1. East-Asia AGN Workshop 2017
Recent progress on VLBI study of the jets in Narrow-line Seyfert 1 galaxies
Minfeng Gu (SHAO)
Collaborators: Zhiqiang Shen, Yongjun Chen (SHAO); Weimin Yuan (NAOC); S. Komossa, J. A. Zensus (MPIfR); Hongyan Zhou (USTC); K. Wajima (KASI);
East-Asia AGN Workshop 2017
Kagoshima, Japan

2. Outline Introduction radio-loud AGNs
narrow-line Seyfert 1 galaxies (NLS1s)
The radio structure of radio-loud NLS1s
progress
VLBA observations
comparison with other AGNs
scenarios
Ongoing and future work
Summary

3. AGN structure and radio-loud
Radio loudness:
R>10 radio-loud; <1 radio-quiet; 1<R<10 radio intermediate (Kellermann et al. 1994)
Radio luminosity: (Miller et al. 1990)
only 10%–20% were qualified as radio-loud objects in optically selected samples (e.g., Kellermann et al. 1989; Hooper et al. 1995).
Urry & Padovani (1995)

4. Narrow Line Seyfert 1 galaxies (NLS1s)
Boroson (2002)
Balmer lines broader than forbidden lines but narrower than normal type 1 AGNs (FWHM < 2000km/s)
Peculiar properties: softer X-ray spectra, fast X-ray variability, strong optical Fe IIs
Relatively small black hole mass M(e.g. Collin & Kawaguchi 2004), however still controversial: viewing angle, radiation pressure …
High accretion rate Lbol >> 0.1 LEdd (up to Lbol/Ledd ~ 1)
Accretion possible via slim disk (e.g. Abramowicz et al. 1988; Mineshige et al. 2000)

5. Radio-loud NLS1s (RLNLS1s)
NLS1s were long thought to be radio-quiet. Radio-loud NLS1s are rare, but they do exist (Siebert et al 1999 ; Grupe et al. 2000; Zhou & Wang 2002; Zhou et al. 2003; Whalen et al. 2006; Komossa et al. 2006; Yuan et al. 2008).
RL NLS1s sample from SDSS: >100 out of ~2000 NLS1s (Zhou et al. 2006) – RL (R>10) fraction = 7%; very radio-loud (R>100) NLS1s: very rare – 23 from SDSS DR5 (Yuan et al. 2008).
Out of NLS1s: 555 detections in FIRST (5%), 378 radio-loud (3.4%) (Rakshit et al. 2017)
Komossa et al. (2006): the radio loud NLS1 galaxies are generally compact, steep spectrum sources.
Several of the radio loudest NLS1 galaxies display blazar characteristics and harbor relativistic jets (Doi et al. 2007; Zhou et al. 2007; Yuan et al. 2008)
Flat radio spectra, large-amplitude flux and spectral variability, compact radio cores, very high variability brightness temperatures, enhanced optical continuum emission, flat X-ray spectra, and blazar-like SEDs.

6. Compact at arcsec scale
Arcsecond-resolution observations have resolved the structures of only a few NLS1s because they are generally quite compact (e.g. Ulvestad et al. 1995, Moran et al. 2000, Stepanian et al. 2003, Doi et al. 2012).
Kpc-scale structure has bee detected in only eleven NLS1s (Doi+12, Richards & Lister 2015,Mrk relic, Congiu et al. 2017)

7. Host galaxies
Almost all the low redshift NLS1s are hosted by spiral galaxies (Crenshaw et al. 2003, Deo et al. 2006)

8. Host galaxies of RLNLS1s:unclear
1H : HST and NOT images–one-armed galaxy morphology or a circumnuclear ring – the spiral arm of the host galaxy or the residual of a galaxy merger (Zhou et al. 2007, Anton et al. 2008, Leon Tavares et al. 2014)
A bulge-disk-bar (pseudobulge) morphology in PKS (Kotilainen et al. 2016)
A barred lenticular galaxy (SB0), pseudobulge in FBQS J (Olguin-Iglesias et al. 2017)
SDSS images
Zhou et al. (2007), Foschini (2011)

9. RLNLS1s in overall AGNs
Relatively smaller MBH, and larger accretion rate.
Two sequences on R - Eddington ratio plane (Sikora et al. 2007).

