The current status of galaxy formation

Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.

SDSS J1042-0018:a Broad Line AGN but Misclassified as an HⅡGalaxy in the BPT Diagram by Flux Ratios of Narrow Emission Lines

In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN).The emission lines around Hαand around Hβare 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 fiuxes,but the different narrow emission line fiux ratios lead SDSS J1042-0018 as an H II galaxy in the BPT diagram.In order to explain the unique properties of the misclassified broad line AGN SDSS J1042-0018,two methods are proposed,the star-forming contributions and the compressed narrow emission line regions with high electron densities near to critical densities of forbidden emission lines.Fortunately,the strong star-forming contributions can be preferred in SDSS J1042-0018.The misclassified broad line AGN SDSS J1042-0018,well explained by star-forming contributions,could provide further clues on the applications of BPT diagrams to the normal broad line AGNs.

UV and X-ray variability of the narrow-line Seyfert 1 galaxy Ark 564

We analyze eight XMM-Newton observations of the bright Narrow Line Seyfert 1 galaxy Arakelian 564（Ark 564）. These observations, separated bye^6 days, allow us to look for correlations between the simultaneous ultraviolet（UV） emission（from th Optical Monitor） with not only the X-ray flux but also with different X-ray spectral parameters. The X-ray spectra from all the observations are found to be adequately fitted by a double Comptonization model where the soft excess and the hard X-ray power law are represented by thermal Comptonization in a low temperature plasma and hot corona, respectively. Apart from the fluxes of each component, the hard X-ray power law index is found to be variable. These results suggest that the variability is associated with changes in the geometry of the inner region. The UV emission is found to be variable and well correlated with the high energy index while the correlations with the fluxes of each component are found to be weaker. Using viscous timescale arguments we rule out the possibility that the UV variation is due to the fluctuating accretion rate in the outer disk. If the UV variation is driven by X-ray reprocessing, then our results indicate that the strength of the X-ray reprocessing depends more on the geometry of the X-ray producing inner region rather than on the X-ray luminosity alone.

Is TOL 1326–379 a Prototype ofγ-Ray Emitting FR0 Radio Galaxy?

With the possible spacial association to the Fermi/LAT source 3 FGL J 1330.0-3818,TOL 1326-379 may be the first one that is identified as a 7-ray emitting Fanaroff-Riley type 0 radio galaxy(FRO RG).We analyze the~12 yr Fermi/LAT observation data of thisγ-ray source and examine its association to TOL 1326-379.We show that theγ-ray source(named as J1331.0-3818)is tentatively detected with a TS value of 28.7,3 FGL J 1330.0-3818 is out of the 95%containment of J1331.0-3818,and their positions are spatially separated~0°.2.4 FGL J1331.3-3818 falls into the 68%containment of J1331.0-3818,suggesting that our result agrees with that reported in the Fourth Fermi LAT Source Catalog.TOL 1326-379 is out of the 95%containment of J1331.0-3818,and their positions are spatially separated~0°.4,indicating that the association between J1331.0-3818 and TOL 1326-379 is quite ambiguous.However,we do not find other possible potential radio or X-ray counterpart within the circle centered at J1331.0-3818 with a radius of 0°.4.The spectral energy distribution(SED)of TOL 1326-379 shows a bimodal feature as seen in theγ-ray emitting RGs.We fit the SED with the one-zone leptonic model and find that the average energy spectrum of J1331.0-3818 agrees with the model prediction.Assuming that J1331.0-3818 is an unidentified 7-ray source,we derive the upper-limit of theγ-ray flux for TOL 1326-379.It is not tight enough to exclude this possibility with the SED modeling.Based on these results,we cautiously argue that theγ-ray source J1331.0-3818 is associated with TOL 1326-379 and its jet radiation physic is similar to thoseγ-ray emitting RGs.

Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy

Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank （RGB） catalog are presented （Brinkmann et al. 1997） which have been spectroscopically observed in the Sloan Digital Sky Survey （SDSS） DR5. The SDSS spectra of the optical counterparts are modeled in a careful and selfconsistent way by incorporating the host galaxy＇s starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4- 5 GHz spectral indices estimated using （non-simultaneous） archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei （AGNs）, particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies （NLRGs）, as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs （low-ionization nuclear emission regions）, based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to ＇weak line radio galaxies＇, are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 10623 - 10^26 W Hz^- 1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies （NLS 1 s）, a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs （HBLs）, as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.

The inner～40 pc radial distribution of the star formation rate for a nearby Seyfert 2 galaxy M51

We investigate the spatially resolved specific star formation rate （SSFR） in the inner -40 pc for a nearby Seyfert 2 galaxy, M51 （NGC 5194） by analyzing spectra obtained with the Hubble Space Telescope （HST） Space Telescope Imaging Spectrograph （STIS）. We present 24 radial spectra measured along the STIS long slit in M51, extending - 1＂ from the nucleus （i.e., -41.5 pc to 39.4 pc）. By simple stellar population synthesis, the stellar contributions in these radial optical spectra are modeled. It is found that the mean flux fraction of young stellar populations （younger than 24.5 Myr） is about 9%. Excluding some regions with zero young flux fraction near the center （from -6 pc to 2 pc）, the mean mass fraction is about 0.09%. The young stellar populations are not required in the center inner -8 pc in M51, suggesting a possible SSFR suppression in the circumnuclear region （- 10 pc） from the feedback of active galactic nuclei （AGNs）. The radial distribution of SSFR in M51 is not symmetrical with respect to the long slit in STIS. This unsymmetrical SSFR distribution is possibly due to the unsymmetrical AGN feedback in M51, which is related to its jet.

XMM-Newton observations of H_2O maser galaxy NGC 7479

The XMM-Newton observations of H2O megamaser galaxy NGC 7479 are presented. Its smoothed X-ray image clearly shows spiral morphology, which matches well with its optical asymmetric spiral structure. One prominent source can be found at the tip of its northern spiral arm, which is much brighter than its nuclear X-ray source （about a 50% higher count rate）. For the nuclear source （a circular region with a radius of 20 ″）, the spectra show soft excess below 2 keV and a strong iron Kα emission line. The best fitting model includes a partially absorbed model for the hard continuum and one thermal plasma model for the soft scatter component. Both the high column density （NH - 6.88 × 10^23 cm^-2） and strong fluorescent iron line （with an equivalent width of - 1.5 keV） support the existence of one heavily obscured AGN. For the bright prominent source, its radial profile is consistent with that of a single point-like source. Its spectra are extracted from the circular region around its peak, with a radius of 20″ and 6″ respectively and both spectra show models for the ultra-luminous X-ray source no significant difference. Four alternative （ULXs） can reproduce the spectra well： an absorbed power law, thermal bremsstrahlung, multicolor blackbody disk plus another blackbody or power law. Further observations （e.g., the tremendous improvement in the spatial resolution of the Chandra X-ray observations） and studies are desirable for probing the nature of this prominent source. In addition, we also estimate the mass of its central engine to be 1.18 × 10^7 M⊙ and maser disk parameters： the disk radius of -0.7 pc and the dimensionless accretion rate （L2-10kev/LEdd） of 1.2 × 10^-4.

Optical monitoring of the Seyfert galaxy NGC 4151 and possible periodicities in its historical light curve

We report B, V and R band CCD photometry of the Seyfert galaxy NGC 4151 obtained with the 1.0m telescope at Weihai Observatory of Shandong University and the 1.56 m telescope at Shanghai Astronomical Observatory from 2005 December to 2013 February. Combining all available data from literature, we have constructed a historical light curve from 1910 to 2013 to study the periodicity of the source using three different methods （the Jurkevich method, the Lomb-Scargle periodogram method and the Discrete Correlation Function method）. We find possible periods of P1 = 4 ± 0.1,/92 = 7.5 ±0.3 and P3 = 15.9± 0.3 yr.

