Relation between Starlight and Nebular Emission Lines of Star-Forming Galaxies

We present an exercise that intends to establish a relationship between the strength of nebular emission lines and optical stellar features in the spectrum of a galaxy. After accurately subtracting the stellar continuum and the underlying stellar absorption, we made reliable measurements of the emission lines of all the galaxies in the Sloan Digital Sky Survey Data Release 2 (SDSS DR2). More than 4000 star-forming galaxies with high S/N ratio of both the stellar spectrum and the emission lines are selected. These galaxy spectra are fitted with the 10 PCs of Yip et al., after all the emission line regions have been filtered out. We find that the flux of hydrogen Balmer emission lines, Hα and Hβ can be well recovered from the PCs, while the metal lines are not well reproduced. The fluxes of Hα and Hβ measured from the PC-reconstructed spectra and from the observed spectra agree well with an rms scatter of only - 0.1 dex. This result suggests that, with moderate spectral resolution and S/N ratio, the optical stellar spectrum of a galaxy can serve as an indicator of star formation rate.     

Elliptical Galaxies with Emission Lines from the Sloan Digital Sky Survey

As part of a study of star formation history along the Hubble sequence, we present here the results for 11 elliptical galaxies with strong nebular emission lines.After removing the dilution from the underlying old stellar populations by use of stellar population synthesis model,we derive the accurate fluxes of all the emission lines in these objects,which are then classified,using emission line ratios, into one Seyfert 2,six LINERs and four HII galaxies.We also identify one HII galaxy (A1216 04)as a hitherto unknown Wolf-Rayet galaxy from the presence of the Wolf- Rayet broad bump at 4650 (?).We propose that the star-forming activities in elliptical galaxies are triggered by either galaxy-galaxy interaction or the merging of a small satellite/a massive star cluster,as has been suggested by recent numerical simulations.     

Spectral principal component analysis of the Hβ region of low-redshift SDSS quasars

Studying the relationships among quasar spectral features is essential to unveil the origins of the emission lines and the quasars' physical processes. Principal component analysis(PCA) is a powerful tool to investigate correlations between variables. Here, we present the results of PCA on the spectra of low-redshift SDSS quasars. The rest-frame wavelength range studied is 4000 – 5500 ?, involving some typical features of quasar spectra, such as Hβ, [O Ⅲ] and Fe Ⅱ emission lines. The first principal component is the anti-correlation between [O Ⅲ] and Fe Ⅱ, the well-known eigenvector one(EV1). The next six principal components also show clear(anti-)correlations between line strengths and/or velocity widths of various features, which agree well with measured spectral properties. By comparing the weights of these principal components with other quasar properties, we can identify their underlying drivers. We find that the second principal component represents spectral slope, and can quantify quasar host fraction, intrinsic slope and reddening well. The third component exhibits the velocity width variation of Hβ, and may be a proxy for orientation. In addition, we calculate the fractional-contribution spectra to investigate which components dominate the variance at individual wavelength ranges. Our results also indicate that the optical Fe Ⅱ emission may have distinct origins.     

C~(18)O Observations of the Dark Molecular Cloud L134 and Gas Depletion onto Dust

We map the dark molecular cloud core of L134 in the C18O (J = 1 - 0) emission line using the PMO 13.7m telescope, and present a contour map of integrated intensity of C18O (J = 1 - 0) emission. The C18O cloud is inside the distribution of extinction AB, the visual extinction of blue light, as well as inside the 13CO cloud in the L134 region. The depletion factors in this C18O cloud are generally greater than unity, which means there is gas depletion onto dust. Since only a minimum AB = 9.7 mag is available, and our observations measure both undepleted and depleted regions along the line of sight, the depletion factors could very likely be larger in the central core than the calculated value. So we conclude that depletion does occur in the bulk of the C18O cloud through a comparison between the C18O and blue extinction maps in the L134 region. There is no direct evidence as yet for star formation in L134, and so cores on the verge of collapse will not be visible in CO and other gas molecules.     

