Red Active Galactic Nuclei Research Articles

Mapping the oxygen abundance in Red Geysers and its relation with the gas kinematics using megacubes

ABSTRACT Red Geysers are galaxies with low-star formation rates and galactic scale ionized outflows likely driven by low-luminosity active galactic nuclei (AGN). We investigated the impact of AGN winds on the oxygen abundance using integral field spectroscopic data from Mapping Nearby Galaxies for Red Geysers, control galaxies (quiescent galaxies without outflows), and AGN hosts within the inner 1.5 kpc radius. Red Geyser galaxies have higher W$_{80}$ values compared to those of AGN and controls, with 64 per cent showing W$_{80}\gt 500$ km s$^{-1}$ that is indicative of outflow. Only 40 per cent of controls and 31 per cent of AGNs reach this value. We found a small tendency of the oxygen abundance distribution of controls to be biased towards higher values than those of Red Geysers. However, Red Geysers do not show a correlation between H$\alpha$ width (parametrized by the W$_{\rm 80}$) and oxygen abundance, which indicates that AGN winds are not significantly impacting the chemical abundance of the nuclear region of these galaxies. The oxygen abundance distribution mean value for the tree samples is $\rm 12+log(O/H)\sim$8.7 ($\mathit{Z}\sim \rm Z_{\odot })$. On the other hand, AGN hosts show a positive correlation between W$_{80}$ and O/H which could be due to star formation that outflows from the active nuclei could induce; or to the reservoir of gas that makes the nucleus active, and its is also used in the star formation.

Survey of gravitationally lensed objects in HSC imaging (SuGOHI) – IX. Discovery of strongly lensed quasar candidates

ABSTRACT We report the discovery of new lensed quasar candidates in the imaging data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) Data Release 4, covering $1\, 310\deg ^2$ of the sky with median seeing in the i band of ≈0.6 arcsec. In addition to two catalogues of Million Quasars Catalog v7.2 and AllWISE Catalog of Mid-Infra Red Active Galactic Nuclei, containing confirmed and candidate quasars, we preselect quasar sources using colour cuts from the HSC (grizy) and unWISE (W1 + W2) photometric data based on SDSS spectroscopic catalogues. We search for the presence of multiple point sources with similar colour through the convolution of the Laplacian of the preselected quasar image cutouts with the Laplacian of the point spread function, resulting in a reduction of lens candidates from 1 652 329 to 121 511 (7.4 per cent). After visual binary classification, we grade 6 199 (0.4 per cent) potential lenses on a scale of 0 to 3, with 3 indicating a lens and 0 indicating a non-lens. Finally we obtain 162 lens candidates with an average grade of ≥2, and among them, we successfully recover 18 known lenses. By fitting the light distribution and removing the known contaminants, we discover that 57 new systems contain at least two point sources and a galaxy in between, including 10 possible quadruply lensed quasars. This new sample exhibits a median separation of 1.26 arcsec and a magnitude limit of i ≈ 22. Spectroscopic or high-resolution imaging follow up on these newly discovered lensed quasar candidates will further allow their natures to be confirmed.

Bolometric luminosity estimators using infrared hydrogen lines for dust obscured active galactic nuclei

ABSTRACT Bolometric luminosity is an important quantity that tells us the radiative energy output of an active galactic nucleus (AGN). A common way to estimate bolometric luminosity is to use ultraviolet (UV) or optical luminosities as its proxies, but the UV- or optical-based-bolometric luminosity estimators can be easily affected by dust extinction. In this study, we present new methods for estimating bolometric luminosities using infrared (IR) hydrogen Paschen and Brackett line luminosities to alleviate the dust extinction effects. We show that there exist tight correlations between the bolometric luminosities and the IR hydrogen line luminosities, and present the IR hydrogen line-based-bolometric luminosity estimators. As an example, we apply the relation to dust obscured red AGNs, confirming previous results that red AGNs have higher Eddington rations than unobscured AGNs. The new bolometric luminosity estimator will be useful for studying obscured AGNs (e.g. red AGNs, Compton thick AGNs, and Type 2 AGNs), during the coming era of sensitive near-infrared (NIR) and mid-infrared (MIR) missions, such as the James Webb Space Telescope.

