Sloan Digital Sky Survey Spectroscopy Research Articles

White dwarf pollution: one star or two?

ABSTRACT The accretion of tidally disrupted planetary bodies is the current consensus model for the presence of photospheric metals commonly detected in white dwarfs. While most dynamical studies have considered a single star and associated planetary instabilities, several investigations have instead considered the influence of widely bound stellar companions as potential drivers of white dwarf pollution. This study examines the prevalence of wide binaries among polluted white dwarfs using Gaia Data Release 3 astrometry, where three samples are investigated: 71 DAZ stars with metals detected in the ultraviolet using Hubble Space Telescope, and two groups of DZ stars identified via Sloan Digital Sky Survey spectroscopy, comprised of 116 warmer and 101 cooler sources. Each sample was searched for spatially resolved, comoving companions, and compared to the same analysis of thousands of field white dwarfs within overlapping regions of the Gaia Hertzsprung–Russell diagram. The wide binary fraction of the DAZ sample is $10.6_{-3.2}^{+3.9}$ per cent, and within $1\sigma$ of the corresponding field. However, the search yields wide binary fractions of less than 1.8 per cent for the two independent DZ star catalogues, which are each distinct from their fields by more than $3\sigma$. Both sets of results support that pollution in white dwarfs is not the result of stellar companions, and the delivery of metals to white dwarf surfaces is caused by major planets. The discrepancy between the DAZ and DZ star wide binary fractions cannot be caused by white dwarf spectral evolution, suggesting these two populations may have distinct planetary architectures.

Cosmological inference from an emulator based halo model. II. Joint analysis of galaxy-galaxy weak lensing and galaxy clustering from HSC-Y1 and SDSS

We present high-fidelity cosmology results from a blinded joint analysis of galaxy-galaxy weak lensing (ΔΣ) and projected galaxy clustering (wp) measured from the Hyper Suprime-Cam Year-1 (HSC-Y1) data and spectroscopic Sloan Digital Sky Survey (SDSS) galaxy catalogs in the redshift range 0.15<z<0.7. We define luminosity-limited samples of SDSS galaxies to serve as the tracers of wp in three spectroscopic redshift bins, and as the lens samples for ΔΣ. For the ΔΣ measurements, we select a single sample of 4×106 source galaxies over 140 deg2 from HSC-Y1 with photometric redshifts (photo z) greater than 0.75, enabling a better handle of photo-z errors by comparing the ΔΣ amplitudes for the three lens redshift bins. The deep, high-quality HSC-Y1 data enable significant detections of the ΔΣ signals, with integrated signal-to-noise ratio S/N∼15 in the range 3≤R/[h−1 Mpc]≤30 for the three lens samples, despite the small area coverage. For cosmological parameter inference, we use an input galaxy-halo connection model built on the dark emulator package (which uses an ensemble set of high-resolution N-body simulations and enables fast, accurate computation of the clustering observables) with a halo occupation distribution that includes nuisance parameters to marginalize over modeling uncertainties. We model the ΔΣ and wp measurements on scales from R≃3 and 2 h−1 Mpc, respectively, up to 30 h−1 Mpc (therefore excluding the baryon acoustic oscillations information) assuming a flat ΛCDM cosmology, marginalizing over about 20 nuisance parameters and demonstrating the robustness of our results to them. With various tests using mock catalogs described in Miyatake et al. [preceding paper, Phys. Rev. D 106, 083519 (2022)], we show that any bias in the clustering amplitude S8≡σ8(Ωm/0.3)0.5 due to uncertainties in the galaxy-halo connection is less than ∼50% of the statistical uncertainty of S8, unless the assembly biaseffect is unexpectedly large. Our best-fit models have S8=0.795−0.042+0.049 (mode and 68% credible interval) for the flat ΛCDM model; we find tighter constraints on the quantity S8(α=0.17)≡σ8(Ωm/0.3)0.17=0.745−0.031+0.039.23 MoreReceived 29 November 2021Accepted 22 August 2022DOI:https://doi.org/10.1103/PhysRevD.106.083520© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmologyDark energyGravitational lensesGravitation, Cosmology & Astrophysics

