Extragalactic Astronomy & Cosmology Distance Ladder Jane Turner Joint Center for Astrophysics UMBC &...

Extragalactic Astronomy & Cosmology

Distance LadderJane Turner

Joint Center for AstrophysicsUMBC & NASA/GSFC

2003 Spring

[4246] Physics 316

Jane Turner [4246] PHY 316 (2003 Spring)

Cosmic Distance Ladder


Back to the Cosmic Distance Ladder1) Measuring distances within the solar system-radar 2) Use parallax to determine distance to nearby stars CALIBRATE NEXT RUNG: - Determine the intrinsic brightness of MS &

Cepheid Variables3) For other galaxies, assume brightness of MS distribution same as our

galaxy, get distance of other galaxy4) For more distant galaxies, assume know absolute brightness

(luminosity) of Cepheids, get distance of host galaxy CALIBRATE NEXT RUNG:- Determine absolute brightness of Supernovae5) Measure supernovae in very distant galaxies, get distance of host

galaxyGet absolute brightness of distant galaxies from rotation rates (Tully-Fisher) -thus get distance from apparent brightness

CALIBRATE NEXT RUNG:- Determine distances to distant galaxies, determine redhsift from spectra and derive relation between distance and redshift

6) Using relation established from lower rungs, measure spectra, redshifts and derive distances from galaxies which are furthest away


RUNG 5: Tully-Fisher Relation


The Tully-Fisher Relation

The Tully-Fisher (TF) relation is an empirical relation between L luminosity & rotational velocity Vc for Spiral Galaxies (see H&H page 275)

L Vc4

Thus, measure Vc, & integrated flux of a galaxy F derive the distance r (L = 4 r2 F)

Calibrated using the spirals in the Local Group (M33 & M31).

Other nearby spirals reveals scatter in the relation


TF Calibrators M31 & M33

M31 (Andromeda)

M33 (Triangulum)


TF Calibrators Three Others

M81 (Bode’s Galaxy)NGC2403

NGC3351


TF Relation - Problems

Potential Problems: Does not obviously include the effects of dark matter (which we will discuss later- thought to dominate the masses

of galaxies) assumes circular symmetry assumes all galaxies have the same mass/luminosity ratio assumes all galaxies have the same surface brightness

But it seems to work ! Measure velocity and thus determine luminosity - another

distance estimator, accurate and useful out to 100 to 200 Mpc


Distance from TF for 5 clusters

[Ima

ge C

redit:S

ho

ko S

akai, U

CL

A]]

Distance from TF

Rec

essi

on

Vel

oci

ty (

v ia

oth

er m

ean

s)


Distance from TF for 5 clusters

[Ima

ge C

redit:S

ho

ko S

akai, U

CL

A]]

H0 = 73 km s-1 Mpc -1 !!

Distance from TF

Rec

essi

on

Vel

oci

ty (

v ia

oth

er m

ean

s)

v=

H0d


Several Thousand Galaxies

[Ima

ge C

redit: K

LU

N G

rou

p]]

Recession Velocity (via other means)

Dis

tan

ce f

rom

TF H0 = 55 km s-1 Mpc -1 !!

(H0 = 72 km s-1 Mpc -1)

But most estimates: H0 = 81+/-11 km s-1 Mpc -1 (Jacoby 1992)


Supernovae -also rung 5

We know how supernovae occur…


SN Examples


Classification Schemes

Supernovae are classified into several types, based (primarily) on shape of light curve & elements observed in spectrum

Type II (eg SN1054, SN1987A) - H + heavies in the spectrum - collapse of degenerate Fe core in massive stars i.e. > 8 or 9 M - Rate is one every 44 yr in our Galaxy

Subdivided into two classes based on shape of light curve Type II-L - Light decline relatively smoothly Type II-P - Light curves exhibit a "plateau" 1 to 3 months after peak

[Possible distance indicator but out of favor as luminosities have some range]


Classification Schemes (cont)

Type I (eg “Tycho” & “Kepler” SNRs) - no H in spectrum - Rate is one every 36 yr in our Galaxy

Subdivided into three classes based on their spectra Type Ic - weak He lines in spectrum Type Ib - strong He lines in spectrum

Type Ia - strong Si II (615nm) lines death of short-lived massive stars(similar to Type II)

These are the ones of cosmological interest "explosion" of a White Dwarf (WD) star in a close binary which has reached the 1.4 solar-mass limit through accretion of material from the companion Bright !

Process yields same luminosity in all -> Fixed peak Luminosity -> measure distance


Classification Schemes (cont)

Type Ia - turn out to be the most useful, these are the white dwarf nova/binary systems gone into SNe

Type 1b and Type 1c were so-named due to spectral characteristics suggesting they were slight variations on the white dwarf style of SNe

In fact WRONG! They are now believed to also be from massive stars like Type II SNe.

