arXiv subjects

K. Mattila

Publications and source records attributed to K. Mattila.

31 records · Page 2Linked to original sources

arXiv2004

ISO observations of 3 - 200 micron emission by three dust populations in an isolated local translucent cloud

We present ISOPHOT spectrophotometry of three positions within the isolated high latitude cirrus cloud G 300.2 - 16.8, spanning from the near- to far-infrared. The positions exhibit contrasting emission spectrum contributions from the UIBs, very small grains and large classical grains, and both semi-empirical and numerical models are presented. At all three positions, the UIB spectrum shapes are found to be similar, and the large grain emission may be fitted by an equilibrium temperature of ~17.5 K. The energy requirements of both the observed emission spectrum and optical scattered light are shown to be satisfied by the incident local ISRF. The FIR emissivity of dust in G 300.2 - 16.8 is found to be lower than in globules or dense clouds, and is even lower than model predictions for dust in the diffuse ISM. The results suggest physical differences in the ISM mixtures between positions within the cloud, possibly arising from grain coagulation processes.

astro-ph↗

arXiv2003

Morphology and kinematics of Lynds 1642

The high latitude translucent molecular cloud L1642 has been mapped in the J=1-0 and J=2-1 transitions of 12CO, 13CO and C18O using the SEST radio telescope. We have analysed the morphology and velocity structure of the cloud using the Positive Matrix Factorization (PMF) method. The results show that L1642 is composed of a main structure at radial velocity 0.2 km/s while the higher velocity components at ~0.5 and 1.0 km/s form an incomplete ring around it, suggesting an expanding shell structure. Fainter emission extends to the north with a still higher velocity of up to 1.6 km/s. Such a velocity structure suggests an elongated morphology in the line of sight direction. The physical properties of the cloud have been investigated assuming LTE conditions, but non-LTE radiative transfer models are also constructed for the 13CO observations. We confirm that L1642 follows an r^-1 density distribution in its outer parts while the distribution is considerably flatter in the core. The cloud is close to virial equilibrium. In an Appendix the PMF results are compared with the view obtained through the analysis of channel maps and by the use of Principal Component Analysis (PCA). Both PMF and PCA present the observations as a linear combination of basic spectral shapes that are extracted from the data. Comparison of the methods shows that the PMF method in particular is able to produce a presentation of the complex velocity that is both compact and easily interpreted.

astro-ph↗

arXiv2003

Unidentified Infrared Bands in the Interstellar Medium across the Galaxy

We present a set of 6-12 micron ISOPHOT-S spectra of the general interstellar medium of the Milky Way. This part of the spectrum is dominated by a series of strong, wide emission features commonly called the Unidentified Infrared Bands. The sampled area covers the inner Milky Way from l = -60 degr to +60 degr with a ten-degree step in galactic longitude and nominal latitudes 0,+-1 degr. For each grid position the actual observed direction was selected from IRAS 100 micron maps to minimize contamination by point sources and molecular clouds. All spectra were found to display the same spectral features. Band ratios are independent of band strength and Galactic coordinates. A comparison of total observed flux in band features and IRAS 100 micron emission, a tracer for large interstellar dust grains, shows high correlation at large as well as small 1-arcmin scales. This implies a strong connection between large dust grains and the elusive band carriers; the evolutionary history and heating energy source of these populations must be strongly linked. The average mid-infrared spectrum of the Milky Way is found to be similar to the average spectrum of spiral galaxy NGC 891 and the spectra of other spirals. The common spectrum can therefore be used as a template for the 6-12 micron emission of late-type spiral galaxies. Finally, we show that interstellar extinction only weakly influences the observed features even at lambda = 10 microns, where the silicate absorption feature is strongest.

astro-ph↗

arXiv2003

Submillimeter Emission from Water in the W3 Region

We have mapped the submillimeter emission from the 1(10)-1(01) transition of ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at -39 km/s; however, some positions in the map show a single strong line at -43 km/s. We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region.

