The population of planetary nebulae and H II regions in M 81 - A study of radial metallicity gradients and chemical evolution

Context. M81 is an ideal laboratory to investigate the galactic chemical and dynamical evolution through the study of its young and old stellar populations. Aims. We analyze the chemical abundances of planetary nebulae and H ii regions in the M81 disk for insight on galactic evolution, and compare it with that of other galaxies, including the Milky Way. Methods. We acquired Hectospec/MMT spectra of 39 PNe and 20 H ii regions, with 33 spectra viable for temperature and abundance analysis. Our PN observations represent the first PN spectra in M81 ever published, while several H ii region spectra have been published before, although without a direct electron temperature determination. We determine elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon in PNe and H ii regions, and determine their averages and radial gradients. Results. The average O/H ratio of PNe compared to that of the H ii regions indicates a general oxygen enrichment in M81 in the last ∼10 Gyr. The PN metallicity gradient in the disk of M81 is Δlog(O/H)/ΔRG = −0.055 ± 0.02 dex/kpc. Neon and sulfur in PNe have a radial distribution similar to that of oxygen, with similar gradient slopes. If we combine our H ii sample with the one in the literature we find a possible mild evolution of the gradient slope, with results consistent with gradient steepening with time. Additional spectroscopy is needed to confirm this trend. There are no type I PNe in our M81 sample, consistently with the observation of only the brightest bins of the PNLF, the galaxy metallicity, and the evolution of post-AGB shells. Conclusions. Both the young and the old populations of M81 disclose shallow but detectable negative radial metallicity gradient, which could be slightly steeper for the young population, thus not excluding a mild gradients steepening with the time since galaxy formation. During its evolution M81 has been producing oxygen; its total oxygen enrichment exceeds that of other nearby galaxies.

[1]  L. Stanghellini,et al.  THE GALACTIC STRUCTURE AND CHEMICAL EVOLUTION TRACED BY THE POPULATION OF PLANETARY NEBULAE , 2010, 1003.0759.

[2]  L. Stanghellini,et al.  Metal production in M 33: space and time variations , 2009, 0912.2616.

[3]  B. Draine.  Interstellar dust models: Extinction, absorption and emission , 2009 .

[4]  T. Davidge.  THE STELLAR DISK OF M81 , 2009, 0904.0026.

[5]  L. Stanghellini,et al.  THE PLANETARY NEBULA POPULATION OF M33 AND ITS METALLICITY GRADIENT: A LOOK INTO THE GALAXY'S DISTANT PAST , 2009, 0901.2273.

[6]  James Binney,et al.  Chemical evolution with radial mixing , 2008, 0809.3006.

[7]  F. Walter,et al.  The Recent Star Formation Histories of M81 Group Dwarf Irregular Galaxies , 2008, 0809.5059.

[8]  L. Stanghellini,et al.  The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale , 2008, 0807.1129.

[9]  M. Mountain,et al.  Holmberg IX: The Nearest Young Galaxy , 2008, 0802.4446.

[10]  J. Lattanzio,et al.  Stellar Models and Yields of Asymptotic Giant Branch Stars , 2007, Publications of the Astronomical Society of Australia.

[11]  E. Corbelli,et al.  The building up of the disk galaxy M 33 and the evolution of the metallicity gradient , 2007, 0704.3187.

[12]  L. Morbidelli,et al.  The chemical gradient of oxygen in the Galaxy from planetary nebulae , 2006 .

[13]  M. Dennefeld,et al.  Planetary nebulae in the Magellanic Clouds , II. Abundances and element production , 2006, astro-ph/0609408.

[14]  K. Cunha,et al.  Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way , 2006, astro-ph/0607480.

[15]  O. Dors,et al.  Abundance segregation in Virgo spiral galaxies , 2006 .

[16]  I. Karachentsev,et al.  Masses of the local group and of the M81 group estimated from distortions in the local velocity field , 2006 .

[17]  Michael J. Kurtz,et al.  Hectospec, the MMT’s 300 Optical Fiber‐Fed Spectrograph , 2005, astro-ph/0508554.

[18]  M. Mollá,et al.  A grid of chemical evolution models as a tool to interpret spiral and irregular galaxies data , 2005 .

