Gas kinematics in massive star-forming regions from the Perseus spiral arm

We present results of a survey of 14 star-forming regions from the Perseus spiral arm in CS(2-1) and 13CO(1-0) lines with the Onsala Space Observatory 20 m telescope. Maps of 10 sources in both lines were obtained. For the remaining sources a map in just one line or a single-point spectrum were obtained. On the basis of newly obtained and published observational data we consider the relation between velocities of the "quasi-thermal" CS(2-1) line and 6.7 GHz methanol maser line in 24 high-mass star-forming regions in the Perseus arm. We show that, surprisingly, velocity ranges of 6.7 GHz methanol maser emission are predominantly red-shifted with respect to corresponding CS(2-1) line velocity ranges in the Perseus arm. We suggest that the predominance of the "red-shifted masers" in the Perseus arm could be related to the alignment of gas flows caused by the large-scale motions in the Galaxy. Large-scale galactic shock related to the spiral structure is supposed to affect the local kinematics of the star-forming regions. Part of the Perseus arm, between galactic longitudes from 85deg to 124deg, does not contain blue-shifted masers at all. Radial velocities of the sources are the greatest in this particular part of the arm, so the velocity difference is clearly pronounced. 13CO(1-0) and CS(2-1) velocity maps of G183.35-0.58 show gas velocity difference between the center and the periphery of the molecular clump up to 1.2 km/s. Similar situation is likely to occur in G85.40-0.00. This can correspond to the case when the large-scale shock wave entrains the outer parts of a molecular clump in motion while the dense central clump is less affected by the shock.Comment: accepted by Astronomy Report

Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey

Signatures of the re-occurrence of activity in radio-loud AGNs, indicated either by the so-called double-double or X-shaped structures, have been observed in a number of radio sources. All such objects known to date have linear sizes of the order of a megaparsec. A number of the sources that are appreciably more compact than this, but that exhibit hints of a past phase of activity, were found in the VLA FIRST survey. Their structures show symmetric relic lobes straddling relatively bright, unresolved cores. Observations of the cores of 15 such structures with MERLIN at 5 GHz have shown that four of them are doubles or core-jets on the subarcsecond scale. Misalignments of \Delta PA \ga 30 degr. between the axis of the inner structure and the line connecting the fitted maxima of the arcminute-scale relic lobes are clearly visible in three of the four sources. From these results, we can infer that a rapid repositioning of the central engine in each of these three radio sources is the most plausible interpretation of the observed morphology and that a merger is most likely the original cause of such a repositioning. In the case of TXS 1033+026, the optical image extracted from the SDSS archives clearly suggests that two objects separated by only 2.7 kpc (projected onto the sky plane) are indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be interpreted as double-lobed, and consequently, these sources could be of the double-double type; but further multifrequency observations are necessary to provide support for such an interpretation.Comment: 9 pages, 5 figures, matches the version printed in Astronomy & Astrophysics, very minor correction of Table

Molecular gas in high-mass filament WB673

We studied the distribution of dense gas in a filamentary molecular cloud containing several dense clumps. The center of the filament is given by the dense clump WB673. The clumps are high-mass and intermediate-mass star-forming regions. We observed CS(2-1), 13CO(1-0), C18O(1-0) and methanol lines at 96GHz toward WB673 with the Onsala Space Observatory 20-m telescope. We found CS(2-1) emission in the inter-clump medium so the clumps are physically connected and the whole cloud is indeed a filament. Its total mass is $10^4$ M$_{\odot}$ and mass-to-length ratio is 360 M$_{\odot}$pc$^{-1}$ from 13CO(1-0) data. Mass-to-length ratio for the dense gas is $3.4-34$ M$_{\odot}$pc$^{-1}$ from CS(2-1) data. The PV-diagram of the filament is V-shaped. We estimated physical conditions in the molecular gas using methanol lines. Location of the filament on the sky between extended shells suggests that it could be a good example to test theoretical models of formation of the filaments via multiple compression of interstellar gas by supersonic waves

Monitoring of the prompt radio emission from the unusual supernova 2004dj in NGC2403

Supernova 2004dj in the nearby spiral galaxy NGC2403 was detected optically in July 2004. Peaking at a magnitude of 11.2, this is the brightest supernova detected for several years. Here we present Multi-Element Radio Linked Interferometer Network (MERLIN) observations of this source, made over a four month period, which give a position of R.A. = 07h37m17.044s, Dec =+65deg35'57.84" (J2000.0). We also present a well-sampled 5 GHz light curve covering the period from 5 August to 2 December 2004. With the exception of the unusual and very close SN 1987A, these observations represent the first detailed radio light curve for the prompt emission from a Type II-P supernova.Comment: (1) Jodrell Bank Observatory (2) University of Valencia (3) University of Sheffield 6 pages, 1 figure. To appear in ApJ letter