Hundreds of Low-mass Active Galaxies in the Galaxy And Mass Assembly (GAMA) Survey

We present an entirely new sample of 388 low-mass galaxies (M ⋆ ≤ 1010 M ⊙) that have spectroscopic signatures indicating the presence of massive black holes (BHs) in the form of active galactic nuclei (AGNs) or tidal disruption events. Of these, 70 have stellar masses in the dwarf galaxy regime with 108 ≲ M ⋆/M ⊙ ≲ 109.5. We identify the active galaxies by analyzing optical spectra of a parent sample of ∼23,000 low-mass emission-line galaxies in the Galaxy and Mass Assembly (GAMA) Survey Data Release 4, and employing four different diagnostics based on narrow emission-line ratios and the detection of high-ionization coronal lines. We find that 47 of the 388 low-mass active galaxies exhibit broad Hα in their spectra, corresponding to virial BH masses in the range M BH ∼ 105.0–7.7 M ⊙ with a median BH mass of 〈M BH〉 ∼ 106.2 M ⊙. Our sample extends to higher redshifts (z ≤ 0.3; 〈z〉 = 0.13) than previous samples of AGNs in low-mass/dwarf galaxies based on Sloan Digital Sky Survey spectroscopy, which can be attributed to the spectroscopic limit of GAMA being ∼2 mag deeper. Moreover, our multi-diagnostic approach has revealed low-mass active galaxies spanning a wide range of properties, from blue star-forming dwarfs to luminous “miniquasars” powered by low-mass BHs. As such, this work has implications for BH seeding and AGN feedback at low masses.

Relation of internal attenuation, dust emission, and the size of spiral galaxies

Aims.Dust in spiral galaxies produces emission in the far-infrared (FIR) and internal absorption in visible wavelengths. However, the relation of the two amounts is not trivial because optical absorption may saturate, but the FIR emission does not. Moreover, the volume concentration of dust plays a role in the relation of absorption and emission, which depends on the size of the galaxy. We explore the relation of these three quantities.Methods.In order to understand the geometrical problem, we developed a model of dust distribution. We also investigated the relation of the three variables with real data of spiral galaxies atz &lt; 0.2 using the spectroscopic Sloan Digital Sky Survey and FIR AKARI survey. Internal absorptions were derived with two different methods: the ratio of emission lines Hαand Hβ, and a previously calibrated relation based on the color variations as a function of absolute magnitude and concentration index.Results.We find that in our low-zsample, the dependence of the average internal attenuation on galaxy size is negligible on average because of the relation of dust mass with size. It allows us to derive the internal attenuation of the galaxy,AV, even when we only know its FIR flux. This attenuation approximately depends on the inclination of the galaxyiasAV̄ =γV̄ log101cos i, whereγVis a constant. We found thatγVhas a maximum value for galaxies of 1.45 ± 0.27 magnitudes. When similar properties of dust are assumed, a general expression can be used at anyz:γV̄ = (1.45 ± 0.27)fMexp[−(1.0 ± 0.6)fM] andfM= 7.6 × 10−6αhR−1.75× (FFIR/700 Jy) 1.87 ×fcosmol.(z); the dependence on the cosmological model is embedded infcosmol.(z) =dL(z)(Mpc)2(1 + z)(1.75η − 1.87), whereη = 2 for cosmologies following Etherington’s relation,dLis the luminosity distance,αhRis the angular size of the scalelength, andFFIRthe flux at wavelength 100(1 + z) μm.Conclusions.For cases of nonsaturation (f ≲ 3.6), this might be used as a cosmological test because the factorfcosmol.at highzvaries strongly in different cosmologies. Although the present-day sensitivity of FIR or millimeter surveys does not allow us to carry out this cosmological test within the standard model, it may be used in the future, when we can observe galaxies atz = 3−5 with a sensitivity at ∼500 μm better than ∼10 μJy, for instance. For much lowerzor different cosmological models, a test might be feasible at present.

