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Ultraviolet and far-infrared observations of galaxies: constraints on dust attenuation. V. Buat, J. Iglesias-Paramo, D. Burgarella, A. Inoue, P. Panuzzo, T. Takeuchi Tracing dust in spiral galaxies:radiative transfer studies in the dawn of a new generation of observing facilities-

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ultraviolet and far infrared observations of galaxies constraints on dust attenuation

Ultraviolet and far-infrared observations of galaxies: constraints on dust attenuation

V. Buat, J. Iglesias-Paramo, D. Burgarella, A. Inoue, P. Panuzzo, T. Takeuchi

Tracing dust in spiral galaxies:radiative transfer studies in the dawn of a new generation of observing facilities-

Gent 14-16 may 2007

the galex surveys p i c martin caltech participation of cnes lam
The GALEX surveysP.I: C. Martin, Caltech, participation of CNES/ LAM

GALEX satellite, launch: Avril 2003, still observing

Imaging mode at 1530Å(FUV) and 2315 Å (NUV), spatial resolution ~5 arcsec, FOV~1 deg2

  • « All Sky » Shallow Imaging [email protected] 20-21ABmag/14000 fields
  • Medium Imaging [email protected] 23 ABmag/1200 fields
  • Deep Imaging Surveys @ 25.5 ABmag/150 fields
  • Nearby Galaxies Survey: ~1000 galaxies

Slitless spectroscopy in the FUV and NUV bands

X-correlations with surveys at other wavelengths

slide4
Z=0 samples and related studies

FIR (60µm) SELECTED SAMPLE

  • IRAS(PSCZ) / GALEX AIS: UV photometry of each IRAS source

94% detected in FUV-1530A (FUV< 20.5 AB mag)

93% of the sources detected in H (2MASS) stellar masses

all the galaxies have a known distance (radial velocity)

FUV SELECTED SAMPLE

  • GALEX (FUV(1530A) / IRAS(FSC)

83% detected at 60 microns

89% of the sources detected in H (2MASS)  stellar masses

91% of the galaxies have a known distance (radial velocity)

First samples (Buat et al. 05): ~100 sources in each sample

Second samples (Buat et al. 06) ~750 sources in each sample

Unfortunately the overlap with SDSS is very small: 20% of the FOV

slide5
LTIR/LFUV (i.e. dust attenuation) versus Lbol young stars

(Buat et al. 06, ApJS in press, astroph 0609738)

A(FUV)

  • A general increase of the dust attenuation with the luminosity (SFR of the galaxies).
  • Similar trends for different selections for intermediate luminosities 109
  • For bright IR selected galaxies: a monotonic increase
  • For bright UV selected galaxies: some hint for a lower dust attenuation than for IR galaxies of the same Lbol

4 mag

2 mag

0.5 mag

(TIR+FUV)

  • LTIR : 8-1000 µm, LFUV : . L
  • A(FUV) is calculated as a function of log(LTIR/LFUV) using the calibration of Buat et al 2005
slide6
LTIR/LFUV (i.e. dust attenuation) versus Mstar at z=0:

A shallow increase of LTIR/LFUV when Mstar increases

theoretical models show that the f dust f uv flux ratio is a robust tracer of the dust attenuation
Theoretical modelsshow that the Fdust/FUVflux ratio is a robust tracer of the dust attenuation

A(NUV) mag

Various star formation histories Buat et al 05 ApJL special issue (GALEX)

Various geometries/dust properties

Gordon et al. 2000

slide8
The « IRX-ß » in galactic disks

We will focus on studies based on integrated fluxes or data averaged over large disk areas

IRX: Ldust/LUV ( sometimes LFIR(40-120 µm)/LUV), a quantitative tracer of dust obscuration

ß: slope of the UV continuum with f()  , estimated from the FUV-NUV color for GALEX data,

ß is expected to be constant after more than 10 Myr of active star formation, any departure is attributed to a wavelength dependent dust attenuation

