Challenges in Finding AGNs in the Low Luminosity Regime Shobita Satyapal Nick Abel(UC), Nathan Secrest (NRL), Amrit Singh (GMU), Sara Ellison(UVIC)
Motivation and Overview Why are low luminosity AGNs important? Finding low mass SMBHs (L Edd ~10 42 ergs s -1 for M BH =10 4 M ) insight into SMBH seeds Understanding BH growth in minor mergers (~3 x more frequent than major mergers) Understanding of merger-free pathways to BH growth Link between active and quiescent galaxies (only 1% of galaxies are highly accreting!)
Motivation and Overview Why are low luminosity AGNs important? Crucial to understanding of the origin of SMBHs and their connection to galaxy evolution Difficulty: Low Luminosity AGNs are difficult to find
Challenges with Optical Diagnostics Dust obscuration (LLAGN can have very high N H ; Annuar et al. in prep, Ricci et al. 2015) Optical lines dominated by SF Overlap in low metallicity AGNs with SF on BPT logu=-4.0 100% AGN (Trump et al. 2015) More significant in low mass galaxies 0% AGN (Satyapal et al.2016)
Challenges with Optical Diagnostics Type II SNe can look like AGNs L Hα from broad lines comparable to SNe (e.g. Greene & Ho 2007) Majority of broad lines in dwarfs fade within a few years (Baldassare et al. 2016) (Fillipenko 1987)
Challenges with Optical Diagnostics Type II SNe can look like AGNs L Hα from broad lines comparable to SNe (e.g. Greene & Ho 2007) Majority of broad lines in dwarfs fade within a few years (Baldassare et al. 2016) (Fillipenko 1987) Optical diagnostics limited in finding low luminosity AGNs
Optically Identified AGNs: Almost all in Massive Bulge-dominated Hosts (Kauffmann et al. 2003) Optical studies don t tell the full story
Challenges with X-ray Diagnostics (Mineo et al. 2014) (Fragos et al. 2013) Contamination by XRBs X-ray enhancement with metallicity More significant in low mass galaxies
Challenges with X-ray Diagnostics HLXs (Walton et al. 2011) Separation (kpc) LLAGNs have X-ray luminosities comparable to ULXs At z=0.35 1 = 5 kpc More significant in starburst galaxies X-ray observations alone not sufficient to confirm low luminosity AGNs
Challenges with IR Diagnostics Model SED of 5 Myr starburst
Challenges with IR Diagnostics (Satyapal et al. 2016) Model SED of 5 Myr starburst AGN heats dust to high T Different SED in mid-ir Obscuration-independent diagnostic
Challenges with IR Diagnostics (Satyapal et al. 2016) Model SED of 5 Myr starburst AGN heats dust to high T Different SED in mid-ir Obscuration-independent diagnostic Less effective when L AGN < 50% L tot
Challenges with IR Diagnostics AGN demarcation (Jarret et al. 20011) SDSS AGNs identified through BPT classification (Kewely et al. 2001) Only 9% in AGN mid-ir color selection wedge Most optically identified AGNs are not identified as AGNs through mid-ir color selection Mid-IR color selection selects only dominant AGNs
Challenges with IR Diagnostics Question: Can a pure starburst theoretically produce MIR colors like an AGN? 2.5% of optically classified star forming galaxies have AGNlike in mid-ir colors
Challenges with IR Diagnostics
Challenges with IR Diagnostics (Satyapal et al, in prep) Extreme starbursts can look like an AGN in mid-ir colors
Challenges with IR Diagnostics X-ray Point sources associated with optically quiescent galaxies
Challenges with IR Diagnostics Many optically quiescent AGNs are likely AGN
Challenges with IR Diagnostics Many optically quiescent AGNs are likely AGN
Example Bulgeless or Dwarfs with Candidate AGNs J1329+3234 J1329+3234 (Secrest et al. 2015) L 2-10 kev = (1.1 ± 0.4) 10 40 erg s -1 J1224+5555 J1224+5555 (Satyapal et al. 2016) L 2-10 kev = (4.8 ± 1.1) 10 40 erg s -1
Mid Infrared Spectroscopic Diagnostics NeV Insensitive to extinction Insensitive to dilution by SF No confusion with XRBs, ULXs NeV Robust way to find low luminosity AGNs (Veilleux et al. 2009)
AGN Detection Rate vs. Hubble Type Detection rate of ~ 30% at 10 38 ergs s -1 Roughly 4 times the detection rate of optical studies! Optically studies significantly miss AGNs in late-type hosts (Satyapal et al. 2007, 2008, 2009) NGC 3621 NGC 4178
Tip of the Iceberg: Weak AGNs not found with WISE Bulgeless AGNs with [NeV] emission NGC 1042 He 2-10 NGC 3621 NGC 4178
Archival Spitzer IRS Sample Inami (2013) Veilleux (2009) Dale (2009) Dudik (2007, 2009) Goulding (2009) Tommasin (2008, 2010) Farrah (2007) Petric (2011) Satyapal (2008, 2009) Bernard Salas (2009) Pereira-Santaella (2010) Gorjian (2007) 692 Galaxies with observations Truth Sample of AGNs Can test other detection methods
AGNs Missed by Optical Selection Optically normal AGNs
AGNs Missed by X-ray Selection XRB regime
AGNs Missed by X-ray Selection XRB regime Obscuration and dilution plays a role
AGNs Missed by Mid-IR Color Selection Consistent with SF galaxies
AGNs Missed by Mid-IR Color Selection Obscuration and dilution plays a role
Key Points Low Luminosity AGNs are crucial in understanding origin of BH and BH/Galaxy evolution Optical studies limited by extinction and dilution by SF X-ray studies limited by XRB/ULX contamination Mid-IR color selection limited by dilution by SF
Future Prospects Variability studies for low mass BHs need required cadence and baseline; host cannot dominate High spatial resolution MIR observations (JWST MIRI can get to tens of parsecs in nearby galaxies) MIR spectroscopy (JWST can detect [NeVI] 7.6 µm to z~2.2)