L. V. Toth

The European Large Area ISO Survey – VIII. 90-μm final analysis and source counts

We present a re-analysis of the European Large Area Infrared Space Observatory (ISO) Survey (ELAIS) 90-mum observations carried out with ISOPHOT, an instrument on board the ISO of the European Space Agency. With more than 12 deg(2), the ELAIS survey is the largest area covered by ISO in a single programme and is about one order of magnitude deeper than the IRAS 100-mum survey. The data analysis is presented and was mainly performed with the PHOT interactive analysis software but using the pairwise method of Stickel et al. for signal processing from edited raw data to signal per chopper plateau. The ELAIS 90-mum catalogue contains 237 reliable sources with fluxes larger than 70 mJy and is available in the electronic version of this article. Number counts are presented and show an excess above the no-evolution model prediction. This confirms the strong evolution detected at shorter (15 mum) and longer (170 mum) wavelengths in other ISO surveys. The ELAIS counts are in agreement with previous works at 90 mum and in particular with the deeper counts extracted from the Lockman hole observations. Comparison with recent evolutionary models show that the models of Franceschini et al. and Guiderdoni et al. (which includes a heavily extinguished population of galaxies) give the best fit to the data. Deeper observations are nevertheless required to discriminate better between the model predictions in the far-infrared, and are scheduled with the Spitzer Space Telescope, which has already started operating, and will also be performed by ASTRO-F.

Far-infrared loops in the 2nd Galactic Quadrant

We present the results of an investigation of the large-scale structure of the diffuse interstellar medium in the 2nd Galactic Quadrant (90 ◦ ≤ l ≤ 180 ◦ ). 145 loops were identified on IRAS-based far-infrared maps. Our catalogue lists their basic physical properties. The distribution clearly suggests that there is an efficient process that can generate loop-like features at high Galactic latitudes. Distances are provided for 30 loops. We also give an observational estimate of the volume filling factor of the hot gas in the Local Arm, 4.6% ≤ f2nd < 6.4%.

A very young star forming region detected by the ISOPHOT serendipity survey

We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 µm ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex (M � 760 M⊙) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature (T � 16 K) and large mass (M� 120 M⊙) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar o bjects discovered across the region: I) Two candidate Class 0 objects with masses of 8 and 3.5 M⊙, II) a gravitationally bound, cold (T � 12 K) and dense (n(H2) � 2 · 10 5 cm −3 ) cloud core with a mass of 50 M⊙ and III) a Herbig B2 star with a mass of 6.5 M⊙ and a bolometric luminosity of 2200 L⊙, showing evidence for ongoing accretion and a stellar age of less than 40000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is a bout 14 %.

Star count analysis of the interstellar matter in the region of L1251

We studied the ISM distribution in and around the star forming cloud L1251 with optical star counts. A careful calculation with a maximum likelihood based statistical approach resulted in B, V, R, I extinction distributions from the star count maps. A distance of 330 ± 30 pc was derived. The extinction maps revealed an elongated dense cloud with a bow shock at its eastern side. We estimated a Mach number of M ≈ 2 for the bow shock. A variation of the apparent dust properties is detected, i.e. the RV = AV /EB−V total to selective extinction ratio varies from 3 to 5.5, peaking at the densest part of L1251. The spatial structure of the head of L1251 is well modelled with a Schuster-sphere (i.e. n = 5 polytropic sphere). The observed radial distribution of mass fits the model with high accuracy out to 2.5 pc distance from the assumed center. Unexpectedly, the distribution of NH3 1.3 cm line widths is also well matched by the Schuster solution even in the tail of the cloud. Since the elongated head-tail structure of L1251 is far from the spherical symmetry the good fit of the linewidths in the tail makes it reasonable to assume that the present cloud structure has been formed by isothermal contraction.

HST/NICMOS observations of a proto-brown dwarf candidate

We present deep HST/NICMOS observations peering through the outflow cavity of the protostellar candidate IRAS 04381+2540 in the Taurus Molecular Cloud-1. A young stellar object as central source, a jet and a very faint and close (0.6 �� ) companion are identified. The primary and the companion have similar colours, consistent with strong reddening. We argue that the companion is neither a shock-excited knot nor a background star. The colour/magnitude information predicts a substellar upper mass limit for the companion, but the final confirmation will require spectroscopic information. Because of its geometry, young age and its rare low-mass companion, this system is likely to provide a unique insight into the formation of brown dwarfs.

