Search

[O III]$\lambda\lambda$4960,5008 doublet are often the strongest narrow emission lines in starburst galaxies and quasi-stellar objects (QSOs), and thus are a promising probe to possible variation of the fine-structure constant $\alpha$ over cosmic time. Previous such studies using QSOs optical spectra were limited to $z<1$. In this work, we constructed a sample of 40 spectra of Ly$\alpha$ emitting galaxies (LAEs) and a sample of 46 spectra of QSOs at $1.09

In this paper, we present an intercomparison study of two quasars, SDSS J145618.32+340037.2 and SDSS J215331.50-025514.1, which have proximate damped Lya systems (PDLAs) with residual flux upon the Lya absorption trough. Though they both have residual flux as luminous as $10^{43}erg/s$, their PDLAs are quite different in, e.g., HI column density, metal line absorption strength, high-ionization absorption lines as well as residual flux strength. For J1456, the HI column density is $20.6\pm0.2$, with za=2.3138, nearly identical to the quasar redshift (z=2.3142) determined from the [OIII] emission line. The metallicity of this system is typical of DLAs and there is high ionization therein, suggesting that the PDLA system is multiphase, putting it in the quasar environment. For J2153, we measure the HI column density to be $21.5\pm0.1$ at za=3.511, slightly redshifted with respect to the quasar (z=3.490) measured from CIII]. The metallicity of this system is quite low and there is a lack of significant high-ionization absorption lines therein, suggesting that the system is beyond the quasar host galaxy. The residual flux is wide (1000 km/s) in J1456, with a significance of $8\sigma$, while also wide (1500 km/s) but with a smaller significance of $3\sigma$ in J2153. Among many explanations, we find that Lya fuzz or resonant scattering can be used to explain the residual flux in the two sources while partial coverage cannot be excluded for J1456. By comparing these two cases, together with similar cases reported previously, we suggest that the strength of the residual flux is related to properties such as metallicity and high-ionization absorption lines of PDLAs. The residual flux recorded upon the PDLA absorption trough opens a window for us to see the physical conditions and processes of the quasar environment, and their profile and strength further remind us of their spatial scales., Comment: 11 pages, ApJ in press, comments welcome

Broad emission-line outflows of active galactic nuclei (AGNs) have been proposed for many years but are very difficult to quantitatively study because of the coexistence of the gravitationally-bound and outflow emission. We present detailed analysis of a heavily reddened quasar, SDSS J000610.67+121501.2, whose normal ultraviolet (UV) broad emission lines (BELs) are heavily suppressed by the Dusty Torus as a natural "Coronagraph", thus the blueshifted BELs (BBELs) can be reliably measured. The physical properties of the emission-line outflows are derived as follows: ionization parameter $U \sim 10^{-0.5}$, column density $N_{\rm H}\sim 10^{22.0}$ cm$^{-2}$, covering fraction of $\sim 0.1$ and upper limit density of $n_{\rm H}\sim 10^{5.8}$ cm$^{-3}$. The outflow gases are located at least 41 pc away from the central engine, which suggests that they have expanded to the scale of the dust torus or beyond. Besides, Lya shows a narrow symmetric component, to our surprise, which is undetected in any other lines. After inspecting the narrow emission-line region and the starforming region as the origin of the Lya narrow line, we propose the end-result of outflows, diffusing gases in the larger region, acts as the screen of Lya photons. Future high spatial resolution spectrometry and/or spectropolarimetric observation are needed to make a final clarification., Comment: 26 pages, 7 figures, submited to the ApJ

