Infrared Spectral Energy Distributions of Submillimetre Galaxies

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Infrared Spectral Energy Distributions of
Submillimetre Galaxies

• Alexandra Pope (UBC)
• Deep06 Sintra
• October 13, 2006

JCMT 15m Hawaii
Collaborators Ranga Chary (SSC), Mark Dickinson
(NOAO), David Frayer (SSC), Minh Huynh (SSC),
Douglas Scott (UBC)
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Galaxy Evolution
Arp220- HST NICMOS

• Sub-mm galaxies
• high redshift z2 (Chapman et al. 2005, Pope
  et al. 2005)
• high star formation rates SFR100-1000M?yr-1
  (Lilly et al. 1999, Chapman et al. 2005)
• massive Mgas31010M? M?1011M?
  (Greve et al. 2005, Borys
  et al. 2005)

Antennae galaxies- Spitzer IRAC
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The GOODS-N sub-mm super-map
S/N map
Noise map 35 sources 2-20mJy
Pope et al. 2005, MNRAS, 358, 149
RectangleGOODS-North
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Using Spitzer to find counterparts
z850
3.6?m
24?m
1.4 GHz

• 94 (33/35) of sub-mm sources in GOODS-North
  have a counterpart in IRAC and/or MIPS
• Radio 74 (26/35)
• MIPS 91 (32/35)
• Very little overlap with other high z
  optical/near-IR selected populations BzKs, DRGs,
  LBGs, etc.

Pope et al., 2006, MNRAS, 370, 1185
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Mid-IR/Sub-mm flux ratios
Mrk231
Arp220
Cool CE01
Pope et al., 2006, MNRAS, 370, 1185
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Mid-IR/Sub-mm flux ratios
BzK (Daddi et al. 2005)
Pope et al., 2006, MNRAS, 370, 1185
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Spectral Energy Distribution
Ssub-mm/Sradio
Warm SED
Cool
Cool SED
Warm
Average 850?m selected galaxy is
cool LIR6?1012L?, SFR1100M?yr-1
Pope et al., 2006, MNRAS, 370, 1185
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Spitzer 70?m Observations
850?m
70?m

• 2/35 detected at 70?m - both low z, low
  S850 gt not typical sub-mm galaxies
• Confirms cool IR SEDs

Huynh, Pope et al., 2006, ApJ submitted
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Mid-IR spectra of sub-mm galaxies
z2.81
z2.8
PAH emission features
Lutz et al. 2005
PAH emission features 6.2, 7.7, 8.6, 11.3?m Si
absorption feature 9.7?m
Line diagnostics use strengths of
lines/continuum to infer SB vs AGN, extinction,
etc.
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IRS Spectra of Sub-mm Galaxies in GOODS-N GO2
program 90 hours PI R. Chary
Pope et al. in prep
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Composite spectrumgt starburst dominated

• mid-IR SED of average sub-mm galaxies looks like
  M82
• very little contribution of AGN to LIR

M82
Arp220
Cool CE01
Spitzer IRAC image
Pope et al. in prep
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Mid-IR Line Diagnostics
Genzel et al. 1998
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Mid-IR Line Diagnostics
Genzel et al. 1998
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Mid-IR Line Diagnostics
Sub-mm galaxies do not have mid-IR SEDs
consistent with AGN Work in progress more
results to come on this IRS project..
Genzel et al. 1998
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Sub-mm galaxies are cold..so what?
850?m overpredicts LIR when local T-L relation is
used
LIR (24850radio)
Need to get better constraints on far-IR SEDs in
order to properly estimate SFRD at high z
LIR (850)
Pope et al., 2006, MNRAS, 370, 1185
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Conclusions

• 24?m850?mradio suggests that sub-mm galaxies
  are cooler than local ULIRGs of same
  luminosity..confirmed with 70?m observations
• 2. IRS spectra tells us that the intense
  luminosities in sub-mm galaxies are powered by
  starbursts and not AGN
• 3. S850?m overpredicts LIR when you force the
  local L-T relation

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Redshift
distribution
Pope et al. 2005
Chapman et al. 2005
ltzgt2.5 (34/35) lt17 lie at zgt4
Pope et al. 2005