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Active galactic nuclei in low surface brightness galaxies

Active galactic nuclei in low surface brightness galaxies. Weimin Yuan Yunnan Observatory. Based on Master thesis work of Lin Mei In collaboration with X.B. Dong (USTC). astro-ph/0902.0862. Questions to address. What is the fraction of LSBG that host an AGN?

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Active galactic nuclei in low surface brightness galaxies

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  1. Active galactic nuclei in low surface brightness galaxies Weimin Yuan Yunnan Observatory Based on Master thesis work of Lin Mei In collaboration with X.B. Dong (USTC) astro-ph/0902.0862

  2. Questions to address • What is the fraction of LSBG that host an AGN? • How the AGN fraction depends on the properties of LSBG?

  3. Low surface brightness galaxies • Disk central surface brightness μ0(B) significantly fainter than the classical Freeman value μ0(B) ≈21.65mag arcsec−2 • definition: μ0(B) of galactic disk >22-23 mag arcsec−2 (μ(B) of night sky background) • A significant constitution of all galaxies in the Universe, could be over 50% (e.g., Freeman 1970; McGaugh et al. 1995, Bothun et al. 1997)

  4. Comparison with high surface brightness galaxies (HSBG) • Low star-formation rate • Low surface gas density (Auld et al.) • Low metallicity, ~1/3 solar (Impey & Bothun 1997) • low dust • Rich in HI gas • Less evolved system prevents enrichment of the ISM, prevents cooling and resulting in a less evolved system

  5. Bulges in LSBG • Most LSBG are either • bulgeless, late-type "normal-sized" galaxies, or • giant galaxies with a significant bulge component • Bulge and disk relation • bulge and disk scale length are correlated • bulge-to-disk ratio is independent of galaxy type (Galaz. 2006)‏

  6. A prototype LSBG: Malin 1 • μ0 (B) = 25.5mag arcsec−2 • Size >100kpc • HI mass ~1011Msun • Seyfert nuclear activity (Impey 1989)

  7. Why study AGN in LSBG? • A census of central SMBH in LSBG • May provide a complementary clue to understanding the formation and growth of SMBH As LSBG may have experienced a different route in the formation and evolution from HSBG few or no merging history ? • Feedback from powerful AGN may have ecological effects on the evolution LSBG • Hints from comparing AGN properties in LSBG and in HSBG • Dependence of AGN activity on host galaxy properties • AGN triggering mechanism

  8. studies of AGN in LSBG --- rare and controversial Not well studied: only a few cases of secured AGN detections A high AGN detection rate was ever suggested for LSBG • Sprayberry et al. (1993) found 5 AGN (4 Seyfert1 + 1 Seyfert 2) in 10 giant LSBG • Schombert (1998) claimed ~50% of large, HI-rich LSBG have signatures of low-L AGN (based on [NII] and [SII], plus [OI])‏ • But cannot be confirmed by Impey et al. (2001), who found AGN in only <~ 5% LSBG previous work suffered from problems of: • sample: small size, strong biases, etc. • low quality data: low R and S/N spectra • data analysis: e.g. no proper subtraction of host galaxy light

  9. Sample and data • parent LSBG sample: Impey et al. 1996 • UK Schmidt survey plate scanned by APM • 693 LSBG within 786 sqr.deg. in the local universe (z<0.1) • largest and homogeneous LSBG sample in northern sky • our sample: spectroscopically observed in SDSS DR5 194 LSBG • comparative HSBG sample: • need reliable morphological classification and matching distributions in distances, magnitudes, etc. • 3rd Reference Catalogue of Bright Galaxies (RC3) (de Vaucouleurs et al. 1991) --- a catalogue of typical HSBG • 142 HSBG with SDSS spectra

  10. SDSS-APM LSBG sample and comparative HSBG sample Compatible at z<0.04

  11. Analysis of SDSS spectra Using the algorithm developed by Tinggui Wang’s group at USTC (Zhou et al. 2006) • Spectral decomposition: AGN + host galaxy Self-consistent modeling of host stellar spectrum and AGN (emission line + continuum) spectrum (Lu et al. 2006) • Spectral fitting(Dong et al. 2005, zhou et al. 2006) de-blending of broad and narrow emission lines • Also available: stellar velocity dispersion σin the central part (bulge) of the galaxy (by modeling stellar absorption features)

  12. Example of AGN found in LSBG:broad line (type1)AGN in SDSS J122912.9+004903.7 Narrow Ha [NII] Original SDSS spectrum Broad Ha stellar spectrum AGN continuum AGN emission lines

