a simplified view of blazars: why bl lacertae is actually ... · 2 the two blazar classes •...
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A simplified view of blazars: why BL Lacertae is actually a quasar in
disguise* Paolo Padovani, ESO, Germany
P. Giommi, G. Polenta, S. Turriziani, V. D’Elia (ASDC), S. Piranomonte (INAF)
November 11, 2011 P. Padovani − "Fermi and Jansky" Workshop * Based on Giommi, Padovani, et al., (2011), MNRAS, in press (arXiv:1110.4706)
• The two blazar classes�
• A new, simplified hypothesis tested by numerical simulations�
• Results and implications�
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The two blazar classes
• What’s the dividing line between BL Lacs and FSRQs?�• And when does a radio galaxy become a BL Lac? �
November 10, 2011 P. Padovani − "Fermi and Jansky" Workshop
BL Lac Flat spectrum radio quasar
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• BL Lac definitions:� Stickel, PP, et al. (1991) [radio selected]: flat spectrum
(αr ≤ 0.5) and EWrest < 5 Å � Stocke et al. (1991) [X-ray selected]: EW < 5 Å and Ca
H&K break, C < 25% (C ~ 50% in ellipticals)� Scarpa & Falomo (1997): no evidence of bimodal EW
distribution� Marchã et al. (1996) [radio selected]: region of EW – C
space (C up to 40%) � Landt, PP, & Giommi (2002): confirmed C < 40% �
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The BL Lac/FSRQ and BL Lac/radio galaxy separation
November 10, 2011 P. Padovani − "Fermi and Jansky" Workshop
C = 1 - fblue/fred
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• Optical spectra (by definition); but a few transition objects: e.g., BL Lac, 3C 279�
• Extended radio powers: generally FSRQs FR II-like and BL Lacs FR I-like; but radio-selected BL Lacs can reach FR II levels (e.g., Rector & Stocke 2001, Kharb et al. 2011)�
• Redshift distributions; BL Lacs: <z> ~ 0.4 (but ~ 45% no z), FSRQs: <z> ~ 1.4 �
• Evolution (Stickel et al. 1991; Rector et al. 2000; Padovani et al. 2007; Giommi et al. 2009): � FSRQs and radio-selected BL Lacs similar positive
evolution � X-ray selected BL Lacs no or even negative evolution�
Differences between BL Lacs and FSRQs
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BL Lacs
FSRQs
Vermeulen et al. (1995)
EW ~ 7 Å
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• Synchrotron peak frequencies�• Different mix in radio and X-ray selected samples: e.g.
WMAP5: ~ 15 % BL Lacs; EMSS: ~ 70 % BL Lacs �
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Differences between BL Lacs and FSRQs (continued)
November 10, 2011 P. Padovani − "Fermi and Jansky" Workshop
Giommi et al. (2011)
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A new scenario • Some of these differences explained by unified schemes:
BL Lacs FR Is and FSRQs FR IIs �• However, no explanation for (e.g.,): �
transition objects � different evolution of radio- and X-ray-selected BL Lacs� widely different νpeak distributions for FSRQs and BL Lacs�
• Our approach: start from unified schemes and add dilution and selection effects as new important components�
• Observed optical spectrum is result of: � three components: �o non-thermal, jet-related�o thermal, accretion-disk related�o host galaxy�
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• Single luminosity function and evolution WMAP5 blazar sample (f ≥ 0.9 Jy; 200 sources)�
• Luminosity evolution P(z) = P(0) (1+z)k-βz ( zpeak ~ 1.9); + progressively weaker evolution for Pr ≤ 1026 W/Hz �
• Non-thermal component: SSC with single distribution of electron peak energies, B = 0.15 G, and Doppler factors (<δ> = 15)�
• Thermal component + broad lines (SDSS template) associated only with evolving sources (HERGs vs. LERGs)�
• EW distribution of radio-quiet AGN�• Host galaxy: giant elliptical (standard candle)�• Non-thermal – thermal link (disk/jet power ratio): from
the SEDs a large number of blazars �7
Monte Carlo simulations
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Monte Carlo simulations • Two samples simulated (10,000 sources each): $�
radio-selected, f ≥ 0.9 Jy (matched to WMAP5)� X-ray selected, fx (0.3-3.5 keV) ≥ 5 10-13 c.g.s. (≈ matched
