Download from z=0 to z=1

Bright Side versus Dark Side of
Star Formation: UV and IR Views
C. Kevin Xu, IPAC, Caltech
Veronique Buat, LAM, Marseille
Collaborators: J. Iglesias-Paramo, T. Tekeuchi,
M. Rowan-Robinson, GALEX team, SWIRE team
Question: Do UV and IR surveys see the
two sides of SF of the same population,
or SF of two different populations?
1 population:
Total
SFR
2 populations:
Total
SFR
UV surveys
IR surveys
Talk plan
• Local UV and IR galaxies: how much do they overlap?
• comparisons of IR/UV ratio, L_tot, Hubble type, mass, clustering
• UV LF of IR galaxies and IR LF of UV galaxies
• IR-quiet UV galaxies (low metallicity dwarfs)
• UVLGs and ULIRGs
• LBGs and SCUBA galaxies: UV and IR galaxies at z ~ 3
• UV and IR galaxies at intermediate redshifts (0.5 < z < 0.7)
--- early results from a GALEX/SWIRE comparison study
• evolution of attenuation in UV and IR selected galaxies
• evolution of stellar mass in UV and IR selected galaxies
• Summary
FIR-UV bivariate luminosity function of
local UV+FIR galaxies
Martin et al. 2005, ApJL, GALEX Edition
• Saturation of L_UV at
~ 2 x10^10 L_sun
• bi-modality (of L_IR/L_UV
ratio)
•Strong dependence of L_IR/L_UV
(best A_FUV indicator) on
L_tot
L_tot LF of local UV+IR galaxies
Martin et al. 2005, ApJL, GALEX Edition
L_tot=L_FUV+L_60
Solid line -log-normal fit
Blue -- UV selected
(GALEX src)
Red -- IR selected
(IRAS src)
UV galaxies are
absent in high
L_tot (>10^11) end!
Local samples: IR selected
versus UV selected
(details in
J. Iglesias’ talk)
IR selected (126):
f60 > 0.6 Jy
UV selected (61):
NUV < 16 mag
UV: low L_60/L_FUV
IR: high L_60/L_FUV
L_IR/L_FUV distributions of
IR and UV selected galaxies
• Very different.
• The overlap between
the two samples is
~ 30%.
•The mean ratio of IR
galaxies is ~ 10 times
higher than that of UV
galaxies!
Mean attenuations from the Fdust/F(UV) ratio
NUV selected sample
<A(NUV)>=0.8+/-0.3 mag
<A(FUV)>=1.1+/-0.3 mag
FIR selected sample
<A(NUV)>=2.1+/-1.0 mag
<A(FUV)>=2.9+/-1.0 mag
NUV
(Buat et al. 2005, ApJL, GALEX edition)
FUV
Confirm pre-GALEX results
L_IR/L_FUV v.s. L_tot
(`Adelberger plot’)
Two populations are
separated:
IR: high L_tot, high
L_IR/L_UV ratio
UV: low L_tot, low
L_IR/L_UV ratio
Explanation:
Consequence of selection
effect on L_IR/L_UV
ratio, and the strong
correlation between the
ratio and L_tot.
L_tot LFs of local UV and IR galaxies
Using L_IR/L_UV ratio
to convert to L_tot
•The L_tot of UV galaxies has a
sharp cutoff at ~ 10^11 L_sun
Comparison of Hubble type distributions
of local UV and IR galaxies
Good overlap in the middle:
both populations peak around
~ Sbc
IR galaxies:
• excess of interacting galaxies
(~ 30%)
• more early types (S0/Sa/Sb)
UV galaxies:
• more late types
(Sc/Sd/Ir/CB ~ 50%)
Comparison of
correlation lengths
UV (FOCA sources):
r_0=3.2 (+0.8, -2.3) h-1 Mpc
(Heinis et al. 2004)
(FOCA result)
IRAS galaxies
IR (IRAS sources):
r_0=3.9+-1.8 h-1 Mpc
(Strauss et al. 1992)
UV galaxies seem to be less
clustered than IR galaxies
(confirmed by preliminary
GALEX results)
(Heinis et al. 2004 A&A 424, L9)
Comparisons of stellar mass distributions
Mstars: estimated from L_K
(Cole et al. 2001 calibration,
H_0= 70 km s-1 Mpc-1).
`Survival Tech.’ used.
Good overlap between two
populations: medians differ
< 2, both are sub-M*.
Though:
IR: slightly tilted for more
massive end
UV: more galaxies with low
mass (<10^10 L_sun).