Host galaxy and orientation differences between different AGN types

Aims. The main purpose of this study is to investigate aspects regarding the validity of the active galactic nucleus (AGN) unification paradigm (UP). In particular, we focus on the AGN host galaxies, which according to the UP should show no systematic differences depending on the AGN classification. Methods. For the purpose of this study, we used (a) the spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 14 catalogue, in order to select and classify AGNs using emission line diagnostics, up to a redshift of z = 0.2, and (b) the Galaxy Zoo Project catalogue, which classifies SDSS galaxies in two broad Hubble types: spirals and ellipticals. Results. We find that the fraction of type 1 Seyfert nuclei (Sy1) hosted in elliptical galaxies is significantly larger than the corresponding fraction of any other AGN type, while there is a gradient of increasing spiral-hosts from Sy1 to LINER, type 2 Seyferts (Sy2) and composite nuclei. These findings cannot be interpreted within the simple unified model, but possibly by a co-evolution scheme for supermassive black holes and galactic bulges. Furthermore, for the case of spiral host galaxies we find the Sy1 population to be strongly skewed towards face-on configurations, while the corresponding Sy2 population range in all host galaxy orientation configurations has a similar, but not identical, orientation distribution to star-forming galaxies. These results also cannot be interpreted by the standard unification paradigm, but point towards a significant contribution of the galactic disc to the obscuration of the nuclear region. This is also consistent with the observed preference of Sy1 nuclei to be hosted by ellipticals, that is, the dusty disc of spiral hosts contributes to the obscuration of the broad-line region, and thus relatively more ellipticals are expected to appear hosting Sy1 nuclei.

A Chandra and HST View of WISE-selected AGN Candidates in Dwarf Galaxies

Abstract Reliably identifying active galactic nuclei (AGNs) in dwarf galaxies is key to understanding black hole (BH) demographics at low masses and constraining models for BH seed formation. Here we present Chandra X-ray Observatory observations of 11 dwarf galaxies that were chosen as AGN candidates using Wide-field Infrared Survey Explorer (WISE) mid-infrared (mid-IR) color–color selection. Hubble Space Telescope images are also presented for 10 of the galaxies. Based on Sloan Digital Sky Survey spectroscopy, six galaxies in our sample have optical evidence for hosting AGNs and five are classified as star-forming. We detect X-ray point sources with luminosities above that expected from X-ray binaries in the nuclei of five of the six galaxies with optical evidence of AGNs. However, the X-ray emission from these AGNs is generally much lower than expected based on AGN scaling relations with infrared and optical tracers. We do not find compelling evidence for AGNs in the five optically-selected star-forming galaxies despite having red mid-IR colors. Only two are detected in X-rays and their properties are consistent with stellar-mass X-ray binaries. Based on this multiwavelength study, we conclude that two-color mid-IR AGN diagnostics at the resolution of WISE cannot be used to reliably select AGNs in optically-star-forming dwarf galaxies. Future observations in the infrared with the James Webb Space Telescope offer a promising path forward.

On the AGN nature of broad balmer emission in four low-redshift metal-poor galaxies

ABSTRACT We report on continued, ∼15-yr long, broad Balmer emission lines in three metal-poor dwarf emission-line galaxies selected from Sloan Digital Sky Survey spectroscopy. The persistent luminosity of the broad Balmer emission indicates the galaxies are active galactic nuclei (AGNs) with virial black hole masses of ∼106.7–107.0 M⊙. The lack of observed hard X-ray emission and the possibility that the Balmer emission could be due to a long-lived stellar transient motivated additional follow-up spectroscopy. We also identify a previously unreported blueshifted narrow absorption line in the broad H α feature in one of the AGNs, indicating an AGN-driven outflow with hydrogen column densities of order 1017 cm−2. We also extract light curves from the Catalina Real-Time Transient Survey and the Zwicky Transient Facility. We detect probable AGN-like variability in three galaxies, further supporting the AGN scenario. This also suggests the AGNs are not strongly obscured. This sample of galaxies are among the most metal-poor that host an AGN (Z = 0.05–0.16 Z⊙). We speculate they may be analogues to seed black holes which formed in unevolved galaxies at high redshift. Given the rarity of metal-poor AGNs and small sample size available, we investigate prospects for their identification in future spectroscopic and photometric surveys.

