Abstract
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 ≲10
31
erg s
−1
, typical of a PMS with mass ≥2
M
⊙
. 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 ≳100 K, in addition to the dominant dust component at 14 K, originating with the associated reflection nebula.
ABSTRACT
Red ultra-compact massive galaxies, called red nuggets were formed at high redshifts (z ∼ 2–3). Survivors of red nuggets, known as relics, observed at lower redshifts (z < 2) are believed to ...remain almost unchanged since their formation. For the first time, we verify the environmental properties of red nuggets at intermediate redshift (0.5 < z < 0.9) using 42 red, massive (log(Mstar/M⊙) ≥ 10.9), and ultra compact (Re < 1.5 kpc) from the VIMOS Public Extragalactic Redshift Survey (VIPERS). We found that the increasing fraction of red galaxies, when moving to denser environments, is driven by the red massive normal-size galaxies. Red nuggets, similarly to red intermediate-mass (10.4 ≲ log (Mstar/M⊙) < 10.9) ultra-compact galaxies, are found in various types of environments, with consistent (within 1σ) fractions across all local densities. Analysis of red nugget stellar ages suggests that relics are preferably found in high-density regions while quiescent red nuggets are overabundant in low-density environments. We speculate that red nuggets have survived to lower redshifts via two channels: i) in low-density environments, where the fraction of red nuggets decreases as time passes due to (very) limited merger activity, ii) in high-density environments, where the number of red nuggets drops at higher redshift due to merger activity and is preserved at lower redshift as the high velocities of clusters prevent them from being cannibalized. Even more, the fraction of red nuggets in clusters may increase due to the addition of red massive normal-size galaxies deprived of their envelopes with cosmic time.
Context. Accretion of gas from the intergalactic medium is required to fuel star formation in galaxies. We have recently suggested that this process can be studied using host galaxies of gamma-ray ...bursts (GRBs). Aims. Our aim is to test this possibility by studying in detail the properties of gas in the closest galaxy hosting a GRB (980425). Methods. We obtained the first ever far-infrared (FIR) line observations of a GRB host, namely Herschel/PACS resolved C ii 158 μm and O i 63 μm spectroscopy, and an APEX/SHeFI CO(2–1) line detection and ALMA CO(1–0) observations of the GRB 980425 host. Results. The GRB 980425 host has elevated C ii/FIR and O i/FIR ratios and higher values of star formation rates (SFR) derived from line (C ii, O i, Hα) than from continuum (UV, IR, radio) indicators. C ii emission exhibits a normal morphology, peaking at the galaxy centre, whereas O i is concentrated close to the GRB position and the nearby Wolf-Rayet region. The high O i flux indicates that there is high radiation field and high gas density at these positions, as derived from modelling of photo-dissociation regions. The C ii/CO luminosity ratio of the GRB 980425 host is close to the highest values found for local star-forming galaxies. Indeed, its CO-derived molecular gas mass is low given its SFR and metallicity, but the C ii-derived molecular gas mass is close to the expected value. Conclusions. The O i and H i concentrations and the high radiation field and density close to the GRB position are consistent with the hypothesis of a very recent (at most a few tens of Myr ago) inflow of atomic gas triggering star formation. In this scenario dust has not had time to build up (explaining high line-to-continuum ratios). Such a recent enhancement of star formation activity would indeed manifest itself in high SFRline/SFRcontinuum ratios because the line indicators are sensitive only to recent (≲10 Myr) activity, whereas the continuum indicators measure the SFR averaged over much longer periods (~100 Myr). Within a sample of 32 other GRB hosts, 20 exhibit SFRline/SFRcontinuum> 1 with a mean ratio of 1.74 ± 0.32. This is consistent with a very recent enhancement of star formation that is common among GRB hosts, so galaxies that have recently experienced inflow of gas may preferentially host stars exploding as GRBs. Therefore GRBs may be used to select a unique sample of galaxies that is suitable for the investigation of recent gas accretion.
