arXiv subjects

Daniel Vanden Berk

Publications and source records attributed to Daniel Vanden Berk.

At least 19 recordsLinked to original sources

arXiv2014

The dust, nebular emission and dependence on QSO radio properties of the associated Mg II absorption line systems

We studied dust reddening and [O II] emission in 1730 Mg II associated absorption systems (AAS; relative velocity with respect to QSOs, < 3000 km/s; in units of velocity of light, \b{eta}, < 0.01) with 0.4 < z_abs < 2 in the SDSS DR7, focusing on their dependence on the radio and other QSO properties. We used control samples, several with matching radio properties to show (i) AAS in radio detected (RD) QSOs cause 2.6 +/- 0.2 times higher dust extinction than those in radio undetected (RUD) ones which, in turn, cause 2.9 +/- 0.7 times the dust extinction in the intervening systems; (ii) AAS in core-dominated QSOs cause 2.0 +/- 0.1 times higher dust extinction than in lobe-dominated QSOs; (iii) occurrence of AAS is 2.1 +/- 0.2 times more likely in RD QSOs than in RUD QSOs and 1.8 +/- 0.1 time more likely in QSOs having black holes with masses larger than 1.23 x 10^{9} M_sun than in those with lower mass black holes; (iv) there is excess flux in [O II]λ3727 emission in the composite spectra of the AAS samples compared to those of the control samples, which is at the emission redshift. Presence of AAS enhances the O II emission from the AGN and/or the host galaxy. This excess is similar for both RD and RUD samples, and is 2.5 +/- 0.4 times higher in lobe-dominated compared to core-dominated samples. The excess depends on the black hole mass and Eddington ratio. All these point to the intrinsic nature of the AAS except for the systems with z_abs > z_em which could be infalling galaxies.

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arXiv2013

Probing the Extended Gaseous Regions of M31 with Quasar Absorption Lines

We present HST-COS spectra of ten quasars located behind M31, selected to investigate the properties of gas associated with its extended disk and high velocity clouds (HVCs). The sightlines have impact parameters ranging between b= 13 kpc and 112 kpc. No absorption is detected in the four sightlines beyond b=57 kpc. Of the six remaining sightlines, all of which lie at b<32 kpc and within the N(HI)= 2E18 cm^{-2} boundary of the HI disk of M31, we detect low-ionization absorption at M31 velocities along four of them (three of which include MgII absorption). We also detect MgII absorption from an HVC. We find that along sightlines where both are detected, the velocity location of the low-ion gas tracks the peak in 21 cm emission. High-ionization absorption is detected along the three inner sightlines, but not along the three outer sightlines, for which CIV data exist. As inferred from 21 cm emission line maps, only one sightline may have a damped Ly-alpha system. This sightline has b= 17.5 kpc, and we detect both low- and high-ion absorption lines associated with it. The impact parameters through M31 are similar to the impact parameters of galaxies identified with MgII absorbers at redshifts 0.1<z<1.0 in a 2011 study by Rao et al. However, the M31 MgII2796 rest equivalent width values are significantly smaller. In comparison, moderate-to-strong MgII absorption from Milky Way gas is detected along all ten sightlines. Thus, this study indicates that M31 does not present itself as an absorbing galaxy which is typical of higher-redshift galaxies inferred to give rise to moderate-strength quasar absorption lines. M31 also appears not to possess an extensive large gaseous cross section, at least not along the direction of its major axis. (Abridged.)

