1 Introduction

Ultra-luminous IR galaxies (ULIRGs) emit the bulk of their energy in the mid- and far-infrared with $L_{\rm IR} > 10^{\rm 12}$ $L_{\odot}$. Optical and near-infrared images show a disturbed morphology and signatures of interaction and merging. Spectra show emission lines characteristic for strong starbursts, shocks (LINERs) and in some cases also Seyfert types (AGNs). Sanders et al. (1988a) suggested that the ULIRGs form an evolutionary link between starburst galaxies and quasars. The current literature and the research state are excellently reviewed by Sanders & Mirabel (1996), and most recently by Genzel & Cesarsky (2000).

Here we focus on the following topics:

1)

While the luminosity of an ULIRG originates from warm T > 100 K and cool T > 30 K dust, the bulk of the dust in normal spiral galaxies is much colder at $T \approx 15$ K. Do ULIRGs also have such cold cirrus-like dust, or is all the dust already heated up to T > 30 K? This is observationally related to: how does the IR SED continue beyond 100 $\mu$m into the submm range? For bright but less luminous IRAS galaxies a three component model - with cirrus, starburst and AGN dust - has been proposed and successfully applied by Rowan-Robinson & Crawford (1989).

2)

What can we learn about the evolution of ULIRGs from such a cold dust stage? How far can the merging state be inferred from the relative amounts of cool and cold dust? For example, with respect to the Sanders et al. (1988a) conjecture this means: do AGN-ULIRGs have less cold dust than starburst dominated SB-ULIRGs?

3)

Can the dust mass and opacity provide clues in favour of or against hidden AGNs? How does this compare to the near- and mid-IR emission of ULIRGs whose optical and MIR spectra favor their power to be dominated by either AGNs or SBs? Observationally this relates to measuring the NIR-MIR SEDs, which are currently known only for a few ULIRGs.

These topics introduce new aspects for exploring the ULIRGs. In this paper, based on IR to mm photometry, we present a sample of observational templates, and confine the discussion to a few basic implications, which may further stimulate more detailed analyses.

 

 

Table 1: Measured flux densities in Jy as a function of wavelength in $\mu$m. The objects are listed by IRAS name, except when another name is more common, then the IRAS name is given in the footnote. The statistical errors from signal processing are typically about 5% at 100-150 $\mu$m, and reach in the other passbands 10-20% of the quoted fluxes depending mainly on the source/sky brightness contrast as seen by the apertures used. In case of uncertainties larger than 30% 3$\sigma$ upper limits are listed. The apertures used are 30 $\hbox {$^{\prime \prime }$ }\times 30\hbox {$^{\prime \prime }$ }$ at 1.2 and 2.2 $\mu$m, circular with 52 $\hbox {$^{\prime \prime }$ }$ diameter at 10-25 $\mu$m, 46 $\hbox {$^{\prime \prime }$ }\times 46\hbox {$^{\prime \prime }$ }$ at 60 and 90 $\mu$m, 184 $\hbox {$^{\prime \prime }$ }\times 184\hbox {$^{\prime \prime }$ }$ at 120-200 $\mu$m, and circular with 8 $\hbox {$^{\prime \prime }$ }$, 15 $\hbox {$^{\prime \prime }$ }$, 24 $\hbox {$^{\prime \prime }$ }$ diameters at 450, 850, 1300 $\mu$m, respectively.

