arXiv subjects

P. Palmeirim

Publications and source records attributed to P. Palmeirim.

At least 19 recordsLinked to original sources

arXiv2022

On the typical width of Herschel filaments

Herschel studies suggest that nearby (d < 500 pc) molecular filaments have a typical half-power width ~0.1pc, but this finding has been questioned on the ground that the measured widths tend to increase with distance. Here we revisit the dependence of measured filament widths on distance or equivalently spatial resolution, in an effort to determine whether nearby molecular filaments have a characteristic half-power width or whether this is an artifact of the finite resolution of the Herschel data. We perform a convergence test on the B211/213 filament in Taurus, by degrading the resolution of the Herschel data several times and re-estimating the filament width from the resulting column density profiles. We also compare the widths measured for the Taurus filament and other filaments from the Herschel Gould Belt survey to those found for synthetic filaments with various types of simple, idealized column density profiles. We find that the measured filament widths do increase slightly as the spatial resolution worsens and/or the distance to the filaments increases. However, this trend is entirely consistent with what is expected from simple beam convolution for filaments with density profiles that are Plummer-like and have intrinsic half-power diameters ~0.08-0.1 pc and logarithmic slopes 1.5 < p < 2.5 at large radii, as observed in many cases including the Taurus filament. Due to the presence of background noise fluctuations, deconvolution of the measured widths from the telescope beam quickly becomes inaccurate. We conclude that the typical half-power filament width ~0.1 pc measured with Herschel in nearby clouds most likely reflects the presence of a true common scale in the filamentary structure of the cold interstellar medium, at least in the solar neighborhood. We suggest that this common scale may correspond to the magnetized turbulent correlation length in molecular clouds.

astro-ph.GA↗

arXiv2022

Filament coalescence and hub structure in MonR2: Implications to massive star and cluster formation

Here we study the MonR2 star forming region, which has a rich network of filaments joining in a star cluster forming hub, aiming at understanding the hub structure and to examine the mass fraction residing in the hub and in the filaments, which is a key factor that influences massive star formation. We conducted a multi-scale, multi-component analysis of the Herschel column density maps (resolution of 18.2" or $\sim$0.07 pc at 830 pc) of the region using a newly developed algorithm "getsf" to identify the structural components, namely, extended cloud, filaments, and sources. We find that cascades of lower column density filaments coalesce to form higher density filaments eventually merging inside the hub (0.8 pc radius). As opposed to the previous view of the hub as a massive clump with $\sim$1 pc radius, we find it to be a network of short high-density filaments. The total mass reservoir in the MonR2 HFS (5 pc $\times$ 5 pc) is split between filaments (54%), extended cloud (37%) and sources (9%). The M/L of filaments increase from $\sim$ 10 Msun/pc at 1.5pc from the hub to $\sim$ 100 Msun/pc at its centre, while the number of filaments per annulus of 0.2pc width decreases from 20 to 2 in the same range. The observed radial column density structure of the HFS (filament component only) displays a power-law dependence of $N_{\mathrm{H}_2} \propto r^{-2.17}$ up to a radius of $\sim$2.5 pc from the central hub, resembling a global collapse of the HFS. We present a scenario where the HFS can be supported by magnetic fields which interact, merge and reorganize themselves as the filaments coalesce. In the new view of the hub as a network of high-density filaments, we suggest that only the stars located in the network can benefit from the longitudinal flows of gas to become massive, which may explain the reason for the formation of many low-mass stars in cluster centres.

astro-ph.GA↗

arXiv2021

Probing the structure of a massive filament: ArTeMiS 350 and 450 micron mapping of the integral-shaped filament in Orion A

