Why would you want accurate quasar redshifts? Paul Hewett (IoA, Cambridge) James Allen (U. Sydney)

Outline Motivation: quasar clustering, host-galaxy and local quasar environment, relation to Lyα-absorbers and the inter-galactic medium, outflow properties of quasars themselves Current redshift accuracy for high-redshift, z>2.0, quasars and what do we need? Decomposing spectra into components to do better - redshifts using Independent Component Analysis applied to the ~1900A CIII]+SiIII]+AlIII complex Comparison to BOSS DR10 pipeline and PCA redshifts What is now possible

Galaxies 2dF Galaxy Survey redshift wedge Redshift due to `Hubble flow’ component plus `peculiar velocity’ due to influence of mass inhomogeneities over age of Universe For optical galaxy spectra can reach σ~30km/s For Hubble Constant ~70km/s/Mpc approx 0.5Mpc λ Observed = λ Restframe ×(1+z) with z=redshift

Want same for quasars but also have ability to study relation of quasars to gas along line-of-sight: probes host-galaxy, local environment and inter-galactic medium (Michael Murphy)

Last decade produced revolution in quasar surveys – Sloan Digital Sky Survey (SDSS) -DR quasars (2007); DR12 (BOSS) quasars (2014) -3D quasar clustering and 3D quasar-absorber studies possible -Quasar host-galaxy and environment studies also viable Wild+2008

Blackhole, fed by accretion disk with associated Broad Line Region (BLR) clouds and more distant Narrow Line Region (NLR) clouds Cloud distances ~1 parsec (BLR), 1000 parsec (NLR) with associated velocities ~5000 and 1000km/s respectively NASA

Rest-frame ultraviolet and optical quasar spectrum Continuum (from accretion disk) broad and narrow emission lines Encouraging in that emission from common elements evident At low-redshift, see host-galaxy spectrum and quasar Can work up to higher redshift using emission lines with rest-frame wavelengths >2500Ǻ - find redshift accuracy no worse than σ~170km/s BUT at shorter wavelengths, equivalent to redshift z>2.0 for ground-based spectra, quasar spectral energy distribution (SED) shows significant variations

Observationally, strong asymmetries (blueshifts) evident for high-ionization emission lines (Gaskell 1982, Carswell, Tytler,…), i.e the broad emission lines have different shapes One explanation invokes presence of `disk winds’ with material at high outflow velocities contributing to the emission-line profiles Systematic dependence on viewing orientation, L/L Eddington, luminosity relative to Eddington luminosity,…

Not a subtle effect – 3000km/s shifts mean redshifts awry by up to 100× galaxy redshift errors [~15Mpc Hubble flow] True for optical spectra of z>2 quasars – key epoch and essential for quasar-IGM studies

Relationship between quasar and environment also severely compromised

Observed frequency distribution of redshift differences,, for C iv absorbers using both SDSS (blue) and HW (red) redshifts for quasars with redshifts 1.55< z <3.5. Paul C. Hewett, and Vivienne Wild MNRAS 2010;405: © 2010 The Authors. Journal compilation © 2010 RAS

Low ionization lines, including MgII 2800 provide stable reference – good for redshifts z 2.0 key Hewett+Wild (2010) scheme major improvement for SDSS DR7 but essentially based on a single-”template” All single-template schemes have no information on spectra differences – hence SED-dependent systematic errors Amplitude of systematics >1000km/s, whereas want ~200km/s for host-galaxy, environment, clustering,…investigations Widely recognised that a natural solution involves – Parametrize quasar spectra into a number of “components” – Each quasar represented by sum of components with different weights – Reconstruct spectrum of each quasar determining component weights and redshift similtaneously – Allows for SED-variation, e.g. component(s) might include `outflow’ signature and be present in different amounts from quasar to quasar Quasar Redshifts: Status

Spectra as a linear combination of components S = W C spectra = weights × components Good if C<<S Differing rules/constraints on “component” derivation – Principal Component Analysis (PCA) – Independent Component Analysis (ICA) Mean Field ICA (Allen, Hewett MN ) – Very different from most ICA implementations – Priors, constraints on components possible – Extremely compact (i.e. #components small) – Example using SDSS low-z Post starburst galaxies (“answer known”) Decomposing Spectra

For the SDSS BOSS quasar survey [ quasars nearly all with z>2] Two main redshift estimates – Z_VI (pipeline/visual inspection) – Z_PCA (Paris+ 2011,2012) hope to be SED-independent Z_PCA unbiased, σ~750km/s relative to MgII 2800 – not great Statistical analysis using Lyα-forest – Cross-correlation with Lyα-forest gives Z_VI=231km/s low, Z_PCA=154km/s low (Font-Ribera 2013) [both +/-30km/s] Both BOSS schemes use quasar spectra down to 1400Ǻ MFICA components [6] applied to just the low ionization CIII]+SiIII]+AlIII complex. ~2400 BOSS where MgII visible [use well-behaved MgIIλ2800 as reference] SDSS DR12 Quasar Redshifts

Current Status Confirmation of BOSS-projects own redshift uncertainty determinations MFICA CIII]-complex redshifts reduce errors to σ~200km/s (cf. current σ~750km/s) – Possible for SDSS DR7 and BOSS to z<4.0 – Possible for any quasar spectrum where CIII]- complex covered Accurate individual errors from an MCMC scheme using component weight and redshift errors – on the way

Quasar environments (host-galaxy, group/clusters,…) and absorber outflow properties as a function of black-hole mass, L/L Eddington, radio-properties,… Example from Wild (2009) for MgII 2800 absorbers – host(?), outflow and intervening absorber components defined Full SDSS DR7 and DR12 analysis will produce vast improvement in statistics

Summary Many astrophysical investigations involving quasars at z>2 limited by errors in redshift determinations MFICA CIII]-complex redshifts reduce errors to σ~200km/s (cf. current σ~750km/s) – Possible for SDSS DR7 and BOSS to z<4.5 – Possible for any quasar spectrum where CIII]- complex covered