- ID:
- ivo://CDS.VizieR/J/ApJS/252/32
- Title:
- MIR outbursts in nearby SDSS gal. (MIRONG). I.
- Short Name:
- J/ApJS/252/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical time-domain astronomy has grown rapidly in the past decade, but the dynamic infrared sky is rarely explored. Aiming to construct a sample of mid-infrared outbursts in nearby galaxies (MIRONG), we have conducted a systematical search of low-redshift (z<0.35) Sloan Digital Sky Survey spectroscopic galaxies that have experienced recent mid-infrared (MIR) flares using their Wide-field Infrared Survey Explorer (WISE) light curves. A total of 137 galaxies have been selected by requiring a brightening amplitude of 0.5mag in at least one WISE band with respect to their quiescent phases. Only a small fraction (10.9%) has corresponding optical flares. Except for the four supernovae (SNe) in our sample, the MIR luminosities of the remaining sources (L_4.6{mu}m_>10^42^erg/s) are markedly brighter than known SNe, and their physical locations are very close to the galactic center (median <0.1"). Only four galaxies are radio-loud, indicating that synchrotron radiation from relativistic jets could contribute to MIR variability. We propose that these MIR outbursts are dominated by the dust echoes of transient accretion onto supermassive black holes, such as tidal disruption events (TDEs) and turn-on (changing-look) active galactic nuclei. Moreover, the inferred peak MIR luminosity function is generally consistent with the X-ray and optical TDEs at the high end, albeit with large uncertainties. Our results suggest that a large population of transients has been overlooked by optical surveys, probably due to dust obscuration or intrinsically optical weakness. Thus, a search in the infrared band is crucial for us to obtain a panoramic picture of nuclear outburst. The multiwavelength follow-up observations of the MIRONG sample are in progress and will be presented in a series of subsequent papers.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/895/114
- Title:
- Optical, radio and X-ray properties for 113 QSOs
- Short Name:
- J/ApJ/895/114
- Date:
- 16 Mar 2022 00:19:12
- Publisher:
- CDS
- Description:
- We investigate whether the correlation between the hard X-ray photon index ({Gamma}) and accretion rate for super-Eddington accreting quasars is different from that for sub-Eddington accreting quasars. We construct a sample of 113 bright quasars from the Sloan Digital Sky Survey Data Release 14 quasar catalog, with 38 quasars as the super-Eddington subsample and 75 quasars as the sub-Eddington subsample. We derive black hole masses using a simple-epoch virial mass formula based on the H{beta} lines, and we use the standard thin disk model to derive the dimensionless accretion rates (M) for our sample. The X-ray data for these quasars are collected from the Chandra and XMM-Newton archives. We fit the hard X-ray spectra using a single power-law model to obtain {Gamma} values. We find a statistically significant (R_S_=0.43, p=7.75x10^-3^) correlation between {Gamma} and M for the super-Eddington subsample. The {Gamma}-M correlation for the sub-Eddington subsample is also significant, but weaker (R_S_=0.30, p=9.98x10^-3^). Linear regression analysis shows that {Gamma}=(0.34{+/-}0.11)log(M)+(1.71{+/-}0.17) and {Gamma}=(0.09{+/-}0.04)log(M)+(1.93{+/-}0.04) for the super- and sub-Eddington subsamples, respectively. The {Gamma}-M correlations of the two subsamples are different, suggesting different disk-corona connections in these two types of systems. We propose one qualitative explanation of the steeper {Gamma}-M correlation in the super-Eddington regime that involves larger seed photon fluxes received by the compact coronae from the thick disks in super-Eddington accreting quasars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/2918
- Title:
- Photometry & line luminosities for ASASSN-14li
- Short Name:
- J/MNRAS/455/2918
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ground-based and Swift photometric and spectroscopic observations of the candidate tidal disruption event (TDE) ASASSN-14li, found at the centre of PGC 043234 (d~90 Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source had a peak bolometric luminosity of L~10^44^ erg/s and a total integrated energy of E~7x10^50^ erg radiated over the ~6 months of observations presented. The UV/optical emission of the source is well fitted by a blackbody with roughly constant temperature of T~35000 K, while the luminosity declines by roughly a factor of 16 over this time. The optical/UV luminosity decline is broadly consistent with an exponential decline, L{prop.to}e^-t/t0^, with t_0_~60 d. ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the optical and UV emission but declining at a slower rate, and the X-ray emission now dominates. Spectra of the source show broad Balmer and helium lines in emission as well as strong blue continuum emission at all epochs. We use the discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by ASAS-SN, finding an average rate of r~4.1x10^-5^/yr per galaxy with a 90 per cent confidence interval of (2.2-17.0)x10^-5^/yr per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia supernovae in 2014, a rate that is much higher than that of other surveys.