(abridged) Within the Orion A molecular cloud, the integral-shaped filament (ISF) is a prominent, degree-long structure of dense gas and dust, with clear signs of recent and on-going high-mass star formation. We used the ArTeMiS bolometer camera at APEX to map a 0.6x0.2 deg^2 region covering OMC-1, OMC-2, OMC-3 at 350 and 450 micron. We combined these data with Herschel-SPIRE maps to recover extended emission. The combined Herschel-ArTeMiS maps provide details on the distribution of dense, cold material, with a high spatial dynamic range, from our 8'' resolution (0.016 pc) up to the size of the map ~10-15 deg. By combining Herschel and ArTeMiS data at 160, 250, 350 and 450 micron, we constructed high-resolution temperature and H2 column density maps. We extracted radial profiles from the column density map in several, representative portions of the ISF, that we fitted with Gaussian and Plummer models to derive their intrinsic widths. We also compared the distribution of material traced by ArTeMiS with that seen in the higher density tracer N2H+(1-0) recently observed with the ALMA interferometer. All the radial profiles that we extracted show clear deviation from a Gaussian, with evidence for an inner plateau, previously not seen using Herschel-only data. We measure intrinsic half-power widths in the range 0.06 to 0.11 pc. This is significantly larger than the Gaussian widths measured for fibers seen in N2H+, which probably traces only the dense innermost regions of the large-scale filament. These half-power widths are within a factor of two of the value of 0.1 pc found for a large sample of nearby filaments in various low-mass star-forming regions, which tends to indicate that the physical conditions governing the fragmentation of prestellar cores within transcritical or supercritical filaments are the same over a large range of masses per unit length.

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arXiv2021

The Hi-GAL compact source catalogue -- II. The 360° catalogue of clump physical properties

We present the $360^\circ$ catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 $μ$m. This release not only completes the analogous catalogue previously produced by the Hi-GAL collaboration for $-71^\circ \lesssim \ell \lesssim 67^\circ$, but also meaningfully improves it thanks to a new set of heliocentric distances, 120808 in total. About a third of the 150223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 $μ$m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23~per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from $λ=21$ to 1100 $μ$m, gives the source luminosity and other bolometric quantities, while a modified black body fitted to data for $λ\geq 160\, μ$m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions.

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arXiv2020

Physical properties of the ambient medium and of dense cores in the Perseus star-forming region derived from Herschel Gould Belt Survey observations

(Abridged) In this paper, we present analyses of images taken with the Herschel ESA satellite from 70mu to 500mu. We first constructed column density and dust temperature maps. Next, we identified compact cores in the maps, and characterize the cores using modified blackbody fits to their SEDs: we identified 684 starless cores, of which 199 are bound and potential prestellar cores, and 132 protostars. We also matched the Herschel-identified young stars with GAIA sources to model distance variations across the Perseus cloud. We measure a linear gradient function with right ascension and declination for the entire cloud. From the SED fits, mass and temperature of cores were derived. The core mass function can be modelled with a log-normal distribution that peaks at 0.82~$M_\sun$ suggesting a star formation efficiency of 0.30. The high-mass tail can be modelled with a power law of slope $\sim-2.32$, close to the Salpeter's value. We also identify the filamentary structure of Perseus, confirming that stars form preferentially in filaments. We find that the majority of filaments where star formation is ongoing are transcritical against their own internal gravity because their linear masses are below the critical limit of 16~$M_\sun$pc$^{-1}$ above which we expect filaments to collapse. We find a possible explanation for this result, showing that a filament with a linear mass as low as 8~$M_\sun$pc$^{-1}$ can be already unstable. We confirm a linear relation between star formation efficiency and slope of dust probability density function and a similar relation is also seen with the core formation efficiency. We derive a lifetime for the prestellar core phase of $1.69\pm0.52$~Myr for Perseus but different regions have a wide range in prestellar core fractions, hint that star-formation has started only recently in some clumps. We also derive a free-fall time for prestellar cores of 0.16~Myr.

