Timothy A. Reichard

Johns Hopkins University, Baltimore, Maryland, United States

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Publications (13)54.53 Total impact

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    ABSTRACT: We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release. An automated algorithm was used to match a continuum to each quasar and to identify regions of flux at least 10% below the continuum over a velocity range of at least 1000 km s-1 in the C and Mg absorption regions. The model continuum was selected as the best-fit match from a set of template quasar spectra binned in luminosity, emission line width, and redshift, with the power-law spectral index and amount of dust reddening as additional free parameters. We characterize our sample through the traditional "balnicity" index and a revised absorption index, as well as through parameters such as the width, outflow velocity, fractional depth, and number of troughs. From a sample of 16,883 quasars at 1.7 ≤ z ≤ 4.38, we identify 4386 (26.0%) quasars with broad C absorption, of which 1756 (10.4%) satisfy traditional selection criteria. From a sample of 34,973 quasars at 0.5 ≤ z ≤ 2.15, we identify 457 (1.31%) quasars with broad Mg absorption, 191 (0.55%) of which satisfy traditional selection criteria. We also provide a supplementary list of 39 visually identified z > 4.38 quasars with broad C absorption. We find that broad absorption line quasars may have broader emission lines on average than other quasars.
    The Astrophysical Journal Supplement Series 12/2008; 165(1):1. · 16.24 Impact Factor
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    ABSTRACT: We have used the Sloan Digital Sky Survey (SDSS) to undertake an investigation of lopsidedness in a sample of ~25,000 nearby galaxies (z < 0.06). We use the m=1 azimuthal Fourier mode between the 50% and 90% light radii as our measure of lopsidedness. The SDSS spectra are used to measure the properties of the stars, gas, and black hole in the central-most few-kpc-scale region. We show that there is a strong link between lopsidedness in the outer parts of the galactic disk and the youth of the stellar population in the central region. This link is independent of the other structural properties of the galaxy. These results provide a robust statistical characterization of the connections between accretion/interactions/mergers and the resulting star formation. We also show that residuals in the galaxy mass-metallicity relation correlate with lopsidedness (at fixed mass, the more metal-poor galaxies are more lopsided). This suggests that the events causing lopsidedness and enhanced star formation deliver lower metallicity gas into the galaxy's central region. Finally, we find that there is a trend for the more powerful active galactic nuclei to be hosted by more lopsided galaxies (at fixed galaxy mass, density, or concentration). However if we compare samples matched to have both the same structures and central stellar populations, we then find no difference in lopsidedness between active and non-active galaxies. This leads to the following picture. The presence of cold gas in the central region of a galaxy (irrespective of its origin) is essential for both star-formation and black hole growth. The delivery of cold gas is aided by the processes that produce lopsidedness. Other processes on scales smaller than we can probe with our data are required to transport the gas to the black hole. Comment: 39 pages, 16 figures, 3 tables, accepted to ApJ. Updated author affiliations
    The Astrophysical Journal 09/2008; · 6.73 Impact Factor
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    ABSTRACT: We present a catalog of 224 broad absorption line quasars (BALQSOs) from the Sloan Digital Sky Survey's Early Data Release Quasar Catalog, including a relatively complete and homogeneous subsample of 131 BALQSOs. Since the identification of BALQSOs is subject to considerable systematic uncertainties, we attempt to create a complete sample of SDSS BALQSOs by combining the results of two automated selection algorithms and a by-eye classification scheme. One of these automated algorithms finds broad absorption line troughs by comparing with a composite quasar spectrum. We present the details of this algorithm and compare this method with one that uses a power-law fit to the continuum. The BALQSOs in our sample are further classified as high-ionization BALQSOs (HiBALs), low-ionization BALQSOs (LoBALs), and BALQSOs with excited iron absorption features (FeLoBALs); composite spectra of each type are presented. We further present a study of the properties of the BALQSOs in terms of the balnicity distribution, which rises with decreasing balnicity. This distribution of balnicities suggests that the fraction of quasars with intrinsic outflows may be significantly underestimated.
