分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The main objective of the paper, the first paper in a dedicated series, is to report basic results on systematic research of low-redshift optically selected SDSS Type-2 AGN but with apparent optical variabilities. For all the pipeline classified Type-2 AGN in SDSS DR16 with $z10$, long-term optical V-band light curves are collected from Catalina Sky Survey. Through all light curves described by Damped Random Walk process with process parameters of $\sigma/(mag/days^{0.5})$ and $\tau/days$, 156 Type-2 AGN have apparent variabilities with process parameters at least three times larger than corresponding uncertainties and with $\ln(\sigma/(mag/days^{0.5}))>-4$, indicating central AGN activity regions directly in line-of-sight, leading the 156 Type-2 AGN as mis-classified Type-2 AGN. Furthermore, based on spectroscopic emission features around H$\alpha$, 31 out of the 156 AGN have broad H$\alpha$, indicating the 31 Type-2 AGN are actually Type-1.8/1.9 AGN. Meanwhile, 14 out of the 156 AGN have multi-epoch SDSS spectra. After checking multi-epoch spectra of the 14 objects, no clues for appearance/disappearance of broad lines indicate true Type-2 AGN rather than changing-look AGN are preferred in the collected Type-2 AGN with long-term variabilities. Moreover, a small sample of Type-2 AGN have long-term variabilities with features roughly described by theoretical TDEs expected $t^{-5/3}$, indicating probable central TDEs as further and strong evidence to support true Type-2 AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The main objective is to check the Unified Model (UM) expected similar stellar velocity dispersions between Type-1 AGN and Type-2 AGN, then to provide further clues on BH mass properties. Not similar as previous comparisons of BH masses estimated by \msig relations to Type-2 AGN but Virial BH masses in Type-1 AGN, reliable stellar velocity dispersions $\sigma$ measured through absorption features around 4000\AA~ are directly compared between so-far the largest samples of 6260 low redshift ($z~<~0.3$) Type-1 AGN and almost all the Type-2 AGN in SDSS DR12. Although half of Type-1 AGN do not have measured $\sigma$ due to unapparent absorption features overwhelmed by AGN activities, both properties of mean spectra of Type-1 AGN with and without measured $\sigma$ and positive dependence of $\sigma$ on [O~{\sc iii}] luminosity can lead to statistically larger $\sigma$ of all the Type-1 AGN than the 6260 Type-1 AGN with measured stellar velocity dispersions. Then, direct $\sigma$ comparisons can lead to statistically larger $\sigma$ in Type-1 AGN, with confidence level higher than 10sigma, after considering necessary effects of different redshift and different central AGN activities. Although Type-1 AGN have $\sigma$ only about $(9\pm3)$\% larger than Type-2 AGN, the difference cannot be well explained at current stage. Unless there was strong evidence to support different \msig relations or to support quite different evolution histories between Type-1 AGN and Type-2 AGN, the statistically larger $\sigma$ in Type-1 AGN provides a strong challenge to the Unified model of AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the Letter, interesting evidence is reported to support a central tidal disruption event (TDE) in the known AGN NGC 1097. Considering the motivations of TDE as one probable origination of emission materials of double-peaked broad emission lines and also as one probable explanation to changing-look AGN, it is interesting to check whether are there clues to support a TDE in NGC 1097, not only a changing-look AGN but also an AGN with double-peaked broad emission lines. Under the assumption that the onset of broad H$\alpha$ emission was due to a TDE, the 13years-long (1991-2004) variability of double-peaked broad H$\alpha$ line flux in NGC 1097 can be well predicted by theoretical TDE model, with a $(1-1.5){\rm M_\odot}$ main-sequence star tidally disrupted by the central BH with TDE model determined mass about $(5-8)\times10^7{\rm M_\odot}$. The results provide interesting evidence to not only support TDE-related origin of double-peaked broad line emission materials but also support TDE as an accepted physical explanation to physical properties of changing-look AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the Letter, a new candidate for central tidal disruption event (TDE) is reported in SDSS J014124+010306 (=SDSS J0141) with broad Mg~{\sc ii} line at redshift $z=1.06$. Based on long-term photometric $ugriz$-band variabilities from SDSS Stripe82 Database and PHOTOOBJALL database, a central TDE is preferred with a 1.3${\rm M_\odot}$ main-sequence star tidally