分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We perform a systematic survey of active galactic nucleus (AGN) continuum lags using $\sim$3 day cadence $gri$-band light curves from the Zwicky Transient Facility. We select a sample of 94 type 1 AGN at $z<0.8$ with significant and consistent inter-band lags based on the interpolated cross-correlation function method and the Bayesian method JAVELIN. Within the framework of the lamp-post reprocessing model, our findings are: 1) The continuum emission (CE) sizes inferred from the data are larger than the disk sizes predicted by the standard thin disk model; 2) For a subset of the sample, the CE size exceeds the theoretical limit of the self-gravity radius (12 lt-days) for geometrically thin disks; 3) The CE size scales with continuum luminosity as $R_{\mathrm{CE}} \propto L^{0.48\pm0.04}$ with a scatter of 0.2 dex, analogous to the well-known radius-luminosity relation of broad H$\mathrm{\beta}$. These findings suggest a significant contribution of diffuse continuum emission from the broad-line region (BLR) to AGN continuum lags. We find that the $R_{\mathrm{CE}}-L$ relation can be explained by a photoionization model that assumes $\sim$23% of the total flux comes from the diffuse BLR emission. In addition, the ratio of the CE size and model-predicted disk size anti-correlates with the continuum luminosity, indicative of a potential non-disk BLR lag contribution evolving with luminosity. Finally, a robust positive correlation between CE size and black hole mass is detected.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Spectroscopic reverberation mapping (RM) is a direct approach widely used to estimate the mass of black holes (BHs) in active galactic nuclei (AGNs). However, it is very time-consuming and difficult to apply to a large AGN sample. The empirical relation between the broad-line region (BLR) size and luminosity (H$\beta$ $R_{\rm BLR}\unicode{x2013}L_{\rm}$) provides a practical alternative yet subject to large scatter and systematic bias. AGN continuum RM (CRM) recently discovered a similar relation between the continuum emitting region (CER) size and luminosity ($R_{\rm CER}\unicode{x2013}L$). Here we present a new method to estimate BH masses via optical CRM assuming continuum lags dominated by the diffuse continuum emission. This method will significantly facilitate the estimation of RM BH mass thanks to the short continuum lags and the easily accessible high-cadence and large-area photometric data. Using a sample of 21 AGNs with both CER and BLR size, we find a tight $R_{\rm BLR}\unicode{x2013}R_{\rm CER}$ relation (scatter $\sim0.28$ dex), with $R_{\rm BLR}$ on average 8.1 times of $R_{\rm CER}$ at 5100\r{A}. This tight relation enables the BH mass estimation based on the CRM combined with the velocity information. Applying the relation to rest objects in our CRM sample, we demonstrate that the predicted $R_{\rm BLR,CRM}$ follow the existing H$\beta$ $R_{\rm BLR}\unicode{x2013}L_{\rm}$ relation well and the estimated CRM BH masses are consistent with the RM/single-epoch BH masses using H$\beta$. Our proposed method will be a promising BH mass estimator in the era of Legacy Survey of Space and Time.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Precise interstellar dust extinction laws are important to infer the intrinsic properties of reddened objects and correctly interpret observations. In this work, we attempt to measure the optical--infrared extinction laws of the Large and Small Magellanic Clouds (LMC and SMC) by using red supergiant (RSG) stars and classical Cepheids as extinction tracers. The spectroscopic RSG samples are constructed based on the APOGEE spectral parameters, Gaia astrometric data, and multi-band photometry. We establish the effective temperature--intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(lambda-GRP)/E(GBP-GRP) for LMC and SMC. We use classical Cepheids to derive base relative extinction A_GRP/E(GBP-GRP). The results are 1.589+-0.014 and 1.412+-0.041 for LMC and SMC. By combining CERs with A_GRP /E(GBP-GRP), the optical--infrared extinction coefficients A_lambda/A_GRP are determined for 16 bands. We adjust the parameters of Rv-dependent extinction laws and obtain the average extinction law of LMC and SMC as Rv=3.40+-0.07 and Rv=2.53+-0.10, which are consistent with Gordon et al. (2003). In the optical bands, the adjusted Rv extinction curves agree with the observations with deviations less than 3%.