Far infrared CO and H2_2O emission in intermediate-mass protostars

Intermediate-mass young stellar objects (YSOs) provide a link to understand how feedback from shocks and UV radiation scales from low to high-mass star forming regions. Aims: Our aim is to analyze excitation of CO and H$_2$O in deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with bolometric luminosities of $L_\mathrm{bol}\sim10^2 - 10^3$ $L_\odot$. The maps cover spatial scales of $\sim 10^4$ AU in several CO and H$_2$O lines located in the $\sim55-210$ $\mu$m range. Results: Rotational diagrams of CO show two temperature components at $T_\mathrm{rot}\sim320$ K and $T_\mathrm{rot}\sim700-800$ K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H$_2$O show a single component at $T_\mathrm{rot}\sim130$ K, as seen in low-mass protostars, and about $100$ K lower than in high-mass protostars. Since the uncertainties in $T_\mathrm{rot}$ are of the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity, or whether the change is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation in intermediate-mass protostars is comparable to the central $10^{3}$ AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at $3\cdot10^{3}$ AU scales, suggesting similar shock conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table

Feedback from deeply embedded low- and high-mass protostars. Surveying hot molecular gas with Herschel

Protostars interact violently with their natal cocoons within dense molecular clouds. Characterizing this feedback is key to understanding the efficiency of the star formation process and the chemical processing of material that will be available for planet formation. In this thesis, the imprints of physical processes on molecular gas are analyzed using state-of-the-art far-infrared spectroscopy from Herschel / PACS. Interpretation of the origin of far-infrared line emission allows us to quantify the physical conditions and the role of shocks and ultraviolet radiation during the 'kindergarten years' of low- and high-mass protostars.UBL - phd migration 201

Herschel observations of the circumstellar environment of the two Herbig Be stars R Mon and PDS27

We report and analyse FIR observations of two Herbig Be stars, R Mon and PDS 27, obtained with Herschel's instruments PACS and SPIRE. We construct SEDs and derive the infrared excess. We extract line fluxes from the PACS and SPIRE spectra and construct rotational diagrams in order to estimate the excitation temperature of the gas. We derive CO, [OI] and [CI] luminosities to determine physical conditions of the gas, as well as the dominant cooling mechanism. We confirm that the Herbig Be stars are surrounded by remnants from their parental clouds, with an IR excess that mainly originates in a disc. In R Mon we detect [OI], [CI], [CII], CO (26 transitions), water and OH, while in PDS 27 we only detect [CI] and CO (8 transitions). We attribute the absence of OH and water in PDS 27 to UV photo-dissociation and photo-evaporation. From the rotational diagrams, we find several components for CO: we derive $T_{rot}$ 949$\pm$90 K, 358$\pm$20 K & 77$\pm$12 K for R Mon, 96$\pm$12 K & 31$\pm$4 K for PDS 27 and 25$\pm$8 K & 27$\pm$6 K for their respective compact neighbours. The forsterite feature at 69$\mu$m was not detected in either of the sources, probably due to the lack of (warm) crystalline dust in a flat disc. We find that cooling by molecules is dominant in the Herbig Be stars, while this is not the case in Herbig Ae stars where cooling by [OI] dominates. Moreover, we show that in the Herbig Be star R Mon, outflow shocks are the dominant gas heating mechanism, while in Herbig Ae stars this is stellar. The outflow of R Mon contributes to the observed line emission by heating the gas, both in the central spaxel/beam covering the disc and the immediate surroundings, as well as in those spaxels/beams covering the parabolic shell around it. PDS 27, a B2 star, has dispersed a large part of its gas content and/or destroyed molecules; this is likely given its intense UV field.Comment: Accepted for publication in Astronomy & Astrophysic

Spectroscopic Diagnostics of the Mid-Infrared Features of the Dark Globule, DC 314.8-5.1, with the Spitzer Space Telescope