L_tot v.s. mass
L_IR/L_UV v.s. mass
• UV galaxies of lowest mass (< 10^10) have lowest L_tot and IR/UV
• most massive IR galaxies (>10^12) are not galaxies with highest L_tot
• brightest IR galaxies (~ ULIRGs) have mass ~ M*
• for given mass, UV galaxies have lower L_tot and IR/UV ratio than IR
galaxies
60m LF of UV galaxies
FUV LF of IR galaxies
L
• UV galaxies substantially underrepresent galaxies of L_IR >
10^11 L_sun (LIGs).
• ULIRGs (L_IR > 10^12) are
completely absent in UV sample.
• IR galaxies can fully account
for all UV galaxies of L_UV >
10^9 (L* ~ 4 10^9).
• some fainter UV galaxies (L_UV
< 10^9) could be missing in IR
sample.
IR-quiet UV galaxies
I Zw 18: prototype
metallicity = 1/50 solar
(lowest known)
low mass (star+gas):
~ 2 10^8 M_sun
distance=15 Mpc
L(FUV)=2.5 10^8
not detected in FIR:
L_dust/L_FUV < 0.25
(from NED, Hubble Heritage Gallery image)
SBS0335-052
another prototype IRquiet UV galaxy:
metallicity = 1/35 solar
(2nd lowest)
undetected by IRAS, but detected by
both ISO and Spitzer: very different
IR SED from normal galaxies
M82
mass (star+gas)
~ 2 10^9 M_sun
distance=58.3 Mpc
L(FUV) ~ 10^9
L_dust/L_FUV ~ 0.4
(Houck et al. 2004, ApJS, Spitzer edition)
Characteristics of IR
quiet UV galaxies
dwarf galaxies of
low metallicity < ~1/10 solar
IR-quiet
mass: a few 10^8 -- 10^9
UV lum: a few 10^8 -- 10^9
(~ 10 times < L* of FUV,
not z~0 LBG)
L_dust/L_FUV ~0.3
(~ a few % of UV galaxies)
IR-quiet
UV luminous galaxies (UVLG): z~0 LBGs
(Heckman et al 05, ApJL GALEX edition)
FUV Surface Brightness vs. Stellar Mass
(kpc)
(L๏ kpc-2)
(L๏/kpc2)
FUV Luminosity vs. Half-light Radius
Compact
Large
(L๏)
(M๏)
•Nearby galaxies brighter than L_UV=2 1010 L(sun) with z<0.3
•10-5 galaxy/Mpc3 (~100 times less dense than LBGs)
Population Comparison
Large UVLGs, Compact UVLGs, LBGs
(Slide courtesy of Chris Martin)
Log LUV
Log rUV
12
1.5
12
11
1
10
9
M*
AUV
Log b
[O/H]
3
2
9
11
2
1
8.5
0.5
10
1
0
8
9
9
0
-1
7.5
A_FUV vs. SFR plot of UVLGs:
comparison with ULIRGs and others
• UVLGs occupy
the bright end of UV
population, but still
they have L_tot
cutoff at ~ 2 10^11.
• Their attenuation
(IR/UV ratio) spans
the same range as
that of major UV
population.
• None of UVLGs is
as bright as ULIRGs
(>10^12).
/LIRGs
LBGs and SCUBA galaxies: UVLGs and ULIRGs at z~3
•Blue dots: LBG galaxies.
L_dust/L_1600 estimated
using UV slope (very
uncertain).
•Red squares: SCUBA
galaxies (radio preselected) studied in
Chapman et al. 2004.
• The overlap between the
two populations is small:
only 1 LBG detected by
SCUBA (Chapman et al.
2000). Only 1 red square
(SCUBA) has IR/UV < 100.
(Adelberger & Steidel 2001)
SCUBA galaxies: HST ACS images
overlaid by radio contours
Extended UV
emission outside
the radio/FIR
emission region:
unobscured UV
light.
3”
(Chapman et al. 2004, ApJ 611, 732)
Rest frame V-band luminosity
and mass
SCUBA galaxies:
stellar mass
(estimated from
rest V-band lum.)
plus gas mass
~ 5 10^10 M_sun,
(Spitzer measurements
of rest frame K may
be ~2 times higher).
A few times (~1.5
mag) more massive
than LBGs (green curve).