10. Jet formation Jets in BHBs and AGNs: similar ?
Jet-production related parameters: black hole mass, spin, host galaxy, accretion rate, environments …
Fender et al. (2004) Yuan & Narayan (2014)

11. Progress of VLBI studies
Five radio-loud NLS1s: RXS J , RXS J , and B (VLBA Gu & Chen 2010, Doi et al. 2011, JVN Doi et al. 2007), RX J (JVN Doi et al. 2007, VLBA Doi et al. 2011), B (EVN, VLBA Chen & Gu in prep.).
Six gamma-ray NLS1s: compact at kpc scale, but resolved at pc scale (SBS , PKS and PKS , VLBA D’Ammando et al. 2012, Orienti et al. 2012,2015); SDSS J (VLBA Doi et al. 2006, Foschini et al. 2011, global e-VLBI Giroletti et al. 2011), 1H (VLBA Zhou et al. 2007), FBQS J (JVN Doi et al. 2007, VLBA Doi et al. 2011).
In total, only about 11 RLNLS1s (out of 117) have published VLBI images.
Fourteen RLNLS1s with FIRST 1.4 GHz flux >10 mJy (VLBA, Gu et al. 2015), including two gamma-ray sources: SDSS J , SDSS J (Liao et al. 2015, 2017 to be submitted), and SDSS J (D’Ammando et al. 2016)
Nineteen RLNLS1s with FIRST 1.4 GHz flux density >=3.5 mJy (VLBA, Gu et al. to be submitted)
One gamma-ray source: SDSS J (Yao et al. 2015, MOJAVE)
VERA observations of 12 NLS1s at 22 GHz (Doi et al. 2016)

12. Early studies
The existence of relativistic jets (e.g. high brightness temperature), either intrinsically radio loud (e.g. steep-spectrum sources), or apparently radio loud due to jet beaming effect (e.g. flat-spectrum, high brightness temperature) (Doi et al. 2007; Gu & Chen 2010; Doi et al. 2011)
gamma-ray detection 
(D’Ammando+16)

13. Gamma-ray RLNLS1s
Core-jet structure, high brightness temperature, superluminal or subluminal motions, flat spectrum (D’Ammando+16, Lister+16, Schulz+16)
Based on the superluminal motion, at least some sources have Lorentz factors in excess of 10, and viewing angles less than 10 degree (Lister+16)
However, see SDSS J , J and J in our sample

14. PMN J
A bright and compact component with an inverted spectrum, and a faint jet feature.
Beaming effect indicated from the variable emission and high brightness temperature.
First Fermi-detected NLS1s - third class of gamma-ray AGNs.
Superluminal motion: 11.5c (MOJAVE, Lister+16)
15 GHz VLBA (Foschini et al. 2011) GHz global e-VLBI (Giroletti et al. 2011)

15. SBS 0846+513 (z=0.5835): (D’Ammando et al. 2013)
Strong γ -ray flares; an apparent superluminal velocity of (5.84± 0.88)c (MOJAVE, Lister+16).
Blazar-like; at the low end of the blazar’s black hole mass distribution.

16. PKS
High frequency peakers (HFPs) selected by Dallacasa et al. (2000), but rejected due to the variability (Orienti et al. 2008).
Apparent speed: 1.14c (MOJAVE, Lister+16)

17. PKS
Compact steep spectrum source: a steep spectrum at high frequency (above 8.4 GHz), the absence of significant flux density variability, and unresolved at arcsecond-resolution (e.g. ATCA) (Gallo et al. 2006).
Included in the CRATES catalog of flat spectrum objects (Healey et al. 2007) due to its flatter spectrum below 4.8 GHz.
1.5 GHz VLBA image GHz TANAMI image (Schulz+16)
(Orienti et al. 2012).