Neutral Helium multiplets, HeI*3189,3889,10830 are very useful diagnostics to the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of HeI* detections have been reported. Using a newly developed method, we detected HeI*3889 absorption line in 101 sources of a well-defined sample of 285 MgII BAL quasars selected from the SDSS DR5. This has increased the number of HeI* BAL quasars by more than one order of magnitude. We further detected HeI*3189 in 50% (52/101) quasars in the sample. The detection fraction of HeI* BALs in MgII BAL quasars is about 35% as a whole, and increases dramatically with increasing spectral signal-to-noise ratios, from 18% at S/N <= 10 to 93% at S/N >= 35. This suggests that HeI* BALs could be detected in most MgII LoBAL quasars, provided spectra S/N is high enough. Such a surprisingly high HeI* BAL fraction is actually predicted from photo-ionization calculations based on a simple BAL model. The result indicates that HeI* absorption lines can be used to search for BAL quasars at low-z, which cannot be identified by ground-based optical spectroscopic survey with commonly seen UV absorption lines. Using HeI*3889, we discovered 19 BAL quasars at z<0.3 from available SDSS spectral database. The fraction of HeI* BAL quasars is similar to that of LoBAL objects., Comment: Accepted for publication in ApJS. Tables 3, 4, 8, and 9 are now available in its entirety at the arXiv website along with the manuscript file, and will also be available via the link to the machine-readable tables on the ApJS website

We present the variability study of broad absorption lines (BALs) in a uniformly radio-selected sample of 28 BAL quasars using the archival data from the FIRST Bright Quasar Survey (FBQS) and the Sloan Digital Sky Survey (SDSS), as well as those obtained by ourselves, covering time scales $\sim 1-10$ years in the quasar's rest-frame. To our surprise, 5 quasars showing strong variations are all belong to a special subclass of overlapping iron low ionization BAL (OFeLoBAL) quasars, however, other 4 non-overlapping FeLoBALs (non-OFeLoBALs) are invariable except one case with weak optical depth change. Meanwhile, we also find 6 typical variations of high-ionization and low-ionization BALs in this BAL quasar sample. Photoionization models suggest that OFeLoBALs are formed in a relative dense ($n_e>10^6$ cm$^{-3}$) outflows at a distance from the subparsec to the dozens of parsecs from the continuum source. They differ from those of non-OFeLoBALs, which are likely produced by low-density gas, locating at a distance of hundreds to thousands parsecs. Thus, OFeLoBALs and non-OFeLoBALs, i.e., FeLoBALs with/without strong BAL variations, perhaps represent the bimodality of Fe II absorption, the former is located in the active galactic nucleus environment rather than the host galaxy. We suggest that high density and small distance are the necessary conditions that cause OFeLoBALs. As suggested in the literature, strong BAL variability is possibly due to variability of the covering factor of BAL regions caused by clouds transiting across the line of sight rather than ionization variations., Comment: 19 pages, 5 figures, ApJ accepted

We report the discovery of excess broad band absorption near 2250 A (EBBA) in the spectra of seven broad absorption line (BAL) quasars. By comparing with the statistical results from the control quasar sample, the significance for the detections are all above the > 4{\sigma} level, with five above > 5{\sigma}. The detections have also been verified by several other independent methods. The EBBAs present broader and weaker bumps at smaller wavenumbers than the Milky Way, and similar to the Large Magellanic Cloud. The EBBA bump may be related to the 2175 A bump seen in the Local Group and may be a counterpart of the 2175 A bump under different conditions in the early Universe. Furthermore, five objects in this sample show low-ionization broad absorption lines (LoBALs), such as Mg II and Al III, in addition to the high-ionization broad absorption lines (HiBALs) of C IV and Si IV. The fraction of LoBALs in our sample, ~70%, is surprisingly high compared to that of general BAL quasars, ~10%. Although the origin of the bump is still not clear, the coexistence of both BALs and bumps and the significantly high fraction of LoBALs may indicate the bump carriers is closely related to the early evolution phase of quasars., Comment: 14 pages, 4 Tables, 9 figures, Submit to The ApJ

