L. Metcalfe

An ISOCAM survey through gravitationally lensing galaxy clusters - I. Source lists and source counts for A370, A2218 and A2390

PCT No. PCT/DE89/00650 Sec. 371 Date Mar. 6, 1991 Sec. 102(e) Date Mar. 6, 1991 PCT Filed Oct. 12, 1989 PCT Pub. No. WO90/04702 PCT Pub. Date May 3, 1990.A partial flue gas stream is used for the production of electrical energy and/or heating and operational heat by utilizing combustion heat from fossil fuels, prior to combustion dried in an indirectly heated fluidized bed dryer, with combustion flue gas used as a carrier medium for the fluidized bed dryer. The mixture of flue gases and steam, deriving from the drying process, is after an intermediate treatment, if necessary, discharged with the main flue gas stream.

The Herschel Lensing Survey (HLS): Overview

The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of ∼40 massive clusters of galaxies. The strong gravitational lensing power of these clusters will enable us to penetrate through the confusion noise, which sets the ultimate limit on our ability to probe the Universe with Herschel. Here we present an overview of our survey and a summary of the major results from our science demonstration phase (SDP) observations of the Bullet cluster (z = 0.297). The SDP data are rich and allow us to study not only the background high-redshift galaxies (e.g., strongly lensed and distorted galaxies at z = 2.8 and 3.2) but also the properties of cluster-member galaxies. Our preliminary analysis shows a great diversity of far-infrared/submillimeter spectral energy distributions (SEDs), indicating that we have much to learn with Herschel about the properties of galaxy SEDs. We have also detected the Sunyaev-Zel’dovich (SZ) effect increment with the SPIRE data. The success of this SDP program demonstrates the great potential of the Herschel Lensing Survey to produce exciting results in a variety of science areas.

Far-infrared photometry of a statistical sample of late-type Virgo cluster galaxies

We present deep diffraction-limited far-infrared (FIR) strip maps of a sample of 63 galaxies later than S0 and brighter than BT ¼ 16:8, selected from the Virgo Cluster Catalogue of Binggeli, Sandage, & Tammann. The ISOPHOT instrument on board the Infrared Space Observatory was used to achieve sensitivities typically an order of magnitude deeper than IRAS in the 60 and 100 lm bands and to reach the confusion limit at 170 lm. The averaged 3 � upper limits for integrated flux densities of point sources at 60, 100, and 170 lm are 43, 33, and 58 mJy, respectively. A total of 63.5% are detected at all three wavelengths. The highest detection rate (85.7%) is in the 170 lm band. In many cases the galaxies are resolved, allowing the scale length of the infrared disks to be derived from the oversampled brightness profiles in addition to the spatially integrated emission. The data presented should provide the basis for a variety of statistical investigations of the FIR spectral energy distributions of gas-rich galaxies in the local universe spanning a broad range in star formation activity and morphological types, including dwarf systems and galaxies with rather quiescent star formation activity. Subject headings: catalogs — galaxies: clusters: individual (Virgo) — galaxies: photometry — galaxies: statistics — infrared: galaxies — surveys On-line material: machine-readable tables

Disappearance of stellar debris disks around main-sequence stars after 400 million years

Almost 5 billion years ago, the Sun formed in a local contraction of a cloud of molecular gas. A rotating disk of gas and dust is believed to have fed material onto the proto-Sun for the first few million years of its life, and to have formed the planets, comets and other Solar System objects. Similar disks, but with less mass, have been observed around a few main-sequence stars such as Vega. The dust particles orbiting stars like Vega will be removed on timescales of the order of 1 Myr (Vega is about 350 Myr old), and therefore must be resupplied, at least for a time. But earlier surveys lacked the sensitivity to determine how many nearby stars have dust disks, and to investigate how long such disks survive. Here we report infrared observations indicating that most stars younger than 300 Myr have dust disks, while most older than 400 Myr do not: ninety per cent of the disks disappear when the star is between 300 and 400 Myr old. Several events that are related to the ‘clean up’ of debris in the early history of our Solar System have a similar timescale.

