ISOPHOT Serendipity Survey Research Articles

An infrared-submillimeter study of starforming regions selected by the ISOSS 170 μm survey

Using the ISOPHOT Serendipity Survey (ISOSS) at 170um a sample of galactic star-forming regions exhibiting very cold dust temperatures (< 20 K) and high masses (> 100 M_sun) has been established. We characterise the star-forming content of five regions that were selected as potential sites for early stage high-mass star formation using SCUBA (JCMT) and Spitzer observations. In every region we identify one to four submillimeter clumps with projected sizes between 0.1 and 0.4 pc. The dust temperatures range from 11.6 to 21.3 K and the estimated clump masses are 2 to 166 M_sun. Towards the majority of submillimeter peaks we find point sources in the near- to mid-infrared. Most are interpreted as low-mass young stellar objects but we also detect very red sources. They probably represent very young and deeply embedded protostars that continue to accrete clump material and may reach higher masses. Several candidate intermediate-mass proto- or pre-main-sequence stars embedded in the clumps are identified. A subset of four clumps may be massive enough (> 100 M_sun) to form high-mass stars and accompanying clusters. The absence of stellar precursors with current masses in the high-mass regime leave the type of star formation occuring in the clumps unsettled. We confirm the presence of large fractions of cold material as derived from large-scale far-infrared measurements which dominates the emission of most clumps and suggests that the star-forming process will continue.

The ISOPHOT 170 $\mathsf{\mu}$m Serendipity Survey

Aims. To shed more light on the integrated FIR properties of galaxies, the ≈ 2000 compact sources in the ISOPHOT Serendipity Survey associated with identified galaxies are investigated statistically. They provide the only sample large enough to determine the FIR properties such as dust temperatures and masses, FIR luminosities, and HI-to-dust ratios not only for the group as a whole, but also divided into several subgroups of different Hubble types. Only with this catalog, the high flux end of the $\mathrm{170~{\mu}m}$ galaxy number counts can be established, which is crucial as a complement to the much deeper ISOPHOT studies at this wavelength in much smaller sky areas. Methods. The differential distributions of integrated FIR properties and the cumulative number counts are analysed. Results. The galaxy list of the ISOPHOT Serendipity Survey has a $\mathrm{170~{\mu}m}$ completeness limit of ≈ 2 Jy. The statistical analysis confirmed that the ${F_{170~{\mu}{\rm m}}} / {F_{100~{\mu}{\rm m}}}$ flux ratios peak at ≈ 1, corresponding to a dust color temperature of ≈ 20 K. FIR luminosities and dust masses cover a large range with peaks near $L{_\mathrm{1-1000} \approx 10^{10.5 \pm 1}\,L_{\odot}}$ and $M{_{\rm Dust} \approx 10^{7.5 \pm 0.5}~M_{\odot}}$, respectively. HI-to-dust ratios range from ≈ 10 and ≈ 10 4 , rendering the notion of fiducial HI-to-dust ratio for conversion between gas and dust masses almost useless. The latest models of the cumulative $\mathrm{170~{\mu}m}$ number counts are in reasonable agreement with the deep as well as the shallow surveys from ISO up to fluxes of ≈ 50 Jy.

The ISOPHOT 170 ${\mathsf \mu}$m Serendipity Survey

Aims.To further increase the scientific utilization of the strip scanning measurements of the ISOPHOT Serendipity Survey (ISOSS), the slew data has been assembled to a sky atlas with ≈15% sky coverage in the hitherto unobserved far-infrared wavelength band around 170 μm.

A (Sub)Millimeter survey of massive star-forming regions identified by the ISOPHOT Serendipity Survey (ISOSS)

AbstractA sample of potential massive starforming regions identified at 170 m by ISO was observed in the submillimeter and millimeter regime. These observations allow us to infer physical properties of the molecular cloud cores. Two sources are presented in detail: ISOSS J23053+5953 and J183640221 show viable candidates for massive protocluster cores. Our analysis shows very low temperatures and low levels of turbulence of the major mass fraction in the molecular cloud cores besides active star formation at an early evolutionary stage. These conditions seem similar to the low mass case and may precede phases of luminous infrared emission observed towards young massive protostars.