We present an analysis of the mid-infrared spectra, obtained from the Spitzer Space Telescope, of the dark globule, DC 314.8--5.1, which is at the onset of low-mass star formation. The target has a serendipitous association with a B-type field star, which illuminates a reflection nebula in the cloud. We focus on the polycyclic aromatic hydrocarbon (PAH) emission features prevalent throughout the mid-infrared range. The analysis of the spectra with the PAHFIT software as well as pypahdb package, shows that (i) the intensities of PAH features decrease over distance from the ionizing star toward the cloud center, some however showing a saturation at larger distances; (ii) the relative intensities of the 6.2 and 8.6 features with respect to the 11.2 micron feature remain high throughout the globule, suggesting a larger cation-to-neutral PAH ratio of the order of unity; the breakdown from pypahdb confirms a high ionized fraction within the cloud; (iii) the pypahdb results display a decrease in large PAH fraction with increased distance from HD 130079, as well as a statistically significant correlation between the large size fraction and the ionized fraction across the globule; (iv) the 7.7 PAH feature displays a peak nearer to 7.8 microns, suggesting a chemically processed PAH population with a small fraction of UV-processed PAHs; (v) the H2 S(0) line is detected at larger distances from the ionizing star. All in all, our results suggest divergent physical conditions within the quiescent cloud DC 314.8--5.1 as compared to molecular clouds with ongoing starformation.Comment: Accepted for publication by the Astrophysical Journa

Multiwavelength study of dark globule DC 314.8–5.1 : point-source identification and diffuse emission characterization

We present an analysis of multiwavelength observations of the dark globule DC 314.8–5.1, using data from the Gaia optical, Two Micron All Star Survey near-infrared, and Wide-field Infrared Survey Explorer mid-infrared surveys, dedicated imaging with the Spitzer Space Telescope, and X-ray data obtained with the Swift X-Ray Telescope (XRT). The main goal was to identify possible pre-main-sequence stars (PMSs) and young stellar objects (YSOs) associated with the globule. For this, we studied the infrared colors of all point sources within the boundaries of the cloud. After removing sources with nonstellar spectra, we investigated the Gaia parallaxes for the YSO candidates and found that none are physically related to DC 314.8–5.1. In addition, we searched for X-ray emission from PMSs with Swift-XRT, and found no 0.5–10 keV emission down to a luminosity level $\lesssim$ 10$^{31}$ erg s$^{-1}$, typical of a PMS with mass $\geq$ 2 M$_{\bigodot}$. Our detailed inspection therefore supports a very young, "prestellar core" evolutionary stage for the cloud. Based on archival Planck and IRAS data, we moreover identify the presence of hot dust, with temperatures $\gtrsim$ 100K, in addition to the dominant dust component at 14 K, originating with the associated reflection nebula

Unsupervised classification reveals new evolutionary pathways

While we already seem to have a general scenario of the evolution of different types of galaxies, a complete and satisfactory understanding of the processes that led to the formation of all the variety of today's galaxy types is still beyond our reach. To solve this problem, we need both large datasets reaching high redshifts and novel methodologies for dealing with them. The VIPERS survey statistical power, which observed $\sim90,000$ galaxies at $z > 0.5$, and the application of an unsupervised clustering algorithm allowed us to distinguish 12 galaxy classes. Studies of their environmental dependence indicate that this classification may actually reflect different galaxy evolutionary paths. For instance, a class of the most passive red galaxies gathers galaxies $\sim20\%$ smaller than other red galaxies of a similar stellar mass, revealing the first sample of red nuggets at intermediate redshift. On the other end, a class of blue dwarf galaxies is composed mainly of AGN, challenging commonly used mid-infrared AGN selections.Comment: Accepted for publication in the ML4ASTRO (ICML 2022) proceeding boo

OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS

OH is a key species in the water chemistry of star-forming regions, because its presence is tightly related to the formation and destruction of water. This paper presents OH observations from 23 low- and intermediate-mass young stellar objects obtained with the PACS integral field spectrometer on-board Herschel in the context of the Water In Star-forming Regions with Herschel (WISH) key program. Most low-mass sources have compact OH emission (< 5000 AU scale), whereas the OH lines in most intermediate-mass sources are extended over the whole PACS detector field-of-view (> 20000 AU). The strength of the OH emission is correlated with various source properties such as the bolometric luminosity and the envelope mass, but also with the OI and H2O emission. Rotational diagrams for sources with many OH lines show that the level populations of OH can be approximated by a Boltzmann distribution with an excitation temperature at around 70 K. Radiative transfer models of spherically symmetric envelopes cannot reproduce the OH emission fluxes nor their broad line widths, strongly suggesting an outflow origin. Slab excitation models indicate that the observed excitation temperature can either be reached if the OH molecules are exposed to a strong far-infrared continuum radiation field or if the gas temperature and density are sufficiently high. Using realistic source parameters and radiation fields, it is shown for the case of Ser SMM1 that radiative pumping plays an important role in transitions arising from upper level energies higher than 300 K. The compact emission in the low-mass sources and the required presence of a strong radiation field and/or a high density to excite the OH molecules points towards an origin in shocks in the inner envelope close to the protostar.Comment: Accepted for publication in Astronomy and Astrophysics. Abstract abridge

Multiwavelength Study of Dark Globule DC 314.8-5.1: Point Source Identification and Diffuse Emission Characterization

We present an analysis of multi-wavelength observations of the dark globule DC\,314.8--5.1, using data from the Gaia optical, 2MASS near-infrared, and WISE mid-infrared surveys, dedicated imaging with the Spitzer Space Telescope, and X-ray data obtained with the Swift-XRT Telescope (XRT). The main goal was to identify possible pre-main sequence stars (PMSs) and young stellar objects (YSOs) associated with the globule. For this, we studied the infrared colors of all point sources within the boundaries of the cloud. After removing sources with non-stellar spectra, we investigated the Gaia parallaxes for the YSO candidates, and found that none are physically related to DC\,314.8--5.1. In addition, we searched for X-ray emission from pre-main sequence stars with Swift-XRT, and found no 0.5--10\,keV emission down to a luminosity level $\lesssim 10^{31}$erg\,s$^{-1}$, typical of a PMS with mass\,$\ge 2 M_\odot$. Our detailed inspection therefore supports a very young, ``pre-stellar core'' evolutionary stage for the cloud. Based on archival Planck and IRAS data, we moreover identify the presence of hot dust, with temperatures $\gtrsim 100$\,K, in addition to the dominant dust component at 14\,K, originating with the associated reflection nebula.Comment: Accepted to A

CO in Protostars (COPS): HerschelHerschel-SPIRE Spectroscopy of Embedded Protostars

We present full spectral scans from 200-670$\mu$m of 26 Class 0+I protostellar sources, obtained with $Herschel$-SPIRE, as part of the "COPS-SPIRE" Open Time program, complementary to the DIGIT and WISH Key programs. Based on our nearly continuous, line-free spectra from 200-670 $\mu$m, the calculated bolometric luminosities ($L_{\rm bol}$) increase by 50% on average, and the bolometric temperatures ($T_{\rm bol}$) decrease by 10% on average, in comparison with the measurements without Herschel. Fifteen protostars have the same Class using $T_{\rm bol}$ and $L_{\rm bol}$/$L_{\rm submm}$. We identify rotational transitions of CO lines from J=4-3 to J=13-12, along with emission lines of $^{13}$CO, HCO$^+$, H$_{2}$O, and [CI]. The ratios of $^{12}$CO to $^{13}$CO indicate that $^{12}$CO emission remains optically thick for $J_{\rm up}$ < 13. We fit up to four components of temperature from the rotational diagram with flexible break points to separate the components. The distribution of rotational temperatures shows a primary population around 100 K with a secondary population at $\sim$350 K. We quantify the correlations of each line pair found in our dataset, and find the strength of correlation of CO lines decreases as the difference between $J$-level between two CO lines increases. The multiple origins of CO emission previously revealed by velocity-resolved profiles are consistent with this smooth distribution if each physical component contributes to a wide range of CO lines with significant overlap in the CO ladder. We investigate the spatial extent of CO emission and find that the morphology is more centrally peaked and less bipolar at high-$J$ lines. We find the CO emission observed with SPIRE related to outflows, which consists two components, the entrained gas and shocked gas, as revealed by our rotational diagram analysis as well as the studies with velocity-resolved CO emission.Comment: 50 pages, 18 figures, accepted to ApJS. Revised for Table 6 and Figure