The ISM Properties of distant
star-forming galaxies as
constrained by the parameter
(in its various guises)
M. Sargent (MPIA) & you
I.
update on the (on-going) IR-radio
relation work
II.
disk galaxy opacity at z ~ 0.7
III.
final VLA-COSMOS Joint Catalog
COSMOS Team Meeting ‘10 | June 10, 2010
Intro
Radio & 60 m luminosity
functions of galaxies in the
IRAS 2 Jy-sample (Yun+ ‘01):
‘monsters’
Common link due to life cycle
of massive stars:
Non-thermal radio
(synchrotron) emission and,
in the IR, re-radiated UV
light.
June 3, 2010
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Intro - local galaxies (II)
Early IRAS results, integrated
IR/radio flux (Helou+ ‘85) :
q = log(SIR/Sradio)
log(1.4 GHz flux [mJy])
radio-loud AGN
nascent
starbursts
‘regular’
star-forming log(FIR flux [Wm-2])
galaxies
June 3, 2010
1.5 kpc regions in individual
SINGS galaxies (Murphy+ ‘06) … and
the transition to integrated IR/radio
flux ratios (Yun+ ‘01)
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Intro - Reasons to study the evolution
• Calibration of radio continuum emission as a star formation tracer in distant
galaxies (see Alex’ talk!)
• Does or doesn’t the IR-radio relation evolve with redshift (see somewhat ambiguous
results in the literature) ?
• Changes in the correlation due to (understandable) external factors could
shed light on:
- the physical processes shaping the relation (also at low-z)
- state of the ISM (magnetic fields, intensity of UV radiation field, dust absorption)
• “…for the […] galaxies studied here, luminosity extrapolations based
on the radio emission are considerably more reliable than those
based on the mid-IR emission” (Magnelli+ ‘10)
- the calculation of SFRs is affected less by uncertain radio
spectral indices than by a sparsely sampled IR-SED
- interferometric radio observations have a high spatial
resolution, aiding the correct identification and attribution of
flux to (multi-) counterparts
June 3, 2010
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Evolution of the brightest IR-emitters
Sargent+ (‘10b)
ULIRGs:
median 〈qTIR〉
LIR > 1012 L☉
SFR > 100 M☉/yr
〈qTIR〉 ∝ (1+z)-0.01±0.06
After compensating for
selection biases - NO
evolution at z < 2
(implies B ~ 50 G).
redshift
• volume-limited sample of ULIRGs (rather than comparing most strongly starbursting systems at high z with
mixture of high & low luminosity systems at low z)
• IR/radio non-detections included with survival analysis
• probabilistic (using rest-frame optical colours) classification into SFGs/AGN
June 3, 2010
(cf. Smolčić+ ‘08)
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Evolution of less extreme starbursts
Sargent+ (‘10d), in prog.
No differing behaviour
between stacked and
high(er) luminosity
samples!
Alex’ hard work
q70, obs.
normalization of starburst template
SEDs adopted from direct detections
Expected evolution of q70 for
galaxies with IR dust SEDs
similar to local galaxies
increasing
stellar mass
redshift
•1.4 GHz image stacks of reach rms noise of ~400 nJy thanks to 100s of sources in each
mass/redshift bin -> statistical detections of LIRG luminosities out to z ~ 3
• Sample based on 3.6 m IRAC detections in COSMOS field (cf. Sanders+ ‘07, Ilbert+ ‘09)
-> expect unbiased estimate of average IR/radio ratios (as sample not IR- or radio-selected)
• Actively star forming galaxies selected with (NUV-r) colours (cf. Ilbert+ ‘09)
Other IR/radio miscellanea… (Sargent+ ‘10a)
〈q〉IR-sel. > 〈q〉radio-sel.
June 3, 2010
➠
At 2.5 < z < 5: 〈qTIR〉= 2.71+0.09
,
-0.14
consistent with local average.
➠
➠
At z < 1.5: many (optically classified) AGN
have the same IR/radio ratios as starforming galaxies.
Analytical prediction of offset
between IR- and radio-selected
samples, qbias = ln(10) [-1] 2,
(e.g. Kellermann ‘64; Condon ‘84) can
reconcile discrepancies in the
literature.
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The Effects of Dust…
Parametrization of average variation of
surface brightness with inclination due
to dust attenuation:
z ~0
opacity
increase
surface brightness increase
z~0.7
Driver+ (‘07)
Sargent+ (‘10c)
June 3, 2010
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Attenuation vs. inclination
blue-band surface brightness
brighter
redshifted local disk galaxies
q = b/a
‘real’ distant disk galaxies
At z~0.7: less variation between the
average sur-face
brightness of faceon and edge-on,
large disk galaxies.
QuickTime™ and a
decompressor
are needed to see this picture.
1 - cosine(inclination angle)
• low-z reference galaxies (from Kampczyk+ ‘07) show expected (cf. Möllenhoff+ ‘06; Driver+ ‘07) surface
brightness variations also once redshifted; distant galactic disks behave as if (nearly
perfectly!) optically thick…
• Scant evidence for different extinction laws in distant galaxies
(e.g., Calzetti+ ‘01; Conroy+ ‘10),
a
different distribution of attenuating material seems a likely explanation
• Correction relative to face-on ‘homogenizes’ population but does not provide the re-sidual
face-on attenuation ➠ interpret shape of inclination-dependence with dust models
June 3, 2010
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Summary
Evolution of the IR-radio relation:
• No compelling evidence for an evolution of the IR-radio relation out to high redshift,
also in luminosity ranges in which the observation of evolution would not have been a
surprise…
• The understanding/awareness of selection effects is essential for the derivation of
the correct (non-)evolution
• Many optically-selected AGN at z < 1 have similar IR/radio ratios as star forming
galaxies
Inclination-dependent attenuation in disk galaxies at z ~ 0.7:
• Blue light escapes high- and low-z disk galaxies with a different (3D-)angular
emission pattern, suggesting a different distribution of attenuating material
Plus…:
• final VLA-COMOS Joint (source catalog from survey components ‘Large’ & ‘Deep’)
catalog is available @ IRSA and published as Schinnerer+ ‘10, ApJS, 188, 384
June 3, 2010
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Final VLA-COSMOS Joint catalog
rms ~30 Jy
(irsa.ipac.caltech.edu/data/COSMOS/tables/vla/…
…vla-cosmos_dp_sources_20100504.tbl)
• central 1 deg2 (seven pointings)
re-imaged for additional 8.3 hr
each
• 2865 sources with S/N > 5
• 1.4 GHz maps @ resolution 1.5”
& 2.5” available
• rms at field centre ~10 Jy
• 1/3 spectroscopically followed-up
(pre 20k)
• catalog paper accepted to ApJS
• Counterpart searches ➠ use new Joint catalog
• Statistical studies requiring flux-limited samples ➠ use revised Large
Project catalog
June 3, 2010
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