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arXiv2012

Galaxies with Background QSOs, I: A Search for Strong Galactic H-alpha Lines

A search for emission lines in foreground galaxies in quasar spectra (z(gal) < z(QSO)) of the Sloan Digital Sky Survey (SDSS) data release 5 (DR5) reveals 23 examples of quasars shining through low redshift, foreground galaxies at small impact parameters (< 10 kpc). About 74,000 quasar spectra were examined by searching for narrow Hα emission lines at z < 0.38, at a flux level greater than 5 \times 10^-17 ergs cm^-2 s^-1, then confirming that other expected emission lines of the H II regions in the galaxy are detected. The galaxies were deblended from the quasar images to get colors and morphologies. For cases that allow the galaxy and the quasar to be deblended, the galaxies are blue (0.95 <(u-r)< 1.95). Extinction and reddening through the galaxies is determined from the (g-i) color excesses of the quasars. These reddening values are compared with the flux ratio of Hα to Hβ, which reflect the extinction for an undetermined fraction of the sightline through each galaxy. No trends were found relating E(B-V)_(g-i), impact parameter (b), and (u-r) for the galaxies or between E(B-V) derived from (g-i) and that derived from Hα/Hβ. Comparison with previous studies of quasar absorption systems indicate our sample is more reddened, suggesting disk-dominated absorber galaxies. Measurement or limits on galactic, interstellar Ca II and Na I absorption lines are given from the quasar spectrum. No trends were found relating Ca II equivalent width (W (Ca II)) or Na I equivalent width (W (Na I)) to b, but a correlation of r_s = -0.77 (α = 0.05) was found relating W (Ca II) and E(B-V)(g-i) .

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arXiv2012

A Quasar Catalog with Simultaneous UV, Optical and X-ray Observations by Swift

We have compiled a catalog of optically-selected quasars with simultaneous observations in UV/optical and X-ray bands by the Swift Gamma Ray Burst Explorer. Objects in this catalog are identified by matching the Swift pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The final catalog contains 843 objects, among which 637 have both UVOT and XRT observations and 354 of which are detected by both instruments. The overall X-ray detection rate is ~60% which rises to ~85% among sources with at least 10 ks of XRT exposure time. We construct the time-averaged spectral energy distribution for each of the 354 quasars using UVOT photometric measurements and XRT spectra. From model fits to these SEDs, we find that the big blue bump contributes about 0.3 dex to the quasar luminosity. We re-visit the alpha_ox-L_uv relation by selecting a clean sample with only type 1 radio-quiet quasars; the dispersion of this relation is reduced by at least 15% compared to studies that use non-simultaneous UV/optical and X-ray data. We only found a weak correlation between L/L_Edd and alpha_uv. We do not find significant correlations between alpha_x and alpha_ox, alpha_ox and alpha_uv, and alpha_x and Log L(0.3-10 keV). The correlations between alpha_uv and alpha_x, alpha_ox and alpha_x, alpha_ox and alpha_uv, L/L_Edd and alpha_x, and L/L_Edd and alpha_ox are stronger amongst low-redshift quasars, indicating that these correlations are likely driven by the changes of SED shape with accretion state.

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arXiv2011

Exploring the dust content of SDSS DR7 damped Lyman alpha systems at 2.15$\le z_{ab}< $5.2

We have studied a sample of 1084 intervening absorption systems with 2.15$\le z_{ab}\le$5.2, having log(N$_{\rm HI}$) $>$ 20.0 in the spectra of QSOs in Sloan Digital Sky Survey (SDSS) data release 7 (DR7), with the aim of understanding the nature and abundance of the dust and the chemical abundances in the DLA absorbers. Composite spectra were constructed for the full sample and several subsamples, chosen on the basis of absorber and QSO properties. Average extinction curves were obtained for the samples by comparing their geometric mean composite spectra with those of two samples of QSOs, matching in z$_{em}$ and i magnitude with the DLA sample, one sample without any absorbers along their lines of sight and the other without any DLAs along their lines of sight irrespective of the presence of other absorption systems. While the average reddening in the DLA sample is small, we find definite evidence for the presence of dust in subsamples based on absorber properties, in particular the strength of metal absorption lines. DLAs along lines of sight to QSOs which are not colour selected are found to be more dusty compared to those along the lines of sight to the more numerous colour selected QSOs. From these studies and from the strengths of absorption lines in the composite spectra, we conclude that $\le$ 10% of the DLAs in SDSS DR7 cause significant reddening, have stronger absorption lines and have higher abundances as compared to the rest of the sample. The rest of the sample shows little reddening. Due to the dominant color selection method used to target QSOs in the SDSS DR7, this fraction of 10% likely represents a lower limit for the global fraction of dusty DLAs at high-z.

