Abstract Accretion rates ( M ̇ ) of young stars show a strong correlation with object mass ( M ); however, extension of the M ̇ – M relation into the substellar regime is less certain. Here, we ...present the Comprehensive Archive of Substellar and Planetary Accretion Rates (CASPAR), the largest compilation to date of substellar accretion diagnostics. CASPAR includes: 658 stars, 130 brown dwarfs, and 10 bound planetary mass companions. In this work, we investigate the contribution of methodological systematics to scatter in the M ̇ – M relation and compare brown dwarfs to stars. In our analysis, we rederive all quantities using self-consistent models, distances, and empirical line flux to accretion luminosity scaling relations to reduce methodological systematics. This treatment decreases the original 1 σ scatter in the log M ̇ – log M relation by ∼17%, suggesting that it makes only a small contribution to the dispersion. The CASPAR rederived values are best fit by M ̇ ∝ M 2.02 ± 0.06 from 10 M J to 2 M ⊙ , confirming previous results. However, we argue that the brown-dwarf and stellar populations are better described separately and by accounting for both mass and age. Therefore, we derive separate age-dependent M ̇ – M relations for these regions and find a steepening in the brown-dwarf M ̇ – M slope with age. Within this mass regime, the scatter decreases from 1.36 dex to 0.94 dex, a change of ∼44%. This result highlights the significant role that evolution plays in the overall spread of accretion rates, and suggests that brown dwarfs evolve faster than stars, potentially as a result of different accretion mechanisms.
We present new Atacama Large Millimeter Array (ALMA) dust continuum observations of 101 galaxies in the COSMOS field to study the effect of the environment on the interstellar medium at z ∼ 0.7. At ...this redshift, our targets span a wide range of environments allowing for a diverse sample of galaxies with densities of = 0.16-10.5 Mpc−2 (per Δz = 0.024). Using the ALMA observations, we calculate the total interstellar medium (ISM) mass (MISM) and look for depletion as a function of galaxy density in order to understand the quenching or triggering of star formation in galaxies in different environments. MISM is found to have a small dependence on the environment, while the depletion timescale remains constant (∼200 Myr) across all environments. We find elevated MISM values at intermediate densities and lower values at high densities compared to low (field) densities. Our observed evolution in gas fraction with density in this single redshift slice is equivalent to the observed evolution with cosmic time over 2-3 Gyr. To explain the change in the gas mass fraction seen in galaxies in intermediate and high densities, these results suggest environmental processes such as mergers and ram pressure stripping are likely playing a role in dense filamentary cluster environments.
Abstract
We use hydrodynamical simulations of star-forming gas with stellar feedback and sink particles—proxies for young stellar objects (YSOs)—to produce and analyze synthetic 1.1 mm continuum ...observations at different distances (150–1000 pc) and ages (0.49–1.27 Myr). We characterize how the inferred core properties, including mass, size, and clustering with respect to diffuse natal gas structure, change with distance, cloud evolution, and the presence of YSOs. We find that atmospheric filtering and core segmentation treatments have distance-dependent impacts on the resulting core properties for
d
< 300 pc and 500 pc, respectively, which dominate over evolutionary differences. Concentrating on synthetic observations at further distances (650–1000 pc), we find a growing separation between the inferred sizes and masses of cores with and without YSOs in the simulations, which is not seen in recent observations of the Monoceros R2 (Mon R2) cloud at 860 pc. We find that the synthetic cores cluster in smaller groups, and that their mass densities are correlated with gas column density over a much narrower range, than those in the Mon R2 observations. Such differences limit the applicability of the evolutionary predictions we report here, but will motivate our future efforts to adapt our synthetic observation and analysis framework to next generation simulations, such as Star Formation in Gaseous Environments (STARFORGE). These predictions and systematic characterizations will help to guide the analysis of cores on the upcoming TolTEC Clouds to Cores Legacy Survey on the Large Millimeter Telescope Alfonso Serrano.