to EMSS) �• Source classification: �
FSRQ: EWrest of any line in the observer’s window (3,800 – 8,000 Å) > 5 Å�
BL Lac: EWrest of all lines in the observer’s window < 5 Å; non-measurable z if EWrest < 2 Å or fjet > 10 x fgalaxy �
Radio Galaxy: Ca H&K break > 40%�
Goal: to keep assumptions down to a minimum and obtain robust results (not to reproduce perfectly ALL observables)�
Simulations have also predictive power!�
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• Properties of high flux density radio- and X-ray-selected blazar samples are reproduced:� BL Lac & FSRQ fractions� evolutionary properties (<V/Vm>)� redshift distributions� νpeak distributions � fraction of BL Lacs without redshift determination�
• Results are stable to changes in: � evolution and LF slope (±1σ away from WMAP best fit) � evolution and LF (after Urry & Padovani 1995)� <δ> (from 5 to 20), including also a dependence on Pr�
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Main Results
P. Padovani − "Fermi and Jansky" Workshop
radio X-ray
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Implications
• 80% of radio-selected BL Lacs have an accretion disk:� emission lines in observer’s window swamped by jet� EWrest(Hα) > 5 Å! (Hα outside the window for z > 0.22)
FSRQs with strong IR lines �• 30% of X-ray selected BL Lacs have an accretion disk;
indeed, fewer EMSS BL Lacs with lines than 1 Jy BL Lacs�• 5 – 15% of our sources classified as radio-galaxies: blazars
with non-thermal component swamped by host galaxy. Agrees with Dennett-Thorpe & Marchã (2000), Giommi et al (2002, 2005), Anton & Browne (2005)�
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Implications
• BL Lacs belong to two physically different classes:� intrinsically weak lined objects� beamed FSRQs with diluted emission lines�
• BL Lacertae is not a BL Lac! �• There are only two blazar types: non-evolving LERGs and
evolving HERGs�
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• different νpeak distributions for BL Lacs and FSRQs NOT due to synchrotron cooling but selection effects:�
most blazars in X-ray selected samples have high νpeak high fx/fr low fr and low Pr LERGs� blazars with high νpeak likely to have emission lines and host galaxy swamped by non-thermal continuum �
• > 80% of our sources with νpeak > 1015 Hz and Pr > 1026 W/Hz have no z (swamping of emission lines); indeed, 55% of Fermi BL Lacs have no redshift. Predicted <z> ~ 1.4 agrees with recent photometric redshift study (Rau et al., A&A, submitted) �
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Implications
Giommi et al. (2005)
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The blazar sequence
Fossati et al. (1998)
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12 14 16 18
4042
4446
Log(
L)
5G
Hz
Log( Speak)
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12 14 16 18
4042
4446
Log(
L)
5G
Hz
Log( Speak)
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Summary
• We have put together many pieces of a puzzle which has been in the making for the past 20 years or so�
• Starting point: two populations� high-excitation (standard accretion disk), high Pr,
evolving� low-excitation, low Pr, non-evolving �
• Add non-thermal (jet), thermal (accretion), and host galaxy components�
November 11, 2011 P. Padovani − "Fermi and Jansky" Workshop
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Summary • Main results: �
blazar properties (incl. BL Lac/FSRQ differences) explained�
BL Lacs are of two types: �o beamed FSRQs with swamped emission lines (HERGs)
[“fake BL Lacs”]: need to be grouped with FSRQs!�o weak-lined radio sources with strong jet (LERGs)
[“real BL Lacs”] � some optically classified radio-galaxies are still blazars � blazar sequence due to selection effects� featureless BL Lacs high νpeak & high Pr, <z> ≈ 1.4 �
Stay tuned for more results for the γ-ray band!�November 11, 2011 P. Padovani − "Fermi and Jansky" Workshop
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November 10, 2011 P. Padovani − "Fermi and Jansky" Workshop 18
arXiv:1107.4706