Galaxy Ontogeny : 23 Jun 2009 Spitzer LVL Luminosity- and Mass-Metallicity Relations for Star-Forming Dwarf Galaxies in the Local Volume “Galaxy Metabolism”, Sydney - 23 June 2009 • 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 1
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Galaxy Ontogeny : 23 Jun 2009
Spitzer LVL Luminosity- and Mass-Metallicity Relationsfor Star-Forming Dwarf Galaxies in the Local Volume
“Galaxy Metabolism”, Sydney - 23 June 2009
• 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
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Galaxy Ontogeny : 23 Jun 2009
Pre-lunch themes
“Ingestion, digestion, excretion”
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Galaxy Ontogeny : 23 Jun 2009
Pre-lunch themes
“Ingestion, digestion, excretion”
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Galaxy Ontogeny : 23 Jun 2009
Pre-lunch themes
“Ingestion, digestion, excretion”
• e.g., Heavens, Noeske, Hopkins :★ SFR density maximum at z ~ 1★ SFH of galaxies are mass-dependent (“downsizing”)
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Galaxy Ontogeny : 23 Jun 2009
Pre-lunch themes
“Ingestion, digestion, excretion”
• e.g., Heavens, Noeske, Hopkins :★ SFR density maximum at z ~ 1★ SFH of galaxies are mass-dependent (“downsizing”)
• e.g., Cooper :★ Some scatter in high-mass M-Z (SDSS T04) correlated with
local environment
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Galaxy Ontogeny : 23 Jun 2009
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
• 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?
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Galaxy Ontogeny : 23 Jun 2009
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.
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Galaxy Ontogeny : 23 Jun 2009
“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
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Galaxy Ontogeny : 23 Jun 2009
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)
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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; Perez-Montero et al. 2008; Lamareille et al. 2008; note also Monday’s talks ...
• 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; ...
Mannucci & Maiolino 2008
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Galaxy Ontogeny : 23 Jun 2009
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)
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Galaxy Ontogeny : 23 Jun 2009
Why 3.6, 4.5 µm
Galliano et al. 2005
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Galaxy Ontogeny : 23 Jun 2009
Why 3.6, 4.5 µm
Galliano et al. 2005
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Galaxy Ontogeny : 23 Jun 2009
Why 3.6, 4.5 µm
1 µm 10 µm
stars
PAHs
VSGs BGs
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Galaxy Ontogeny : 23 Jun 2009
Why 3.6, 4.5 µm
1 µm 10 µm
stars
PAHs
VSGs BGs
3.6+
4.5µm
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Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
J. Lee et
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Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
UGC 5829 (DDO 84); Dale et al. 2009
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Galaxy Ontogeny : 23 Jun 2009
Local Volume Legacy Survey : D < 11 Mpc (z < 0.003)
UGC 8320 (DDO 168)Halpha3.6 µm24 µm
Dale et al. 2009
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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
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Galaxy Ontogeny : 23 Jun 2009
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
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L-Z relation, B
HL et al., in prep.
solar
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Galaxy Ontogeny : 23 Jun 2009
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
12+log(O/H) = a M! + b
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Observed M-Z : Mstar < 1010 Msun
HL et al., in prep.
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Observed M-Z : Mstar < 1010 Msun
HL et al., in prep.
Z ∝ Ln ∝ Mstarn, n = 0.3-0.4
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Galaxy Ontogeny : 23 Jun 2009
Metals loss (1)
Tremonti et al. 2004 Simple model for chemical evolution:
ZO = yO ln (1 + Mstar/Mgas)
yeff = ZO / ln (1 + Mstar/Mgas)
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Metals loss (1)
Tremonti et al. 2004HL et al, in prep.
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Galaxy Ontogeny : 23 Jun 2009
Metals loss (1)
Tremonti et al. 2004HL et al, in prep.
50% loss
90% loss
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mass-dependent SF efficiencycf. 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 ~ 0.01-0.1ε0 ~ 0.8log(M0/Msun) ~ 109.6
Grazing (2)
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Galaxy Ontogeny : 23 Jun 2009
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)