149 research outputs found
Identifying the counterpart of HESS J1858+020
HESS J1858+020 is a weak gamma-ray source that does not have any clear
cataloged counterpart at any wavelengths. Recently, the source G35.6-0.4 was
re-identified as a SNR. The HESS source lies towards the southern border of
this remnant. The purpose of this work is to investigate the interstellar
medium around the mentioned sources in order to look for possible counterparts
of the very-high energy emission. Using the 13CO J=1-0 line from the Galactic
Ring Survey and mid-IR data from GLIMPSE we analyze the environs of HESS
J1858+020 and SNR G35.6-0.4. The 13CO data show the presence of a molecular
cloud towards the southern border of SNR G35.6-0.4 and at the same distance as
the remnant. This cloud is composed by two molecular clumps, one, over the SNR
shell and the other located at the center of HESS J1858+020. We estimate a
molecular mass and a density of ~ 5 X 10^{3} Msun and ~ 500 cm^{-3},
respectively for each clump. Considering the gamma-ray flux observed towards
HESS J1858+020, we estimate that a molecular cloud with a density of at least
150 cm^{-3} could explain the very-high energy emission hadronically. Thus, we
suggest that the gamma-ray emission detected in HESS J1858+020 is due to
hadronic mechanism. Additionally, analyzing mid-IR emission, we find that the
region is active in star formation, which could be considered as an alternative
or complementary possibility to explain the very-high energy emission.Comment: 6 pages, 3 figures, accepted for publication in A&A Lette
Unveiling the circumstellar environment towards a massive young stellar object
As a continuation of a previous work, in which we found strong evidence of
massive molecular outflows towards a massive star forming site, we present a
new study of this region based on very high angular resolution observations
with the aim of discovering the outflow driven mechanism. Using near-IR data
acquired with Gemini-NIRI at the broad H- and Ks-bands, we study a region of
22" x 22" around the UCHII region G045.47+0.05, a massive star forming site at
the distance of about 8 kpc. To image the source with the highest spatial
resolution possible we employed the adaptative optic system ALTAIR, achieving
an angular resolution of about 0.15". We discovered a cone-like shape nebula
with an opening angle of about 90 degree extending eastwards the IR source
2MASS J19142564+1109283, a very likely MYSO. This morphology suggests a cavity
that was cleared in the circumstellar material and its emission may arise from
scattered continuum light, warm dust, and likely emission lines from
shock-excited gas. The nebula, presenting arc-like features, is connected with
the IR source through a jet-like structure, which is aligned with the blue
shifted CO outflow found in a previous study. The near-IR structure lies ~3"
north of the radio continuum emission, revealing that it is not spatially
coincident with the UCHII region. The observed morphology and structure of the
near-IR nebula strongly suggest the presence of a precessing jet. In this study
we have resolved the circumstellar ambient (in scale of a thousand A.U.) of a
distant MYSO, indeed one of the farthest cases.Comment: Accepted in A&A Letters (October 2013
Mapping the 13CO/C18O abundance ratio in the massive star forming region G29.96-0.02
Estimating molecular abundances ratios from the direct measurement of the
emission of the molecules towards a variety of interstellar environments is
indeed very useful to advance in our understanding of the chemical evolution of
the Galaxy, and hence of the physical processes related to the chemistry. It is
necessary to increase the sample of molecular clouds, located at different
distances, in which the behavior of molecular abundance ratios, such as the
13CO/C18O ratio (X), is studied in detail. We selected the well-studied
high-mass star-forming region G29.96-0.02, located at a distance of about 6.2
kpc, which is an ideal laboratory to perform this kind of studies. To study the
X towards this region it was used 12CO J=3-2 data obtained from COHRS, 13CO and
C18O J=3-2 data from CHIMPS, and 13CO and C18O J=2-1 data retrieved from the
CDS database (observed with the IRAM 30m telescope). The distribution of column
densities and X throughout the molecular cloud was studied based on LTE and
