Sloan Digital Sky Survey Type Research Articles

Different Dependence of Narrow Hα Line Luminosity on Optical Continuum Luminosity between Star-forming Galaxies and Type 2 Active Galactic Nuclei: Globally Negative AGN Feedback in Local Type 2 AGN?

In this manuscript, clues are provided to support globally negative active galactic nuclei (AGN) feedback on star formation in the host galaxies of the local low-redshift Sloan Digital Sky Survey (SDSS) Type 2 AGN, based on the different dependence of narrow Hα line luminosity L Hα on optical continuum luminosity λ L cont between star-forming galaxies and Type 2 AGN. Through the measured L Hα and λ L cont in SDSS star-forming galaxies, there is a strong linear correlation between λ L cont and L Hα , accepted as a standard correlation without the effects of AGN activity. Meanwhile, considering the apparent contribution of AGN activity to the narrow Hα line emissions in Type 2 AGN, the correlation between λ L cont and L Hα in the SDSS Type 2 AGN leads to a statistically lower L Hα in Type 2 AGN than in star-forming galaxies, with a significance level higher than 5σ, even after considering necessary effects (including effects of host galaxy properties), leading to the accepted conclusion on the globally negative AGN feedback in the local Type 2 AGN. Meanwhile, the properties of Dn(4000) and Hδ A can provide indirect clues to support the globally negative AGN feedback in local Type 2 AGN, due to older stellar ages in Type 2 AGN. Moreover, it is interesting to expect more than 50% narrow Hα emissions globally suppressed in the host galaxies of Type 2 AGN relative to the star-forming galaxies. The results not only support globally negative AGN feedback in local Type 2 AGN, but also show further clues on the quantification of suppressions of star formation by the globally negative AGN feedback.

Finding of a Population of Active Galactic Nuclei Showing a Significant Luminosity Decline in the Past ∼103–104 yr

Recent observations have revealed an interesting active galactic nucleus (AGN) subclass that shows strong activity at large scales (∼1 kpc) but weaker at small scales (<10 pc), suggesting a strong change in the mass accretion rate of the central engine in the past 103–104 yr. We systematically search for such declining or fading AGNs by cross-matching the Sloan Digital Sky Survey type 1 AGN catalog at z < 0.4, covering the [O iii] λ5007 emission line, which is a tracer for the narrow-line region emission, with the Wide-field Infrared Survey Explorer (WISE) mid-infrared (MIR) catalog covering the emissions from the dusty tori. Out of the 7653 sources, we found 57 AGNs whose bolometric luminosities estimated from the MIR band are at least one order of magnitude fainter than those estimated from the [O iii] λ5007 emission line. This luminosity-declining AGN candidate population shows four important properties: (1) the past AGN activity estimated from the [O iii] λ5007 line reaches approximately the Eddington limit; (2) more than 30% of the luminosity-declining AGN candidates show a large absolute variability of ΔW1 > 0.45 mag in the previous ∼10 yr at the WISE 3.4 μm band; (3) the median ratio of log([N ii] λ6584/Hα λ6563) = −0.52, suggesting a lower gas metallicity and/or higher ionization parameter compared to other AGN populations; and (4) the second-epoch spectra of the population indicate a spectral type change for 15% of the sources. This population provides insights on the possible connection between the luminosity decline that started ∼103–104 yr ago and the decline in the recent 10 yr.

Bayesian AGN Decomposition Analysis for SDSS spectra: a correlation analysis of [O iii] λ5007 outflow kinematics with AGN and host galaxy properties

ABSTRACT We present Bayesian active galactic nucleus (AGN) Decomposition Analysis for Sloan Digital Sky Survey (SDSS) Spectra, an open source spectral analysis code designed for automatic detailed deconvolution of AGN and host galaxy spectra, implemented in python, and designed for the next generation of large-scale surveys. The code simultaneously fits all spectral components, including power-law continuum, stellar line-of-sight velocity distribution, Fe ii emission, as well as forbidden (narrow), permitted (broad), and outflow emission line features, all performed using Markov chain Monte Carlo to obtain robust uncertainties and autocorrelation analysis to assess parameter convergence. Our code also utilizes multiprocessing for batch fitting large samples of spectra while efficiently managing memory and computation resources and is currently being used in a cluster environment to fit thousands of SDSS spectra. We use our code to perform a correlation analysis of 63 SDSS type 1 AGNs with evidence of strong non-gravitational outflow kinematics in the [O iii] λ5007 emission feature. We confirm findings from previous studies that show the core of the [O iii] profile is a suitable surrogate for stellar velocity dispersion σ*, however there is evidence that the core experiences broadening that scales with outflow velocity. We find sufficient evidence that σ*, [O iii] core dispersion, and the non-gravitational outflow dispersion of the [O iii] profile form a plane whose fit results in a scatter of ∼0.1 dex. Finally, we discuss the implications, caveats, and recommendations when using the [O iii] dispersion as a surrogate for σ* for the MBH−σ* relation.

