the low-z sn ia sample: critical to...

The Low-z SN Ia Sample:Critical to Cosmology

Saurabh JhaKavli Institute for Particle Astrophysics and Cosmology

Stanford Linear Accelerator Center

PPC 2007 Texas A & M University May 17, 2007

Hubble’s Law

the cosmological distance ladder

measured distances using bright stars in other galaxies and average

galaxy properties

measured galaxy redshifts with spectroscopy, using the Doppler

shift of atomic spectral lines

Hubble (1929)

Hubble’s Law

the cosmological distance ladder

measured distances using bright stars in other galaxies and average

galaxy properties

measured galaxy redshifts with spectroscopy, using the Doppler

shift of atomic spectral lines

Hubble (1929)

-5 pts

wrong units!

History and Future of the Expansion

different pasts and futures depend on gravity and contents of the Universe

History and Future of the Expansion

redshift yields the cosmic scale factor distance tells the time, but we need a good distance indicator

different pasts and futures depend on gravity and contents of the Universe

Type Ia SN 1998bu in M96

March 14, 1997

Suntzeff et al. (1999), Jha et al. (1999)

Type Ia SN 1998bu in M96

March 14, 1997 May 18, 1998

one star in this galaxy becomes as bright as 10 billion stars!

Suntzeff et al. (1999), Jha et al. (1999)

SN 1999cl in NGC 4501 (M 88)

supernovae can bedifficult to study

★ unpredictable★ rare★ fleeting

ESSENCE+SNLS Hubble Diagram

– 57 –

Fig. 8.— Luminosity distance modulus vs. redshift for the ESSENCE, SNLS, and nearby

SNe Ia for MLCS2k2 with the “glosz” AV prior. For comparison the overplotted solid lineand residuals are for a !CDM (w, "M, "!) = (!1, 0.27, 0.73) Universe.

ESSENCE+SNLS Hubble Diagram

– 57 –

Fig. 8.— Luminosity distance modulus vs. redshift for the ESSENCE, SNLS, and nearby

SNe Ia for MLCS2k2 with the “glosz” AV prior. For comparison the overplotted solid lineand residuals are for a !CDM (w, "M, "!) = (!1, 0.27, 0.73) Universe.

Critical to Cosmology

Astier et al. (2006), Wood-Vasey et al. (2007)

• nearby sample: z < 0.15 (arbitrary, but practical defintion)

• anchor the Hubble diagram, essentially independent of ΩM, Λ, w

• provide the empirical correlations that make Ia’s precisely calibrated candles

• studied in greatest detail

ESSENCE + SNLS120 SN Ia

nearby sample45 SN Ia

Nearby SN Ia photometry samples: today

• Calán/Tololo (1990-1993; Hamuy et al. 1996)• photographic search and CCD follow-up• 29 objects, BVI template-subtraction photometry• mean redshift cz = 13500 km/s

The Groundbreaking Work: Calán/Tololo

Hamuy et al. (1996a,b)

1996AJ....112.2391H

1996AJ....112.2398H



• CfA I (1993-1996; Riess et al. 1999)• follow-up only, 22 objects, BVRI photometry• mean redshift cz = 7500 km/s

• CfA II (1997-2000; Jha et al. 2006)• 44 objects, UBVRI photometry• mean redshift cz = 5300 km/s

CfA II: 44 UBVRI light curvesJha et al. (2006)



• CfA I (1993-1996; Riess et al. 1999)• follow-up only, 22 objects, BVRI photometry• mean redshift cz = 7500 km/s

• CfA II (1997-2000; Jha et al. 2006)• 44 objects, UBVRI photometry• mean redshift cz = 5300 km/s

• APO/CTIO (Krisciunas et al. 2000,03,04ab,06,07; 19 objects 1999-2004)

• ESO (Altavilla et al. 2004; 18 objects 1991-2000)