astro-ph↗

arXiv2003

First detection of NH3 (1,0 - 0,0) from a low mass cloud core: On the low ammonia abundance of the rho Oph A core

Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (J,K = 1,0 - 0,0). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH) = 3e-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(NH3) = 8e-10.

astro-ph↗

arXiv2003

First NH3 detection of the Orion Bar

Odin has successfully observed three regions in the Orion A cloud, i.e. Ori KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. 2001. Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H2 = 5E-9.

astro-ph↗

arXiv2002

Far infrared observations of pre-protostellar sources in Lynds 183

Using ISOPHOT maps at 100 and 200um and raster scans at 100, 120, 150 and 200um we have detected four unresolved far-infrared sources in the high latitude molecular cloud L183. Two of the sources are identified with 1.3mm continuum sources found by Ward-Thompson et al. and are located near the temperature minimum and the coincident column density maximum of dust distribution. For these two sources, the ISO observations have enabled us to derive temperatures (about 8.3 K) and masses (about 1.4 and 2.4 solar masses). They are found to have masses greater than or comparable to their virial masses and are thus expected to undergo gravitational collapse. We classify them as pre-protostellar sources. The two new sources are good candidates for pre-protostellar sources or protostars within L183.

astro-ph↗

arXiv2001

Far-Infrared Emission from Intracluster Dust in Abell Clusters

The ISOPHOT instrument aboard ISO has been used to observe extended FIR emission of six Abell clusters. The raw profiles of the I_(120 um) / I_(180 um) surface brightness ratio including zodiacal light show a bump towards Abell 1656 (Coma), dips towards Abell 262 and Abell 2670, and are without clear structure towards Abell 400, Abell 496, and Abell 4038. After subtraction of the zodiacal light, the bump towards Abell 1656 is still present, while the dips towards Abell 262 and Abell 2670 are no longer noticable. This indicates a localized excess of emitting material outside the Galaxy towards Abell 1656, while the behavior in Abell 262 and Abell 2670 can be reconciled with galactic cirrus structures localized on the line-of-sight to these clusters. The excess towards Abell 1656 (Coma) is interpreted as thermal emission from intracluster dust distributed in the hot X-ray emitting intracluster medium. The absence of any signature for intracluster dust in five clusters and the rather low inferred dust mass in Abell 1656 indicates that intracluster dust is likely not responsible for the excess X-ray absorption seen in cooling flow clusters. These observations thereby represent a further unsuccessful attempt in detecting the presumed final stage of the cooling flow material, in accord with quite a number of previous studies in other wavelengths regions. Finally, the observed dimming of the high-redshift supernovae is unlikely be attributable to extinction caused by dust in the intracluster or even a presumed intercluster medium.

astro-ph↗

arXiv2001

Far-infrared and molecular line observations of Lynds 183 - studies of cold gas and dust

We have mapped the dark cloud L183 in the far-infrared at 100um and 200um with the ISOPHOT photometer aboard the ISO satellite. The observations make it possible for the first time to study the properties of the large dust grains in L183 without confusion from smaller grains. The observations show clear colour temperature variations which are likely to be caused by changes in the emission properties of the dust particles. In the cloud core the far-infrared colour temperature drops below 12K. The data allow a new determination of the cloud mass and the mass distribution. The mass within a radius of 10 arcmin from the cloud centre is 25 Msun. We have mapped the cloud in several molecular lines including DCO+(2-1) and H13CO+(1-0). These species are believed to be tracers of cold and dense molecular material and we detect a strong anticorrelation between the DCO+ emission and the dust colour temperatures. In particular, the DCO+(2-1) emission is not detected towards the maximum of the 100um emission where the colour temperature rises above 15K. The H13CO+ emission follows the DCO+ distribution but CO isotopes show strong emission even towards the 100um peak. A comparison of the DCO+ and C18O maps shows sharp variations in the relative intensities of the species. Morphologically the 200um dust emission traces the distribution of dense molecular material as seen e.g. in C18O lines. A comparison with dust column density shows that C18O is depleted by a factor of 1.5 in the cloud core. We present results of R- and B-band starcounts. The extinction is much better correlated with the 200um than with the 100um emission. Based on the 200um correlation at low extinction values we deduce a value of ~17mag for the visual extinction towards the cloud centre.

