The correlation of line strength with luminosity and redshift from composite quasi-stellar object spectra (original) (raw)
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The Astrophysical Journal Supplement Series, 2002
UV/optical emission lines offer some of the most detailed information obtainable about the intrinsic properties of quasars. Studies of the density, ionization and metal abundance of gas near the accreting black hole are probed through an intriguing but poorly understood complex of correlations between emission lines and overall quasar spectral energy distributions that has long suffered from a lack of large, consistently measured samples. As part of a broader effort to expand and systematize the data upon which these studies are built, we present measurements of the UV/optical emission line parameters in a sample of 158 active galactic nuclei observed with the Faint Object Spectrograph on the Hubble Space Telescope (HST), prior to the installation of COSTAR. We use an automated technique that accounts for galactic reddening, includes iron emission blends, galactic and intrinsic absorption lines, and performs multicomponent fits to the emission line profiles. We present measured line parameters (equivalent width and FWHM) for a large number (28) of different UV/optical lines, including upper limits for undetected lines. We also study the relations between the emission line equivalent widths and luminosity (the Baldwin effect), as well as redshift (evolution). We compare results from this HST FOS sample with our previous measurements of 993 QSOs in the Large Bright Quasar Survey using the same analysis technique and sum the samples to achieve better coverage of the luminosity-redshift plane. We confirm a significant Baldwin effect for UV iron emission from Green et al. and find that evolution dominates the effect for iron and for Si iv emission. The values of the Baldwin effect slopes for all UV emission lines and the dependence of the slopes on the sample's luminosity range point to a change of the SED as the cause of the Baldwin effect in the FOS sample.
Astronomy and Astrophysics, 2007
Aims. In this work the luminosity function of QSOs is measured in the redshift range 3.5 < z < 5.2 for the absolute magnitude interval −21 < M 145 < −28. Determining the faint-end of the luminosity function at these redshifts provides important constraints on models of the joint evolution of galaxies and AGNs. Methods. We have defined suitable criteria to select faint QSOs in the GOODS fields, checking their effectiveness and completeness in detail. A spectroscopic follow-up of the resulting QSO candidates was carried out. The confirmed sample of faint QSOs is compared with a brighter one derived from the SDSS. We used a Monte-Carlo technique to estimate the properties of the luminosity function, checking various parameterizations for its shape and evolution. Results. Models based on pure density evolution show better agreement with observation than do models based on pure luminosity evolution. However, a different break magnitude with respect to z ∼ 2.1 is required at 3.5 < z < 5.2. Models with a steeper faint-end score a higher probability. We do not find any evidence for a bright-end flattening at redshift z > 3.5. Conclusions. The estimated space density evolution of QSOs indicates a suppression of the formation and/or feeding of supermassive black holes at these redshifts. The QSO contribution to the UV background is insufficient for ionizing the IGM at 3.5 < z < 5.2.
A comparison of line intensities in the spectra of galactic and extragalactic emission objects
1959
This thesis has been submitted in partial fulfillment of re quirements for an advanced degree at The University of Arizona and is deposited in The University Library to be made available to bor rowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
The Astrophysical Journal, 2018
We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGNs), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec-size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity (L FIR), dust infrared color, L FIR to molecular gas mass ratio (L FIR /M mol), and FIR surface brightness (Σ FIR). The correlations between the [C II]/FIR or [O I]/FIR ratios with Σ FIR are remarkably tight (∼0.3 dex scatter over almost four orders of magnitude in Σ FIR). We observe that galaxies with L M L M 80 FIR mol 1 - and Σ FIR 10 11 L e kpc −2 tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes 1 kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II. The combined analysis of the [C II], [N II] 122 μm, and [O III] 88 μm lines reveals that the fraction of the [C II] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in H II regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-z studies.
2011
Star formation and accretion onto supermassive black holes in the nuclei of galaxies are the two most energetic processes in the Universe, producing the bulk of the observed emission throughout its history. We simulated the luminosity functions of star-forming and active galaxies for spectral lines that are thought to be good spectroscopic tracers of either phenomenon, as a function of redshift. We focused on the infrared (IR) and sub-millimeter domains, where the effects of dust obscuration are minimal. Using three different and independent theoretical models for galaxy formation and evolution, constrained by multi-wavelength luminosity functions, we computed the number of star-forming and active galaxies per IR luminosity and redshift bin. We converted the continuum luminosity counts into spectral line counts using relationships that we calibrated on mid-and far-IR spectroscopic surveys of galaxies in the local universe. Our results demonstrate that future facilities optimized for surveymode observations, i.e., the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and the Cerro Chajnantor Atacama Telescope (CCAT), will be able to observe thousands of z>1 galaxies in key fine-structure lines, e.g., [Si II], [O I], [O III], [C II], in a half-square-degree survey, with one hour integration time per field of view. Fainter lines such as [O IV], [Ne V] and H 2 (0-0)S1 will be observed in several tens of bright galaxies at 1 < z < 2, while diagnostic diagrams of active-nucleus vs star-formation activity will be feasible even for normal z∼1 galaxies. We discuss the new parameter space that these future telescopes will cover and that strongly motivate their construction.