ISOPHOT far-infrared serendipity sky survey

The ISOPHOT Serendipity Survey utilizes the slew time between ISOs pointed observations with strip scanning measurements of the sky in the far-IR at 170 micrometers . The slews contain information about two fundamentally different types of objects, namely unresolved galactic and extragalactic far-IR sources as well as extended regions of galactic cirrus emission. Since the structure of the obtained data is almost unique, the development of dedicated software to extract astrophysically interesting parameters for the crossed sources is mandatory. Data analysis is currently in its early stages and concentrates on the detection of point sources. First results from an investigation of a high galactic latitude field near the North Galactic Pole indicate that the detection completeness with respect to previously known IRAS sources will be almost 100 percent for sources with f(subscript 100micrometers > 2 Jy, dropping below approximately equals 50 percent for f(subscript 100micrometers < 1.5 Jy. Nevertheless, even faint sources down to a level of f(subscript 170micrometers approximately equals 1 Jy can be detected. Since the majority of the detected point sources are galaxies, the Serendipity Survey will result in a large database of approximately equals 2000 galaxies.

Extending the limits of globule detection - ISOPHOT Serendipity Survey observations of interstellar clouds II

Small isolated clouds were discovered by the ISOPHOT 170 m Serendipity Survey (ISOSS) as faint I170 < 13 MJy sr 1 FIR sources. One of them is ISOSS J20246+6540, a cold (Td 14:5 K) pointlike ISOSS source without an IRAS pointsource counterpart. In the Digitized Sky Survey B band it is seen as a 3 0 size bipolar nebulosity with an average excess DSS blue band surface brightness of 8% of the backgrounds photographical density. The CO column density distribution determined by multi-isotopic, multi-level CO measurements with the IRAM-30 m telescope agrees well with the optical appearance. An av- erage hydrogen column density of10 21 cm 2 was derived from both the FIR and CO data. Using a kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO + , and CS measurements gives a peak density of10 4 cm 3 . The multiwave- length data characterise ISOSS 20246+6540 as a representative of a class of globules which has not been discovered so far due to their small angular size and low 100m brightness. A significant overabundance of 13 CO is found X( 13 CO) 150X(C 18 O).

Infrared straylight measurements of the ISO telescope

Measurements were performed to verify the straylight suppression in the IR Space Observatory telescope using the ISOPHOT instrument. These test comprised the near-field straylight by bright stars and planets as well as the far- field straylight by the Sun, the Earth, and the Moon. No significant straylight above the specifications reflecting the astronomical needs for low surface brightness absolute sky measurements could be detected at 25 and 170 micrometers . In some cases comparison to preflight straylight simultaneous were possible. The consistency of the predictions from the models with the measurement results confirms the reasonable assumptions made for the simulations. This will allow to further optimize the telescope design for future low background IR space telescopes.

Multi-Wavelength Data Mining of the ISOPHOT Serendipity Sky Survey

The ISOPHOT C200 stressed Ge:Ga array aboard the Infrared Space Observatory was used to carry out scientific observations while the telescope was moved from one target to the next. These strip scanning measurements of the sky in the far-infrared (FIR) at 170 μm comprise the ISOPHOT Serendipity Survey, the first slew survey designed as an integral part of a space observatory mission. The ISOPHOT Serendipity Survey is the only large scale sky survey in the unexplored wavelength region beyond the IRAS 100 μm limit to date. Within nearly 550 hours more than 12000 slew measurements with a total slew length of more than 150000 degrees were collected, corresponding to a sky coverage of about 15%. The slew data analysis has been focused on the detection of compact sources, which required the development of special algorithms. A severe problem at 170 μm is the confusion of genuine compact sources with foreground galactic cirrus knots and ridges. The selection and identification of objects therefore necessarily requires a multi-wavelengths approach, which makes use of a broad variety of additional data from databases and other surveys. Known galaxies were identified by cross-correlating the Serendipity Survey source positions with galaxy entries in the NED and Simbad databases and a subsequent cross-check of optical images from the Digital Sky Survey. A large catalogue with 170 μm fluxes for ≈2000 galaxies is being complied. The particularly interesting rare galaxies with very cold dust and very large dust masses further require additional FIR data from the IRAS survey as well as measured redshifts. A large fraction of the compact galactic structures are prestellar cores inside cold star forming regions. Early stages of medium and high mass star forming regions are identified by combining compact bright and cold Serendipity Survey sources with the near-infrared 2MASS and MSX surveys, the combination of which indicates large dust masses in conjunction with embedded young stars of early spectral types. In all the studied samples of different object classes the 170 μm flux provides the crucial data point for a complete characterization of the FIR spectral energy distributions and the derivation of total dust masses. Follow-up observations are underway to study selected objects in more detail.

ISOPHOT Surveys and the Extragalactic Background

The higher spatial resolution and sensitivity of ISO allowed several extragalactic surveys to be extended to greater depth than obtained with IRAS. With the extended wavelength range deep surveys were performed for the first time at wavelengths up to rv 200 uu». They favour galaxy models with strong evolution. With ISOs new capabilities the spectral energy distributions of larger samples of ULIRGs in the local universe and those of quasars and radio galaxies were determined. These data are applicable as templates to the more distant universe. Foreground components from zodiacal light and cirrus to the intracluster dust emission were studied in connection with their separation from the extragalactic background radiation.