The comparison of H_2CO(1_(10)–1_(11)),C~(18)O(1–0) and the continuum towards molecular clouds

We present large scale observations of C18O(1–0) towards four massive star forming regions: MON R2,S156,DR17/L906 and M17/M18. The transitions of H2CO(110–111),C18O(1–0) and the 6 cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non–LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 – 8 K. The excitation of the H2 CO absorption line is affected by strong background continuum emission. From a comparison of H2 CO and C18 O maps,we found that the extent of H2 CO absorption is broader than that of C18 O emission in the four regions. Except for the DR17 region,the maximum in H2 CO absorption is located at the same position as the C18 O peak. A good correlation between intensities and widths of H2 CO absorption and C18 O emission lines indicates that the H2 CO absorption line can trace the dense,warm regions of a molecular cloud. We find that N(H2CO) is well correlated with N(C18O) in the four regions and that the average ratio of column densities is N(H2CO)/N(C18O) ～ 0.03.     

Quasar SDSS J142507.32+323137.4: dual AGNs?

We analyze the optical spectrum of type 1 QSO SDSS J1425+3231.This object is interesting since its narrow emission lines,such as O IIIλλ4959,5007,are double-peaked,and the line structure can be modeled well by three Gaussian components:two components for the two peaks (we refer to the peaks at low/high redshift as the blue/red component) and another one for the line wing which has the same line center as that of the blue component,but is ～ 3 times broader.The separation between the blue and red components i...     

The Mg Ⅱ absorption line systems in quasar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Making use of quasar spectra from LAMOST,in the spectral data around the Mg Ⅱ emission lines,research described in this paper has detected 217 Mg Ⅱ narrow absorption lines(NALs) with W_r ~(λ2796)≥3σ_w and W_r~(λ2803)≥ 2σ_w in a redshift range of 0.4554≤z_(abs)≤2.1110.For quasars observed by both LAMOST and SDSS,we find that 135 Mg Ⅱ NALs were obviously observed in the LAMOST spectra,347 Mg Ⅱ NALs were were apparent in the SDSS spectra,and 132 Mg Ⅱ NALs were clearly present in both the SDSS and LAMOST spectra.The missed Mg Ⅱ NALs are likely ascribed to low signal-to-noise ratios of corresponding spectra.Among the Mg 11 NALs obviously observed in SDSS or LAMOST spectra,eight Mg 11 NALs were significantly changed with |ΔW_r ~(λ2796)|≥3σ_w in time intervals of ΔMJD/(1+z_(em))=359-2819 d.     

Origin and Properties of Strong MgⅡ Quasar Absorption Line Systems

Strong MgⅡ quasar absorption line systems provide us with a useful tool to understand the gas that plays an important role in galaxy formation. In this paper, placing the theories of galaxy formation in a cosmological context, we present semi-analytic models and Monte-Carlo simulations for strong MgⅡ absorbers produced in gaseous galactic haloes and/or galaxy discs. We investigate the redshift path density for the MgⅡ absorption lines and the properties of galaxy/absorber pairs, in particular the anti-correlation between the equivalent width of MgⅡ absorption line and the projected galaxy-to-sightline distance. The simulated result of the mean redshift path density of strong MgⅡ systems is consistent with the observational result. The fraction of strong MgⅡ systems arising from galaxy disks is predicted to be-10^ of the total. There exists an anti-correlation between the absorption line equivalent and the projected distance of sightline to galaxy center and galaxy luminosity.We determined that the mean absorbing radius Rabs≈29h^-1 kpc(LB/LB*)^0.35. After taking selection effects into consideration, this becomes Rabs≈38h^-1 kpc(LB/LB*)^0.18,which is in good agreement with the observational result. This shows the importance of considering selection effects when comparing models with observations.     

