SN IaSN IaMargutti Margutti Raffaella,2005Raffaella,2005

1. Observational methods1. Observational methods

(High-z Supernova Team)

High-z SN experience

2.SN types and Progenitors2.SN types and Progenitors

SNe II:SNe II:

1. We can find them only in spiral galaxies (extreme I population).

2. Type II SNe mark the end of the nuclear energy production in massive stars (>8 solar masses), and the start of a ‘new’ life as a neutron star.

3. They are believed to originate from CORE COLLAPSE of a massive progenitor star with plenty of H. To be more precise it’s important to say that for SN IIb most (NOT all) H is removed during evolution by tidal stripping.

1987A 1969L 1980K 1993J

Mej/Msun 15 17 2.2 3.26

E51 1.7 1.7 1.0 1.7

R0/1012 (cm)

3 15 22 0.7

M(56Ni)/Msun

0.075 0.075 0.075 0.075

Galaxy LMC NGC

1058

NGC

6946

M81

D(Mpc) 0.050 10.8 5.7 3.6

Type II Supernovae Parameters

From : “Supernovae and Nucleosynthesis”,Arnett,1996.

SNe I:SNe I:

I aI a1. In all Hubble type galaxies (Pop II or disk).2. They are believed to originate from thermonuclear

disruptions of accreting WDs in close binary systems.3. The issue of how the WDs grow to the Chandrasekhar

mass is still an open question. We have different possibilities. Among them:

Mergers of double degenerates resulting in the formation of a M>MCH and carbon ignition.

Accretion of H from a main sequence or evolved companion.

Sub-Chandra explosions.

What energies are available from What energies are available from thermonuclear events?thermonuclear events?

Fuel Ashes Erg/g 1051erg/Msun

4He 56Ni 1.57 3.0074He 28Si+32S 1.40 2.6774He 12C+16O 7.28 1.44612C 24Mg 5.60 1.11312C+16O 56Co 8.22 1.64512C+16O 56Ni 7.86 1.56112C+16O 28Si+32S 6.20 1.231

From : “Supernovae and Nucleosynthesis”,Arnett,1996.

1991T 1989B 1992A 1991bg

Mej/Msun 1.33 1.1 1.1 1.1

E51 1.27 1.7 1.7 1.7

R0/1012 (cm)

0.001 0.001 0.001 0.001

M(56Ni)/Msun

0.692 0.2 0.15 0.075

Galaxy NGC

4527

NGC

3627

NGC

1380

NGC

4374

Type Ia Supernovae Parameters

From : “Supernovae and Nucleosynthesis”,Arnett,1996.

I b-cI b-c

1. We can find them only in spiral galaxies (extreme pop I).

2. They are believed to be the result of an iron core collapse, and hence to be physically related to type II SNe.

From an observational point of view we are able to recognize SN types from their

Spectra. Light curve.

See next slides for more…

3. Spectra3. Spectra

4.Light-curves4.Light-curves

SN IISN II

(From Arnett,1996.)

SN IaSN Ia The rate of the decline of the light curve correlates with the

absolute magnitude at maximum (Phillips relation,2003) The peak is proportional to the mass of 56Ni synthesized during the

explosion. The light curve is powered by a “late time “ source: that is the

radioactive decay: (56Ni 56Co 56Fe) The light curves peaks at 10-15 days after core collapse and then

declines because of the increasing transparency of the ejecta and because of the decreasing number of radioactive elements.

Galaxies having a younger stellar population appear to host the most luminous SNeI-a.

See Arnett,1996,Appendix D, for a complete derivation of supernovae light curve shapes.

Cappellaro et al. 1997

5.Properties of a perfect standard 5.Properties of a perfect standard candle:candle:

1. It would be extremely bright.2. It would always have exactly the same

ABSOLUTE magnitude. (in particular this means that it wouldn’t suffer of EVOLUTION).

3. If the absolute magnitude depends on the environment (e.g. Hubble type) it should be well known.

4. Small corrections should be applied (fore/back ground absorption).

5. Easy to calibrate.

Standard CandlesA population of unevolving

sources, having a fixed intrinsic luminosity at

ALL redshifts

6.SNe Ia as distance indicators6.SNe Ia as distance indicators1. They are exceedingly luminous , with peak MB

averaging -19 mag if H0= 72 (Kms-1Mpc-1).(Filippenko,2004)

2. “Normal” SNe Ia have small dispersion around their peak absolute magnitudes σ ≤ 0.3 mag.(Filippenko,2004).

