galaxies (and stars) in the far infrared: results from the akari all-sky survey agnieszka pollo ipj...

Galaxies (and stars) in the far infrared:

results from the AKARI All-Sky Survey

Agnieszka PolloIPJ

Warszawa, 15.04.2011

Electromagnetic spectrum

Infrared range: longer than optical and shorter than microvawe waves.

Infrared

Astronomers roughly divide infrared into three ranges:

1. near- (NIR: 1 – 5 micrometers),

2. mid- (Mid-IR: – 5 -- 30 micrometers)

3. far- (FIR: 30 – >200 micrometers).

Infrared = heatAll objects in the Universe with ANY temperature radiate in the infrared

Humans in the Infrared

Human body of a normal temperature has radiates with a maximum in the infrared around 10-12 microns.

Infrared astronomical observations

Astronomy: observations in the infrared

Atmosphere– absorbs infrared– emits in the infrared itself

Atmospheric emission is the strongest at ~10 μm

There are a few IR “windows” in the atmosphere where there is no emission and no strong absorption, mainly above ~ 4 μm (NIR).

Infrared windows in the atmosphere

Band Sky Transparency J high H high very low K high very low

L low

M low high

N very high

17 - 40 microns very low very high

WavelengthRange

Sky Brightness 1.1 - 1.4

microns low at night 1.5 - 1.8 microns 2.0 - 2.4 microns

3.0 - 4.0 microns

3.0 - 3.5 microns: fair3.5 - 4.0 microns:

high 4.6 - 5.0 microns

7.5 - 14.5 microns

8 - 9 microns and 10 -12 microns: fair

others: low 17 - 25 microns: Q28 - 40 microns: Z

Astronomical observations in the infrared

Telescopes in high dry mountains (Atacama)

airplanes

balloons

satellites

What can we observe in IR?

Everything hidden behind dust

Everything cold:– dust – cold stars– planets

Everything (?) far: strongly redshifted galaxies

Spitzer: star forming regions in Cygnus


Everything hidden behind dus



Spitzer, “hot Jupiter” HD 189733b

650oC 930oC


Hubble Deep Field in NIR

Spitzer:cosmic IR background from very first galaxies?(Kashlinsky et al.2007)

Everything hidden behind dust




Astronomical objects in IR look different than in other wavelengths

Different parts of the spectrum show different things: Far IR: dust, UV: young hot stars optical: most of stars which are not obscured by

dust near-IR: stars hidden behind the dust (here the

dust becomes relatively transparent)


This makes IR a very important range for galaxy observations

– it allows to see the parts of galaxies which are completely hidden by dust (and sometimes whole galaxies faint or invisible in optical range) – important for a total census of stellar light (and mass) in the Universe

– it gives a possibility to discover very distant galaxies

Copyright by: Kasia Małek

Orion in optical and IR

M31 (Andromeda)

optical

FUVFIR

IRAS

Satellite IR observatories

First IR satellite, launched by NASA in January 1983

First ever map of (almost - 98%) all sky in IR during a ten month period from January to November, 1983

All sky in IR - IRAS (80')

IRAS – All Sky in IR 60 cm helium-cooled

telescope 4 IR bands at effective

wavelengths: 12, 25, 60, 100 μm

The angular resolution varied between about 0.5' at 12 microns to about 2' at 100 microns

After a 10 month long mission, IRAS exhausted its cryogen and ceased operations on November 21, 1983

IRAS – All Sky in IR ~ 350 000 IR point sources

in the sky which increased the number

of cataloged astronomical sources of 70%

most of them belong to Milky Way: cool stars, nebulae, cirruses...

plus a few tens of dusty galaxies

some sources still remain unidentified

AKARI

• 68.5 cm diameter telescope• two main instruments:

– the Infrared Camera (IRC) – for mid-IR– the Far-Infrared Surveyor (FIS) – for FIR

• launched in February 2006• 16 month cryogenic mission lifetime

between May 2006 and August 2007 (needed for FIR observations; liquid helium ran out on 26 August 2007 )

