167 research outputs found
The Aquila prestellar core population revealed by Herschel
The origin and possible universality of the stellar initial mass function (IMF) is a major issue in astrophysics. One of the main objectives of the Herschel Gould Belt Survey is to clarify the link between the prestellar core mass function (CMF) and the IMF. We present and discuss the core mass function derived from Herschel data for the large population of prestellar cores discovered with SPIRE and PACS in the Aquila rift cloud complex at d ~ 260 pc. We detect a total of 541 starless cores in the entire ~11 deg^2 area of the field imaged at 70–500 μm with SPIRE/PACS. Most of these cores appear to be gravitationally bound, and thus prestellar in nature. Our Herschel results confirm that the shape of the prestellar CMF resembles the stellar IMF, with much higher quality statistics than earlier submillimeter continuum ground-based surveys
Dense cores in the dark cloud complex LDN1188
We present a molecular line emission study of the LDN1188 dark cloud complex
located in Cepheus. In this work we focused on the densest parts of the cloud
and on the close neighbourhood of infrared point sources. We made ammonia
mapping with the Effelsberg 100-m radio telescope and identified 3 dense cores.
CS(1--0), CS(2--1) and HCO(1--0) measurements performed with the Onsala
20\,m telescope revealed the distribution of dense molecular material. The
molecular line measurements were supplemented by mapping the dust emission at
1.2\,mm in some selected directions using the IRAM 30\,m telescope. With these
data we could work out a likely evolutionary sequence in this dark clould
complex.Comment: YouResAstro2012 conference presentation; accepted to Astronomishen
Nachrichten (25-July-2013
The dust masses of powerful radio galaxies: clues to the triggering of their activity
We use deep Herschel Space Observatory observations of a 90% complete sample
of 32 intermediate-redshift 2Jy radio galaxies (0.05 < z < 0.7) to estimate the
dust masses of their host galaxies and thereby investigate the triggering
mechanisms for their quasar-like AGN. The dust masses derived for the radio
galaxies (7.2x10^5 < M_d < 2.6x10^8 M_sun) are intermediate between those of
quiescent elliptical galaxies on the one hand, and ultra luminous infrared
galaxies (ULIRGs) on the other. Consistent with simple models for the
co-evolution of supermassive black holes and their host galaxies, these results
suggest that most of the radio galaxies represent the late time re-triggering
of AGN activity via mergers between the host giant elliptical galaxies and
companion galaxies with relatively low gas masses. However, a minority of the
radio galaxies in our sample (~20%) have high, ULIRG-like dust masses, along
with evidence for prodigious star formation activity. The latter objects are
more likely to have been triggered in major, gas-rich mergers that represent a
rapid growth phase for both their host galaxies and their supermassive black
holes.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
Witnessing the fragmentation of a filament into prestellar cores in Orion B/NGC 2024
Recent Herschel observations of nearby clouds have shown that filamentary
structures are ubiquitous and that most prestellar cores form in filaments.
