118 research outputs found
Young Stellar Objects in the Gould Belt
We present the full catalog of Young Stellar Objects (YSOs) identified in the
18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks"
(c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed
by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of
which survive visual inspection and form our final catalog of YSOs in the Gould
Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and
tabulate the infrared spectral index, bolometric luminosity, and bolometric
temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and
1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III,
respectively, and show that the Class III sample suffers from an overall
contamination rate by background AGB stars between 25% and 90%. Adopting
standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs
and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass
uncertainties in the adopted assumptions. Including information from
(sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as
Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr
(Class I). We revisit infrared color-color diagrams used in the literature to
classify YSOs and propose minor revisions to classification boundaries in these
diagrams. Finally, we show that the bolometric temperature is a poor
discriminator between Class II and Class III YSOs.Comment: Accepted for publication in ApJS. 29 pages, 11 figures, 14 tables, 4
appendices. Full versions of data tables (to be published in machine-readable
format by ApJS) available at the end of the latex source cod
Star Formation in the Milky Way. The Infrared View
I present a brief review of some of the most recent and active topics of star
formation process in the Milky Way using mid and far infrared observations, and
motivated by the research being carried out by our science group using data
gathered by the Spitzer and Herschel space telescopes. These topics include
bringing together the scaling relationships found in extragalactic systems with
that of the local nearby molecular clouds, the synthetic modeling of the Milky
Way and estimates of its star formation rate.Comment: 12 pages, 9 figures. To apper in "Cosmic-ray induced phenomenology in
star-forming environments: Proceedings of the 2nd Session of the Sant Cugat
Forum of Astrophysics" (April 16-19, 2012), Olaf Reimer and Diego F. Torres
(eds.
A Mid-Infrared Census of Star Formation Activity in Bolocam Galactic Plane Survey Sources
We present the results of a search for mid-infrared signs of star formation
activity in the 1.1 mm sources in the Bolocam Galactic Plane Survey (BGPS). We
have correlated the BGPS catalog with available mid-IR Galactic plane catalogs
based on the Spitzer Space Telescope GLIMPSE legacy survey and the Midcourse
Space Experiment (MSX) Galactic plane survey. We find that 44% (3,712 of 8,358)
of the BGPS sources contain at least one mid-IR source, including 2,457 of
5,067 (49%) within the area where all surveys overlap (10 deg < l < 65 deg).
Accounting for chance alignments between the BGPS and mid-IR sources, we
conservatively estimate that 20% of the BPGS sources within the area where all
surveys overlap show signs of active star formation. We separate the BGPS
sources into four groups based on their probability of star formation activity.
Extended Green Objects (EGOs) and Red MSX Sources (RMS) make up the highest
probability group, while the lowest probability group is comprised of
"starless" BGPS sources which were not matched to any mid-IR sources. The mean
1.1 mm flux of each group increases with increasing probability of active star
formation. We also find that the "starless" BGPS sources are the most compact,
while the sources with the highest probability of star formation activity are
on average more extended with large skirts of emission. A subsample of 280 BGPS
sources with known distances demonstrates that mass and mean H_2 column density
also increase with probability of star formation activity.Comment: 20 pages, 12 figures, 3 tables. Accepted for publication in ApJ. Full
Table 2 will be available online through Ap
The Pipe Nebula as seen with Herschel: Formation of filamentary structures by large-scale compression ?
A growing body of evidence indicates that the formation of filaments in
interstellar clouds is a key component of the star formation process. In this
paper, we present new Herschel PACS and SPIRE observations of the B59 and Stem
regions in the Pipe Nebula complex, revealing a rich, organized network of
filaments. The asymmetric column density profiles observed for several
filaments, along with the bow-like edge of B59, indicates that the Pipe Nebula
is being compressed from its western side, most likely by the winds from the
nearby Sco OB2 association. We suggest that this compressive flow has
contributed to the formation of some of the observed filamentary structures. In
B59, the only region of the entire Pipe complex showing star formation
activity, the same compressive flow has likely enhanced the initial column
density of the clump, allowing it to become globally gravitationally unstable.
Although more speculative, we propose that gravity has also been responsible
for shaping the converging filamentary pattern observed in B59. While the
question of the relative impact of large-scale compression and gravity remains
open in B59, large-scale compression appears to be a plausible mechanism for
the initial formation of filamentary structures in the rest of the complexComment: 9 pages, 9 figures, accepted for publication in A&
The Zurich Environmental Study (ZENS) of galaxies in groups along the cosmic web. V. properties and frequency of merging satellites and centrals in different environments
We use the Zurich ENvironmental Study (ZENS) database to investigate the
environmental dependence of the merger fraction and merging galaxy
properties in a sample of ~1300 group galaxies with and
0.05<z<0.0585. In all galaxy mass bins investigated in our study, we find that
decreases by a factor of ~2-3 in groups with halo masses
relative to less massive systems, indicating a
suppression of merger activity in large potential wells. In the fiducial case
of relaxed groups only, we measure a variation dex, which is almost independent of galaxy mass
and merger stage. At galaxy masses , most mergers are dry
accretions of quenched satellites onto quenched centrals, leading to a strong
increase of with decreasing group-centric distance at these mass
scales.Both satellite and central galaxies in these high mass mergers do not
differ in color and structural properties from a control sample of nonmerging
galaxies of equal mass and rank. At galaxy masses , where
we mostly probe satellite-satellite pairs and mergers between star-forming
systems, close pairs (projected distance kpc) show instead
enhanced (specific) star formation rates and
larger sizes than similar mass, nonmerging satellites. The increase in both
size and SFR leads to similar surface star-formation densities in the merging
and control-sample satellite populations.Comment: Published in ApJ, 797, 12
Cluster-formation in the Rosette molecular cloud at the junctions of filaments
For many years feedback processes generated by OB-stars in molecular clouds,
including expanding ionization fronts, stellar winds, or UV-radiation, have
been proposed to trigger subsequent star formation. However, hydrodynamic
models including radiation and gravity show that UV-illumination has little or
no impact on the global dynamical evolution of the cloud. The Rosette molecular
cloud, irradiated by the NGC2244 cluster, is a template region for triggered
star-formation, and we investigated its spatial and density structure by
applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and
probability density functions (PDFs) on Herschel column density maps, obtained
within the HOBYS key program. The analysis reveals not only the filamentary
structure of the cloud but also that all known infrared clusters except one lie
at junctions of filaments, as predicted by turbulence simulations. The PDFs of
sub-regions in the cloud show systematic differences. The two UV-exposed
regions have a double-peaked PDF we interprete as caused by shock compression.