• now – the “warm” phase • deeper; much better resolution than IRAS

AKARI

6 IR bands from 9 to 180 μm (broader range than IRAS and reaching longer wavelengths)

Results:All Sky Survey + two deep surveys (NEP and

ADF-S) + a series of dedicated pointed observations

Improvement of resolution comparing to IRAS

In MIR

In FIR

Akari All Sky Surveys: point source catalogs at FIR and MIR

• public release of bright source catalogue 31 March 2010

• work still on-going on:– faint sources– diffuse emission

Akari All Sky Surveys: point source catalogs at FIR and MIR

• in total, more than 1.3 mln sources (> 3 times more than IRAS) in 6 bands

• AKARI-IRC Point Source Catalogue v. 1:– 870 973 objects in two MIR bands (9 and 18

μm) – 10 times more sensitive (at 18 μm) than

IRAS– an accuracy of an order of arcseconds

(compared to arcminutes with IRAS)• AKARI-FIS Bright Source Catalogue v. 1:

– 427 071 sources in 4 FIR bands (65, 90, 140, and 160 μm)

– (IRAS longest band was 100 μm)

Infrared sources at 9 μm: blue, at 18 μm: green, at 90 μm: red.

Galactic center Galactic plane

AKARI All-Sky survey at 9 μm

• Emission from the photospheres of stars dominates the 9 μm catalogue: the galactic disc and nuclear bulge are clearly visible at this wavelength

NEP (North Ecliptic Pole)

ADF-S (South Ecliptic Pole, AKARI Deep Field South)

AKARI All-Sky survey at 9 μm

Infrared sources at 9 μm: blue, at 18 μm: green, at 90 μm: red.

Galactic center

Galactic plane

•dust and star formation in the disc of our Galaxy become more prominent at 90 micrometres;

•Away from the Galactic Plane, many extragalactic objects are detected

FIR: AKARI ASS (AKARI All-Sky Survey: Bright Source Catalog)

v. β-1: 94% of the sky in 16 months

>43 000 sources with fluxes measured in all four FIS bands (160, 140, 90, 65 μm), i.e. “colors”

What are these sources?

• Statistical analysis of all sky surveys provides a powerful tool to understand the properties of all classes of objects in the Universe.

• But first, we need to know: what they are?• From our point of view, the crucial point was:

which of these sources are the galaxies, how they can be distinguished from sources which belong to Milky Way?

• If, e.g., we want to make a (costly) measurement of galaxy distances by spectrophotometry, we do not want our sample to be “polluted” by too many stars (and vice versa, stellar researches do not want to be bothered by galaxies).

What are these sources?

• In case of FIR studies there is no credible way to find good galaxy candidates (yet)

• At first, we have at our disposal only FIR fluxes (i.e. FIR colors)

Preceding Study from IRAS

With IRAS four bands (12, 25, 60, 100 μm), a very detailed classification was possible. However, in the case of AKARI FIS ASS, we must rely only on four FIR bands (at longer wavelengths), and this cannot be a trivial application of IRAS methodology, since the physical processes behind emission in these bands are different.

(Walker et al. 1989)

Classical method: color-color diagrams.

The color-color diagrams

• The basic idea: different classes of astronomical (and not not only) objects have different colors

• Color is defined as a difference between fluxes at different wavelengths (also far from optical)


• Such differences were first observed in the optical range: it is well known that, e.g. young stars are bluer than old ones, and spiral galaxies are bluer than ellipticals.


• This is (broadly speaking) related to the fact, that different objects have different spectra, and their shape may in a complex way vary depending on their properties

Here: templates from Buzzoni at al. 2005

1. The sample was matched with SIMBAD and NED (astronomical database for stars, nebulae, and galaxies).

Star-Galaxy Separation by FIS Color-Color Diagrams

Data

• Since we were looking mainly for galaxies, we selected sources in a low-cirrus region (I100 < 10 MJy sr-1) on the sky to avoid contamination in FIR flux (5176 objects), which in practice meant mainly avoiding Galactic plane.