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arXiv2010

Near-Ultraviolet Properties of a Large Sample of Type Ia Supernovae as Observed with the Swift UVOT

We present ultraviolet (UV) and optical photometry of 26 Type Ia supernovae (SNe~Ia) observed from March 2005 to March 2008 with the NASA {\it Swift} Ultraviolet and Optical Telescope (UVOT). The dataset consists of 2133 individual observations, making it by far the most complete study of the UV emission from SNe~Ia to date. Grouping the SNe into three subclasses as derived from optical observations, we investigate the evolution of the colors of these SNe, finding a high degree of homogeneity within the normal subclass, but dramatic differences between that group and the subluminous and SN 2002cx-like groups. For the normal events, the redder UV filters on UVOT ($u$, $uvw1$) show more homogeneity than do the bluer UV filters ($uvm2$, $uvw2$). Searching for purely UV characteristics to determine existing optically based groupings, we find the peak width to be a poor discriminant, but we do see a variation in the time delay between peak emission and the late, flat phase of the light curves. The UV light curves peak a few days before the $B$ band for most subclasses (as was previously reported by Jha et al. 2006a), although the SN 2002cx-like objects peak at a very early epoch in the UV. That group also features the bluest emission observed among SNe~Ia. As the observational campaign is ongoing, we discuss the critical times to observe, as determined by this study, in order to maximize the scientific output of future observations.

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arXiv2010

The Absolute Magnitudes of Type Ia Supernovae in the Ultraviolet

We examine the absolute magnitudes and light-curve shapes of 14 nearby(redshift z = 0.004--0.027) Type Ia supernovae (SNe~Ia) observed in the ultraviolet (UV) with the Swift Ultraviolet/Optical Telescope. Colors and absolute magnitudes are calculated using both a standard Milky Way (MW) extinction law and one for the Large Magellanic Cloud that has been modified by circumstellar scattering. We find very different behavior in the near-UV filters (uvw1_rc covering ~2600-3300 A after removing optical light, and u ~3000--4000 A) compared to a mid-UV filter (uvm2 ~2000-2400 A). The uvw1_rc-b colors show a scatter of ~0.3 mag while uvm2-b scatters by nearly 0.9 mag. Similarly, while the scatter in colors between neighboring filters is small in the optical and somewhat larger in the near-UV, the large scatter in the uvm2-uvw1 colors implies significantly larger spectral variability below 2600 A. We find that in the near-UV the absolute magnitudes at peak brightness of normal SNe Ia in our sample are correlated with the optical decay rate with a scatter of 0.4 mag, comparable to that found for the optical in our sample. However, in the mid-UV the scatter is larger, ~1 mag, possibly indicating differences in metallicity. We find no strong correlation between either the UV light-curve shapes or the UV colors and the UV absolute magnitudes. With larger samples, the UV luminosity might be useful as an additional constraint to help determine distance, extinction, and metallicity in order to improve the utility of SNe Ia as standardized candles.

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arXiv2009

Probing Spectroscopic Variability of Galaxies & Narrow-Line Active Galactic Nuclei in the Sloan Digital Sky Survey

Under the unified model for active galactic nuclei (AGNs), narrow-line (Type 2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured accretion disk. We would therefore expect the optical continuum emission from Type 2 AGN to be composed mainly of stellar light and non-variable on the time-scales of months to years. In this work we probe the spectroscopic variability of galaxies and narrow-line AGNs using the multi-epoch data in the Sloan Digital Sky Survey (SDSS) Data Release 6. The sample contains 18,435 sources for which there exist pairs of spectroscopic observations (with a maximum separation in time of ~700 days) covering a wavelength range of 3900-8900 angstrom. To obtain a reliable repeatability measurement between each spectral pair, we consider a number of techniques for spectrophotometric calibration resulting in an improved spectrophotometric calibration of a factor of two. From these data we find no obvious continuum and emission-line variability in the narrow-line AGNs on average -- the spectroscopic variability of the continuum is 0.07+/-0.26 mag in the g band and, for the emission-line ratios log10([NII]/Halpha) and log10([OIII]/Hbeta), the variability is 0.02+/-0.03 dex and 0.06+/-0.08 dex, respectively. From the continuum variability measurement we set an upper limit on the ratio between the flux of varying spectral component, presumably related to AGN activities, and that of host galaxy to be ~30%. We provide the corresponding upper limits for other spectral classes, including those from the BPT diagram, eClass galaxy classification, stars and quasars.