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We perform a systematic survey of active galactic nucleus (AGN) continuum lags using $\sim$3 day cadence $gri$-band light curves from the Zwicky Transient Facility. We select a sample of 94 type 1 AGN at $z<0.8$ with significant and consistent inter-band lags based on the interpolated cross-correlation function method and the Bayesian method JAVELIN. Within the framework of the lamp-post reprocessing model, our findings are: 1) The continuum emission (CE) sizes inferred from the data are larger than the disk sizes predicted by the standard thin disk model; 2) For a subset of the sample, the CE size exceeds the theoretical limit of the self-gravity radius (12 lt-days) for geometrically thin disks; 3) The CE size scales with continuum luminosity as $R_{\mathrm{CE}} \propto L^{0.48\pm0.04}$ with a scatter of 0.2 dex, analogous to the well-known radius-luminosity relation of broad H$\mathrm{\beta}$. These findings suggest a significant contribution of diffuse continuum emission from the broad-line region (BLR) to AGN continuum lags. We find that the $R_{\mathrm{CE}}-L$ relation can be explained by a photoionization model that assumes $\sim$23% of the total flux comes from the diffuse BLR emission. In addition, the ratio of the CE size and model-predicted disk size anti-correlates with the continuum luminosity, indicative of a potential non-disk BLR lag contribution evolving with luminosity. Finally, a robust positive correlation between CE size and black hole mass is detected.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shu Wang
Linhua Jiang
Yue Shen
Luis C. Ho
Marianne Vestergaard
Eduardo Banados
Chris J. Willott
Jin Wu
Siwei Zou
Jinyi Yang
Feige Wang
Xiaohui Fan
Xue-Bing Wu
摘要： Broad line regions (BLRs) in high-redshift quasars provide crucial
information of chemical enrichment in the early universe. Here we present a
study of BLR metallicities in 33 quasars at redshift $5.7
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Red clump stars (RCs) are useful tracers of distances, extinction, chemical abundances, and Galactic structures and kinematics. Accurate estimation of the RC parameters -- absolute magnitude and intrinsic color -- is the basis for obtaining high-precision RC distances. By combining astrometric data from Gaia, spectroscopic data from APOGEE and LAMOST, and multi-band photometric data from Gaia, APASS, Pan-STARRS1, 2MASS, and WISE surveys, we use the Gaussian process regression to train machine learners to derive the multi-band absolute magnitudes $M_\lambda$ and intrinsic colors $(\lambda_1-\lambda_2)_0$ for each spectral RC. The dependence of $M_\lambda$ on metallicity decreases from optical to infrared bands, while the dependence of $M_\lambda$ on age is relatively similar in each band. $(\lambda_1-\lambda_2)_0$ are more affected by metallicity than age. The RC parameters are not suitable to be represented by simple constants but are related to the Galactic stellar population structure. By analyzing the variation of $M_\lambda$ and $(\lambda_1-\lambda_2)_0$ in the spatial distribution, we construct $(R, z)$ dependent maps of mean absolute magnitudes and mean intrinsic colors of the Galactic RCs. Through external and internal validation, we find that using three-dimensional (3D) parameter maps to determine RC parameters avoids systematic bias and reduces dispersion by about 20% compared to using constant parameters. Based on Gaia's EDR3 parallax, our 3D parameter maps, and extinction-distance profile selection, we obtain a photometric RC sample containing 11 million stars with distance and extinction measurements.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Cepheid variables in SMC, LMC, the Milky Way, M33 and M31 are used to examine the dependence of pulsation mode on metallicity which was previously found in red supergiants. The initial samples of Cepheids are collected from the Cepheid catalogs identified from the OGLE, PS1, DIRECT, WISE and ZTF surveys. The contaminants are removed with the help of the Gaia/EDR3 astrometric information for extra galaxies or by comparing the geometric distance and the distance from the P-L relation for the Milky Way. The division of fundamental and first-overtone mode is refined according to the gap between the two modes in the P-L diagram of the objects in each galaxy. The ratio of FU/(FU+1O) is found to be 0.59, 0.60, 0.69, 0.83 and 0.85 for SMC, LMC, the Milky Way, M33 and M31 respectively in order of metallicity, which confirms that the pulsation mode depends on metallicity in the way that the ratio of FU/(FU+1O) increases with metallicity. This dependence is not changed if the incompleteness of the samples is taken into account.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jin Wu
Yue Shen
Linhua Jiang
Eduardo Bañados
Xiaohui Fan
Luis C. Ho
Marianne Vestergaard
Feige Wang
Shu Wang
Xue-Bing Wu
Jinyi Yang
摘要： We study the demographics of z ~ 6 broad-line quasars in the black hole (BH) mass-luminosity plane using a sample of more than 100 quasars at 5.7 10^8.5 M_Sun, with a median 1-sigma uncertainty of ~0.5 dex in abundance. The intrinsic Eddington ratio distribution of M_BH > 10^8.5 M_Sun quasars can be approximated by a mass-dependent Schechter model, with a broad peak around log(L_bol/L_Edd}) ~ -0.9. We also find that, at 4.5 < z < 6, the number densities of more massive BHs tend to decline more rapidly with increasing redshift, contrary to the trend at 2.5 < z < 4.5 reported previously.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jin Wu