The photometric monitoring of γ-ray-loud narrow-line Seyfert 1 galaxy 1H0323+342 from 2006 to 2010

1H 0323＋342 is a γ-ray-loud narrow-line Seyfert 1 galaxy（NLS1）. The variability mechanism of γ-ray-loud NLS1 s remains unclear. We have observed 1H 0323＋342 photometrically from 2006 to2010 with a total of 41 nights of observations in order to constrain the variability mechanism. Intraday variabilities（IDVs） are detected on four nights. When considering the nights with time spans 〉 2 hours,the duty cycle is 28.3%. The average variability amplitude is 10.8% for IDVs and possibly variable nights. In the color-magnitude diagram, there are bluer-when-brighter chromatic trends for intraday and long-term timescales, which could be explained by the shock-in-jet model, and also could possibly be due to two distinct components or an accretion disk model.

A study of active galactic nuclei in low surface brightness galaxies with Sloan Digital Sky Survey spectroscopy

Active galactic nuclei （AGNs） in low surface brightness galaxies （LSBGs） have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. （1996） APM LSBG sample which has been observed spectroscopically by the Sloan Digital Sky Survey Data Release 5 （SDSS DR5）. Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear processes in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% of LSBGs. We find that, contrary to some previous claims, the fraction of galaxies that contain AGNs is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. This result holds true even within each morphological type from Sa to Sc. LSBGs that have larger central stellar velocity dispersions or larger physical sizes tend to have a higher chance of harboring an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-σ. relation established for normal galaxies and AGNs.

Geometry of Broad Line Regions of Active Galactic Nuclei

It has long remained an open question as to the geometry of the broad line region （BLR） in active galactic nuclei （AGNs）. The reverberation mapping technique which measures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by CoUin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value LBol/LEdd - 0.1. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR.

Multicolor Optical Monitoring of the γ-Ray Emitting Narrow-line Seyfert 1 Galaxy PMN J0948+0022 from 2020 to 2021

In order to study the physical properties of the γ-ray emitting narrow-line Seyfert 1(NLS1) galaxy population,photometric and spectral observations of the γ-ray emitting NLS1 PMN J0948+0022 were made with the Lijiang2.4 m optical telescope of Yunnan Observatories,Chinese Academy of Sciences.Photometric data in the B and R bands were collected for 50 nights from 2020 January to 2021 December.During the observation epoch,the variability amplitudes are 73.67% in the B band and 79.96% in the R band.Intra-day variability is found in two observation nights,and the duty cycle value is 29% with variability amplitude> 12.9% in the R band,which support the presence of the relativistic jets in the target.The redder-when-brighter(RWB) chromatic trend(or steeper-when-brighter trend) appears on intra-day and long timescales.The RWB trend is dominated by the radiation of accretion disk and jet,and resembles those in flat spectrum radio quasars.When PMN J0948+0022 is brighter than 17.5 in the R band,there is no color change trend.By analyzing the spectral data of PMN J0948+0022,we obtained the black hole mass of M.=1.61×10^(7) Mand accretion rate of M=93,and confirmed that PMN J0948+0022 is a super-Eddington accreting NLS1.The redshifts of reverberation mapped super-Eddington accreting active galactic nuclei can be expanded by PMN J0948+0022 up to above 0.5.Super-Eddington accreting NLS1 galaxies were chosen as a new type of cosmological candle in the literature.PMN J0948+0022 may be used as a target for the next step of reverberation mapping monitoring project of super-Eddington accreting massive black holes.

Do Radio-loud Active Galactic Nuclei really follow the same M_(BH)-σ_* Relation as Normal Galaxies?

In an examination of the relationship between the black hole mass MBH and stellar velocity dispersion σ＊ in radio-loud active galactic nuclei （AGNs）, we studied two effects which may cause uncertainties in the black hole mass estimates of radio-loud AGNs： the relativistic beaming effect on the observed optical continuum radiation and the orientation effect on the broad emission line width. After correcting these two effects, we re-examined the MBH- σ[OIII] relation for a sample of radio-loud and radio-quiet AGNs, and found the relation for radio-loud AGNs still deviated from that for nearby normal galaxies and radio-quiet AGNs. We also found there is no significant correlation between radio jet power and narrow [OIII] line width, indicating absence of strong interaction between radio jet and narrow line region. It may be that the deviation of the MBH-σ＊ relation of radio-loud AGNs is intrinsic, or that the [OIII] line width is not a good indicator of σ＊ for radio-loud AGNs.

