A multi-band view on the evolution of A multi-band view on the evolution of starburst merging galaxiesstarburst merging galaxies

Yiping Wang（王益萍）

Purple Mountain Observatory, China

National Astronomical Observatories of China

In 70’s, a few very luminous infrared galaxies were

observed

In 80’s, IRAS satellite gave for the first time a proper census of the infrared emission of galaxies (up to Lir ~10^12 Lsun) at low redshift.

Lagache et al. 2005

Emission properties of infrared galaxies

Stellar light

PAH bump Dust emission

(Sanders & Mirabel 1996)

IR Local Luminosity Function:

IRAS number counts:(Hacking et al. 1987)

Spitzer deep surveys could reach LIGs down to redshift z~3.

IRAS 80’s ~100mJy

ISO (late 90’s) ~0.1mJy

Spitzer (now) ~0.01mJy

ISOCAM and Spitzer 24um source counts:

Papovich et al. 2004Elbaz et al. 1999

Z<0.3

Z<2

a) ~100% local ULIGs are merging systems (Kim et al. 2001);

b) >50% high redshift ULIGs give indication of interacting; part of SCUBA sources are suggested to be high redshift counterparts of local ULIGs and LIGs (Smail et al. 1998)

Nature of local and distant ULIGs:

Morphological study of distant Spitzer galaxies

ACS images in CDF-S/GEMS area (Papovich et al. 2004)

Statistics given by Bell et al. 2005: (z~0.7, 1500 galaxies)Strongly interacting galaxies <30% Spiral morphologies >50%E/S0 morphologies ~20%

X 2 in the deeper GOODS data

Aggregation dynamics and the simultaion

Why do such a model?1)Statistically understand the role w

hich mergers actually could play in the galaxy evolution studies.

2)Whether ULIGs and LIGs could evolve in a continuous way.

3)Whether density and luminosity evolution could come out naturely and simply.

Modelling the infrared burst phase at high z

1) Mass-light ratio for faint blue starburst galaxies

L/L = ( M/M )^L (z) ~ f(z, )

where Cavaliere & Menci, 1997)

2) ULIGs from gas rich mergers of high redshift

=2.8 (an infrared burst phase) (observation and N-body )

3) Differential dimming ~ (L_{ir}/Lc)^ means the

brighter ones dim faster.

(Wang & Biermann 2000, Wang 2002)

~0.4 at FIR

Selected SEDs for ULIGs and LIGs:

Model fitting of ISOCAM and Spitzer results:

Perez-Gonzalez et al. 2005Franceschini et al. 2001

Cosmic star formation history associated with accretion

based on X-ray deep surveys (Wang et al. 2003)

The contribution of LIGs, ULIGs to the 24um source counts:

Source count fitting at longer wavelengths:

Constraints from Spitzer & VLA deep surveys:

Cowie et al. 2004

Barger et al. 2000

Stellar budget estimation (upper limits):

Stellar budget estimation (upper limits):

Conclusions:1)A population of LIGs or ULIGs triggered by galactic interactions at z~1 could successfully account for the upturn of IRAS, ISO, Spitzer and VLA number counts at faint flux level. .2)The decrease of merger rate with cosmic time alone is not sufficient for such strong evolution, an infrared burst phase is crucial for the steep slope of the ISO and Spitzer differential counts at sub-mJy.

3)Dusty starburst galaxies triggered by galactic interactions at z~1 would contain about 30%~50% of the stellar mass in the Universe, Comparing with the NIR deep surveys and the background measurements.