XMM-Newton (cross)-calibration

ESAs large X-ray space observatory XMM-Newton is in its fifth year of operations. We give a general overview of the status of calibration of the five X-ray instruments and the Optical Monitor. A main point of interest in the last year became the cross-calibration between the instruments. A cross-calibration campaign started at the XMM-Newton Science Operation Centre at the European Space Astronomy Centre in collaboration with the Instrument Principle Investigators provides a first systematic comparison of the X-ray instruments EPIC and RGS for various kind of sources making also an initial assessment in cross calibration with other X-ray observatories.

An Infrared Space Observatory Atlas of Bright Spiral Galaxies

In this first paper in a series we present an atlas of infrared images and photometry from 1.2 to 180 μm for a sample of bright spiral galaxies. The atlas galaxies are an optically selected, magnitude-limited sample of 77 spiral and S0 galaxies chosen from the Revised Shapley-Ames Catalog (RSA). The sample is a representative sample of spiral galaxies and includes Seyfert galaxies, LINERs, interacting galaxies, and peculiar galaxies. Using the Infrared Space Observatory (ISO), we have obtained 12 μm images and photometry at 60, 100, and 180 μm for the galaxies. In addition to its imaging capabilities, ISO provides substantially better angular resolution than is available in the IRAS survey, and this permits discrimination between infrared activity in the central regions and global infrared emission in the disks of these galaxies. These ISO data have been supplemented with JHK imaging using ground-based telescopes. The atlas includes 2 and 12 μm images. Following an analysis of the properties of the galaxies, we have compared the mid-infrared and far-infrared ISO photometry with IRAS photometry. The systematic differences we find between the IRAS Faint Source Catalog and ISO measurements are directly related to the spatial extent of the ISO fluxes, and we discuss the reliability of IRAS Faint Source Catalog total flux densities and flux ratios for nearby galaxies. In our analysis of the 12 μm morphological features we find that most but not all galaxies have bright nuclear emission. We find 12 μm structures such as rings, spiral arm fragments, knotted spiral arms, and bright sources in the disks that are sometimes brighter than the nuclei at mid-infrared wavelengths. These features, which are presumably associated with extranuclear star formation, are common in the disks of Sb and later galaxies but are relatively unimportant in S0–Sab galaxies.

An ISOCAM survey through gravitationally lensing galaxy clusters IV. Luminous infrared galaxies in Cl 0024+1654 and the dynamical status of clusters

Observations of the core of the massive cluster Cl 0024+1654, at a redshift z=0.39, were obtained with the Infrared Space Observatory using ISOCAM at 6.7 mum and 14.3 mum (hereafter 15 mum). Thirty five sources were detected at 15 mum and thirteen of them are spectroscopically identified with cluster galaxies. The remaining sources consist of four stars, one quasar, one foreground galaxy, three background galaxies and thirteen sources with unknown redshift. The ISOCAM sources have best-fit SEDs typical of spiral or starburst models observed 1 Gyr after the main starburst event. The median infrared luminosity of the twelve cluster galaxies is 1.0x10^11 Lsun, with 10 having infrared luminosity above 9x10^10 Lsun, and so lying near or above the 1x10^11 Lsun threshold for identification as a luminous infrared galaxy (LIRG). The [OII] star formation rates obtained for 3 cluster galaxies are one to two orders of magnitude lower than the infrared values, implying that most of the star formation is missed in the optical because it is enshrouded by dust in the starburst galaxy. The counterparts of about half of the 15 mum cluster sources are blue, luminous, star-forming systems and the type of galaxy that is usually associated with the Butcher-Oemler effect. Dust obscuration may be a major cause of the 15 mum sources appearing on the cluster main sequence. The majority of the ISOCAM sources in the Butcher-Oemler region of the colour-magnitude diagram are best fit by spiral-type SEDs whereas post-starburst models are preferred on the main sequence, with the starburst event probably triggered by interaction with one or more galaxies. Finally, the mid-infrared results on Cl 0024+1654 are compared with four other clusters observed with ISOCAM.