Objects in the All Sky Survey

• In this way, we found– 4272 galaxies– 382 other

extragalactic objects– 399 Galactic objects– among them, 349

Milky Way stars– for 101 sources it

remains unclear whether they are Galactic or not

– only 22 sources were left unidentified

Color-color diagram (an example)

We found that we can define a separation line on practically all the FIS color-color plots to select >97% of galaxies and reject > 80\% of stars. (Pollo, Rybka & Takeuchi, 2010, A&A).

galaxies

stars

Other and unidentified objects

Only sources with the best photometry:

stars (green)

galaxies (red) other

(violet)

Star-galaxy separation in the color-color plots

• Color-color diagrams allow for a very good star-galaxy separation

• Stars form two branches: – a bigger, “bluer” branch is dominated by optically

bright stars, mostly evolved stars and pulsating variables (often Mira-type)

– a smaller branch overlapping galaxies contains few bright stars with known IR excess (due to, e.g. dusty disks) – most notable among them is Vega, some faint (poorly known) stars and a certain number of planetary nebulae

Star-galaxy separation in the color-color plots

• Our method allows for a good separation of galaxies from stars – the contamination of a “blue branch” of stars by galaxies is very low

• This applies to FIR-bright objects from outside of the Galactic plane

• Most of the observed galaxies (with known z) are nearby galaxies (z<0.1) – however, we expect that more distant galaxies should be even redder – the method should remain valid

Modeling of the galaxy evolution

Galaxies evolve in various senses. Among others, the most prominent aspect of galaxy evolution is that of stellar population and resulting change of metallicity, appearing in their colors and spectral features (lines, breaks, etc.). This is the key factor of galaxy evolution.

-> evolutionary synthesis models of galaxies Evolution of galaxies can be studies in various ways.

One of them is the detailed analysis of one particular galaxy with the aim to apply the conclusions to a broader class of similar galaxies. The most obvious candidate for such “case studies” is, of course, our Milky Way.

Modeling of the galaxy spectral evolution

• Key ingredients:– Various populations of stars– Interstellar matter: dust and gas– Relations between star formation and late

stages of stellar evolution: through the content of interstellar matter

– This can be tested observationally mainly thanks to the IR data

Evolution of Stars

The life of stars is determined by their initial mass.

Light stars live long, end with a moderate ejection of gas and subsequent cooling.

Heavy stars live short, end with violent explosions and mass ejections.

Stellar evolution: the Hertzsprung-Russel (HR) diagram

(Schaller 1992)

Timescales:Main sequence lifetimes1.0 Msun: 9.0×109 yr2.2 Msun: 5.0×108 yr15 Msun: 1.0×107 yr

Giant branch lifetimes1.0 Msun: 1.0×109 yr2.2 Msun: 3.8×107 yr15 Msun: 1.5×106 yr

Supply of metals to the intergalactic space occurs

mainly by: Stellar winds Matter ejections in the final stages of life of

(more or less massive) stars 1) supernovae 2) planetary nebulae

-> To reproduce well galaxy spectra (and their evolution), we need to trace accurately 1) their stellar populations and their evolution 2) metal supply due to various mechanisms

Supply of metals to the interstellar space I: stellar wind

Some of very massive stars expel their outer hydrogen layer by radiation pressure: stellar winds. This occurs for almost all stars, but is especially efficient for OB and Wolf-Rayet stars.

This is often observed with a specific spectral feature: P-Cygni profile.

Supply of metals to the interstellar space I: stellar wind

WR124

Stars with masses similar to the Sun run out the hydrogen in the core, change their equilibrium structure and expand, and become cool huge stars (red giant branch stars: RGBs).

After the RGB phase, these stars become unstable and repeat expansion and contraction (thermal pulse asymptotic giant branch stars: TPAGB). Because of this pulsation, the outer layer of a star is expelled into the interstellar space and forms a gas nebula, called planetary nebula (PN). The nebulae expand into the space, mix with the interstellar medium (ISM), and provide heavy elements contained in the gas.

The death of light stars : planetary nebulae (PNe)

Supply of metals to the interstellar space II: final life stages of stars

M57 (Ring Nebula)

NGC6543 (Cat’s Eye Nebula)

Menzel 3 (Ant Nebula)

Then, finally they end their life with a very energetic explosion (supernova: SN). The ejected gas from a star forms a nebula, called a supernova remnant (SNR). This also provides the ISM with heavy elements.