Very Cold and Massive Cores near ISOSS J18364−0221: Implications for the Initial Conditions of High‐Mass Star Formation

We report the discovery of two very cold and massive molecular cloud cores in the region ISOSS J18364-0221. The object has been identified by a systematic search for very early evolutionary stages of high-mass stars using the 170 μm ISOPHOT Serendipity Survey (ISOSS). Submillimeter continuum and molecular line measurements reveal two compact cores within this region. The first core has a temperature of 16.5 K, shows signs of ongoing infall and outflows, has no near- or mid-infrared counterpart, and is massive enough (M ~ 75 M☉) to form at least one O star with an associated cluster. It is therefore considered a candidate for a genuine high-mass protostar and a high-mass analog to the Class 0 objects. The second core has an average gas and dust temperature of only ~12 K and a mass of M ~ 280 M☉. Its temperature and level of turbulence are below the values found for massive cores so far, and we suggest that this represents the initial conditions from which high-mass star formation occurs.

Clumpy filaments of the Chamaeleon I cloud: C$\mathsf{^{18}}$O mapping with the SEST

The Chamaeleon  dark cloud (Cha ) has been mapped in C 18 O( J = 1−0) with an angular resolution of 1 � using the SEST telescope. The large scale structures previously observed with lower spatial resolution in the cloud turn into a network of clumpy filaments. The automatic Clumpfind routine developed by Williams et al. (1994) is used to identify individual clumps in a consistent way. Altogether 71 clumps were found and the total mass of these clumps is 230 M� . The dense de- tected with the NANTEN telescope (Mizuno et al. 1999) and the very cold cores detected in the ISOPHOT serendipity survey (Toth et al. 2000) form parts of these filaments but decompose into numerous clumps. The filaments are preferentially ori- ented at right angles to the large-scale magnetic field in the region. We discuss the cloud structure, the physical characteristics of the clumps and the distribution of young stars. The observed clump mass spectrum is compared with the predictions of the turbulent fragmentation model of Padoan & Nordlund (2002). Agreement is found if fragmentation has been driven by very large-scale hypersonic turbulence, and if by now it has had time to dissipate into modestly supersonic turbulence in the inter- clump gas. According to numerical simulations, large-scale turbulence should have resulted in filamentary structures as seen in Cha . The well-oriented magnetic field does not, however, support this picture, but suggests magnetically steered large-scale collapse. The origin of filaments and clumps in Cha  is thus controversial. A possible solution is that the characterization of the driving turbulence fails and that in fact different processes have been effective on small and large scales in this cloud.

A Gas and Dust Rich Giant Elliptical Galaxy

AbstractThe bolometric luminosity of LFIR = 2×1012 L⊙ makes ISOSS J 15079+7247 one of the most luminous and unusual galaxies detected by the 170 μm ISOPHOT Serendipity Survey (ISOSS). The detection of CO (1-0) emission identifies a giant elliptical galaxy at redshift z = 0.2136 as the counterpart of the FIR source. The derived high gas mass of 3 × 1010 M⊙ favours the picture that the dust emission is associated with this elliptical galaxy. The ultraluminous IR emission can be explained by a hidden starburst in the center of the elliptical. This is supported by the strength of non-thermal radio continuum emission. The huge dust mass of 5×108 M⊙ corresponds to a visual extinction of AV ~ 1000 mag, being consistent with the non-detection of any signatures of a strong starburst in ISOSS J 15079+7247 in optical spectra.

A gas and dust rich giant elliptical galaxy in the ISOPHOT Serendipity Survey

We present a multi-wavelength study of the unusual galaxy ISOSS J 15079+7247. With a bolometric luminosity of this object is one of the most luminous galaxies detected by the 170 ISOPHOT Serendipity Survey (ISOSS). We have obtained 1.2 mm continuum and CO (1–0) line observations, optical spectra and deep R-band images of the system. The CO emission originates from a giant elliptical galaxy at redshift , yielding a molecular gas mass of . The high gas mass favors the picture that the dust emission is associated with the elliptical galaxy. The nature of the ultraluminous IR emission can be explained by an opaque, hidden starburst in the center of the elliptical. The huge dust mass of corresponds to a visual extinction of . This is consistent with the non-detection of any optical signatures of a strong starburst in ISOSS J 15079+7247 and the strength of non-thermal radio continuum emission.

