Contributed talk at "Galaxy Metabolism" meeting in Sydney, Australia (2009). I'm disappointed there is no "science" category on Slideshare.

1. Spitzer LVL Luminosity- and Mass-Metallicity Relations
for Star-Forming Dwarf Galaxies in the Local Volume
•
•
•
•
•
•
Henry Lee (Gemini Observatory)
Liese van Zee (Indiana University)
Evan Skillman (University of Minnesota)
Janice Lee (Carnegie Observatories)
Rob Kennicutt (Cambridge University)
and the LVL Team
“Galaxy Metabolism”, Sydney - 23 June 2009
Galaxy Ontogeny : 23 Jun 2009
1

2. Pre-lunch themes
“Ingestion, digestion, excretion”
Galaxy Ontogeny : 23 Jun 2009
2

3. Pre-lunch themes
“Ingestion, digestion, excretion”
Galaxy Ontogeny : 23 Jun 2009
2

4. Pre-lunch themes
“Ingestion, digestion, excretion”
• e.g., Heavens, Noeske, Hopkins :
★
★
SFR density maximum at z ~ 1
SFH of galaxies are mass-dependent (“downsizing”)
Galaxy Ontogeny : 23 Jun 2009
2

5. Pre-lunch themes
“Ingestion, digestion, excretion”
• e.g., Heavens, Noeske, Hopkins :
★
★
SFR density maximum at z ~ 1
SFH of galaxies are mass-dependent (“downsizing”)
“A Nurturing Environment”
• Cole : “free-range, organic, pesticide-free (galaxies)...”
• e.g., Cooper :
★
Some scatter in high-mass M-Z (SDSS T04) correlated with
local environment
Galaxy Ontogeny : 23 Jun 2009
2

6. Why low-mass galaxies are important
• Most abundant galaxy-type : “building blocks” ?
• Representative of conditions present in early universe ?
• Detailed SFHs from CMDs and resolved stellar populations
• Ongoing assembly in MW, M31 : stellar-streams, new dwarfs ...
• Galactic archaeology : oldest, lowest-Z stars
• ISM metallicity evolution tied to dust evolution
• Possible candidate-hosts to distant gamma ray bursts
•
e.g., Bland-Hawthorn, Karlsson, Cole, Guhathakurta, Zucker, Yeh, Lopez-Sanchez, Levesque, Muller, ...
Galaxy Ontogeny : 23 Jun 2009
3

7. Why low-mass galaxies are important
• Nearest dwarfs show great diversity in properties & SFH
• Despite low-M, dwarfs sufficiently robust to form stars steadily
• Evolution a combination of low-SF + metals-loss ?
• Can environment hasten the evolution of low-M galaxies?
Galaxy Ontogeny : 23 Jun 2009
3

8. Why low-mass galaxies are important
• Nearest dwarfs show great diversity in properties & SFH
• Despite low-M, dwarfs sufficiently robust to form stars steadily
• Evolution a combination of low-SF + metals-loss ?
• Can environment hasten the evolution of low-M galaxies?
Detailed studies of nearby dwarf galaxies help tie down
a picture of galaxy evolution at low-M and at low-z.
Galaxy Ontogeny : 23 Jun 2009
3

9. “Personal diets (& lunch with friends)”
• Processes associated with galaxy assembly
✴
✴
✴
✴
Conversion of gas into stars ? Galactic winds ?
At given epoch, SFH & gas flows affect mass and metallicity
Luminosity-metallicity (L-Z) commonly used as proxy for
mass-metallicity (M-Z) ...
L-Z stronger correlation than vs. Mdyn, vs MHI
Galaxy Ontogeny : 23 Jun 2009
4

10. L-Z for Nearby Dwarf Galaxies
• Gas-rich galaxies :
✴
✴
✴
✴
✴
✴
✴
✴
Lequeux et al. 1979
Skillman et al. 1989
Zaritsky et al. 1994
Richer & McCall 1995
Garnett 2002
HL et al. 2003
van Zee et al. 2006
HL et al. 2006
H. Lee et al. 2006 (N=27)
Galaxy Ontogeny : 23 Jun 2009
5

11. L-Z & M-Z Relations
• Collections of galaxies at z > 1 :
✴
e.g., Perez-Gonzalez et al. 2003;
Savaglio et al. 2005; Erb et al. 2006;
Maiolino et al. 2008; Rodrigues et al.
2008; Hayashi et al. 2008; PerezMontero et al. 2008; Lamareille et al.
2008; note also Monday’s talks ...
Mannucci & Maiolino 2008
• Recent models :
✴
e.g., Brooks et al. 2007; Cid
Fernandes et al. 2007; Davé &
Oppenheimer 2007; De Rossi et al
2007; Köppen et al. 2007; Ellison et
al. 2008; Erb 2008; Baldry et al.
2008; Bertone et al. 2008; Bovil &
Ricotti 2008; Vale Asari et al. 2009; ...
Galaxy Ontogeny : 23 Jun 2009
6

12. Why 3.6, 4.5 µm
• Near-infrared : 1-5 µm
✴
✴
✴
✴
tracer of underlying stellar mass
minimize extinction by dust
minimize how light from recent SF affects L, Mstar/L
contributions by PAHs or hot dust not significant
(e.g., Jackson et al. 2006)
Galaxy Ontogeny : 23 Jun 2009
7

