ALMA-IMF Pouteau, Y.; Motte, F.; Nony, T. ...
Astronomy and astrophysics (Berlin),
08/2022, Letnik:
664
Journal Article
Recenzirano
Odprti dostop
Aims.
The processes that determine the stellar initial mass function (IMF) and its origin are critical unsolved problems, with profound implications for many areas of astrophysics. The W43-MM2&MM3 ...mini-starburst ridge hosts a rich young protocluster, from which it is possible to test the current paradigm on the IMF origin.
Methods.
The ALMA-IMF Large Program observed the W43-MM2&MM3 ridge, whose 1.3 mm and 3 mm ALMA 12 m array continuum images reach a ~2500 au spatial resolution. We used both the best-sensitivity and the line-free ALMA-IMF images, reduced the noise with the multi-resolution segmentation technique
MnGSeg
, and derived the most complete and most robust core catalog possible. Using two different extraction software packages,
getsf
and
GExt2D
, we identified ~200 compact sources, whose ~100 common sources have, on average, fluxes consistent to within 30%. We filtered sources with non-negligible free-free contamination and corrected fluxes from line contamination, resulting in a W43-MM2&MM3 catalog of 205
getsf
cores. With a median deconvolved FWHM size of 3400 au, core masses range from ~0.1
M
⊙
to ~70
M
⊙
and the
getsf
catalog is 90% complete down to 0.8
M
⊙
.
Results.
The high-mass end of the core mass function (CMF) of W43-MM2&MM3 is top-heavy compared to the canonical IMF. Fitting the cumulative CMF with a single power-law of the form
N
(> log
M
) ∝
M
α
, we measured
α
= −0.95 ± 0.04, compared to the canonical
α
= −1.35 Salpeter IMF slope. The slope of the CMF is robust with respect to map processing, extraction software packages, and reasonable variations in the assumptions taken to estimate core masses. We explore several assumptions on how cores transfer their mass to stars (assuming a mass conversion efficiency) and subfragment (defining a core fragment mass function) to predict the IMF resulting from the W43-MM2&MM3 CMF. While core mass growth should flatten the high-mass end of the resulting IMF, core fragmentation could steepen it.
Conclusions.
In stark contrast to the commonly accepted paradigm, our result argues against the universality of the CMF shape. More robust functions of the star formation efficiency and core subfragmentation are required to better predict the resulting IMF, here suggested to remain top-heavy at the end of the star formation phase. If confirmed, the IMFs emerging from starburst events could inherit their top-heavy shape from their parental CMFs, challenging the IMF universality.
Abstract
In recent years, dramatic outbursts have been identified toward massive protostars via infrared and millimeter dust continuum and molecular maser emission. The longest lived outburst (>6 yr) ...persists in NGC 6334 I-MM1, a deeply embedded object with no near-IR counterpart. Using FORCAST and HAWC+ on SOFIA, we have obtained the first mid-IR images of this field since the outburst began. Despite being undetected in pre-outburst ground-based 18
μ
m images, MM1 is now the brightest region at all three wavelengths (25, 37, and 53
μ
m), exceeding the UCHII region MM3 (NGC 6334 F). Combining the SOFIA data with ALMA imaging at four wavelengths, we construct a spectral energy distribution of the combination of MM1 and the nearby hot core MM2. The best-fit Robitaille radiative transfer model yields a luminosity of (4.9 ± 0.8) × 10
4
L
⊙
. Accounting for an estimated pre-outburst luminosity ratio MM1:MM2 = 2.1 ± 0.4, the luminosity of MM1 has increased by a factor of 16.3 ± 4.4. The pre-outburst luminosity implies a protostar of mass 6.7
M
⊙
, which can produce the ionizing photon rate required to power the pre-outburst HCHII region surrounding the likely outbursting protostar MM1B. The total energy and duration of the outburst exceed the S255IR-NIRS3 outburst by a factor of ≳3, suggesting a different scale of event involving expansion of the protostellar photosphere (to ≳20
R
⊙
), thereby supporting a higher accretion rate (≳0.0023
M
⊙
yr
−1
) and reducing the ionizing photon rate. In the grid of hydrodynamic models of Meyer et al., the combination of outburst luminosity and magnitude (3) places the NGC 6334 I-MM1 event in the region of moderate total accretion (∼0.1–0.3
M
⊙
) and hence long duration (∼40–130 yr).
