Krista Lynne Smith M. Koss R.M. Mushotzky

Transcription

1 Krista Lynne Smith M. Koss R.M. Mushotzky Texas Symposium December 12, 2013

2 X-ray Bright, Optically Normal Galaxy Luminous compact hard X-ray source No optical emission lines to indicate nuclear activity. Optically Elusive (optically-dull) AGN Luminous compact hard X-ray source Has emission line ratios indicative of HII regions. Both would be missed by optical AGN surveys! 40-60% of Chandra sources are optically normal!

3

4 Typical AGN in terms of L X and L opt? Cocchia et al. (2007)

5

6 Dust extinction eliminates light from central regions. Rigby et al. (2006): host galaxy dust. Ueda et al. (2007): dust with 4π covering factor of nucleus. Optical and IR tests: Dust in galaxy images E(B-V) reddening calculation Silicate absorption in Spitzer data

7 Widespread dust in the host?

8 Our sample is more reddened on average. E(B-V) of all SDSS DR7 = ± E(B-V) of XBONGs/elusives = ± 0.06 Column densities are high, but not Compton thick.

9 Elusive XBONG XBONG Features at 9.7 μm and 18 μm indicate amorphous silicate dust in line of sight.

10

11 The four optically elusive AGN are all classified as starburst/hii regions in the standard BPT line-ratio diagnostic diagram.

12 Rodriguez-Ardila et al. (2004) find that IR line ratios successfully distinguish between HII regions and AGN. H μm emission in AGN is mainly thermal in origin, not from UV fluorescence. [Fe II] / Pa β sensitive to photoionization versus shock excitation. Larkin et al. (1998): H 2 / Br γ and [Fe II] / Pa β are linearly correlated.

13 log ( [Fe II] / Pab ) Can IR line ratios classify the optically-elusive objects as AGN, where optical diagnostics 1 failed? Yes! 0.5 KUG A Mrk 18 NGC 5610 UGC Riffel et al. (2006) Type 2 Riffel et al. (2006) SB Veilleux et al. (1997) Type 2 LINERs 0 AGN -0.5 SBs log ( H 2 /Brg )

14 Cannot be excited by UV radiation. Collisionally excited forbidden transitions requiring hard ionizing radiation. [Si X] 1.43 μm [Si VI] 1.96 μm [Ca VIII] 2.32 μm [Ne V] 14.3 μm / 24.3 μm NIR: Marginal detection in 3 objects, but only ~2σ. 2MFGC 00829, Mrk 18, NGC 4686 MIR: Significant detection in 2/3 Spitzer objects. NGC 4686, Mrk 18, but not NGC 4992

15 KUG A has unambiguously revealed itself as an AGN in the NIR: Hα Hβ Pa γ Pa β Pa α

16 Optical normalcy unlikely to be due to: Starlight dilution Radiatively-Inefficient Accretion Flows Likely causes include: Star formation in select objects Heavy circumnuclear dust obscuration Infrared detection methods find 6 of our 8 XBONGs and elusive AGN, but many are marginal.

17 Starlight Dilution: are they normal AGN? Excessive Star Formation Radiatively-Inefficient Accretion Flows

18 High z : entire host galaxy falls within spectrographic slit or fiber. Moran et al. (2002)

19 Our sample is low redshift: < z < 0.071

20 Nuclear starburst could cause SF features to overwhelm AGN features. No difference between our sample and matched-m * control sample. U-R of control sample: 2.41 ± 0.12 U-R of XBONGs/elusives: 2.42 ± 0.15 BUT: could be obscured by dust as well.

21 Below a certain accretion rate, an optically-thick accretion disk fails to form at small radii. No accretion disk = no ionizing radiation = no lines! Trump et al. (2011): threshold accretion rate for RIAF formation: L bol /L edd << 10-2 Average accretion rate of our objects: L bol /L edd = 0.05, not discrepant from normal Type 2 Seyferts.

22

23 Swift XRT survey of the Kepler field. 4 modules so far 3 more modules upcoming Confirmation of AGN status at Lick Observatory X-ray active planet host? Discovered in Swift XRT survey. 10 ks of additional TOO time have just come in. Kepler pipeline for AGN Work with Rick Edelson and Martin Still (NASA AMES)

24

25

26

27

28

29 Edelson & Malkan (2012) developed S I criterion: 2MASS and WISE colors differentiate AGN from non-agn. Most sources with S I < tend to be genuine AGN. Surprise: all but two of our objects fail. Dust obscuration inhibits nuclear continuum even at IR wavelengths. Starlight continuum in IR overwhelms dust emission.

30 Baumgartner et al. (2013)

31

32

33 Selected from the Swift-BAT X-ray survey. Definitely AGN in the ultra-hard X-ray! ( kev) Low redshift: < z < Four XBONGs, four optically elusive AGN Selected by Mike Koss during an optical study of Swift-BAT sources. NIR observations from IRTF, optical data from SDSS, 6DF, Kitt Peak

34 K-band extinction is ~10x less than in optical. Numerous IR indicators of AGN activity. Infrared line ratios Coronal emission lines Ne V emission (MIR) Hidden broad-line region Infrared Photometry