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arXiv2008

A Catalog of Broad Absorption Line Quasars in Sloan Digital Sky Survey Data Release 5

We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range >= 2000 km/s. We have fit ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range -25,000 to 0 km/s for SiIV $λ$1400, CIV $λ$1549, AlIII $λ$1857, and MgII $λ$2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise (S/N); for higher-S/N sources, we find an observed BAL fraction of approximately 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their CIV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker CIV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from over-ionization and enable radiative acceleration....

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arXiv2008

Ultraviolet Light Curves of Supernovae with Swift Uvot

We present ultravioliet (UV) observations of supernovae (SNe) obtained with the UltraViolet/Optical Telescope (UVOT) on board the Swift spacecraft. This is the largest sample of UV light curves from any single instrument and covers all major SN types and most subtypes. The UV light curves of SNe Ia are fairly homogenous while SNe Ib/c and IIP show more variety in their light curve shapes. The UV-optical colors clearly differentiate SNe Ia and IIP, particularly at early times. The color evolution of SNe IIP, however, makes their colors similar to SNe Ia at about 20 days after explosion. SNe Ib/c are shown to have varied UV-optical colors. The use of UV colors to help type SNe will be important for high redshift SNe discovered in optical observations. These data can be added to ground based optical and near infrared data to create bolometric light curves of individual objects and as checks on generic bolometric corrections used in the absence of UV data. This sample can also be compared with rest-frame UV observations of high redshift SNe observed at optical wavelengths.

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arXiv2008

Narrow associated QSO absorbers: clustering, outflows and the line-of-sight proximity effect

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3) we investigate how narrow (<700km/s) CIV and MgII quasar absorption line systems are distributed around quasars. The CIV absorbers lie in the redshift range 1.6 < z < 4 and the MgII absorbers in the range 0.4 40% of CIV absorbers within 3,000km/s of the QSO are not a result of large-scale clustering but rather are directly associated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow velocities of order 12,000km/s; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars; and (v) that a small high-velocity outflow component is observed in the MgII population, but any further intrinsic absorber component is undetectable in our clustering analysis. We also find an indication that absorption systems within 3,000km/s are more abundant for radio-loud than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive halos, or that their radio activity generates an additional low-velocity outflow, or both.

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arXiv2007

Exploring the Variable Sky with the Sloan Digital Sky Survey

We quantify the variability of faint unresolved optical sources using a catalog based on multiple SDSS imaging observations. The catalog covers SDSS Stripe 82, and contains 58 million photometric observations in the SDSS ugriz system for 1.4 million unresolved sources. In each photometric bandpass we compute various low-order lightcurve statistics and use them to select and study variable sources. We find that 2% of unresolved optical sources brighter than g=20.5 appear variable at the 0.05 mag level (rms) simultaneously in the g and r bands. The majority (2/3) of these variable sources are low-redshift (<2) quasars, although they represent only 2% of all sources in the adopted flux-limited sample. We find that at least 90% of quasars are variable at the 0.03 mag level (rms) and confirm that variability is as good a method for finding low-redshift quasars as is the UV excess color selection (at high Galactic latitudes). We analyze the distribution of lightcurve skewness for quasars and find that is centered on zero. We find that about 1/4 of the variable stars are RR Lyrae stars, and that only 0.5% of stars from the main stellar locus are variable at the 0.05 mag level. The distribution of lightcurve skewness in the g-r vs. u-g color-color diagram on the main stellar locus is found to be bimodal (with one mode consistent with Algol-like behavior). Using over six hundred RR Lyrae stars, we demonstrate rich halo substructure out to distances of 100 kpc. We extrapolate these results to expected performance by the Large Synoptic Survey Telescope and estimate that it will obtain well-sampled 2% accurate, multi-color lightcurves for ~2 million low-redshift quasars, and will discover at least 50 million variable stars.

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arXiv2006

GRB 060313: A New Paradigm for Short-Hard Bursts?