Massive young stellar objects (MYSOs) are known to undergo an evolutionary phase in which high mass accretion rates drive strong outflows. A class of objects believed to trace this phase accurately ...is the Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) Extended Green Object (EGO) sample, so named for the presence of extended 4.5 m emission on size scales of ∼0.1 pc in Spitzer images. We have been conducting a multiwavelength examination of a sample of 12 EGOs with distances of 1-5 kpc. In this paper, we present mid-infrared images and photometry of these EGOs obtained with the Stratospheric Observatory for Infrared Astronomy and subsequently construct spectral energy distributions (SEDs) for these sources from the near-infrared to submillimeter regimes using additional archival data. We compare the results from graybody models and several publicly available software packages that produce model SEDs in the context of a single massive protostar. The models yield typical R ∼ 10 R , T ∼ 103-104 K, and L ∼ 1-40 × 103 L ; the median L/M for our sample is 24.7 L /M . Model results rarely converge for R and T , but they do for L , which we take to be an indication of the multiplicity and inherently clustered nature of these sources even though, typically, only a single source dominates in the mid-infrared. The median L/M value for the sample suggests that these objects may be in a transitional stage between the commonly described "IR-quiet" and "IR-bright" stages of MYSO evolution. The median Tdust for the sample is less conclusive but suggests that these objects are either in this transitional stage or occupy the cooler (and presumably younger) part of the IR-bright stage.
We present (sub)millimeter imaging at 0 5 resolution of the massive star-forming region G358.93−0.03 acquired in multiple epochs at 2 and 3 months following the recent flaring of its 6.7 GHz CH3OH ...maser emission. Using the Submillimeter Array and Atacama Large Millimeter/submillimeter Array, we have discovered 14 new Class II CH3OH maser lines ranging in frequency from 199 to 361 GHz, which originate mostly from = 1 torsionally excited transitions and include one = 2 transition. The latter detection provides the first observational evidence that Class II maser pumping involves levels in the = 2 state. The masers are associated with the brightest continuum source (MM1), which hosts a line-rich hot core. The masers present a consistent curvilinear spatial velocity pattern that wraps around MM1, suggestive of a coherent physical structure 1200 au in extent. In contrast, the thermal lines exhibit a linear pattern that crosses MM1 but at progressive position angles that appear to be a function of either increasing temperature or decreasing optical depth. The maser spectral profiles evolved significantly over one month, and the intensities dropped by factors of 3.0-7.2, with the = 2 line showing the largest change. A small area of maser emission from only the highest excitation lines closest to MM1 has disappeared. There are seven additional dust continuum sources in the protocluster, including another hot core (MM3). We do not find evidence for a significant change in (sub)millimeter continuum emission from any of the sources during the one month interval, and the total protocluster emission remains comparable to prior single-dish measurements.
Abstract
We have observed a sample of nine Extended Green Objects (EGOs) at 1.3 and 5 cm with the Very Large Array (VLA) with subarcsecond resolution and ∼7–14
μ
Jy beam
−1
-sensitivities in order to ...characterize centimeter continuum emission as it first appears in these massive protoclusters. We find an EGO-associated continu um emission—within 1″ of the extended 4.5
μ
m emission—in every field, which is typically faint (order 10
1
–10
2
μ
Jy) and compact (unresolved at 0″.3–0″.5). The derived spectral indices of our 36 total detections are consistent with a wide array of physical processes, including both non-thermal (19% of detections) and thermal free–free processes (e.g., ionized jets and compact H
ii
regions, 78% of sample) and warm dust (1 source). We also find an EGO-associated 6.7 GHz CH
3
OH and 22 GHz H
2
O maser emission in 100% of the sample and a NH
3
(3,3) masers in ∼45%; we do not detect any NH
3
(6,6) masers at ∼5.6 mJy beam
−1
sensitivity. We find statistically-significant correlations between
L
radio
and
L
bol
at two physical scales and three frequencies, consistent with thermal emission from ionized jets, but no correlation between
L
H
2
O
and
L
radio
for our sample. From these data, we conclude that EGOs likely host multiple different centimeter continuum-producing processes simultaneously. Additionally, at our ∼1000 au resolution, we find that all EGOs except G18.89−0.47 contain 1 ∼ 2 massive sources based on the presence of CH
3
OH maser groups, which is consistent with our previous work suggesting that these are typical massive protoclusters, in which only one to a few of the young stellar objects are massive.
Abstract
We present a catalog of 315 protostellar outflow candidates detected in SiO
J
= 5 − 4 in the ALMA-IMF Large Program, observed with ∼2000 au spatial resolution, 0.339 km s
−1
velocity ...resolution, and 2–12 mJy beam
−1
(0.18–0.8 K) sensitivity. We find median outflow masses, momenta, and kinetic energies of ∼0.3
M
⊙
, 4
M
⊙
km s
−1
, and 10
45
erg, respectively. Median outflow lifetimes are 6000 yr, yielding median mass, momentum, and energy rates of
M
̇
= 10
−4.4
M
⊙
yr
−1
,
P
̇
= 10
−3.2
M
⊙
km s
−1
yr
−1
, and
E
̇
= 1
L
⊙
. We analyze these outflow properties in the aggregate in each field. We find correlations between field-aggregated SiO outflow properties and total mass in cores (∼3
σ
–5
σ
), and no correlations above 3
σ
with clump mass, clump luminosity, or clump luminosity-to-mass ratio. We perform a linear regression analysis and find that the correlation between field-aggregated outflow mass and total clump mass—which has been previously described in the literature—may actually be mediated by the relationship between outflow mass and total mass in cores. We also find that the most massive SiO outflow in each field is typically responsible for only 15%–30% of the total outflow mass (60% upper limit). Our data agree well with the established mechanical force−bolometric luminosity relationship in the literature, and our data extend this relationship up to
L
≥ 10
6
L
⊙
and
P
̇
≥ 1
M
⊙
km s
−1
yr
−1
. Our lack of correlation with clump
L
/
M
is inconsistent with models of protocluster formation in which all protostars start forming at the same time.