We have investigated a sample of 2099 broad absorption line (BAL) quasars with z=1.7-2.2 built from the Sloan Digital Sky Survey Data Release Seven and the Wide-field Infrared Survey. This sample is collected from two BAL quasar samples in the literature, and refined by our new algorithm. Correlations of outflow velocity and strength with hot dust indicator (beta_NIR) and other quasar physical parameters, such as Eddington ratio, luminosity and UV continuum slope, are explored in order to figure out which parameters drive outflows. Here beta_NIR is the near-infrared continuum slope, a good indicator of the amount of hot dust emission relative to accretion disk emission. We confirm previous findings that outflow properties moderately or weakly depends on Eddington ratio, UV slope and luminosity. For the first time, we report moderate and significant correlations of outflow strength and velocity with beta_NIR in BAL quasars. It is consistent with the behavior of blueshifted broad emission lines in non-BAL quasars. The statistical analysis and composite spectra study both reveal that outflow strength and velocity are more strongly correlated with beta_NIR than Eddington ratio, luminosity and UV slope. In particular, the composites show that the entire C IV absorption profile shifts blueward and broadens as beta_NIR increases, while Eddington ratio and UV slope only affect the high and low velocity part of outflows, respectively. We discuss several potential processes and suggest that dusty outflow scenario, i.e. dust is intrinsic to outflows and may contribute to the outflow acceleration, is most likely. The BAL quasar catalog is available from the authors upon request., Comment: 16 pages, 10 figures, 2 tables; Accepted for publication in The Astrophysical Journal

Correlations of hot dust emission with outflow properties are investigated, based on a large z~2 non-broad absorption lines quasar sample built from the Wide-field Infrared Survey and the Sloan Digital Sky Survey data releases. We use the near infrared slope and the infrared to UV luminosity ratio to indicate the hot dust emission relative to the emission from the accretion disk. In our luminous quasars, these hot dust emission indicators are almost independent of the fundamental parameters, such as luminosity, Eddington ratio and black hole mass, but moderately dependent on the blueshift and asymmetry index (BAI) and full width at half-maximum (FWHM) of CIV lines. Interestingly, the latter two correlations dramatically strengthen with increasing Eddington ratio. We suggest that, in high Eddington ratio quasars, CIV regions are dominated by outflows so the BAI and FWHM(CIV) can reliably reflect the general properties and velocity of outflows, respectively. While in low Eddington ratio quasars, CIV lines are primarily emitted by virialized gas so the BAI and FWHM(CIV) become less sensitive to outflows. Therefore, the correlations for the highest Eddington ratio quasars are more likely to represent the true dependence of hot dust emission on outflows and the correlations for the entire sample are significantly diluted by the low Eddington ratio quasars. Our results show that an outflow with a large BAI or velocity can double the hot dust emission on average. We suggest that outflows either contain hot dust in themselves or interact with the dusty interstellar medium or torus., Comment: 14 page, 4 figures, accepted for publication in ApJL

We present results of follow-up optical spectroscopic observations of seven rare, extreme coronal line emitting galaxies reported by Wang et al. (2012) with Multi-Mirror Telescope (MMT). Large variations in coronal lines are found in four objects, making them strong candidates of tidal disruption events (TDE). For the four TDE candidates, all the coronal lines with ionization status higher than [Fe VII] disappear within 5-9 years. The [Fe VII] faded by a factor of about five in one object (J0952+2143) within 4 years, whereas emerged in other two without them previously. A strong increment in the [O III] flux is observed, shifting the line ratios towards the loci of active galactic nucleus on the BPT diagrams. Surprisingly, we detect a non-canonical [O III]5007/[O III]4959 2 in two objects, indicating a large column density of O$^{2+}$ and thus probably optical thick gas. This also requires a very large ionization parameter and relatively soft ionizing spectral energy distribution (e.g. blackbody with $T < 5\times 10^4$ K). Our observations can be explained as echoing of a strong ultraviolet to soft X-ray flare caused by tidal disruption events, on molecular clouds in the inner parsecs of the galactic nuclei. Re-analyzing the SDSS spectra reveals double-peaked or strongly blue-shouldered broad lines in three of the objects, which disappeared in the MMT spectra in two objects, and faded by a factor of ten in 8 years in the remaining object with a decrease in both the line width and centroid offset. We interpret these broad lines as arising from decelerating biconical outflows. Our results demonstrate that the signatures of echoing can persist for as long as ten years, and can be used to probe the gas environment in the quiescent galactic nuclei., Comment: 30 Pages, 10 Figures, 2 Tables, Accepted for Publication in ApJ