We report the simultaneous observations of the prompt emission in the gamma-ray and hard X-ray bands by the Swift-BAT and the KONUS-Wind instruments of the short-hard burst, GRB 060313. The observations reveal multiple peaks in both the gamma-ray and hard X-ray bands suggesting a highly variable outflow from the central explosion. We also describe the early-time observations of the X-ray and UV/Optical afterglows by the Swift XRT and UVOT instruments. The combination of the X-ray and UV/Optical observations provide the most comprehensive lightcurves to date of a short-hard burst at such an early epoch. The afterglows exhibit complex structure with different decay indices and flaring. This behavior can be explained by the combination of a structured jet, radiative loss of energy, and decreasing microphysics parameters occurring in a circum-burst medium with densities varying by a factor of approximately two on a length scale of 10^17 cm. These density variations are normally associated with the environment of a massive star and inhomogeneities in its windy medium. However, the mean density of the observed medium (n approximately 10^−4 cm^3) is much less than that expected for a massive star. Although the collapse of a massive star as the origin of GRB 060313 is unlikely, the merger of a compact binary also poses problems for explaining the behavior of this burst. Two possible suggestions for explaining this scenario are: some short bursts may arise from a mechanism that does not invoke the conventional compact binary model, or soft late-time central engine activity is producing UV/optical but no X-ray flaring.

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arXiv2006

Average Extinction Curves and Relative Abundances for QSO Absorption Line Systems at 1 <= z_abs < 2

We have studied a sample of 809 Mg II absorption systems with 1.0 < z_abs < 1.86 in the spectra of SDSS QSOs, with the aim of understanding the nature and abundance of the dust and the chemical abundances in the intervening absorbers. Normalized, composite spectra were derived, for abundance measurements, for the full sample and several sub-samples, chosen on the basis of the line strengths and other absorber and QSO properties. Average extinction curves were obtained for the sub-samples by comparing their geometric mean spectra with those of matching samples of QSOs without absorbers in their spectra. There is clear evidence for the presence of dust in the intervening absorbers. The 2175 A feature is not present in the extinction curves, for any of the sub-samples. The extinction curves are similar to the SMC extinction curve with a rising UV extinction below 2200 A. The absorber rest frame colour excess, E(B-V), derived from the extinction curves, depends on the absorber properties and ranges from < 0.001 to 0.085 for various sub-samples. The column densities of several ions do not show such a correspondingly large variation. The depletion pattern is similar to halo clouds in the Galaxy. Assuming an SMC gas-to-dust ratio we find a trend of increasing abundance with decreasing extinction; systems with N_H I \~ 10^{20} cm^{-2} show solar abundance of Zn. The large velocity spread of strong Mg II systems seems to be mimicked by weak lines of other elements. The ionization of the absorbers, in general appears to be low. QSOs with absorbers are, in general, at least three times as likely to have highly reddened spectra as compared to QSOs without any absorption systems in their spectra.

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arXiv2005

Large Scale Clustering of Sloan Digital Sky Survey Quasars: Impact of the Baryon Density and the Cosmological Constant

We report the first result of the clustering analysis of Sloan Digital Sky Survey (SDSS) quasars. We compute the two-point correlation function (2PCF) of SDSS quasars in redshift space at $8h^{-1}{\rm Mpc} < s < 500h^{-1}{\rm Mpc}$, with particular attention to its baryonic signature. Our sample consists of 19986 quasars extracted from the SDSS Data Release 4 (DR4). The redshift range of the sample is $0.72 \le z \le 2.24$ (the mean redshift is $\bar z = 1.46$) and the reddening-corrected $i$-band apparent magnitude range is $15.0 \le m_{i,{\rm rc}} \le 19.1$. Due to the relatively low number density of the quasar sample, the bump in the power spectrum due to the baryon density, $Ω_{\rm b}$, is not clearly visible. The effect of the baryon density is, however, to distort the overall shape of the 2PCF.The degree of distortion makes it an interesting alternate measure of the baryonic signature. Assuming a scale-independent linear bias and the spatially flat universe, i.e., $Ω_{\rm b} + Ω_{\rm d} + Ω_Λ=1$, where $Ω_{\rm d}$ and $Ω_Λ$ denote the density parameters of dark matter and the cosmological constant, we combine the observed quasar 2PCF and the predicted matter 2PCF to put constraints on $Ω_{\rm b}$ and $Ω_Λ$. Our result is fitted as $0.80- 2.8Ω_{\rm b} < Ω_Λ< 0.90 - 1.4Ω_{\rm b}$ at the 2$σ$ confidence level, which is consistent with results from other cosmological observations such as WMAP. (abridged)

