A TALE OF TWO MONSTERS: EMBEDDED AGN IN NGC6418 AND IRAS

Transcription

1 A TALE OF TWO MONSTERS: EMBEDDED AGN IN NGC6418 AND IRAS Photometry Aperture Optical 3.6 µm E 4.5 µm N Normalized flux Figure 3.1: NGC6418 false color image from the Spitzer space telescope at 3.6 µm. The white circle has a radius of 6 pixels and represents the aperture (diameter 7.2 ) used for the photometry for the cross-correlation analysis. 1.2 flux. Therefore, the flux vs. aperture function should plateau with increasing radii. All Figures for all AGNs can be found in Appendix A. All the mean flux density plots exhibit, as expected, a rapidly increasing flux density that plateaus at larger aperture sizes with some exceptions. NGC6418, UGC10697, MRK885, AKN524 and KAZ163 exhibit aperture 0.8 analysis plots that increase in mean flux without reaching a plateau. This behavior is explained by the extended emission from their host galaxies as seen in Figures 3.1, A.49, A.41, A.17 and 3.2. In addition, KAZ163 is the southern 0.6member of an interacting galaxy pair. The companion galaxy is the fainter object visible in 3.2. The companion galaxy is at a distance greater than pixels (12 ). This aperture55500 size is the largest used in the analysis. The knee of the flux vs. aperture function is used to determine the best MJD aperture. To determine the knee, the simple definition of the intersection of the slopes of the first two data points with the last two data points is used. On average, the obtained knee values agree with the ideal aperture found via visual inspection. It is important to note that there is no significant di erence between the aperture analysis for the 3.6 µm and 4.5 µm channels. As an example, Figures 3.3 and A.4 show the analysis done for both channels for NGC6418. There is less than a pixel di erence between the two channels Andy Robinson 22 Rochester Institute of Technology

2 Outline Two (contrasting) examples of dust enshrouded AGN NGC6418 isolated Seyfert IR reverberation mapping with Spitzer changing look AGN Billy Vazquez; Michael Richmond; Triana Almeyda; Shawn Foster; + Spitzer reverberation mapping collaboration Vazquez et al. 2015, ApJ, 801, 127 Robinson et al., in preparation IRAS merger system Multiwavelength SED modeling Evidence for a deeply embedded AGN Dinalva Sales; Jack Gallimore; Moshe Elitzur + Sales et al. 2015, ApJ, 799,

3 Spitzer monitoring campaign 2.5- year IR optical monitoring campaign Aug Jan type 1 AGN monitored at 3.6 and 4.5 µm with Spitzer Optical data from Liverpool Telescope, CSS, PTF Some results presented in Billy Vazquez s talk (Tuesday) Triana Almeyda poster on reverberation models B. Vazquez, 2015 PhD 3

4 Dust reverberation mapping Response of torus dust emission to UV- optical variations depends on size, geometry, cloud distribution etc. Relative amplitude Transfer function encodes torus properties 0.2 Almeyda et al., in prep optical dust emission 15 Delay convolution with driving optical light curve IR light curve 1.6 At short wavelengths, IR lag ~ inner radius of torus, usually taken to be dust sublimation radius Relative flux # L & # 1500K & R d 0.4% ( % ( $ erg 1 ' $ ' T sub (Nenkova et al. 2008b, Barvainis 1987) 2.6 pc Time

5 NGC6418 optical & IR light curves Seyfert 1 in Sab host; z = Optical 3.6 µm 4.5 µm Normalized flux Vazquez et al Cycle 8 (3 days) Cycle 9 (30 days) MJD 5

6 NGC6418 optical & IR light curves Seyfert 1 in Sab host; z = Optical 3.6 µm 4.5 µm Normalized flux Cycle 8 (3 days) Cycle 9 (30 days) MJD 6

7 Cross- correlation analysis Increase in IR optical lags following flare 3.6 µm vs optical 4.5 µm vs optical Cycle 8 ('.) τ = 33.3 %&.' (&.) τ = 41.4 %&.0 (-.) τ = 64.5 %-.. ('.. τ = 80.3 %'.0 Cycle 9 7

8 Cross- correlation analysis 4.5 µm lags 3.6 µm; lag increased following flare Cycle µm vs 3.6 µm (-.4 τ = 12.4 %'.- For dust grains in radiative equilibrium: R 6 R 7 ~ T :;< T > 6 ; a 2.6 for ISM composition Expect: t 4.5 /t 3.6 ~ 1.8 Cycle 9!"#$%$&'&()*+,-.&()!"#'!"#&$!"#&!"#%$!"#% ('.- τ = 20.3 %'.- Measured: t 4.5 /t (in both cycles) Favours clumpy dust distribution!"#"$!"!%"!%$!&"!&$!'" ()*!+,)-./ 8