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 micron 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$_{\odot}$) 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$_{\odot}$) 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 objects discovered across the regio n: I) Two candidate Class 0 objects with masses of 8 and 3.5 M$_{\odot}$, II) a gravitationally bound, cold (T ~ 12 K) and dense (n(H$_{2}$) \~ 2 x 10$^{5}$ cm$^{-3}$) cloud core with a mass of 50 M$_{\odot}$ and III) a Herbig B2 star with a mass of 6.5 M$_{\odot}$ and a bolometric luminosity of 2200 L$_{\odot}$, 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 about 14 %.

Solar system objects in the ISOPHOT 170μm serendipity survey

The ISOPHOT Serendipity Survey (ISOSS) covered approximately 15% of the sky at a wavelength of 170m while the ISO satellite was slewing from one target to the next. By chance, ISOSS slews went over many solar system objects (SSOs). We identied the comets, asteroids and planets in the slews through a fast and eective search procedure based on N-body ephemeris and flux estimates. The detections were analysed from a calibration and scientic point of view. Through the measurements of the well-known asteroids Ceres, Pallas, Juno and Vesta and the planets Uranus and Neptune it was possible to improve the photometric calibration of ISOSS and to extend it to higher flux regimes. We were also able to establish calibration schemes for the important slew end data. For the other asteroids we derived radiometric diameters and albedos through a recent thermophysical model. The scientic results are discussed in the context of our current knowledge of size, shape and albedos, derived from IRAS observations, occultation measurements and lightcurve inversion techniques. In all cases where IRAS observations were available we conrm the derived diameters and albedos. For the ve asteroids without IRAS detections only one was clearly detected and the radiometric results agreed with sizes given by occultation and HST observations. Four dierent comets have clearly been detected at 170 ma nd two have marginal detections. The observational results are presented to be used by thermal comet models in the future. The nine ISOSS slews over Hale-Bopp revealed extended and asymmetric structures related to the dust tail. We attribute the enhanced emission in post-perihelion observations to large particles around the nucleus. The signal patterns are indicative of a concentration of the particles in the trail direction.

Dense gas and cold dust in the dark core B217

The Barnard object B217 was observed in the infrared and radio region. The 170 m continuum was detected with ISOPHOT, the ammonia 1.3 cm radio lines with the Eelsberg 100 m-telescope. Mapping B217SW in (J;K )=( 1; 1) and (2; 2) inversion lines revealed the temperature and density distribution of the gas and made it possible to investigate the dynamical state of this dense core inside B217. The ISOPHOT Serendipity Survey (ISOSS) detected the cold dust emission of B217 in all of 3 slews crossing the region. Combining ISOSS with IRAS data, we derive the core parameters of the dust from FIR emission and compare them with the NH3 data, which sample the densest region of the core. This study shows the power of combining ISOSS 170 mw ith IRAS/HIRES data in order to study the dust characteristics in nearby star forming regions on small spatial scales. The (170m/100m) dust colour temperature is 11 K{12 K in the dense cores and 12 K{14 K in the other regions of B217. The low dust temperatures cannot be explained by attenuation of the interstellar radiation eld alone and may reflect a change in the optical properties of the dust as compared to diuse clouds. In B217SW, molecular depletion through freeze-out onto grains is suggested by the comparison of our FIR and NH3 data with previous C 18 O observations. On the basis of our ammonia data investigation, we nd in B217SW dense gas with kinetic temperatures between 9 K and 12 K, increasing outwards. Using near-infrared extinction and NH3 collisional excitation calculations, the fractional ammonia abundance (N(NH3)=N (H2)) is found to be 3{5 10 8 , and the comparison of gas and dust observations supports this range. Knowing the ammonia abundance, we calculate the thermal, turbulent and gravitational energies of the dense core, which appears to be close to hydrostatic equilibrium. Our results are compatible with B217SW being now on the verge of collapse or in an early collapse phase.