• many papers with individual or a few objects

Si

MLCS2k2 light curve fits

μ = 33.46 ± 0.07 mag μ = 33.49 ± 0.10 mag

SN 1999cp KAIT BVRI photometry SN 2002cr

Si

MLCS2k2 light curve fits

SN 1999cp and SN 2002cr are both in NGC 5468μ = 33.46 ± 0.07 mag μ = 33.49 ± 0.10 mag

SN 1999cp KAIT BVRI photometry SN 2002cr

Si

Correcting for Intrinsic Variations and Dust

Nearby Hubble Diagram

m = 5 log10 cz + (M − 5 log10 H0 + 25)

Low-z cosmology: the Hubble constant

HST/ACS Cepheids

σvelocity < σdistance ≃ 10%

Measuring the Hubble Constant


✔~3% precision


?!✔

~3% precision


• Cepheid-calibrated supernovae: two groups

• SN Ia Project (Saha et al. 2001)

• Key Project (Freedman et al. 2001)

• same HST Cepheid data, same supernova data

?!✔

~3% precision

Hubble Trouble: measuring H0

same HST Cepheid data! same SN distances!

Key Project (Freedman et al. 2001)

SN Ia Project (Saha et al. 2001)

Hubble Trouble: measuring H0

same HST Cepheid data! same SN distances!

Key Project (Freedman et al. 2001)

SN Ia Project (Saha et al. 2001)

from 4 “ideal” calibrators: H0 = 73 ± 6 km s-1 Mpc -1 (Riess et al. 2005)5% precision in the near(-IR) future, bypassing the LMC...

Going with the flows

σdistance ≲ few × σvelocity

Jha, Riess, & Kirshner (2006)




data also amenable to more sophisticated analysis(e.g., Haugbølle et al. 2006, Neill et al. 2007, Wang 2007)

The smooth Hubble flow

σvelocity ≲ σdistance

Hubble flow Hubble diagram

Si

Hubble’s Law extended

6

ESSENCE, SNLS

Hubble flow Hubble diagram

Higher-Z/HST

A Hubble Bubble?

a 6% difference in the expansion rate at a radius of 100 Mpc, roughly isotropic


A Hubble Bubble?

a 6% difference in the expansion rate at a radius of 100 Mpc, roughly isotropic

statistical signifcance is 2.5σ,but robust with subsamples, other distance techniques



A Hubble Bubble?


• a real local void?

• K-corrections?

• photometric offset?

• new data vs. Calán/Tololo?

• morphology/extinction?

A Hubble Bubble?


• a real local void?

• K-corrections?

• photometric offset?

• new data vs. Calán/Tololo?

• morphology/extinction?

a potentially large systematic➔ test with more nearby objects!

A Hubble Bubble?

Comparing light-curve fitters

1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)

THE HUBBLE BUBBLE AND SN Ia COLORS 3

5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (S

ALT)

5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (M

LCS2

k2)

Fig. 2.— The Hubble bubble as a function of the velocity of thestep in the Hubble constant, czvoid. The left panel shows resultsfor SALT (with ! = 1.82), and the right panel for MLCS2k2. Thegrey band is the error in "H/H. The constant value for 16000 <cz < 19000 km/sec simply reflects the lack of any SN in this range.

1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)

Fig. 3.— "H/H vs. the value of ! used to convert the measuredcolor parameter into a luminosity correction for SIFTO. The rela-tion is almost, but not quite, linear. Fits to low-z and SNLS datagive ! = 2.35± 0.16.

ror in one or more of the packages. However, the ac-tual cause is more interesting: if one sets ! = 4.1 forSALT/SALT2/SIFTO, they do find evidence for a Hub-ble bubble at > 2.5", as shown in figure 3. The colormodel for the most recent version of !m15, which alsofavors the bubble, is similar to that of MLCS2k2. Thequestion of the Hubble bubble therefore boils down tothe appropriate value of ! – is it the ! 4 of Milky-Waylike dust, or is something more complicated going on?

