An all-sky Support Vector Machine selection of WISE YSO Candidates

We explored the AllWISE catalogue of the Wide-field Infrared Survey Explorer mission and identified Young Stellar Object candidates. Reliable 2MASS and WISE photometric data combined with Planck dust opacity values were used to build our dataset and to find the best classification scheme. A sophisticated statistical method, the Support Vector Machine (SVM) is used to analyse the multi-dimensional data space and to remove source types identified as contaminants (extragalactic sources, main sequence stars, evolved stars and sources related to the interstellar medium). Objects listed in the SIMBAD database are used to identify the already known sources and to train our method. A new all-sky selection of 133,980 Class I/II YSO candidates is presented. The estimated contamination was found to be well below 1% based on comparison with our SIMBAD training set. We also compare our results to that of existing methods and catalogues. The SVM selection process successfully identified >90% of the Class I/II YSOs based on comparison with photometric and spectroscopic YSO catalogues. Our conclusion is that by using the SVM, our classification is able to identify more known YSOs of the training sample than other methods based on colour-colour and magnitude-colour selection. The distribution of the YSO candidates well correlates with that of the Planck Galactic Cold Clumps in the Taurus--Auriga--Perseus--California region.Comment: 27 pages, 15 figures, 15 table

Unveiling the weak radio quasar population at z≥4

We applied image stacking on empty-field Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey maps centred on optically identified high-redshift quasars at $z\geq4$ to uncover the hidden $\mu$Jy radio emission in these active galactic nuclei (AGN). The median stacking procedure for the full sample of $2229$ optically identified AGN uncovered an unresolved point source with an integrated flux density of 52$~\mu$Jy, with a signal-to-noise ratio $\sim10$. We co-added the individual image centre pixels to estimate the characteristic monochromatic radio power at $1.4~$GHz considering various values for the radio spectral index, revealing a radio population with $P_\mathrm{1.4GHz}\sim10^{24}~$W Hz$^{-1}$. Assuming that the entire radio emission originates from star-forming (SF) activity in the nuclear region of the host galaxy, we obtained an upper limit on the characteristic star formation rate, $\sim4200~$M$_\odot~$yr$^{-1}$. The angular resolution of FIRST images is insufficient to distinguish between the SF and AGN origin of radio emission at these redshifts. However, a comparison with properties of individual sources from the literature indicates that a mixed nature is likely. Future very long baseline interferometry radio observations and ultra-deep Square Kilometre Array surveys are expected to be sensitive enough to detect and resolve the central $1-10~$kpc region in the host galaxies, and thus discriminate between SF and AGN related emission.Comment: 9 pages, 3 figures, 3 tables, accepted for publication in MNRA

A galaktikus és extragalaktikus háttérsugárzás infravörös vizsgálata = Infrared studies of the galactic and extragalactic background radiation

