Kinematic Evidence of Different PN Populations in Elliptical

Galaxy NGC 4697

Niranjan Sambhus, Ortwin GerhardAstronomy Institute, University of Basel, Switzerland

&

Roberto H. MendezInstitute for Astronomy, University of Hawaii, USA

Extragalactic PNs

• Universal PNLF: distance determination

• Discrete kinematic tracers: mass, angular momentum distribution in halos of galaxies

• Tracers of diffuse intra-cluster stellar population

• Tools for metallicity measurements in outer regions of galaxies

• Ubiquitous in galaxies irrespective of Hubble type

NGC 4697

• Axisymmetric E 4/5, ~ edge-on, MB = -20.1

• Re ~ 95” , <B-V> ~ 0.9, age ~ 9 Gyr, [Z/H]C ~ 0.4

• X-ray: point sources (XPS) (Zezas et al 2003: HMXBs?)

• Distance: 11.75 Mpc (SBF, = 30.35), 10.5 Mpc (PNLF, =

30.1) in front of the Virgo group

• Stellar kinematics within Re consistent with no DM

4’

PNs in NGC 4697 (Mendez et al

2001)

• Detection: 535 PNs up to ~ 300”• Velocity data: 531 PNs (max error of 40 km/s)• Velocity and magnitude data: Total sample (526

PNs)

• Complete sample: m5007 < 27.6 outside a central ellipse with semi-major axis 60” (320 PNs)

• FORS1 on VLT: ON - OFF blinking on-dispersed image shift

• On-band filter: FWHM = 60 Å, peak transmission = 0.76

• Grism 600B: 1.2 Å pixel-1 at 5000 Å

PN system in NGC 4697

Asymmetric rotation

526 PNs

Maj Min

Vsys = 1274 km/s

PNs in Velocity - Magnitude plane

• Sense of rotation: velocity folding, U = sign(x) * (V - Vsys)

• Co-rotation: U > 0 , Counter-rotation: U < 0• Velocity coverage not biased by PN magnitude• Complete sample: Velocity - Magnitude correlation !• Brightest counter-rotating PNs differ in kinematics

320526

Spatial distribution of bright PNs

• Bright PNs: Left-right asymmetry• Radial distribution: Bright and

Faint PNs are KS compatible (92%), follow the surface brightness profile

• Azimuthal distribution: KS incompatible (1.8%), similar to XPS

counterCo-rot

m(5007) < 26.2

m(5007) > 26.9

Azimuthal kinematics of bright & faint PNs

• Bright PNs incompatible with faint PNs as well as stellar kinematic data:- +ve velocity along major axis

- -ve velocity along minor axis

- azimuthally varying dispersion

(100 km/s < < 200 km/s)

• Faint PNs follow stellar kinematics:- No minor axis rotation

- Peak major axis velocity ~ 60 km/s

- constant dispersion (120 km/s)

Bright

Faint

Azimuthal as well as kinematic distribution of bright PNs in NGC 4697 differs significantly from that of the faint PNs as well as the underlying galaxy stellar population

Which PN population in NGC 4697 is “normal”? Criteria:

m(5007) < 26.2

m(5007) > 26.2

- magnitudes ? - Kinematics ?

- Spatial distn ?

m(5007) - U correlation: 12/18 kinematic outliers are highly counter-rotating

10/12 PNs lie in the angular over-

density region First Approximation of Normal PN population:- 200 km/s VPN -100 km/s AND- All PNs with m(5007) > 26.2 - For PNs with m(5007) 26.2, after removing the angular over-density

LF of the “normal” PNs in NGC 4697

Complete

Scaled

SubtractedC

= 0.3 !

Sub

Sub

0.15This could be a lower limit

Errors & Contamination issues:

• Observations Unbiased velocity coverage: FORS1 filter width is 1800

km/s around Vsys of NGC 4697, and peak transmission of

0.76 with positional error corrections < 5%

Photometric rms errors < 0.2 mag ( 0.1 for m(5007) < 26.5 )

E & W field: positional error < 0.3 pixel ( < 20 km/s)

Max velocity error ~ 40 km/s including contributions from image calibration, registration, guiding & spectrograph deformation

• Contamination of bright PNs (m5007 < 26.2)?