18. 1H 0323+342: hosted in a spiral galaxy
1H : hosted in a spiral galaxy ? core + weak extended (MOJAVE source, 1.2 pc/mas) (proper motion: 9.02c, MOJAVE, Lister et al. 2016)
Zhou et al. (2007), Foschini (2011)

19. SDSS J1222+0413 At the highest redshift (z=0.966, Yao+15)
Apparent speed: 0.94c (MOJAVE, Lister et al. 2016)

20. Results of our VLBA observations (Gu et al
Results of our VLBA observations (Gu et al. 2015, ApJS, 221, 3, Gu et al. 2016, AN, Gu 2017, IAUS)
The largest sample of 117 RLNLS1s (R>10) has been constructed by combining various samples available so far, which are mostly from our own work.
Fourteen RLNLS1s with FIRST 1.4 GHz flux >10 mJy were observed with a total of 15 hours at 5 GHz using VLBA on Oct. and Nov., 2013.
The additional 19 RLNLS1s with FIRST flux density >=3.5 mJy have been observed with VLBA in a total of 24 hours in Nov. and Dec. 2014, yielding the biggest VLBI sample of 33 sources.
This is the first and largest systematic high resolution radio study of RLNLS1s.
The jet physics: the jet formation in these accretion systems.
The accretion – jet relation: early stages in both activities ?
Feedback: jet – cloud interactions ?

21. Sample

22. Morphology
Generally compact: seven sources show compact core only, and other seven objects have core-jet structure.
Core only

23. Core-jet

24. Radio spectra
From the multi-band radio data, seven sources show flat or even inverted spectra, while steep spectra are found in rest objects.
Steep radio spectrum – resemble to Compact Steep Spectrum sources
Flat radio spectrum – blazar like
(see also Orienti et al for VLBA images)

25. Polarization
The higher fractional polarization in jets: the strong Faraday rotation in nuclei region due to the high plasma density, and/or depolarization due to the complex core structure.
Fractional polarization variations in the jet: the jet-ISM interaction at the locations of high fractional polarization due to the jet bulk motion

26. Gamma-ray sources 1) SDSS J1246+0238: flat-spectrum,
core only, log Tb = 9.7 (K),
TS = 79, Γ=2.59±0.09 (D’Ammando et al. 2016)
2) SDSS J : log Tb = 10.3 (K), the first RLNLS1 with gamma-ray emission at high significance from Fermi/LAT and with radio properties similar to compact steep-spectrum sources (TS ~ 70, Liao+15,+17).

27. 3) SDSS J 1305+5116: steep spectrum (151 MHz – 4
3) SDSS J : steep spectrum (151 MHz – 4.85 GHz), and compact (<10kpc from FIRST image)
Core-jet structure: core log Tb ~ 10.8 K; TS ~ 28.5

28. Brightness temperature
The core brightness temperature ranges from to K with a median value of K, indicating that the beaming effect is generally not significant.
Typical blazars have K with a median value near 1012 K (Kovalev et al. 2005, 2009).
The bulk jet speed may likely be low in our sources (see also Angelakis et al. 2015, Richards & Lister 2015).
The Lorentz factors obtained for 1H and SBS are at the lower end of the blazar Lorentz factor distribution (Fuhrmann+16)
Kovalev et al. 2009

29. Comparisons to typical CSSs: VLBI morphology
Most high-power CSSs show double or triple morphologies (O’Dea 1998, Dallacasa et al. 2013)

30. Core and core-jet in low-power CSSs
The compact core only, or core-jet structure have been detected in relatively low-power CSS sources (Kunert-Bajraszewska et al. 2006; Kunert-Bajraszewska & Marecki 2007)

31. Evolution
Our sources occupy the space below the main evolutionary path of radio objects (An & Baan 2012).
However, the difference is that our sources have small black hole mass and high accretion rate.

32. Scenario: low jet speed
a) The outflows/jets accelerated from the hot corona above the disk by the magnetic field and radiation force, with high mass loss rate but low speed (Cao 2014).
The MBH - Γ correlation: the faster moving jets are magnetically accelerated by the magnetic fields threading the horizon of more rapidly rotating black holes (Chai, Cao & Gu 2012).
b) The low jet speed could be due to the low spin, supported by low/intermediate average spins (a < 0.84) from composite broad Fe K line (Liu et al. 2015).

33. Thanks for your attention !
Summary
Powerful jets may present in systems with small MBH and high accretion rate, e.g. NLS1s.
The jet properties of radio-loud NLS1s are diverse on mas scale, in terms of the morphology and spectral shape.
The jet speed in these sources is likely low, which is due to either the jet acceleration by the magnetic field and radiation force, or low spin in BZ mechanism.
The slow jet speed or mildly relativistic jet, in combination with the low kinetic/radio power, could be responsible for the compact VLBA radio structure in most sources.
The gamma-ray emission has been detected in both flat- and steep-spectrum NLS1s.
Thanks for your attention !