Planetary Nebula abundances in NGC 5128 with FORS

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Planetary Nebula abundances in NGC 5128with FORS

• J. R. Walsh, ST-ECF, ESO
• G. H. Jacoby, WIYN
• R. Pelletier, Kapteyn Lab.
• N. A. Walton, IoA, Cambridge

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Motivation

• Measure PN abundances in an elliptical galaxy (Z
  gt Milky Way)
• Determine abundance gradient (a-elements, e.g. O)
  from PN compare with stellar values (Fe/H)
• From spectra determine if the brightest PN are
  pathological (upper L cut-off of PNLF)
• Compare kinematics with abundances halo PN with
  lower Z or groups of PN with similar abundances
  (merger remnant?)
• Input to galaxy evolution models and star
  formation history

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4m-class PN spectra in NGC 5128

• ESO 3.6m EFOSC long-slit spectra
• 3 slit positions, max exp. 9hrs
• 5 PN selected from Hui et al. (1993)

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FORS1 MOS Observations

• Three fields at a range of radial offsets (4, 7.5
  14.5)
• PN selected from Hui et al. (1993) catalogue
  maximizing PN observed with18 slitlets
• Blue spectra (600B) 3500-5500A, R2.3Å for O
  II 3727 to O III5007Å
• Red spectra - (300V) 4500-8500Å R5Å for Ha/Hß,
  He I, N II, etc.
• Exposures to 4hrs per field per spectral range

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Results

• ? flux calibrate each slitlet, extract all PN
  spectra
• Field F56 20 PN F42 21 PN
  F34 9 PN
  50 PN detected
  23.5 lt m5007 lt 28.1

PN not in Hui catalog m5007 28.1 m5007 27.5
? calib F56 MOS spectrum
PN 5601 300V spectrum
Skybackground subtracted
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Spectra and abundances

• Tie blue and red spectra together with O
  III5007Å
• Three brightest spectra analysed in each field
• O III4363Å detected in 4 PN 3 in outer field
  (low background) and in 5601
• No O III4363Å, use 5007Å/Hß and Excitation
  class Teff relation of Dopita et al (1992) to
  give Te
• Determined O/H, N/O and He/H where lines
  available
• PN spectra normal. One with N/Ogt1. One PN with
  c0.4, most low (lt0.2). One lower excitation

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Galaxy scale abundances

• O/H v. r gradient?
• Harris et al. (1999, 2000, 2002) determined old
  Red Giant Branch metallicities from HST
  photometry in 3 fields (two halo, one central)
• Find broad Metallicity Distribution Function
  (MDF) with peak Z declining with radius
• Naïve O/Fe 0.2
• Point comparison of O v. Fe in NGC 5128 GCs

PN4211 ?V-190km/s
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Prospects/Conclusions

• Analysis still in progress. About 40/50 PN have
  most strong lines (H, O II, O III, N II,
  etc) detected, m5007lt25.5, for at least O
  abundance determination
• NGC 5128 PN show a range of metallicity (cf.
  stellar MDF) but no obvious radial gradient
• Previous puzzling result that PN show sub-solar
  O/H confirmed, but some higher values (to solar)
• Velocity data (rotation curve) required to
  determine true radial distance for abundance
  gradient
• 8-10m multi-object low resolution spectra
  feasible (O III4363Å detection) for PN
  abundance samples to 10Mpc