The deviations of the PDF from the log-normal shape typically associated with
low- and high-mass star-forming regions at Av~3-4m and 8-10m, respectively, are
found here within the very same cloud. This shows that there is no fundamental
difference in the density structure of low- and high-mass star-forming regions.
We conclude that star-formation in Rosette - and probably in high-mass
star-forming clouds in general - is not globally triggered by the impact of
UV-radiation. Moreover, star formation takes place in filaments that arose from
the primordial turbulent structure built up during the formation of the cloud.
Clusters form at filament mergers, but star formation can be locally induced in
the direct interaction zone between an expanding HII--region and the molecular
cloud.Comment: A&A Letter, in pres
The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis
We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2
field including the Corona Australis (CrA) star-forming region. At a distance
of 130 pc, CrA is one of the closest regions known to be actively forming
stars, particularly within its embedded association, the Coronet. Using the
Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include
sources in the well-studied Coronet cluster as well as distributed throughout
the molecular cloud. Twelve of the YSOs discussed are new candidates, one of
which is located in the Coronet. Known YSOs retrieved from the literature are
also added to the list, and a total of 116 candidate YSOs in CrA are compiled.
Based on these YSO candidates, the star formation rate is computed to be 12 M_o
Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also
performed, finding that the main cluster core, consisting of 68 members, is
elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc
and mean surface density of 150 pc^-2.
In addition, we analyze outflows and jets in CrA by means of new CO and H_2
data. We present 1.3 mm interferometric continuum observations made with the
Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712
(IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows,
study their proper motions, and identify exciting sources. The Spitzer and
ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a
CO (2-1) outflow detected in the SMA observations. There is also clear evidence
for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA
2 region, likely driven by SMA 2 or IRS 7A.Comment: Accepted for publication in ApJS. 112 pages, 42 figures (quality
reduced), 13 tables. Full resolution version can be found at
http://www.cfa.harvard.edu/~dpeterson/CrA/CrA_highres.pd
Bars in early- and late-type disks in COSMOS
We investigate the (large-scale) bar fraction in a mass-complete sample of M
> 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction
of barred disks strongly depends on mass, disk morphology, and specific star
formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun)
the bar fraction in early-type disks is much higher, at all redshifts, by a
factor ~2, than that in late-type disks. This trend is reversed at higher
stellar mass (M > 10^11 Msun), where the fraction of bars in early-type disks
becomes significantly lower, at all redshifts, than that in late-type disks.
The bar fractions for galaxies with low and high SSFRs closely follow those of
the morphologically-selected early-type and late-type populations,
respectively. This indicates a close correspondence between morphology and SSFR
in disk galaxies at these earlier epochs. Interestingly, the total bar fraction
in 10^10.5 < M < 10^11 Msun disks is built up by a factor of ~2 over the
redshift interval explored, while for M > 10^11 Msun disks it remains roughly
constant. This indicates that, already by z ~ 0.6, spectral and morphological
transformations in the most massive disk galaxies have largely converged to the
familiar Hubble sequence that we observe in the local Universe, while for
intermediate mass disks this convergence is ongoing until at least z ~ 0.2.
Moreover, these results highlight the importance of employing mass-limited
samples for quantifying the evolution of barred galaxies. Finally, the
evolution of the barred galaxy populations investigated does not depend on the
large-scale environmental density (at least, on the scales which can be probed
with the available photometric redshifts).Comment: 10 pages, 4 figures, updated to reflect version accepted by MNRA
Herschel Observations of a Potential Core Forming Clump: Perseus B1-E
We present continuum observations of the Perseus B1-E region from the
Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of
substructures at 160 - 500 micron not seen in previous submillimetre
observations. We measure temperature and column density from these data and
select the nine densest and coolest substructures for follow-up spectral line
observations with the Green Bank Telescope. We find that the B1-E clump has a
mass of ~ 100 solar masses and appears to be gravitationally bound.
Furthermore, of the nine substructures examined here, one substructure (B1-E2)
appears to be itself bound. The substructures are typically less than a Jeans
length from their nearest neighbour and thus, may interact on a timescale of ~
1 Myr. We propose that B1-E may be forming a first generation of dense cores,
which could provide important constraints on the initial conditions of
prestellar core formation. Our results suggest that B1-E may be influenced by a
strong, localized magnetic field, but further observations are still required.Comment: 14 pages, 8 figures, published in A&A: Minor calibration correctio
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