Fornax 3D project: Automated detection of planetary nebulae in the centres of early-type galaxies and first results

Abstract

Extragalactic planetary nebulae (PNe) are detectable through relatively strong nebulous [O III] emission and act as direct probes into the local stellar population. Because they have an apparently universal invariant magnitude cut-off, PNe are also considered to be a remarkable standard candle for distance estimation. Through detecting PNe within the galaxies, we aim to connect the relative abundances of PNe to the properties of their host galaxy stellar population. By removing the stellar background components from FCC 167 and FCC 219, we aim to produce PN luminosity functions (PNLF) of these galaxies, and thereby also estimate the distance modulus to these two systems. Finally, we test the reliability and robustness of our novel detection and analysis method. It detects unresolved point sources by their [O III] 5007 Å emission within regions that have previously been unexplored. We model the [O III] emissions in the spatial and spectral dimensions together, as afforded to us by the Multi Unit Spectroscopic Explorer, and we draw on data gathered as part of the Fornax3D survey. For each source, we inspect the properties of the nebular emission lines to remove other sources that might hinder the safe construction of the PNLF, such as supernova remnants and H II regions. As a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach through a set of simulations. By applying this novel detection and modelling approach to integral field unit observations, we report for the distance estimates and luminosity-specific PNe frequency values for the two galaxies. Furthermore, we include an overview of source contamination, galaxy differences, and possible effects on the PNe populations in the dense stellar environments.

The Fornax 3D project: PNe populations and stellar metallicity in edge-on galaxies

“…In order to characterise the PNe populations of our edge-on galaxies we follow the method of Spriggs et al (2020). This consists of five separate steps: i) identification of PNe candidate using [O iii] λ5007 signal-to-noise maps obtained from our dedicated spaxel-by-spaxel GandALF fits, ii) dedicated 3D-fitting of such PNe candidates for their kinematics and total [O iii] λ5007 flux while imposing a fixed spatial profile for their [O iii] λ5007 emission according to the (pre-determined) spatial Moffat pointspread function (PSF) 1 , iii) isolating and removing PNe interlopers based on the comparison with the host-galaxy stellar kinematics and unresolved HII-regions or supernovae remnant PNe impostors using line diagnostics, iv) construction of the PNLF and of our PNe detection incompleteness function (Section 3.1) and v) finally, estimation of the total luminosity-specific number of PNe within a given magnitude limit (Section 3.2).…”

“…where M 5007 = −4.52 mag is the characteristic bright-end cut-off (according to the latest calibration of Ciardullo 2012) that makes the PNLF a useful distance indicator. Following Spriggs et al (2020) we define the PNe detection completeness at a given apparent magnitude m 5007 as the fraction of galaxy stellar light within the MUSE FoV where a PNe of that particular magnitude can be detected. For this, we apply our PNe detection criteria on a spaxel-by-spaxel basis, by first computing the peak [O iii] λ5007 flux for PNe of apparent magnitude m 5007 (given our PSF model) and subsequently checking if the corresponding peak A [O iii] spectral amplitude (given the MUSE spectral resolution and the typical PNe intrinsic σ of ∼ 40 km s −1 ) exceeds three times the local residual-noise level from our previous spaxel-by-spaxel GandALF spectral fitting.…”

“…In the case of our MUSE observations, we have chosen the SDSS g-band to compute the observed m g and absolute M g magnitude of the in and off-plane regions in our edge-on galaxies. As for deriving the bolometric correction, we follow the procedure described by Spriggs et al (2020) whereby BC g is derived using the optimal combination of EMILES stellar templates (Vazdekis et al 2016) that best matches the MUSE integrated spectrum observed within the region of interest (i.e. our in and off-plane region in both central and halo pointing).…”

“…Weijmans et al 2009) and detection of PNe deeply embedded in the central bright regions of galaxies (thanks to a detailed spectral modelling, e.g. Sarzi et al 2011;Pastorello et al 2013;Spriggs et al 2020), where they are otherwise inaccessible to narrow-band imaging or counter-dispersed slit-less spectroscopy (e.g. Gerhard et al 2005;Douglas et al 2007;Ventimiglia et al 2011).…”

Fornax 3D project: Assessing the diversity of IMF and stellar population maps within the Fornax Cluster

“…The unique capabilities of MUSE power the ambitious goals of the Fornax 3D project, which range from characterizing compact, unresolved systems (Fahrion et al 2020b,a;Spriggs et al 2020), to studying the orbital heating mechanisms (Pinna et al 2019a,b;Poci et al 2021) and the dust and gas properties within the cluster (Viaene et al 2019;Zabel et al 2020).…”