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Register a new userIdentification of blazar candidates behind Small and Large Magellanic Clouds
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We report the identification of blazar candidates behind the Magellanic Clouds. The objects were selected from the Magellanic Quasars Survey (MQS), which targeted the entire Large Magellanic Cloud (LMC) and 70% of the Small Magellanic Cloud (SMC). Among the 758 MQS quasars and 898 of unidentified (featureless spectra) objects, we identified a sample of 44 blazar candidates, including 27 flat spectrum radio quasars and 17 BL Lacertae objects, respectively. All the blazar candidates from our sample were identified with respect to their radio, optical, and mid-infrared properties. The newly selected blazar candidates possess the long-term, multi-colour photometric data from the Optical Gravitational Lensing Experiment, multi-colour mid-infrared observations, and archival radio data for one frequency at least. In addition, for nine of them the radio polarization data are available. With such data, these objects can be used to study the physics behind the blazar variability detected in the optical and mid-infrared bands, as a tool to investigate magnetic field geometry of the LMC and SMC, and as an exemplary sample of point like sources most likely detectable in $gamma$-ray range with the newly emerging Cherenkov Telescope Array.
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We present an optical variability study of 44 newly identified blazar candidates behind the Magellanic Clouds, including 27 flat spectrum radio quasars (FSRQs) and 17 BL Lacertae objects (BL Lacs). All objects in the sample possess high photometric accuracy and irregularly sampled optical light curves (LCs) in I filter from the long-term monitoring conducted by the Optical Gravitational Lensing Experiment. We investigated the variability properties to look for blazar-like characteristics and to analyze the long-term behaviour. We analyzed the LCs with the Lomb-Scargle periodogram to construct power spectral densities (PSDs), found breaks for several objects, and linked them with accretion disk properties. In this way we constrained the black hole (BH) masses of 18 FSRQs to lie within the range $8.18leqlog (M_{rm BH}/M_odot)leq 10.84$, assuming a wide range of possible BH spins. By estimating the bolometric luminosities, we applied the fundamental plane of active galactic nuclei variability as an independent estimate, resulting in $8.4leqlog (M_{rm BH}/M_odot)leq 9.6$, with a mean error of 0.3. Many of the objects have very steep PSDs, with high frequency spectral index in the range $3-7$. An alternative attempt to classify the LCs was made using the Hurst exponent, $H$, and the $mathcal{A}-mathcal{T}$ plane. Two FSRQs and four BL Lacs yielded $H>0.5$, indicating presence of long-term memory in the underlying process governing the variability. Additionally, two FSRQs with exceptional PSDs, stand out also in the $mathcal{A}-mathcal{T}$ plane.
We present results of a variability study in the optical band of 44 newly identified blazar candidates behind the Magellanic Clouds. Our sample contains 27 flat spectrum radio quasars (FSRQs) and 17 BL Lacertae objects (BL Lacs). However, only nine of them are considered as secure blazar candidates, while the classification of the remaining 35 objects is still uncertain. All studied blazar candidates possess infrequently sampled optical light curves (LCs) in I filter provided by the Optical Gravitational Lensing Experiment group. The LCs were analysed with the Lomb-Scargle periodogram, the Hurst exponent $H$, and the $mathcal{A}-mathcal{T}$ plane, to look for blazar-like characteristic features and to study the long-term behaviour of the optical fluxes. The power law (PL) indices of the Lomb-Scargle power spectral density (PSD) of the FSRQ blazar candidates mostly lie in the range (1,2). In case of the BL Lacs they are located in the range (1,1.8). The PL PSD is indicative of a self-affine stochastic process characterised by $H$, underlying the observed variability. We find that the majority of analysed objects have $Hleq 0.5$, indicating short-term memory, whereas four BL Lacs and two FSRQs have $H>0.5$, implying long-term memory. 41 blazar candidates are located in the $mathcal{A}-mathcal{T}$ plane in the region available to PL plus Poisson noise processes. Interestingly, one FSRQ is located marginally below this region, while two FSRQs lie above the line $mathcal{T}=2/3$, i.e. they are even more noisy than white noise. The BL Lac candidates are characterised by higher $mathcal{A}$ values than FSRQs, i.e. $0.71pm 0.06$ and $0.29pm 0.05$, respectively.