Context. Long gamma-ray bursts (GRBs) can potentially be used as a tool to study star formation and recent gas accretion onto galaxies. However, the information about gas properties of GRB hosts is ...scarce. In particular, very few carbon monoxide (CO) line detections of individual GRB hosts have been reported. It has also been suggested that GRB hosts have lower molecular gas masses than expected from their star formation rates (SFRs). Aims. The objectives of this paper are to analyse molecular gas properties of the first substantial sample of GRB hosts and test whether they are deficient in molecular gas. Methods. We obtained CO(2-1) observations of seven GRB hosts with the APEX and IRAM 30 m telescopes. We analysed these data together with all other hosts with previous CO observations. From these observations we calculated the molecular gas masses of these galaxies and compared them with the expected values based on their SFRs and metallicities. Reults. We obtained detections for 3 GRB hosts (980425, 080207, and 111005A) and upper limits for the remaining 4 (031203, 060505, 060814, and 100316D). In our entire sample of 12 CO-observed GRB hosts, 3 are clearly deficient in molecular gas, even taking into account their metallicity (980425, 060814, and 080517). Four others are close to the best-fit line for other star-forming galaxies on the SFR-MH2 plot (051022, 060505, 080207, and 100316D). One host is clearly molecule rich (111005A). Finally, the data for 4 GRB hosts are not deep enough to judge whether they are molecule deficient (000418, 030329, 031203, and 090423). The median value of the molecular gas depletion time, MH2/SFR, of GRB hosts is ∼0.3 dex below that of other star-forming galaxies, but this result has low statistical significance. A Kolmogorov–Smirnov test performed on MH2/SFR shows an only ∼2σ difference between GRB hosts and other galaxies. This difference can partly be explained by metallicity effects, since the significance decreases to ∼1σ for MH2/SFR versus metallicity. Conclusions. We found that any molecular gas deficiency of GRB hosts has low statistical significance and that it can be attributed to their lower metallicities; and thus the sample of GRB hosts has molecular properties that are consistent with those of other galaxies, and they can be treated as representative star-forming galaxies. However, the molecular gas deficiency can be strong for GRB hosts if they exhibit higher excitations and/or a lower CO-to-H2 conversion factor than we assume, which would lead to lower molecular gas masses than we derive. Given the concentration of atomic gas recently found close to GRB and supernova sites, indicating recent gas inflow, our results about the weak molecular deficiency imply that such an inflow does not enhance the SFRs significantly, or that atomic gas converts efficiently into the molecular phase, which fuels star formation. Only if the analysis of a larger GRB host sample reveals molecular deficiency (especially close to the GRB position) would this support the hypothesis of star formation that is directly fuelled by atomic gas.
Context. Herschel observations of water and highly excited CO (J> 9) have allowed the physical and chemical conditions in the more active parts of protostellar outflows to be quantified in detail for ...the first time. However, to date, the studied samples of Class 0/I protostars in nearby star-forming regions have been selected from bright, well-known sources and have not been large enough for statistically significant trends to be firmly established. Aims. We aim to explore the relationships between the outflow, envelope and physical properties of a flux-limited sample of embedded low-mass Class 0/I protostars. Methods. We present spectroscopic observations in H sub(2) O, CO and related species with Herschel HIFI and PACS, as well as ground-based follow-up with the JCMT and APEX in CO, HCO super(+) and isotopologues, of a sample of 49 nearby (d< 500pc) candidate protostars selected from Spitzer and Herschel photometric surveys of the Gould Belt. This more than doubles the sample of sources observed by the WISH and DIGIT surveys. These data are used to study the outflow and envelope properties of these sources. We also compile their continuum spectral energy distributions (SEDs) from the near-IR to mm wavelengths in order to constrain their physical properties (e.g. L sub(bol), T sub(bol) and M sub(env)). Results. Water emission is dominated by shocks associated with the outflow, rather than the cooler, slower entrained outflowing gas probed by ground-based CO observations. These shocks become less energetic as sources evolve from Class 0 to Class I. Outflow force, measured from low-J CO, also decreases with source evolutionary stage, while the fraction of mass in the outflow relative to the total envelope (i.e. M sub(out)/M sub(env)) remains broadly constant between Class 0 and I. The median value of ~1% is consistent with a core to star formation efficiency on the order of 50% and an outflow duty cycle on the order of 5%. Entrainment efficiency, as probed by F sub(CO)/M sub(acc), is also invariant with source properties and evolutionary stage. The median value implies a velocity at the wind launching radius of 6.3kms super(-1), which in turn suggests an entrainment efficiency of between 30 and 60% if the wind is launched at ~1 AU, or close to 100% if launched further out. LOI is strongly correlated with L sub(bol) but not with M sub(env), in contrast to low-J CO, which is more closely correlated with the latter than the former. This suggests that Oi traces the present-day accretion activity of the source while CO traces time-averaged accretion over the dynamical timescale of the outflow. H sub(2) O is more strongly correlated with M sub(env) than L sub(bol), but the difference is smaller than low-J CO, consistent with water emission primarily tracing actively shocked material between the wind, traced by OI, and the entrained molecular outflow, traced by low-J CO. LOi does not vary from Class 0 to Class I, unlike CO and H sub(2) O. This is likely due to the ratio of atomic to molecular gas in the wind increasing as the source evolves, balancing out the decrease in mass accretion rate. Infall signatures are detected in HCO super(+) and H sub(2) O in a few sources, but still remain surprisingly illusive in single-dish observations.