Extended Star Formation and Molecular Gas in the Tidal Arms near NGC3077

We report the detection of ongoing star formation in the prominent tidal arms near NGC 3077 (member of the M 81 triplet). In total, 36 faint compact HII regions were identified, covering an area of ~4x6 kpc^2. Most of the HII regions are found at HI column densities above 1x10^21 cm^-2 (on scales of 200 pc), well within the range of threshold columns measured in normal galaxies. The HII luminosity function resembles the ones derived for other low-mass dwarf galaxies in the same group; we derive a total star formation rate of 2.6x10^-3 M_sun/yr in the tidal feature. We also present new high-resolution imaging of the molecular gas distribution in the tidal arm using CO observations obtained with the OVRO interferometer. We recover about one sixth of the CO flux (or M_H2~2x10^6 M_sun, assuming a Galactic conversion factor) originally detected in the IRAM 30m single dish observations, indicating the presence of a diffuse molecular gas component in the tidal arm. The brightest CO peak in the interferometer map (comprising half of the detected CO flux) is coincident with one of the brightest HII regions in the feature. Assuming a constant star formation rate since the creation of the tidal feature (presumably ~3x10^8 years ago), a total mass of ~7x10^5 M_sun has been transformed from gas into stars. Over this period, the star formation in the tidal arm has resulted in an additional enrichment of Delta(Z)>0.002. The reservoir of atomic and molecular gas in the tidal arm is ~3x10^8 M_sun, allowing star formation to continue at its present rate for a Hubble time. Such wide-spread, low-level star formation would be difficult to image around more distant galaxies but may be detectable through intervening absorption in quasar spectra.Comment: Accepted for publication in the Astronomical Journa

Bunge’s Mathematical Structuralism Is Not a Fiction

In this paper, I explore Bunge’s fictionism in philosophy of mathematics. After an overview of Bunge’s views, in particular his mathematical structuralism, I argue that the comparison between mathematical objects and fictions ultimately fails. I then sketch a different ontology for mathematics, based on Thomasson’s metaphysical work. I conclude that mathematics deserves its own ontology, and that, in the end, much work remains to be done to clarify the various forms of dependence that are involved in mathematical knowledge, in particular its dependence on mental/brain states and material objects

Star formation around the H II region Sh2-235

We present a picture of star formation around the H ii region Sh2-235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1-0) and CS (2-1) emission toward S235 with the Onsala Space Observatory 20-m telescope and analysed the star density distribution with archival data from the Two Micron All-Sky Survey (2MASS). Dense molecular gas forms a shell-like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star-forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast-moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the 'collect-and-collapse' scenario and the compression of pre-existing dense clumps by the shock wave. Journal compilation © 2008 RAS

Star formation around the H II region Sh2-235

We present a picture of star formation around the H ii region Sh2-235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1-0) and CS (2-1) emission toward S235 with the Onsala Space Observatory 20-m telescope and analysed the star density distribution with archival data from the Two Micron All-Sky Survey (2MASS). Dense molecular gas forms a shell-like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star-forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast-moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the 'collect-and-collapse' scenario and the compression of pre-existing dense clumps by the shock wave. Journal compilation © 2008 RAS

The link between gas and stars in the S254-S258 star-forming region

The paper aims to study relation between the distributions of the young stellar objects (YSOs) of different ages and the gas-dust constituents of the S254-S258 star formation complex. This is necessary to study the time evolution of the YSO distribution with respect to the gas and dust compounds that are responsible for the birth of the young stars. For this purpose, we use correlation analysis between different gas, dust, and YSO tracers. We compared the large-scale CO, HCO+, near-IR extinction, and far-IR Herschel maps with the density of YSOs of the different evolutionary classes. The direct correlation analysis between these maps was used together with the wavelet-based spatial correlation analysis. This analysis reveals a much tighter correlation of the gas-dust tracers with the distribution of class I YSOs than with that of class II YSOs. We argue that class I YSOs that were initially born in the central bright cluster S255-IR (both N and S parts) during their evolution to class II stage (similar to 2 Myr) had enough time to travel through the whole S254-S258 star formation region. Given that the region contains several isolated YSO clusters, the evolutionary link between these clusters and the bright central S255-IR (N and S) cluster can be considered. Despite the complexity of the YSO cluster formation in the non-uniform medium, the clusters of class II YSOs in the S254-258 star formation region can contain objects born in the different locations of the complex.Peer reviewe