Composite Spectral Energy Distributions and Infrared–Optical Colors of Type 1 and Type 2 Quasars

Abstract We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. However, these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 and 2 matched in redshift and [O iii] luminosity, we produce composite rest-frame 0.2–15 μm SEDs based on SDSS, UKIDSS, and Wide-field Infrared Survey Explorer photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the active galactic nucleus (AGN) relative to the host galaxy increases with AGN luminosity ( L [ O III ] ) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously ( W 1 – W 2 &gt; 0.7 ; Vega), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical–IR colors (for example, ( u – W 3 [ AB ] ) &gt; 1.4 ( W 1 – W 2 [ Vega ] ) + 3.2 ). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of MIR and optical photometry.

Co-evolution of black hole growth and star formation from a cross-correlation analysis between quasars and the cosmic infrared background

We present the first cross-correlation measurement between Sloan Digital Sky Survey (SDSS) Type 1 quasars and the cosmic infrared background (CIB) measured by Herschel. The distribution of the quasars at 0.15<z<3.5 covers the redshift range where we expect most of the CIB to originate. We detect the sub-mm emission of the quasars, which dominates on small scales, as well as correlated emission from dusty star-forming galaxies (DSFGs) dominant on larger scales. The mean sub-mm flux densities of the DR7 quasars (median redshift <z>=1.4) is $11.1^{+1.6}_{-1.4}$, $7.1^{+1.6}_{-1.3}$ and $3.6^{+1.4}_{-1.0}$ mJy at 250, 350 and 500 microns, respectively, while the mean sub-mm flux densities of the DR9 quasars (<z>=2.5) is $5.7^{+0.7}_{-0.6}$, $5.0^{+0.8}_{-0.7}$ and $1.8^{+0.5}_{-0.4}$ mJy. We find that the correlated sub-mm emission includes both the emission from satellite DSFGs in the same halo as the central quasar and the emission from DSFGs in separate halos (correlated with the quasar-hosting halo). The amplitude of the one-halo term is ~10 times smaller than the sub-mm emission of the quasars, implying the the satellites have a lower star-formation rate than the quasars. The satellite fraction for the DR7 quasars is $0.008^{+0.008}_{-0.005}$ and the host halo mass scale for the central and satellite quasars is $10^{12.36\pm0.87}$ M$_{\odot}$ and $10^{13.60\pm0.38}$ M$_{\odot}$, respectively. The satellite fraction of the DR9 quasars is $0.065^{+0.021}_{-0.031}$ and the host halo mass scale for the central and satellite quasars is $10^{12.29\pm0.62}$ M$_{\odot}$ and $10^{12.82\pm0.39}$ M$_{\odot}$, respectively. Thus, the typical halo environment of the SDSS Type 1 quasars is found to be similar to that of DSFGs, which supports the generally accepted view that dusty starburst and quasar activity are evolutionarily linked.

Type 1 AGN at low z- I. Emission properties

We analyse the emission properties of a new sample of 3579 type 1 AGN, selected from Sloan Digital Sky Survey (SDSS) Data Release 7 based on the detection of broad Hα emission. The sample extends over a broad Hα luminosity LbHα of and a broad Hα full width at half-maximum (FWHM) of ⁠, which covers the range of black hole mass 106 < MBH/M⊙ < 109.5 and luminosity in Eddington units 10−3 < L/LEdd < 1. We combine ROSAT, GALEX and 2MASS observations to form the spectral energy distribution (SED) from 2.2 m to 2 keV. We find the following. (1) The distribution of the Hα FWHM values is independent of luminosity. (2) The observed mean optical–ultraviolet (optical–UV) SED is well matched by a fixed-shape SED of luminous quasars, which scales linearly with LbHα, and a host galaxy contribution. (3) The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission-line galaxies (NEGs), consistent with a fixed fraction of ∼3 per cent of NEGs hosting an AGN, regardless of the host luminosity. (4) The hosts of lower luminosity AGN have a mean z-band luminosity and u−z colour which are identical to NEGs with the same redshift distribution. With increasing LbHα the AGN hosts become bluer and less luminous than NEGs. The implied increasing star formation rate with LbHα is consistent with the relation for SDSS type 2 AGN of similar bolometric luminosity. (5) The optical–UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. (6) There is a rather tight relation between and LbHα, which provides a useful probe for unobscured (true) type 2 AGN. (7) The primary parameter that drives the X-ray to UV emission ratio is luminosity, rather than MBH or L/LEdd.