We investigate the spatial clustering of galaxies around quasars at redshifts from 0.6 to 1.2 using the photometric data from Sloan Digital Sky Survey (SDSS) Stripe 82. The quasar and galaxy cross-correlation functions are measured through the projected galaxy number density n(r_p) on scales $0.05

Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGN). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog to SDSS spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad and narrow line AGN, star-forming and passive galaxies and composite systems, also updating relationships between optical (Ha and [OIII]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGN between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope aox, and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states., Comment: 12 pages, 10 figures, submitted to ApJ. Full online table will be provided via ApJ

We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad Halpha emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN--galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range $8 \times 10^4$--$2 \times 10^6$ \msun (with a median of $1.2 \times 10^6$ solar mass), using the virial mass estimator based on the broad Halpha line. About half of our sample of low-mass BHs differs from that of Greene & Ho, with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from $<~0.01$ to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local Universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of $L^*$ field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1 Gyr., Comment: Accepted for publication in ApJ

Correlations are investigated of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the CIV line (Wang et al. 2011), with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey. We find that most of the line ratios of other ions to CIV prominently increases with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of dominant coolant, CIV line, decreases and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using SiIV+OIV]/CIV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicitiy and the outflow strength of quasars over a wide range of 1.7 to 6.9 times solar abundance. Our result implies that the metallicity plays an important role in the formation of quasar outflows, likely via affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment., Comment: 13 pages, 4 figures, 1 table, accepted for publication in ApJ

Tidal disruption of stars by supermassive black holes at the centers of galaxies is expected to produce unique emission line signatures, which have not yet been explored adequately. Here we report the discovery of extremely strong coronal lines from [Fe X] up to [Fe XIV] in a sample of seven galaxies (including two recently reported cases), that we interpret as such signatures. This is the first systematic search for objects of this kind, by making use of the immense database of the Sloan Digital Sky Survey. The galaxies, which are non-active as evidenced by the narrow-line ratios, show broad emission lines of complex profiles in more than half of the sample. Both the high ionization coronal lines and the broad lines turn out to be fading on time scales of years in objects observed with spectroscopic follow-ups, suggesting their transient nature. Variations of inferred non-stellar continua, which have absolute magnitudes of at least -16 to -18 mag in the g band, are also detected in more than half of the sample. These extreme coronal line emitters reside in sub-L_* disk galaxies (-21.3 < M_i < -18.5) with small stellar velocity dispersions. The sample seems to form two distinct types based on the presence or absence of the [Fe VII] lines, with the latter having relatively low luminosities of [O III], [Fe XI], and the host galaxies. These characteristics can most naturally be understood in the context of transient accretion onto intermediate mass black holes at galactic centers following tidal disruption of stars in a gas-rich environment. We estimate the incidence of such events to be around 10^-5 per year for a galaxy with -21.5 < M_i < -18.5., Comment: 32 pages, 12 figures, ApJ accepted, typos corrected

We present a statistical study of a large, homogeneously analyzed sample of narrow-line Seyfert 1 (NLS1) galaxies, accompanied by a comparison sample of broad-line Seyfert 1 (BLS1) galaxies. Optical emission-line and continuum properties are subjected to correlation analyses, in order to identify the main drivers of active galactic nuclei (AGN) correlation space, and of NLS1 galaxies in particular. For the first time, we have established the density of the narrow-line region as a key parameter in Eigenvector 1 space, as important as the Eddington ratio L/Ledd. This is important because it links the properties of the central engine with the properties of the host galaxy; i.e., the interstellar medium (ISM). We also confirm previously found correlations involving the line width of Hbeta, and the strength of the FeII and [OIII]5007 emission lines, and we confirm the important role played by L/Ledd in driving the properties of NLS1 galaxies. A spatial correlation analysis shows that large-scale environments of the BLS1 and NLS1 galaxies of our sample are similar. If mergers are rare in our sample, accretion-driven winds on the one hand, or bar-driven inflows on the other hand, may account for the strong dependence of Eigenvector 1 on ISM density., Comment: 31 pages, 7 figures, 5 tables, to appear in AJ

