Star formation in Perseus. IV. Mass dependent evolution of dense cores

In our SCUBA survey of Perseus, we find that the fraction of protostellar cores increases towards higher masses and the most massive cores are all protostellar. In this paper we consider the possible explanations of this apparent mass dependence in the evolutionary status of these cores, and the implications for protostellar evolution and the mapping of the embedded core mass function (CMF) onto the stellar IMF. We consider the following potential causes: dust temperature; selection effects in the submillimetre and in the mid-infrared observations used for pre/protostellar classification; confusion and multiplicity; transient cores; and varying evolutionary timescales. We develop Core Mass Evolution Diagrams (CMEDs) to investigate how the mass evolution of individual cores maps onto the observed CMF. Two physical mechanisms -- short timescales for the evolution of massive cores, and continuing accumulation of mass onto protostellar cores -- best explain the relative excess of protostars in high mass cores and the rarity of massive starless cores. In addition, confusion both increases the likelihood that a protostar is identified within a core, and increases mass assigned to a core. The observed pre/protostellar mass distributions are consistent with faster evolution and a shorter lifetime for higher-mass prestellar cores. We rule out longer timescales for higher-mass prestellar cores. The differences in the prestellar and protostellar mass distributions imply that the prestellar CMF (and possibly the combined pre+protostellar CMF) should be steeper than the IMF. A steeper prestellar CMF can be reconciled with the observed similarity of the CMF and the IMF in some regions if a second opposing effect is present, such as the fragmentation of massive cores into multiple systems.Comment: 11 pages, 5 figures. Accepted by A&

What can the SEDs of first hydrostatic core candidates reveal about their nature?

The first hydrostatic core (FHSC) is the first stable object to form in simulations of star formation. This stage has yet to be observed definitively, although several candidate FHSCs have been reported. We have produced synthetic spectral energy distributions (SEDs) from 3D hydrodynamical simulations of pre-stellar cores undergoing gravitational collapse for a variety of initial conditions. Variations in the initial rotation rate, radius and mass lead to differences in the location of the SED peak and far-infrared flux. Secondly, we attempt to fit the SEDs of five FHSC candidates from the literature and five newly identified FHSC candidates located in the Serpens South molecular cloud with simulated SEDs. The most promising FHSC candidates are fitted by a limited number of model SEDs with consistent properties, which suggests the SED can be useful for placing constraints on the age and rotation rate of the source. The sources we consider most likely to be in FHSC phase are B1-bN, CB17-MMS, Aqu-MM1 and Serpens South candidate K242. We were unable to fit SerpS-MM22, Per-Bolo 58 and Chamaeleon-MMS1 with reasonable parameters, which indicates that they are likely to be more evolved.Comment: 26 pages, 28 figures. Accepted for publication in MNRA

The JCMT Gould Belt Survey: understanding the influence of outflows on Gould Belt clouds

JOURThis is the final version of the article. It was first published by Oxford Journals for the Royal Astronomical Society via http://dx.doi.org/10.1093/mnrasl/slv202Using James Clerk Maxwell Telescope (JCMT) Gould Belt Survey data from CO J = 3 → 2 isotopologues, we present a meta-analysis of the outflows and energetics of star-forming regions in several Gould Belt clouds. The majority of the regions are strongly gravitationally bound. There is evidence that molecular outflows transport large quantities of momentum and energy. Outflow energies are at least 20 per cent of the total turbulent kinetic energies in all of the regions studied and greater than the turbulent energy in half of the regions. However, we find no evidence that outflows increase levels of turbulence, and there is no correlation between the outflow and turbulent energies. Even though outflows in some regions contribute significantly to maintaining turbulence levels against dissipation, this relies on outflows efficiently coupling to bulk motions. Other mechanisms (e.g. supernovae) must be the main drivers of turbulence in most if not all of these regions

The JCMT Gould Belt Survey: the effect of molecular contamination in SCUBA-2 observations of Orion A

