7 research outputs found
ALMA resolves molecular clouds in the metal poor Magellanic Bridge A
(Abridged)We characterize gas and dust emission in Magellanic Bridge A, which
has the highest 870m excess of emission found in single dish surveys.
Using the ALMA telescope, we mapped the Magellanic Bridge A molecular cloud
with sub-parsec resolution, in 1.3 mm continuum and CO(2-1) line emission. We
also map the cloud in 870m continuum and CO(2-1) line emission at ~6 pc
resolution with APEX. We combine the ALMA and APEX CO(2-1) line cubes to study
the molecular gas emission. Magellanic Bridge A breaks up into two distinct
molecular clouds in dust and CO(2-1) emission, which we call North and South.
Dust emission in the North source, according to our best parameters from
fitting the far-infrarred fluxes, is ~3 K colder than in the South source in
correspondence to its less developed star formation. Both dust sources present
large submillimeter excesses in LABOCA data: according to our best fits the
excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum
are ~7 and ~3 for the North and South sources respectively. Nonetheless, we do
not detect the corresponding 1.3 mm continuum with ALMA. Our limits are
compatible with the extrapolation of the MBB fits and therefore we cannot
independently confirm the excess at this longer wavelength. The CO(2-1)
emission is in two parsec-sized clouds with virial masses around 400 and 700 Mo
each. Their volume densities are ~700-2600 cm, larger than typical bulk
densities of Galactic molecular clouds. The CO-to-H2 conversion factor is 6.5
and 15 M (K km s pc) for the North and South
clouds, calculated using their respective virial masses and CO(2-1)
luminosities. Gas mass estimates from our MBB fits to dust emission yields
masses M and M for
North and South respectively, a factor ~4 larger than the virial masses we
infer from CO.Comment: Astronomy & Astrophysics in press. 14 pages, 6 figures, 7 table
Flow of gas detected from beyond the filaments to protostellar scales in Barnard 5
Infall of gas from outside natal cores has proven to feed protostars after
the main accretion phase (Class 0). This changes our view of star formation to
a picture that includes asymmetric accretion (streamers), and a larger role of
the environment. However, the connection between streamers and the filaments
that prevail in star-forming regions is unknown. We investigate the flow of
material toward the filaments within Barnard 5 (B5) and the infall from the
envelope to the protostellar disk of the embedded protostar B5-IRS1. Our goal
is to follow the flow of material from the larger, dense core scale, to the
protostellar disk scale. We present new HCN line data from the NOEMA and
30m telescopes covering the coherence zone of B5, together with ALMA HCO
and CO maps toward the protostellar envelope. We fit multiple Gaussian
components to the lines so as to decompose their individual physical
components. We investigate the HCN velocity gradients to determine the
direction of chemically-fresh gas flow. At envelope scales, we use a clustering
algorithm to disentangle the different kinematic components within HCO
emission. At dense core scales, HCN traces the infall from the B5 region
toward the filaments. HCN velocity gradients are consistent with accretion
toward the filament spines plus flow along them. We found a au
streamer in HCO emission which is blueshifted with respect to the protostar
and deposits gas at outer disk scales. The strongest velocity gradients at
large scales curve toward the position of the streamer at small scales,
suggesting a connection between both flows. Our analysis suggests that the gas
can flow from the dense core to the protostar. This implies that the mass
available for a protostar is not limited to its envelope, and can receiving
chemically-unprocessed gas after the main accretion phase.Comment: 25 pages, 27 figures, accepted for publication on Astronomy and
Astrophysics. The scripts used for analysis can be seen at
https://github.com/tere-valdivia/Barnard_5_infal
PRODIGE -- Envelope to Disk with NOEMA II. Small-scale temperature structure and a streamer feeding the SVS13A protobinary using CH3CN and DCN
Aims. We present high sensitivity and high-spectral resolution NOEMA
observations of the Class 0/I binary system SVS13A, composed of the low-mass
protostars VLA4A and VLA4B with a separation of ~90 au. VLA4A is undergoing an
accretion burst that enriches the chemistry of the surrounding gas. This gives
us an excellent opportunity to probe the chemical and physical conditions as
well as the accretion process. Methods. We observe the (12K-11K) lines of CH3CN