  13. Example of AGN found in LSBG:narrow line (type 2)AGN

  14. Spectral classification of emission line nuclei: AGN vs. star-formation AGN fraction of emission line galaxies ~ 68% Kewley et al. 2001 AGN= Seyfert + LINER + transition starformation Kauffmann et al. 2003 A significant fraction (~50%) of LSBG have ongoing central star-formation

  15. Spectral classification of emission line nuclei: Seyfert vs. LINER We regard LINER as powered by AGN Kewley et al. 2006

  16. Demography of nuclear activity in LSBG The AGN fraction is lower than 40% found for HSBG in the local universe (Ho 1997)

  17. AGN found across morphological types for LSBG All emission line LSBG • AGN fraction • Lower for later types of galaxies • but significantly higher for interacting galaxies • the same as HSBG Star-formation nuclei AGN

  18. Comparison with HSBG at z<0.04 comparative HSBG sample LSBG sample at z<0.04 All emission line galaxies nuclear Star-formation AGN 47% consistent with the result of Ho (1997) Conclusion: LSBG have a smaller AGN fraction than HSBG, and a comparable or even higher fraction of nuclear star-formation robust results: the same data set and analysis algorithm

  19. Dependence of AGN fraction on size of galaxy AGN fraction AGN tend to reside in galaxies of larger size physical size of galaxies (kpc)

  20. Dependence of AGN fraction on central stellar velocity dispersion LSBG HSBG Central stellar velocity dispersion AGN tend to reside in galaxies with larger central σ  For both LSBG and HSBG

  21. What causes the difference in AGN fraction between LSBG and HSBG? • AGN fraction in LSBG depends on • size of galaxy • central stellar velocity dispersion ( of bulges) • Since bulge and disk scale length are correlated (Galaz. 2006), galaxies with more massive bulges have a higher AGN fraction consistent with result for general AGN (e.g.Kauffmann et al. 2003) • Reason for different AGN fraction btw. LSBG/HSBG: they occupy different parts of the bulge distribution for given morphological types of galaxies • LSBG: lower end of bulge distribution  low AGN chance • HSBG: higher end of bulge distribution high AGN chance • But possibly not due to disk surface brightness • hinted from observations but should be tested explicitly

  22. Some properties of AGN in LSBG • Vast majority are weak, low-luminosity AGN • L[OIII]<1040erg/s • Less dust extinction than HSBG nuclei, based on Balmer decrement of narrow lines, for both AGN and nuclear HII • Lower electron density of narrow line region than that of HSBG AGN ([SII]6717/[SII]6731 line ratio) • Both types found, radio-loud (~20%) and radio-quiet

  23. Kinematics of NLR Central stellar V dispersion Width of narrow line ([NII]) The same as AGN in normal HSBG, the kinematics of NLR traces well the galactic bulge potential

  24. black hole growth in LSBG M-σrelation HSBG with AGN follow the well known M-σ relation for normal galaxies Black hole mass 3 LSBG AGN with detected broad Ha emission line Central stellar V dispersion Tremaine et al. (2002) Is SMBH-galaxy co-evolution also happening in LSBG? How do black holes grow in LSBG? More data are needed!

  25. conclusion I -- demography of nuclear activity in LSBG • Emission-line nuclei are common (68%), mostly star-forming nuclei (52%) • Similarity to HSBG: • AGN found in a wide range of morphological types from Sa to latter types. Interacting galaxies have the highest fraction • AGN tend to reside in galaxies with larger/massive bulges • difference in AGN fraction btw LSBG and HSBG • Overall fraction of AGN in LSBG is ~15%, smaller than ~40% for normal HSBG • may be due to different bulge distribution for the same morphological type • likely NOT due to the difference in disk surface brightness

  26. conclusion II -- AGN properties • some similar properties to AGN in HSBG • NLR kinematics traces well the bulge gravitational potential • Both radio-loud and radio-quiet (similar fraction) • Differences from AGN in HSBG • Less nuclear dust extinction • lower electron density of NLR • More data are needed to constrain BH and bulge growth in LSBG

  27. Questions raised • How do SMBH grow in LSBG, which experience little or no merging? • Are all SMBH grow via galaxy merging?

  28. Next step • Deep imaging of LSBG for bulge/disk decomposition (using the YNAO Lijiang 2.4m) • Distribution of black hole mass and Eddington ratio • Better constraint to the BH growth and M-σrelation for LSBG • Select new LSBG samples from SDSS and other imaging survey data

  29. Thank you for your attention

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