galactic metallicity gradients and their evolution

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galactic metallicity gradients and their evolution

GALACTIC

METALLICITY

GRADIENTS AND

THEIR EVOLUTION

A spectroscopic study of planetary nebulae and H II regions in nearby

spiral galaxies: M33 and M81

Letizia Stanghellini (NOAO), Laura Magrini (Arcetri), Eva Villaver Univ.

Autonoma Madrid), Daniele Galli (Arcetri), and Edvige Corbelli (Arcetri)

2nd MMT Science Symposium May 19, 2010

Wednesday, May 19, 2010


CONSTRAINING GALACTIC

CHEMICAL EVOLUTION

Nearby, nearly face-on spiral galaxies are ideal

laboratories to test star formation history, stellar

nucleosynthesis, and the mechanisms of galaxy

assembly and evolution

We performed a study of HII regions and PNe in M33

and M81 with Hectospec to determine their α-element

abundances, gradients, and their evolution

Excellent space and time constraints are needed for

chemical evolutionary models, since predictions are

extremely sensitive to adopted parameters

Space distribution of metals, gradients (α-elements) and

their evolution (i.e., time-tagging metallicity probes: HII

regions t=0; 1-2 M PN progenitors t~1-10 Gyr; evolution

of PN progenitors does not modify α-element abundance)

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


MMT/HECTOSPEC OBSERVATIONS

MMT/Hectospec is ideal for emission-line source

spectroscopy in M33, M81(nearby, spiral galaxies,

nearly face-on)

A single setup (270 mm -1 grating, 1.2 A/pixel

dispersion) includes both HII regions and PNe with

good coverage of galaxy disks, + sky fibers

M33 (2007): 8x1800s in 2 nights, spectra of 48 HII regions

and 103 PNe

M81 (2008): 16x1800s in 4 nights, spectra of 24 HII regions

and 19 PNe

Aiming at λ4363 T e

[OIII] and λλ6717/6731 N e

[SII]

diagnostic line, and helium, oxygen, neon, argon,

sulfur, nitrogen abundances

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


M33 AND M81: FOV AND TARGETS

::Skycat

Wednesday, May 19, 2010

cat53962.fits

1:33:51.117 30:39:35.60 J2000

2nd MMT Science Symposium May 19, 2010

Mar 30, 2007 at 17:07:19


PN10 IN M33 (M [OIII] =23.73)

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010

Magrini et al. 2009


FAINTEST SOURCES: M81 PNE

Stanghellini et al. 2010

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


ABUNDANCE ANALYSIS

High quality, based on auroral lines and plasma

diagnostics

M33

93 PNe (MMT, Magrini et al. 09)

Lit: ~8 PNe (WHT, Magrini et al. 04) ~16 PNe (Keck

+Subaru, Bresolin et al 10)

33 HII regions (MMT, Magrini et al. 10)

Lit: ~15 HII (WHT, Magrini et al. 07a) ~60 HII (Keck,

Rosolowsky & Simon 08)

M81

19 PNe (MMT, Stanghellini et al. 2010)

14 HII regions (MMT, Stanghellini et al. 2010)

Lit: 17 HII in M81 (Garnett & Shields 87), only bright lines

detected, photoionization models

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


OXYGEN AND NEON LOCKSTEP IN

M33

Filled: Type I

Open: Type II

PNe

Slope~0.9

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


OXYGEN AND NEON LOCKSTEP IN

M81

Filled: PNe

Open: HII

Slope~0.8

A(X)=log(X/H)+12

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


METALLICITY GRADIENTS – M33

PN

HII

PNe, MMT data

Δ log(O/H)/ΔR=-0.031 (±0.013) dex/kpc

non-Type I PNe (open)

HII

Δ log(O/H)/ΔR=-0.03 (±0.013) dex/kpc

Type I PNe, M>2 M progenitors (filled)

Δ log(O/H)/ΔR =-0.039 (±0.033) dex/kpc

regions

Filled: MMT, open: lit.