We report the discovery of Balmer broad absorption lines (BALs) in the quasar LBQS 1206+1052 and present a detailed analysis of the peculiar absorption line spectrum. Besides Mg II $\lambda \lambda 2796, 2803$ doublet, BALs are also detected in He I* multiplet at $\lambda \lambda 2946, 3189, 3889$ \AA arising from metastable helium $2^3S$ level, and in H$\alpha$ and H$\beta$ from excited hydrogen H I* $n=2$ level, which are rarely seen in quasar spectra. We identify two components in the BAL troughs of $\Delta v\sim$2000 km s$^{-1}$ width: One component shows an identical profile in H I*, \hei* and \mgii with its centroid blueshifted by $-v_{\rm c}\approx 726$ km\ s$^{-1}$. The other component is detected in \hei* and \mgii with $-v_{\rm c}\approx 1412$ km s$^{-1}$. We estimate the column densities of H I*, He I*, and Mg II, and compare them with possible level population mechanisms. Our results favor the scenario that the Balmer BALs originate in a partially ionized region with a column density of $N_{\rm H}\sim 10^{21-22}$ cm$^{-2}$ for an electron density of $n_e\sim 10^{6-8} $cm$^{-3}$ via Ly$\alpha$ resonant scattering pumping. The harsh conditions needed may help to explain the rarity of Balmer absorption line systems in quasar spectra. With an $i$-band PSF magnitude of 16.50, LBQS 1206+1052 is the brightest Balmer-BAL quasar ever reported. Its high brightness and unique spectral properties make LBQS 1206+1052 a promising candidate for follow-up high-resolution spectroscopy, multi-band observations, and long-term monitoring., Comment: 16 pages,4 figures

Variable super-strong coronal emission lines were observed in one galaxy, SDSS J095209.56+214313.3, and their origin remains controversy. In this paper, we report the detection of variable broad spectral bumps, reminiscent of supernova (SN) II-Plateau (II-P) spectra taken a few days after the shock breakout, in the second galaxy with variable super-strong coronal lines, SDSS J074820.67+471214.3. The coronal line spectrum shows unprecedented high ionization with strong [Fe X], [Fe XI], [Fe XIV], [S XII] and [Ar XIV], but without detectable optical [Fe VII] lines. The coronal line luminosities are similar to that observed in bright Seyfert galaxies, and 20 times more luminous than that reported in the hottest Type IIn SN 2005ip. The coronal lines ($\sigma ~120-240$ km s-1) are much broader than the narrow lines ($\sigma \sim 40$ km/s) from the star forming regions in the galaxy, but at nearly the same systematic redshift. We also detected a variable non-stellar continuum in optical and UV. In the follow-up spectra taken 4-5 years later, the coronal lines, SN-like feature, and non-stellar continuum disappeared, while the [O III] intensity increased by about a factor of ten. Our analysis suggests that the coronal line region should be at least ten light days in size, and be powered either by a quasi-steady ionizing source with a soft X-ray luminosity at least a few 10^{42} erg s-1 or by a very luminous soft X-ray outburst. These findings can be more naturally explained by a star tidally disrupted by the central black hole than by an SN explosion., Comment: 21 pages, 6 figures, accepted to ApJ

There are mutually contradictory views in the literature of the kinematics and structure of high-ionization line (e.g. CIV) emitting regions in active galactic nuclei (AGNs). Two kinds of broad emission line region (BELR) models have been proposed, outflow and gravitationally bound BELR, which are supported respectively by blueshift of the CIV line and reverberation mapping observations. To reconcile these two apparently different models, we present a detailed comparison study between the CIV and MgII lines using a sample of AGNs selected from the Sloan Digital Sky Survey. We find that the kinematics of the CIV region is different from that of MgII, which is thought to be controlled by gravity. A strong correlation is found between the blueshift and asymmetry of the CIV profile and the Eddington ratio. This provides strong observational support for the postulation that the outflow is driven by radiation pressure. In particular, we find robust evidence that the CIV line region is largely dominated by outflow at high Eddington ratios, while it is primarily gravitationally bounded at low Eddington ratios. Our results indicate that these two emitting regions coexist in most of AGNs. The emission strength from these two gases varies smoothly with Eddington ratio in opposite ways. This explanation naturally reconciles the apparently contradictory views proposed in previous studies. Finally, candidate models are discussed which can account for both, the enhancement of outflow emission and suppression of normal BEL, in AGN with high Eddington ratios., Comment: 34 pages, 9 figures, accepted for publication in ApJ