Name	1.2	2.2	10	12	15	25	60	90	120	150	180	200	450	850	1300
00199-7426			0.057	<0.120	0.09	0.25			7.50	5.34	4.21	3.00
00262+4251*	0.0054	0.0055	<0.087	0.043	0.10	0.36	3.36	2.60	2.90	2.40	2.40	<2.10
00406-3127									0.77	0.63	0.44	0.32
03068-5346			<0.063	0.040	0.05	0.15	3.60	3.34	3.33	2.78	1.72	1.35
03158+4227			<0.165	0.085	<0.21	0.25	5.25	3.88	3.19	1.75	<1.79	1.05
03538-6432									1.37	1.07	0.85	0.62
04232+1436	0.0055	0.0106	<0.108	0.065	0.07	0.39	3.88	4.14	3.50	2.30	1.60	1.10
05189-2524			0.600	0.800	1.00	3.08	13.02	10.70	10.00	6.80	4.36	3.84			<0.036
06035-7102			0.090	0.130	0.15	0.53	5.86	5.05	5.15	2.90	2.01	1.35
06206-6315			<0.072	0.040	0.11	0.24	4.84	4.20	4.57	2.90	1.87	1.50
12112+0305			0.065	0.100	0.20	0.44	9.94	8.95	8.31	5.87	3.93	2.93
MK231a			1.425	2.400	2.90	8.66	31.68	27.34	24.32	14.74	9.75	6.88
MK273b			0.100	0.250	0.50	2.07	27.45	23.78	19.99	13.10	8.69	7.40
MK463c			0.425	0.580	0.80	1.79	2.33	1.94	1.60	0.99	<0.84	0.45
14348-1447			<0.096	0.108	<0.27	0.42	8.21	7.23	6.66	5.61	3.76	2.69	0.21	0.024	<0.009
14378-3651			<0.276	<0.399	<0.36	0.41	8.53	7.49	5.90	3.60	2.80	2.45			<0.010
15245+1019			<0.084	0.051	<0.18	0.22	5.25	5.43	5.58	3.60	1.94	1.31
15250+3609			<0.267	0.238	0.56	1.31	8.63	6.66	4.16	2.37	1.60	1.16
Arp 220d			0.147	0.600	1.14	8.28	113.35	111.50	109.00	87.89	63.95	54.81
15462-0450*			0.064	0.100	0.15	0.38	2.81			2.80	2.44	<2.5
16090-0139			<0.252	0.100	<0.21	0.20	6.70	5.80	4.00	2.75	2.00	1.21	<0.13	<0.017
NGC 6240e			0.259	0.750	1.00	3.31	23.60	26.70	25.90	18.91	12.73	9.00	1.00	0.150
17208-0014			0.080	0.200	0.25	1.32	32.22	31.90	30.00	23.00	17.50	12.50	1.07	0.155
17463+5806									0.63	0.58	0.37	0.23
18090+0130*	0.0200	0.0195	0.187	0.300	<0.38	0.59			16.63	14.50	10.48	9.74
18470+3234	0.0027	0.0036	<0.081	0.135	0.15	0.44	4.15	3.55	3.20	2.45	1.70	1.25
19254-7245f			0.123	0.200	0.40	1.32	5.57	5.26	4.27	3.06	2.30	1.61			0.012
19458+0944*			<0.396	<0.540	<0.77	0.26		5.82		7.61		7.05
20046-0623	0.0039	0.0040	<0.084	0.125	<0.39	0.47	4.50	4.71	3.69	3.18	2.79	1.40	<0.16	<0.026
20087-0308			<0.117	0.070	0.10	0.25	5.54	4.85	5.96	4.05	2.95	2.30	<0.10	<0.010
20100-4156			<0.090	0.090	0.14	0.34	6.53	5.11	4.51	3.36	2.09	1.86			<0.014
20414-1651			<0.168	<0.117	<0.18	0.25	6.16	4.22	3.60	2.56	1.54	<1.35
ESO 286-19g			<0.204	0.275	0.50	2.11	13.90	9.26	6.73	4.14	2.56	1.80
21130-4446			<0.090	0.055	<0.45	0.15	4.03	3.60	4.50	3.94	3.14	2.90			<0.023
21504-0628	0.0055	0.0057	0.040	0.050	0.15	0.28	3.33	2.82	2.80	1.52	1.26	0.70	<0.11	<0.016
22491-1808			<0.063	0.080	0.11	0.50	6.80	5.45	3.55	2.70	1.95	1.70	<0.20	0.019
ESO 148-2h			0.126	0.250	0.36	1.55	12.50	11.36	10.00	6.40	4.70	3.50
23230-6926			0.035	0.060	0.10	0.29	4.80	3.98	4.10	3.00	2.00	1.70			0.010
23365+3604	0.0075	0.0065	<0.120	0.080	0.15	0.65	7.78	6.76	6.75	4.81	3.35	3.01	0.17	0.020
23389-6139			<0.075	0.031	<0.26	0.20	3.88	3.30	4.03	2.83	1.99	1.52			<0.005
23515-2917									0.80	0.64	0.48	0.33

^* ISO data partly distorted and uncertain; ^a 12540+5708; ^b 13428+5608; ^c 13536+1836; ^d 15327+2340; ^e 16504+0228; ^f "Super-Antennae''; ^g 20551-4250; ^h 23128-5919.