arXiv subjects

Gerald Moriarty-Schieven

Publications and source records attributed to Gerald Moriarty-Schieven.

8 recordsLinked to original sources

arXiv2025

The JCMT Gould Belt Survey: First results from the Corona Australis molecular cloud and evidence of variable dust emissivity indices in the Coronet region

We present 450$μ$m and 850$μ$m James Clerk Maxwell Telescope (JCMT) observations of the Corona Australis (CrA) molecular cloud taken as part of the JCMT Gould Belt Legacy Survey (GBLS). We present a catalogue of 39 starless and protostellar sources, for which we determine source temperatures and masses using SCUBA-2 450$μ$m/850$μ$m flux density ratios for sources with reliable 450$μ$m detections, and compare these to values determined using temperatures measured by the Herschel Gould Belt Survey (HGBS). In keeping with previous studies, we find that SCUBA-2 preferentially detects high-volume-density starless cores, which are most likely to be prestellar (gravitationally bound). We do not observe any anti-correlation between temperature and volume density in the starless cores in our sample. Finally, we combine our SCUBA-2 and Herschel data to perform SED fitting from 160-850$μ$m across the central Coronet region, thereby measuring dust temperature $T$, dust emissivity index $β$ and column density $N({\rm H}_2)$ across the Coronet. We find that $β$ varies across the Coronet, particularly measuring $β= 1.55 \pm 0.35$ in the colder starless SMM-6 clump to the north of the B star R CrA. This relatively low value of $β$ is suggestive of the presence of large dust grains in SMM-6, even when considering the effects of $T-β$ fitting degeneracy and $^{12}$CO contamination of SCUBA-2 850$μ$m data on the measured $β$ values.

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arXiv2024

The JCMT BISTRO Survey: The Magnetic Fields of the IC 348 Star-forming Region

We present 850 $μ$m polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation (BISTRO) survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power-law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis-Chandrasekhar-Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45-2.20 and 0.63-2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament is 0.33-1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale ($\sim$ 0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS.

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arXiv2022

The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2

We present and analyze observations of polarized dust emission at 850 $μ$m towards the central 1 pc $\times$ 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the BISTRO (B-fields in Star-forming Region Observations) survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well-described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis-Chandrasekhar-Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from $Herschel$ data and the C$^{18}$O ($J$ = 3-2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 $\pm$ 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 $\pm$ 0.02. Additionally, the mean Alfvén Mach number is 0.35 $\pm$ 0.01. This suggests that in Mon R2, magnetic fields provide resistance against large-scale gravitational collapse, and magnetic pressure exceeds turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically sub-critical.

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arXiv2022

Accretion Burst Echoes as Probes of Protostellar Environments and Episodic Mass Assembly

Protostars likely accrete material at a highly time variable rate, however, measurements of accretion variability from the youngest protostars are rare, as they are still deeply embedded within their envelopes. Sub-mm/mm observations can trace the thermal response of dust in the envelope to accretion luminosity changes, allowing variations in the accretion rate to be quantified. In this paper, we present contemporaneous sub-mm/mm light curves of variable protostars in Serpens Main, as observed by the ALMA ACA, SMA, and JCMT. The most recent outburst of EC 53 (V371 Ser), an $\sim 18$ month periodic variable, is well-sampled in the SMA and JCMT observations. The SMA light curve of EC 53 is observed to peak weeks earlier and exhibit a stronger amplitude than at the JCMT. Stochastic variations in the ACA observations are detected for SMM 10 IR with a factor $\sim 2$ greater amplitude than as seen by the JCMT. We develop a toy model of the envelope response to accretion outbursts to show EC 53's light curves are plausibly explained by the delay associated with the light travel time across the envelope and the additional dilution of the JCMT response by the incorporation of cold envelope material in the beam. The larger JCMT beam can also wash out the response to rapid variations, which may be occurring for SMM 10 IR. Our work thus provides a valuable proof of concept for the usage of sub-mm/mm observations as a probe of both the underlying accretion luminosity variations and the protostellar environment.