- ID:
- ivo://CDS.VizieR/J/AJ/162/72
- Title:
- Random forests method to discover high-redshift QSOs
- Short Name:
- J/AJ/162/72
- Date:
- 14 Mar 2022 07:01:17
- Publisher:
- CDS
- Description:
- We present a method of selecting quasars up to redshift ~6 with random forests, a supervised machine-learning method, applied to Pan-STARRS1 and WISE data. We find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. We present a candidate set for the redshift range 4.8-6.3, which includes the region around z=5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. We demonstrate that, under our survey restrictions, we can reach a high completeness (66%{+/-}7% below redshift 5.6/83_-9_^+6^% above redshift 5.6) while maintaining a high selection efficiency (78_-8_^+10^%/94_-8_^+5^% ). Our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. The final catalog of 515 candidates includes 225 known quasars. We predict the candidate catalog to contain additional 148_-33_^+41^ new quasars below redshift 5.6 and 45_-8_^+5^ above, and we make the catalog publicly available. Spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6<~z<~5.5, 2z~5.7). These observations are consistent with our predictions on efficiency. We argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/42
- Title:
- Reverberation mapping & opt. spectra data of AGNs
- Short Name:
- J/ApJ/886/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radius-luminosity (R_H{beta}_-L_5100_) relationship of active galactic nuclei (AGNs) established by the reverberation mapping (RM) observations has been widely used as a single-epoch black hole mass estimator in the research of large AGN samples. However, the recent RM campaigns discovered that the AGNs with high-accretion rates show shorter time lags by factors of a few comparing with the predictions from the R_H{beta}_-L_5100_ relationship. The explanation of the shortened time lags has not been finalized yet. We collect eight different single-epoch spectral properties to investigate how the shortening of the time lags correlates with those properties and to determine the origin of the shortened lags. We find that the flux ratio between FeII and H{beta} emission lines shows the most prominent correlation, thus confirming that accretion rate is the main driver for the shortened lags. In addition, we establish a new scaling relation including the relative strength of FeII emission. This new scaling relation can provide less biased estimates of the black hole mass and accretion rate from the single-epoch spectra of AGNs.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/36
- Title:
- SDSS/FIRST dwarf galaxies with VLA high res. obs.
- Short Name:
- J/ApJ/888/36
- Date:
- 25 Oct 2021 10:17:58
- Publisher:
- CDS
- Description:
- We present a sample of nearby dwarf galaxies with radio-selected accreting massive black holes (BHs), the majority of which are non-nuclear. We observed 111 galaxies using sensitive, high-resolution observations from the Karl G. Jansky Very Large Array (VLA) in its most extended A-configuration at X band (~8-12GHz), yielding a typical angular resolution of ~0.25" and rms noise of ~15{mu}Jy. Our targets were selected by crossmatching galaxies with stellar masses M_*_<=3x10^9^M_{sun}_ and redshifts z<0.055 in the NASA-Sloan Atlas with the VLA Faint Images of the Radio Sky at Twenty centimeters Survey. With our new high-resolution VLA observations, we detect compact radio sources toward 39 galaxies and carefully evaluate possible origins for the radio emission, including thermal HII regions, supernova remnants, younger radio supernovae, background interlopers, and active galactic nuclei (AGNs) in the target galaxies. We find that 13 dwarf galaxies almost certainly host active massive BHs, despite the fact that only one object was previously identified as having optical signatures of an AGN. We also identify a candidate dual radio AGN in a more massive galaxy system. The majority of the radio-detected BHs are offset from the center of the host galaxies, with some systems showing signs of interactions/mergers. Our results indicate that massive BHs need not always live in the nuclei of dwarf galaxies, confirming predictions from simulations. Moreover, searches attempting to constrain BH seed formation using observations of dwarf galaxies need to account for such a population of "wandering" BHs.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/57
- Title:
- SDSS & MMT obs. of extremely massive QSOs & gal.
