Planetary Nebula abundances in NGC 5128 with FORS

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Planetary Nebula abundances in NGC 5128 with FORS J. R. Walsh, ST-ECF, ESO G. H. Jacoby, WIYN R. Pelletier, Kapteyn Lab. N. A. Walton, IoA, Cambridge

description

Planetary Nebula abundances in NGC 5128 with FORS. J. R. Walsh, ST-ECF, ESO G. H. Jacoby, WIYN R. Pelletier, Kapteyn Lab. N. A. Walton, IoA, Cambridge. Motivation. Measure PN abundances in an elliptical galaxy (Z > Milky Way) - PowerPoint PPT Presentation

Transcript of Planetary Nebula abundances in NGC 5128 with FORS

Page 1: Planetary Nebula abundances  in NGC 5128 with FORS

Planetary Nebula abundances in NGC 5128

with FORS

J. R. Walsh, ST-ECF, ESOG. H. Jacoby, WIYN

R. Pelletier, Kapteyn Lab.N. A. Walton, IoA, Cambridge

Page 2: Planetary Nebula abundances  in NGC 5128 with FORS

Motivation

• Measure PN abundances in an elliptical galaxy (Z > Milky Way)

• Determine abundance gradient (α-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, R~2.3Å for [O II] 3727 to [O III]5007Å

• Red spectra - (300V) 4500-8500Å R~5Å for Hα/Hβ, He I, [N II], etc.

• Exposures to 4hrs per field per spectral range

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Results• λ & flux calibrate each

slitlet, extract all PN spectra

• Field F56: 20 PN F42: 21 PN F34: 9 PN 50 PN detected 23.5 < m5007 < 28.1

PN #5601 300Vspectrum

λ calib F56 MOSspectrum

Sky+background subtracted

PN not in Hui catalogm5007 = 28.1m5007 = 27.5

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Spectra and abundances

• Tie blue and red spectra together with [O III]5007Å

• Three brightest spectra analysed in each field

• [O III]4363Å detected in 4 PN; 3 in outer field (low background) and in #5601

• No [O III]4363Å, use 5007Å/Hβ 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/O>1. One PN with c=0.4, most low (<0.2). 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 GC’s

PN#4211 ΔV=-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, m5007<25.5, 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 III]4363Å detection) for PN abundance samples to ~10Mpc