The 2dF Galaxy Redshift Survey: Galaxy luminosity functions per spectral type
Monthly Notices of The Royal Astronomical Society, 2001
We calculate the optical b J luminosity function of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission and absorption line strength in the galaxy rest-frame spectrum and hence is a useful indicator of the present star formation. We use a total of 75,000 galaxies in our calculations, chosen from a sample of high signal-tonoise ratio, low redshift galaxies observed before January 2001. We find that there is a systematic steepening of the faint end slope (α) as one moves from passive (α = −0.54) to active (α = −1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest-frame characteristic magnitude M * − 5 log 10 (h) (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies (M bJ − 5 log 10 (h) fainter than −16.0), perhaps suggesting the presence of a significant dwarf population. The luminosity functions presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent K-corrections and investigate possible fibreaperture biases.
The Astrophysical Journal, 2014
Emission line diagnostic diagrams probing the ionization sources in galaxies, such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used extensively to distinguish AGN from purely starforming galaxies. Yet, they remain poorly understood at higher redshifts. We shed light on this issue with an empirical approach based on a z ∼ 0 reference sample built from ∼300,000 SDSS galaxies, from which we mimic selection effects due to typical emission line detection limits at higher redshift. We combine this low-redshift reference sample with a simple prescription for luminosity evolution of the global galaxy population to predict the loci of high-redshift galaxies on the BPT and Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate distributions agree remarkably well with direct observations of galaxies out to z ∼ 1.5, including the observed stellar mass-metallicity (M Z) relation evolution. As a result, we infer that high-redshift star-forming galaxies are consistent with having normal ISM properties out to z ∼ 1.5, after accounting for selection effects and line luminosity evolution. Namely, their optical line ratios and gas-phase metallicities are comparable to that of low-redshift galaxies with equivalent emission-line luminosities. In contrast, AGN narrow-line regions may show a shift toward lower metallicities at higher redshift. While a physical evolution of the ISM conditions is not ruled out for purely star-forming galaxies, and may be more important starting at z 2, we find that reliably quantifying this evolution is hindered by selections effects. The recipes provided here may serve as a basis for future studies toward this goal. Code to predict the loci of galaxies on the BPT and MEx diagnostic diagrams, and the M Z relation as a function of emission line luminosity limits, is made publicly available.
Deep Spectroscopy of Ultra-Strong Emission-Line Galaxies
The Astrophysical Journal, 2009
Ultra-strong emission-line galaxies (USELs) with extremely high equivalent widths (EW(Hβ) ≥ 30Å) can be used to pick out galaxies of extremely low metallicity in the z = 0 − 1 redshift range. Large numbers of these objects are easily detected in deep narrow band searches and, since most have detectable [O III]λ4363, their metallicities can be determined using the direct method. These large samples hold out the possibility for determining whether there is a metallicity floor for the galaxy population. In this, the second of our papers on the topic, we describe the results of an extensive spectroscopic follow-up of the Kakazu et al. (2007) catalog of 542 USELs carried out with the DEIMOS spectrograph on Keck. We have obtained high S/N spectra of 348 galaxies. The two lowest metallicity galaxies in our sample have 12+log(O/H) = 6.97±0.17 and 7.25±0.03-values comparable to the lowest metallicity galaxies found to date. We determine an empirical relation between metallicity and the R23 parameter for our sample, and we compare to this to the relationship for low redshift galaxies. The determined metallicity-luminosity relation for this sample is compared with that of magnitude selected samples in the same redshift range. The emission line selected galaxies show a metal-luminosity relation where the metallicity decreases with luminosity and they appear to define the lower bound of the galaxy metallicity distribution at a given continuum luminosity. We also compute the Hα luminosity function of the USELs as a function of redshift and use this to compute an upper bound on the Lyα emitter luminosity function over the z = 0 − 1 redshift range.
Studies of absorption lines in the spectra of quasi-stellar objects
Furthermore, the general absence of self-reversal in the Mg II X2798 emission line places a constraint on models of QSO emission-line regions; this constraint may rule out spherically-symmetric photoionization models which are optically thick in the Lyman continuum. An attempt is made to directly test the intervening hypothesis by searching for 21 cm absorption due to known rich clusters of galaxies. No detections of features of width 10-100 km s and optical depth typically less than 0.0 6 are made at the 5 a level. However, it is shown that because of the small number of QSOs examined (17), no strong argument can be made against the intervening-galaxy hypothesis.