disrupted by central black hole (BH) of $(14\pm2)\times10^6{\rm M_\odot}$ in SDSS J0141. Moreover, CAR process has been applied to confirm that the probability is only about 0.4\% that the long-term variabilities in SDSS J0141 are not related to TDE but from intrinsic AGN activities. Meanwhile, based on the apparent broad Mg~{\sc ii} emission lines, virial BH mass can be estimated as $245\times10^6{\rm M_\odot}$, 18 times larger than the TDE-model determined BH mass, providing further clues to support a central TDE in SDSS J0141, similar as the case in the TDE candidate SDSS J0159 with virial BH mass two magnitudes larger than M-sigma relation expected BH mass. Among the reported optical TDE candidates, SDSS J0141 is the candidate at the highest redshift. The results in the Letter indicate it should be common to detect TDE candidates in high redshift galaxies with broad Mg~{\sc ii} lines.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, we report a new changing-look QSO (CLQSO) SDSS J2241 at $z=0.059$. Based on the multi-epoch SDSS spectra from 2011 to 2017, the flux ratio of broad H$\alpha$ to broad H$\beta$ has been changed from 7\ in 2011 to 2.7\ in 2017, leading SDSS J2241 with spectral index $\alpha_\lambda\sim-5.21\pm0.02$ ($\lambda< 4000$\AA) in 2017 to be so-far the bluest CLQSO. Based on the SDSS spectrum in 2011, the host galaxy contributions with stellar velocity dispersion $\sim86{\rm km/s}$ can be well determined, leading to the M-sigma relation expected central BH mass $\sim3\times10^6{\rm M_\odot}$. However, through properties of the broad H$\alpha$, the virial BH mass is $\sim10^8{\rm M_\odot}$, about two magnitudes larger than the mass through the M-sigma relation. The different BH masses through different methods indicate SDSS J2241 is one unique CLQSO. Meanwhile, the long-term photometric light curve shows interesting variability properties, not expected by DRW process commonly applied in AGN but probably connected to a central TDE. Furthermore, based on continuum emission properties in 2017 with no dust obscurations, only considering the moving dust clouds cannot be preferred to explain the CLQSO SDSS J2241, because the expected intrinsic reddening corrected continuum emissions were unreasonably higher than the unobscured continuum emissions in 2017.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the manuscript, we discuss properties of SDSS J1451+2709, a normal blue quasar but mis-classified as a HII galaxy in the BPT diagram (called as a mis-classified quasar). The emission lines around H$\alpha$ and H$\beta$ are well measured by different model functions with broad Balmer lines being described by Gaussian or Lorentz functions, in the SDSS spectrum in 2007 and in the KPNO spectrum in 1990. After considering variations of broad emission lines, different model functions lead to different fluxes of narrow emission lines, but the different narrow emission line flux ratios lead the SDSS J1451+2709 to be classified as a HII galaxy in the BPT diagram. In order to explain the unique properties of the mis-classified quasar SDSS J1451+2709 in the BPT diagram, two methods are proposed, the starforming contributions and compressed NLRs with high electron densities near to critical densities of forbidden emission lines. Unfortunately, the two methods cannot be preferred in the SDSS J1451+2709, further efforts are necessary to find the physical origin of the unique properties of the mis-classified quasar SDSS J1451+2709 in the BPT diagram. Meanwhile, there are not quite different long-term variabilities of SDSS J1451+2709 from the normal quasars. The mis-classified quasar SDSS J1451+2709, an extremely unique case or a special case among the normal quasars, could provide further clues on the applications of BPT diagrams to the normal broad line AGN and to narrow emission line objects, indicating part of narrow emission line HII galaxies actually harbouring central AGN activities.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, central BH mass is determined in the tidal disruption event (TDE) candidate SDSS J0159, through the nine years long variabilities, in order to check whether the virial BH mass is consistent with the mass estimated by another independent methods. First, host galaxy spectroscopic features are described by 350 simple stellar templates, to confirm the total stellar mass about $7\times10^{10}{\rm M_\odot}$ in SDSS J0159, indicating the virial BH mass about two magnitudes larger than the BH mass estimated by the total stellar mass. Second, based on an efficient method and fitting procedure, through theoretical TDE model applied to describe the SDSS $ugriz$-band light curves of SDSS J0159, central BH mass