- ID:
- ivo://CDS.VizieR/J/A+A/602/A77
- Title:
- HOBYS: 46 MDCs found in NGC 6334
- Short Name:
- J/A+A/602/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To constrain models of high-mass star formation, the Herschel-HOBYS key program aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes. We used Herschel/PACS and SPIRE 70-500{mu}m images of the NGC 6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their spectral energy distributions (SEDs). We also identified the densest pc-scale cloud structures of NGC 6334, one 2pcx1pc ridge and two 0.8pcx0.8pc hubs, with volume-averaged densities of ~10^5^cm^-3^. A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75M_{sun}_ for MDCs in NGC 6334. MDCs have temperatures of 9.5-40K, masses of 75-1000M_{sun}_, and densities of 1x10^5^-7x10^7^cm^-3^. Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70{mu}m emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7x10^4^yr and at most 3x10^5^yr respectively, suggest a dynamical scenario of high-mass star formation. The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC 6334, favoring a scenario presented here, which simultaneously forms clouds, ridges, MDCs, and high-mass protostars.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/595/A80
- Title:
- H_2_O lines reduced spectra in 11 ULIRGs or HyLIRGs
- Short Name:
- J/A+A/595/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report rest-frame submillimeter H_2_O emission line observations of 11 ultra- or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z~2-4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H_2_O emission lines. These include five 3_21_-3_12_ ortho-H_2_O lines (Eup/k=305K) and nine J=2 para-H_2_O lines, either 2_02_-1_11_ (E_up/k=101K) or 2_11_-2_02_ (E_up/k = 137K). The apparent luminosities of the H_2_O emission lines are {mu}L_H2O_~6-21x10^8^L_{sun}_ (3<{mu}<15, where {mu} is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15Jy.km/s. We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H_2_O lines are found to be similar, generally within 1{sigma} errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H_2_O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H_2_O (LH_2_O) and infrared (LIR) that LH_2_O~LIR^(1.1-1.2)^, with our new detections. This correlation could be explained by a dominant role of far-infrared pumping in the H_2_O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature T_warm_~45-75K, H_2_O column density per unit velocity interval N_H2O_/{DELTA}V>~0.3x10^15^km/s/cm^2^ and 100{mu}m continuum opacity {tau}_100_>1 (optically thick), indicating that H_2_O is likely to trace highly obscured warm dense gas. However, further observations of J>=4 H_2_O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H_2_O^+^ emission in three sources. A tight correlation between L_H_2_O and L_H_2_O^+^ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H_2_O^+^ and H_2_O suggests that cosmic rays generated by strong star formation are possibly driving the H_2_O^+^ formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/1626
- Title:
- HST Frontier Fields Herschel sources
- Short Name:
- J/MNRAS/459/1626
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a complete census of all Herschel-detected sources within the six massive lensing clusters of the HST Frontier Fields (HFF). We provide a robust legacy catalogue of 263 sources with Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey and PEP/HerMES Key Programmes. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying counterparts to gain source redshifts. For each Herschel-detected source we also present magnification factor ({mu}), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of the magnified population, including more than 20 background sub-LIRGs unreachable by Herschel without the assistance gravitational lensing.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A68
- Title:
- Images of molecular and ionized gas around Sgr A*
- Short Name:
- J/A+A/603/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report serendipitous detections of line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) in bands 3, 6, and 7 in the central parsec down to within 1" around Sgr A* at an up to now highest resolution (<0.5") view of the Galactic center (GC) in the submillimeter (sub-mm) domain. From the 100GHz continuum and the H39{alpha} emission we obtain a uniform electron temperature around Te~6000K for the minispiral. The spectral index (S{prop.to}{nu}^{alpha}^) of Sagittarius A* (Sgr A*) is ~0.5 at 100-250GHz and ~0.0 at 230-340GHz. The bright sources in the center show spectral indices around -0.1 implying Bremsstrahlung emission, while dust emission is emerging in the minispiral exterior. Apart from CS, which is most widespread in the center, H^13^CO^+^, HC_3_N, SiO, SO, C_2_H, CH_3_OH, ^13^CS and N_2_H+ are also detected. The bulk of the clumpy emission regions is at positive velocities and in a region confined by the minispiral