Abstract
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 that 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 with the pypahdb package shows that (i) the intensities of PAH features decrease over distance from the ionizing star toward the cloud center, with 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
μ
m feature remain high throughout the globule, suggesting a higher 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
μ
m, suggesting a chemically processed PAH population with a small fraction of UV-processed PAHs; and (v) the H
2
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 star formation.
Context. Simulations suggest that gas heating due to radiative feedback is a key factor in whether or not multiple protostellar systems will form. Chemistry is a good tracer of the physical structure ...of a protostellar system, since it depends on the temperature structure. Aims. We aim to study the relationship between envelope gas temperature and protostellar multiplicity. Methods. Single dish observations of various molecules that trace the cold, warm, and UV-irradiated gas were used to probe the temperature structure of multiple and single protostellar systems on 7000 AU scales. Results. Single, close binary, and wide multiples present similar current envelope gas temperatures, as estimated from H2CO and DCO+ line ratios. The temperature of the outflow cavity, traced by c-C3H2, on the other hand, shows a relation with bolometric luminosity and an anticorrelation with envelope mass. Although the envelope gas temperatures are similar for all objects surveyed, wide multiples tend to exhibit a more massive reservoir of cold gas compared to close binary and single protostars. Conclusions. Although the sample of protostellar systems is small, the results suggest that gas temperature may not have a strong impact on fragmentation. We propose that mass, and density, may instead be key factors in fragmentation.
We have observed the massive protostar AFGL 2136 IRS 1 in multiple wavelength windows in the near- to mid-infrared at high (∼3 km s−1) spectral resolution using VLT+CRIRES, SOFIA+EXES, and Gemini ...North+TEXES. There is an abundance of H2O absorption lines from the ν 1 and ν 3 vibrational bands at 2.7 μm, from the ν 2 vibrational band at 6.1 μm, and from pure rotational transitions near 10–13 μm. Analysis of state-specific column densities derived from the resolved absorption features reveals that an isothermal absorbing slab model is incapable of explaining the relative depths of different absorption features. In particular, the strongest absorption features are much weaker than expected, indicating optical depth effects resulting from the absorbing gas being well mixed with the warm dust that serves as the “background” continuum source at all observed wavelengths. The velocity at which the strongest H2O absorption occurs coincides with the velocity centroid along the minor axis of the compact disk in Keplerian rotation recently observed in H2O emission with ALMA. We postulate that the warm regions of this dust disk dominate the continuum emission at near- to mid-infrared wavelengths, and that H2O and several other molecules observed in absorption are probing this disk. Absorption line profiles are not symmetric, possibly indicating that the warm dust in the disk that produces the infrared continuum has a nonuniform distribution similar to the substructure observed in 1.3 mm continuum emission.
ABSTRACT
We have used data from the Outer Galaxy High-Resolution Survey (OGHReS) to refine the velocities, distances, and physical properties of a large sample of 3584 clumps detected in ...far-infrared/submillimetre emission in the Hi-GAL survey located in the ℓ = 250°–280° region of the Galactic plane. Using 12CO and 13CO spectra, we have determined reliable velocities to 3412 clumps (95 per cent of the sample). In comparison to the velocities from the Hi-GAL catalogue, we find good agreement for 80 per cent of the sample (within 5 km s−1). Using the higher resolution and sensitivity of OGHReS has allowed us to correct the velocity for 632 clumps and provide velocities for 687 clumps for which no velocity had been previously allocated. The velocities are used with a rotation curve to refine the distances to the clumps and to calculate the clumps’ properties using a distance-dependent gas-to-dust ratio. We have determined reliable physical parameters for 3200 outer Galaxy dense clumps (∼90 per cent of the Hi-GAL sources in the region). We find a trend of decreasing luminosity-to-mass ratio with increasing Galactocentric distance, suggesting the star formation efficiency is lower in the outer Galaxy or that it is resulting in more lower mass stars than in the inner Galaxy. We also find a similar surface density for protostellar clumps located in the inner and outer Galaxy, revealing that the surface density requirements for star formation are the same across the Galactic disc.
Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal ...tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.
![GRB 980425 host: [C II], [O...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361_1432-0746/small "GRB 980425 host: [C II], [O I], and CO lines reveal recent enhancement of star formation due to atomic gas inflow")
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