The value of ! is relevant because the nearby portionof the low-z SN sample is redder than the distant por-tion (figure 4). This is probably due to Malmquist bias(Malmquist et al. 1936) or other selection e"ects, sinceredder supernova are fainter and harder to detect. Thee"ects of the color correction are to (relatively) make theblue SNe dimmer and the red SNe brighter. Malmquistbias has little e"ect as long as the appropriate value of !is applied across the whole sample; however, if the rightvalue is ! = 2 and instead 4 is used, then the distantportion will be made too faint, and the nearby portiontoo bright, which is exactly the e"ect observed in J07.MLCS2k2 usually includes a prior on AV , and the de-fault one does not take into account the redshift depen-dent e"ects of Malmquist bias. Adjusting the prior toreflect this increases the value of #H/H.

0 10000 20000 30000 40000cz (km/sec)

!0.1

0.0

0.1

0.2

0.3

0.4

0.5

SA

LT

co

lor

c (

ma

g)

Fig. 4.— The colors of the low-z supernova sample using SALT.The distant portion of the sample is bluer than the nearby portion,which is probably caused by selection e!ects.

4. THE VALUE OF !

If, in fact, ! = RB (i.e., it is purely dust), then weshould note that a large range of RBs have been observedin di"erent environments. However, a sample mean valueof RB = 2 would be quite surprising (Draine 2003), evenwith selection e"ects.

The empirical values for ! were calculated in a modelthat assumed a smooth local Hubble flow. It is possiblethat this could be artificially suppressing #H/H, so wechecked this by refitting ! using only high-z SNLS SN,only the low-z SN below czvoid, and simultaneously withour fits to #H/H. These give essentially the same result(! ! 2), albeit with larger errors than the full sample.Therefore, ! is robust against the presence of a Hubblebubble. Monte Carlo studies indicate that the bias in !(b!) due to errors in the measurement uncertainties andcovariances is |b! | < 0.02 for fairly extreme cases.

We can also analyze the results of the MLCS2k2 fitsusing the ! framework. This di"ers from what is meantin J07 by fitting RV (which enforces a certain relation be-tween the wavelength dependence and scaling of the colorexcess relation), and is more similar to the analysis car-ried out in Riess et al. (1996), who found RV = 2.5± 0.3(corresponding to ! = 3.5) using a smaller sample andan earlier version of MLCS. We first remove the extinc-tion correction from the MLCS2k2 distance estimates,then convert AV into E (B " V ) using RV , and finallyuse this to fit for the value of ! by minimizing the resid-uals with respect for the Hubble line via a !E (B " V )term. We work in B, and find ! = 2.7±0.3, which againshould be compared with the expected value of 4.1. Re-stricting the fit to only SN below czvoid does not changethe results. The fits are shown in figure 5.

Another technique for estimating the amount of ex-tinction is to use late time (! 45 days after peak) colormeasurements. The idea is that at late times all SN Iahave a simple relationship between color and epoch, andso any di"erence between the observed colors and themodel at these epochs measures extinction (Phillips et al.1999, hereafter P99). The evidence for this is based ona handful of SN for which there is independent evidencefor low extinction, and the distribution of the measuredlate-time colors (J07, figure 6). A version of this is usedin the training process of MLCS2k2.

This suggests one more test of !. We take the subsam-ple of our 61 SNe that have late-time color measurements

Conley et al. (2007)


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)


5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (S

ALT)

5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (M

LCS2

k2)


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)




0 10000 20000 30000 40000cz (km/sec)

!0.1

0.0

0.1

0.2

0.3

0.4

0.5

SA

LT

co

lor

c (

ma

g)


4. THE VALUE OF !







a strong change in color excess across the low-redshift sample


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)


5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (S

ALT)

5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (M

LCS2

k2)


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)




0 10000 20000 30000 40000cz (km/sec)

!0.1

0.0

0.1

0.2

0.3

0.4

0.5

SA

LT

co

lor

c (

ma

g)


4. THE VALUE OF !








the Hubble Bubble signature depends critically on the

luminosity/color-excess correction


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)


5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (S

ALT)

5000 10000 15000 20000cz void (km/sec)

!0.05

0.00

0.05

0.10

! H

/ H (M

LCS2

k2)


1 2 3 4 5 6!

