The Planetary Nebula Luminosity Function (PNLF): Contamination from Supernova Remnants
Brian D. Davis, Robin Ciardullo, John J. Feldmeier, George H. Jacoby
TThe Planetary Nebula Luminosity Function (PNLF): Contamination fromSupernova Remnants
Brian D. Davis, Robin Ciardullo, John J. Feldmeier, and George H. Jacoby Pennsylvania State University Youngstown State University Lowell Observatory
Keywords: galaxies: distances and redshifts – ISM: planetary nebulae – ISM: supernova remnantsINTRODUCTIONSince the 1980’s, [O
III ] λ ∼
20 Mpc. The bright end of these PNLFs exhibit sharpexponential cutoffs, which are used in determining these distances. To this day, the method remains reliable androbust. A summary of the history of the PNLF is given in Jacoby et al. (1992).Ferrarese et al. (2000) suggested that there may be a larger systematic error associated with the method thanpreviously estimated for distances >
10 Mpc, claiming that at these distances, intracluster planetary nebulae (PNe)can lead to an underestimate of the bright-end cutoff magnitude by up to 0.2 mag. A rebuttal by Ciardullo et al. (2002)argued that the apparent offset in distances may arise from a systematic difference between the internal extinction ofnearby spiral galaxies and that within distant elliptical systems, and that the effect is also present in distances basedon surface brightness fluctuations. Recent results from Kreckel et al. (2017) have presented a third alternative: thatthe PNLFs of spiral galaxies at large distances are contaminated by supernova remnants (SNRs). Here we test thisthird hypothesis.A characteristic relationship exists between the [O
III ] λ α flux, and [O III ] λ > log R > − . M − . , where R = I ([O III ] λ I (H α + [N II ]) is the ratio of the [O III ] λ α flux (whose bandpass also includes the [N II ] lines). Any spatially unresolved SNRs with flux ratios fallingwithin this cone could be mistaken for PNe. At fixed seeing, this will occur more frequently at large distances. Thusour test: would the known SNRs in nearby spiral galaxies be classified as PNe if unresolved, and would these alter thePNLF bright-end cutoff magnitudes for these galaxies?OBSERVATIONSWe measure the narrowband fluxes of PNe and SNRs in M31 and M33. We choose these two particular galaxiesfor their proximity, and for the fairly complete PN and SNR surveys that have previously been performed in them.The PNe that we observe in M31 and M33 come from Merrett et al. (2006) and Ciardullo et al. (2004), respectively.The SNR survey used for the M31 analysis is from Lee & Lee (2014). In this survey, objects with roughly circularshapes and flux ratios I ([S II ]) / I (H α ) > . A V = 0 .
170 and A V = 0 . α , and [O III ] λ a r X i v : . [ a s t r o - ph . GA ] F e b RESULTSIn M31, we measure 446 PNe and 25 SNRs. In this sample, none of the SNRs fall within the PN cone. This meansthat none of the SNRs would be confused with PNe, even at distances >
10 Mpc. The PNLF is therefore unaffectedby contamination.Our findings are only slightly different in M33. Figure 1 plots the flux ratios and [O
III ] λ R <
1, and thus are notconfused with the brightest PNe, which are 1 to 2 magnitudes brighter. In fact, no SNR (even outside of the cone) hasan excitation indicative of a bright PN ( R (cid:38) R >
1. The bright end of the PNLF is unaffectedby SNR contamination. I ([ O III ] ) / I ( H + [ N II ]) PNeSNRs
Figure 1.
PNe and SNRs in M33, represented by green circles and orange crosses, respectively. The dotted blue lines give thePN cone defined by Herrmann et al. (2008). Objects not within the standard PN cone are shown in gray. The vertical axis isthe flux ratio of [O
III ] λ α +[N II ]. The PN measurements are from Ciardullo et al. (2004). In the case of M31 and M33, contamination of the PNLF by SNRs does not change the shape or location of thePNLF’s bright-end cutoff. Because bright SNRs reside outside of the PN cone, PN/SNR confusion does not appearto be an important factor for galaxies at >
10 Mpc, where compact SNRs are morphologically indistinguishable fromPNe. It is possible that the result from Kreckel et al. (2017) may have been somewhat of an anomaly.REFERENCES10 Mpc, where compact SNRs are morphologically indistinguishable fromPNe. It is possible that the result from Kreckel et al. (2017) may have been somewhat of an anomaly.REFERENCES