Multi-wavelength Surveys for AGN & AGN Variability Vicki Sarajedini University of Florida
What are Active Galactic Nuclei (AGN)? Galaxies with a source of non-stellar emission arising in the nucleus (excessive UV, IR, radio and X-ray light) Central Black Hole accreting material from host galaxy (Lynden-Bell 1969) Quasars luminous (M B <-23) objects with broad emission lines, distant, many are strong radio sources Seyferts fainter (M B >-23), most identified locally, spiral hosts Sey 1s broad emission lines Sey 2s narrow emission lines LINERs transition objects with ionization signatures between those of Seyferts and starburst galaxies (where ionization is due to hot stars
Supermassive black holes appear to be fundamental to galaxies The black hole mass is correlated with the stellar mass of the galaxy s central bulge AGN may be an evolutionary phase for many galaxies, during which the black hole grows Galaxy evolution and the evolution of AGN are correlated
Detecting AGN Optical thermal emission from accretion disk, BLR or NLR color selection emission-lines via spectroscopy variability accretion disk instabilities/hot spots X-ray inverse-compton scattering of UV photons by hot corona above disk Mid-IR UV photons reprocessed by dust in the AGN X-ray! Optical! Alexander et al. 2003 Lacy et al. 2006
Optical Variability in AGNs QSOs and Seyfert nuclei have long been recognized as variable Optical flux changes occur on timescales of months to years Variability likely due to accretion disk instabilities Surveys find that between ~80% and 100% of AGN selected through other means (spectroscopic, color selection, UV excess) are variable when observed over several years (e.g. MacLeod et al. 2010). Optical variability surveys (high-resolution with HST): identify and/or confirm faint AGN without bias towards AGN-dominated galaxies optical method that can be done cheaply with 2 or more field images (rather than more expensive spectroscopy)
Variability in the Hubble Deep Field North (Sarajedini, Gilliland & Kasm 2003) HST images separated by 5 years revealed 16 galaxies with variable nuclei to V nuc =27.5 (8% of galaxies). 44% of the variables are associated with X-ray sources. 31% detected at 1.4GHz and 44% in the mid-ir. The AGN sky density from deep optical variability is 10 20 times greater than any other optical technique and rivals X-ray detection.
Confirming the Nature of X-ray Emission The X-ray luminosities of the variable sources range from logl x 43.7 to 39.8 Half of the variables that are X-ray sources have such low F x /F opt, they would not be classified as AGN in X- ray surveys alone.
The GOODS North and South Fields (Great Observatories Origins Deep Survey) Total of 320 sq arcminutes 5 epochs obtained at 45-day intervals (V-band) Search for short-term variability (expect to find 60% of Seyferts varying on these timescales) and longer term variability (~2 years) over a smaller area Extensive multi-wavelength and spectroscopic follow-up (Keck & ESO z s, Chandra X- ray, Spitzer mid-ir, etc.)
Variability in GOODS 85 variables detected in 4174 galaxies 2% are variable (consistent with HDF-N and GSS results) 48% of variables are also X- ray detected; 14% are mid-ir power-law sources ~50% of variables are neither X-ray or mid-ir detected AGN; consistent with other recent variability surveys (Trevese et al. 2008, Morokuma et al. 2008). Increase AGN density by ~20%. What is the nature of non-x-ray detected variables? RIAFs or otherwise X-ray inefficient (e.g. lack hot corona)
Variability in GOODS - South Variability identifies AGN at a range of redshifts and luminosities low-luminosity AGN (fainter than M~22) are detected at all redshifts X-ray surveys miss these...
X-ray selected AGN typically fill in the green valley between blue SF galaxies and red/ dead Ellipticals. Non-X-ray detected variables extend to bluer colors and fainter magnitudes - may trace onset of accretion or lowerlevel accretion activity in galaxies... Future projects with GOODS sample study SED s, host galaxy morphologies, examine long-term variability...
Ongoing AGN Variability surveys: HST cluster survey 12 z=0.5-0.9 clusters with ACS 2 to 3 optical epochs for variability, also X-ray and IRAC mid-ir Compare cluster AGN density to field density Examine trends with cluster radial distribution to investigate questions about AGN fueling Klesman & Sarajedini 2011, in prep
Mid-IR Variability with Spitzer Variability study in the mid-ir (3.6 & 4.5 micron 5 deep fields (0.9 sq degree). ~3-4 epochs, 6 month separation, 3 hrs each (total 2108 hrs!) IR variability (reprocessed optical/uv photons) may be more sensitive to obscured AGN. ~2% of galaxies display significant variability in the mid-ir (Townsend et al., in prep)
SDSS Variability Survey Compare photometric and spectroscopic photometry for several thousand SDSS broad-line AGN Investigate trends with variability and time lag, AGN luminosity and BH mass Variability amplitude increases with decreasing AGN magnitude, but reaches maximum around M agn -18 Desjardins & Sarajedini, in prep Ground-based surveys (targets z=0.2 to 0.5 AGN): The ESO Supernova Search Survey ESO/MPE 2.2m and WFI 5.1 square degrees 1200s in V, 5 epochs (months) The Deep Lens Survey KPNO 4m and Mosaic CCD 4 square degrees 600s in V (varying time sampling months) Z=0.4 AGN
NIR Spectroscopic surveys with Gemini and the GTC Current spectroscopic follow-up surveys of HST fields cover the optical wavelength range - often miss important emission features necessary for spectral classification for higher redshift galaxies (z=1.5 to 3). Flamingos II NIR multi-object spectrograph now commissioning at Gemini South survey AGN candidates in GOODS-S. GOYA survey will use EMIR NIR MOS at the Gran Telescopio Canarias - survey GOODS- N and EGS.