Probing the density () and velocity () structure of filaments is crucial
for the understanding of the star formation process. To characterize both the
and the field of a fragmenting filament, we mapped NGC2024. 13CO, C18O,
and H13CO+ trace the filament seen in the data. The radial profile
from the data shows ~0.081 pc, which is similar to the
Herschel findings. The from 13CO and C18O are broader, while the
from H13CO+ is narrower, than from Herschel. These results
suggest that 13CO and C18O trace only the outer part of the filament and H13CO+
only the inner part. The H13CO+ map reveals gradients along
both filament axis, as well as oscillations with a period ~0.2 pc
along the major axis. Comparison between the and the distribution shows
a tentative /4 shift in H13CO+ or C18O. This /4 shift is not
simultaneously observed for all cores in any single tracer but is tentatively
seen in either H13CO+ or C18O. We produced a toy model taking into account a
transverse gradient, a longitudinal gradient, and a longitudinal
oscillation mode caused by fragmentation. Examination of synthetic data shows
that the oscillation component produces an oscillation pattern in the velocity
structure function (VSF) of the model. The H13CO+ VSF shows an oscillation
pattern, suggesting that our observations are partly tracing core-forming
motions and fragmentation. We also found that the mean corresponds
to the effective in the filament. This is consistent with a scenario
in which higher-mass cores form in higher line-mass filaments.Comment: accepted in A&
Far-Infrared Observations Of A Massive Cluster Forming In The Monoceros R2 Filament Hub
We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Herschel Space Observatory as part of the Herschel imaging survey of OB young stellar objects (HOBYS) Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C18O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments
Deep Herschel observations of the 2 Jy sample: assessing the non-thermal and AGN contributions to the far-IR continuum
Herschel survey of brown dwarf disks in Rho Ophiuchi
Recent observations of the Rho Ophiuchi cluster with the Herschel Space
Observatory allow us to probe the spectral energy distribution (SED) of the
brown dwarf population in the far-IR, where the disk emission peaks. We
performed aperture photometry at 70, 100, and 160 micron, and constructed SEDs
for all previously known brown dwarfs detected. These were complemented with
ancillary photometry at shorter wavelengths. We compared the observed SEDs to a
grid of synthetic disks produced with the radiative transfer code MCFOST, and
used the relative figure of merit estimated from the Bayesian inference of each
disk parameter to analyse the structural properties. We detected 12 Class II
brown dwarfs with Herschel, which corresponds to one-third of all currently
known brown dwarf members of Rho Ophiuchi. We do not detect any of the known
Class III brown dwarfs. Comparison to models reveals that the disks are best
described by an inner radius between 0.01 and 0.07 AU, and a flared disk
geometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude
values of the disk scale-height lower than 10 AU (measured at a fiducial radius
of 100 AU). We combined the Herschel data with recent ALMA observations of the
brown dwarf GY92 204 (ISO-Oph 102), and by comparing its SED to the same grid
of disk models, we derived an inner disk radius of 0.035 AU, a scale height of
15 AU with a flaring index of beta~1.15, an exponent for dust settling of -1.5,
and a disk mass of 0.001 MSun. This corresponds to a disk-to-central object
mass ratio of ~1%. The structural parameters constrained by the extended SED
coverage (inner radius and flaring index) show a narrow distribution for the 11
young brown dwarfs detected in Rho Ophiuchi, suggesting that these objects
share the same disk evolution and, perhaps, formation.Comment: Accepted for publication in A&
What determines the density structure of molecular clouds? A case study of Orion B with <i>Herschel</i>
A key parameter to the description of all star formation processes is the density structure of the gas. In this Letter, we make use of probability distribution functions (PDFs) of Herschel column density maps of Orion B, Aquila, and Polaris, obtained with the Herschel Gould Belt survey (HGBS). We aim to understand which physical processes influence the PDF shape, and with which signatures. The PDFs of Orion B (Aquila) show a lognormal distribution for low column densities until AV ~ 3 (6), and a power-law tail for high column densities, consistent with a ρα r-2 profile for the equivalent spherical density distribution. The PDF of Orion B is broadened by external compression due to the nearby OB stellar aggregates. The PDF of a quiescent subregion of the non-star-forming Polaris cloud is nearly lognormal, indicating that supersonic turbulence governs the density distribution. But we also observe a deviation from the lognormal shape at AV > 1 for a subregion in Polaris that includes a prominent filament. We conclude that (1) the point where the PDF deviates from the lognormal form does not trace a universal AV -threshold for star formation, (2) statistical density fluctuations, intermittency, and magnetic fields can cause excess from the lognormal PDF at an early cloud formation stage, (3) core formation and/or global collapse of filaments and a non-isothermal gas distribution lead to a power-law tail, and (4) external compression broadens the column density PDF, consistent with numerical simulations
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