Self-supervised Representation Learning for Astronomical Images

Abstract Sky surveys are the largest data generators in astronomy, making automated tools for extracting meaningful scientific information an absolute necessity. We show that, without the need for labels, self-supervised learning recovers representations of sky survey images that are semantically useful for a variety of scientific tasks. These representations can be directly used as features, or fine-tuned, to outperform supervised methods trained only on labeled data. We apply a contrastive learning framework on multiband galaxy photometry from the Sloan Digital Sky Survey (SDSS), to learn image representations. We then use them for galaxy morphology classification and fine-tune them for photometric redshift estimation, using labels from the Galaxy Zoo 2 data set and SDSS spectroscopy. In both downstream tasks, using the same learned representations, we outperform the supervised state-of-the-art results, and we show that our approach can achieve the accuracy of supervised models while using 2–4 times fewer labels for training. The codes, trained models, and data can be found at https://portal.nersc.gov/project/dasrepo/self-supervised-learning-sdss.

The Diverse Morphologies and Structures of Dwarf Galaxies Hosting Optically Selected Active Massive Black Holes

Abstract We present a study of 41 dwarf galaxies hosting active massive black holes (BHs) using Hubble Space Telescope observations. The host galaxies have stellar masses in the range of M ⋆ ∼ 108.5–109.5 M ⊙ and were selected to host active galactic nuclei (AGNs) based on narrow emission line ratios derived from Sloan Digital Sky Survey spectroscopy. We find a wide range of morphologies in our sample including both regular and irregular dwarf galaxies. We fit the HST images of the regular galaxies using GALFIT and find that the majority are disk-dominated with small pseudobulges, although we do find a handful of bulge-like/elliptical dwarf galaxies. We also find an unresolved source of light in all of the regular galaxies, which may indicate the presence of a nuclear star cluster and/or the detection of AGN continuum. Three of the galaxies in our sample appear to be Magellanic-type dwarf irregulars and two galaxies exhibit clear signatures of interactions/mergers. This work demonstrates the diverse nature of dwarf galaxies hosting optically selected AGNs. It also has implications for constraining the origin of the first BH seeds using the local BH occupation fraction at low masses—we must account for the various types of dwarf galaxies that may host BHs.

Searching for Low-mass Population III Stars Disguised as White Dwarfs

Abstract It is uncertain whether or not low-mass Population III stars ever existed. While limits on the number density of Population III stars with M * ≈ 0.8 M ⊙ have been derived, using Sloan Digital Sky Survey (SDSS) data, little is known about the occurrence of Population III stars at lower masses. In the absence of reliable parallaxes, the spectra of metal-poor main-sequence (MPMS) stars with M * ≲ 0.8 M ⊙ can easily be confused with those of cool white dwarfs. To resolve this ambiguity, in this paper we present a classifier that differentiates between MPMS stars and white dwarfs, based on photometry and/or spectroscopy without the use of parallax information. We build and train our classifier using state-of-the-art theoretical spectra, and evaluate it on existing SDSS-based classifications for objects with reliable Gaia DR2 parallaxes. We then apply our classifier to a large catalog of objects with SDSS photometry and spectroscopy to search for MPMS candidates. We discover several previously unknown, extremely metal-poor (EMP) candidate stars, and recover numerous confirmed EMP stars already noted in the literature. We conclude that archival SDSS spectroscopy has already been exhaustively searched for EMP stars. We predict that the lowest-mass stars of primordial composition will have redder optical-to-infrared colors than cool white dwarfs at constant effective temperature, due to surface gravity-dependent collision-induced absorption from molecular hydrogen. We suggest that the application of our classifier to data produced by next-generation spectroscopic surveys will set stronger constraints on the number density of low-mass Population III stars in the Milky Way.