9 Torus radius- luminosity relation Opt. IR lags small compared to predicted sublimation radius for standard ISM dust composition, but increase in lags following flare ~ consistent with increase in dust sublimation radius, R ~ L 0.5 9

10 Optical spectra: SDSS Apr Relative F λ Relative Flux Broad line Ha /Hb 6; A V Wavelength (Å) 0.8 Optical 3.6 µm 4.5 µm MJD 11

11 Optical spectra: Jan APO Jan Relative F λ Relative Flux Broad line Ha /Hb 3; A V Wavelength (Å) Optical 3.6 µm 4.5 µm MJD 12

12 Optical spectra: Aug APO Aug Relative F λ 30 Relative Flux Broad line Ha /Hb 6; A V Wavelength (Å) 0.8 Optical 3.6 µm 4.5 µm MJD 13

13 Optical spectra: Feb WHT 17 Feb Relative F λ Relative Flux Wavelength (Å) Optical 3.6 µm 4.5 µm MJD 14

14 NGC6418 as a changing look AGN Factor 2 increase in optical luminosity accompanied by similar increase in IR luminosity and followed by Emergence of Sy 1 spectrum Increase in optical - IR lags, consistent with L 0.5, suggesting increase in sublimation radius Line- of- sight extinction to BLR decreased from A V 2 0 Timescales: opt.- IR flare ~ 100 days; change in spectrum 1 year Seems to be returning to low activity state (Jan 2014 present) Change in look Flare in accretion disk luminosity Increase in BLR luminosity Increase in torus inner radius Destruction of line- of- sight dust 15

15 OH Megamaser Galaxies ~ 20% of (U)LIRGs contain extremely luminous OH masers emitting primarily in the 1667 and 1665 MHz lines luminosities L Represent distinct evolutionary phase in gas- rich mergers? Probe of high z star formation? Multiwavelength study of ~80 OHMG Optical NIR: HST observations archive data; Gemini integral field spectroscopy IR- sub mm: Spitzer + Herschel archive data Radio: VLA observations + archive data IRAS (z = 0.027) LIRG (L FIR L ; L OH L ) mid- late stage merger 19

16 Multiwavelength Morphology of IRAS z = => Mpc HST/ACS 0.4 µm HST/ACS 0.8 µm HST/NICMOS 1.6 µm HST/ACS Hα+[NII] Spitzer/IRAC 8.0 µm PAH VLA 1.49 GHz Double nuclei in common, tidally distorted envelope è midstage major, gas rich, merger. 21

17 IRAS Optical spectrum 100 IRAS IRAS obj IRAS IRAS IRAS FIG. 2.ÈContinued IRAS obj 2 6 IRAS IRAS obj IRAS IRAS IRAS obj IRAS obj l (Å) FIG. 2.ÈContinued South nucleus: starburst IRAS IRAS obj IRAS IRAS IRAS IRAS obj obj IRAS Nucleus separation 3.4 kpc IRAS North nucleus: Low Ionization nuclear emission 53 region weak AGN(?) IRAS obj 1 15 IRAS (Spectra from Kewley et al. FIG. 2.ÈContinued 2001) IRAS IRAS obj 2 0 IRAS obj IRAS obj IRAS IRAS IRAS IRAS IRAS obj

18 Multiwavelength Morphology of IRAS '' Green: Hα+[NII] (HST ACS) Red: 1.49 GHz VLA Contours: ISM PAH-dust 8µm emission (from Spitzer IRAC 8.0 & 3.6 µm images) Extended and compact components of radio emission consistent with star formation Red: 1.49 GHz VLA Blue: Chandra kev X-ray Compact X- ray source associated with N nucleus, but weak: L x (0.5 2 kev) ~ 5x10 40 erg/s 23

19 Mid- Infrared Spectrum (nuclei not resolved) [NeV], [OIV] not detected Low-resolution Spitzer IRS spectrum. Vertical solid lines indicate absorption bands of water ice (6.0µm) and HACs (6.85µm and 7.25µm) 24