Abstract
Accretion signatures from bound brown dwarf and protoplanetary companions provide evidence for ongoing planet formation, and accreting substellar objects have enabled new avenues to study ...the astrophysical mechanisms controlling the formation and accretion processes. Delorme 1 (AB)b, a ∼30–45 Myr circumbinary planetary-mass companion, was recently discovered to exhibit strong H
α
emission. This suggests ongoing accretion from a circumplanetary disk, somewhat surprising given canonical gas disk dispersal timescales of 5–10 Myr. Here, we present the first NIR detection of accretion from the companion in Pa
β
, Pa
γ
, and Br
γ
emission lines from SOAR/TripleSpec 4.1, confirming and further informing its accreting nature. The companion shows strong line emission, with
L
line
≈ 1–6 × 10
−8
L
⊙
across lines and epochs, while the binary host system shows no NIR hydrogen line emission (
L
line
< 0.32–11 × 10
−7
L
⊙
). Observed NIR hydrogen line ratios are more consistent with a planetary accretion shock than with local line excitation models commonly used to interpret stellar magnetospheric accretion. Using planetary accretion shock models, we derive mass accretion rate estimates of
M
̇
pla
∼
3
–4 × 10
−8
M
J
yr
−1
, somewhat higher than expected under the standard star formation paradigm. Delorme 1 (AB)b’s high accretion rate is perhaps more consistent with formation via disk fragmentation. Delorme 1 (AB)b is the first protoplanet candidate with clear (signal-to-noise ratio ∼5) NIR hydrogen line emission.
Abstract
The NRAO VLA Sky Survey (NVSS) rotation measure (RM) catalogue is invaluable for the study of cosmic magnetism. However, the RM values reported in it can be affected by nπ-ambiguity, ...resulting in deviations of the reported RM from the true values by multiples of $\pm 652.9\, {\rm rad\, m}^{-2}$. We therefore set off to observationally constrain the fraction of sources in the RM catalogue affected by this ambiguity. New broad-band spectro-polarimetric observations were performed with the Karl G. Jansky Very Large Array (VLA) at 1–$2\, {\rm GHz}$, with 23 nπ-ambiguity candidates selected by their peculiarly high |RM| values. We identified nine sources with erroneous RM values due to nπ-ambiguity and 11 with reliable RM values. In addition, we found two sources to be unpolarized and one source to be inconsistent with neither nπ-ambiguity nor reliable RM cases. By comparing the statistical distributions of the above two main classes, we devised a measure of how much a source’s RM deviates from that of its neighbours: Δ/σ, which we found to be a good diagnostic of nπ-ambiguity. With this, we estimate that there are at least 50 sources affected by nπ-ambiguity among the 37 543 sources in the catalogue. Finally, we explored the Faraday complexities of our sources revealed by our broad-band observations.
The Smith Cloud is a high-velocity cloud with an orbit suggesting it has made at least one passage through the Milky Way disk. A magnetic field found around this cloud has been thought to provide ...extra stability as it passes through the Galactic halo. We use the Karl G. Jansky Very Large Array to measure Faraday rotation measures (RMs) toward 1105 extragalactic background point sources behind and next to the Smith Cloud to constrain the detailed geometry and strength of its magnetic field. The RM pattern across the cloud gives the detailed morphology of the magnetic field structure, which indicates a field draped over the ionized gas and compressed at the head of the cloud. We constrain the peak line-of-sight magnetic field strength to +5 G and create a model of the magnetic field to demonstrate that a draped configuration can qualitatively explain the morphology of the observed RMs.
Abstract
The NRAO VLA Sky Survey (NVSS) rotation measure (RM) catalogue has enabled numerous studies in cosmic magnetism, and will continue being a unique data set complementing future polarization ...surveys. Robust comparisons with these new surveys will however require further understandings in the systematic effects present in the NVSS RM catalogue. In this paper, we make careful comparisons between our new on-axis broad-band observations with the Karl G. Jansky Very Large Array and the NVSS RM results for 23 sources. We found that two unpolarized sources were reported as polarized at about 0.5 per cent level in the RM catalogue, and noted significant differences between our newly derived RM values and the catalogue values for the remaining 21 sources. These discrepancies are attributed to off-axis instrumental polarization in the NVSS RM catalogue. By adopting the 0.5 per cent above as the typical off-axis instrumental polarization amplitude, we quantified its effect on the reported RMs with a simulation, and found that on average the RM uncertainties in the catalogue have to be increased by ${\approx } 10\, {{\ \rm per\ cent}}$ to account for the off-axis instrumental polarization effect. This effect is more substantial for sources with lower fractional polarization, and is a function of the source’s true RM. Moreover, the distribution of the resulting RM uncertainty is highly non-Gaussian. With the extra RM uncertainty incorporated, we found that the RM values from the two observations for most (18 out of 21) of our polarized targets can be reconciled. The remaining three are interpreted as showing hints of time variabilities in RM.
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