Δ log(O/H)/ΔR =-0.044 (±0.009) dex/kpc

Excluding central kpc (undersampled)

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


METALLICITY GRADIENTS, M33




Gradients steeper for younger

populations

Ne, S gradients similar to oxygen

HII gradients shallower than

previously found (bias toward

bright/giant HII regions in past data

samples)

Binned HII regions from MMT+lit.

Triangles: giant HII regions

SB α

>5.5x10 -19 [cgs]

R>15 [arcsec]

Δ log(O/H)/ΔR =-0.089

Filled squares: All HII regions

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


SPATIAL METAL DISTRIBUTION IN

M33

A(O) superimposed to mass contours

Left: HII regions; right: PNe

Offset of maximum oxygen abundance

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


METALLICITY GRADIENTS, M81

PN

Top: PNe

Δ log(O/H)/ΔR =-0.055 (±0.02) dex/kpc

No Type I PNe (as expected from brightest

end of PNLF in high metallicity galaxies)

In red: extinction correction uncertain

HII

Bottom: HII regions

MMT (filled) cover limited R G range -> no

gradient estimate

Combining with Garnett & Shileds 87’s sample

(open)

Δ log(Ο/Η) / ΔR =-0.093 (±0.02) dex/kpc

Gradients generally steeper than in M33.

A(X)=log(X/H)+12

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


METALLICITY GRADIENTS, M81

PN

Top: PNe

Δ log(O/H)/ΔR =-0.055 (±0.02) dex/kpc

No Type I PNe (as expected from brightest

end of PNLF in high metallicity galaxies)

In red: extinction correction uncertain

HII

Bottom: HII regions

MMT (filled) cover limited R G range -> no

gradient estimate

Combining with Garnett & Shileds 87’s sample

(open)

Δ log(Ο/Η) / ΔR =-0.093 (±0.02) dex/kpc

Gradients generally steeper than in M33.

A(X)=log(X/H)+12

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


SULFUR AND NEON, M81

Top: Ne bottom: S

Filled: PNe Open: HII

MMT data

PN gradients very similar to O/H:

Δlog(Ne/H)/ΔR =-0.047 dex/kpc

Δlog(S/H)/ΔR =-0.069 dex/kpc

HII regions S and Ne abundances

compatible with those of PNe, no

clear signature of enrichment, no

sulfur anomaly (Henry et al 04).

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010

A(X)=log(X/H)+12


CHEMICAL ENRICHMENT

M81

M33

MW

LMC

SMC

MW

PNe: Stanghellini & Haywood 2010

HII: Peimbert 1999

M81

PNe and HII: MMT

(note: using O/H for targets within

same distance range)

LMC and SMC

Garnett 1999

M33

PNe: MMT

HII: MMT

Solar value: Asplund et al. 2005

t=0: HII regions (probing current galactic α-

element)

t>1 Gyr: PNe (probing α-element earlier in

galactic evolution history)

A(O ) t=0

– A(O) t>1Gyr

defines the α-element

enrichment

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


EVOLUTION OF METALLICITY

GRADIENTS




Gradient slopes vs. population

age

t(HII)=0

t(PNe)= average and ranges from

progenitor mass, turnoff timing,

and PN types studiedt

errorbars represent ranges


Open square: MMT+GS87 HII

regions, slope uncertain

MW

M33

M81

For all spiral/disk galaxies

examined, radial metallicity

gradient seem to flatten with

population ages -> radial

metallicity gradients may

steepen with time since galaxy

formation

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010


CONCLUSIONS AND FUTURE WORK

MMT/Hectospec proved ideal for abundance

analysis of emission-line stellar probes in nearby

galaxies

Data yield strong constraints to chemical

evolutionary models for M33 and M81

Metallicity gradients and average metallicity

discloses O/H evolution in M81, and generally

steeper gradients in M81 than other spiral

galaxies.

Oxygen gradients seem to steepen with time

since galaxy formation. MMT observations of M81

HII regions covering a larger R G

range are needed

to confirm trend for this galaxy.

Wednesday, May 19, 2010

2nd MMT Science Symposium May 19, 2010

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