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Photoionized regions in NGC 6822. Liliana Hern á ndez-Mart í nez [email protected] Instituto de Astronom í a Universidad Nacional Auton ó ma de M é xico. IAC-150408. Dwarf Irregular Galaxies. Low mass Low metallicity Gas rich. Star Formation Chemical homogeneity. IAC-150408.

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photoionized regions in ngc 6822

Photoionized regions in NGC 6822

Liliana Hernández-Martínez

[email protected]

Instituto de Astronomía

Universidad Nacional Autonóma de México

IAC-150408

dwarf irregular galaxies
Dwarf Irregular Galaxies
  • Low mass
  • Low metallicity
  • Gas rich.
  • Star Formation
  • Chemical homogeneity

IAC-150408

slide4

NGC 6822

N

E

Barred dwarf galaxy of type Ir IV-V

  • Lv=9.44x107Lsun
  • Mtot=1.6x109Msun
  • Distance 490 ± 40 kpc
  • Vel Hel:-54 Km/s

- Optical radius

2.9kpc x 2.9kpc

(Mateo, 1998)- HI radius

6kpc x 14kpc

(Blok & Walter, 2000)

NGC 6822. Three colors: H-green, OIII-red and continuum-blue. MOSAIC2 image (4m Blanco, CTIO). 36.8 x 36.8 arcmin.

Hernández-Martínez, L., & Peña, M. Sep-Oct, 2005.

IAC-150408

objects with emission lines ngc 6822 previous knowledge
Objects with emission Lines NGC 6822 (previous knowledge)

 Killen & Dufour (1982):

- 36 emission stellar objects

- 31 diffuse and extended objects

- 14 compact HII regions

- 14 stars with H emission line.

Hodge et al (1988): 157 HII regions

Ford & Peng (2002): 7 PNe.

Leisy et al (2005): 17 PNe (total).

IAC-150408

extragalactic pne
Extragalactic PNe

 Baade (1955): 5 PNe in M31

 Westerlund (1968): ~100 PNe in LMC and SMC

Jacoby & Lesser (1981) found NPs in 5 galaxies in the LG

 Ciardullo et al. (1989): 429 PNe in M31

 Magrini et al. (2000): 134 PNe in M33

 Merrett et al. (2003): 2611 PNe in M31

The “Local Group Census” (2001-2004): survey in 14 galaxies.

IAC-150408

slide8

Extragalactic PNe

 Planetary Nebulae Luminosity Function (PNLF) - distance determination.

 PNe emission lines -“easy to measure” stellar cinematic

 Chemical tracers of the past component of the ISM

IAC-150408

slide9

E

N

PNe in NGC6822 (CTIO)

36.8arcmin

Dithered (to cover the gaps)

IAC-150408

slide10

NGC 6822 MOSAIC2 CTIO

Observations: sept 4th and oct 9th, 2005.

CTIO - Mosaic II CCD imager - 8 CCD’s - 36.8 arcmin.

4 filters:

[OIII] 4990Å 50Å (2hrs)

D51 (DDO) 5130Å 154Å (1.3hrs)Halpha 6563Å 80Å (1hr)

Halpha+8 6650Å 80Å(1hr)

Reduction: mscred (IRAF). Buell T. Jannuzi, Jenna Claver, and Frank Valdes, June 2003.

http://www.noao.edu/noao/noaodeep/ReductionOpt/framesv6.html.

- cross talk correction, trimsec, overscan, bias, flats, bpm (bad pixel mask), astrometric calibration - wcs (USNO-A2.0 catalogue), crmask, fixpix (bpm y crmask), tangent-plane projected, skysub.

IAC-150408

searching for pne
Searching for PNe…

8 OIII average images

4 D51 average images

Continuum subtracted

[OIII] - D51

IAC-150408

new pne in ngc6822
New PNe in NGC6822.

Selection criteria:

- objects in OIII, but not in continuum

- objects in H,but not in continuum

Pollution agents:

-compact Supernova Remnants

-compact HII regions (stellar continuum, stars of PNe are 2mag fainter)

 apparent magnitudes (punctual objects) measured with digiphot.apphot.phot (IRAF).

