scholarly journals Changing look active galactic nuclei in the MaNGA survey

2020 ◽  
Vol 497 (1) ◽  
pp. 192-203
Author(s):  
Wei Jeat Hon ◽  
Rachel Webster ◽  
Christian Wolf
Keyword(s):  
Active Galactic Nuclei ◽  
Selection Criteria ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Short Time ◽  
Cross Matching ◽  
The Continuum

ABSTRACT Changing look active galactic nuclei (CLAGNs) are rare cases of AGNs, where the continuum flux increases/decreases and the broad emission lines appear/disappear within short time-scales. These extreme changes challenge our understanding of accretion disc dynamics. We present a sample of four new CLAGNs at 0.026 < z < 0.107, which were found by cross-matching the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey with AGNs from the SDSS spectroscopic data base. Our results show that the selection criteria of $\gt \mathopen |0.5\mathclose |$ mag change in SDSS-g band is ineffective at lower redshifts. This is, in part, due to the fact that the g band is probing a different part of the AGNs spectral energy distribution at these redshifts. The bigger issue is that the galaxy continuum dominates the spectrum and thus overwhelms any variation of the AGNs continuum that might contribute to photometric variations. This suggests the need to use different methods for future low-redshift CLAGNs searches.

scholarly journals To TDE or not to TDE: the luminous transient ASASSN-18jd with TDE-like and AGN-like qualities

2020 ◽  
Vol 494 (2) ◽  
pp. 2538-2560 ◽  
Author(s):  
J M M Neustadt ◽  
T W-S Holoien ◽  
C S Kochanek ◽  
K Auchettl ◽  
J S Brown ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
Tidal Disruption ◽  
Optical Telescope ◽  
X Ray ◽  
Radiated Energy ◽  
The Galaxy ◽  
Order Of Magnitude

ABSTRACT We present the discovery of ASASSN-18jd (AT 2018bcb), a luminous optical/ultraviolet(UV)/X-ray transient located in the nucleus of the galaxy 2MASX J22434289–1659083 at z = 0.1192. Over the year after discovery, Swift UltraViolet and Optical Telescope (UVOT) photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with temperature $T \sim 2.5 \times 10^{4} \, {\rm K}$, a maximum observed luminosity of $L_{\rm max} = 4.5^{+0.6}_{-0.3}\times 10^{44} \, {\rm erg \,s}^{-1}$, and a radiated energy of $E = 9.6^{+1.1}_{-0.6} \times 10^{51} \, {\rm erg}$. X-ray data from Swift X-Ray Telescope (XRT) and XMM–Newton show a transient, variable X-ray flux with blackbody and power-law components that fade by nearly an order of magnitude over the following year. Optical spectra show strong, roughly constant broad Balmer emission and transient features attributable to He ii, N iii–v, O iii, and coronal Fe. While ASASSN-18jd shares similarities with tidal disruption events (TDEs), it is also similar to the newly discovered nuclear transients seen in quiescent galaxies and faint active galactic nuclei (AGNs).

scholarly journals The XXL Survey

2020 ◽  
Vol 638 ◽  
pp. A45
Author(s):  
V. A. Masoura ◽  
I. Georgantopoulos ◽  
G. Mountrichas ◽  
C. Vignali ◽  
E. Koulouridis ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Selection Criteria ◽  
Galactic Nuclei ◽  
Host Galaxy ◽  
Spectral Energy ◽  
Energy Distributions ◽  
X Ray ◽  
Spectral Fitting ◽  
The Galaxy ◽  
X Ray Absorption

The combination of optical and mid-infrared (MIR) photometry has been extensively used to select red active galactic nuclei (AGNs). Our aim is to explore the obscuration properties of these red AGNs with both X-ray spectroscopy and spectral energy distributions (SEDs). In this study, we re-visit the relation between optical/MIR extinction and X-ray absorption. We use IR selection criteria, specifically the W1 and W2 WISE bands, to identify 4798 AGNs in the XMM-XXL area (∼25 deg2). Application of optical/MIR colours (r−W2 >  6) reveals 561 red AGNs (14%). Of these, 47 have available X-ray spectra with at least 50 net (background-subtracted) counts per detector. For these sources, we construct SEDs from the optical to the MIR using the CIGALE code. The SED fitting shows that 44 of these latter 47 sources present clear signs of obscuration based on the AGN emission and the estimated inclination angle. Fitting the SED also reveals ten systems (∼20%) which are dominated by the galaxy. In these cases, the red colours are attributed to the host galaxy rather than AGN absorption. Excluding these ten systems from our sample and applying X-ray spectral fitting analysis shows that up to 76% (28/37) of the IR red AGNs present signs of X-ray absorption. Thus, there are nine sources (∼20% of the sample) that although optically red, are not substantially X-ray absorbed. Approximately 50% of these sources present broad emission lines in their optical spectra. We suggest that the reason for this apparent discrepancy is that the r−W2 criterion is sensitive to smaller amounts of obscuration relative to the X-ray spectroscopy. In conclusion, it appears that the majority of red AGNs present considerable obscuration levels as shown by their SEDs. Their X-ray absorption is moderate with a mean of NH ∼ 1022 cm−2.

