The Galactic Structure and Chemical Evolution Traced by the Population of Planetary Nebulae

Abstract

Planetary nebulae (PNe) derive from the evolution of ∼1-8 M ⊙ mass stars, corresponding to a wide range of progenitor ages, thus are essential probes of the chemical evolution of galaxies, and indispensable to constrain the results from chemical models. We use an extended and homogeneous data set of Galactic PNe to study the metallicity gradients and the Galactic structure and evolution. The most up-to-date abundances, distances (calibrated with Magellanic Cloud PNe), and other parameters have been employed, together with a novel homogeneous morphological classification, to characterize the different PN populations. We confirm that morphological classes have a strong correlation with PN Peimbert's Type, and also with their distribution on the Galactic landscape.We studied the α-element distribution within the Galactic disk, and found that the best selected disk population (i.e., excluding bulge and halo component), together with the most reliable PN distance scale yields to a radial oxygen gradient of ∆log(O/H)/∆R G =-0.023±0.006 dex kpc −1 for the whole disk sample, and of ∆log(O/H)/∆R G = -0.035±0.024, -0.023±0.005, and -0.011±0.013 dex kpc −1 respectively for Type I, II, and III PNe, i.e., for high-, intermediate-, and low-mass progenitors. Neon gradients for the same PN types confirm the trend. Accurate statistical analysis show moderately high uncertainties in the slopes, but also confirm the trend of steeper gradient for PNe with more massive progenitors, indicating a possible steepening with time of the Galactic disk metallicity gradient for what the α-elements are concerned. We found that the metallicity gradients are almost independent on the distance scale model used, as long as these scales are equally well calibrated with the Magellanic Clouds. The PN metallicity gradients presented here are consistent with the local metallicity distribution; furthermore, oxygen gradients determined with young and intermediate age PNe -3show good consistency with oxygen gradients derived respectively from other young (OB stars, H II regions) and intermediate (open cluster) Galactic populations. We also extend the Galactic metallicity gradient comparison by revisiting the open cluster [Fe/H] data from high resolution spectroscopy. The analysis suggests that they could be compliant with the same general picture of a steepening of gradient with time. Subject headings: (ISM:) planetary nebulae: general -Galaxy: Disk, Evolution, Structure. Roberston et al. 2004). In this respect, radial variations of properties of the Galactic disk may provide important observational constraints, but this has been hampered by the lack of tracers for which distance can be measured with the relevant accuracy, explaining why the magnitude of abundance gradients in the disk is still actively debated.Nonetheless, it can be considered that a consensus on the existence of gradients has been reached, and there is little doubt that inner regions are, in the mean, more metal rich than the outer parts of the disk (Davies et al. 2009), and this effect...

Chemical Cartography With Apogee: Large-Scale Mean Metallicity Maps of the Milky Way Disk

“…Recent models of chemical and galaxy evolution predict that radial migration can wipe out gradients of older populations, causing younger populations to have steeper observed gradients (e.g., Roškar et al 2008;Loebman et al 2011;Kubryk et al 2013). Our result of the steepening of the gradient with time are compatible with these models and the results from Stanghellini & Haywood (2010). Frinchaboy et al (2013) measured a single radial fit of −0.09 dex kpc −1 for their sample of open clusters observed with APOGEE, but find that it is potentially better fit with two components: a steeper gradient of −0.2 dex kpc −1 between 7.9 < R < 10 kpc, and a flat radial gradient for clusters with R > 10 kpc.…”

“…There is disagreement in the literature over this result. Stanghellini & Haywood (2010) observed planetary nebula across a range of ages and find that older populations have shallower metallicity gradients than younger populations. However, in a similar study of a different set of planetary nebula, Maciel & Costa (2009) find the opposite result; they observed the gradient to flatten with time, with older populations having steeper gradients.…”

“…Various tracers have been used including Cepheid variables (e.g., Lemasle et al 2013), planetary nebulae (e.g., Henry et al 2010;Stanghellini & Haywood 2010), H ii regions (e.g., Balser et al 2011), open clusters (e.g., Carrera & Pancino 2011;Frinchaboy et al 2013), B stars (e.g., Daflon & Cunha 2004;Daflon et al 2009), and surveys of main sequence stars (e.g., Cheng et al 2012b for the Sloan Extension for Galactic Understanding and Exploration (SEGUE; Yanny et al 2009) of the Sloan Digital Sky Survey (SDSS; York 2000); Nordström et al 2004 for the GenevaCopenhagen Survey (GCS; Boeche et al 2013) for the Radial Velocity Experiment (Steinmetz et al 2006)). Near the solar circle, the measured amplitude of the Milky Way radial gradient ranges from −0.04 dex kpc −1 in [S/H] in OB stars (Daflon et al 2009) to −0.099 dex kpc −1 in [Fe/H] in main sequence stars between 4 < Gyr < 6 from the GCS (Nordström et al 2004).…”

The evolution of the oxygen abundance radial gradient in the Milky Way Galaxy disk

“…The problem is that each type of objects shows a different evolution. Thus, PNs which gave a steep radial gradient for a time ∼8 Gyr compared with the one corresponding to the present time given by Hii regions, give now, following the most recent findings, a flat evolution along the time; that is, the radial gradient for O is basically the same from 5-6 Gyr ago until now , or even has steepen slightly on time Stanghellini & Haywood (2010). A radial gradient constant along the time is also obtained by Magrini et al (2016) for M33, M31, M81 and NGC300, comparing their radial distributions of Oxygen abundances given by Hii regions and PN, finding no evidences of evolution of the radial gradient with time.…”

A new planetary nebula in the outer reaches of the Galaxy

“…One of the major sources of this confusion is the unsettled PNe distance determination problem allied with the extreme paucity of nebulae at large galactocentric distances. In fact, in the most recent works, those by Henry et al (2010) and Stanghellini & Haywood (2010), only two PNe with D GC > 17 kpc are included in each sample (K3-64, K3-70, and M1-9, K3-66, respectively), all four PNe having mediocrily determined O abundances (quoted errors from 0.2 to 0.5 dex) and distances. However, these distant nebulae are obviously critical for the gradient determination.…”