LBG
(Shapley
et al 2001)
(Smail et al. 2004, ApJ 616, 71)
Corrlations lengths
of SCUBA galaxies
and LBGs
SCUBA galaxies:
r_0=6.9+-2.1 h-1 Mpc
Significantly larger
than that of LBGs
(~ 3 -- 4 h-1 Mpc)
(Blain et al. 2004,
ApJ 611, 725)
SCUBA
LBGs
UV and IR galaxies at intermediate redshifts
(z ~ 0.6) --- early results of a
GALEX/SWIRE comparison study
• Why z=0.6?
• close to the peak of cosmic SF suggested by some ISO and SDSS
fossil studies
• for z ~ 1 or larger , NUV is affected by rest frame Ly
emission/absorption (K-correction for L_UV very uncertain)
• at z~0.6:
• NUV ( 2300A) ---> rest frame FUV (1500A)
• MIPS 24m ---> rest frame 15m (L_IR indicator)
• IRAC 3.6m ---> rest frame K band (stellar mass indicator)
Field:
GALEX ELAISE-N1_00
(~ 1 deg2)
(inside SWIRE
ELAISE-N1 ~ 9 deg2)
restrictions:
- within 1 deg circle
of GALEX field
- exclude the
SWIRE gap
Final area: 0.6 deg2
NUV sources: 8995
F3.6 sources: 19100
F24 sources: 2080
Matches f24/NUV: 1086
(52% of f24 srcs,
12% of NUV srcs)
ELAIS-N1_00
NUV
NUV
ELAIS-N1, 24μ m
Sample selection of 0.5<z<0.7 galaxies
• redshifts: photo-z
catalog of ELAIS-N1
(ugriz + IRAC, by
Rowan-Robinson)
• GALEX sources:
1124 (NUV <~ 24)
• MIPS sources:
396 (F24 ~
> 0.2mJy)
• NUV/F24 matches:
F24 ~ 0.2mJy, z~0.6 --> L_dust ~ 10^11 L_sun
159 ( 40% of F24
NUV ~ 24, z~0.6 --> L_FUV~ 10^9.5 L_sun
src, but only 14%
of NUV src!!).
Mean f24 flux of z=0.6 UV sources from stacking
9.4 < log(L_FUV) < 9.8:
212 sources, <f24>=39 Jy
Stacked f24 image of UV sources
in bin 9.4 < log(L_FUV) < 9.8
9.8 < log(L_FUV) < 10.2:
422 sources, <f24>=70 Jy
10.2 < log(L_FUV) < 10.5:
95 sources, <f24>=107 Jy
10.5 < log(L_FUV) < 10.8:
17 sources, <f24>=219 Jy
(212 sources)
L_dust of z=0.6 UV galaxies:
comparison with z=0 couterparts
<f24> --> < L(15m)>
in rest frame
•L_dust = 11.1 x L(15m)
(Chary & Elbaz 2001,
Elbaz et al. 2002)
•Error bar estimated from
fraction of F24 > 0.2mJy
In the 2 fainter L_UV bins,
the means of z=0.6 and
z=0 galaxies are close to
each other, both are a
factor of few below the
SWIRE detection limit.
Comparison of mean L_dust/L_FUV
ratios of z=0.6 and z=0 UV galaxies
• for galaxies of L_FUV
< 10^10.2 L_sun, the
IR/UV ratio does not
show any evolution
from z=0 to z=0.6.
• for brighter galaxies
of L_FUV > 10^10.2
L_sun, there seems to
be a negative evolution
in the sense that z=0.6
galaxies have lower ratios.
However, is the extrapolation
from L(15m) to L_dust
reliable???
SEDs of the 160um source at z=0.6
Need to check the SEDs of
z=0.6 sources which are also
detected in MIPS 70m band
and 160m band.
Only 1 z=0.6 source in
24m sample (395 sources)
is also detected in both
70m and 160m band.
It is a ULIRG with an SED
close to that Arp220! (M82 SED is closer to Elbaz calib.)
F24 image of the f160 source at z=0.6
The green circle:
160m beam (40”)
An isolated,
clean source
(no confusion).
Other 4 z=0.6
sources are detected
in 70m, but not
in 160m:
2 have log(L_dust)
< 12 and M82 like
SEDs.
~
2 have log(L_dust)
>12
~ and SEDs
closer to Arp220.
Conclusion:
SEDs span a wide
range.
SEDs of 70m sources at z=0.6
effect of different calibrations
When Arp220 SED
is used in converting
L(15m) to L_dust,
the mean IR/UV ratio
of z=0.6 UV galaxies
in 2 bright bins
(log(L_FUV)>10.2)
is in good agreement
with that of z=0
galaxies.
