Improved redshifts for SDSS quasar spectra Hewett, Paul C.; Wild, Vivienne
Monthly Notices of the Royal Astronomical Society,
07/2010, Letnik:
405, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A systematic investigation of the relationship between different redshift estimation schemes for more than 91 000 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 6 is presented. The ...publicly available SDSS quasar redshifts are shown to possess systematic biases of (600 km s−1) over both small and large redshift intervals. Empirical relationships between redshifts based on (i) Ca ii H&K host galaxy absorption, (ii) quasar O ii 3728, (iii) O iii 4960, 5008 emission and (iv) cross-correlation (with a master-quasar template) that includes, at increasing quasar redshift, the prominent Mg ii 2799, C iii 1908 and C iv 1549 emission lines are established as a function of quasar redshift and luminosity. New redshifts in the resulting catalogue possess systematic biases, a factor of 20 lower compared to the SDSS redshift values; systematic effects are reduced to the level of (30 km s−1) per unit redshift or per unit absolute magnitude. Redshift errors, including components due both to internal reproducibility and to the intrinsic quasar-to-quasar variation among the population, are available for all quasars in the catalogue. The improved redshifts and their associated errors have wide applicability in areas such as quasar absorption outflows, quasar clustering, quasar-galaxy clustering and proximity-effect determinations.
ABSTRACT
Using a sample of ≃144 000 quasars from the Sloan Digital Sky Survey Data Release 14, we investigate the outflow properties, evident in both absorption and emission, of high-ionization broad ...absorption line (BAL) and non-BAL quasars with redshifts 1.6 ≲ $z$ ≤ 3.5 and luminosities 45.3 erg s−1 < log10(Lbol) < 48.2 erg s−1. Key to the investigation is a continuum and emission-line reconstruction scheme, based on mean-field independent component analysis, that allows the kinematic properties of the C iv λ1550 emission line to be compared directly for both non-BAL and BAL quasars. C iv emission blueshift and equivalent width (EW) measurements are thus available for both populations. Comparisons of the emission-line and BAL trough properties reveal strong systematic correlations between the emission and absorption properties. The dependence of quantitative outflow indicators on physical properties such as quasar luminosity and luminosity relative to Eddington luminosity is also shown to be essentially identical for the BAL and non-BAL populations. There is an absence of BALs in quasars with the hardest spectral energy distributions (SEDs), revealed by the presence of strong He ii λ1640 emission, large C iv λ1550 emission EW, and no measurable blueshift. In the remainder of the C iv emission blueshift versus EW space, BAL and non-BAL quasars are present at all locations; for every BAL quasar, it is possible to identify non-BAL quasars with the same emission-line outflow properties and SED hardness. The co-location of BAL and non-BAL quasars as a function of emission-line outflow and physical properties is the key result of our investigation, demonstrating that (high-ionization) BALs and non-BALs represent different views of the same underlying quasar population.
Correcting C iv-based virial black hole masses Coatman, Liam; Hewett, Paul C; Banerji, Manda ...
Monthly Notices of the Royal Astronomical Society,
02/2017, Letnik:
465, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The C IV...1498,1501 broad emission line is visible in optical spectra to redshifts exceeding z ~ 5. C IV has long been known to exhibit significant displacements to the blue and these 'blueshifts' ...almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from C IV velocity widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (LBol = 10...-10... erg s...), redshift 1.5 < z < 4.0 quasars with both C IV and Balmer line spectra, we have quantified the bias in C IV BH masses as a function of the C IV blueshift. C IV BH masses are shown to be a factor of 5 larger than the corresponding Balmer-line masses at C IV blueshifts of 3000 km s... and are overestimated by almost an order of magnitude at the most extreme blueshifts, ...5000 km s... Using the monotonically increasing relationship between the C IV blueshift and the mass ratio BH(C IV)/BH(Ha), we derive an empirical correction to all C IV BH masses. The scatter between the corrected C IV masses and the Balmer masses is 0.24 dex at low C IV blueshifts (~0 km s...) and just 0.10 dex at high blueshifts (~3000 km s...), compared to 0.40 dex before the correction. The correction depends only on the C IV line properties -- i.e. full width at half-maximum and blueshift -- and can therefore be applied to all quasars where C IV emission line properties have been measured, enabling the derivation of unbiased virial BH-mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature. (ProQuest: ... denotes formulae/symbols omitted.)
Black hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. At high redshift, z ≳ 2.1, black hole ...masses are normally derived using the velocity width of the C iv
$\tt \lambda \lambda$
1548, 1550 broad emission line, based on the assumption that the observed velocity widths arise from virial-induced motions. In many quasars, the C iv emission line exhibits significant blue asymmetries (‘blueshifts’) with the line centroid displaced by up to thousands of km s−1 to the blue. These blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. We have obtained near-infrared spectra, including the Hα
$\tt \lambda$
6565 emission line, for 19 luminous (L
Bol = 46.5–47.5 erg s−1) Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with C iv emission lines spanning the full range of blueshifts present in the population. A strong correlation between C iv velocity width and blueshift is found and, at large blueshifts, >2000 km s−1, the velocity widths appear to be dominated by non-virial motions. Black hole masses, based on the full width at half-maximum of the C iv emission line, can be overestimated by a factor of 5 at large blueshifts. A larger sample of quasar spectra with both C iv and H β, or Hα, emission lines will allow quantitative corrections to C iv-based black hole masses as a function of blueshift to be derived. We find that quasars with large C iv blueshifts possess high Eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately 4 relative to a sample limited by black hole mass.