Thermal emission from cold dust grains in giant molecular clouds can be used to probe the physical properties, such as density, temperature and emissivity in star-forming regions. We present the SCUBA-2 shared-risk observations at 450 $\mu$m and 850 $\mu$m of the Orion A molecular cloud complex taken at the James Clerk Maxwell Telescope (JCMT). Previous studies showed that molecular emission lines can contribute significantly to the measured fluxes in those continuum bands. We use the HARP $^{12}$CO J=3-2 integrated intensity map for Orion A in order to evaluate the molecular line contamination and its effects on the SCUBA-2 maps. With the corrected fluxes, we have obtained a new spectral index $\alpha$ map for the thermal emission of dust in the well-known integral-shaped filament. Furthermore, we compare a sample of 33 sources, selected over the Orion A molecular cloud complex for their high $^{12}$CO J=3-2 line contamination, to 27 previously identified clumps in OMC-4. This allows us to quantify the effect of line contamination on the ratio of 850 $\mu$m to 450 $\mu$m flux densities and how it modifies the deduced spectral index of emissivity $\beta$ for the dust grains. We also show that at least one Spitzer-identified protostellar core in OMC-5 has a $^{12}$CO J=3-2 contamination level of 16 %. Furthermore, we find the strongest contamination level (44 %) towards a young star with disk near OMC-2. This work is part of the JCMT Gould Belt Legacy Survey.Comment: 13 pages, 6 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS

AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region

We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Perseus molecular cloud by the Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). We detect 72% of Class 0 objects from this sample and 31% of Class I objects. No starless cores are detected. We use the flux densities measured from these data to improve constraints on the correlations between radio luminosity and bolometric luminosity, infrared luminosity and, where measured, outflow force. We discuss the differing behaviour of these objects as a function of protostellar class and investigate the differences in radio emission as a function of core mass. Two of four possible very low luminosity objects (VeLLOs) are detected at 1.8 cm.Comment: 18 pages, 9 figures, accepted MNRA

The warm and dense Galaxy - tracing the formation of dense cloud structures out to the Galactic Center

The past two decades have seen extensive surveys of the far-infrared to submillimeter continuum emission in the plane of our Galaxy. We line out prospects for the coming decade for corresponding molecular and atomic line surveys which are needed to fully understand the formation of the dense structures that give birth to clusters and stars out of the diffuse interstellar medium. We propose to work towards Galaxy wide surveys in mid-J CO lines to trace shocks from colliding clouds, Galaxy-wide surveys for atomic Carbon lines in order to get a detailed understanding of the relation of atomic and molecular gas in clouds, and to perform extensive surveys of the structure of the dense parts of molecular clouds to understand the importance of filaments/fibers over the full range of Galactic environments and to study how dense cloud cores are formed from the filaments. This work will require a large (50m) Single Dish submillimeter telescope equipped with massively multipixel spectrometer arrays, such as envisaged by the AtLAST project.Comment: Science white paper submitted to the Astro2020 Decadal Surve

The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds

Motivated by the long-standing "luminosity problem" in low-mass star formation whereby protostars are underluminous compared to theoretical expectations, we identify 230 protostars in 18 molecular clouds observed by two Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions, calculate Lbol for each source, and study the protostellar luminosity distribution. This distribution extends over three orders of magnitude, from 0.01 Lsun - 69 Lsun, and has a mean and median of 4.3 Lsun and 1.3 Lsun, respectively. The distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (Lbol < 0.5 Lsun) Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infrared and submillimeter (70 um < wavelength < 850 um) and have Lbol underestimated by factors of 2.5 on average, and up to factors of 8-10 in extreme cases. Correcting these underestimates for each source individually once additional data becomes available will likely increase both the mean and median of the sample by 35% - 40%. We discuss and compare our results to several recent theoretical studies of protostellar luminosities and show that our new results do not invalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausible accretion scenario that can match observations, future attention is clearly needed. The better statistics provided by our increased dataset should aid such future work.Comment: Accepted for publication in AJ. 21 pages, 10 figures, 4 table

Young Stellar Objects in the Gould Belt

We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the Gould Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background AGB stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.Comment: Accepted for publication in ApJS. 29 pages, 11 figures, 14 tables, 4 appendices. Full versions of data tables (to be published in machine-readable format by ApJS) available at the end of the latex source cod