!0.05

0.00

0.05

0.10

0.15

" H

/ H (S

IFTO

)




0 10000 20000 30000 40000cz (km/sec)

!0.1

0.0

0.1

0.2

0.3

0.4

0.5

SA

LT

co

lor

c (

ma

g)


4. THE VALUE OF !








the Hubble Bubble signature depends critically on the

luminosity/color-excess correction

using the same correction, all the light-curve fitters (MLCS2k2, SALT,

SALT2, and SIFTO) agree.

What’s the correct correction?

!0.1 0.0 0.1 0.2 0.3 0.4 0.5c

!0.5

0.0

0.5

1.0

1.5

2.0

resid

s (n

o co

lor c

orr)

SIFTO

!0.1 0.0 0.1 0.2 0.3 0.4 0.5c

SALT

!0.1 0.0 0.1 0.2 0.3 0.4 0.5AV/RV

!0.5

0.0

0.5

1.0

1.5

2.0re

sids

(no

colo

r cor

r)MLCS2k2

!0.1 0.0 0.1 0.2 0.3 0.4 0.5E(B!V)+35

SIFTO w/ late time colour


empirical fits:β ≃ 2

normal dust:β ≃ 4

So what’s the answer?

Weird dust, even in cases with low extinction? (e.g., scattering: Wang 2005)A second parameter? Luminosity correlated with an intrinsic color excess?

A melange of normal & weird dust + intrinsic variations!? (see Wang 2007)

Sharpening our precision tools

– 44 –

Fig. 15.— Correlations with host-galaxy morphology and projected galactocentric distance

(GCD). The top panels show mean values of the light-curve shape parameter ! for the full sample,

and the middle panels show the distribution of host-galaxy extinction A0V. The bottom panels show

the residuals relative to the best fit Hubble line for the Hubble flow sample only (after MLCS2k2

correction for luminosity di"erences and extinction). Projected GCDs are calculated using the

angular o"sets presented in Table 1, with angular diameter distances (#M = 0.3, #$ = 0.7) calcu-

lated from the redshift for objects with czCMB ! 2500 km s"1 and from the MLCS2k2 supernova

distances for objects with lower recession velocities.


Sharpening our precision tools

– 44 –

Fig. 15.— Correlations with host-galaxy morphology and projected galactocentric distance

(GCD). The top panels show mean values of the light-curve shape parameter ! for the full sample,

and the middle panels show the distribution of host-galaxy extinction A0V. The bottom panels show

the residuals relative to the best fit Hubble line for the Hubble flow sample only (after MLCS2k2

correction for luminosity di"erences and extinction). Projected GCDs are calculated using the

angular o"sets presented in Table 1, with angular diameter distances (#M = 0.3, #$ = 0.7) calcu-

lated from the redshift for objects with czCMB ! 2500 km s"1 and from the MLCS2k2 supernova

distances for objects with lower recession velocities.

Are we battling the fog of dust?Intrinsic dispersion of subsamples could be much lower: 3% distances?

➔ we need more nearby objects!


Nearby SN Ia photometry samples: tomorrow• Lick Observatory SN Search (and follow-up!)

• 96 SN Ia from 1998-2004, BVRI light curves• mean redshift cz = 6000 km/s (Ganeshalingam et al. 2007, in prep)

Lick Observatory SN Search

KAIT

8283958268384020

LOSS SNe

All Nearby SNe

Lick Observatory SN Search

KAIT

world’s most successful nearby SN search!

8283958268384020

LOSS SNe

All Nearby SNe

New Data from KAIT

preliminary

!