20 Spectral energy distribution fits ISM dust/pah model (Draine & Li 2007) Clumpy torus model (Nenkova et al. 2008a,b) Stellar population model (GRASIL Silva et al. 1998) SED fits using MCMC code clumpydream (Gallimore) Simultaneous fits to both nuclei, unresolved points at l >14 µm treated as upper limits 27

21 SED fit North nucleus with AGN Model L AGN (erg/s) L ISM (erg/s) SFR FIR (M /yr) 3.4x x10 44 erg/s 11.6 Bayes information criterion (BIC) = 872 Measured (M /yr) SFR X-ray 10.3±3.7 SFR 8μm 4.2±0.6 SFR 1.4GHz 6.0±0.7 28

22 SED fit North nucleus without AGN Model L ISM (erg/s) SFR FIR (M /yr) 5.1x Bayes information criterion (BIC) = 1225 Measured Measured (system) (M /yr) SFR X-ray 10.3±3.7 SFR 8μm 4.2±0.6 SFR 1.4GHz 6.0±0.7 (M /yr) SFR 8μm 19.4±2.9 SFR 24μm 23.2±3.2 SFR 1.4GHz 13.7±1.5 29

23 SED fit South nucleus (no AGN) Model L AGN (erg/s) L ISM (erg/s) SFR FIR (M /yr) 8.9x10 43 erg/s 3.6 Measured (M /yr) SFR 8μm 3.0±0.4 SFR 1.4GHz 2.7±0.2 30

24 North nucleus torus parameters Y TORI. II. OBSERVATIONAL IMPLICATIONS 161 optical depth V at visual, occupy a toroidal volume from inner radius R d,determinedbydustsublimation nisapowerlawr q, and the total number of clouds along a radial equatorial ray is N 0.Variousangular onsidered.theangulardistributionhasasharpedgeontheleftandasmoothboundary(e.g.,agaussian)on mission at short e flux measured though its image flicts all IR studd to dominate the mission requires ut longer wavecontribution can fortunately, there er AGN has been bservations have orus component, source which are here are no easy round is to forgo D) in individual of many sources to the torus sigburst component Parameter Size (R o ) From Nenkova et al Value tion; the ionization cones dust is optically thin, and therefore its IR emission is isotropic and cannot generate 20 the pcobserved differences between types 1 and 2. Here we invoke both approaches in comparing our model predictions with observations. We start by assembling dusty clouds into complete models of the torus, as described in x 2. Our model predictions for torus emission and the implications for IR observations are presented in xx 3Y5, while in x 6wediscussaspects of clumpiness that are unrelated to the IR emission, such as the torus mass and unification statistics. In x 7weconcludewitha summary and discussion. Angular height (σ) 66 Inclination (i) 60 N clouds (N d ) 14 Opt. depth (τ V ) MODEL OF A CLUMPY TORUS Covering frac. (C f ) Consider an AGN with bolometric luminosity L surrounded by a toroidal distribution of dusty clouds (Fig. 1). The naked AGN flux at distance D is F AGN ¼ L/4D 2 at any direction, but because of absorption and reemission by the torus clouds the actual flux distribution is anisotropic, with the level of anisotropy strongly dependent on wavelength. The grain mix has standard interstellar properties (see x of Paper I for details), and the Quasi-spherical distribution of optical thick clouds 31

25 Origin of optical line emission? North nucleus covering fraction => 0.1% of AGN photons (Q AGN ) escape Q esc = (1 C f )Q AGN 3.6x10 53 ionizing photons/s Hα luminosity due to AGN photoionization: L Hα,AGN C ISM p Hα hν Hα Q esc 4.9x10 39 erg/s (since C ISM 1) C ISM = fraction ionizing photons absorbed by ISM p Hα 0.45, probability Hα photon emitted per H recombination only 2% of observed Hα luminosity of N nucleus (L Hα,obs 3x10 41 erg/s) LINER spectrum not due to AGN photoionization probably results from shock ionization 33

26 Summary NGC6418 Isolated Seyfert galaxy Changing look AGN caught in the act Intrinsic increase in AGN luminosity AND decrease in extinction Evidence for increase in torus inner radius, following optical flare Timescale < 1 yr IRAS Gas- rich, mid- stage, major merger, nuclei separated by 3 kpc North nucleus contains moderately luminous AGN, embedded in ~spherical dust cloud distribution Embedded AGN cannot produce LINER spectrum; probably shocks associated with merger driven gas flows Torus covering fraction may not scale simply with instantaneous luminosity LINER spectrum does not necessarily indicate presence of AGN 35