6 research outputs found
The SOFIA Massive (SOMA) Star Formation Survey. III. From Intermediate- to High-Mass Protostars
We present m SOFIA-FORCAST images of 14 intermediate-mass
protostar candidates as part of the SOFIA Massive (SOMA) Star Formation Survey.
We build spectral energy distributions (SEDs), also utilizing archival Spitzer,
Herschel and IRAS data. We then fit the SEDs with radiative transfer (RT)
models of Zhang & Tan (2018), based on Turbulent Core Accretion theory, to
estimate key protostellar properties. With the addition of these
intermediate-mass sources, SOMA protostars span luminosities from
, current protostellar masses from
and ambient clump mass surface densities, from . A wide range of evolutionary states of
the individual protostars and of the protocluster environments are also probed.
We have also considered about 50 protostars identified in Infrared Dark Clouds
and expected to be at the earliest stages of their evolution. With this global
sample, most of the evolutionary stages of high- and intermediate-mass
protostars are probed. From the best fitting models, there is no evidence of a
threshold value of protocluster clump mass surface density being needed to form
protostars up to . However, to form more massive protostars,
there is tentative evidence that needs to be
. We discuss how this is consistent with
expectations from core accretion models that include internal feedback from the
forming massive star.Comment: 40 pages, 21 figures, 4 tables, accepted to Ap
The JWST Galactic Center Survey -- A White Paper
The inner hundred parsecs of the Milky Way hosts the nearest supermassive
black hole, largest reservoir of dense gas, greatest stellar density, hundreds
of massive main and post main sequence stars, and the highest volume density of
supernovae in the Galaxy. As the nearest environment in which it is possible to
simultaneously observe many of the extreme processes shaping the Universe, it
is one of the most well-studied regions in astrophysics. Due to its proximity,
we can study the center of our Galaxy on scales down to a few hundred AU, a
hundred times better than in similar Local Group galaxies and thousands of
times better than in the nearest active galaxies. The Galactic Center (GC) is
therefore of outstanding astrophysical interest. However, in spite of intense
observational work over the past decades, there are still fundamental things
unknown about the GC. JWST has the unique capability to provide us with the
necessary, game-changing data. In this White Paper, we advocate for a JWST
NIRCam survey that aims at solving central questions, that we have identified
as a community: i) the 3D structure and kinematics of gas and stars; ii)
ancient star formation and its relation with the overall history of the Milky
Way, as well as recent star formation and its implications for the overall
energetics of our galaxy's nucleus; and iii) the (non-)universality of star
formation and the stellar initial mass function. We advocate for a large-area,
multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy
in the form of a Treasury GO JWST Large Program that is open to the community.
We describe how this survey will derive the physical and kinematic properties
of ~10,000,000 stars, how this will solve the key unknowns and provide a
valuable resource for the community with long-lasting legacy value.Comment: This White Paper will be updated when required (e.g. new authors
joining, editing of content). Most recent update: 24 Oct 202
Vibrationally-excited Lines of HCN Associated with the Molecular Disk around the G24.78+0.08 A1 Hyper-compact H Region
We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of
the hyper-compact H region G24.78+0.08 A1 (G24 HC H)
and report the detection of vibrationally-excited lines of HCN
(, ). The spatial distribution and kinematics of a
vibrationally-excited line of HCN (, , ) are
found to be similar to the CHCN vibrationally-excited line (),
which indicates that the HCN emission is tracing the disk around the G24
HC H region previously identified by the CHCN lines. We
derive the CHCN/HCCCN abundance ratios around G24 and
compare them to the CHCN/HCN abundance ratios in disks around
Herbig Ae and T Tauri stars. The CHCN/HCCCN ratios around
G24 () are higher than the CHCN/HCN ratios in the
other disks () by more than one order of magnitude. The higher
CHCN/HCN ratios around G24 suggest that the thermal desorption of
CHCN in the hot dense gas and efficient destruction of HCN in the
region irradiated by the strong UV radiation are occurring. Our results
indicate that the vibrationally-excited HCN lines can be used as a disk
tracer of massive protostars at the HC H region stage, and the
combination of these nitrile species will provide information of not only
chemistry but also physical conditions of the disk structures.Comment: 21 pages, 13 figures, 5 tables, Accepted by The Astrophysical Journa
Isolated Massive Star Formation in G28.20-0.05
We report high-resolution 1.3mm continuum and molecular line observations of
the massive protostar G28.20-0.05 with ALMA. The continuum image reveals a
ring-like structure with 2,000 au radius, similar to morphology seen in
archival 1.3cm VLA observations. Based on its spectral index and associated
H30 emission, this structure mainly traces ionized gas. However, there
is evidence for 30 M of dusty gas near the main mm continuum peak
on one side of the ring, as well as in adjacent regions within 3,000 au. A
virial analysis on scales of 2,000 au from hot core line emission yields
a dynamical mass of 80M. A strong velocity gradient in the
H30 emission is evidence for a rotating, ionized disk wind, which
drives a larger-scale molecular outflow. An infrared SED analysis indicates a
current protostellar mass of m24 M forming from a core with
initial mass in a clump with mass surface density of
. Thus the SED and other properties of
the system can be understood in the context of core accretion models.
Structure-finding analysis on the larger-scale continuum image indicates
G28.20-0.05 is forming in a relatively isolated environment, with no other
concentrated sources, i.e., protostellar cores, above 1 M found
from 0.1 to 0.4 pc around the source. This implies that a massive star is
able to form in relative isolation and the dearth of other protostellar
companions within the 1 pc environs is a strong constraint on massive
star formation theories that predict the presence of a surrounding
protocluster.Comment: Submitted to ApJ, comments welcom
The SOFIA Massive (SOMA) Star Formation Survey. IV. Isolated Protostars
We present âŒ10â40 ÎŒ m SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 ÎŒ m imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, developed within the framework of turbulent core accretion (TCA) theory, to estimate key protostellar properties. Here, we release the sedcreator python package that carries out these methods. The SEDs are generally well fitted by the TCA models, from which we infer initial core masses M _c ranging from 20â430 M _â , clump mass surface densities ÎŁ _cl ⌠0.3â1.7 g cm ^â2 , and current protostellar masses m _* ⌠3â50 M _â . From a uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold ÎŁ _cl for massive star formation. However, the upper end of the m _* âÎŁ _cl distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher ÎŁ _cl conditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an âŒ40 yr baseline