    The Astronomical Journal 12/2007; 125(4):1711. · 4.97 Impact Factor
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    ABSTRACT: We investigate the continuum and emission-line properties of 224 broad absorption line quasars (BALQSOs) with 0.9 z 4.4 drawn from the Sloan Digital Sky Survey Early Data Release, which contains 3814 bona fide quasars. We find that low-ionization BALQSOs (LoBALs) are significantly reddened as compared with normal quasars, in agreement with previous work. High-ionization BALQSOs (HiBALs) are also more reddened than the average non-BALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount of reddening needed to explain HiBALs is E(B-V) ~ 0.023 and LoBALs is E(B-V) ~ 0.077 (compared with the ensemble average of the entire quasar sample). We find that there are differences in the emission-line properties between the average HiBAL, LoBAL, and non-BAL quasar. These differences, along with differences in the absorption-line troughs, may be related to intrinsic quasar properties such as the slope of the intrinsic (unreddened) continuum; more extreme absorption properties are correlated with bluer intrinsic continua. Despite the differences among BALQSO subtypes and non-BALQSOs, BALQSOs appear to be drawn from the same parent population as non-BALQSOs when both are selected by their UV/optical properties. We find that the overall fraction of traditionally defined BALQSOs, after correcting for color-dependent selection effects due to different SEDs of BALQSOs and non-BALQSOs, is 13.4% ± 1.2% and shows no significant redshift dependence for 1.7 ≤ z ≤ 3.45. After a rough completeness correction for the effects of dust extinction, we find that approximately one in every six quasars is a BALQSO.
    The Astronomical Journal 12/2007; 126(6):2594. · 4.97 Impact Factor
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    ABSTRACT: Using a sample of 3814 quasars from the Early Data Release of the Sloan Digital Sky Survey, we confirm that high-ionization, broad emission lines, such as C IV, are significantly blueshifted with respect to low-ionization, broad emission lines, such as Mg II, which are thought to be close to the systemic redshift. We examine the velocity shifts of the Mg II and C IV emission lines with respect to [O III] and Mg II, respectively. C IV emission-line peaks have a range of shifts from a redshift of 500 km s-1 to blueshifts well in excess of 2000 km s-1 as compared with Mg II. We confirm previous results that suggest an anticorrelation between the shift of the C IV emission-line peak and the rest equivalent width of the C IV emission line. Furthermore, by creating composite quasar spectra as a function of C IV shift, we are able to study in detail the profiles of the line as a function of velocity shift. We find that the apparent shift of the C IV emission-line peak is not a shift so much as it is a lack of flux in the red wing for the composite with the largest apparent shift. This observation should strongly constrain models for the broad emission-line region in quasars. The emission-line blueshift and equivalent width of C IV are also discussed in light of the well-known anticorrelation between the equivalent width of C IV emission and continuum luminosity, otherwise known as the Baldwin effect. We further discuss the C IV emission-line shift as a function of other quasar properties, such as spectral index, radio and X-ray detection. We find a possible correlation between the C IV emission-line shifts and the radio properties of the quasars, which is suggestive of orientation as the cause of the C IV velocity shifts. Finally, we explore whether the C IV emission-line blueshifts correlate with the presence of broad absorption line absorption troughs or with narrow, "associated" absorption, and how these might be related to orientation.
    The Astronomical Journal 12/2007; 124(1):1. · 4.97 Impact Factor
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    ABSTRACT: We investigate the overall continuum and emission-line properties of quasars as a function of their optical/UV spectral energy distributions. Our sample consists of 4576 quasars from the Sloan Digital Sky Survey (SDSS) that were chosen using homogeneous selection criteria. Expanding on our previous work, which demonstrated that the optical/UV color distribution of quasars is roughly Gaussian but with a red tail, here we distinguish between (1) quasars that have intrinsically blue (optically flat) power-law continua, (2) quasars that have intrinsically red (optically steep) power-law continua, and (3) quasars whose colors are inconsistent with a single power-law continuum. We find that 273 (6.0%) of the quasars in our sample fall into the latter category and appear to be redder because of SMC-like