northern arm (NA), bar, and the sources IRS 3 and 7. Although partly spatially overlapping with the radio recombination line (RRL) emission at same negative velocities, the relation to the minispiral remains unclear. A likely explanation is an infalling clump consisting of denser cloud cores embedded in diffuse gas. This central association (CA) of clouds shows three times higher CS/X (X: any other observed molecule) ratios than the circumnuclear disk (CND) suggesting a combination of higher excitation, by a temperature gradient and/or infrared (IR) pumping, and abundance enhancement due to UV and/or X-ray emission. Hence, we conclude that this CA is closer to the center than the CND. Moreover, we find molecular line emission at velocities up to 200km/s. Apart from the CA, we identified two intriguing regions in the CND. One region shows emission in all molecular species and higher energy levels tested in this and previous observations and contains a methanol class I maser. The other region shows similar behavior of the line ratios such as the CA. Outside the CND, we find the traditionally quiescent gas tracer N_2_H^+^ coinciding with the largest IR dark clouds (IRDC) in the field. Methanol emission is found at and around previously detected methanol class I masers in the same region. We propose to make these particular regions subject to further studies in the scope of hot core, cold core, and extreme photon and/or X-ray dominated region (PDR/XDR) chemistry and consequent star formation in the central few parsecs.
- ID:
- ivo://CDS.VizieR/J/A+A/531/L2
- Title:
- Images of Vega at 1.3mm
- Short Name:
- J/A+A/531/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies have found that Vega is surrounded by an extended debris disc that is very smooth in the far infrared, but displays possible clumpiness at 850um and dust emission peaks at 1.3mm. We reobserved Vega at 1.3mm with PdBI to constrain its circumstellar dust distribution.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A70
- Title:
- Imaging GRB 980425 in millimetic and submm
- Short Name:
- J/A+A/562/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gamma-ray bursts (GRBs) have been proposed as a tool to study star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way special compared with other star-forming galaxies. Here we present spatially resolved maps of dust emission of the host galaxy of the closest known GRB 980425 at z=0.0085 using our new high-resolution observations from Herschel, APEX, ALMA and ATCA. We modeled the spectral energy distributions of the host and of the star-forming region displaying the Wolf-Rayet signatures in the spectrum (WR region), located 800pc away from the GRB position. The host is characterised by low dust content and high fraction of UV-visible star-formation, similar to other dwarf galaxies. Such galaxies are abundant in the local universe, so it is not surprising to find a GRB in one of them, assuming the correspondence between the GRB rate and star-formation. The WR region contributes substantially to the host emission at the far-infrared, millimeter and radio wavelengths and we propose this to be a consequence of its high gas density. If dense environments are also found close to the positions of other GRBs, then the ISM density should also be considered as an important factor influencing whether a given stellar population can produce a GRB, in a similar way as metallicity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/398/109
- Title:
- Imperial IRAS-FSC redshift catalogue (IIFSCz)
- Short Name:
- J/MNRAS/398/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalogue, the Imperial IRAS-FSC Redshift Catalogue (IIFSCz), of 60303 galaxies selected at 60um from the IRAS Faint Source Catalogue (FSC). The IIFSCz consists of accurate position, optical, near-infrared and/or radio identifications, spectroscopic redshift (if available) or photometric redshift (if possible), predicted far-infrared (FIR) and submillimetre (submm) fluxes ranging from 12 to 1380um based upon the best-fitting infrared template. About 55% of the galaxies in the IIFSCz have spectroscopic redshifts, and a further 20% have photometric redshifts obtained through either the training set or the template-fitting method. For S(60)>0.36Jy, the 90% completeness limit of the FSC, 90% of the sources have either spectroscopic or photometric redshifts. Scientific applications of the IIFSCz include validation of current and forthcoming infrared and submm/mm surveys such as AKARI, Planck and Herschel, follow-up studies of rare source populations, large-scale structure and galaxy bias, local multiwavelength luminosity functions and source counts. The catalogue is publicly available at http://astro.imperial.ac.uk/~mrr/fss/.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/97
- Title:
- Infall/expansion velocities in 3 dense cores
- Short Name:
