▪ Abstract More than a decade ago the IRAS satellite opened the realm of external galaxies for studies in the 10 to 100 μm band and discovered emission from tens of thousands of normal and active galaxies With the 1995–1998 mission of the Infrared Space Observatory1, the next major steps in extragalactic infrared astronomy became possible: detailed imaging, spectroscopy, and spectrophotometry of many galaxies detected by IRAS, as well as deep surveys in the mid- and far-IR The spectroscopic data reveal a wealth of detail about the nature of the energy source(s) and about the physical conditions in galaxies ISO's surveys for the first time explore the infrared emission of distant, high-redshift galaxies ISO's main theme in extragalactic astronomy is the role of star formation in the activity and evolution of galaxies

Extragalactic Results from the Infrared Space Observatory

Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.

/pdf/a-swedish-heterodyne-facility-instrument-for-the-apex-1vcbnlegc4.pdf

A Swedish heterodyne facility instrument for the APEX telescope

We present the results of a homogeneous X-ray analysis for 82 nearby low-ionisation, narrow emission-line regions (LINERs) selected from the catalogue of Carrillo et al. (1999, Rev. Mex. Astron. Astrofis., 35, 187). All sources have available Chandra (68 sources) and/or XMM-Newton (55 sources) observations. This is the largest sample of LINERs with X-ray spectral data (60 out of the 82 objects), and it significantly improves our previous analysis based on Chandra data for 51 LINERs (Gonzalez-Martin et al. 2006b, A&A, 460, 45). It both increases the sample size and adds XMM-Newton data . New models permit the inclusion of double absorbers in the spectral fits. Nuclear X-ray morphology is inferred from the compactness of detected nuclear sources in the hard band (4.5–8.0 keV). Sixty per cent of the sample shows a compact nuclear source and are classified as active galactic nucleus (AGN) candidates. The spectral analysis indicates that best fits involve a composite model: 1) absorbed primary continuum and 2) soft spectrum below 2 keV described by an absorbed scatterer and/or a thermal component. The resulting median spectral parameters and their standard deviations are  = 2.11 ±  0.52,  = 0.54 ±  0.30 keV,  = 21.32  0.71 and  = 21.93  1.36. We complement our X-ray results with an analysis of HST optical images and literature data on emission lines, radio compactness, and stellar population. After adding all these multiwavelength data, we conclude that evidence supports the AGN nature of their nuclear engine for 80% of the sample (66 out of 82 objects).

http://digital.csic.es/bitstream/10261/20275/1/0905.2973.pdf

An X-ray view of 82 LINERs with Chandra and XMM-Newton data

Galaxy interactions at low and high redshift

We report the results of our ongoing search for extincted supernovae (SNe) at near-infrared wavelengths. We have monitored at 2.2m a sample of 46 Luminous Infrared Galaxies and detected 4 SNe. The number of detections is still small but sucient to provide the first estimate of supernova rate at near-infrared wavelengths. We measure a SN rate of SN NIR = 7:6 3:8 SNu which is an order of magnitude larger than observed in quiescent galaxies. On the other hand, the observed near- infrared rate is still a factor 3 10 smaller than that estimated from the far-infrared luminosity of the galaxies. Among various possibilities, the most likely scenario is that dust extinction is so high ( AV> 30) to obscure most SNe even in the near-IR. The role of type Ia SNe is also discussed within this context. We derive the type Ia SN rate as a function of the stellar mass of the galaxy and find a sharp increase toward galaxies with higher activity of star formation. This suggests that a significant fraction of type Ia SNe are associated with young stellar populations. Finally, as a by-product, we give the average K-band light curve of core-collapse SNe based on all the existing data, and review the relation between SN rate and far-infrared luminosity.

/pdf/the-infrared-supernova-rate-in-starburst-galaxies-5e50vt0rxu.pdf

The infrared supernova rate in starburst galaxies

Ring galaxies are believed to represent a special case of a collision between two galaxies, in which one of the galaxies impacts and passes through the center of another disk system (e.g. Lynds & Toomre 1976). Although rare, this kind of low orbital-angular-momentum collision leads to a recognizable structure, namely a luminous blue star-forming ring (Appleton & Marston 1997), which should be easily identifiable even at moderate redshift. Indeed, Lavery et al. (dy1996) have used this fact, and their relative rarity at low-redshift, to conclude that rings (and therefore presumably all collisions) are over-represented in deep HST fields.