dust extinction and reddening rather than because of synchrotron emission. Even though the SDSS quasar survey is optically selected and flux-limited, we demonstrate that it is sensitive to dust reddened quasars with E(B-V) 0.5, assuming a classical SMC extinction curve. The color distribution of our SDSS quasar sample suggests that the population of moderately dust reddened, but otherwise normal (i.e., type 1) quasars is smaller than the population of unobscured quasars: we estimate that a further 10% of the quasar population with Mi < -25.61 is missing from the SDSS sample because of extinction, bringing the total fraction of dust-reddened quasars to 15% of broad-line quasars. We also investigate the emission- and absorption-line properties of these quasars as a function of color and comment on how some of these results relate to Boroson-Green–type eigenvectors. Quasars with intrinsically red (optically steep) power-law continua tend to have narrower Balmer lines and weaker C IV, C III], He II, and 3000 Å bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 Å bump appears to be dominated by the Balmer continuum and not by Fe II emission. The dust-reddened quasars have even narrower Balmer lines and weaker 3000 Å bumps, in addition to having considerably larger equivalent widths of [O II] and [O III] emission. The fraction of broad absorption line quasars (BALQSOs) increases from ~3.4% for the bluest quasars to perhaps as large as 20% for the dust-reddened quasars, but the intrinsic color distribution will be much bluer if all BALQSOs are affected by dust reddening.
    The Astronomical Journal 12/2007; 126(3):1131. · 4.97 Impact Factor
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    ABSTRACT: We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release (Cat. ). An automated algorithm was used to match a continuum to each quasar and to identify regions of flux at least 10% below the continuum over a velocity range of at least 1000km/s in the CIV and MgII absorption regions. The model continuum was selected as the best-fit match from a set of template quasar spectra binned in luminosity, emission line width, and redshift, with the power-law spectral index and amount of dust reddening as additional free parameters. We characterize our sample through the traditional balnicity index and a revised absorption index, as well as through parameters such as the width, outflow velocity, fractional depth, and number of troughs. (1 data file).
    VizieR Online Data Catalog. 11/2007;
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    ABSTRACT: Large-scale asymmetries in the stellar mass distribution in galaxies are believed to trace non-equilibrium situations in the luminous and/or dark matter component. These may arise in the aftermath of events like mergers, accretion, and tidal interactions. These events are key in the evolution of galaxies. In this paper we quantify the large-scale lopsidedness of light distributions in 25155 galaxies at z < 0.06 from the Sloan Digital Sky Survey Data Release 4 using the m = 1 azimuthal Fourier mode. We show that the lopsided distribution of light is primarily due to a corresponding lopsidedness in the stellar mass distribution. Observational effects, such as seeing, Poisson noise, and inclination, introduce only small errors in lopsidedness for the majority of this sample. We find that lopsidedness correlates strongly with other basic galaxy structural parameters: galaxies with low concentration, stellar mass, and stellar surface mass density tend to be lopsided, while galaxies with high concentration, mass, and density are not. We find that the strongest and most fundamental relationship between lopsidedness and the other structural parameters is with the surface mass density. We also find, in agreement with previous studies, that lopsidedness tends to increase with radius. Both these results may be understood as a consequence of several factors. The outer regions of galaxies and low-density galaxies are more susceptible to tidal perturbations, and they also have longer dynamical times (so lopsidedness will last longer). They are also more likely to be affected by any underlying asymmetries in the dark matter halo. Comment: 42 pages, 13 figures, 3 tables, accepted to ApJ
    The Astrophysical Journal 10/2007; · 6.73 Impact Factor