Also show some variations between SNe of this type, making them less useful than Type Ia

Summary: Massive stars yield Type 1b, 1c and II and have some use as distance indicators

White dwarf binary systems yield Type 1a and are most useful as they are the most luminous (can see them in more distant galaxies) and most predictable in absolute brightness (luminosity).


SN Examples


Acceleration !

Riess (2000)


SN Examples


Recap on which Supernovae to use…


Potential Problems with SNe Ia

Use of SNe Ia as "standard candles" remains somewhat controversial

Other problems (real or potential) include:

- ideally the SN would be caught prior to the peak luminosity. obviously very difficult observationally.

- reddening is notoriously difficult to measure towards SNe

- lingering concerns that there is a significant spread in the peak luminosity.

- zero point is not calibrated using the Local Group, rather using more distant galaxies

- supernovae not available for all galaxies


Low-z SNe Ia & H0

Throughout the 1990s, technique of using SNe Ia as standard candles been refined.

now understood they are NOT perfect standard candles: They do NOT constitute a perfectly homogeneous sub-class. Spectroscopic and photometric (light-curve) peculiarities are been noted with increasing frequency.

However once the "peculiar" & highly-reddened objects removed from the sample, many astronomers consider SNe Ia to be "nearly perfect" standard candles

Currently a large observational effort directed towards SNe Ia. Understanding will (hopefully) increase as a result.


SNe Ia for Cosmology (z < 0.1)

H0 = 60 to 70 km s-1 Mpc -1

By the mid 1990s, large number of SNe Ia been observed (& systematic errors thought sufficiently well understood)

Can do cosmology...

(50 objects)


SNe Ia for Cosmology (z < 0.1)

Fili

ppe

nko

& R

iess

(20

00

)

H0 = 65+/-2 km s-1 Mpc -1

“Raw” data

“Corrected” data

(50 objects)

statisticalerror only


Some of the Main Groups

The High-z Supernova Search Team (HZT) led by Brian Schmidt (Mt Stromlo & Siding Springs Observatories)

The Supernova Cosmology Project (SCP) led by Saul Perlmutter (Lawrence Berkley Laboratory)

The Lick Observatory Supernova Search (LOSS)

So why all the effort ? ...


Can we Measure acceleration/deceleration ?

To Quote Bothun (p. 59)"Indeed, some particularly optimistic groups hope to use

[Type Ia SNe] as a means for estimating the deceleration parameter of the Universe by

measuring the rate of change of H0 over look-back times of a

few billion years"

[written in 1995]

deceleration/acceleration parameter tells us whether universe expansion is speeding up or slowing down, hence the fate of the universe


What are we trying to do ?

Filippenko & Riess (2000)

Low-z SNe Ia

High-z SNe Ia ?

So if H0 does not change with timeWe expect all the data to lie along here

If expansion rate was lower in the past - distant objects should be closer than the H=constant case So data will be here

Further/fainter than expected

Brighter /closerthan expected


So, where’s the data?

Filippenko & Riess (2000)

=1,=0,

q=0.5

We see Acceleration !


Sne Ia for Cosmology (z > 0.1)

However in the mid/late 1990s, as SNe 1a were detected out to greater distances (z > 0.1)

became clear that the observed fluxes of SNe 1a at 0.3 < z < 0.8 were systematically lower than expected

eg. for a critical density (matter-dominated) universe, & even for a constant-velocity (empty of matter) universe. The SNe must have gotten farther than expected for some epoch of the universe The universe appears to have been accelerating between the epoch equivalent to z ~ 0.5 and now !

i.e. expanding faster and faster !


Acceleration !

Riess et al (2001)

And Deceleration ! (?)

The very latest results on a SN Ia at z=1.7 imply prior to z ~ 1 the universe appears to have been decelerating !So early on, the universe expansion was slowing, then suddenly sped up

68,95,99%confidence contours

z-binnedmeans


Where do they do this ?

Primary search engine for both the High-z Supernova Search TeamSupernova Cosmology Project is the CTIO 4m Blanco Telescope (near La Serena, Chile)

Large-format CCDs


CTIO 4m Blanco Telescope

altitude 2.2 kmover-looking Pacific


LOTOSS instruments

Primary search engine for theLick Observatory and the Tanagra Observatory Supernova Search (LOTOSS) is the KAIT @ Lick Observatory, Mount Hamilton

(just East of San Jose, Ca),


KAIT

Katzman Automatic Imaging Telescope

76cm entirely automatic telescope almost solely used to the search for Sne

images of 1000 galaxies/nightautomatically reobserves best candidates undergrads examine candidates

9 SNe in 2002 Jan 6 SNe in 2002 Feb (so far)


Follow-up Spectra

Using one of the 10m Keck telescopes (Mauna Kea, Hawa’ii)

and/or Hubble Space Telescope, + ...