[19]  Firenze,et al.  Stochastic processes, galactic star formation, and chemical evolution - Effects of accretion, stripping, and collisions in multiphase multi-zone models , 2005, astro-ph/0502221.

[20]  D. Calzetti,et al.  Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81 , 2004, astro-ph/0406064.

[21]  L. Morbidelli,et al.  A reanalysis of chemical abundances in galactic PNe and comparison with theoretical predictions , 2004 .

[22]  B. Balick,et al.  Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV. Synthesis and the Sulfur Anomaly , 2004, astro-ph/0401156.

[23]  A. Manchado,et al.  The Dynamical Evolution of the Circumstellar Gas around Low- and Intermediate-Mass Stars. II. The Planetary Nebula Formation , 2002, astro-ph/0208323.

[24]  R. Corradi,et al.  New candidate planetary nebulae in M 81 , 2001, astro-ph/0109436.

[25]  L. Stanghellini,et al.  Synthetic Post-Asymptotic Giant Branch Evolution: Basic Models and Applications to Disk Populations , 2000, astro-ph/0005527.

[26]  Xu Zhou,et al.  Spatially Resolved Spectrophotometry of M81: Age, Metallicity, and Reddening Maps , 2000, astro-ph/0002266.

[27]  L. Deharveng,et al.  Oxygen and helium abundances in Galactic H ii regions — II. Abundance gradients , 2000 .

[28]  P. Marigo.  Chemical Yields from Low- and Intermediate-Mass Stars , 1999, astro-ph/0012181.

[29]  R. Benjamin,et al.  Improving Predictions for Helium Emission Lines , 1998, astro-ph/9810087.

[30]  J. Walsh,et al.  Chemical Evolution from Zero to High Redshift , 1999 .

[31]  M. Yun,et al.  Tidal Interactions in M81 Group , 1999 .

[32]  M. Peimbert.  Galactic H II Region Abundances , 1999 .

[33]  C. Maraston.  Evolutionary synthesis of stellar populations: a modular tool , 1998, astro-ph/9807338.

[34]  H. Ford,et al.  Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant , 1998, astro-ph/9801080.

[35]  P. Ho,et al.  A high-resolution image of atomic hydrogen in the M81 group of galaxies , 1994, Nature.

[36]  M. Barlow,et al.  Elemental abundances for a sample of southern galctic planetary nebulae , 1994 .

[37]  R. Walterbos,et al.  Diffused ionized gas in the spiral galaxy M31 , 1994 .

[38]  R. Shaw,et al.  The FIVEL Nebular Modelling Package in STSDAS , 1994 .

[39]  J. Huchra,et al.  H II regions and the abundance properties of spiral galaxies , 1994 .

[40]  L. Stanghellini,et al.  Search for Ionized Cores in Proto-Planetary Nebulae , 1993 .

[41]  G. Gilmore,et al.  The Milky Way as a galaxy , 1990 .

[42]  H. Ford,et al.  Planetary nebulae as standard candles. III - The distance to M81 , 1989 .

[43]  L. Stanghellini,et al.  Electron Densities in Planetary Nebulae , 1989 .

[44]  D. Osterbrock,et al.  Astrophysics of Gaseous Nebulae and Active Galactic Nuclei , 1989 .

[45]  R. Clegg.  Collisional effects in He I lines and helium abundances in planetary nebulae , 1987 .

[46]  A. Walker.  CCD photometry of galactic clusters containing Cepheid variables – V. Ruprecht 79 , 1987 .

[47]  D. Garnett,et al.  Composition gradient across M81 , 1987 .

[48]  J. Mathis.  Interstellar dust and extinction , 1987 .

[49]  P. W. Hodge,et al.  An atlas of H II regions in 125 galaxies , 1983 .

[50]  R. Davies,et al.  The neutral hydrogen content of the M81/M82 group of galaxies – I. The observations , 1981 .

[51]  Bernard E. J. Pagel,et al.  On the composition of H II regions in southern galaxies – I. NGC 300 and 1365 , 1979 .

[52]  L. Weliachew,et al.  A High Resolution Neutral Hydrogen Study of the Galaxy M 51 , 1973 .

[53]  L. Thompson,et al.  DISTRIBUTION OF GAS AND DUST IN M81 , 1972 .