The nearby Magellanic Clouds system covers more than 200 square degrees on the sky. Much of it has been mapped across the electromagnetic spectrum at high angular resolution and sensitivity X-ray (XMM-Newton), UV (UVIT), optical (SMASH), IR (VISTA, WISE, Spitzer, Herschel), radio (ATCA, ASKAP, MeerKAT). This provides us with an excellent dataset to explore the galaxy populations behind the stellar-rich Magellanic Clouds. We seek to identify and characterise AGN via machine learning algorithms on this exquisite data set. Our project focuses not on establishing sequences and distributions of common types of galaxies and active galactic nuclei (AGN), but seeks to identify extreme examples, building on the recent accidental discoveries of unique AGN behind the Magellanic Clouds.
We present a comprehensive multi-frequency catalogue of radio sources behind the Large Magellanic Cloud between 0.2 and 20 GHz, gathered from a combination of new and legacy radio continuum surveys. This catalogue covers an area of $sim$144~deg$^2$ at angular resolutions from 45 arcsec to $sim$3 arcmin. We find 6434 discrete radio sources in total, of which 3789 are detected at two or more radio frequencies. We estimate the median spectral index ($alpha$; where $S_{v}sim u^alpha$) of $alpha = -0.89 $ and mean of $-0.88 pm 0.48$ for 3636 sources detected exclusively at two frequencies (0.843 and 1.384 GHz) with similar resolution (FWHM $sim$40-45 arcsec). The large frequency range of the surveys makes it an effective tool to investigate Gigahertz Peak Spectrum (GPS), Compact Steep Spectrum (CSS) and Infrared Faint Radio sources populations within our sample. We find 10 GPS candidates with peak frequencies near 5 GHz, from which we estimate their linear size. 1866 sources from our catalogue are (CSS) candidates with $alpha <-0.8$. We found six candidates for High Frequency Peaker (HFP) sources, whose radio fluxes peak above 5 GHz and no sources with unconstrained peaks and $alpha~>0.5$. We found optical counterparts for 343 of the radio continuum sources, of which 128have a redshift measurement. Finally, we investigate the population of 123 Infrared Faint Radio Sources (IFRSs) found in this study.
We used the red clump stars from the Optical Gravitational Lensing Experiment (OGLE II) survey and the the Magellanic Cloud Photometric Survey (MCPS), to estimate the line of sight depth. The observed dispersion in the magnitude and colour distribution of red clump stars is used to estimate the line of sight depth, after correcting for the contribution due to other effects. This dispersion due to depth, has a range from minimum dispersion that can be estimated, to 0.46 mag (a depth of 500 pc to 10.44 Kpc), in the LMC. In the case of SMC, the dispersion ranges from minimum dispersion to 0.35 magnitude (a depth of 665 pc to 9.53 Kpc). The thickness profile of LMC bar indicates that it is flared. The average depth in the bar region is 4.0$pm$1.4 kpc. The halo of the LMC (using RR Lyrea stars) is found to have larger depth compared to the disk/bar, which supports the presence of inner halo for the LMC. The large depth estimated for the LMC bar and the disk suggests that the LMC might have had minor mergers. In the case of SMC, the bar depth (4.90$pm$1.23 Kpc) and the disk depth (4.23$pm$1.48 Kpc) are found to be within the standard deviations. We find evidence for increase in depth near the optical center (up to 9 kpc). On the other hand, the estimated depth for the halo (RR Lyrea stars) and disk (RC stars) for the bar region of the SMC is found to be similar. Thus, increased depth and enhanced stellar as well as HI density near the optical center suggests that the SMC may have a bulge.
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