Analysis of the 3C 445 soft X-ray spectrum as observed by Chandra high-energy gratings

We present a detailed analysis of the soft X-ray emission of 3 C 445 using an archival Chandra High Energy Transmission Grating(HETG) spectrum. Highly-ionized H-and He-like Mg, Si and S lines, as well as a resolved low-ionized Si Kα line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X radiative recombination continua(RRC) feature in the spectrum seems to prefer a photoionized environment. The spectrum is subsequently modeled with a photoionization model, and the results are compared with those of a collisional model. Through a detailed analysis of the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are log ξ = 3.3_(-0.3)~(+0.4) erg cm s~(-1), n H = 5_(-4.5)~(+15)× 10~(10) cm~(-3) and NH = 2.5_(-1.7)~(+3.8)× 10~(20) cm~(-2).According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred radial distance(6 × 10~(14)-8 × 10~(15) cm), we suggest the emission lines originating from matter are located in the broad line region(BLR).     

A Study of the Star-forming Dwarf Galaxy NGC 855 with Spitzer

We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band Hα and Spitzer data. Both the Hα and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate (SFR) of 0.022 and 0.025M◎yr-1,respectively,from the Spitzer IRAC 8.0μm and MIPS 24μm emission data. The HI observa-tion suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0μm bands,located at about 10 away from the nucleus of NGC 855. Given the strong 8.0μm but faint Hα emission,we expect that it is a heavily obscured star-forming region,which needs to be confirmed by further optical spectroscopic observations.     

X-ray absorption and 9.7 μm silicate feature as a probe of AGN torus structure

The dusty torus plays a vital role in unifying active galactic nuclei(AGNs).However,the physical structure of the torus remains largely unclear.Here we present a systematical investigation of the torus mid-infrared(MIR) spectroscopic feature,i.e.,the 9.7μm silicate line,of 175 AGNs selected from the Swift/BAT Spectroscopic Survey(BASS).Our sample is constructed to ensure that each of the 175 AGNs has Spizter/IRS MIR,optical,and X-ray spectroscopic coverage.Therefore,we can simultaneously measure the silicate strength,optical emission lines,and X-ray properties(e.g.,the column density and the intrinsic X-ray luminosity).We show that,consistent with previous works,the silicate strength is weakly correlated with the hydrogen column density(N_H~X),albeit with large scatters.For X-ray unobscured AGNs,the silicate-strength-derived V-band extinction and the broad-Hα-inferred one are both small;however,for X-ray obscured AGNs,the former is much larger than the latter.In addition,we find that the optical type1 AGNs with strong X-ray absorption on average show significant silicate absorption,indicating that their X-ray absorption might not be caused by dust-free gas in the broad-line region.Our results suggest that the distribution and structure of the obscuring dusty torus are likely to be very complex.We test our results against the smooth and clumpy torus models and find evidence in favor of the clumpy torus model.     

X-ray Spectroscopy of Dips of Cir X-1

We present X-ray spectral analyses of the low-mass X-ray binary Cir X-1 dur- ing X-ray dips,using the Rossi X-ray Timing Explorer(RXTE)data.Each dip was divided into several segments,and the spectrum of each segment was fitted with a three-component blackbody model,in which the first two components are affected by partial covering and the third one is unaffected.A Gaussian emission line is also included in the spectral model to represent the Fe Kαline at～6.4 keV.The fitted temperatures of the two partially covered components are about 2 keV and 1 keV,while the uncovered component has a temperature of～0.5-0.6 keV.The equivalent blackbody emission radius of the hottest component is the smallest and that of the coolest component is the largest.During the dips the fluxes of the two hot components are linearly correlated,while that of the third component does not show any significant variation.The Fe line flux remains constant,within the errors,during the short dips.However,during the long dips the line flux varies significantly and is positively correlated with the fluxes of the two hot components.These results suggest:(1)that the tem- perature of the X-ray emitting region decreases with radius,(2)that the Fe Kαline emitting region is close to the hot continuum emitting region,and(3)that the size of the Fe line emit- ting region is larger than that of the obscuring matter causing the short dips but smaller than the region of that causing the long dips.     