Kutatásunk célja az ESA csillagászati mesterséges holdja, az Infrared Space Observatory (ISO) 1995. novembere és 1998. áprilisa között végzett 2-240 mikrométeres hullámhosszú háttérméréseinek feldolgozása, a bolygóközi és a galaktikus előtérkomponensek valamint a kozmológiai eredetű extragalaktikus infravörös háttérsugárzás tanulmányozása. Eredményeink: (1) Adatbázisokat állítottunk fel az ISOPHOT legjobb minőségű infravörös háttérméréseiből; (2) Jelentősen javítottuk az ISOPHOT felületi fényesség fotometriájának kalibrációját; (3) Az így újrakalibrált ISOPHOT méréseket szisztematikus összevetettük a COBE/DIRBE hold eredményeivel és kimutattuk, hogy nincs jelentős különbség a két fotometriai rendszer között; (4) Analizáltuk az állatövi fény közép-infravörös színképét. A színkép térbeli változásait pusztán geometriai okokkal magyarázni tudtuk; (5) Kifejlesztettünk egy modellt a kisbolygó populáció infravörös emissziójának statisztikus leírására; (6) Fourier analízis segítségével tanulmányoztuk a galaktikus cirrus emissziójának térbeli szerkezetét, és váratlan függést találtunk a terület abszolút fényességétől; (7) Kimutattuk, hogy a csillagközi por emisszivitása függ a porszemcsék hőmérsékletétől; (8) Elsőként beépítettük az aszteroidák által okozott konfúziós zajt a modellekbe. Az adatbázisaink jelenleg folyó újraprocesszálása új szoftvercsomagunkkal lehetővé teszi a háttérsugárzás komponensekre bontását. | The aim of our project was to collect, calibrate and analyse measurements of the infrared sky brightness obtained by ISOPHOT the photometer on-board ESA's Infrared Space Observatory. Our main results are the following: we (1) built up databases of sky observations using data obtained in the most reliable ISOPHOT observing modes; (2) made significant improvements in the surface brightness calibration of ISOPHOT; (3) compared the surface brightness values with those derived from COBE/DIRBE and showed a good agreement; (4) analysed the mid-infrared spectrum of the zodiacal light, and found that the spatial variations of the spectrum can be explained by geometrical effects (no need for changing dust properties); (5) developed a new model for the statistical description of emission from the asteroidal population; (6) performed Fourier analysis of infrared maps of galactic cirrus clouds and showed that the spectral index unexpectedly depends on the surface brightness; (7) proved that the emissivity of interstellar dust grains changes with temperature; (8) produced confusion noise estimates for different space instruments (asteroidal component is also included). The bulk reprocessing of the sky measurement databases using our new software provides a good basis for the reliable separation of components of the infrared sky brightness

Statistical properties of Fermi GBM GRBs' spectra

Statistical studies of gamma-ray burst (GRB) spectra may result in important information on the physics of GRBs. The Fermi GBM catalog contains GRB parameters (peak energy, spectral indices, intensity) estimated fitting the gamma-ray SED of the total emission (fluence, flnc), and during the time of the peak flux pflx. Using contingency tables we studied the relationship of the models best fitting pflx and flnc time intervals. Our analysis revealed an ordering of the spectra into a power law - Comptonized - smoothly broken power law - Band series. This result was further supported by a correspondence analysis (CA) of the pflx and flnc spectra categorical variables. We performed a linear discriminant analysis (LDA) to find a relationship between categorical (spectral) and model independent physical data. LDA resulted in highly significant physical differences among the spectral types, that is more pronounced in the case of the pflx spectra, than for the flnc spectra. We interpreted this difference as caused by the temporal variation of the spectrum during the outburst. This spectral variability is confirmed by the differences in the low energy spectral index and peak energy, between the pflx and flnc spectra. We found that the synchrotron radiation is significant in GBM spectra. The mean low energy spectral index is close to the canonical value of {\alpha} = -2/3 during the peak flux. However, $\alpha$ is ~ -0.9 for the spectra of the fluences. We interpret this difference as showing that the effect of cooling is important only for the fluence spectra.Comment: Manuscript accepted for publication in MNRA