and CH313CN, the DCN (3-2) line, and the C18O (2-1) line toward SVS13A using
NOEMA. Results. We find complex line profiles at disk scales which cannot be
explained by a single component or pure Keplerian motion. By adopting two
velocity components to model the complex line profiles, we find that the
temperatures and densities are significantly different between these two
components. This suggests that the physical conditions of the emitting gas
traced via CH3CN can change dramatically within the circumbinary disk. In
addition, combining our observations of DCN (3-2) with previous ALMA
high-angular-resolution observations, we find that the binary system (or VLA4A)
might be fed by an infalling streamer from envelope scales (~700 au). If this
is the case, this streamer contributes to the accretion of material onto the
system with a rate of at least 1.4x10-6 Msun yr-1. Conclusions. We conclude
that the CH3CN emission in SVS13A traces hot gas from a complex structure. This
complexity might be affected by a streamer that is possibly infalling and
funneling material into the central region.Comment: 20 pages, 19 figures, accepted to A&
PRODIGE -- Envelope to disk with NOEMA I. A 3000 au streamer feeding a Class I protostar
Context. In the past few years, there has been a rise in the detection of
streamers, asymmetric flows of material directed toward the protostellar disk
with material from outside the star's natal core. It is unclear how they affect
the process of mass accretion, in particular beyond the Class 0 phase. Aims. We
investigate the gas kinematics around Per-emb-50, a Class I source in the
crowded star-forming region NGC 1333. Our goal is to study how the mass infall
proceeds from envelope to disk scales in this source. Results. We discover a
streamer delivering material toward Per-emb-50 in HCO and CO
emission. The streamer's emission can be well described by the analytic
solutions for an infalling parcel of gas along a streamline with conserved
angular momentum, both in the image plane and along the line of sight
velocities. The streamer has a mean infall rate of M yr, times higher than the current accretion rate of the
protostar. SO and SO emission reveal asymmetric infall motions in the inner
envelope, additional to the streamer around Per-emb-50. Furthermore, the
presence of SO could mark the impact zone of the infalling material.
Conclusions. The streamer delivers sufficient mass to sustain the protostellar
accretion rate and might produce an accretion burst, which would explain the
protostar's high luminosity with respect to other Class I sources. Our results
highlight the importance of late infall for protostellar evolution: streamers
might provide a significant amount of mass for stellar accretion after the
Class 0 phase.Comment: 20 pages, 14 figures, accepted for publication in A&
PRODIGE - Envelope to disk with NOEMA: I. A 3000 au streamer feeding a Class I protostar
International audienceContext. In the past few years, there has been a rise in the detection of streamers, asymmetric flows of material directed toward the protostellar disk with material from outside the star's natal core. It is unclear how they affect the process of mass accretion, in particular beyond the Class 0 phase.Aims. We investigate the gas kinematics around Per-emb-50, a Class I source in the crowded star-forming region NGC 1333. Our goal is to study how the mass infall proceeds from envelope to disk scales in this source. Methods. We use new NOEMA 1.3 mm observations, including C 18 O, H 2 CO and SO, in the context of the PRODIGE MPG-IRAM program, to probe the core and envelope structures toward Per-emb-50.Results. We discover a streamer delivering material toward Per-emb-50 in H 2 CO and C 18 O emission. The streamer's emission can be well described by the analytic solutions for an infalling parcel of gas along a streamline with conserved angular momentum, both in the image plane and along the line of sight velocities. The streamer has a mean infall rate of 1.3 × 10 −6 M yr −1 , 5 − 10 times higher than the current accretion rate of the protostar. SO and SO 2 emission reveal asymmetric infall motions in the inner envelope, additional to the streamer around Per-emb-50. Furthermore, the presence of SO 2 could mark the impact zone of the infalling material.Conclusions. The streamer delivers sufficient mass to sustain the protostellar accretion rate and might produce an accretion burst, which would explain the protostar's high luminosity with respect to other Class I sources. Our results highlight the importance of late infall for protostellar evolution: streamers might provide a significant amount of mass for stellar accretion after the Class 0 phase