The Spitzer View of the Small Magellanic Cloud

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The Spitzer View of the Small Magellanic Cloud
3.6 um Blue 4.5 um Green 8.0 um Red
Alberto Bolatto (Berkeley) S. Stanimirovic, J.
Simon, A. Leroy, K. Sandstrom, L. Blitz, F.
Walter, N. Mizuno, the S 3MC team
http//celestial.berkeley.edu/spitzer
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Outline

• Background
• Some S3MC results
• Young stellar objects in NGC 346
• Ongoing massive star formation
• The FIR continuum
• Hidden molecular gas?
• The Radio-continuum/FIR correlation on small
  spatial scales
• Evidence for breakup of the linearity
• SF efficiency in SMC-like dwarfs
• A SNR at 24 um
• Dust production in the ISM

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The S3MC imaging the SMC

• A survey of 3 ? deg of the SMC in all of
  Spitzers bands
• http//celestial.berkeley.edu/spitzer
• 49 hours of cycle-1 time, not a legacy project
• First partial data release done in January

• Designed to fit in the small project category
• Includes most star forming regions, most emission
  seen by IRAS, and highest HI column densities

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Dust in Lyman Break Galaxies appears SMC-like

• Much of the LBG data cannot be fit by Milky
  Way-like dust (2175 Å bump in the extinction
  curve)
• The 2175 Å feature is associated with small
  carbonaceous grains and PAHs (Li Draine 2001)
• Extinction curves toward the SMC and other metal
  poor star-forming dwarfs show none (or weak) 2175
  Å feature (Galliano et al. 2005)

MW dust
SMC dust
Vijh, Witt, Gordon (2003)
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Whats in a name?

• It could have been worse
• MIPS and
• IRAC
• Survey of the
• SMC
• In
• Seven
• Spitzer
• Infrared
• Photometric
• Passbands
• I (one)
• DOOFAAS the Dumb Or Overly Forced Astronomical
  Acronym Site
• http//cfa-www.harvard.edu/gpetitpas/Links/Astroa
  cro.html

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Where are those bands?
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The SMC in the midIR
3.6 um Blue 8.0 um Green 24 um Red
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CTIO emission line imaging of the SMC (OIII, SII,
Ha) C. Smith, F. Winkler, the MCELS team
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Star formation in NGC 346
3.6 um Blue 4.5 um Green 8.0 um Red
Notta et al., HST
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Identifying YSOs in NGC 346
(Josh Simon)
CANDIDATE YSOs (Whitney et al. 2004)
TIP OF RGB
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What sources do we see in Spitzer?
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Star formation and molecular gas

• Conundrum SMC-like dwarfs have anomalously
  high SFR for their H2 content, as inferred from
  their CO emission

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The classical dust continuum
24 um Blue 70 um Green 160 um Red
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Global temperature and opacity distributions
(Adam Leroy)
T
t
ALL REGIONS REGIONS WITH CO
Higher emissivity per atomic gas nucleon suggest
presence of H2 with large Xco Log Xsmc/Xmw1.30.4
(Israel 1997)
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The resolved radio FIR relationship in the SMC
K. Sandstrom, work in progress
SSFR f/radio
SSFR f/FIR

• Widely used but poorly understood
• SF ? massive stars ? dust heating ? SN ? Fermi e-
  acceleration in shocks ? nonthermal radio
  synchrotron emission
• Unchanged to the smallest resolutions probed (35
  pc)
• SSFR(RC) ? SSFR(FIR)1.3 ? breaking of the
  linearity

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The resolved radio FIR relationship in the SMC
Large Galaxies
LRC
SMC
LFIR

• Turn down in relationship hinted at in Yun et al.
  (2001)
• Causes
• Relativistic e- escape in winds, poor containment
  in B fields
• Break down of calorimeter model if tesclttsyn
  (Thompson et al. 2006)?
• But, low dust abundance means ISM also partially
  transparent to UV, leading to low UV?FIR
  conversion efficiency

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The resolved radio FIR relationship in the SMC
SSFR f/radio
SSFR f/FIR

• Points associated with molecular clouds fall
  under the relationship
• Suggests more efficient UV?FIR conversion
  molecular clouds are more opaque to UV photons
  than the average ISM
• Consistent with a x2 correction to SFR from FIR
  (lower limit)

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Back again to star formation and molecular gas

• Conundrum SMC-like dwarfs have anomalously
  high SFR for their H2 content
• Applying the virial Xco correction still leaves
  them far from the correlation
• Dust results suggest another x2 increase to Xco
  for SMC
• RC-FIR correlation suggests gtx2 increase to SFR
  (consistent with Bell 2003)

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Genuinely high SF efficiencies?

• Are the narrower linewidths in these small
  galaxies indicating reduced turbulent support and
  shorter cloud lifetimes?

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The SMC at 24 um
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SNR 0102 and dust production

• O-rich, type Ib/c, age1000yr
• Progenitor Mgt20 Msun, rich in O, Ne, and Mg

• Model expectations for dust mixed in SNR T130 K
  (Dwek 1987)
• Our data is consistent with Tdust120 K
• Models predict 0.08 to 0.3 Msun of dust produced
  per SN (Dwek Scalo 1980 Todini Ferrara 2001
  Morgan Edmunds 2003)
• We measure Mdust 3 to 8?10-4 Msun
• Consistent with other SNR results (e.g., Cass A)
• Given SN rate, SN account for 0.1 of dust in SMC
• Check out Stanimirovic et al. 2005

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A unique dataset
3.6 um Blue 4.5 um Green 8.0 um Red
3.6 um Blue 8.0 um Green 24 um Red
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A unique dataset
3.6 um Blue 4.5 um Green 8.0 um Red
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A unique dataset
3.6 um Blue 4.5 um Green 8.0 um Red
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Conclusions

• A SNR at 24 um
• Dust production by SNe appears negligible
• Work in progress
• The FIR continuum
• Molecular gas with large CO/H2 ratio
• Young stellar objects in NGC 346
• Ongoing massive star formation
• The Radio-continuum/FIR correlation on small
  spatial scales
• The simple LRC LFIR breaks down at low
  luminosities
• First partial data release online MIPS images
  and multiwavelength photometry