Pre-protostelláris felhőmagok fizikája = Physics of pre-protostellar cloud cores

Bizonyítottuk, hogy jelentős szerepe van a külső hatásoknak a kistömegű csillagok keletkezésében már a pre-protostelláris felhőmagok kialakulásától kezdve. 1. A Naprendszer 2kpc sugarú környezetében a hideg csillagközi anyag kb. 40%-a van lassú frontok és a csillagközi ionizáló sugárzási tér (trigger) hatása alatt. 2. A csillagközi felhők relatív száma a nyugalomban lévő és külső hatás alatt lévő térrészben hasonló, de a sűrű felhőmagok gyakoribbak a triggerelt csillagközi anyagban. 3. A külső trigger hatások alkalmasak a csillagkeletkezés beindítására a sűrűség fluktuációk megnövelésén keresztül. 4. A trigger esetek száma jelentős, minden harmadik a Naphoz hasonló tömegű fiatal csillag triggerelt csillagközi felhőben születik. További eredményeink: Több mint 10 új felhőmagot azonosítottunk. Felfedeztünk több mint egy tucat új T-asszociációt. A szakirodalomban elsőként felfedeztünk egy keletkező barna törpe jelöltet a Taurusban. Megadtuk a Taurus Molecular Ring szerkezeti és kinematikai leírását. | Trigger mechanisms play an important role in the low mass star formation already in the formation of pre-protostellar cores. 1) As much as 40% of the nearby (within 2kpc) interstellar medium (ISM) mass is exposed to slow interstellar shock fronts, and an enhanced ionizing interstellar radiation field, i.e. the typical trigger mechanisms. 2) Clouds form with the same frequency in the relaxed and in the triggered ISM, but there are far more dense cores in triggered clouds. 3) Triggers like above may turn ISM density enhancements to star forming cloud cores. 4) The triggered fraction of low mass star formation is statistically significant in large Galactic regions, at least 30% of the solar type low mass stars are formed in triggered clouds. Further results: We identified more than a dozen of new cloud cores, and T-associations. A candidate brown dwarf was discovered in Taurus, still in the phase of formation. The Taurus Molecular Ring ISM structure and kinematics was uncovered

A kozmikus por fejlődése a Tejútrendszerben és a távoli Univerzumban = Evolution of cosmic dust in the Milky Way and in the distant Universe

Kutatómunkánk során foglalkoztunk az eredeti munkatervben megjelölt mindhárom témakörrel: a por szerepe és tulajdonságai csillagközi felhőkben, csillagok körüli korongokban, valamint kozmológiai távolságú rendszerekben. Megmutattuk, hogy a sűrű csillagközi felhőkben a porszemcsék optikai tulajdonságai megváltoznak, arra utalva, hogy méretük valamilyen fizikai hatás következtében (összetapadás, jégköpeny képződés) megnő. Az extragalaktikus por tanulmányozására távoli (z <= 1) galaxisokat figyeltünk meg a Spitzer Űrtávcsővel. A legnagyobb hangsúlyt a hirtelen kifényesedést mutató eruptív fiatal csillagok körüli por- és gázkorongok tanulmányozására fektettük. A V1647 Ori kitörése során interferometrikus mérésekkel fel tudtuk bontani a csillagkörüli korong belső részét, és megmutattuk, hogy a kitörés során a belső rész geometriája megváltozik. Az EX Lupi 2008-as kitörését az Európai Déli Obszervatórium és a Spitzer Űrtávcső műszereivel követtük. A kitörés előtt felvett színkép tanúsága szerint az EX Lupit körülvevő korong felszínét kisméretű és amorf szerkezetű por borította, a kitörés csúcsát követően azonban már nagyrészt kristályos porszemcsék spektroszkópiai nyomát láthattuk. Így első ízben sikerült közvetlenül megfigyelni a porszemcsék kristályosodását egy csillagkörüli korongban, lehetséges forgatókönyvet javasolva naprendszerbeli üstökösök anyagának keletkezésére is. A felfedezést a Nature közölte 2009-ben. | We made progress in all three research areas defined in the workplan of the OTKA project: the role and properties of dust in interstellar clouds, in circumstellar disks, and in galaxies at cosmological distances. We demonstrated that the infrared emisivity of the dust particles increases in dense interstellar clouds, suggesting a particle growth via coagulation or the appearance of ice mantels. In order to study the extragalactic dust we performed far-infrared observations of SN Ia host galaxies with the Spitzer Space Telescope. Our most productive research line was, however, the investigation of gas- and dust disks around young eruptive stars. Using interferometric observations, we were able to resolve the inner disk around V1647 Ori, and concluded that the the geometrical structure of the inner part changed during the outburst. The 2008 Jan-Sep eruption of EX Lupi was followed using ESO and Spitzer instruments. Comparing pre-outburst and outburst mid-infrared spectra, we showed that while in quiescence the surface of the disk was dominated by submicron size amorphous particles, during outburst signatures of crystalline dust appeared. It was the first direct detection of on-going crystal formation in a cosmic object, offering also a scenario for the formation of the silicate crystals located in comet nuclei in the Solar System. This result was published in Nature in 2009 May