astro-ph↗

arXiv2000

Cirrus spectra of low surface brightness regions

We have studied the galactic cirrus in low surface brightness regions using ISOPHOT raster maps at 90, 150 and 180um. Observations are used to determine dust emission spectra and dust temperatures. The data extend to longer wavelengths than IRAS observation. Compared with DIRBE data the resolution and the sensitivity are better and this makes it possible to study faint cirrus emission in individual fields. We will discuss the calibration of the observations and present results of a comparison between ISOPHOT and DIRBE surface brightness values. The correspondence was found to be better than 30%. At 90um the ISOPHOT surface brightnesses tend to be slightly higher than the DIRBE values while at longer wavelength the situation is reversed. Surface brightness variations caused by cirrus fluctuations make it possible to determine the spectrum of the dust emission. Cirrus spectra were obtained for six fields with surface brightnesses in the range 1-2 MJy/sr after the Zodiacal light and the contribution of extragalactic sources have been subtracted. Assuming f^2 emissivity law the dust temperatures are in the range 18-20 K. Temperature variations can be seen even within individual fields. These values are higher than values from DIRBE but this can be explained by differences in the calibration.

astro-ph↗

arXiv2000

ISOPHOT CIRB project: FIR source counts at 90, 150 and 180 um

Far-infrared maps obtained with ISOPHOT have been searched for point-like sources. The majority of the 55 sources is believed to be extragalactic and in most cases no previously known sources can be associated with them. Based on the far-infrared spectral energy distributions it is likely that dust-enshrouded, distant galaxies form a significant fraction of the sources. We estimate the number densities of extragalactic sources at 90, 150 and 180 um wavelengths and at flux density levels down to 100 mJy. The counts are compared with models of galaxy evolution. The counts exceed the predictions of current models, even those with strong evolution, and no-evolution models are rejected at a high confidence level. Comparison with recent results from COBE mission indicates that at 90 um the detected sources correspond to over 20% of the extragalactic background light. At longer wavelengths the corresponding fraction is 10%.

astro-ph↗

arXiv2000

Far infrared extragalactic background radiation: I. Source counts with ISOPHOT

As a part of the ISOPHOT CIRB (Cosmic Infrared Background Radiation) project we have searched for point-like sources in eight fields mapped at two or three wavelengths between 90 and 180um. Most sources are previously unknown and based on the far-infrared (FIR) spectral energy distributions dust-enshrouded, distant galaxies form a significant fraction of the sources. We present a list of the new extragalactic FIR-sources and discuss the uncertainties of the source detection from the ISOPHOT maps. We estimate the source number densities at 90, 150 and 180um and at flux density levels down to 100mJy to be 10^5, 2 10^5, and 3 10^5 1/sr, respectively. Strong galaxy evolution models are in best agreement with our results, although the number of detections exceeds most model predictions. No-evolution models can be rejected at a high confidence level. Comparison with COBE results indicates that at 90um the detected sources correspond to some 20% of the extragalactic background light. At longer wavelengths the corresponding fraction is closer to 10%.

astro-ph↗

arXiv1998

Detection of widely distributed UIR band emission in the disk of NGC 891

The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 [micro]m has been observed for the first time in the disk of an external galaxy. We have used the low-resolution spectrometer of the ISOPHOT instrument aboard ISO. The UIR bands at 6.2, 7.7 and 11.3 [micro]m have absolute intensities which are similar to the values observed for the diffuse emission of our own Galaxy. The UIR bands between 5.9 and 11.7 [micro]m contribute ~9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emissions are similar to the diffuse emission of the Milky Way, pointing to a common carrier for the UIR bands in the two galaxies. However, there are some notable variations of the band ratios along the major axis of the galaxy.

astro-ph↗