Background sources:

- HII regions: Spectra of 13 of these PNs (Mendez et al 2005) show no detectable continuum & line ratios of metal-rich PNs

- Emission line sources: Ly galaxies would have m(5007) > 26.2, detectable in radial velocity

Foreground sources (ICPN?):- NGC 4697 (d = 10.5 Mpc) is closer than virgo (M87: d = 13.8

Mpc)

- Velocity dispersion of bright Pns, ~ 170 km/s, much smaller than those of Virgo ICPNs (~ 800 km/s)

- Radial distribution of both bright and faint PNs are KS compatible (92%), are concentrated towards the center, and follow the galaxy light

- Surface density of bright PNs is ~0.58 PNs/armin2; mean surface density of Virgo ICPNs is ~0.02 PNs/arcmin2

• Other galaxies:

– Large, complete sample with velocity is needed

Currently NGC 4697 is one of the largest such samples.

– PN.S sample: ~ 200s, magnitude distribution & completeness under investigation

– Cen A (merger remnant): Old sample ( = 0.3, filter transmission uncertainities), New sample: under investigation.

Origins• A large fraction of bright PNs belongs to a dynamically

young population that is not well mixed in the gravitational potential of NGC 4697

• Spatial distribution is similar to XPS (possibly HMXBs). Zezas et al 2003 suggest a merger or late tidal infall, though not observed in photometry

• 13/42 bright PNs have near solar metallicity outside Re , stellar population inside this radius has solar or higher [Z/H] (Mendez et al 2005). [Z/H] does not appear to be the reason for population difference

• Marigo et al 2004 suggest age difference to be a possible driver

• If so, scenario consistent with Zezas et al 2003 argument of XPS being HMXBs formed several 108 years ago in tidal tails now falling back. Bright PNs could trace an age range different but similar to XPS (no signatures in photometry)

• Extinction effects in young, bright PNs?

Conclusions• Bright & faint PNs in NGC 4697 have significantly different

radial velocity distribution. Their mean velocities are co-rotating and ~0 (94% confidence), dispersions differ with 99.3% confidence. PNs in NGC 4697 do not constitute a single population that is a fair tracer of stellar distribution

• Luminosity functions of extreme counter-rotating sub-sample and the main population are different with 99.8% confidence. PNLF appears to depend on kinematic selection

• At least two sub-populations: secondary population is prominent in bright PNs with extreme couter-rotation

• Spatial distribution of bright PNs is different from that of faint PNs. Secondary population is NOT in dynamical equilibrium in galaxy potential

• Normal population has a bright-end cutoff in PNLF uncertain by ~ 0.2 mag (could be larger)

PN spectra • Mendez et al 2005 have FORS1 & Keck LRIS spectra of

13/42 of these bright PNs.– Detect, or put upper limits on [OII] 3727, [OIII] 4363, 4959,

H, H, HeII 4686, [OIII]5007, [NeIII]3868– PNs with strong 5007 line:

• CLOUDY solutions: Tele = 12000 K, Neb Radius = 0.017pc, nele = 4 * 104 cm-3 , L* > 7000 Lsun (higher if nebula leaks H-ionizing photons,

• H luminosity ~ 1035 erg/s, T* ~ 105 K, Abundances: O (8.60), Ne (7.88), [Z/H] = -0.1

– PNs with weak 5007 line: • Not inconsistent with solar metallicity• No [OIII] 4363 detected, Tele not very high • O abundance ~ 8.2 (Lower limits)

– Bright PN: rich in O than faint PNs (M31, MC studies needed)Almost solar metallicity for 80% of studied PNs (bulge of M31)

– Metallicity - PN brightness, selection effects, …