East Asian VLBI Network observations of active galactic nuclei jets:imaging with KaVA+Tianma+Nanshan

The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions.After the combination of the Korean VLBI Network(KVN) and the VLBI Exploration of Radio Astrometry(VERA) into Ka VA,further expansion with the joint array in East Asia is actively promoted.Here we report the first imaging results(at 22 and 43 GHz) of bright radio sources obtained with Ka VA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China.To test the EAVN imaging performance for different sources,we observed four active galactic nuclei(AGN) having different brightness and morphology.As a result,we confirmed that the Tianma 65-m Radio Telescope(TMRT) significantly enhances the overall array sensitivity,a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of Ka VA only.The addition of the Nanshan 26-m Radio Telescope(NSRT) further doubled the east-west angular resolution.With the resulting high-dynamic-range,high-resolution images with EAVN(Ka VA+TMRT+NSRT),various fine-scale structures in our targets,such as the counter-jet in M87,a kink-like morphology of the 3 C 273 jet and the weak emission in other sources are successfully detected.This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general.Ongoing expansion of EAVN will further enhance the angular resolution,detection sensitivity and frequency coverage of the network.

Observational signatures of close binaries of supermassive black holes in active galactic nuclei

Inspired by the General Relativity for many decades,experimental physicists and astronomers have a solid dream to detect gravitational waves(GWs)from mergers of black holes,which came true until the excellent performance of the Laser Interferometer Gravitational-Wave Observatory(LIGO)at hundreds Hz.Nano-Hz GWs are expected to be radiated by close-binaries of supermassive black holes(CB-SMBHs;defined as those with separations less than^0.1 pc)formed during galaxy mergers and detected through the Pulsar Timing Array(PTA)technique.As of the writing,there remains no nano-Hz GWs detection.Searching for CB-SMBHs is also observationally elusive though there exist a number of possible candidates.In this review,we focus on observational signatures of CB-SMBHs from theoretic expectations,simulations and observations.These signatures appear in energy distributions of multiwavelength continuum,long term variations of continuum,jet morphology,reverberation delay maps and spectroastrometry of broad emission lines,AGN type transitions between type-1 and type-2(changing-look),and gaseous dynamics of circumbinary disks,etc.Unlike hundred-Hz GWs from stellar mass black hole binaries,the waveform chirping of nano-Hz GWs is too slow to detect in a reasonable human timescale.We have to resort to electromagnetic observations to measure orbital parameters of CB-SMBHs to test nano-Hz GW properties.Reverberation mapping is a powerful tool for probing kinematics and geometry of ionized gas in the gravitational well of SMBHs(single or binary)and therefore provides a potential way to determine orbital parameters of CB-SMBHs.In particular,a combination of reverberation mapping with spectroastrometry(realized at the Very Large Telescope Interferometer)will further reinforce this capability.The Atacama Large Millimeter/submillimeter Array(ALMA)and the forthcoming Square Kilometre Array(SKA)are suggested to reveal dynamics of circumbinary disks through molecular emission lines.

The Origin of The Soft X-Ray Excess in the Seyfert 1.5 Galaxy ESO 362-G18

We review the Seyfert 1.5 Galaxy ESO 362-G18 for exploring the origin of the soft X-ray excess.The Warm Corona and Relativistic Reflection models are two main scenarios to interpret the soft X-ray excess in active galactic nuclei at present.We use the simultaneous X-ray observation data of XMM-Newton and Nu STAR on2016 September 24 to perform spectral analysis in two steps.First,we analyze the time-average spectra by using Warm Corona and Relativistic Reflection models.Moreover,we also explore the Hybrid model,Double Reflection model and Double Warm Corona model.We find that both the Warm Corona and Relativistic Reflection models can interpret the time-average spectra well but cannot be distinguished easily based on the time-averaged spectra fit statistics.Second,we add the rms and covariance spectra to perform the spectral analysis with time-average spectra.The result shows that the warm corona could reproduce all of these spectra well.The hot,optical thin corona and neutral distant reflection will increase their contribution with the temporal frequency,meaning that the corona responsible for X-ray continuum comes from the inner compact X-ray region and the neutral distant reflection is made of some moderate scale neutral clumps.