PSF=6.5pix

 comparative photometry (PN7, Leisy et al. 2005)

IAC-150408

spatial distribution

N

E

Spatial Distribution

26 PNe candidates in NGC 6822.

IAC-150408

slide16

Cumulative Planetary Nebula Luminosity Function.

m*=19.35

Nexp(-0.307= 6.72x10-3

N = normalization constant

= apparent distance modulus

m* = apparent peak magnitudes of the luminosity function

IAC-150408

cumulative pnlf
…Cumulative PNLF.

Hernandez-Martinez, L. et al, in preparation

IAC-150408

absolute peak magnitud of the pnlf
Absolute peak magnitud of the PNLF.

We can use the true distance modulus

23.48mag (Van de Bergh 2000)

and the extinction

AV=0.73 (Gallart et al, 1996)

to derive a peak absolute magnitude of the luminosity function of NGC 6822.

M*=-4.47±0.05

Ciardullo et. al (2002)

M*5007(0) -4.83

This work

M*=-4.57, NGC3109

Peña et al, 2007

IAC-150408

spectroscopy
Spectroscopy…
  • VLT Multi-Object Spectrograph observations, carried on August 19th to 22nd, 2006.
  • - We used FORS-2 spectrograph with a field of 6.8’x6.8’ covering the central part of the galaxy.

IAC-150408

slide20

N

E

PN4

PN1

IAC-150408

slide21

Spectrophotometric Standards

EG274 600B 600 RI

LDS749B 600B 600RI

BPM16274 600B 600RI

9 Planetary Nebulae

2 HII regions

Observations

PN1,PN4

PN7, HII8, PN14, PN13, PN19, PN11

and PN9, PN12, H24, quiet faint

IAC-150408

slide22

VLT spectra:

IAC-150408

slide23

H

4363

4471

PN1 blue

IAC-150408

slide24

H

[NII]

[NII]

6678

[SII]

PN1 red

IAC-150408

data analysis
Data analysis
  • Reddening correction:

c(H)F(H)/F(H) red

F(H)/F(H) blue

F(H)/F(H) blue

  • Direct Method (4363)

Te, Ne, ionic abundances.

IRAF: temden, ionic

  • Total abundances:

Ionization Correction Factors (ICFs,Kingsburgh & Barlow, 1994).

IAC-150408

ionic abundances
Ionic Abundances

7 PNe,VLT

1 HII Region

IAC-150408

total abundances

Peimbert et al. 2006

Total Abundances

*

I

I

*

Richer & McCall 2007

Richer & McCall 2007

IAC-150408

slide28

PN-VLT

HII-VLT

PN-M

HII-M

HII-P

IAC-150408

chemical evolution model ira
Chemical evolution Model (IRA)
  • Accretion (f).
  • Chemical abundances of the accreted gas (Xaccretedi).
  • Star Formation Rate (SFR, ).
  • Initial Mass Function (IMF, ). (Kroupa et al, 1993)
  • Stellar Yields (Yi, R).
  • Galactic winds (w).
  • Metallicity dependence

IAC-150408

infall
Infall

Carigi et al. 2006

IAC-150408

initial mass function
Initial Mass Function

IMF normalized from

0.01 to 60 M_sun

IAC-150408

star formation rate
Star Formation Rate
  • Carigi et al, 2006

IAC-150408

yields
Yields

Karakas & Lattanzio,2007

Geneva’s group &

Woosley & Weaver (1995)

IAC-150408

conclusions
Conclusions.
  • We have increased the PNe sample. The distribution of HII regions appear to be confined to the center of the galaxy instead PNe apparently being over the whole galaxy.
  • We have derived the peak absolute magnitude of the luminosity function of NGC 6822. We get M*>4.48, Metallicity dependent?, problems with calibrations? Galactic extinction?
  • In this work we obtained the abundances of 7 PNe. Given a total number of 10 PNe abundances for this galaxy.
  • Two PNe in our sample are Type I (2.4-8 Msun).
  • Two are oxygen self-enrichment. This are not useful as observational constraint of Oxygen.
  • All these results will be taken into account in our chemical model of NGC 6822.

IAC-150408

on band off band
On-band, off-band

UCLAN 260308

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