Galaxy properties of type 1 and 2 X-ray selected AGN and a comparison among different classification criteria

We present analyses of host galaxy properties of type 1 and type 2 X-ray selected Active galactic nuclei (AGNs) in the XMM-XXL field, which have an available optical spectroscopic classification. We modelled their optical to far-infrared spectral energy distributions (SEDs) using the X-CIGALE code. X-CIGALE allows for the fitting of X-ray flux and accounts for the viewing angle of dusty torus and the attenuation from polar dust. By selecting matched type 1 and 2 sub-samples in the X-ray luminosity and redshift parameter space, we find that both types live in galaxies with similar star formation. However, type 2 AGN tend to reside in more massive systems (10.87−0.12+0.06 M⊙) compared to their type 1 counterparts (10.57−0.12+0.20 M⊙). In the second part of our analysis, we compare the spectroscopic classification with that from the SED fitting. X-CIGALE successfully identifies all spectroscopic type 2 sources either by estimating an inclination angle that corresponds to edge on viewing of the source or by measuring increased polar dust in these systems. Approximately 85% of spectroscopic type 1 AGN are also identified as such, based on the SED fitting analysis. There is a small number of sources (∼15% of the sample) that present broad lines in their spectra, but they show strong indications of obscuration, based on SED analysis. These could be systems that are viewed face on and have an extended dust component along the polar direction. The performance of X-CIGALE in classifying AGN is similar at low and high redshifts, under the condition that there is sufficient photometric coverage. Finally, the usage of optical/mid-IR colour criteria to identify optical red AGN (u − W3) suggests that these criteria are better suited for IR selected AGN and their efficiency drops for the low to moderate luminosity sources included in X-ray samples.

Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle

According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s−1 along l=264∘,b=48∘. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology.

The XXL Survey

The combination of optical and mid-infrared (MIR) photometry has been extensively used to select red active galactic nuclei (AGNs). Our aim is to explore the obscuration properties of these red AGNs with both X-ray spectroscopy and spectral energy distributions (SEDs). In this study, we re-visit the relation between optical/MIR extinction and X-ray absorption. We use IR selection criteria, specifically the W1 and W2 WISE bands, to identify 4798 AGNs in the XMM-XXL area (∼25 deg2). Application of optical/MIR colours (r−W2 > 6) reveals 561 red AGNs (14%). Of these, 47 have available X-ray spectra with at least 50 net (background-subtracted) counts per detector. For these sources, we construct SEDs from the optical to the MIR using the CIGALE code. The SED fitting shows that 44 of these latter 47 sources present clear signs of obscuration based on the AGN emission and the estimated inclination angle. Fitting the SED also reveals ten systems (∼20%) which are dominated by the galaxy. In these cases, the red colours are attributed to the host galaxy rather than AGN absorption. Excluding these ten systems from our sample and applying X-ray spectral fitting analysis shows that up to 76% (28/37) of the IR red AGNs present signs of X-ray absorption. Thus, there are nine sources (∼20% of the sample) that although optically red, are not substantially X-ray absorbed. Approximately 50% of these sources present broad emission lines in their optical spectra. We suggest that the reason for this apparent discrepancy is that the r−W2 criterion is sensitive to smaller amounts of obscuration relative to the X-ray spectroscopy. In conclusion, it appears that the majority of red AGNs present considerable obscuration levels as shown by their SEDs. Their X-ray absorption is moderate with a mean of NH ∼ 1022 cm−2.