- Short Name:
- J/ApJ/871/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Black hole mass scaling relations suggest that extremely massive black holes (EMBHs) with M_BH_>~10^9.4^M_{sun}_ are found in the most massive galaxies with M_star_>~10^11.6^M_{sun}_, which are commonly found in dense environments, like galaxy clusters. Therefore, one can expect that there is a close connection between active EMBHs and dense environments. Here, we study the environments of 9461 galaxies and 2943 quasars at 0.24<~z<~0.40, among which 52 are extremely massive quasars with log(M_BH_/M_{sun}_)>=~9.4, using Sloan Digital Sky Survey and MMT Hectospec data. We find that, on average, both massive quasars and massive galaxies reside in environments more than ~2 times as dense as those of their less massive counterparts with log(M_BH_/M_{sun}_)<~9.0. However, massive quasars reside in environments about ~2 times less dense than inactive galaxies with log(M_BH_/M_{sun}_)>=9.4, and only about one third of massive quasars are found in galaxy clusters, while about two thirds of massive galaxies reside in such clusters. This indicates that massive galaxies are a much better signpost for galaxy clusters than massive quasars. The prevalence of massive quasars in moderate to low density environments is puzzling, considering that several simulation results show that these quasars appear to prefer dense environments. Several possible reasons for this discrepancy are discussed, although further investigation is needed to obtain a definite explanation.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/6
- Title:
- SEAMBHs IX. 10 new H{beta} light curves
- Short Name:
- J/ApJ/856/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As one paper in a series reporting on a large reverberation mapping campaign of super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs), we present the results of 10 SEAMBHs monitored spectroscopically during 2015-2017. Six of them are observed for the first time, and have generally higher 5100{AA} luminosities than the SEAMBHs monitored in our campaign from 2012 to 2015; the remaining four are repeat observations to check if their previous lags change. Similar to the previous SEAMBHs, the H{beta} time lags of the newly observed objects are shorter than the values predicted by the canonical RH{beta}-L5100 relation of sub-Eddington AGNs, by factors of ~2-6, depending on the accretion rate. The four previously observed objects have lags consistent with previous measurements. We provide linear regressions for the RH{beta}-L5100 relation, solely for the SEAMBH sample and for low-accretion AGNs. We find that the relative strength of Fe ii and the profile of the H{beta} emission line can be used as proxies of accretion rate, showing that the shortening of H{beta} lags depends on accretion rates. The recent SDSS-RM discovery of shortened H{beta} lags in AGNs with low accretion rates provides compelling evidence for retrograde accretion onto the black hole. These evidences show that the canonical RH{beta}-L5100 relation holds only in AGNs with moderate accretion rates. At low accretion rates, it should be revised to include the effects of black hole spin, whereas the accretion rate itself becomes a key factor in the regime of high accretion rates.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/20
- Title:
- SEAMBHs XII. Reberberation mapping for 15 PG QSOs
- Short Name:
- J/ApJS/253/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present the first results of the long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong FeII emission, as a part of a broader reverberation mapping campaign performed using the Calar Alto Observatory's 2.2m telescope. The V-band, 5100{AA} continuum, and H{beta} broad emission line light curves are measured for a set of quasars for periods ranging from dozens to more than a hundred epochs between 2017 May and 2020 July. Accurate time lags between the variations of the H{beta} broad-line fluxes and the optical continuum strength are obtained for all 15 quasars, ranging from 17.0_-3.2_^+2.5^ to 95.9_-23.9_^+7.1^ days in the rest frame. The virial masses of the central supermassive black holes are derived for all 15 quasars, ranging between 0.50_-0.19_^+0.18^ and 19.17_-2.73_^+2.98^ in units of 10^7^M_{sun}_. For 11 of the objects in our sample, this is the first reverberation analysis to be published. Of the rest, two objects have been the subject of previous reverberation studies, but we determine time lags for these that are only half as long as those found in the earlier investigations, which had only been able to sample much more sparsely. The remaining two objects have previously been monitored with high sampling rates. Our results here are consistent with the earlier findings, in the sense that the time lag and the line width vary inversely, consistent with virialization.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/23
- Title:
- SEAMBHs. X. Reverberation mapping campaign compilation
- Short Name:
- J/ApJ/877/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled a sample of 73 active galactic nuclei (AGNs) with reverberation mapping (RM) observations from RM campaigns, including our ongoing campaign of monitoring super-Eddington accreting massive black holes (BHs). This sample covers a large range of BH mass (M_{bullet}_=10^6^-9^M_{sun}_), dimensionless accretion rates (dM/dt=10^-2.7^-10^2.7^), and 5100{AA} luminosity (L_5100_=10^42-46^erg/s), allowing us to systematically study the AGN variability and their relations with BH mass, accretion rates, and optical luminosity. We employed the damped random walk (DRW) model to delineate the optical variability of continuum at 5100{AA} and obtained damped variability timescale ({tau}_d_) and amplitude ({sigma}_d_) using a Markov Chain Monte Carlo method. We also estimated the traditional variability amplitudes (F_var_), which provide a model-independent measure and therefore are used to test the DRW results. We found that AGN variability characteristics are generally correlated with (M_{bullet}_, dM/dt, L_5100_). These correlations are smooth from sub-Eddington to super-Eddington accretion AGNs, probably implying that the AGN variability may be caused by the same physical mechanism.
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