We observed nine primary transits of the hot Jpiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine ...and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jpiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B
* of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of R
p = 1.386+ 0.248
− 0.144 R
Jup is consistent with the planet's optical radius.
We present a catalog of 315 protostellar outflow candidates detected in SiO J=5-4 in the ALMA-IMF Large Program, observed with ~2000 au spatial resolution, 0.339 km/s velocity resolution, and 2-12 ...mJy/beam (0.18-0.8 K) sensitivity. We find median outflow masses, momenta, and kinetic energies of ~0.3 M\(_{\odot}\), 4 M\(_{\odot}\) km/s, and 10\(^{45}\) erg, respectively. Median outflow lifetimes are 6,000 years, yielding median mass, momentum, and energy rates of \(\dot{M}\) = 10\(^{-4.4}\) M\(_{\odot}\) yr\(^{-1}\), \(\dot{P}\) = 10\(^{-3.2}\) M\(_{\odot}\) km/s yr\(^{-1}\), and \(\dot{E}\) = 1 L\(_{\odot}\). We analyze these outflow properties in the aggregate in each field. We find correlations between field-aggregated SiO outflow properties and total mass in cores (~3\(-\)5\(\sigma\)), and no correlations above 3\(\sigma\) with clump mass, clump luminosity, or clump luminosity-to-mass ratio. We perform a linear regression analysis and find that the correlation between field-aggregated outflow mass and total clump mass - which has been previously described in the literature - may actually be mediated by the relationship between outflow mass and total mass in cores. We also find that the most massive SiO outflow in each field is typically responsible for only 15-30% of the total outflow mass (60% upper limit). Our data agree well with the established mechanical force-bolometric luminosity relationship in the literature, and our data extend this relationship up to L \(\geq\) 10\(^6\) L\(_{\odot}\) and \(\dot{P}\) \(\geq\) 1 M\(_{\odot}\) km/s yr\(^{-1}\). Our lack of correlation with clump L/M is inconsistent with models of protocluster formation in which all protostars start forming at the same time.
We present ∼1″-4″ resolution Very Large Array (VLA) observations of four CH3OH -E 25 GHz transitions (J = 3, 5, 8, 10) along with the 1.3 cm continuum toward 20 regions of active massive star ...formation containing Extended Green Objects (EGOs), 14 of which we have previously studied with the VLA in the Class I 44 GHz and Class II 6.7 GHz maser lines. Sixteen regions are detected in at least one 25 GHz line (J = 5), with 13 of 16 exhibiting maser emission. In total, we report 34 new sites of CH3OH maser emission and 10 new sites of thermal CH3OH emission, significantly increasing the number of 25 GHz Class I CH3OH masers observed at high angular resolution. We identify probable or likely maser counterparts at 44 GHz for all 15 of the 25 GHz masers for which we have complementary data, providing further evidence that these masers trace similar physical conditions despite uncorrelated flux densities. The sites of thermal and maser emission of CH3OH are both predominantly associated with the 4.5 m emission from the EGO, and the presence of thermal CH3OH emission is accompanied by 1.3 cm continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3 cm continuum emission, it is associated with the EGO in 16 cases (out of a total of 20 sites), 13 of which are new detections at 1.3 cm. Twelve of the 1.3 cm continuum sources are associated with 6.7 GHz maser emission and likely trace deeply embedded massive protostars.
ABSTRACT
Based on telescopic observations of Jupiter-family comets (JFCs), there is predicted to be a paucity of objects at sub-kilometre sizes. However, several bright fireballs and some meteorites ...have been tenuously linked to the JFC population, showing metre-scale objects do exist in this region. In 2017, the Desert Fireball Network (DFN) observed a grazing fireball that redirected a meteoroid from an Apollo-type orbit to a JFC-like orbit. Using orbital data collected by the DFN, in this study, we have generated an artificial data set of close terrestrial encounters that come within 1.5 lunar distances (LD) of the Earth in the size-range of 0.01–100 kg. This range of objects is typically too small for telescopic surveys to detect, so using atmospheric impact flux data from fireball observations is currently one of the only ways to characterize these close encounters. Based on this model, we predict that within the considered size-range 2.5 × 108 objects ($0.1{{\ \rm per\ cent}}$ of the total flux) from asteroidal orbits (TJ > 3) are annually sent on to JFC-like orbits (2 < TJ < 3), with a steady-state population of about 8 × 1013 objects. Close encounters with the Earth provide another way to transfer material to the JFC region. Additionally, using our model, we found that approximately 1.96 × 107 objects are sent on to Aten-type orbits and ∼104 objects are ejected from the Solar system annually via a close encounter with the Earth.
PDF