Herschel deep far-infrared counts through Abell 2218 cluster-lens

Gravitational lensing by massive galaxy clusters allows study of the population of intrinsically faint infrared galaxies that lie below the sensitivity and confusion limits of current infrared and submillimeter telescopes. We present ultra-deep PACS 100 and 160 μm observations toward the cluster lens Abell 2218 to penetrate the Herschel confusion limit. We derive source counts down to a flux density of 1 mJy at 100 μm and 2 mJy at 160 μm, aided by strong gravitational lensing. At these levels, source densities are 20 and 10 beams/source in the two bands, approaching source density confusion at 160 μm. The slope of the counts below the turnover of the Euclidean-normalized differential curve is constrained in both bands and is consistent with most of the recent backwards evolutionary models. By integrating number counts over the flux range accessed by Abell 2218 lensing (0.94−35 mJy at 100 μ ma nd 1.47−35 mJy at 160 μm), we retrieve a cosmic infrared background surface brightness of ∼8.0 and ∼9.9 nW m −2 sr −1 , in the respective bands. These values correspond to 55 ± 24% and 77 ± 31% of DIRBE direct measurements. Combining Abell 2218 results with wider/shallower fields, these figures increase to 62 ± 25% and 88 ± 32% CIB total fractions, resolved at 100 and 160 μm, disregarding the high uncertainties of DIRBE absolute values.

An ISOCAM survey through gravitationally lensing galaxy clusters - II. The properties of infrared galaxies in the A2218 field

We have observed the cluster Abell 2218 (z = 0.175) with ISOCAM on board the Infrared Space Observatory using two filters, LW2 and LW3, with reference wavelengths of 6.7 and 14.3 μm, respectively. We detected 76 sources down to 54 and 121 μJy (50% completeness levels) at 6.7 and 14.3 μm, respectively. All these sources have visible optical counterparts. We have gathered optical and near-infrared magnitudes for 60 of the 67 non-stellar optical counterparts to the ISOCAM sources, as well as redshifts for 43 of them. We have obtained acceptable and well constrained fits to the observed spectral energy distributions (SEDs) of 41 of these sources, using the GRASIL models of Silva et al. (1998), and have determined their total infrared luminosities (L IR s) and star formation rates (SFRs). The SEDs of 20 (out of 27) ISOCAM cluster members are best fit by models with negligible ongoing star formation, and no major episode of star formation in the last 1 Gyr. Their SEDs resemble those of 5-10 Gyr old early-type galaxies. A slightly higher, but still very mild, star-formation activity is found among the remaining cluster sources, which are mostly spirals. The median IR luminosity of the 27 ISOCAM cluster sources is L IR = 6 x 10 8 L ○. . The ISOCAM-selected cluster galaxies have indistinguishable velocity and spatial distributions from those of the other cluster galaxies, and do not contribute significantly to the Butcher-Oemler effect. If A2218 is undergoing a merger, as suggested by some optical and X-ray analyses, then this merger does not seem to affect the mid-infrared properties of its galaxies. The SEDs of most ISOCAM-selected field sources are best fit by models with moderate ongoing star formation, with a significant fraction of their stellar mass formed in the last ∼1 Gyr. Their SEDs resemble those of massive star-forming spirals or starburst galaxies, observed close to the maximum of their star formation activity, but not necessarily during the short-lived starburst event. The median redshift of these field galaxies is z ≃ 0.6. Their L IR s span almost two orders of magnitudes, from ∼10 10 L ○. to 10 12 L ○. , with a median of 1.2 x 10 11 (eight of the 14 field sources are LIRGs). The SFRs of these 14 ISOCAM-selected field sources range from 2 to 125 M ○. yr -1 , with a median value of 22 M ○. yr -1 . We compare our findings with those obtained in other ISOCAM cluster and field surveys.

ISO’s Contribution to the Study of Clusters of Galaxies

Starting with nearby galaxy clusters like Virgo and Coma, and continuing out to the furthest galaxy clusters for which ISO results have yet been published (z = 0.56), we discuss the development of knowledge of the infrared and associated physical properties of galaxy clusters from early IRAS observations, through the “ISO-era” to the present, in order to explore the status of ISO’s contribution to this field. Relevant IRAS and ISO programmes are reviewed, addressing both the cluster galaxies and the still-very-limited evidence for an infrared-emitting intra-cluster medium.