can be determined as $M_{BH}\sim4.5_{-1.1}^{+1.3}\times10^6{\rm M_\odot}$, well consistent with the M-sigma relation expected BH mass and the total stellar mass expected BH mass. Third, the theoretical TDE model with parameter of central BH mass limited to be higher than $10^8{\rm M_\odot}$ can not lead to reasonable descriptions to the light curves of SDSS J0159, indicating central BH mass higher than $10^8{\rm M_\odot}$ is not preferred in SDSS J0159. Therefore, the TDE model determined central BH mass of SDSS J0159 are about two magnitudes lower than the virial BH mass, to support central BLRs including accreting debris contributions from central TDE, and provide interesting clues to reconfirm that outliers in the space of virial BH mass versus stellar velocity dispersion should be better candidates of TDE.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, central BH mass is determined in the tidal disruption event (TDE) candidate SDSS J0159, through the nine years long variabilities, in order to check whether the virial BH mass is consistent with the mass estimated by another independent methods. First, host galaxy spectroscopic features are described by 350 simple stellar templates, to confirm the total stellar mass about $7\times10^{10}{\rm M_\odot}$ in SDSS J0159, indicating the virial BH mass about two magnitudes larger than the BH mass estimated by the total stellar mass. Second, based on an efficient method and fitting procedure, through theoretical TDE model applied to describe the SDSS $ugriz$-band light curves of SDSS J0159, central BH mass can be determined as $M_{BH}\sim4.5_{-1.1}^{+1.3}\times10^6{\rm M_\odot}$, well consistent with the M-sigma relation expected BH mass and the total stellar mass expected BH mass. Third, the theoretical TDE model with parameter of central BH mass limited to be higher than $10^8{\rm M_\odot}$ can not lead to reasonable descriptions to the light curves of SDSS J0159, indicating central BH mass higher than $10^8{\rm M_\odot}$ is not preferred in SDSS J0159. Therefore, the TDE model determined central BH mass of SDSS J0159 are about two magnitudes lower than the virial BH mass, to support central BLRs including accreting debris contributions from central TDE, and provide interesting clues to reconfirm that outliers in the space of virial BH mass versus stellar velocity dispersion should be better candidates of TDE.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the Letter, interesting evidence is reported to support a central tidal disruption event (TDE) in the known AGN NGC 1097. Considering the motivations of TDE as one probable origination of emission materials of double-peaked broad emission lines and also as one probable explanation to changing-look AGN, it is interesting to check whether are there clues to support a TDE in NGC 1097, not only a changing-look AGN but also an AGN with double-peaked broad emission lines. Under the assumption that the onset of broad H$\alpha$ emission was due to a TDE, the 13years-long (1991-2004) variability of double-peaked broad H$\alpha$ line flux in NGC 1097 can be well predicted by theoretical TDE model, with a $(1-1.5){\rm M_\odot}$ main-sequence star tidally disrupted by the central BH with TDE model determined mass about $(5-8)\times10^7{\rm M_\odot}$. The results provide interesting evidence to not only support TDE-related origin of double-peaked broad line emission materials but also support TDE as an accepted physical explanation to physical properties of changing-look AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The main objective of the paper, the first paper in a dedicated series, is to report basic results on systematic research of low-redshift optically selected SDSS Type-2 AGN but with apparent optical variabilities. For all the pipeline classified Type-2 AGN in SDSS DR16 with $z10$, long-term optical V-band light curves are collected from Catalina Sky Survey. Through all light curves described by Damped Random Walk process with process parameters of $\sigma/(mag/days^{0.5})$ and $\tau/days$, 156 Type-2 AGN have apparent variabilities with process parameters at least three times larger than corresponding uncertainties and with $\ln(\sigma/(mag/days^{0.5}))>-4$, indicating central AGN activity regions directly in line-of-sight, leading the 156 Type-2 AGN as mis-classified Type-2 AGN. Furthermore, based on spectroscopic emission features around H$\alpha$, 31 out of the 156 AGN have broad H$\alpha$, indicating the 31 Type-2 AGN are actually Type-1.8/1.9 AGN. Meanwhile, 14 out of the 156 AGN have multi-epoch SDSS spectra. After checking multi-epoch spectra of the 14 objects, no clues for appearance/disappearance of broad lines