13. Why 3.6, 4.5 µm
Galliano et al. 2005
Galaxy Ontogeny : 23 Jun 2009
7

14. Why 3.6, 4.5 µm
Galliano et al. 2005
Galaxy Ontogeny : 23 Jun 2009
7

15. Why 3.6, 4.5 µm
1 µm
10 µm
stars
PAHs
VSGs
BGs
Galaxy Ontogeny : 23 Jun 2009
7

16. Why 3.6, 4.5 µm
1 µm
3.6
+
4.5
µm
10 µm
stars
PAHs
VSGs
BGs
Galaxy Ontogeny : 23 Jun 2009
7

17. Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
J. Lee et
Galaxy Ontogeny : 23 Jun 2009
8

18. Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
UGC 5829 (DDO 84); Dale et al. 2009
Galaxy Ontogeny : 23 Jun 2009
8

19. Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
UGC 8320 (DDO 168)
Halpha
3.6 µm
24 µm
Dale et al. 2009
Galaxy Ontogeny : 23 Jun 2009
8

20. The numbers, before plots
• B, J, H, K, [3.6], [4.5] luminosities : Dale et al. 2009
✴
✴
Stellar masses, using Bell & de Jong 2001
Different “combinations” for Mstar vary by ~0.2 dex
• ~50 dwarf irregular galaxies with reliable metallicities
✴
✴
[O III] 4363 measurements
Temperatures and direct measures of (O/H)
• M-Z, with M = Mstar commonly seen in models
Galaxy Ontogeny : 23 Jun 2009
9

21. The numbers, before plots
• B, J, H, K, [3.6], [4.5] luminosities : Dale et al. 2009
✴
✴
Stellar masses, using Bell & de Jong 2001
Different “combinations” for Mstar vary by ~0.2 dex
• ~50 dwarf irregular galaxies with reliable metallicities
✴
✴
[O III] 4363 measurements
Temperatures and direct measures of (O/H)
• M-Z, with M = Mstar commonly seen in models
• Dekel & Silk (1986); Dekel & Woo (2003):
✴
✴
Z ∝ Ln, where n = 0.3 to 0.4
log Z ~ m log L, where m = 0.12 to 0.16
Galaxy Ontogeny : 23 Jun 2009
9

22. L-Z relation, B
solar
HL et al., in prep.
Galaxy Ontogeny : 23 Jun 2009
10

23. 12+log(O/H) = a M! + b
λ
a
b
R
σ
B
-0.149
5.67
-0.80
0.15
J
-0.147
5.44
-0.81
0.14
H
-0.156
5.21
-0.77
0.16
K
-0.152
5.24
-0.75
0.17
[3.6]
-0.135
5.53
-0.85
0.14
[4.5]
-0.132
5.36
-0.84
0.14
Galaxy Ontogeny : 23 Jun 2009
11

24. Observed M-Z : Mstar < 1010 Msun
HL et al., in prep.
Galaxy Ontogeny : 23 Jun 2009
12

25. Observed M-Z : Mstar < 1010 Msun
HL et al., in prep.
Z ∝ Ln ∝ Mstarn, n = 0.3-0.4
Galaxy Ontogeny : 23 Jun 2009
12

26. Metals loss (1)
Tremonti et al. 2004
Simple model for chemical evolution:
ZO = yO ln (1 + Mstar/Mgas)
yeff = ZO / ln (1 + Mstar/Mgas)
Galaxy Ontogeny : 23 Jun 2009
13

27. Metals loss (1)
Tremonti et al. 2004
HL et al, in prep.
Galaxy Ontogeny : 23 Jun 2009
13

28. Metals loss (1)
Tremonti et al. 2004
HL et al, in prep.
50% loss
90% loss
Galaxy Ontogeny : 23 Jun 2009
13

29. Grazing (2)
mass-dependent SF efficiency
cf. Baldry et al. 2008
Z = -y ln(μ) = -y ln(Mgas/Mb)
ε ≡ Mstar/Mb = 1 - Mgas/Mb
= 1 - exp(-Z/y)
ε = M/(M+M0) * (ε0-ε1)+ ε1
ε1 ~ 0.01-0.1
ε0 ~ 0.8
log(M0/Msun) ~ 109.6
Galaxy Ontogeny : 23 Jun 2009
14

30. Consumibles
• Spitzer Local Volume Legacy Survey :
✴
✴
providing uniformity in galaxy L (and SF measures)
high-quality (O/H) from measured temperatures
• L-Z with N=50 : B, J, H, K, [3.6], [4.5] :
✴
✴
slope decreases a little with increasing wavelength
dispersion not significantly different from optical to NIR
• M-Z with Mstar derived at each wavelength
✴
✴
M-Z from B to [4.5] are indistinguishable
extending SDSS M-Z down to ~106.5 Mstar
• Mass-dependent SFE (“grazing”) & modest winds can
account for L-Z, M-Z for dwarfs (Mstar < 1010 Msun)
Galaxy Ontogeny : 23 Jun 2009
15