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arXiv2020

Unifying low and high mass star formation through density amplified hubs of filaments

Context: Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarves, and massive O-type(50-100\msun) stars. Aims: To identify candidate hub-filament systems (HFS) in the Milky-Way and examine their role in the formation of the highest mass stars and star clusters. Methods: Filaments around ~35000 HiGAL clumps that are detected using the DisPerSE algorithm. Hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. Results: ~3700~(11\%) are candidate HFS of which, ~2150~(60\%) are pre-stellar, ~1400~(40\%) are proto-stellar. All clumps with L>10^4 Lsun and L>10^5 Lsun at distances respectively within 2kpc and 5kpc are located in the hubs of HFS. The column-densities of hubs are found to be enhanced by a factor of ~2 (pre-stellar sources) up to ~10 (proto-stellar sources). Conclusions: All high-mass stars preferentially form in the density enhanced hubs of HFS. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a "filaments to clusters" unified paradigm for star formation, with the following salient features: a) low-intermediate mass stars form in the filaments slowly (10^6yr) and massive stars quickly (10^5yr) in the hub, b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, c) Feedback dissiption and mass segregation arise naturally due to HFS properties, and c) explain age spreads within bound clusters and formation of isolated OB associations.

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arXiv2020

The accretion history of high-mass stars: An ArTéMiS pilot study of Infrared Dark Clouds

The mass growth of protostars is a central element to the determination of fundamental stellar population properties such as the initial mass function. Constraining the accretion history of individual protostars is therefore an important aspect of star formation research. The goal of the study presented here is to determine whether high-mass (proto)stars gain their mass from a compact (<0.1pc) fixed-mass reservoir of gas, often referred to as dense cores, in which they are embedded, or whether the mass growth of high-mass stars is governed by the dynamical evolution of the parsec-scale clump that typically surrounds them. To achieve this goal, we performed a 350micron continuum mapping of 11 infrared dark clouds, along side some of their neighbouring clumps, with the ArTéMiS camera on APEX. By identifying about 200 compact ArTéMiS sources, and matching them with Herschel Hi-GAL 70micron sources, we have been able to produce mass vs. temperature diagrams. We compare the nature (i.e. starless or protostellar) and location of the ArTéMiS sources in these diagrams with modelled evolutionary tracks of both core-fed and clump-fed accretion scenarios. We argue that the latter provide a better agreement with the observed distribution of high-mass star-forming cores. However, a robust and definitive conclusion on the question of the accretion history of high-mass stars requires larger number statistics.

astro-ph.GA↗

arXiv2020

Angular momentum profiles of Class 0 protostellar envelopes

[abridged] Understanding how the infalling gas redistribute most of its initial angular momentum inherited from prestellar cores before reaching the stellar embryo is a key question. Disk formation has been naturally considered as a possible solution to this "angular momentum problem". However, how the initial angular momentum of protostellar cores is distributed and evolves during the main accretion phase and the beginning of disk formation has largely remained unconstrained up to now. In the framework of the IRAM CALYPSO survey, we used high dynamic range C$^{18}$O (2-1) and N$_2$H$^+$ (1-0) observations to quantify the distribution of specific angular momentum along the equatorial axis in a sample of 12 Class 0 protostellar envelopes from scales ~50 to 10000 au. The radial distributions of specific angular momentum in the CALYPSO sample suggest two distinct regimes within protostellar envelopes: the specific angular momentum decreases as $j \propto r^{1.6 \pm 0.2}$ down to ~1600 au and then tends to become relatively constant around 6 $\times$ 10$^{-4}$ km s$^{-1}$ pc down to ~50 au. The values of specific angular momentum measured in the inner Class 0 envelopes, namely that of the material directly involved in the star formation process ($<$1600 au), is on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales $>$1600 au, suggesting that they may not be related to rotational motions of the envelopes. We conclude that the specific angular momentum observed at these scales could find its origin in core-forming motions (infall, turbulence) or trace an imprint of the initial conditions for the formation of protostellar cores.