indicate true Type-2 AGN rather than changing-look AGN are preferred in the collected Type-2 AGN with long-term variabilities. Moreover, a small sample of Type-2 AGN have long-term variabilities with features roughly described by theoretical TDEs expected $t^{-5/3}$, indicating probable central TDEs as further and strong evidence to support true Type-2 AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the manuscript, central black hole (BH) mass is estimated in the distant TDE (tidal disruption event) of {\it Swift} J2058.4+0516 as the second candidate of relativistic jet birth related to TDE. {\it Swift} J2058.4+0516 have quite different BH masses estimated through different indirect methods in the literature. Therefore, it is necessary and interesting to determine the central BH mass in {\it Swift} J2058.4+0516 by one another independent method. Here, based on the theoretical TDE model applied to describe the long-term time-dependent X-ray variabilities of {\it Swift} J2058.4+0516, the central BH mass can be well determined to be around $1.05_{-0.29}^{+0.39}\times10^5{\rm M_\odot}$, after kind considerations of suggested intrinsic beaming effects from such relativistic jet tightly related to TDE. Moreover, the {\it Swift} J2058.4+0516 is an unique object in the space of BH masses versus energy transfer efficiencies of the reported TDE candidates, providing interesting clues to detect and/or anticipate candidates of relativistic TDE to make the birth of relativistic jets.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, an independent method is proposed to estimate opening angle of dust torus in AGN, through unique properties of Type-1.9 AGN with double-peaked broad H$\alpha$ (Type-1.9 DPAGN) coming from central accretion disk. Type-1.9 AGN without broad H$\beta$ can be expected by the commonly accepted unified model of AGN, considering central BLRs seriously obscured by dust torus with its upper boundary in the line of sight. For the unique Type-1.9 DPAGN, accretion disk originations of double-peaked broad H$\alpha$ can be applied to determine the inclination angle of the central accretion disk, which is well accepted as substitute of the half opening angle of the central dust torus. Then, among low redshift Type-1.9 DPAGN in SDSS, SDSS J1607+3319 at redshift 0.063 is collected, and the half opening angle of the central dust torus is determined to be around 46$\pm$4\degr, after considering disfavoured BBH system to explain the double-peaked broad H$\alpha$ through long-term none variabilities and disfavoured local physical conditions to explain disappearance of broad H$\beta$ through virial BH mass properties. The results indicate that more detailed studying on dust torus of AGN can be appropriately done through Type-1.9 DPAGN in the near future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, an independent method is proposed to estimate opening angle of dust torus in AGN, through unique properties of Type-1.9 AGN with double-peaked broad H$\alpha$ (Type-1.9 DPAGN) coming from central accretion disk. Type-1.9 AGN without broad H$\beta$ can be expected by the commonly accepted unified model of AGN, considering central BLRs seriously obscured by dust torus with its upper boundary in the line of sight. For the unique Type-1.9 DPAGN, accretion disk originations of double-peaked broad H$\alpha$ can be applied to determine the inclination angle of the central accretion disk, which is well accepted as substitute of the half opening angle of the central dust torus. Then, among low redshift Type-1.9 DPAGN in SDSS, SDSS J1607+3319 at redshift 0.063 is collected, and the half opening angle of the central dust torus is determined to be around 46$\pm$4\degr, after considering disfavoured BBH system to explain the double-peaked broad H$\alpha$ through long-term none variabilities and disfavoured local physical conditions to explain disappearance of broad H$\beta$ through virial BH mass properties. The results indicate that more detailed studying on dust torus of AGN can be appropriately done through Type-1.9 DPAGN in the near future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, an interesting method is proposed to test dual core system for double-peaked narrow emission lines, through precious dual core system with double-peaked narrow Balmer lines in one system in main galaxy but with single-peaked narrow Balmer lines in the other system in companion galaxy. Under a dual core system, considering narrow Balmer (H$\alpha$ and H$\beta$) emissions ($f_{e,~\alpha}$ and $f_{e,~\beta}$) from companion galaxy but covered by SDSS fiber for the main galaxy and narrow Balmer emissions ($f_{c,~\alpha}$ and $f_{c,~\beta}$) from the companion galaxy