HOLISMOKES

We present a systematic search for wide-separation (with Einstein radius θE ≳ 1.5″), galaxy-scale strong lenses in the 30 000 deg2 of the Pan-STARRS 3π survey on the Northern sky. With long time delays of a few days to weeks, these types of systems are particularly well-suited for catching strongly lensed supernovae with spatially-resolved multiple images and offer new insights on early-phase supernova spectroscopy and cosmography. We produced a set of realistic simulations by painting lensed COSMOS sources on Pan-STARRS image cutouts of lens luminous red galaxies (LRGs) with redshift and velocity dispersion known from the sloan digital sky survey (SDSS). First, we computed the photometry of mock lenses in gri bands and applied a simple catalog-level neural network to identify a sample of 1 050 207 galaxies with similar colors and magnitudes as the mocks. Second, we trained a convolutional neural network (CNN) on Pan-STARRS gri image cutouts to classify this sample and obtain sets of 105 760 and 12 382 lens candidates with scores of pCNN &gt; 0.5 and &gt; 0.9, respectively. Extensive tests showed that CNN performances rely heavily on the design of lens simulations and the choice of negative examples for training, but little on the network architecture. The CNN correctly classified 14 out of 16 test lenses, which are previously confirmed lens systems above the detection limit of Pan-STARRS. Finally, we visually inspected all galaxies with pCNN &gt; 0.9 to assemble a final set of 330 high-quality newly-discovered lens candidates while recovering 23 published systems. For a subset, SDSS spectroscopy on the lens central regions proves that our method correctly identifies lens LRGs at z ∼ 0.1–0.7. Five spectra also show robust signatures of high-redshift background sources, and Pan-STARRS imaging confirms one of them as a quadruply-imaged red source at zs = 1.185, which is likely a recently quenched galaxy strongly lensed by a foreground LRG at zd = 0.3155. In the future, high-resolution imaging and spectroscopic follow-up will be required to validate Pan-STARRS lens candidates and derive strong lensing models. We also expect that the efficient and automated two-step classification method presented in this paper will be applicable to the ∼4 mag deeper gri stacks from the Rubin Observatory Legacy Survey of Space and Time (LSST) with minor adjustments.

The cosmic atomic hydrogen mass density as a function of mass and galaxy hierarchy from spectral stacking

ABSTRACT We use spectral stacking to measure the contribution of galaxies of different masses and in different hierarchies to the cosmic atomic hydrogen (H i) mass density in the local Universe. Our sample includes 1793 galaxies at z &amp;lt; 0.11 observed with the Westerbork Synthesis Radio Telescope, for which Sloan Digital Sky Survey spectroscopy and hierarchy information are also available. We find a cosmic H i mass density of $\Omega _{\rm H\, \small {I} } = (3.99 \pm 0.54)\times 10^{-4} \, h_{70}^{-1}$ at 〈 z〉 = 0.065. For the central and satellite galaxies, we obtain $\Omega _{\rm H\, {\small {I}}}$ of $(3.51 \pm 0.49)\times 10^{-4} \, h_{70}^{-1}$ and $(0.90 \pm 0.16)\times 10^{-4} \, h_{70}^{-1}$, respectively. We show that galaxies above and below stellar masses of ∼109.3 M⊙ contribute in roughly equal measure to the global value of $\Omega _{\rm H\, \small {I} }$. While consistent with estimates based on targeted H i surveys, our results are in tension with previous theoretical work. We show that these differences are, at least partly, due to the empirical recipe used to set the partition between atomic and molecular hydrogen in semi-analytical models. Moreover, comparing our measurements with the cosmological semi-analytic models of galaxy formation Shark and GALFORM reveals gradual stripping of gas via ram pressure works better to fully reproduce the properties of satellite galaxies in our sample than strangulation. Our findings highlight the power of this approach in constraining theoretical models and confirm the non-negligible contribution of massive galaxies to the H i mass budget of the local Universe.