The broad wing of the [O Ⅲ] λ5007 emission line in active galactic nuclei

We use a sample of type 2 active galactic nuclei(AGNs) from SDSS DR7 in which the [O III] λ5007 emission line can be modeled by two Gaussian components,a broad wing plus a narrow core,to investigate the origin of the broad wing and the connection between the velocity shift of the broad wing and the physical parameters of AGNs,as well as their host galaxies. We find that the flux of the wing components is statistically roughly equal to that of the core components. However,the velocity shift of the wing component has only weak,if any,correlations with the physical properties of AGNs and the host galaxies,such as bolometric luminosity,the Eddington ratio,the mass of supermassive black holes,D4000,HδAor stellar mass. Comparing the velocity shift from our type 2 AGN sample to that from the type 1 sample in Zhang et al.,we suggest that the [O III] broad wing originates from outflow.     

On the diffuse soft X-ray emission from the nuclear region of M51

We present an analysis of the diffuse soft X-ray emission from the nuclear region of M51 combining both XMM-Newton RGS and Chandra data.Most of the RGS spectrum of M51 can be fitted with a thermal model with a temperature of~0.5 ke V except for the O VII triplet,which is forbidden-line dominated.The Fe L-shell lines peak around the southern cloud,where the O VIII and N VII Lyαlines also peak.In contrast,the peak of the O VII forbidden line is about 10′′offset from that of the other lines,indicating that it is from a spatially distinct component.The spatial distribution of the O VII triplet mapped by the Chandra data shows that most of the O VII triplet flux is located at faint regions near edges,instead of the southern cloud where other lines peak.This distribution of the O VII triplet is inconsistent with the photoionization model.Other mechanisms that could produce the anomalous O VII triplet,including a recombining plasma and charge exchange X-ray emission,are discussed.     

Kinematic properties of the dual AGN system J0038+4128 based on long-slit spectroscopy

The study of kiloparsec-scale dual active galactic nuclei(AGN) provides important clues for understanding the co-evolution between host galaxies and their central supermassive black holes undergoing a merging process. We present long-slit spectroscopy of J0038+4128, a kiloparsec-scale dual AGN candidate,discovered recently by Huang et al., using the Yunnan Faint Object Spectrograph and Camera(YFOSC)mounted on the Lijiang 2.4-m telescope administered by Yunnan Observatories. From the long-slit spectra, we find that the average relative line-of-sight(LOS) velocity between the two nuclei(J0038+4128N and J0038+4128S) is about 150 km s~(-1). The LOS velocities of the emission lines from the gas ionized by the nuclei activities and of the absorption lines from stars governed by the host galaxies for different regions of J0038+4128 exhibit the same trend. The same trend in velocities indicates that the gaseous disks are co-rotating with the stellar disks in this ongoing merging system. We also find several knots/giant H_Ⅱ regions scattered around the two nuclei with strong star formation revealed by the observed line ratios from the spectra. Those regions are also clearly detected in images from HST F 336W/U-band and HST F 555W/V-band.     

A Study of the Star-forming Dwarf Galaxy NGC 855 with Spitzer

We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band Hα and Spitzer data. Both the Hα and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate （SFR） of 0.022 and 0.025Mo yr^-1, respectively, from the Spitzer IRAC 8.0 μm and MIPS 24 #m emission data. The HI observation suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0 μm bands, located at about 10＂ away from the nucleus of NGC 855. Given the strong 8.0 μm but faint Hα emission, we expect that it is a heavily obscured star-forming region, which needs to be confirmed by further optical spectroscopic observations.     

