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Register a new userThe AKARI 2.5-5.0 Micron Spectral Atlas of Type-1 Active Galactic Nuclei: Black Hole Mass Estimator, Line Ratio, and Hot Dust Temperature
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We present 2.5-5.0 $mu$m spectra of 83 nearby ($0.002,<,z,<,0.48$) and bright ($K<14$mag) type-1 active galactic nuclei (AGNs) taken with the Infrared Camera (IRC) on board $it{AKARI}$. The 2.5-5.0 $mu$m spectral region contains emission lines such as Br$beta$ (2.63 $mu$m), Br$alpha$ (4.05 $mu$m), and polycyclic aromatic hydrocarbons (PAH; 3.3 $mu$m), which can be used for studying the black hole (BH) masses and star formation activities in the host galaxies of AGNs. The spectral region also suffers less dust extinction than in the ultra violet (UV) or optical wavelengths, which may provide an unobscured view of dusty AGNs. Our sample is selected from bright quasar surveys of Palomar-Green (PG) and SNUQSO, and AGNs with reverberation-mapped BH masses from Peterson et al. (2004). Using 11 AGNs with reliable detection of Brackett lines, we derive the Brackett-line-based BH mass estimators. We also find that the observed Brackett line ratios can be explained with the commonly adopted physical conditions of the broad line region (BLR). Moreover, we fit the hot and warm dust components of the dust torus by adding photometric data of SDSS, 2MASS, $it{WISE}$, and $it{ISO}$ to the $it{AKARI}$ spectra, finding hot and warm dust temperatures of $sim1100,rm{K}$ and $sim220,rm{K}$, respectively, rather than the commonly cited hot dust temperature of 1500 K.
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Black hole (BH) mass of Type I active galactic nuclei (AGN) can be measured or estimated through either reverberation mapping (RM) or empirical $R-L$ relation, however, both of them suffer from uncertainties of the virial factor ($f_{rm BLR}$), thus limiting the measurement accuracy. In this letter, we make an effort to investigate $f_{rm BLR}$ through polarised spectra of the broad-line regions (BLR) arisen from electrons in the equatorial plane. Given the BLR composed of discrete clouds with Keplerian velocity around the central BH, we simulate a large number of spectra of total and polarised flux with wide ranges of parameters of the BLR model and equatorial scatters. We find that the $f_{rm BLR}$-distribution of polarised spectra is much narrower than that of total ones. This provides a way of n accurately estimating BH mass from single spectropolarimetric observations of type I AGN whose equatorial scatters are identified.
We use 317,000 emission-line galaxies from the Sloan Digital Sky Survey to investigate line-ratio selection of active galactic nuclei (AGNs). In particular, we demonstrate that star formation dilution by HII regions causes a significant bias against AGN selection in low-mass, blue, star-forming, disk-dominated galaxies. This bias is responsible for the observed preference of AGNs among high-mass, green, moderately star-forming, bulge-dominated hosts. We account for the bias and simulate the intrinsic population of emission-line AGNs using a physically-motivated Eddington ratio distribution, intrinsic AGN narrow line region line ratios, a luminosity-dependent Lbol/L[OIII] bolometric correction, and the observed Mbh-sigma relation. These simulations indicate that, in massive (log(M*/Msun) > 10) galaxies, AGN accretion is correlated with specific star formation rate but is otherwise uniform with stellar mass. There is some hint of lower black hole occupation in low-mass (log(M*/Msun) < 10) hosts, although our modeling is limited by uncertainties in measuring and interpreting the velocity dispersions of low-mass galaxies. The presence of star formation dilution means that AGNs contribute little to the observed strong optical emission lines (e.g., [OIII] and Ha) in low-mass and star-forming hosts. However the AGN population recovered by our modeling indicates that feedback by typical (low- to moderate-accretion) low-redshift AGNs has nearly uniform efficiency at all stellar masses, star formation rates, and morphologies. Taken together, our characterization of the observational bias and resultant AGN occupation function suggest that AGNs are unlikely to be the dominant source of star formation quenching in galaxies, but instead are fueled by the same gas which drives star formation activity.