Ganeshalingam, Li, Filippenko et al. (in prep)



• CfA III (Hicken et al. 2007, in prep)• ~80 SN Ia from 2000-2004 (and >70 more from 2005-2007)• mean redshift cz = 6800 km/s

Follow-up at FLWO: CfA III

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U=#%5#S(//L')2S)#=64=#D4T%D:D#Y.%<6=)(55#%)#@&Y4)0/&2..(/4=(5#S%=6#=6(#0(&/%)(#.4=(#2V#1X#U4"##I00%=%2)4//N#%=#645#Y(()#5(()#=64=#2Q(./:D%)2:5#U4]5#4.(#V2:)0#%)#/4=(.L=NR(#<4/4T%(5#2Q(.#4#S%0(#.4)<(#2V#R.2G(&=(0#<4/4&=2&()=.%&#0%5=4)&(5#_,73B`##S6%/(#Q(.NLV45=#0(&/%)%)<+#5:Y/:D%)2:5#U4]5#4.(#V2:)0#%)#(4./%(.#=NR(#<4/4T%(5#4)0#4.(#)2=#2V=()#V2:)0#4=#/4.<(#,73B#_("<"#$4D:N#(=#4/"#;[[[`"##U=#562:/0#Y(#)2=(0#=64=#,73B#%5#2)/N#4#/2S(.#/%D%=#2)#=6(#4&=:4/#0%5=4)&(#Y(=S(()#625=#&()=(.#4)0#1X"##K%=6#4#)(S#4)0#%)0(R()0()=#5(=#2V#U4]5+#S(#&2)V%.D#=6%5#=.()0"##U)#V%<"#;#S(#64Q(#&4/&:/4=(0#=6(#0(&/%)(#.4=(#V2.#^?#)(S#U4]5#V.2D#=6(#V%<"#*#3VI#/%<6=#&:.Q(5#4)0#R/2==(0#=6(D#4<4%)5=#=6(%.#625=#<4/4TN#D2.R62/2<N#4)0#R.2G(&=(0#<4/4&=2&()=.%&#0%5=4)&("##E6(#&2/2.L&20%)<#6%<6/%<6=5#=64=#%)0((0#=6(#V45=(5=#0(&/%)(.5#_%)#.(0`#4.(#%)#(//%R=%&4/#4)0#(4./NL=NR(#5R%.4/5#S%=6#/2S#,73B#S6%/(#=6(#5/2S#0(&/%)(.5#_%)#Y/:(`#4.(#V2:)0#4=#4#S%0(#.4)<(#2V#,73B#4)0#2)/N#%)#/4=(.L=NR(#5R%.4/5#4)0#%..(<:/4.5"###X2#Q(.NLV45=#0(&/%)(.5#4.(#V2:)0#%)#2:.#/4=(.L=NR(#625=5"##E6(#R(&:/%4.#1X#;[[J6'#_%)#Y/4&'+#4)0#R255%Y/N#%)#4#)(S#&/455#2V#U4]5#S%=6#=6(#5%D%/4./N#R(&:/%4.#;[[;&T+#5((#,6%//%R5#(=#4/"#;[[^`+#645#4#D20(.4=(/NLV45=#0(&/%)(#.4=(+#Y:=#%5#%)#4)#1I-0#625="###ZQ(./:D%)2:5#1X#U4#=()0#=2#2&&:.#%)#N2:)<(.#5=(//4.#R2R:/4=%2)5#S6%/(#5:Y/:D%)2:5#1X#U4#=()0#=2#2&&:.#%)#2/0(.#R2R:/4=%2)5"##32DR4.%)<#4#/4.<(.#5(=#2V#1X#U4#/%<6=#&:.Q(#R.2R(.=%(5#S%=6#D2.(#9:4)=%=4=%Q(#D(45:.(5#2V#625=#4)0#/2&4/#()Q%.2)D()=#&64.4&=(.%5=%&5#D4N#Y(#:5(V:/#%)#:)0(.5=4)0%)<#1X#U4#R.2<()%=2.5"##