Gemini Multi-Object Spectrograph Integral Field Unit Spectroscopy of the Double-peaked Broad Emission Line of a Red Active Galactic Nucleus

Abstract Galaxy mergers are expected to produce multiple supermassive black holes (SMBHs) in close-separation, but the detection of such SMBHs has been difficult. 2MASS J165939.7 + 183436 is a red active galactic nucleus (AGN) that is a prospective merging SMBH candidate owing to its merging features in Hubble Space Telescope imaging and double-peaked broad emission lines (BELs). Herein, we report a Gemini Multi-Object Spectrograph Integral Field Unit observation of a double-peaked broad Hα line of 2MASS J165939.7+183436. Furthermore, we confirm the existence of two BEL peaks that are kinematically separated by 3000 km s−1, with the SMBH of each BEL component weighing at and , if they arise from independent BELs near the two SMBHs. The BEL components were not separated at >0.″1; however, under several plausible assumptions regarding the fitting of each spaxel, the two components are found to be spatially separated at 0.″085 (∼250 pc). Different assumptions for the fitting can lead to a null (<0.″05) or a larger spatial separation (∼0.″15). Given the uncertainty regarding the spatial separation, various models, such as the disk emitter and multiple SMBH models, are viable solutions to explain the double BEL components. These results will promote future research for finding more multiple SMBH systems in red AGNs, and higher-resolution imaging validates these different models.

Obscuration properties of mid-IR-selected AGN

ABSTRACT The goal of this work is to study the obscuration properties of mid-infrared (mid-IR)-selected active galactic nuclei (AGN). For that purpose, we use Wide-field Infrared Survey Explorer (WISE) sources in the Stripe 82–XMM area to identify mid-IR AGN candidates, applying the Assef et al. criteria. Stripe 82 has optical photometry ≈2 times deeper than any single-epoch Sloan Digital Sky Survey (SDSS) region. XMM–Newton observations cover ∼26 deg2. Applying the aforementioned criteria, 1946 IR AGN are selected. ${\sim} 78{{\, \rm per\, cent}}$ have SDSS detection, while 1/3 of them are detected in X-rays, at a flux limit of $\rm {\sim} 5 \times 10^{-15}\, erg\, s^{-1}\, cm^{-2}$. Our final sample consists of 507 IR AGN with X-ray detection and optical spectra. Applying a $r-W2 > 6$ colour criterion, we find that the fraction of optically red AGN drop from 43 per cent for those sources with SDSS detection to $23{{\, \rm per\, cent}}$ for sources that also have X-ray detection. X-ray spectral fitting reveals 40 (${\sim} 8{{\, \rm per\, cent}}$) X-ray absorbed AGN ($N_\mathrm{ H} > 10^{22}\,{\rm cm}^{-2}$). Among the X-ray unabsorbed AGN, there are 70 red systems. To further investigate the absorption of these sources, we construct spectral energy distributions (SEDs) for the total IR AGN sample. SED fitting reveals that ${\sim} 20{{\, \rm per\, cent}}$ of the optically red sources have such colours because the galaxy emission is a primary component in the optical part of the SED, even though the AGN emission is not absorbed at these wavelengths. SED fitting also confirms that $12{{\, \rm per\, cent}}$ of the X-ray unabsorbed IR AGN are optically obscured.

Medium-resolution Optical and Near-infrared Spectral Atlas of 16 2MASS-selected NIR-red Active Galactic Nuclei at z ∼ 0.3

Abstract We present medium-resolution spectra (R ∼ 2000–4000) at 0.4–1.0 μm and 0.7–2.5 μm of 16 active galactic nuclei (AGNs) selected with red color in the near-infrared (NIR) of J − K > 2.0 mag at z ∼ 0.3. We fit the Hβ, Hα, Pβ, and Pα lines from these spectra to obtain their luminosities and line widths. We derive the E(B − V) color excess values of the NIR-red AGNs using two methods, one based on the line-luminosity ratios and another based on the continuum slopes. The two E(B − V) values agree with each other at rms dispersion ∼0.249. About half of the NIR-red AGNs have g′ − K < 5 magnitude, and we find that these NIR-red, but blue in optical-NIR AGNs, have E(B − V) ∼ 0, suggesting that a significant fraction of the NIR color-selected red AGNs are unobscured or only mildly obscured. After correcting for the dust extinction, we estimate the black hole (BH) masses and the bolometric luminosities of the NIR-red AGNs using the Paschen lines to calculate their Eddington ratios (λ Edd). The median Eddington ratios of nine NIR-red AGNs ( ) are only mildly higher than those of unobscured type 1 AGNs ( ). Moreover, we find that the M BH–σ * relation for three NIR-red AGNs is consistent with that of unobscured type 1 AGNs at similar redshift. These results suggest that the NIR-red color selection alone is not effective at picking up dusty, intermediate-stage AGNs.