Multi-transition study of the peculiar merger Arp 299

We present a multi-transition study to investigate the physical properties of dust and molecular gas in the archetypical merger Arp 299 by using data including James Clerk Maxwell Telescope(JCMT)850 and 450 μm observations, Herschel 500, 350, 250, 160 and 70 μm continuum maps, as well as the CO(3–2), CO(4–3) low-J CO lines and CO(11–10), CO(13–12), CO(14–13) high-J CO lines. The CO(3–2) and CO(4–3) lines are observed by JCMT, and the CO(11–10), CO(13–12), CO(14–13) lines are available on the Herschel Science Archive. The resolution of the Herschel Spectral and Photometric Imaging Receiver(SPIRE) Fourier transform spectrometer(FTS) CO(11–10) data is similar to that of the JCMT CO(3–2) line, while the resolution of the SPIRE/FTS CO(13–12) and Photodetector Array Camera and Spectrometer(PACS) CO(14–13) data is similar to that of JCMT CO(4–3), allowing us to obtain accurate line ratios of I_(CO(11-10))/I_(CO(3-2)), I_(CO(13-12))/I_(CO(4-3))and I_(CO(14-13))/I_(CO(4-3)).By modeling the spectral energy distribution of the continuum data, we conclude that two components(cold and warm) exist in the dust, with the warm component occupying a small percent of the total dust mass. We further use a radiative transfer analysis code, RADEX, to calculate the density, temperature and column density of warm gas in the central region, which shows that the kinetic temperature Tkinis in the range 110 to 150 K and hydrogen density n(H_2) is in the range 10~(4.7)-10~(5.5)cm~(-3). We show that the hot dust is located in the central region of IC 694 with a radius of ~ 4′′and estimate that the warm gas mass is in the range 3.8 × 10~7M_⊙ to 7.7 × 10~7M_⊙, which contains 5.0%–15.0% of the total H_2 mass for the region of IC 694. We also calculate the star formation rate of the galaxy in particular,which is much higher than that of the Milky Way.     

Different Features of Jets and Isotropic Fireballs in Gamma-ray Burst Phase

We investigated physical quantities including the spectrum,emission lines and pulse profiles expected from a uniform jet,a spherical fireball and the 1/Γ region (the portion of the spherical fireball with opening angle 1/Γ)in the prompt emission phase,after taking into consideration of the Doppler effect under the fireball frame- work.Our study shows that:a)for these physical quantities the spherical fireball and the uniform jets do not present obvious differences,so we cannot use these to distinguish a spherical fireball from a uniform jet;b)for the spherical fireball and a uniform jet,the observed quantities mainly come from the 1/Г region,so we can simply use the 1/Г region in approximate calculations;c)broadening of emission lines is a general phenomena,which mainly comes from the curvature effect;d)the 1/Γ region plays different roles in different frequency ranges,and the radiation from the 1/Γ region is greater in the higher than in the lower frequencies.     

Chandra Observations of the Flat Spectrum Seyfert-2 Galaxies NGC 2110 and NGC 7582

Chandra observations of the Seyfert-2 galaxies NGC 2110 and NGC 7582 are presented. With the superb spatial resolution of Chandra we found that in NGC 7582 the soft (≤2 keV) and hard (2-10 keV) X-rays are emitted in different regions, consistent with the report by Xue et al. By comparing the present X-ray data with the previous infrared data, we determined that the soft X-ray region is the site of starburst activities. We found no significant temporal variations during our observations. We confirm the previous finding that NGC 2110 and NGC 7582 are flat-spectrum sources. We argue that the flat spectra may result from a cold absorbing material such as envisaged in the “dual absorbed” model. Strong Fe Kα emission feature is detected in 6-7keV. Its equivalent width is so large that it cannot be reproduced by using the Galactic column density of - 10^22 cm^-2.     

Highly variable γ-ray emission of CTD 135 and implications for its compact symmetric structure

The γ-ray emission properties of CTD 135,a typical compact symmetric object(CSO),are investigated with ～11-year Fermi/LAT observations.We show that it has bright and significantly variable GeV emission,with the γ-ray luminosity of L_γ～ 10~(47) erg s~(-1) and a variation index of TS_(var)=1002.A quasi-periodic oscillation(QPO) with a periodicity of ～460 days is detected in the global 95% false-alarm level.These γ-ray emission features are similar to that of blazars.Its broadband spectral energy distribution(SED) can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region.The SED modeling shows that the γ-rays are from the core region,which has a Doppler boosting factor of δ～10.8 and relativistically moves with a small viewing angle,being similar to blazar jets.On the base of the analysis results,we propose that the episodic activity of the central engine in CTD135 results in a blazar-like jet and the bubble-like lobes as the Fermi bubbles in the Galaxy.The strong 7-ray emission with obvious variability is from the jet radiations and the symmetric radio structure is attributed to the bubbles.The jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio sources,indicating that its jet radiation may also be driven by the Eddington ratio.