We report detections of 39 2175-{\AA} dust extinction bump candidates associated with strong Mg II absorption lines at z$\sim$ 1--1.8 on quasar spectra in Sloan Digital Sky Survey (SDSS) DR3. These strong Mg II absorption line systems are detected among 2,951 strong Mg II absorbers with the rest equivalent width $W_r\lambda2796 >$ 1.0{\AA} at $1.0 < z < 1.86$, which is part of a full sample of 7,421 strong Mg II absorbers compiled by Prochter et al. (2006). The redshift range of the absorbers is chosen to allow the 2175-{\AA} extinction features to be completely covered within the SDSS spectrograph operation wavelength range. An upper limit of the background quasar emission redshift at z$=$2.1 is set to prevent the Ly$\alpha$ forest lines from contaminating the sensitive spectral region for the 2175-{\AA} bump measurements. The FM90 (Fitzpatrick & Massa 1990) parameterization is applied to model the Optical/UV extinction curve in the rest frame of Mg II absorbers of the 2175-{\AA} bump candidates. The simulation technique developed by Jiang et al. (2010a, b) is used to derive the statistical significance of the candidate 2175-{\AA} bumps. A total of 12 absorbers are detected with 2175-{\AA} bumps at a 5$\sigma$ level of statistical significance, 10 are detected at a 4$\sigma$ level and 17 are detected at a 3$\sigma$ level. Most of the candidate bumps in this work are similar to the relatively weak 2175-{\AA} bumps observed in the Large Magellanic Clouds (LMC) LMC2 supershell rather than the strong ones observed in the Milky Way (MW). This sample has greatly increased the total number of 2175-{\AA} extinction bumps measured on SDSS quasar spectra. Follow-up observations may rule out some of possible false detections and reveal the physical and chemical natures of 2175-{\AA} quasar absorbers., Comment: 71 pages, 6 tables, 49 figures, accepted by ApJ, Table 1 is available entirely at http://home.ustc.edu.cn/~jpaty/dataset/qso_dr7.dat ;Table 2 is available entirely at http://home.ustc.edu.cn/~jpaty/dataset/rejected.list

We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-{\AA} dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-{\AA} absorber at $z$=1.64 toward the quasar SDSS J160457.50+220300.5, Noterdaeme et al. (2009) reported a similar dust depletion measurement ([Fe/Zn]=$-1.47$ and [Si/Zn]=$-1.07$) and detected C~I and CO absorption lineson its VLT/UVES spectrum. We conclude that heavy dust depletion (i.e. a characteristic of cold dense clouds in MW) is required to produce a pronounced 2175-{\AA} extinction bump., Comment: 28 Pages, 9 Figures, 5 Tables; Accepted by ApJ

We report the discovery of a luminous ultra-soft X-ray excess in a radio-loud narrow-line Seyfert1 galaxy, RXJ1633+4718, from archival ROSAT observations. The thermal temperature of this emission, when fitted with a blackbody, is as low as 32.5(+8.0,-6.0)eV. This is in remarkable contrast to the canonical temperatures of ~0.1-0.2keV found hitherto for the soft X-ray excess in active galactic nuclei (AGN), and is interestingly close to the maximum temperature predicted for a postulated accretion disc in this object. If this emission is indeed blackbody in nature, the derived luminosity [3.5(+3.3,-1.5)x10^(44)ergs/s] infers a compact emitting area with a size [~5x10^(12)cm or 0.33AU in radius] that is comparable to several times the Schwarzschild radius of a black hole at the mass estimated for this AGN (3x10^6Msun). In fact, this ultra-steep X-ray emission can be well fitted as the (Compton scattered) Wien tail of the multi-temperature blackbody emission from an optically thick accretion disc, whose parameters inferred (black hole mass and accretion rate) are in good agreement with independent estimates using optical emission line spectrum. We thus consider this feature as a signature of the long-sought X-ray radiation directly from a disc around a super-massive black hole, presenting observational evidence for a black hole accretion disc in AGN. Future observations with better data quality, together with improved independent measurements of the black hole mass, may constrain the spin of the black hole., Comment: 8 pages, 4 figures, ApJ in press