Evidence of suppression of star formation by quasar-driven winds in gas-rich host galaxies atz< 1?

Feedback from active galactic nuclei (AGN) is widely considered to be the main driver in regulating the growth of massive galaxies through heating or driving gas out of the galaxy, preventing further increase in stellar mass. Observational proof for this scenario has, however, been scarce. We have assembled a sample of 132 radio-quiet type-2 and red AGN at 0.1<z<1. We measure the kinematics of the AGN-ionized gas, the host galaxies' stellar masses and star formation rates and investigate the relationships between AGN luminosities, specific star formation rates (sSFR) and outflow strengths W90 -- the 90\% velocity width of the [OIII]5007 line power and a proxy for the AGN-driven outflow speed. Outflow strength is independent of sSFR for AGN selected on their mid-IR luminosity, in agreement with previous work demonstrating that star formation is not sufficient to produce the observed ionized gas outflows which have to be powered by AGN activity. More importantly, we find a negative correlation between W90 and sSFR in the AGN hosts with the highest SFRs, i.e., with the highest gas content, where presumably the coupling of the AGN-driven wind to the gas is strongest. This implies that AGN with strong outflow signatures are hosted in galaxies that are more `quenched' than galaxies with weaker outflow signatures. Despite the galaxies' high SFRs, we demonstrate that the outflows are not star-formation driven but indeed due to AGN-powering. This observation is consistent with the AGN having a net suppression, `negative' impact, through feedback on the galaxies' star formation history.

Arecibo Legacy Fast ALFA H i data stacking - II. H i content of the host galaxies of active galactic nuclei

We use a stacking technique to measure the average H I content of a volume-limited sample of 1871 active galactic nucleus (AGN) host galaxies from a parent sample of galaxies selected from the Sloan Digital Sky Survey and GALEX imaging surveys with stellar masses greater than 10 10 Mand redshifts in the range 0.025 < z < 0.05. H I data are available from the Arecibo Legacy Fast ALFA (ALFALFA) survey. In previous work, we found that the H I gas fraction in galaxies correlates most strongly with the combination of optical/ultraviolet colour and stellar surface mass density. We therefore build a control sample of non-AGN matched to the AGN hosts in these two properties. We study trends in H I gas mass fraction (MH I/M� , where Mis the stellar mass) as a function of black hole accretion rate indicator L(O III)/MBH. We find no significant difference in H I content between AGN and control samples at all values of black hole accretion rate probed by the galaxies in our sample. This indicates that AGN do not influence the large-scale gaseous properties of galaxies in the local Universe. We have studied the variation in H I mass fraction with black hole accretion rate in the blue and red galaxy populations. In the blue population, the H I gas fraction is independent of accretion rate, indicating that accretion is not sensitive to the properties of the interstellar medium of the galaxy on large scales. However, in the red population accretion rate and gas fraction do correlate. The measured gas fractions in this population are not too different from the ones expected from a stellar mass-loss origin, implying that the fuel supply in the red AGN population could be a mixture of mass-loss from stars and gas present in discs.