astro-ph.SR↗

arXiv2020

The role of Galactic HII regions in the formation of filaments. High-resolution submilimeter imaging of RCW 120 with ArTéMiS

Massive stars and their associated ionized (HII) regions could play a key role in the formation and evolution of filaments that host star formation. However, the properties of filaments that interact with H regions are still poorly known. To investigate the impact of HII regions on the formation of filaments, we imaged the Galactic HII region RCW 120 and its surroundings where active star formation takes place and where the role of ionization feedback on the star formation process has already been studied. We used the ArTéMiS camera on the APEX telescope and combined the ArTéMiS data at 350 and 450 microns with Herschel-SPIRE/HOBYS. We studied the dense gas distribution around RCW 120 with a resolution of 8 arcsec (0.05 pc at a distance of 1.34 kpc). Our study allows us to trace the median radial intensity profile of the dense shell of RCW 120. This profile is asymmetric, indicating a clear compression from the HII region on the inner part of the shell. The profile is observed to be similarly asymmetric on both lateral sides of the shell, indicating a homogeneous compression over the surface. On the contrary, the profile analysis of a radial filament associated with the shell, but located outside of it, reveals a symmetric profile, suggesting that the compression from the ionized region is limited to the dense shell. The mean intensity profile of the internal part of the shell is well fitted by a Plummer like profile with a deconvolved Gaussian FWHM of 0.09 pc, as observed for filaments in low-mass star-forming regions. This study suggests that compression exerted by HII regions may play a key role in the formation of filaments and may further act on their hosted star formation. ArTéMiS data also suggest that RCW 120 might be a 3D ring, rather than a spherical structure

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arXiv2019

The Hi-GAL catalogue of dusty filamentary structures in the Galactic Plane

The recent data collected by {\it Herschel} have confirmed that interstellar structures with filamentary shape are ubiquitously present in the Milky Way. Filaments are thought to be formed by several physical mechanisms acting from the large Galactic scales down to the sub-pc fractions of molecular clouds, and they might represent a possible link between star formation and the large-scale structure of the Galaxy. In order to study this potential link, a statistically significant sample of filaments spread throughout the Galaxy is required. In this work we present the first catalogue of $32,059$ candidate filaments automatically identified in the Hi-GAL survey of the entire Galactic Plane. For these objects we determined morphological (length, $l^{a}$, and geometrical shape) and physical (average column density, $N_{\rm H_{2}}$, and average temperature, $T$) properties. We identified filaments with a wide range of properties: 2$'$\,$\leq l^{a}\leq$\, 100$'$, $10^{20} \leq N_{\rm H_{2}} \leq 10^{23}$\,cm$^{-2}$ and $10 \leq T\leq$ 35\,K. We discuss their association with the Hi-GAL compact sources, finding that the most tenuous (and stable) structures do not host any major condensation and we also assign a distance to $\sim 18,400$ filaments for which we determine mass, physical size, stability conditions and Galactic distribution. When compared to the spiral arms structure, we find no significant difference between the physical properties of on-arm and inter-arm filaments. We compared our sample with previous studies, finding that our Hi-GAL filament catalogue represents a significant extension in terms of Galactic coverage and sensitivity. This catalogue represents an unique and important tool for future studies devoted to understanding the filament life-cycle.

astro-ph.GA↗

arXiv2019

Probing fragmentation and velocity sub-structure in the massive NGC 6334 filament with ALMA