Using different kinds of velocity tracers derived from the broad H$beta$ profile (in the mean or rms spectrum) and the corresponding virial factors $f$, the central supermassive black hole (SMBH) masses ($M_{rm BH}$) are calculated for a compiled sample of 120 reverberation-mapped (RM) AGNs. For its subsample of RM AGNs with measured stellar velocity dispersion ($sigma_{rm ast}$), the multivariate linear regression technique is used to calibrate the mean value $f$, as well as the variable FWHM-based $f$. It is found that, whether excluding the pseudo-bulges or not, $M_{rm BH}$ from the H$beta$ line dispersion in the mean spectrum ($sigma_{rm Hbeta,mean}$) has the smallest offset rms with respect to the $M_{rm BH}-sigma_{ast}$ relation. For the total sample excluding SDSS-RM AGNs, with respect to $M_{rm BH}$ from $sigma_{rm ast}$ or that from the H$beta$ line dispersion in the rms spectrum ($sigma_{rm Hbeta,rms}$), it is found that we can obtain $M_{rm BH}$ from the $sigma_{rm Hbeta,mean}$ with the smallest offset rms of 0.38 dex or 0.23 dex, respectively. It implies that, with respect to the H$beta$ FWHM, we prefer $sigma_{rm Hbeta,mean}$ to calculate $M_{rm BH}$ from the single-epoch spectrum. Using the FWHM-based $f$, we can improve $M_{rm BH}$ calculation from FWHM(H$beta$) and the mean $f$, with a decreased offset rms from 0.52 dex to 0.39 dex with respect to $M_{rm BH}$ from $sigma_{rm ast}$ for the subsample of 36 AGNs with $sigma_{rm ast}$. The value of 0.39 dex is almost the same as that from $sigma_{rm Hbeta,mean}$ and the mean $f$.
A statistical study of intermediate Palomar Transient Factory supernovae (SNe) in Type 1 AGN has shown a major deficit of supernovae around Type 1 AGN host galaxies, with respect to Type 2 AGN hosts. The aim of this work is to test whether there is any preference for Type 1 AGN to host SN of a specific kind. Through the analysis of SN occurrence and their type (thermonuclear vs core-collapse), we can directly link the type of stars producing the SN events, thus this is an indirect way to study host galaxies in Type 1 AGN. We examine the detection fractions of SNe, the host galaxies and compare the sample properties to typical host galaxies in the Open Supernova Catalog (OSC; Guillochon et al. 2017). The majority of the host galaxies in the AGN sample are late-type, similar to typical galaxies hosting SN within the OSC. The findings are supportive of a deficiency of SNe near Type 1 AGN, although we cannot with certainty assess the overall detection fractions of SNe in Type 1 AGN relative to other SN host galaxies. We can state that Type 1 AGN has equal detection fractions of thermonuclear vs core-collapse SNe. However, we note the possibility of a higher detection rate of core-collapse supernovae in Type-1 AGN with insecure AGN classifications.
The unified model of active galactic nuclei (AGNs) proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring torus. Therefore, this model predicts that type 1 and type 2 AGNs should have similar host-galaxy properties. We investigate this prediction with 2463 X-ray selected AGNs in the COSMOS field. We divide our sample into type 1 and type 2 AGNs based on their spectra, morphologies, and variability. We derive their host-galaxy stellar masses ($M_star$) through SED fitting, and find that the host $M_star$ of type 1 AGNs tend to be slightly smaller than those of type 2 AGNs by $Deltaoverline{mathrm{log}M_star}approx0.2~mathrm{dex}$ ($approx 4sigma$ significance). Besides deriving star-formation rates (SFRs) from SED fitting, we also utilize far-infrared (FIR) photometry and a stacking method to obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are similar once their redshifts and X-ray luminosities are controlled. We also investigate cosmic environment, and find that the surface number densities (sub-Mpc) and cosmic-web environments ($approx 1text{--}10$~Mpc) are similar for both populations. In summary, our analyses show that the host galaxies of type 1 and type 2 AGNs have similar SFR and cosmic environment in general, but the former tend to have lower $M_star$ than the latter. The difference in $M_star$ indicates that the AGN unification model is not strictly correct and both host galaxy and torus may contribute to the optical obscuration of AGNs.
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