Collisional Ring Galaxies

We present the first mid-infrared (Mid-IR) ($\lambda5-15\mu$m) and radio continuum ($\lambda\lambda$20,~6 and 3.6 cm) observations of the star-forming collisional ring galaxy VII Zw 466 and its host group made with the Infrared Space Observatory and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20m radio telescope and upper limits were placed on the mass of molecular gas in those galaxies. The ring galaxy is believed to owe its morphology to a slightly off-center collision between an `intruder' galaxy and a disk. An off-center collision is predicted to generate a radially expanding density wave in the disk which should show large azimuthal variations in overdensity, and have observational consequences. The radio continuum emission shows the largest asymmetry, exhibiting a crescent-shaped distribution consistent with either the trapping of cosmic-ray particles in the target disk, or an enhanced supernova rate in the compressed region. On the other hand, the ISO observations (especially those made at $\lambda9.6\mu$m) show a more scattered distribution, with emission centers associated with powerful star formation sites distributed more uniformly around the ring. Low-signal to noise observations at $\lambda15.0\mu$m show possible emission inside the ring, with little emission directly associated with the \ion{H}{2} regions. The observations emphasize the complex relationship between the generation of radio emission and the development of star formation even in relatively simple and well understood collisional scenarios.

Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations

We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk of NGC 1144, but HI emission is detected over only 1/3 of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is observed. Faint, narrow HI absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes regions of massive star formation and a Seyfert nucleus. The peculiar HI distribution, which is concentrated in the NW disk, seems to be the inverse of the molecular distribution which is concentrated in the SE disk. Although this may partly be the result of the destruction of HI clouds in the SE disk, there is circumstantial evidence that the entire HI emission spectrum of NGC 1144 is affected by a deep nuclear absorption line covering a range of 600 km/s, and is likely blueshifted with respect to the nucleus. In this picture, a high column-density HI stream is associated with the nuclear ionized gas velocity discontinuity, and the absorption effectively masks any HI emission that would be present in the SE disk of NGC 1144.

The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

Ring galaxies are believed to represent a special case of a collision between two galaxies, in which one of the galaxies impacts and passes through the center of another disk system (e.g. Lynds & Toomre 1976). Although rare, this kind of low orbital-angular-momentum collision leads to a recognizable structure, namely a luminous blue star-forming ring (Appleton & Marston 1997), which should be easily identifiable even at moderate redshift. Indeed, Lavery et al. (1996) have used this fact, and their relative rarity at low-redshift, to conclude that rings (and therefore presumably all collisions) are over-represented in deep HST fields.

/pdf/collisional-ring-galaxies-1cfonnld32.pdf

We present mid-infrared images at 6:7 m and 15 m of "The Cartwheel" (AM 0035-33), the prototypical col- lisional ring galaxy. The observations, taken with ISOCAM, reveal the distribution of hot dust in the galaxy and its two com- panions in the north-east. The intensity of the Mid-IR emission from the outer star forming ring of the Cartwheel shows con- siderable azimuthal variation and peaks at the most active H region of the ring. The 15 m to 6.7 m flux ratio of 5.2 is the highest among all the galaxies of our sample. A surprising result of our observations is the discovery of significant emission from the inner regions of the galaxy, including the inner ring, spokes and nucleus, where previously only low level H emission had been reported. At 6.7 m, this emission is stronger than the one from the outer star forming ring, and at 15 m, it represents 40% of the emission from the outer ring. The H to Mid-IR flux ratios from the inner regions are consistent with the heating of grains from weak star formation activity. ? Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the partici- pation of ISAS and NASA.

http://aa.springer.de/papers/9341001/2300069.pdf

Dust in the wheel: The Cartwheel galaxy in the Mid-IR

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Collisional Ring Galaxies

Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations

The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

Collisional Ring Galaxies

Dust in the wheel: The Cartwheel galaxy in the Mid-IR