, E.; Antonucci, R.; Kharb, P.; Lister, M. L.; Tarchi, A.; Caccianiga, A.; Chen, S.; Foschini, L.; Lähteenmäki, A.; Richards, J. L.; Ciroi, S.; Cracco, V.; Frezzato, M.; La Mura, G.; Rafanelli, P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report the first results of a survey on 74 narrow-line Seyfert 1 galaxies (NLS1s) carried out in 2015 with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A-configuration. So far, this is the largest survey aimed to image the radio continuum of NLS1s. We produced radio maps in order to compare the general properties of three different samples of objects: radio-quiet NLS1s (RQNLS1s), steep-spectrum radio-loud NLS1s (S-NLS1s), and flat-spectrum radio-loud NLS1s (F-NLS1s). We find that the three classes correspond to different radio morphologies, with F-NLS1s being more compact, and RQNLS1s often showing diffuse emission on kpc scales. We also find that F-NLS1s might be low-luminosity and possibly young blazars, and that S-NLS1s are part of the parent population of F-NLS1s. Dedicated studies to RQNLS1s are needed to fully understand their role in the unification pictures.
  • SDSS J211852.96-073227.5: The first non-local, interacting, late-type intermediate Seyfert galaxy with relativistic jets
    (2020-04-01) Jarvela, Emilia; Berton, Marco; Ciroi, S.; Congiu, E.; Lähteenmäki, Anne; Di Mille, F.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    It has been often suggested that a tangible relation exists between relativistic jets in active galactic nuclei (AGN) and the morphology of their host galaxies. In particular, relativistic jets may commonly be related to merging events. Here we present for the first time a detailed spectroscopic and morphological analysis of a Seyfert galaxy, SDSS J211852.96-073227.5, at z=0.26. This source has previously been classified as a gamma-ray emitting narrow-line Seyfert 1 galaxy. We re-observed it with the 6.5 m Clay Telescope and these new, high-quality spectroscopic data have revealed that it is actually an intermediate-type Seyfert galaxy. Furthermore, the results of modelling the Ks-band near-infrared images obtained with the 6.5 m Baade Telescope indicate that the AGN is hosted by a late-type galaxy in an interacting system, strengthening the suggested connection between galaxy interactions and relativistic jets.
  • SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries
    (2019-11-01) Andrews, Jennifer E.; Sand, D. J.; Valenti, S.; Smith, Nathan; Dastidar, Raya; Sahu, D. K.; Misra, Kuntal; Singh, Avinash; Hiramatsu, D.; Brown, P. J.; Hosseinzadeh, G.; Wyatt, S.; Vinko, J.; Anupama, G. C.; Arcavi, I.; Ashall, Chris; Benetti, S.; Berton, Marco; Bostroem, K. A.; Bulla, M.; Burke, J.; Chen, S.; Chomiuk, L.; Cikota, A.; Congiu, E.; Cseh, B.; Davis, Scott; Elias-Rosa, N.; Faran, T.; Fraser, Morgan; Galbany, L.; Gall, C.; Gal-Yam, A.; Gangopadhyay, Anjasha; Gromadzki, M.; Haislip, J.; Howell, D. A.; Hsiao, E. Y.; Inserra, C.; Kankare, E.; Kuncarayakti, H.; Kouprianov, V.; Kumar, Brajesh; Li, Xue; Lin, Han; Maguire, K.; Mazzali, P.; McCully, C.; Milne, P.; Mo, Jun; Morrell, N.; Nicholl, M.; Ochner, P.; Olivares, F.; Pastorello, A.; Patat, F.; Phillips, M.; Pignata, G.; Prentice, S.; Reguitti, A.; Reichart, D. E.; Rodríguez; Rui, Liming; Sanwal, Pankaj; Sárneczky, K.; Shahbandeh, M.; Singh, Mridweeka; Smartt, S.; Strader, J.; Stritzinger, M. D.; Szakáts, R.; Tartaglia, L.; Wang, Huijuan; Wang, Lingzhi; Wang, Xiaofeng; Wheeler, J. C.; Xiang, Danfeng; Yaron, O.; Young, D. R.; Zhang, Junbo
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN 2017gmr from hours after discovery through the first 180 days. SN 2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼500 R o progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130 ± 0.026 M o of 56Ni are present, if the light curve is solely powered by radioactive decay, although the 56Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of Hα and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.