Nucleus is obscured by dust in all LINERs w/0 UV nucleus; Probably all LINERs have UV nucleus Pogge et al. (2000)
UV spectrum of LINERs NGC 4579; Barth et al. (1996)
Maoz et al. (1998)
NGC 1741B starburst
So, how to distinguish stellar from nonstellar? VARIABILITY! (defining characteristic of AGNs) Monitor in UV a sample of LINERs:
Snapshot Monitoring with HST/ACS/HRC in at 2500 Ang and 3300 Ang
The sample: (all) 17 LINERs with known UV nuclei L(UV)~10^(39-41) erg/s Includes all kinds: LINERs 1 / 2, radio / X-ray detected / undetected, AGN-like / starburst-like, pure / transition types.
Big worry: detector stability Boffi et al. 2004: ACS stable in UV to < 1% !
Results: F330 f250 “historical” (5~10 yr earlier) level
Summary of results: 1. 11/15 vary significantly on short (month) timescales, typical amplitudes ~10% 2. Correlated variations in 2500 A and 3300 A 3. Long timescale (years-decade) variations common, amplitudes factor few 4. Only 3/17 vary neither on long or short timescales, but even these may be due to sparse sampling 5. All LINER types vary
Conclusion: LINERs are indeed genuine signposts of nonstellar activity (i.e., AGNs). SMBHs in most “normal” galaxies are producing (in one way or another) a LINER spectrum. Variable UV flux gives lower limit on AGN UV luminosity – can constrain accretion models
Nagar et al. (2001) ADAFs predict wrong radio slope; radio emission probably dominated by jets Also, wrong slope in X-rays Terashima & Wilson (2003) Perhaps UV is also from jets?
NGC 4736: a binary/merging BH? b nucleus
6 60 pc
3C 75 7 kpc
Conclusions: 1.Most LINERs are excited by some nonstellar phenomenon near the SMBH (accretion, jets) 2. Sharpens demographic picture and allows probe of accretion process, hence SMBH growth history 3. Possible detection of closest/nearest binary AGN