A tight relation is found for starburst galaxies (Meurer et al. 99) from IUE and IRAS data

models predict dispersed relations between and the attenuation witt gordon 2000
Models predict dispersed relations between  and the attenuation(Witt & Gordon 2000)

A shell distribution and no bump (SMC) are necessary to reproduce the starburst distribution with these models

slide11
The complexity of the IRX-ß plot is confirmed by the first GALEX results (Buat et al. 05 ApJL GALEX special issue, also Seibert et al. 05)

The galaxies do not follow the starburst relation (solid line, Meurer et al. 99) UV selected galaxies under the line, FIR selected galaxies also above the line

(~slope  with f()  )

a result already suggested by pre galex works but with smaller statistics
A result already suggested by pre-GALEX works but with smaller statistics

Bell, 2002, normal galaxies

Goldader et al. 2002, ULIRGs

slide13
« IRX-ß » relation for radial profiles in galaxiesBoissier et al. 2007 ApJS GALEX special issue astroph/0609071
  • Radial profiles for large late-type galaxies with GALEX+IRAS data: again under the « starburst line »
sings sample dale et al 06
SINGS sample (Dale et al. 06)

From Cortese et al. 06

how to interpret these results
How to interpret these results?

The main parameters at work in the IRX-ß plot:

  • The star formation history
  • The dust attenuation: dust characteristics+geometry
  • The IMF (not discussed here)
  • Aperture mismatch between UV (IUE) and IR (IRAS) data for starbursts.
  • Lots of works about the IRX-ß diagnostic:

E.g. Calzetti et al. 05, Boissier et al. 07. Gil de Paz et al. 07, Dale et al. 06, Panuzzo et al. 07, Inoue et al. 06, Burgarella et al. 05, Kong et al. 04, Bell 02, Cortese et al. 06 etc…

My presentation is obviously not exhaustive and probably biased…

slide16
Different star formation histories can lead to some dispersion and may explain the locus of galaxies below the starburst curve (Kong et al 04)

b= sfr0/

Kong et al 2004

Dust attenuation curve from Charlot & Fall (2000)

Log(Ldust/LFUV)

-2 -1  0 1

slide17
Only a very weak trend (if any) is observed between the distance to the starburst line and the birthrate parameter

Panuzzo et al. 2006, UV selection

Cortese et al. 06, Virgo galaxies

dS isthe distance from the starburts line

slide18
An important issue/advantage:the GALEX NUV band overlaps the bump at 2175 Å of the MW extinction curve

MW extinction curves

Starburst attenuation curve

LMC ext. curve

SMC ext. curve

FUV NUV

From Calzetti 2001

grasil models with various scenarii of dust attenuation panuzzo et al 07 mnras 375 640
GRASIL models with various scenarii of dust attenuationPanuzzo et al. 07,MNRAS 375, 640

Starburst line

  • A modified GRASIL model: age dependent extinction AND molecular clouds (t
the role of the albedo inoue et al 2006 mnras 370 380
The role of the albedoInoue et al. 2006, MNRAS 370, 380
  • Young stars (<10 Myr) :clumpy distribution, Molecular Clouds
  • 10-300Myr old stars: smooth dist, clumpy medium, h(stars)
  • >300Myr stars: smooth dist, smooth medium, h(stars)>h(dust)
  • Exponential SFR, e folding rate: 5 Gyr
  • Data from Buat et al 05:
  • UV selection & FIR selection
  • & Models
the role of the albedo 2
The role of the albedo(2)
  • Best models: SMC (Witt & Gordon 2000) albedo ~ct
  • LMC (Weingartner & Draine 2001) albedo 
  • (like in GRASIL models)

Screen configuration

Calzetti law

UV selection

FIR selection

models

X

O

the role of albedo 3 derived attenuation curves
The role of albedo (3):Derived attenuation curves