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arXiv2018

The JCMT Gould Belt Survey: SCUBA-2 Data-Reduction Methods and Gaussian Source Recovery Analysis

The JCMT Gould Belt Survey was one of the first Legacy Surveys with the James Clerk Maxwell Telescope in Hawaii, mapping 47 square degrees of nearby (< 500 pc) molecular clouds in both dust continuum emission at 850 $μ$m and 450 $μ$m, as well as a more-limited area in lines of various CO isotopologues. While molecular clouds and the material that forms stars have structures on many size scales, their larger-scale structures are difficult to observe reliably in the submillimetre regime using ground-based facilities. In this paper, we quantify the extent to which three subsequent data-reduction methods employed by the JCMT GBS accurately recover emission structures of various size scales, in particular, dense cores which are the focus of many GBS science goals. With our current best data-reduction procedure, we expect to recover 100% of structures with Gaussian sigma sizes of $\le$30" and intensity peaks of at least five times the local noise for isolated peaks of emission. The measured sizes and peak fluxes of these compact structures are reliable (within 15% of the input values), but source recovery and reliability both decrease significantly for larger emission structures and for fainter peaks. Additional factors such as source crowding have not been tested in our analysis. The most recent JCMT GBS data release includes pointing corrections, and we demonstrate that these tend to decrease the sizes and increase the peak intensities of compact sources in our dataset, mostly at a low level (several percent), but occasionally with notable improvement.

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arXiv2016

The JCMT Gould Belt Survey: First results from SCUBA-2 observations of the Cepheus Flare Region

We present observations of the Cepheus Flare obtained as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2 instrument. We produce a catalogue of sources found by SCUBA-2, and separate these into starless cores and protostars. We determine masses and densities for each of our sources, using source temperatures determined by the Herschel Gould Belt Survey. We compare the properties of starless cores in four different molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core mass functions for each region typically show shallower-than-Salpeter behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores to Class II protostars, while L1251 and L1174 have a low ratio, consistent with the latter regions being more active sites of current star formation, while the former are forming stars less actively. We determine that, if modelled as thermally-supported Bonnor-Ebert spheres, most of our cores have stable configurations accessible to them. We estimate the external pressures on our cores using archival $^{13}$CO velocity dispersion measurements and find that our cores are typically pressure-confined, rather than gravitationally bound. We perform a virial analysis on our cores, and find that they typically cannot be supported against collapse by internal thermal energy alone, due primarily to the measured external pressures. This suggests that the dominant mode of internal support in starless cores in the Cepheus Flare is either non-thermal motions or internal magnetic fields.

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arXiv2016

Protostellar Outflows in L1340

We have searched the L1340 A, B, and C clouds for shocks from protostellar outflows using the H$_2$ 2.122 $μ$m near-IR line as a shock tracer. Substantial outflow activity has been found in each of the three regions of the cloud (L1340 A, L1340 B, & L1340 C). We find 42 distinct shock complexes (16 in L1340 A, 11 in L1340 B, and 15 in L1340 C). We were able to link 17 of those shock complexes in to 12 distinct outflows and identify candidate source stars for each. We examine the properties (A$_{V}$, T$_{bol}$, and L$_{bol}$) of the source protostars and compare that to the properties of the general population of Class 0/I and flat SED protostars and find that there is an indication, albeit at low statistical significance, that the outflow driving protostars are drawn from a population with lower A$_{V}$, higher L$_{bol}$, and lower T$_{bol}$ than the general population of protostars.

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arXiv1999

Submillimeter observations of IC 10: the dust properties and neutral carbon content of a low metallicity starburst

We present submillimeter observations of the Local Group, metal-poor, irregular dwarf galaxy IC 10, directly relevant to the interaction between interstellar medium and star formation activity in primeval galaxies. Using the JCMT, we have observed the fine structure neutral carbon transition at 492 GHz and the rotational J=3-2 transition of 12CO and 13CO in the most massive giant molecular cloud complex in this galaxy, IC10-SE. We find that, although the I([CII])/I(CO) ratio for this object is a factor of 4 larger than the typical Milky Way value, its [C~I] to CO intensity ratio is I([CI])/I(CO)~18 is similar (only about 50% larger) to that of the Milky Way. Modelling of the [CII]/CO and [CI]/CO intensity ratios with metallicity indicates that, if C+ and C are chiefly produced by UV photodissociation, both ratios should increase sharply with decreasing metallicity (and consequently diminished UV shielding; Bolatto, Jackson, and Ingalls 1999). These data then suggest a different origin for an important fraction of C in these clouds, unrelated to photodissociation. We have also mapped the 850 um continuum in this region using SCUBA. Employing these data in conjunction with KAO and IRAM measurements we find an extremely low emissivity exponent, b~0.5. We conclude that this low exponent is most likely due to the destruction of small dust grains, brought about by the increased penetration of UV radiation in the low metallicity ISM. If a low b in the submillimeter is a general property of metal-poor systems then the interpretation of millimeter and submillimeter surveys of high-z galaxies should be revised.

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