Herschel surveys of Galactic clouds support a paradigm for low-mass star formation in which dense filaments play a crucial role. The detailed fragmentation properties of star-forming filaments remain poorly understood, however, and the validity of the filament paradigm in the high-mass regime is still unclear. To investigate the density/velocity structure of the filament in the high-mass star-forming region NGC6334, we conducted ALMA observations in the 3mm continuum and the N2H+(1-0) line at ~3arcsec resolution. The filament was detected in both tracers. We identified 26 cores at 3mm and 5 velocity-coherent fiber-like features in N2H+ within the filament. The typical length of, and velocity difference between, the fiber-like features of the NGC6334 filament are reminiscent of the properties for the fibers of the low-mass star-forming filament B211/B213. Only 2 or 3 of the 5 velocity-coherent features are well aligned with the filament and may represent genuine, fiber sub-structures. The core mass distribution has a peak at ~10Msun. They can be divided into 7 groups of cores, closely associated with ArTeMiS clumps. The projected separation between cores and the projected spacing between clumps are roughly consistent with the effective Jeans length in the filament and a physical scale of about 4 times the filament width, respectively, suggesting a bimodal filament fragmentation process. Despite being one order of magnitude denser and more massive than the B211/B213 filament, the NGC6334 filament has a similar density/velocity structure. The difference is that the cores in NGC6334 appear to be an order of magnitude denser and more massive than the cores in Taurus. This suggests that dense filaments may evolve and fragment in a similar manner in low- and high-mass star-forming regions, and that the filament paradigm may hold in the intermediate-mass (if not high-mass) star formation regime.

astro-ph.GA↗

arXiv2018

Probing accretion of ambient cloud material into the Taurus B211/B213 filament

Herschel observations have emphasized the role of molecular filaments in star formation. However, the origin and evolution of these filaments are not yet well understood, partly because of the lack of kinematic information. To examine whether the B211/B213 filament is accreting background gas due to its gravitational potential, we produced a toy accretion model and compared its predictions to the 12CO(1--0) and 13CO(1--0) velocity patterns. We also examined the spatial distributions of Halpha, 857 GHz continuum, and HI emission to search for evidence of large-scale external effects. We estimated the depth of the cloud around the B211/B213 filament to be 0.3--0.7 pc under the assumption that the density of the gas is the same as the 13CO critical density. Compared to a linear extent of >10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud is sheet-like. 12CO and 13CO PV diagrams perpendicular to the filament axis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filament and blueshifted to the southwest, respectively, and that the velocities of both components approach the filament velocity as the line of sight approaches the filament crest. The PV diagrams predicted by our accretion model are in good agreement with the observed 12CO and 13CO PV diagrams, supporting the scenario of mass accretion into the filament proposed by Palmeirim et al. Moreover, inspection of the distribution of the Halpha and 857 GHz emission in the Taurus-California-Perseus region suggests that the B211/B213 filament may have formed as a result of an expanding supershell generated by the Per OB2 association. Based on these results, we propose a scenario in which the B211/B213 filament was initially formed by large-scale compression of HI gas and then is now growing in mass due to the gravitational accretion of ambient cloud molecular gas.

astro-ph.GA↗

arXiv2018

Characterizing the properties of nearby molecular filaments observed with Herschel

[Abridged] Molecular filaments have received special attention recently, thanks to new observational results on their properties. In particular, our early analysis of filament properties revealed a narrow distribution of median widths centered at a value of about 0.1 pc. Here, we extend and complement our initial study with the analysis of the filamentary structures observed in eight nearby molecular clouds. We use the column density maps derived from Herschel data and the DisPerSE algorithm to trace a network of filaments in each cloud. We build synthetic maps to assess the completeness limit of our extracted sample and validate our measurements. Our analysis yields a selected sample of 599 filaments with aspect ratios larger than 3 and column density contrasts larger than 0.3. We show that our sample is more than 95% complete for column density contrasts larger than 1, with only 5% of spurious detections. On average, more than 15% of the total gas mass in the clouds, and more than 80% of the dense gas mass, is found to be in the form of filaments, respectively. Analysis of the radial column density profiles of the 599 filaments indicates a narrow distribution of crest-averaged inner widths, with a median value of 0.10 pc and an interquartile range of 0.07 pc. In contrast, the filaments span wide ranges in length, central column density, column density contrast, and mass per unit length. The characteristic filament width is well resolved by Herschel observations, and a median value of 0.1 pc is consistently found using three distinct estimates based on (1) a direct measurement of the width at half power after background subtraction, as well as (2) Gaussian and (3) Plummer fits. The existence of a characteristic filament width is further supported by the presence of a tight correlation between mass per unit length and central column density for the observed filaments.