How do they do this ?

Search: Compare 2 images looking for differences - automated & human filtering Spectra: Confirm ID as a SN 1aLight curves: Multi-color to determine reddening & as part of light-curve fitting technique Luminosity: Measured using PSF fitting, or multi-aperture photometry Calibrate: Using nearby SNe 1a

Details differ between groups, but results are consistent


Warning !

This is cutting-edge observational cosmology - Implications are by no means universally accepted - New results possible at any time ...

Introduced to give you a taste of the latest ideas (why we do all this) - Please no complaints if it turns out wrong ! (Basic ideas might be examined [unless I tell you otherwise])

As mentioned earlier, following Edwin Hubble’s results it took 30 years to realize calibration of the Cepheid Variables was wrong...

Lev Landau

Cosmologists are often in error, but never in doubt


Potential Problems (Gray Dust)

At the present time, the main concerns seem to be:

"Gray Dust" screen absorption that does not have characteristics to enable easy detection (e.g. does NOT "redden" the spectrum). - screen absorbs some of the light from the SNe1a, making them appear dimmer than they actually were. - Indeed offers an alternative explanation to acceleration for the faintness of the SNe Ia with 0.5 < z < 1 - expect the amount of absorption to increase with distance (z) thus does NOT offer a simple explanation of brighter-then-expected SNe Ia at z=1.7


Potential Probs (Lumin Evolution)

"Luminosity Evolution" There is currently limited theoretical understanding of SNe Ia and their progenitors. According to Reiss et al (2001), "the weight of the empirical evidence appears to disfavor evolution as an alternative to" acceleration for the faintness of the SNe Ia with 0.5 < z < 1 However, they also say "the case against evolution remains short of compelling"

(Reiss et al 2001).


Problem - Small Statistics

believe it ?

25% fainter


Acceleration !

if so, also believe this ?

68,95,99%confidence contours


Other ‘Standard Candles’

We have reviewed the most reliable and (thus) widely-used distance determinations.

There exist a variety of other types of object which usually have some determinable luminosity, these can be used to confirm and tighten constraints on cosmological parameters. We note them here:

-planetary nebulae (out to 20 Mpc, 7 million ly)

-globular clusters (out to 5 Mpc, <2 million ly)

Rungs 3 - 4 on our diagram


The PN Luminosity Function

The distance indicator using the Planetary Nebula Luminosity Function (PNLF)

(Luminosity function is a plot of number of PNs versus luminosity)

uses fact that all (currently detectable) PNs appear to lie in a similar range of mass, with a cut-off (at the high-end)

so the ionizing flux & hence the strength of photoionized line such as [OIII] (500.7nm) will have a cut-off in strength (flux)

By constructing a LF of all the PN in a galaxy, one can determine the cut-off flux then use a calibrated PNLF to calculate the distance


A Planetary Nebula...


Another...


And another...


PNLF - Limitations/Potential Problems

the calibration (or "zero-point") is based on PNs in M31 (not our Galaxy) concerns about the number of stars (& hence PNs) required to properly define the LF.

concerns about subtle effects due to differences (from galaxy to galaxy) in average ionization of [OIII]

but it seems to work out to 20 Mpc

H0 = 75 km s-1 Mpc -1 (NGC 3379, Ciardullo, PSU)

H0 = 73+/-10 km s-1 Mpc -1 (Jacoby 1992)


The GC Luminosity Function

There is a distance indicator using the Globular Cluster Luminosity Function (GCLF)

M13-Hercules

Recap: Globular Clusters Group of 10,000-1 million ‘old’ (Pop II) stars (10-15 billion years) , bound by gravity, in galaxy halo. Metal poor.


The GC Luminosity Function

The distance indicator using the Gobular Cluster Luminosity Function (GCLF)

Uses assumption that the GCLF is universal (same everywhere)

So comparing the Flux of the peak (in a distance galaxy)with a (calibrated) Luminosity of the universal peak gives the distance

GCLFs from Nielsen (1998)

Nu

mb

er

Brightness


A Globular Cluster


Another...


And another...


GCLF - Limitations/Problems

location of LF peak (the calibration or "zero point”) is uncertain, even for GCs in out Galaxy (depends on sample selection effects) width of GCLF varies

- GCLF is not universal ...how this affects the location of the peak is not clear.

unclear how the differences between the GC populations in spiral galaxies (used to calibrate the method) & elliptical galaxies might effect the method. But it sometimes seems to work !

out to (only) 5 Mpc (maybe not good for stringent H0 constraints ?)

H0 = 68+/-15 km s-1 Mpc -1 (Jacoby 1992)

Extragalactic Astronomy & Cosmology Distance Ladder Jane Turner Joint Center for Astrophysics UMBC &...

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