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    ABSTRACT: We report on a project using the Fourth Data Release (DR4) of the Sloan Digital Sky Survey to determine the link between large-scale asymmetry in the stellar mass distribution of a galaxy (lopsidedness) and the rate of star formation. We quantify the lopsidedness of the galactic light distribution as the first azimuthal Fourier mode of galaxy light and use this measure as an indicator of the lopsidedness of the galactic mass distribution. An analysis of the DR4 galaxy dataset shows that at low redshift (z < 0.06), a large sample of imaged SDSS galaxies have sufficiently high signal-to-noise ratios, adequate seeing, and low inclination angles that allow an accurate measure of lopsidedness. Lopsided galaxies with mass enhancements of 5-25% are commonplace in this sample. We find a strong link between lopsidedness and star formation, with a smooth transition between two classes of galaxies: a class of lopsided, low-mass, low-concentration galaxies with recent or ongoing star formation, and a class of symmetric, massive, concentrated galaxies with older stellar populations.
    12/2005;
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    ABSTRACT: We review the surveys for quasars that are being conducted with the Sloan Digital Sky Survey (SDSS) imaging data and highlight the need for supplementary multiwavelength observations. We stress that the SDSS is more than a redshift survey and discuss how the SDSS data can contribute to our understanding of the detailed physics of quasars. In particular, optical properties of SDSS quasars can be used to broaden our understanding of the UV/optical continuum, the broad emission line region, and the broad absorption line region. The ensemble average colors of large numbers of quasars promise to provide constraints on the optical/UV continuum emission mechanism. Investigation of emission line properties through analysis of continuum colors, line profiles, and microlensing can be used to trace the structure of the broad emission line region. The scope of the SDSS also means that large numbers of new broad absorption line quasars are being discovered; they can be used to determine whether all quasars have outflows.
    10/2004;
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    ABSTRACT: We review recent results on quasars from the SDSS as they relate to our understanding of the UV/optical continuum, the broad emission line region, and the broad absorption line region. The ensemble average colors of large numbers of quasars promise to provide constraints on the optical/UV continuum emission mechanism. High-ionization emission-line blueshifts and emission line properties as a function of optical/UV spectral index trace the structure of the broad emission line region. Statistical analysis of the broad absorption line quasar population suggests that they are more ubiquitous than one might otherwise think and are not likely to represent a completely distinct population of quasars, but that the BAL trough properties are a function of the underlying optical continuum and emission properties of the quasar.
    01/2004;
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    ABSTRACT: We present a sample of broad absorption line quasars (BALQSOs) from the Sloan Digital Sky Survey Second Data Release (DR2), scheduled for early 2004. These BALQSOs were selected by an automated algorithm which finds broad absorption troughs by comparing quasars to a set of composite spectra spanning luminosity and emission line FWHM space. We study the properties of BALQSOs identified by both the balnicity index and a new absorption index designed to include troughs with lower outflow velocities and/or velocity widths.
    12/2003;
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    ABSTRACT: We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 3814 objects ( 3000 discovered by the SDSS) in the initial SDSS public data release that have at least one emission line with a full width at half-maximum larger than 1000 km s(-1), luminosities brighter than M-i* = -23, and highly reliable redshifts. The area covered by the catalog is 494 deg(2); the majority of the objects were found in SDSS commissioning data using a multicolor selection technique. The quasar redshifts range from 0.15 to 5.03. For each object the catalog presents positions accurate to better than 0".2 rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.05 mag, radio and X-ray emission properties, and information on the morphology and selection method. Calibrated spectra of all objects in the catalog, covering the wavelength region 3800- 9200 Angstrom at a spectral resolution of 1800-2100, are also available. Since the quasars were selected during the commissioning period, a time when the quasar selection algorithm was undergoing frequent revisions, the sample is not homogeneous and is not intended for statistical analysis.
    The Astronomical Journal 02/2002; · 4.97 Impact Factor

Publication Stats

346 Citations
54.53 Total Impact Points

Institutions

  • 2007–2008
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, MD, United States
  • 2002
    • Rensselaer Polytechnic Institute
      • Department of Physics, Applied Physics, and Astronomy
      Troy, New York, United States