Molecular Gas Properties in the Host Galaxy of GRB 080207

We present the results of CO(1–0) and CO(4–3) observations of the host galaxy of a long-duration gamma-ray burst GRB 080207 at z = 2.0858 by using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. The host is detected in CO(1–0) and CO(4–3), becoming the first case for a gamma-ray burst (GRB) host with more than two CO transitions detected combined with CO(2–1) and CO(3–2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion factor, we derive a molecular gas mass of M gas = 8.7 × 1010 M ⊙, which places the host in a sequence of normal star-forming galaxies in an M gas–star formation rate (SFR) plane. A modified blackbody fit to the far-infrared–millimeter photometry results in a dust temperature of 37 K and a dust mass of M dust = 1.5 × 108 M ⊙. The spatially resolved CO(4–3) observations allow us to examine the kinematics of the host. The CO velocity field shows a clear rotation and is reproduced by a rotation-dominated disk model with a rotation velocity of 350 km s‑1 and a half-light radius of 2.4 kpc. The CO spectral line energy distribution derived from the four CO transitions is similar to that of starburst galaxies, suggesting a high excitation condition. Comparison of molecular gas properties between the host and normal (main-sequence) galaxies at similar redshifts shows that they share common properties such as gas mass fraction, gas depletion timescale, gas-to-dust ratio, location in the M gas–SFR (or surface density) relation, and kinematics, suggesting that long-duration GRBs can occur in normal star-forming environments at z ∼ 2

Transient detection capabilities of small satellite gamma-ray detectors

The new, small satellite-based gamma-ray detectors, like Cubesats Applied for MEasuring and Localizing Transients, will provide a new wa to detect gamma transients in the multimessenger era. The efficiency an the detection capabilities of such a system will be compared wit current missions, for example, Fermi Gamma-ray Burst Monitor (GBM). W used the Fermi GBM's observed short gamma-ray burst light curve aggregated from observed discrete detector event for the simulatio input. The corresponding direction-dependent detector response matrice were used to generate photon counts and light curves around a simulate event, enabling to determine the statistics. This method can be used i the future for trigger algorithm and detector system development, an also to estimate the efficiency of the data analysis pipeline regardin the observable gamma-ray bursts' parameters as well as othe electromagnetic transient

SPIRE Point Source Catalog Explanatory Supplement

The Spectral and Photometric Imaging Receiver (SPIRE) was launched as one of the scientific instruments on board of the space observatory Herschel. The SPIRE photometer opened up an entirely new window in the Submillimeter domain for large scale mapping, that up to then was very difficult to observe. There are already several catalogs that were produced by individual Herschel science projects. Yet, we estimate that the objects of only a fraction of these maps will ever be systematically extracted and published by the science teams that originally proposed the observations. The SPIRE instrument performed its standard photometric observations in an optically very stable configuration, only moving the telescope across the sky, with variations in its configuration parameters limited to scan speed and sampling rate. This and the scarcity of features in the data that require special processing steps made this dataset very attractive for producing an expert reduced catalog of point sources that is being described in this document. The Catalog was extracted from a total of 6878 unmodified SPIRE scan map observations. The photometry was obtained by a systematic and homogeneous source extraction procedure, followed by a rigorous quality check that emphasized reliability over completeness. Having to exclude regions affected by strong Galactic emission, that pushed the limits of the four source extraction methods that were used, this catalog is aimed primarily at the extragalactic community. The result can serve as a pathfinder for ALMA and other Submillimeter and Far-Infrared facilities. 1,693,718 sources are included in the final catalog, splitting into 950688, 524734, 218296 objects for the 250\mu m, 350\mu m, and 500\mu m bands, respectively. The catalog comes with well characterized environments, reliability, completeness, and accuracies, that single programs typically cannot provide