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arXiv2018

A catalogue of dense cores and young stellar objects in the Lupus complex based on Herschel Gould Belt Survey observations

The Herschel Gould Belt Survey key project mapped the bulk of nearby star-forming molecular clouds in five far-infrared bands with the aim of compiling complete census of prestellar cores and young, embedded protostars. In this paper, we present the catalogue of the dense cores and YSOs/protostars extracted from the Herschel maps of the Lupus I, III, and IV molecular clouds. The physical properties of the detected objects were derived by fitting their spectral energy distributions. A total of 532 dense cores, out of which 103 are presumably prestellar in nature, and 38 YSOs/protostars have been detected in the three clouds. Almost all the prestellar cores are associated with filaments against only about one third of the unbound cores and YSOs/protostars. Prestellar core candidates are found even in filaments that are on average thermally sub-critical and over a background column density lower than that measured in other star forming regions so far. The core mass function of the prestellar cores peaks between 0.2 and 0.3 solar masses and it is compatible with the log-normal shape found in other regions. Herschel data reveal several, previously undetected, protostars and new candidates of Class 0 and Class II with transitional disks. We estimate the evolutionary status of the YSOs/protostars using two independent indicators: the $α$ index and the fitting of the spectral energy distribution from near- to far-infrared wavelengths. For 70% of the objects, the evolutionary stages derived with the two methods are in agreement. Lupus is confirmed to be a very low-mass star-forming region, both in terms of the prestellar condensations and of the diffuse medium. Noticeably, in the Lupus clouds we have found star formation activity associated with interstellar medium at low column density, usually quiescent in other (more massive) star forming regions.

astro-ph.GA↗

arXiv2018

The dense cores and filamentary structure of the molecular cloud in Corona Australis. Herschel SPIRE and PACS observations from the Herschel Gould Belt Survey

We present a catalogue of prestellar and starless cores within the Corona Australis molecular cloud using photometric data from the Herschel Space Observatory. At a distance of d~130 pc, Corona Australis is one of the closest star-forming regions. Herschel has taken multi-wavelength data of Corona Australis with both the SPIRE and PACS photometric cameras in a parallel mode with wavelengths in the range 70 μm to 500 μm. A complete sample of starless and prestellar cores and embedded protostars is identified. Other results from the Herschel Gould Belt Survey have shown spatial correlation between the distribution of dense cores and the filamentary structure within the molecular clouds. We go further and show correlations between the properties of these cores and their spatial distribution within the clouds, with a particular focus on the mass distribution of the dense cores with respect to their filamentary proximity. We find that only lower-mass starless cores form away from filaments, while all of the higher-mass prestellar cores form in close proximity to, or directly on the filamentary structure. This result supports the paradigm that prestellar cores mostly form on filaments. We analyse the mass distribution across the molecular cloud, finding evidence that the region around the Coronet appears to be at a more dynamically advanced evolutionary stage to the rest of the clumps within the cloud.