The Nv emission line of active galactic nuclei shows peculiar behavior in the line--continuum correlation, which may be indicative of an extra line component in addition to that from the normal broad emission line region. In this paper, we investigate possible contribution to the Nv emission via resonant scattering of both continuum and Ly alpha in a broad absorption line (BAL) outflow, by performing the Sobolev Monte Carlo simulations. The contribution is dependent on the covering factor, optical depth and velocity profile of the outflow, as well as the equivalent width (EW) of Ly alpha. Adopting model parameters constrained by observations, we find that the measured Nv EW in the spectra of non-BAL quasi-stellar objects (QSOs) could have been enhanced by a factor of 1.82~2.73 on average, while there is only moderate absorption of Ly alpha along the BAL outflow direction. Our model can produce a relatively narrow scattering line profile. About 80% of the total scattered flux falls within the central +-4500km/s. We find that the resonant scattering can produce a prominent polarized emission line around Nv. Both the broad excess emission and the unusually large polarized flux observed around Nv in BAL QSOs are considered as strong evidence for the scattering enhancement. Future spectropolarimetric observations and spectroscopic monitoring of luminous QSOs may offer crucial tests for this interpretation, and provide useful information on the physical and geometrical properties of QSO outflows. We argue that the scattering offers a promising and robust process for producing the peculiar behavior of Nv emission compared to the other processes proposed previously., Comment: 34 pages, 13figures. The Astrophysical Journal, Volume 710, Issue 1, pp. 78-90 (2010)

We present a sample of 68 low-z MgII low-ionization broad absorption-line (loBAL) quasars. The sample is uniformly selected from the SDSS5 according to the following criteria: (1) 0.47, and (3) MgII absorption-line width > 1600 \kms. The last criterion is a trade-off between the completeness and consistency with respect to the canonical definition of BAL quasars that have the `balnicity index' BI>0 in CIV BAL. We adopted such a criterion to ensure that ~90% of our sample are classical BAL quasars and the completeness is ~80%, based on extensive tests using high-z quasar samples with measurements of both CIV and MgII BALs. We found (1) MgII BAL is more frequently detected in quasars with narrower Hbeta emission-line, weaker [OIII] emission-line, stronger optical FeII multiplets and higher luminosity. In term of fundamental physical parameters of a black hole accretion system, loBAL fraction is significantly higher in quasars with a higher Eddington ratio than those with a lower Eddington ratio. The fraction is not dependent on the black hole mass in the range concerned. The overall fraction distribution is broad, suggesting a large range of covering factor of the absorption material. (2) [OIII]-weak loBAL quasars averagely show undetected [NeV] emission line and a very small line ratio of [NeV] to [OIII]. However, the line ratio in non-BAL quasars, which is much larger than that in [OIII]-weak loBAL quasars, is independent of the strength of the [OIII] line. (3) loBAL and non-loBAL quasars have similar colors in near-infrared to optical band but different colors in ultraviolet. (4) Quasars with MgII absorption lines of intermediate width are indistinguishable from the non-loBAL quasars in optical emission line properties but their colors are similar to loBAL quasars, redder than non-BAL quasars. We also discuss the implication of these results., Comment: 40 pages, accepeted for publication in ApJ

We investigate the relationship between the linewidths of broad Mg II \lambda2800 and Hbeta in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping. Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe II contamination. We show that, contrary to popular belief, the velocity width of Mg II tends to be smaller than that of Hbeta, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from reverberation mapping, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg II and Hbeta lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature., Comment: Matches version to appear in ApJ, preliminarily 706:1-13, 2009; a minor error corrected (in Table 2 only)