- J/ApJ/833/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although surveys of infall motions in dense cores have been carried out for years, few surveys have focused on mapping infall across cores using multiple spectral-line observations. To fill this gap, we present IRAM 30m telescope maps of N_2_H^+^(1-0), DCO^+^(2-1), DCO^+^(3-2), and HCO^+^(3-2) emission toward two prestellar cores (L492 and L694-2) and one protostellar core (L1521F). We find that the measured infall velocity varies with position across each core and choice of molecular line, likely as a result of radial variations in core chemistry and dynamics. Line-of-sight infall speeds estimated from DCO^+^(2-1) line profiles can decrease by 40-50m/s when observing at a radial offset >=0.04pc from the core's dust continuum emission peak. Median infall speeds calculated from all observed positions across a core can also vary by as much as 65m/s, depending on the transition. These results show that while single-pointing, single-transition surveys of core infall velocities may be good indicators of whether a core is either contracting or expanding, the magnitude of the velocities they measure are significantly impacted by the choice of molecular line, proximity to the core center, and core evolutionary state.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/1926
- Title:
- Infall motions in massive star-forming regions
- Short Name:
- J/MNRAS/450/1926
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive star-forming regions with observed infall motions are good sites for studying the birth of massive stars. In this paper, 405 compact sources have been extracted from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) compact sources that also have been observed in the Millimetre Astronomy Legacy Team 90-GHz (MALT90) survey during years 1 and 2. These observations are complemented with Spitzer GLIMPSE/MIPSGAL mid-IR survey data to help classify the elected star-forming clumps into three evolutionary stages: pre-stellar, proto-stellar and UCHII regions. The results suggest that 0.05g/cm^2^ is a reliable empirical lower bound for the clump surface densities required for massive-star formation to occur. The optically thick HCO^+^(1-0) and HNC(1-0) lines, as well as the optically thin N_2_H^+^(1-0) line were used to search for infall motions towards these sources. By analysing the asymmetries of the optically thick HCO^+^(1-0) and HNC(1-0) lines and the mapping observations of HCO^+^(1-0), a total of 131 reliable infall candidates have been identified. The HCO^+^(1-0) line shows the highest occurrence of obvious asymmetric features, suggesting that it may be a better infall motion tracer than other lines such as HNC(1-0). The detection rates of infall candidates towards pre-stellar, proto-stellar and UCHII clumps are 0.3452, 0.3861 and 0.2152, respectively. The relatively high detection rate of infall candidates towards UCHII clumps indicates that many UCHII regions are still accreting matter. The peak column densities and masses of the infall candidates, in general, display an increasing trend with progressing evolutionary stages. However, the rough estimates of the mass infall rate show no obvious variation with evolutionary stage.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/2288
- Title:
- Infall motions in massive star-forming regions
- Short Name:
- J/MNRAS/461/2288
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we aim to characterize high-mass clumps with infall motions. We selected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz survey, and identified 100 infall candidates. Combined with the results of He et al. (2015, Cat. J/MNRAS/450/1926), we obtained a sample of 732 high-mass clumps, including 231 massive infall candidates and 501 clumps where infall is not detected. Objects in our sample were classified as pre-stellar, proto-stellar, HII or photodissociation region (PDR). The detection rates of the infall candidates in the pre-stellar, proto-stellar, HII and PDR stages are 41.2 per cent, 36.6 per cent, 30.6 per cent and 12.7 per cent, respectively. The infall candidates have a higher H_2_ column density and volume density compared with the clumps where infall is not detected at every stage. For the infall candidates, the median values of the infall rates at the pre-stellar, proto-stellar, HII and PDR stages are 2.6 x 10^-3^, 7.0x10^-3^, 6.5x10^-3^ and 5.5x10^-3^M_{sun}_/yr, respectively. These values indicate that infall candidates at later evolutionary stages are still accumulating material efficiently. It is interesting to find that both infall candidates and clumps where infall is not detected show a clear trend of increasing mass from the pre-stellar to proto-stellar, and to the HII stages. The power indices of the clump mass function are 2.04+/-0.16 and 2.17+/-0.31 for the infall candidates and clumps where infall is not detected, respectively, which agree well with the power index of the stellar initial mass function (2.35) and the cold Planck cores (2.0).
