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Register a new userDouble-peaked Narrow Emission-line Galaxies in LAMOST Survey
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We outline a full-scale search for galaxies exhibiting double-peaked profiles of promi- nent narrow emission lines, motivated by the prospect of finding objects related to merging galaxies, and even dual active galactic nuclei candidates as by-product, from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) Data Re- lease 4. We assemble a large sample of 325 candidates with double-peaked or strong asymmetric narrow emission lines, with 33 objects therein appearing optically resolved dual-cored structures, close companions or signs of recent interaction on the Sloan Dig- ital Sky Survey images. A candidate from LAMOST (J074810.95+281349.2) is also stressed here based on the kinematic and spatial decompositions of the double-peaked narrow emission line target, with analysis from the cross-referenced Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey datacube. MaNGA en- ables us to constrain the origin of double peaks for these sources, and with the IFU data we infer that the most promising origin of double-peaked profiles for LAMOST J074810.95+281349.2 is the `Rotation Dominated + Disturbance structure.
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LAMOST has released more than two million spectra, which provide the opportunity to search for double-peaked narrow emission line (NEL) galaxies and AGNs. The double-peaked narrow-line profiles can be well modeled by two velocity components, respectively blueshifted and redshifted with respect to the systemic recession velocity. This paper presents 20 double-peaked NEL galaxies and AGNs found from LAMOST DR1 using a search method based on multi-gaussian fit of the narrow emission lines. Among them, 10 have already been published by other authors, either listed as genuine double-peaked NEL objects or as asymmetric NEL objects, the remaining 10 being first discoveries. We discuss some possible origins for double-peaked narrow-line features, as interaction between jet and narrow line regions, interaction with companion galaxies and black hole binaries. Spatially resolved optical imaging and/or follow-up observations in other spectral bands are needed to further discuss the physical mechanisms at work.
We present here the results from dual-frequency phase-referenced VLBI observations of the Seyfert galaxy KISSR1494, which exhibits double peaked emission lines in its SDSS spectrum. We detect a single radio component at 1.6 GHz, but not at 5 GHz implying a spectral index steeper than $-1.5pm0.5$ ($S_ upropto u^alpha$). The high brightness temperature of the radio component ($sim1.4times10^7$ K) and the steep radio spectrum support a non-thermal synchrotron origin. A crude estimate of the black hole mass derived from the $M_{BH}-sigma_{star}$ relation is $sim1.4pm1.0times10^8$ Msun; it is accreting at an Eddington rate of $sim0.02$. The radio data are consistent with either the radio emission coming from the parsec-scale base of a synchrotron wind originating in the magnetised corona above the accretion disk, or from the inner ionised edge of the accretion disk or torus. In the former case, the narrow line region (NLR) clouds may form a part of the broad outflow, while in the latter, the NLR clouds may form a part of an extended disk beyond the torus. The radio and NLR emission may also be decoupled so that the radio emission originates in an outflow while the NLR is in a disk, and vice versa. While with the present data, it is not possible to clearly distinguish between these scenarios, there appears to be greater circumstantial evidence supporting the coronal wind picture in KISSR1494. From the kiloparsec-scale radio emission, the time-averaged kinetic power of this outflow is estimated to be $Qapprox1.5times10^{42}$ erg s$^{-1}$, which is typical of radio outflows in low-luminosity AGN. This supports the idea that radio jets and outflowing coronal winds are indistinguishable in Seyfert galaxies.
Double-peaked emission line AGN (DPAGN) have been regarded as binary black hole candidates. We present here results from parsec-scale radio observations with the Very Long Baseline Array (VLBA) of five DPAGN belonging to the KISSR sample of emission-line galaxies. This work concludes our pilot study of nine type 2 Seyfert and LINER DPAGN from the KISSR sample. In the nine sources, dual compact cores are only detected in the offset AGN, KISSR 102. The overall incidence of jets however, in the eight sources detected with the VLBA, is $ge$60%. We find a difference in the missing flux density going from the Very Large Array (VLA) to VLBA scales between Seyferts and LINERs, with LINERs showing less missing flux density on parsec-scales. Using the emission-line modeling code, MAPPINGS III, we find that the emission lines are likely to be influenced by jets in 5/9 sources. Jet-medium interaction is the likely cause of the emission-line splitting observed in the SDSS spectra of these sources. Jets in radio-quiet AGN are therefore energetically capable of influencing their parsec- and kpc-scale environments, making them agents of radio AGN feedback, similar to radio-loud AGN.
AGN with double-peaked narrow lines (DPAGN) may be caused by kiloparsec scale binary AGN, bipolar outflows, or rotating gaseous disks. We examine the class of DPAGN in which the two narrow line components have closely similar intensity as being especially likely to involve disks or jets. Two spectroscopic indicators support this likelihood. For DPAGN from Smith et al. (2010), the equal-peaked objects (EPAGN) have [Ne V]/[O III] ratios lower than for a control sample of non-double peaked AGN. This is unexpected for a pair of normal AGN in a galactic merger, but may be consistent with [O III] emission from a rotating ring with relatively little gas at small radii. Also, [O III]/H-beta ratios of the redshifted and blueshifted systems in the EPAGN are more similar to each other than in a control sample, suggestive of a single ionizing source and inconsistent with the binary interpretation.
Double-peaked emission lines in the narrow- and/or broad-line spectra of AGN have been suggested to arise due to disky broad/narrow line regions, jet-medium interaction, or the presence of binary supermassive black holes. We present the results from 1.5 and 4.9 GHz phase-referenced Very Long Baseline Interferometry (VLBI) observations of the Seyfert type 2 galaxy KISSR 434, which exhibits double-peaked emission lines in its optical spectrum. We detect a steep-spectrum ($alpha<-1$), curved and long (~150 parsec) jet in the VLBI images of KISSR 434. The jet curvature could be a result of precession rather than ram-pressure bending from a rotating ISM. Precession could in turn arise due to a warped accretion disk or the presence of a binary black hole with a separation of 0.015 parsec, not accessible to present day telescopes. An examination of the emission line ratios with the MAPPINGS III code reveals that AGN photoionization is likely to be responsible for the observed line ratios and not shock-ionization due to the jet. A light (with jet-to-ambient medium density ratio of $etasim0.01$) and fast (with speed $v_jgtrsim0.75c$) precessing jet in KISSR 434 may have stirred up the emission-line gas clouds to produce the observed splits in the narrow line peaks but is not powerful enough to shock-ionise the gas.
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