astro-ph.GA↗

arXiv2017

Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data

We describe new Hi-GAL based maps of the entire Galactic Plane, obtained using continuum data in the wavelength range 70-500 $μ$m. These maps are derived with the PPMAP procedure, and therefore represent a significant improvement over those obtained with standard analysis techniques. Specifically they have greatly improved resolution (12 arcsec) and, in addition to more accurate integrated column densities and mean dust temperatures, they give temperature-differential column densities, i.e., separate column density maps in twelve distinct dust temperature intervals, along with the corresponding uncertainty maps. The complete set of maps is available on-line. We briefly describe PPMAP and present some illustrative examples of the results. These include (a) multi-temperature maps of the Galactic HII region W5-E, (b) the temperature decomposition of molecular cloud column-density probability distribution functions, and (c) the global variation of mean dust temperature as a function of Galactocentric distance. Amongst our findings are: (i) a strong localised temperature gradient in W5-E in a direction orthogonal to that towards the ionising star, suggesting an alternative heating source and providing possible guidance for models of the formation of the bubble complex, and (ii) the overall radial profile of dust temperature in the Galaxy shows a monotonic decrease, broadly consistent both with models of the interstellar radiation field and with previous estimates at lower resolution. However, we also find a central temperature plateau within ~ 6 kpc of the Galactic centre, outside of which is a pronounced steepening of the radial profile. This behaviour may reflect the greater proportion of molecular (as opposed to atomic) gas in the central region of the Galaxy.

astro-ph.GA↗

arXiv2017

Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA

The characterization of dust properties in the interstellar medium (ISM) is key for star formation. Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds. However, most of these estimates rely on dust models that need further observational constraints from clouds to prestellar and protostellar cores. We present results of a study of dust emissivity changes based on mm-continuum data obtained with the NIKA camera at the IRAM-30m telescope. Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index ($β$) in the Rayleigh-Jeans tail of the dust spectral energy distribution (SED) far from its peak emission, where the contribution of other parameters (i.e. dust temperature) is important. Focusing on the Taurus molecular cloud, a low-mass star-forming regions in the Gould Belt, we analyze the emission properties of several distinct objects in the B213 filament: three prestellar cores, two Class-0/I protostellar cores and one Class-II object. By means of the ratio of the two NIKA channel-maps, we show that in the Rayleigh-Jeans approximation the dust emissivity index varies among the objects. For one prestellar and two protostellar cores, we produce a robust study using Herschel data to constrain the dust temperature of the sources. By using the Abel transform inversion technique we get accurate radial $β$ profiles. We find systematic spatial variations of $β$ in the protostellar cores that is not observed in the prestellar core. While in the former case $β$ decreases toward the center, in the latter it remains constant. Moreover, $β$ appears anticorrelated with the dust temperature. We discuss the implication of these results in terms of dust grain evolution between pre- and protostellar cores.

astro-ph.GA↗

arXiv2017

Spatial distribution of star formation related to ionized regions throughout the inner Galactic plane

We present a comprehensive statistical analysis of star-forming objects located in the vicinities of 1 360 bubble structures throughout the Galactic Plane and their local environments. The compilation of ~70 000 star-forming sources, found in the proximity of the ionized (Hii) regions and detected in both Hi-GAL and GLIMPSE surveys, provided a broad overview of the different evolutionary stages of star-formation in bubbles, from prestellar objects to more evolved young stellar objects (YSOs). Surface density maps of star-forming objects clearly reveal an evolutionary trend where more evolved star-forming objects are found spatially located near the center, while younger star-forming objects are found at the edge of the bubbles. We derived dynamic ages for a subsample of 182 Hii regions for which kinematic distances and radio continuum flux measurements were available. We detect ~80% more star-forming sources per unit area in the direction of bubbles than in the surrounding fields. We estimate ~10% clump formation efficiency (CFE) of Hi-GAL clumps in bubbles, twice the CFE in fields not affected by feedback. We find higher CFE of protostellar clumps in younger bubbles, whose density of the bubble shells is higher. We argue that the formation rate from prestellar to protostellar phase is probably higher during the early stages of the bubble expansion. Evaluation of the fragmentation time inside the shell of bubbles advocates the preexistence of clumps in the medium before the bubble, as supported by numerical simulations. Approximately 23% of the Hi-GAL clumps are found located in the direction of a bubble, with 15% for prestellar clumps and 41% for protostellar clumps. We argue that the high fraction of protostellar clumps may be due to the acceleration of the star-formation process cause by the feedback of the (Hii) bubbles.

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