NEW ESTIMATORS OF BLACK HOLE MASS IN ACTIVE GALACTIC NUCLEI WITH HYDROGEN PASCHEN LINES

More than 50% of active galactic nuclei (AGNs) are suspected to be red and affected by dust obscuration. Meanwhile, popular spectral diagnostics of AGNs are based on optical or ultraviolet light, making dust obscuration the primary concern for understanding the general nature of AGNs and the supermassive black holes residing in them. To provide a method for investigating properties of dusty AGNs, we derive new black hole (BH) mass estimators based on velocity widths and luminosities of near-infrared (NIR) hydrogen emission lines such as Pα and Pβ, and also investigate the line ratios of these hydrogen lines. To derive the BH mass (MBH) estimators, we used a sample of 37 unobscured type 1 AGNs with an MBH range of 106.8–109.4 M☉, where MBH comes from either the reverberation mapping method or single-epoch measurement method using Balmer lines. Our work shows that MBH can be estimated from the Paschen line luminosities and velocity widths to an accuracy of 0.18–0.24 dex (rms scatter). We also show that the mean line ratios of the Paschen lines and the Balmer lines are , , which are consistent with case B recombination under a typical AGN broad-line region (BLR) environment. These ratios can be used as reference points when estimating the amount of dust extinction over the BLR for red AGNs. We expect the future application of the new BH mass estimators on red, dusty AGNs to provide a fresh view of obscured AGNs.

The effects of an active galactic nucleus on host galaxy colour and morphology measurements

We assess the effects of simulated active galactic nuclei (AGN) on the colour and morphology measurements of their host galaxies. To test the morphology measurements, we select a sample of galaxies not known to host AGN and add a series of point sources scaled to represent specified fractions of the observed V-band light detected from the resulting systems; we then compare morphology measurements of the simulated systems to measurements of the original galaxies. AGN contributions >rsim 20 per cent bias most of the morphology measurements tested, though the extent of the apparent bias depends on the morphological characteristics of the original galaxies. We test colour measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to contribute specified fractions of the rest-frame B-band light detected from the resulting systems. A quasar fraction of 5 per cent can move the NUV −r colour of an elliptical galaxy from the ultraviolet–optical red sequence to the green valley, and 20 per cent can move it into the blue cloud. Combining the colour and morphology results, we find that a galaxy/AGN system with an AGN contribution >rsim 20 per cent may appear bluer and more bulge dominated than the underlying galaxy. We conclude that (1) bulge-dominated, E/S0/Sa, and early-type morphology classifications are accurate for red AGN host galaxies and may be accurate for blue host galaxies, unless the AGN manifests itself as a well-defined point source and (2) although highly unobscured AGN, such as the quasar used for our experiments, can significantly bias the measured colours of AGN host galaxies, it is possible to identify such systems by examining optical images of the hosts for the presence of a point source and/or measuring the level of nuclear obscuration.

The Southern 2MASS Active Galactic Nuclei Survey: Spectroscopic Follow-up with Six Degree Field

AbstractThe Two Micron All-Sky Survey (2MASS) has provided a uniform photometric catalog to search for previously unknown red active galactic nuclei (AGN) and Quasi-Stellar Objects (QSOs).We have extended the search to the southern equatorial sky by obtaining spectra for 1182 AGN candidates using the six degree field (6dF) multifibre spectrograph on the UK Schmidt Telescope. These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey. The candidates were selected using a single color cut of J – Ks &gt; 2 to Ks ≲ 15.5 and a galactic latitude of lbl &gt; 30°. 432 spectra were of sufficient quality to enable a reliable classification. 116 sources (∼27%) were securely classified as type I AGN, 20 as probable type I AGN, and 57 as probable type II AGN. Most of them span the redshift range 0.05 &lt; z &lt; 0.5 and only 8 (∼6%) were previously identified as AGN or QSOs. Our selection leads to a significantly higher AGN identification rate amongst local galaxies (&gt;20%) than in any previous (mostly blue-selected) galaxy survey. A small fraction of the type I AGN could have their optical colors reddened by optically thin dust with AV &lt; 2 mag relative to optically selected QSOs. A handful show evidence of excess far-infrared (IR) emission. The equivalent width (EW) and color distributions of the type I and II AGN are consistent with AGN unified models. In particular, the EW of the [Oiii] emission line weakly correlates with optical–near-IR color in each class of AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the optical properties of the 2MASS red AGN are not dramatically different from those of optically-selected QSOs. Our near-IR selection appears to detect the most near-IR luminous QSOs in the local universe to z≃0.6 and provides incentive to extend the search to deeper near-IR surveys.