':D6#.-$"/#6,6"#8+/"*/!"#$"#%/?.)$6#,)*7/+",/E66./,:DD-#*6%/)./D"#*/E7/*+6/<'F/G#".*/2'>HI&HIJJKL

@(V(.()&(5 8D4%/P##D6%&'()e&V4"64.Q4.0"(0:$4D:N+#!"+#(=#4/"#;[[[+#I>+#*;[+#*Faf,6%//%R5+#!"#!"+#(=#4/"#;[[^+##45=.2LR6c[^**;fJ

Hicken et al. (2007)




• Carnegie Supernova Program (Hamuy et al. 2007)• ~35 SN Ia from 2004-2006 (~100 over 5 years)• wide wavelength coverage: uBVgrizYJH (optical + near-infrared)

– 46 –

670 680 690 700 710 720 730 740 750 760 770

JD (2453000+)

12

13

14

15

16

17

18

19

20

21

22

23

Ma

gn

itu

de

CSP

u’ + 1.5

B + 1

g’ + 0.5

Vr’ - 0.5

i’ - 1Y - 1.5

J - 2.5

H - 3K - 3.5

Fig. 4.— Observed u!g!r!i!BV and Y JHK light curves of SN 2005hk obtained by the CSP.

For clarity, the magnitudes in each band have been shifted by an arbitrary constant whichis given in the legend. The errors in the measurements are smaller than the plot symbolsexcept where indicated. Y JH photometry obtained with RetroCam is plotted with black

symbols; Y JHK measurements made with WIRC are shown in red.

Carnegie SN Program: SN 2005hk

Phillips et al. (2006)





• SDSS-II: ~40 SN Ia/yr with z < 0.15 from 2005-2007

!60 !40 !20 0 20 40 60

!1

01

! (

de

g)

" (deg)

452 supernovae

spectroscopic SN Ia (313)probable SN Ia

core-collapse SN

0 0.1 0.2 0.3 0.4

020

40

# o

f S

N Ia

z

SDSS!II SN SurveyFall 2006 (184 SN Ia)Fall 2005 (129 SN Ia)

M. Sako, U. Pennsylvania

! !

!"#$%&'()*+(",-&'./'#'01-2(*#1.+.

!"#$%&$''(")

&$'*+,)-,.,/0

A. Becker, U. Washington

! !

!"##$%&'()*+),&-../

01234&556&7%%3(8*9&6%)33$%9&:)8")+;&011<

SDSS SN Hubble diagramfrom fall 2005 data

(129 SN Ia in all, 74 “clean”)

H. Lampeitl, STScI

ESSENCE 2006

! !

!"##$%&'()*+),&-../

01234&556&7%%3(8*9&6%)33$%9&:)8")+;&011<

SDSS SN Hubble diagramfrom fall 2005 data

(129 SN Ia in all, 74 “clean”)

H. Lampeitl, STScI

! !

!"#$%%&

'()*))(+,(-%./+,0#+%,(1+#2(34!(56%7+89:(0(",+;"9((.90:"69.9,#(%,(1(0#(<=>?@A

'(0::9::.9,#(%B(:C:#9.0#+-(",-96#0+,#+9:(",896(10C

'(0,0$C:+:(%B()*))()D9(80#0(+,(-%./+,0#+%,(1+#2((%#296()D9(80#0(:9#:(+,(56%E69::

for the first time we have a continuous expansion history measured from SN to z > 1

ESSENCE 2006





• SDSS-II: ~40 SN Ia/yr with z < 0.15 from 2005-2007 (Garnavich talk)

• Nearby SNFactory: IFU spectrophotometry

• Skymapper, Pan-STARRS, etc.





• SDSS-II: ~40 SN Ia/yr with z < 0.15 from 2005-2007 (Garnavich talk)

• Nearby SNFactory: IFU spectrophotometry

• Skymapper, Pan-STARRS, etc.

DETF report requires >500 nearby SN Ia to reach precision envisionedwe’re on our way there...

the low-z sn ia sample: critical to...

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