scholarly journals Near- to mid-infrared spectroscopy of the heavily obscured AGN LEDA 1712304 with AKARI/IRC

2019 ◽  
Vol 626 ◽  
pp. A130
Author(s):  
T. Tsuchikawa ◽  
H. Kaneda ◽  
S. Oyabu ◽  
T. Kokusho ◽  
K. Morihana ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Properties ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Spectral Energy ◽  
Absorption Feature ◽  
Distribution Fitting ◽  
Submillimeter Range ◽  
Spectral Fitting ◽  
Best Fit

Context. Although heavily obscured active galactic nuclei (AGNs) have been found by many observational studies, the properties of the surrounding dust are poorly understood. Using AKARI/IRC spectroscopy, we discovered a new heavily obscured AGN in LEDA 1712304 which shows a deep spectral absorption feature due to silicate dust. Aims. We study the infrared (IR) spectral properties of circumnuclear silicate dust in LEDA 1712304. Methods. We performed IR spectral fitting, considering silicate dust properties such as composition, porosity, size, and crystallinity. Spectral energy distribution fitting was also performed on the flux densities in the UV to submillimeter range to investigate the global spectral properties. Results. The best-fit model indicates 0.1 μm-sized porous amorphous olivine (Mg2xFe2−2xSiO4; x = 0.4) with 4% crystalline pyroxene. The optical depth is τsil ∼ 2.3, while the total IR luminosity and stellar mass are estimated to be LIR = (5 ± 1)×1010 L⊙ and Mstar = (2.7 ± 0.8)×109 M⊙, respectively. In such low LIR and Mstar ranges, there are few galaxies that show such a large τsil. Conclusion. The silicate dust in the AGN torus of LEDA 1712304 has properties that are notably similar to those in other AGNs overall, but slightly different in the wing shape of the absorption profile. The porosity of the silicate dust suggests dust coagulation or processing in the circumnuclear environments, while the crystallinity suggests that the silicate dust is relatively fresh.

scholarly journals Photometric redshifts for X-ray-selected active galactic nuclei in the eROSITA era

2019 ◽  
Vol 489 (1) ◽  
pp. 663-680 ◽  
Author(s):  
M Brescia ◽  
M Salvato ◽  
S Cavuoti ◽  
T T Ananna ◽  
G Riccio ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Large Fraction ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Training Sample ◽  
Spectral Energy ◽  
Ancillary Data ◽  
Photometric Redshifts ◽  
X Ray

ABSTRACT With the launch of eROSITA (extended Roentgen Survey with an Imaging Telescope Array), successfully occurred on 2019 July 13, we are facing the challenge of computing reliable photometric redshifts for 3 million of active galactic nuclei (AGNs) over the entire sky, having available only patchy and inhomogeneous ancillary data. While we have a good understanding of the photo-z quality obtainable for AGN using spectral energy distribution (SED)-fitting technique, we tested the capability of machine learning (ML), usually reliable in computing photo-z for QSO in wide and shallow areas with rich spectroscopic samples. Using MLPQNA as example of ML, we computed photo-z for the X-ray-selected sources in Stripe 82X, using the publicly available photometric and spectroscopic catalogues. Stripe 82X is at least as deep as eROSITA will be and wide enough to include also rare and bright AGNs. In addition, the availability of ancillary data mimics what can be available in the whole sky. We found that when optical, and near- and mid-infrared data are available, ML and SED fitting perform comparably well in terms of overall accuracy, realistic redshift probability density functions, and fraction of outliers, although they are not the same for the two methods. The results could further improve if the photometry available is accurate and including morphological information. Assuming that we can gather sufficient spectroscopy to build a representative training sample, with the current photometry coverage we can obtain reliable photo-z for a large fraction of sources in the Southern hemisphere well before the spectroscopic follow-up, thus timely enabling the eROSITA science return. The photo-z catalogue is released here.

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