The death of heavy stars : supernovae explosions

Stars several times heavier than the Sun repeat expansion and contraction, and change their internal structure a few times depending on the mass.

BC93 Fig. 4a BC93 Fig. 4d

Evolutionary synthesis of galaxy spectra: how to use all the ingredients to model the galaxy evolution

(Bruzual & Charlot 1993)

The effect of star formation history (in optical (as below) we can do it quite well, but other ranges are covered much less in detail, especially FIR )

AGB stars dominate the light of intermediate-age stellar populations

Main Sequence +

He-burning stars dominate the light of young stellar populations

RGB stars dominate the light of old stellar populations

Evolutionary synthesis of galaxy spectra: recent development

Including the late-stage evolution of stars

(Maraston 2005)

The effect of TPAGB stars

AGB and post-AG stars in the Milky Way halo and their input

to the FIR flux of the Galaxy

Among 330 Galactic point sources with the full (new) photometric information outside of the Galactic plane:

270 (i.e. >80 %) are AGB and post-AGB stars60 (~20 %): YSO, MS stars, binaries and

multiple systems, HII regions, supergiants and red giants, faint stars...

Outside Galactic plane, the AGB and post-AGB stars dominate in number among the point sources

AGB and post-AGB stars in the FIR color-color diagrams

Different types of AGB stars are places similarly in the FIR CC diagrams but post-AGB stars form two distinct groups

Input to the FIR flux of the MW from the point sources

• The input from the AGB and post-AGB stars: around 80% (similarly to contribution in number), decreasing above 100 microns


• The input post-AGB stars only: around 20% (while their contribution in number is around 10%), does not decrease above 100 microns


• AGB stars are an important source of the FIR flux

• The contribution from PNe is larger than from AGB stars

• And this ratio is rising with λ, especially after 100 microns

“Red” and “blue” PNe (in FIR)

• This last effect is obviously related to the presence of especially red (as red as galaxies) sub-population of PNe

• However, there is also, equally numerous, sub-population of PNe mixed with AGB stars (admittedly, keeping closer to its red part, but within the area)

“Red” PNe

M 1-7

NGC 3271-2

NGC 3195

IC4406 (Retina N.)

Sp 3M 57

NGC 6905 (Blue Flash)

NGC 2932 Eskimo

“Blue” PNe

A 78

FFrosty Leonis (PPNe)

IC 2149

NGC 3242 (Ghost of Jupiter)

NGC 7009 (Saturn N.)

NGC 7662 (Blue Snowball)

NGC 6826 Blinking N.

NGC 2818

Can we spot any difference between them

• Not so easy but:– “Red” PNe are seem to be often older,

larger, have better developed structures (often bipolar)

– Then:• It is possible that PNe move to the redder part

of the diagram (i.e. become more luminous at λ>100 μ) at more advanced evolutionary stages

• In such a case it could be interpreted as cooling of the dust grains in the nebula

• Does it have anything to do with bipolarity (or brightness in the FIR in general)?

Conclusions• Galaxies and stars can be reasonably well

separated using the FIR information only• The luminous in FIR point sources in the

Milky Way halo are mainly AGB and post-AGB stars, with the contribution from the planetary nebulae rising with the wavelength (especially after 100 μ)

• Some PNe are redder in FIR than the other – an effect of evolution or other factors as well?

• Can this information be used for modeling of the FIR spectra of outer parts of large spiral galaxies?

How does it apply to the Galactic plane

• In the remaining part (i.e. disk an bulge of the Galaxy):

– much more unidentified sources (40% vs 0.5% in the analyzed part) – this is probably related to much better resolution of AKARI with respect to previous experiments

– much less galaxies (15% vs 80%)– similar percentage (!) of stars and nebulae – again,

the reason is most probably the limited resolution of previous observations

– much more sources of unknown nature (observed before but not identified) – 30% vs 3%

– classification of objects from the Galactic plane will require more and much more careful analysis

galaxies (and stars) in the far infrared: results from the akari all-sky survey agnieszka pollo ipj...

Documents

ir iras

ir windows

ir bands

far infrared

mid midir

ir point sources

cosmic ir background

infrared windows