ABSTRACT
We construct a parametric SED model which is able to reproduce the average observed SDSS–UKIDSS–WISE quasar colours to within one-tenth of a magnitude across a wide range of redshift (0 < z ...< 5) and luminosity (−22 > Mi > −29). This model is shown to provide accurate predictions for the colours of known quasars which are less luminous than those used to calibrate the model parameters, and also those at higher redshifts z > 5. Using a single parameter, the model encapsulates an up-to-date understanding of the intra-population variance in the rest-frame ultraviolet and optical emission lines of luminous quasars. At fixed redshift, there are systematic changes in the average quasar colours with apparent i-band magnitude, which we find to be well explained by the contribution from the host galaxy and our parametrization of the emission-line properties. By including redshift as an additional free parameter, the model could be used to provide photometric redshifts for individual objects. For the population as a whole we find that the average emission line and host-galaxy contributions can be well described by simple functions of luminosity which account for the observed changes in the average quasar colours across 18.1 < iAB < 21.5. We use these trends to provide predictions for quasar colours at the luminosities and redshifts which will be probed by the Rubin Observatory LSST and ESA-Euclid wide survey. The model code is applicable to a wide range of upcoming photometric and spectroscopic surveys, and is made publicly available.
Recent evidence highlighting high HIV incidence and prevalence in informal settlements suggests that they are environments that foster HIV risk. Given growing urbanization in sub-Saharan Africa, ...there is a critical need to assess the successes and challenges of implementing HIV testing, prevention and treatment interventions in these contexts.
We randomly selected a household-based sample of 1528 adult men (18-35) and women (18-24) living in 18 randomly selected communities in KZN, South Africa. After the baseline interview, communities were randomized to one of three intervention rollout arms in a stepped wedge design. At approximately 8-month intervals, the Asibonisane Community Responses Program (and in particular the implementation of Stepping Stones, a participatory HIV prevention program focused on strengthening relationships and communication) was rolled at by intervention phase. Using data from this evaluation, we describe levels and trends in HIV testing and treatment during follow-up, and we use fixed effects models to estimate the effects of participation in the program on testing.
Study respondents reported high levels of economic insecurity and mobility, and men report various HIV risk behaviors including about 50% reporting multiple partnerships. About two-thirds of respondents (73% of women, 63% of men) had been tested for HIV in the last six months. Among those living with HIV, treatment levels were high at baseline, and almost universal by endline in 2019. Program participation led to a 17% increase in the probability of testing for women (p<0.05) but had no effect on testing for men due, in part, to the fact that the program did not reach men who were least likely to be tested, including those who had migrated recently, and those who had never been tested at baseline.
Near universal HIV treatment use demonstrates positive trends in access to some HIV services (including treatment as prevention) in these communities. Stepping Stones had positive effects on HIV testing for women, yet barriers to HIV testing remain, especially for men. Redoubled efforts to reach men with testing are vital for improving HIV outcomes for both men and their partners.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ... E(B - V) ... 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS ...(European Southern Obseratory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>10... L...), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Ha equivalent widths relative to unobscured quasars. The average black hole masses (~10...-10... M...) and bolometric luminosities (~10... erg s...) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ~10... erg s... 66 per cent of the reddened quasars are detected at >3s at 22 ...m by WISE. The average 6-...m rest-frame luminosity is log10(L6 ...m/ erg s...) = 47.1 plus or minus 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (-30 < Mi < -27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2-3. At the brightest magnitudes, Mi ... -29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation. (ProQuest: ... denotes formulae/symbols omitted.)
We present new measurements of the mean transmitted flux in the Lyα forest over 2 < z < 5 made using 6065 quasar spectra from the Sloan Digital Sky Survey data release 7 (SDSS DR7). We exploit the ...general lack of evolution in the mean quasar continuum to avoid the bias introduced by continuum fitting over the Lyα forest at high redshifts, which has been the primary systematic uncertainty in previous measurements of the mean Lyα transmission. The individual spectra are first combined into 26 composites with mean redshifts spanning 2.25 ≤ z
comp ≤ 5.08. The flux ratios of separate composites at the same rest wavelength are then used, without continuum fitting, to infer the mean transmitted flux, F(z), as a fraction of its value at z ∼ 2. Absolute values for F(z) are found by scaling our relative values to measurements made from high-resolution data by Faucher-Giguère et al. at z ≤ 2.5, where continuum uncertainties are minimal. We find that F(z) evolves smoothly with redshift, with no evidence of a previously reported feature at z 3.2. This trend is consistent with a gradual evolution of the ionization and thermal state of the intergalactic medium over 2 < z < 5. Our results generally agree with the most careful measurements to date made from high-resolution data, but offer much greater precision and extend to higher redshifts. This work also improves upon previous efforts using SDSS spectra by significantly reducing the level of systematic errors.
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