Consistent with no
evolution in the ratio!
L_dust/L_FUV ratio of z=0.6 IR
galaxies
• Elbaz calibration
• mean ratios derived
from both stacking
and ‘survival tech.’
(consistent with
each other).
• mean ratios of
z=0.6 galaxies in
all lum. bins are
consistent with those
of z=0 galaxies in
the same bins.
Effect of Arp220 calibration
• The arp220 calib.
shifts the points
along the IR/UV
vs. L_dust
correlation line,
so does not change
the result that
the IR/UV ratio
for given L_dust
does not have
any significant
evolution.
Stellar mass of given L_FUV: comparison
of z=0.6 and z=0 UV galaxies
• Stellar mass:
estimated from f3.6
(rest frame K).
• SWIRE sensitivity
limit of 3.6 m band
(the green line).
• The stellar mass
of z=0.6 galaxies
of given L_FUV
is about ~2 times
less than that of
their z=0 counterparts.
blue squares: z=0
pink points: z=0.6
f3.6=3.7Jy
Stellar mass v.s. L_dust: comparison of
z=0.6 and z=0 IR galaxies
No evidence
for evolution
in stellar mass
of IR selected
galaxies.
red points: z=0.6
Evolution seen in IR and in UV:
from z=0 to z=1
(dust) (FUV)
(dust)/
(L0 Mpc-3) (L0 Mpc-3) (FUV)
0.06 6 107
1.8 107
3.3
z
A(FUV)
(mag)
1.2
0.5
30 107
4.1 107
7.4
1.9
0.7
50 107
7.7 107
6.5
1.8
1
96 107
6.9 107
13.9
2.1
• (dust): ~ (1+z)4, Spitzer results of Le Floch et al. (2005).
• (FUV): Schiminovich et al. 2005 (ApJL, GALEX Edition).
• Both IR and UV have luminosity evolution --> at high z galaxies on
average are more luminous, therefore with higher attenuation.
Summary
1. By selection, UV galaxies and IR galaxies have very different
characteristic IR/UV ratios (the means differ by a factor of 10).
2. The morphological and stellar mass distributions of the two
populations have good overlaps (> 70%). IR galaxies tend
to be more massive and earlier types, with an excess of interacting
galaxies, and UV galaxies to be less massive and later types.
3. UV galaxies are less clustered than IR galaxies.
4. Galaxies with the highest SFR (>100 M ๏ /yr, Ltot > 1012 L ๏),
are missed in the UV samples.
5. A population of low metallicity (< 1/10 solar), low mass (<10^9 M )
dwarf UV galaxies (prototype I Zw 18) are `IR quiet’, with the
๏
IR/UV ratio ~ 0.3 or less. They occupy only a few percent of a
UV selected sample.
Summary (continue)
5. The z~0 counterparts of LBGs are a population of compact luminous
UV galaxies (UVLG). In terms of Ltot (SFR), UVLGs are more than
10 times fainter than ULIRGs.
6. LBGs and SCUBA galaxies (UV and IR selected galaxies at z~3)
do not overlap with each other very much. SCUBA galaxies have
significantly higher SFR, higher attenuation, higher stellar mass,
and higher correlation length than LBGs.
7. At intermediate redshifts of z~0.6, UV selected galaxies show
moderate evolution in stellar mass in the sense that for a given
luminosity, galaxies at z=0.6 have stellar mass ~2 times less than
their z=0 counterparts. No evidence for any evolution in the IR/UV
ratio (attenuation) for UV galaxies. For IR (24m) selected galaxies
at z~0.6, no evidence is found for evolution of either the stellar
mass or the IR/UV ratio for given LIR.
8. Both IR and UV evolve significantly from z=0 to z=1, and the ratio
IR/UV increases by ~ 4. This is consistent with the scenario that
high z galaxies are more luminous therefore with higher attenuation.
Star formation history measured
in diff. wavebands
1) They have the
same trend
(rising from z=0
to z ~1, then
becoming
relatively flat).
2) IR (ISO, IRAS,
SCUBA) and
rest frame UV
(blue symbols
and yellow shade)
measurements
agree with each other
within a factor of ~2!!
Schiminovich et al. 2005
I Zw 18 does
have dust:
Balmer decrement
(Hb/H) study
(Cannon et la. 2001)
found dust in
regions delineated
by the boxes in the
H image, covering
only parts of the
bubble-like star
formation regions:
blow-away of dust?
HST H image
(Cannon et al. 2002, ApJ. 595, 931)