An Atlas of Warm Active Galactic Nuclei and Starbursts from the IRAS Deep Fields

We present a set of 180 active galactic nucleus (AGN) candidates based on color selection from the IRAS slow-scan deep observations, with color criteria broadened from the initial Point Source Catalog samples so as to include similar objects with redshifts up to z = 1 and allowing for two-band detections. Spectroscopic identifications have been obtained for 80 (44%); some additional identifications are secure based on radio detections or optical morphology, although yet unobserved spectroscopically. These spectroscopic identifications include 13 type 1 Seyfert galaxies, 17 type 2 Seyferts, 29 starburst galaxies, 7 LINER systems, and 13 emission-line galaxies so heavily reddened as to remain of ambiguous classification. The optical magnitudes range from R = 12.0 to 20.5; the counts suggest that incompleteness is important fainter than R = 15.5. Redshifts extend to z = 0.51, with a significant part of the sample at z > 0.2. Even with the relaxed color criteria, this sample includes slightly more than star-forming systems among those where the spectra contain enough diagnostic feature to make the distinction. The active nuclei include several broad-line objects with strong Fe II emission, and composite objects with the absorption-line signatures of fading starbursts. These with warm far-IR colors have little overlap with the red AGNs identified with 2MASS; only a single Seyfert 1 was detected by 2MASS with J - K > 2. Some reliable IRAS detections have either very faint optical counterparts or only absorption-line galaxies, potentially being deeply obscured AGNs. The IRAS detections include a newly identified symbiotic star, and several possible examples of the Vega phenomenon, including dwarfs as cool as type K. Appendices detail these candidate stars, and the optical-identification content of a particularly deep set of high-latitude IRAS scans (probing the limits of optical identification from IRAS data alone).

Near‐Infrared Colors of Hard X‐Ray–selected Active Galactic Nuclei

We present results of near-infrared photometry (J, H, Ks) for a hard X-ray-selected sample of active galactic nuclei (AGNs) obtained from optical identification of the sources detected in ASCA surveys (total ~75 deg2) with a flux limit of (1-3) × 10-13 ergs s-1 cm-2 (2-10 keV). The sample covers the AGNs at 0.1 z 1 with L2-10 keV ~ 1042-1046 ergs s-1 with very high completeness. The near-infrared photometric data of the sample are obtained from the Two Micron All Sky Survey (2MASS) and observations with Kitt Peak National Observatory 2.1 m telescope and the University of Hawaii 2.2 m telescope. The fraction of red (J-KS > 2 mag) AGNs in our sample is ~2% ± 1%, which is comparable with that for optically or UV-selected quasi-stellar objects (QSOs, i.e., luminous AGNs). The number of red AGNs found in our sample is consistent with that expected from the surface density of red AGNs found in 2MASS by Cutri et al. (2001). We find that the anomalously small dust-to-gas ratios in circumnuclear gas, which is seen in some AGNs with Seyfert-class luminosity, also occur in the QSOs (AGNs with luminosity of L2-10 keV ≥ 1044.5 ergs s-1) in the systematically surveyed sample in hard X-rays. For all the QSOs with an X-ray absorption of NH ≥ 1022 cm-2 in our sample, the values of AV/NH are smaller than the Galactic value by a factor of ~5 to ~100. Since the fraction of this population among the QSOs in our sample is about 30%, the fraction of optical/UV-selected type 1 QSOs known to date may show a type 2 nature in X-ray.

The nature of red active galactic nuclei in X-ray selected samples

BVRI photmetry of a sample of X-ray selected AGNs is examined to determine the cause of the red colors of low-luminosity objects in such samples. It is found that the redness is generally due to the presence of an underlying galaxy and not due to reddening by dust. The B-I color of each object is used to determine the mixing fraction of galaxy light. The contamination of galaxy light is removed to produce corrected values of the optical spectra index for each object. These corrected values show that the variation of the optical spectra index with luminosity observed in optically selected AGNs is also present in X-ray selected AGNs. 66 refs.