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arXiv2005

Soft X-ray and Ultraviolet Emission Relations in Optically Selected AGN Samples

Using a sample of 228 optically selected Active Galactic Nuclei (AGNs) in the 0.01-6.3 redshift range with a high fraction of X-ray detections (81-86%), we study the relation between rest-frame UV and soft X-ray emission and its evolution with cosmic time. The majority of the AGNs in our sample (155 objects) have been selected from the Sloan Digital Sky Survey (SDSS) in an unbiased way, rendering the sample results representative of all SDSS AGNs. The addition of two heterogeneous samples of 36 high-redshift and 37 low-redshift AGNs further supports and extends our conclusions. We confirm that the X-ray emission from AGNs is correlated with their UV emission, and that the ratio of the monochromatic luminosity emitted at 2keV compared to 2500A decreases with increasing luminosity (a_ox=-0.136 l_uv+2.616, where l_uv is in log units), but does not change with cosmic time. These results apply to intrinsic AGN emission, as we correct or control for the effects of the host galaxy, UV/X-ray absorption, and any X-ray emission associated with radio emission in AGNs. We investigate a variety of systematic errors and can thereby state with confidence that (1) the a_ox-l_uv anti-correlation is real and not a result of accumulated systematic errors and (2) any a_ox dependence on redshift is negligible in comparison. We provide the best quantification of the a_ox-l_uv relation to date for normal radio-quiet AGNs; this should be of utility for researchers pursuing a variety of studies.

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arXiv2004

Double-Damped Lyman Alpha Absorption: A Possible Large Neutral Hydrogen Gas Filament Near Redshift z=1

We report the discovery of two damped Ly-alpha absorption-line systems (DLAs) near redshift z=1 along a single quasar sightline (Q1727+5302) with neutral hydrogen column densities of N(HI) = (1.45\pm0.15)\times10^{21} and (2.60\pm0.20)\times10^{21} atoms/cm2. Their sightline velocity difference of 13,000 km/s corresponds to a proper separation of 106h_{70}^{-1} Mpc if interpreted as the Hubble flow (Omega_m=0.3, Omega_Lambda=0.7). The random probability of such an occurrence is significantly less than 3%. With follow-up spectroscopy, we find [Zn/H] = -0.58\pm0.15 (26.5% solar) and -1.32\pm0.28 (4.7% solar), respectively, and [Cr/H] = -1.26\pm0.15 (5.5% solar) and -1.77\pm0.28 (1.7% solar), respectively, which is evidence for depletion onto grains. Follow-up IR images show the two most likely DLA galaxy candidates to have impact parameters of 22h_{70}^{-1} kpc and 32h_{70}^{-1} kpc if near z=1. They are significantly underluminous relative to the galaxy population at z=1. To investigate the possibility of additional high-N(HI) absorbers we have searched the SDSS database for z>1 quasars within 30 arcmin of the original sightline. Five were found, and two show strong MgII-FeII absorption near z=1, consistent with classical DLA absorption approx 37% of the time, but almost always N(HI) > 10^{19} atoms/cm2. Consequently, this rare configuration of four high-N(HI) absorbers with a total sightline velocity extent of 30,600 km/s may represent a large filament-like structure stretching over a proper distance of 241h_{70}^{-1} Mpc along our sightline, and a region in space capable of harboring excessive amounts of neutral gas. Future studies of this region of the sky are encouraged.

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arXiv2004

Eigenspectra of the SDSS DR1 quasars

We construct eigenspectra from the DR1 quasars in the SDSS using the Karhunen-Loève (KL) transform (or Principal Component Analysis, PCA) in different redshift and luminosity bins. We find that the quasar spectra can be classified, by the first two eigenspectra, into a continuous sequence in the variation of the spectral slope. We also find a dependence on redshift and luminosity in the eigencoefficients. The dominant redshift effect is the evolution of the blended Fe~II emission (optical) and the Balmer continuum (the ``small-bump'', $λ_{rest} \approx 2000-4000$Å), while the luminosity effect is related to the Baldwin effect. Correlations among several major broad emission lines are found, including the well-known ``Eigenvector-1''.

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