AGaiaData Release 2 catalogue of white dwarfs and a comparison with SDSS

We present a catalogue of white dwarf candidates selected from the second data release of $Gaia$ (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey (SDSS) to map the entire space spanned by these objects in the $Gaia$ Hertzsprung-Russell diagram. We then defined a set of cuts in absolute magnitude, colour, and a number of $Gaia$ quality flags to remove the majority of contaminating objects. Finally, we adopt a method analogous to the one presented in our earlier SDSS photometric catalogues to calculate a probability of being a white dwarf ($P_{\mathrm{WD}}$) for all $Gaia$ sources which passed the initial selection. The final catalogue is composed of $486\,641$ stars with calculated $P_{\mathrm{WD}}$ from which it is possible to select a sample of $\simeq 260\,000$ high-confidence white dwarf candidates in the magnitude range $8<G<21$. By comparing this catalogue with a sample of SDSS white dwarf candidates we estimate an upper limit in completeness of $85$ per cent for white dwarfs with $G \leq 20$ mag and $T_{\mathrm{eff}} > 7000$ K, at high Galactic latitudes ($|b|>20^{\circ}$). However, the completeness drops at low Galactic latitudes, and the magnitude limit of the catalogue varies significantly across the sky as a function of $Gaia$'s scanning law. We also provide the list of objects within our sample with available SDSS spectroscopy. We use this spectroscopic sample to characterise the observed structure of the white dwarf distribution in the H-R diagram.

Emission Line Ratios for the Circumgalactic Medium and the “Bimodal” Nature of Galaxies

Abstract We find significantly different diagnostic emission line ratios for the circumgalactic gas associated with galaxies of stellar masses above and below 1010.4 M ⊙ using Sloan Digital Sky Survey spectroscopy. Specifically, in a sample of 17,393 galaxies, intersected by 18,535 lines of sight at projected radii between 10 and 50 kpc, we stack measured fluxes for nebular strong emission lines, [O iii] λ5007, Hα, and [N ii] λ6583, and find that the gas surrounding the lower-mass galaxies exhibits similar line ratios to those of gas ionized by star formation and that surrounding the higher-mass galaxies similar to those of gas ionized by active galactic nucleus or shocks. This finding highlights yet another characteristic of galaxies that is distinctly different above and below this stellar mass threshold, but one that is more closely connected to the gas accretion behavior hypothesized to be responsible for this dichotomy.

A Gemini snapshot survey for double degenerates

We present the results from a Gemini snapshot radial-velocity survey of 44 low-mass white dwarf candidates selected from the Sloan Digital Sky Survey spectroscopy. To find sub-hour orbital period binary systems, our time-series spectroscopy had cadences of 2 to 8 min over a period of 20-30 min. Through follow-up observations at Gemini and the MMT, we identify four double degenerate binary systems with periods ranging from 53 min to 7 h. The shortest period system, SDSS J123549.88+154319.3, was recently identified as a subhour period detached binary by Breedt and collaborators. Here we refine the orbital and physical parameters of this system. High-speed and time domain survey photometry observations do not reveal eclipses or other photometric effects in any of our targets. We compare the period distribution of these four systems with the orbital period distribution of known double white dwarfs; the median period decreases from 0.64 to 0.24 d for $M=0.3-0.5 M_{\odot}$ to $M<0.3 M_{\odot}$ white dwarfs. However, we do not find a statistically significant correlation between the orbital period and white dwarf mass.

H2O Megamasers toward Radio-bright Seyfert 2 Nuclei*

Abstract Using the Effelsberg-100 m telescope, we perform a successful pilot survey on H2O maser emission toward a small sample of radio-bright Seyfert 2 galaxies with a redshift larger than 0.04. The targets were selected from a large Seyfert 2 sample derived from the spectroscopic Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). One source, SDSS J102802.9+104630.4 (z ∼ 0.0448), was detected four times during our observations, with a typical maser flux density of ∼30 mJy and a corresponding (very large) luminosity of ∼1135 L ⊙. The successful detection of this radio-bright Seyfert 2 and an additional tentative detection support our previous statistical results that H2O megamasers tend to arise from Seyfert 2 galaxies with large radio luminosity. The finding provides further motivation for an upcoming larger H2O megamaser survey toward Seyfert 2s with particularly radio-bright nuclei with the basic goal to improve our understanding of the nuclear environment of active megamaser host galaxies.