The amplitude of the bump 

and the attenuation law flattens

when extinction 

Also found in other studies (models and data)

an empirical modeling burgarella buat iglesias paramo 05 mnras 360 1413
An empirical modelingBurgarella, Buat & Iglesias-Paramo 05, MNRAS, 360, 1413
  • Populations synthesis models (PEGASE 2) with an exponential SFR+ burst
  • An empirical law for dust attenuation with two parameters: a slope and a (gaussian) bump
  • K()=+Abump exp( -(-mean )2/2)
  • mean = 2175 Å & = 200 Å
  • -2<<-0.25 & 0
  • Range of values covering « classical » extinction and attenuation curves
  • Bayesian method
aperture effects in the irx relation for starbursts seibert et al in prep
Aperture effects in the IRX-ß relation for starbursts- Seibert et al. In prep.

~30 IUE starbursts observed by GALEX

IUE aperture: 10x20 arsec2

Galaxy size: 1 arcmin or more

Shift of the galaxies to redder colors and lower Fdust/Ffuv ratios when integrated fluxes from GALEX are used

Galex/IRAS data

Original IUE/IRAS data

galex spectroscopy may help at understanding dust obscuration processes
GALEX spectroscopy: may help at understanding dust obscuration processes

Rosa-Gonzales et al.

On-going work…

galex spectroscopy of 2 galaxies observed by spitzer
GALEX spectroscopy of 2 galaxies observed by SPITZER

FUV

24 µm

NUV

We subtract a dust-free model(instantaneous starburst or continuous SF) to the observed spectrum dust attenuation curve

Z=0.075

CDFS

70 µm

160 µm

B

V

slide29
Evolution with redshift:IR and UV luminosity densities increase with z but at a different rate: we must understand why

Each wavelength range measures a fraction of the Star Formation in the Universe and their relative contribution evolves with z

Takeuchi, Buat & Burgarella 05

Spitzer 24 m

Galex

slide30
High z studies:

SPITZER/MIPS & GALEX

  • MIPS-GTO/GALEX: CDFS (deep fields ~0.25 deg2 in common)
  • Selection at 24 µm of 190 LIRGs at z~ 0.7
  • 83% detected in NUV (2300 A)--> FUV (1500 A) rest-frame

2. Selection of 420 Lyman Break Galaxies at z~1from GALEX

  • FUV-NUV>2, Xcorrelation with Combo-17 and ESO Imaging Survey
  • 25% detected at 24 µm
  • SWIRE/GALEX sample from z=0.2 to z=0.7 cf Jorge’s talk
slide31
FUV emission of Luminous InfraRed Galaxies (LTIR>1011Lsun) at z=0.7 as compared to a complete sample of LIRGs at z=0

Buat et al. A&A in press/ astroph0703014

The distributions of LTIR/LFUV are found different (confidence level

larger than 95%): the mean dust attenuation decreases by 0.4 mag

=3.82 0.1 mag =3.36 0.1 mag

LIRGs z=0

slide32
GALEX/MIPS-GTO: IR emission of LBGs at z~1

A lower (~1 mag) dust attenuation than for the FUV selection at z~0

Burgarella et al. A&A submitted

Fully consistent with the results of Reddy et al. 05 for an optical-NIR selection of galaxies at z~2

final comments about on going and future works
Final comments about on going and future works

Lots of other works not presented here: metallicities, gas densities, Balmer lines, studies of dust attenuation not based on IR data

Future work:

At z=0

  • SPITZER/GALEX data on resolved galaxies will be used to explore the IRX-ß relation, especially for starburst galaxies accepted archival proposal (Madore, Boissier, Buat et al.)
  • GALEX spectroscopy on a larger sample of galaxies: ~10 very edge-on nearby galaxies & galaxies to be extracted from deep spectroscopic fields

At z>0

  • Analysis of the CDFS-GOODS field with UV and IR selected samples at z=0.7: Buat et al. in prep
  • SWIRE/GALEX analysis: Jorge’s talk…
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