Accretion and star formation rates in low-redshift type II active galactic nuclei

Accretion and star formation (SF) rates in low-redshift Sloan Digital Sky Survey type II active galactic nuclei (AGN) are critically evaluated. Comparison with photoionization models indicates that bolometric luminosity (Lbol) estimates based on L([O iii] λ5007) severely underestimate Lbol in low-ionization sources such as LINERs. An alternative method based on L(Hβ) is less sensitive to the ionization level, and a novel method, based on a combination of L([O iii] λ5007) and L([O i] λ6300), is perhaps the best. Using this method, I show that low-ionization AGN are accreting faster than assumed until now. Other significant related findings are as follows. (1) Any type II AGN property related to the black hole (BH) mass is more reliably obtained by removing blue galaxies from the sample. (2) Seyfert 2s and LINER 2s form a continuous sequence of L/LEdd with no indication for a change in accretion mechanism or mode of mass supply. There are very few, if any, LINERs in all type I samples which results in a much narrower L/LEdd distribution compared with type II samples. (3) There is a strong correlation between the SF luminosity, LSF, and Lbol over more than five orders of magnitude in luminosity. This leads to a simple relationship between bulge and BH growth rates, g(bulge)/g(BH) ∝L−0.2bol, where g(bulge)/g(BH) ≃ 115 for Lbol= 1042 erg s−1. Seyfert 2s and LINER 2s follow the same LSF–Lbol correlation for all sources with a stellar age indicator, Dn4000, smaller than 1.8. This suggests that a similar fraction of SF gas finds its way to the centre in all AGN. (4) Lbol, LSF, L/LEdd and the specific SF rate follow Dn4000 in a similar way.

HOST GALAXIES OF LUMINOUS TYPE 2 QUASARS AT z {approx} 0.5

We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z {approx} 0.5, drawn from the Sloan Digital Sky Survey type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (M{sub V} 1 Gyr) which dominates the stellar mass. Broad emission complexes around He II {lambda}4686 A with luminosities up to 10{sup 8.3} L{sub sun} are unambiguously detected in three out of themore » nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that {approx}5 Myr poststarburst populations contribute substantially to the luminosities (>50% of L{sub 5100}) of all three objects with WR detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity.« less

The quest for Type 2 quasars: Chandra observations of luminous obscured quasars in the Sloan Digital Sky Survey

We report on new Chandra exploratory observations of six candidate Type 2 quasars at z = 0.49-0.73 selected among the most [O III] luminous emitters from the Sloan Digital Sky Survey (SDSS). Under the assumption that [O III] is a proxy for the intrinsic luminosity of the central source, their predicted rest-frame X-ray luminosities are L 2-10 keV ≈ 10 45 erg s -1 . For two of the targets, the photon statistics are good enough to allow for basic X-ray spectral analyses, which indicate the presence of intrinsic absorption (≈10 22-23 cm -2 ) and luminous X-ray emission (L x ? 1044 erg s -1 ). Of the remaining four targets, two are detected with only a few (3-6) X-ray counts, and two are undetected by Chandra. If these four sources have the large intrinsic X-ray luminosities predicted by the [O III] emission, then their nuclei must be heavily obscured (N H > few times 10 23 cm -2 ) and some might be Compton thick (N H > 1.5 × 10 24 cm -2 ). We also present the results for two Type 2 quasar candidates serendipitously lying in the fields of the Chandra targets, and provide an up-to-date compilation of the X-ray properties of eight additional SDSS Type 2 quasars from archival Chandra and XMM-Newton observations (five with moderate-quality X-ray data). The combined sample of 16 SDSS Type 2 quasars (10 X-ray detections) provides further evidence that a considerable fraction of optically selected Type 2 quasars are obscured in the X-ray band (at least all the objects with moderate-quality X-ray spectra), lending further support to the findings presented by Vignali, Alexander & Comastri and unification schemes of active galactic nuclei, and confirms the reliability of [O III] emission in predicting the X-ray emission in obscured quasars.

Extremely Luminous Water Vapor Emission from a Type 2 Quasar at Redshift z = 0.66

A search for water masers in 47 Sloan Digital Sky Survey type 2 quasars using the Green Bank Telescope has yielded a detection at a redshift of z = 0.660. This maser is more than an order of magnitude higher in redshift than any previously known and, with a total isotropic luminosity of 23,000 L☉, also the most powerful. The presence and detectability of water masers in quasars at z ~ 0.3-0.8 may provide a better understanding of quasar molecular tori and disks, as well as fundamental quasar and galaxy properties such as black hole masses. Water masers at cosmologically interesting distances may also eventually provide, via direct distance determinations, a new cosmological observable for testing the reality and properties of dark energy, currently inferred primarily through Type 1a supernova measurements.