The close pair fraction of BCGs since z = 0.5: major mergers dominate recent BCG stellar mass growth

Using the redMaPPer (red-sequence Matched-filter Probabilistic Percolation) cluster catalogue based on the Sloan Digital Sky Survey (SDSS) photometry, we investigate the importance of major mergers in the stellar mass build-up of brightest cluster galaxies (BCGs) between 0.08 ≤ z ≤ 0.50. We use the SDSS spectroscopy, supplemented with spectroscopic observations from the Southern African Large Telescope at higher redshifts, to identify which BCGs and nearby companions are potential major merger candidates. We use the pair fraction as a proxy for the merger fraction in order to determine how much stellar mass growth the BCGs have experienced due to major mergers. We observe a weak trend of the BCG pair fraction increasing with decreasing redshift, suggesting that major mergers may become more important towards the present day. Major mergers are found to contribute, on average, 24 ± 14 (29 ± 17) per cent towards the stellar mass of a present-day BCG since z = 0.32 (0.45), assuming that half of the companion's stellar mass is accreted on to the BCG. Furthermore, using our merger results in conjunction with predictions from two recent semi-analytical models along with observational measurements from the literature, we find that major mergers have sufficient stellar material to account for the stellar mass growth of the intracluster light between z = 0.3 and 0.

Catalog of candidates for quasars at 3 &lt; z &lt; 5.5 selected among X-Ray sources from the 3XMM-DR4 survey of the XMM-Newton observatory

We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3<z<5.5 selected among the X-ray sources of the serendipitous XMM-Newton survey presented in the 3XMM-DR4 catalog (the median X-ray flux is 5x10^{-15} erg/s/cm^2 the 0.5-2 keV energy band) and located at high Galactic latitudes >20 deg in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg^2. Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error Delta z<0.2 and a color i-z<0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences chi^2(z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z=0 and obtained a sample of quasars with photometric redshift estimates 2.75<zphot<5.5. The selection completeness of known quasars at z>3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation is 0.07, while the outlier fraction is eta= 9. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3<z<5.5 will allow the purity of this sample to be estimated more accurately.

The SDSS spectroscopic catalogue of white dwarf-main-sequence binaries: new identifications from DR 9–12

We present an updated version of the spectroscopic catalogue of white dwarf-main sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 939 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effective temperatures, surface gravities and masses, and secondary star spectral types). The analysis of the corresponding stellar parameter distributions shows that the SDSS WDMS binary population is seriously affected by selection effects. We also measure the NaI 8183.27, 8194.81 absorption doublet and Halpha emission radial velocities (RV) from all SDSS WDMS binary spectra identified in this work. 98 objects are found to display RV variations, 62 of which are new. The RV data are sufficient enough to estimate the orbital periods of three close binaries.

RELATIONS BETWEEN CENTRAL BLACK HOLE MASS AND TOTAL GALAXY STELLAR MASS IN THE LOCAL UNIVERSE

Scaling relations between central black hole (BH) mass and host galaxy properties are of fundamental importance to studies of BH and galaxy evolution throughout cosmic time. Here we investigate the relationship between BH mass and host galaxy total stellar mass using a sample of 262 broad-line active galactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79 galaxies with dynamical BH masses. The vast majority of our AGN sample is constructed using Sloan Digital Sky Survey spectroscopy and searching for Seyfert-like narrow-line ratios and broad H-alpha emission. BH masses are estimated using standard virial techniques. We also include a small number of dwarf galaxies with total stellar masses M_stellar < 10^9.5 Msun and a sub-sample of the reverberation-mapped AGNs. Total stellar masses of all 341 galaxies are calculated in the most consistent manner feasible using color-dependent mass-to-light ratios. We find a clear correlation between BH mass and total stellar mass for the AGN host galaxies, with M_BH proportional to M_stellar, similar to that of early-type galaxies with dynamically-detected BHs. However, the relation defined by the AGNs has a normalization that is lower by more than an order of magnitude, with a BH-to-total stellar mass fraction of M_BH/M_stellar ~ 0.025% across the stellar mass range 10^8 < M_stellar/Msun < 10^12. This result has significant implications for studies at high redshift and cosmological simulations in which stellar bulges cannot be resolved.