Yue Shen
Linhua Jiang
Eduardo Bañados
Xiaohui Fan
Luis C. Ho
Marianne Vestergaard
Feige Wang
Shu Wang
Xue-Bing Wu
Jinyi Yang
摘要： We study the demographics of z ~ 6 broad-line quasars in the black hole (BH) mass-luminosity plane using a sample of more than 100 quasars at 5.7 10^8.5 M_Sun, with a median 1-sigma uncertainty of ~0.5 dex in abundance. The intrinsic Eddington ratio distribution of M_BH > 10^8.5 M_Sun quasars can be approximated by a mass-dependent Schechter model, with a broad peak around log(L_bol/L_Edd}) ~ -0.9. We also find that, at 4.5 < z < 6, the number densities of more massive BHs tend to decline more rapidly with increasing redshift, contrary to the trend at 2.5 < z < 4.5 reported previously.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Precise interstellar dust extinction laws are important to infer the intrinsic properties of reddened objects and correctly interpret observations. In this work, we attempt to measure the optical--infrared extinction laws of the Large and Small Magellanic Clouds (LMC and SMC) by using red supergiant (RSG) stars and classical Cepheids as extinction tracers. The spectroscopic RSG samples are constructed based on the APOGEE spectral parameters, Gaia astrometric data, and multi-band photometry. We establish the effective temperature--intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(lambda-GRP)/E(GBP-GRP) for LMC and SMC. We use classical Cepheids to derive base relative extinction A_GRP/E(GBP-GRP). The results are 1.589+-0.014 and 1.412+-0.041 for LMC and SMC. By combining CERs with A_GRP /E(GBP-GRP), the optical--infrared extinction coefficients A_lambda/A_GRP are determined for 16 bands. We adjust the parameters of Rv-dependent extinction laws and obtain the average extinction law of LMC and SMC as Rv=3.40+-0.07 and Rv=2.53+-0.10, which are consistent with Gordon et al. (2003). In the optical bands, the adjusted Rv extinction curves agree with the observations with deviations less than 3%.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Spectroscopic reverberation mapping (RM) is a direct approach widely used to estimate the mass of black holes (BHs) in active galactic nuclei (AGNs). However, it is very time-consuming and difficult to apply to a large AGN sample. The empirical relation between the broad-line region (BLR) size and luminosity (H$\beta$ $R_{\rm BLR}\unicode{x2013}L_{\rm}$) provides a practical alternative yet subject to large scatter and systematic bias. AGN continuum RM (CRM) recently discovered a similar relation between the continuum emitting region (CER) size and luminosity ($R_{\rm CER}\unicode{x2013}L$). Here we present a new method to estimate BH masses via optical CRM assuming continuum lags dominated by the diffuse continuum emission. This method will significantly facilitate the estimation of RM BH mass thanks to the short continuum lags and the easily accessible high-cadence and large-area photometric data. Using a sample of 21 AGNs with both CER and BLR size, we find a tight $R_{\rm BLR}\unicode{x2013}R_{\rm CER}$ relation (scatter $\sim0.28$ dex), with $R_{\rm BLR}$ on average 8.1 times of $R_{\rm CER}$ at 5100\r{A}. This tight relation enables the BH mass estimation based on the CRM combined with the velocity information. Applying the relation to rest objects in our CRM sample, we demonstrate that the predicted $R_{\rm BLR,CRM}$ follow the existing H$\beta$ $R_{\rm BLR}\unicode{x2013}L_{\rm}$ relation well and the estimated CRM BH masses are consistent with the RM/single-epoch BH masses using H$\beta$. Our proposed method will be a promising BH mass estimator in the era of Legacy Survey of Space and Time.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Linhua Jiang
Shu Wang
Bing Zhang
Nobunari Kashikawa
Luis C. Ho
Zheng Cai
Eiichi Egami
Gregory Walth
Yi-Si Yang
Bin-Bin Zhang
Hai-Bin Zhao
摘要： In Jiang et al., we detected a bright flash (hereafter GN-z11-flash) that appeared as compact continuum emission during our Keck MOSFIRE observations of the galaxy GN-z11 at z ~ 11. We performed a comprehensive analysis of the origin of the flash using all available information and our current understanding of known man-made objects or moving objects in the solar system. We found that GN-z11-flash was likely a rest-frame UV flash associated with a long gamma-ray burst (GRB) from GN-z11. Recently, Steinhardt et al., Michalowski et al., and Nir et al. reported that GN-z11-flash was more likely from a satellite. While one cannot completely rule out the possibility of unknown satellites (or debris), we find that either the chance probabilities of being a satellite estimated by these authors have been largely overestimated or their identified satellites have been ruled out in our original analysis. Our new calculations show that the probability of GN-z11-flash being a satellite is still lower than that of it being a signal originated from GN-z11.
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