covered by SDSS fiber for the companion galaxy, the same flux ratios $f_{e,~\alpha}/f_{c,~\alpha}=f_{e,~\beta}/f_{c,~\beta}$ can be expected, due to totally similar physical conditions of each narrow Balmer emission region. Then, the precious dual core system in SDSS J2219-0938 is discussed. After subtracting pPXF code determined stellar lights, double-peaked narrow Balmer emission lines are confirmed in the main galaxy with confidence level higher than $5\sigma$, but single-peaked narrow Balmer emission lines in the companion galaxy. Through measured fluxes of emission components, $f_{e,~\alpha}/f_{c,~\alpha}$ is around 0.82, different from $f_{e,~\beta}/f_{c,~\beta}\sim0.52$, to disfavour a dual core system for the double-peaked narrow Balmer emission lines in SDSS J2219-0938.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this manuscript, an interesting method is proposed to test dual core system for double-peaked narrow emission lines, through precious dual core system with double-peaked narrow Balmer lines in one system in main galaxy but with single-peaked narrow Balmer lines in the other system in companion galaxy. Under a dual core system, considering narrow Balmer (H$\alpha$ and H$\beta$) emissions ($f_{e,~\alpha}$ and $f_{e,~\beta}$) from companion galaxy but covered by SDSS fiber for the main galaxy and narrow Balmer emissions ($f_{c,~\alpha}$ and $f_{c,~\beta}$) from the companion galaxy covered by SDSS fiber for the companion galaxy, the same flux ratios $f_{e,~\alpha}/f_{c,~\alpha}=f_{e,~\beta}/f_{c,~\beta}$ can be expected, due to totally similar physical conditions of each narrow Balmer emission region. Then, the precious dual core system in SDSS J2219-0938 is discussed. After subtracting pPXF code determined stellar lights, double-peaked narrow Balmer emission lines are confirmed in the main galaxy with confidence level higher than $5\sigma$, but single-peaked narrow Balmer emission lines in the companion galaxy. Through measured fluxes of emission components, $f_{e,~\alpha}/f_{c,~\alpha}$ is around 0.82, different from $f_{e,~\beta}/f_{c,~\beta}\sim0.52$, to disfavour a dual core system for the double-peaked narrow Balmer emission lines in SDSS J2219-0938.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the Letter, an interesting method is proposed to estimate size of narrow emission lines regions (NLRs) of a Type-2 AGN SDSS J083823.91+490241.1 (=SDSS J0838) at a redshift of 0.101, by comparing spectroscopic properties through the SDSS fiber (MJD=51873) (diameter of 3 arcseconds) and through the eBOSS fiber (MJD=55277) (diameter of 2 arcseconds). After subtractions of pPXF method determined host galaxy contributions, the narrow emission lines of SDSS J0838 in the SDSS spectrum and in the eBOSS spectrum can be well measured by Gaussian functions, leading more than 90\% of [O~{\sc iii}] emissions to be covered by the eBOSS fiber with diameter of 2 arcseconds. Meanwhile, both none broad emission components and none-variabilities of ZTF 3years-long g/r-band light curves can be applied to confirm SDSS J0838 as a Type-2 AGN, indicating few orientation effects on the projected NLRs size in SDSS J0838. Therefore, upper limit about 1arcsecond (2250pc) of the NLRs size can be reasonably accepted in SDSS J0838. Combining with the intrinsic reddening corrected [O~{\sc iii}] line luminosity, the upper limit of NLRs size in SDSS J0838 well lies within the 99.9999\% confidence bands of the R-L empirical relation for NLRs in AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the manuscript, we discuss properties of the SDSS J1042-0018 which is a broad line AGN but mis-classified as a HII galaxy in the BPT diagram (SDSS J1042-0018 called as a mis-classified broad line AGN). The emission lines around H$\alpha$ and around H$\beta$ are well described by different model functions, considering broad Balmer lines to be described by Gaussian or Lorentz functions. Different model functions lead to different determined narrow emission line fluxes, but the different narrow emission line flux ratios lead the SDSS J1042-0018 as a HII galaxy in the BPT diagram. In order to explain the unique properties of the mis-classified broad line AGN SDSS J1042-0018, two methods are proposed, the starforming contributions and the compressed NLRs with high electron densities near to critical densities of forbidden emission lines. Fortunately, the strong starforming contributions can be preferred in the SDSS J1042-0018. The mis-classified broad line AGN SDSS J1042-0018, well explained by starforming contributions, could provide further clues on the applications of BPT diagrams to the normal broad line AGN.
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