3. Our understanding of the progenitors and explosion mechanism of SNe Ia is on a reasonably firm physical basis.

4. Little cosmic evolution is expected in the peak luminosity, and it can be modeled.

5. It’s possible to perform local tests of various possible complications and evolutionary effect by comparing nearby SNe in different environments.

7.Possible evolution of SNe Ia7.Possible evolution of SNe IaEVOLUTION ( linked with changes in metallicity, mass and

C/O ratio of the progenitor,) could lead to: 1.Lower peak luminosity of SNe at high redshift; Overestimated distances2.More powerful explosions; Underestimated distancesProblem: it’s difficult to obtain an accurate, independent

measure of the peak luminosity it’s difficult to directly test for LUMINOSITY EVOLUTION.

Solution: we can easily determine if whether other observable properties of high-z and low-z SNe Ia differ. (If they are all the same is probable that the peak luminosity is constant a well !!!!)

Observational results about evolution:Observational results about evolution:1. SNe Ia & host galaxy morphology: the SCP

(Supernova Cosmology Project) found no clear differences between the cosmological results obtained with SNe Ia in late-type and early-type galaxies. (Sullivan et al.,2003)

2. SNe Ia & rise time (from explosion to maximum brightness): no significant difference between high-z and low-z SNe Ia (even if at high red-shift we have usually shorter rises times). (Filippenko,2004).

3. Number of progenitors: higher in high-z SNe.Although there is NO clear signs that cosmic

evolution of SNe Ia seriously comprises our results, it is wise to remain vigilant for possible problems.

8.Possible effects of extinction:8.Possible effects of extinction:Luminosity distances have to corrected for interstellar

absorption occurring in the host galaxy and in the Milky Way. From an observational point of view:

1. Extinction corrections based on the relation between SN Ia colors and luminosity improve distance precision for a sample of nearby SNe Ia which include objects with substantial extinction (Riees et al.,1996).

2. The consistency of the measured Hubble flow from SNe Ia with late-type and early-type host galaxies shows that the extinction corrections applied to dusty SNe Ia at low red-shift don’t alter the expansion rate from its value measured from SNe Ia in low dust environments

3. The scatter in the Hubble diagram is much reduced. (See next slide).

Hubble diagram for SNe IaHubble diagram for SNe Ia

(The ordinate shows the distance modulus)

TOP: The objects are assumed to be standard candles and there is no correction for extinction; the result is σ=0.42 mag.

BOTTOM: the same objects after corrections for extinction and intrinsic differences in luminosity. The result is σ=0.15 mag.

(From Filippenko, 2004).

Gray dust:Gray dust:THE PROBLEM:THE PROBLEM:Large dust grains ( GRAY DUST) ,would not imprint the

reddening signature of typical interstellar extinction upon which our corrections necessarily rely.

Could a evolution in dust-grain size cause us to underestimate the extinction?

THE SOLUTION:THE SOLUTION:Viewing SNe through such gray interstellar grains would

also induce a dispersion in the derived distances. With a mean gray extinction σ ≈ 0.25 mag (the value required to explain the measured distances without a cosmological constant), the expected dispersion would be σ ≈ 0.40 mag. This is significantly larger than the 0.21 mag dispersion observed.

The observational results favor the NO-Dust hypothesis (Riess et al.,2000).

(1999)

9.Cosmological results9.Cosmological results

• From SNe Ia • From CBR studies

WMAP (2003):WMAP (2003):

ΩΩMM = 0.27±0.04 = 0.27±0.04ΩΩΛ Λ = 0.73±0.04= 0.73±0.04ΩΩtottot = 1.02 = 1.02±0. 02±0. 02

SN Ia (2004):SN Ia (2004):

ΩΩtottot = 0.94 = 0.94±0.26±0.26

10.References10.References

• Arnett,1996: “Supernovae and Nucleosynthesis”, Princeton University Press.

• Filippenko,2004: The accelerating universe and dark energy: evidence from type Ia supernovae,Lect.Notes Phys,646, 191-221.

• Riees et al.,1996:Astroph. J.,473,88.• Riees et al.,2000:Astroph. J.,536,62.• Sullivan et al.,2003:astro-ph/0211444.