Local Group CensusLocal Group Census

NGC 6822NGC 6822

P. Leisy (1,3) L. Magrini (2), R. Corradi (1), P. Leisy (1,3) L. Magrini (2), R. Corradi (1), A. Mampaso (3)A. Mampaso (3)

(1) Isaac Newton Group (1) Isaac Newton Group (La Palma, SPAIN)(La Palma, SPAIN)(2) Universita’ di Firenze (2) Universita’ di Firenze (ITALY)(ITALY)(3) Instituto Astrofisico Canarias (3) Instituto Astrofisico Canarias (Tenerife, SPAIN)(Tenerife, SPAIN)

IntroductioIntroductionn

Irregular DwarfIrregular Dwarf galaxy Ir IV-V galaxy Ir IV-V

Distance Distance 490 Kpc490 Kpc (m-M= (m-M=23.4823.48))

Low metallicityLow metallicity Log(O/H)+12~ Log(O/H)+12~8.18.1 (HII) (HII)7.917.91 Chandar et al. 2000Chandar et al. 20008.258.25 Skillman et al. 1989 or Pagel et al 1980Skillman et al. 1989 or Pagel et al 1980 -2.0 < [Fe/H] ~-1.0 -2.0 < [Fe/H] ~-1.0 Tolstoy et al. 2001Tolstoy et al. 2001

Gas rich galaxyGas rich galaxy – Huge HI envelope – Huge HI envelope

currently ongoing “low” star formation taking currently ongoing “low” star formation taking

placeplace

Several set of Several set of datadata

• ImagingImagingESO/WFIESO/WFI HH, [OIII], [SII], B, , [OIII], [SII], B,

continuumcontinuum

ING/WFCING/WFC HH, [OIII], [SII], r, Str Y, [OIII], [SII], r, Str Y

• SpectraSpectraESO / NTTESO / NTT (8 long slit spectra) (8 long slit spectra)

ING / WHT-AF2ING / WHT-AF2 (fiber multi-spec 40’ ) (fiber multi-spec 40’ )

Filters Filters usedused

NGC 6822 PNe / NGC 6822 PNe / outliersoutliers

Supergiant HI shell r>40’ or ~6Kpc Blok & Walter 2000

Red giant extension (6 scale length) Letarte et al. 2002

Criteria Criteria

Ha – [OIII] emitter Ha – [OIII] emitter

Point-like Point-like (at 500Kpc 1” = 2.5pc)(at 500Kpc 1” = 2.5pc)

No ContinuumNo Continuum

Not usingNot using

R=[OIII]/(Ha+[NII]) > 1R=[OIII]/(Ha+[NII]) > 1 loose some PN loose some PN

Ratio-[OIII]/HaRatio-[OIII]/Ha

Ratio Ha/ContRatio Ha/Cont PNe>100-200 PNe>100-200 - HII ~ 30-50 - HII ~ 30-50

Most PNe distributed in the bar Most PNe distributed in the bar young young

population population ??

2-3 intergalactic PN2-3 intergalactic PN candidates ? (~15 Kpc) candidates ? (~15 Kpc)

PNe PNe candidatescandidates

Diagram Ha/NII Ha/SIIDiagram Ha/NII Ha/SIIFirst introduced First introduced

Sabbadin & D’ Oddorico Sabbadin & D’ Oddorico 19781978

Great potential to select candidates; place HII vary inside the Local Group Great potential to select candidates; place HII vary inside the Local Group galaxiesgalaxiesG. Delgado 2003, IAC Master Thesis, 2003 G. Delgado 2003, IAC Master Thesis, 2003 Delgado, Viironen, Mampaso, Corradi II Internat. workshop of science with Delgado, Viironen, Mampaso, Corradi II Internat. workshop of science with GTC 2004GTC 2004

Ha/[OIII]-Ha/[SII].jpg

PNLF with 19 PNLF with 19 PNePNe

Completeness ~3 magCompleteness ~3 mag 2 ind. sets of data 2 ind. sets of data

(Jacoby)(Jacoby)

Dist = 23.91+/- 0.19Dist = 23.91+/- 0.19

Extinction correctionExtinction correction Av=0.26-0.45 Av=0.26-0.45

mean~0.32mean~0.328 PNe : 0.45<C(H8 PNe : 0.45<C(H<<

or Av ~ 0.3-1.0or Av ~ 0.3-1.0

Dist = 23.6 +/- 0.4Dist = 23.6 +/- 0.4 23.48 +/- 0.06 (2003)23.48 +/- 0.06 (2003)

SpectraSpectra

NTT spectra of PNe / HIINTT spectra of PNe / HII

10-20mn exposure time10-20mn exposure time

high S/N ratio (brightest objects)high S/N ratio (brightest objects)

need observations with 8-10m class need observations with 8-10m class telescopestelescopes

Diag. N/O - Diag. N/O - HeHe

NGC 6822 (M33)

more He ? or

much less N

LMC – SMCLarge N/O

Diag. N/O - Diag. N/O - OO

NGC 6822 Oxygen ? sample too small

LMC – SMCdest O 2nd Type Islight prod O 2x ? (Carbon 10-100x)

M33same trends MC

ConclusionsConclusions

15 new PNe15 new PNe in NGC6822 (19 in total) in NGC6822 (19 in total)Difficulty distinguish Difficulty distinguish PNe/compact HIIPNe/compact HII spectraspectra distance distance PNLF ~23.6PNLF ~23.6 +/- 0.4 (~500 +/- 0.4 (~500 Kpc)Kpc) individual extinction derived from spectraindividual extinction derived from spectra

High High He, He, faintfaint N N (like in M33)(like in M33) N/ON/O ratio ratio SMALLSMALL (compare to LMC-(compare to LMC-SMC)SMC)

Laura MAGRINISextans A / Sextans B VLT m-o spectroscopy

Diag. N/O - Diag. N/O - NN

NGC 6822 - M33Faint N (N/O)