Fermi/LAT observations of lobe-dominant radio galaxy 3C 207 and possible radiation region of γ-rays

3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data acquired during the past 9 years. Different from the radio and optical emission from the core, it is found that theγ-ray emission is steady without detection of flux variation at over a 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical and X-ray data of knot-A,the closest knot from the core at 1.4′′, and compile its spectral energy distribution(SED). Although the single-zone synchrotron+SSC+IC/CMB model that assumes knot-A is at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates from the equipartition condition by 3 orders of magnitude. Assuming that knot-A is moving relativistically, its SED from radio to γ-ray bands would be represented well with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition. These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with radio data.

X-ray source population in the polar ring galaxy NGC 660 as observed by Chandra

We present Chandra observations of the nearby polar ring galaxy NGC 660 to study its X-ray source population.Based on our analysis,we detected a total of 23 X-ray sources in the 0.5-8 keV band,with luminosities ranging from~1037 to~1039 erg s-1.Twenty-two of these sources are located offnuclear and have luminosities below the ultraluminous X-ray source(ULX)threshold value of L0.5-8 keV<1039 erg s-1,suggesting that they are likely to be X-ray binary(XRB)candidates.The remaining source is located at the center of the galaxy,suggesting it is an active galactic nucleus(AGN).However,we estimated that four of the detected sources could be associated with background objects.Based on the source count rates in each of the Chandra observations,we found evidence for variability in nine of the 23 sources,including the AGN.However,further investigation with spectral analysis suggested no significant differences in the AGN luminosities between the observations.The X-ray luminosity distribution of the galaxy was found to be generally lower than that expected from previous studies on star forming and collisional ring galaxies.No ULX was also detected in the galaxy,in contrast with what was expected from the galaxy’s SFR and metallicity(i.e.,SFR=14.43±0.19 M⊙yr-1 and Z=0.94±0.01 Z⊙,respectively).These results suggest a deficit in the X-ray sources detected.Based on source hardness ratio distribution,we found evidence that the fainter sources have a harder source spectrum,indicating higher absorption.This further suggests that there could be more X-ray sources that were not detected in the galaxy due to significant obscuration.

The Origin of Infrared Emission from the Infrared Luminous Galaxy NGC 4418

We present a study of the origin of infrared (IR) emission in the opticallynormal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features andcontinua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellarpopulations, we derive the stellar properties for the nuclear region of NGC 4418. We compare theobserved infrared luminosity with the one derived from the starburst model, and find thatstar-forming activity contributes only 7% to the total IR emission, that as the IR emission regionis spatially very compact, the most possible source for the greater part of the IR emission is adeeply embedded AGN, though an AGN component is found to be unnecessary for fitting the opticalspectrum.

AGN Lifetimes in UV-selected Galaxies: A Clue to Supermassive Black Hole-galaxy Coevolution

The coevolution between supermassive black holes(SMBHs) and their host galaxies has been proposed for more than a decade,albeit with little direct evidence about black hole accretion activities regulating galaxy star formation at z> 1.In this paper,we study the lifetimes of X-ray active galactic nuclei(AGNs) in UV-selected red sequence(RS),blue cloud(BC) and green valley(GV) galaxies,finding that AGN accretion activities are most prominent in GV galaxies at z ~1.5-2,compared with RS and BC galaxies.We also compare AGN accretion timescales with typical color transition timescales of UV-selected galaxies.We find that the lifetime of GV galaxies at z~1.5-2 is very close to the typical timescale when the AGNs residing in them stay in the high-accretion-rate mode at these redshifts;for BC galaxies,the consistency between the color transition timescale and the black hole strong accretion lifetime is more likely to happen at lower redshifts(z <1).Our results support the scenario where AGN accretion activities govern UV color transitions of host galaxies,making galaxies and their central SMBHs coevolve with each other.