non-LTE methods. Values of X between 1.5 to 10.5, with an average of 5, were
found, showing that, besides the dependency between X and the galactocentric
distance, the local physical conditions may strongly affect this abundance
ratio. We found that correlating the X map with the location of the ionized gas
and dark clouds allows us to suggest in which regions the far-UV radiation
stalls in dense gaseous components, and in which ones it escapes and
selectively photodissociates the C18O isotope. The non-LTE analysis shows that
the molecular gas has very different physical conditions, not only spatially
across the cloud, but also along the line of sight. This kind of studies may
represent a tool to indirectly estimate (from molecular lines observations) the
degree of photodissociation in molecular clouds, which is indeed useful to
study the chemistry in the interstellar medium.Comment: Accepted in A&A (July 10, 2018
Discovering a misaligned CO outflow related to the red MSX source G034.5964-01.0292
The red MSX source G034.5964-01.0292 (MSXG34), catalogued as a massive YSO,
was observed in molecular lines with the aim of discover and study molecular
outflows. We mapped a region of 3'x3' centered at MSXG34 using the Atacama
Submillimeter Telescope Experiment in the 12CO J=3-2 and HCO+ J=4-3 lines with
an angular and spectral resolution of 22" and 0.11 km/s, respectively.
Additionally, public 13CO J=1-0 and near-IR UKIDSS data obtained from the
Galactic Ring Survey and the WFCAM Sciencie Archive, respectively, were
analyzed. We found that the 12CO spectra towards the YSO present a
self-absorption dip, as it is usual in star forming regions, and spectral wings
evidencing outflow activity. The HCO+ was detected only towards the MSXG34
position at v_LSR ~ 14.2 km/s, in coincidence with the 12CO absorption dip and
approximately with the velocity of previous ammonia observations. HCO+ and NH3
are known to be enhanced in molecular outflows. Analyzing the spectral wings of
the 12CO line, we discovered misaligned red- and blue-shifted molecular
outflows associated with MSXG34. The near-IR emission shows a cone-like shape
nebulosity composed by two arc-like features related to the YSO, which can be
due to a cavity cleared in the circumstellar material by a precessing jet. This
can explain the misalignment in the molecular outflows. From the analysis of
the 13CO J=1--0 data we suggest that the YSO is very likely related to a
molecular clump ranging between 10 and 14 km/s. This suggests that MSXG34, with
an associated central velocity of about 14 km/s, may be located in the
background of this clump. Thus, the blue-shifted outflow is probably deflected
by the interaction with dense gas along the line of sight.Comment: Accepted in A&A June 10, 201
Studying the Molecular Ambient towards the Young Stellar Object EGO G35.04-0.47
We are performing a systematic study of the interstellar medium around
extended green objects (EGOs), likely massive young stellar objects driving
outflows. EGO G35.04-0.47 is located towards a dark cloud at the northern-west
edge of an HII region. Recently, H2 jets were discovered towards this source,
mainly towards its southwest, where the H2 1-0 S(1) emission peaks. Therefore,
the source was catalogued as the Molecular Hydrogen emission-line object MHO
2429. In order to study the molecular ambient towards this star-forming site,
we observed a region around the aforementioned EGO using the Atacama
Submillimeter Telescope Experiment in the 12CO J=3--2, 13CO J=3--2, HCO+
J=4--3, and CS J=7--6 lines with an angular and spectral resolution of 22" and
0.11 km s-1, respectively. The observations revealed a molecular clump where
the EGO is embedded at v_LSR ~ 51 km s-1, in coincidence with the velocity of a
Class I 95 GHz methanol maser previously detected. Analyzing the 12CO line we
discovered high velocity molecular gas in the range from 34 to 47 km s-1, most
likely a blueshifted outflow driven by the EGO. The alignment and shape of this
molecular structure coincide with those of the southwest lobe of MHO 2429
mainly between 46 and 47 km s-1, confirming that we are mapping its CO
counterpart. Performing a SED analysis of EGO G35.04-0.47 we found that its
central object should be an intermediate-mass young stellar object accreting
mass at a rate similar to those found in some massive YSOs. We suggest that
this source can become a massive YSO.Comment: accepted to be published in PASJ - 24 September 201
Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1
We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and
G352.7-0.1, to understand the causes of such morphology. The research was
carried out based on new and reprocessed archival VLA observations and
XMM-Newton archival data. The surrounding was investigated based on data
extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring
Survey and the HI Southern Galactic Plane Survey. The present study revealed
that the overall morphology of both SNRs is the result of the mass-loss history
of their respective progenitor stars. Kes79 would be the product of the
gravitational collapse of a massive O9 star evolving near a molecular cloud and
within the precursor's wind-driven bubble, while G352.7-0.1 would be the result
of interactions of the SNR with an asymmetric wind from the progenitor together
with projection effects. No radio point source or pulsar wind nebula was found
associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray
study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray
radiation completely fills in the interior of the remnant and originates in
heated ejecta. Characteristic parameters, like radio flux, radio spectral
index, age, distance, shock velocity, initial energy and luminosity, were
estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and
Astrophysic
Early phases of star formation: testing chemical tools
The star forming processes strongly influence the ISM chemistry. Nowadays,
there are available many high-quality databases at millimeter wavelengths.
Using them, it is possible to carry out studies that review and deepen previous
results. If these studies involve large samples of sources, it is preferred to
use direct tools to study the molecular gas. With the aim of testing these
tools such as the use of the HCN/HNC ratio as a thermometer, and the use of
HCO, HCN, NH, and CH as "chemical clocks",
we present a molecular line study towards 55 sources representing massive young
stellar objects (MYSOs) at different evolutive stages: infrared dark clouds
(IRDCs), high-mass protostellar objects (HMPOs), hot molecular cores (HMCs) and
ultracompact HII regions (UCHII). We found that the use of HCN/HNC ratio as an
universal thermometer in the ISM should be taken with care because the HCN
optical depth is a big issue that can affect the method. Hence, this tool
should be used only after a careful analysis of the HCN spectrum, checking that
no line, neither the main nor the hyperfine ones, present absorption features.
We point out that the analysis of the emission of HCO, HCN,
NH, and CH could be useful to trace and distinguish regions
among IRDCs, HMPOs and HMCs. The molecular line widths of these four species
increase from the IRDC to the HMC stage, which can be a consequence of the gas
dynamics related to the star-forming processes taking place in the molecular
clumps. Our results do not only contribute with more statistics regarding to
probe such chemical tools, useful to obtain information in large samples of
sources, but also complement previous works through the analysis on other types
of sources.Comment: accepted to be published in Research in Astronomy & Astrophysics,
October 13, 202
12CO and 13CO J=3-2 observations toward N11 in the Large Magellanic Cloud
After 30 Doradus, N11 is the second largest and brightest nebula in the LMC.
This large nebula has several OB associations with bright nebulae at its
surroundings. N11 was previously mapped at the lowest rotational transitions of
CO (J=1--0 and 2--1), and in some particular regions pointings of the
CO J=1--0 and 2--1 lines were also performed. Using ASTE we mapped the
whole extension of the N11 nebula in the CO J=3--2 line, and three
sub-regions in the CO J=3--2 line. The regions mapped in the CO
J=3--2 were selected based on that they may be exposed to the radiation at
different ways: a region lying over the nebula related to the OB association
LH10 (N11B), another one that it is associated with the southern part of the
nebula related to the OB association LH13 (N11D), and finally a farther area at
the southwest without any embedded OB association (N11I). We found that the
morphology of the molecular clouds lying in each region shows some signatures
that could be explained by the expansion of the nebulae and the action of the
radiation. Fragmentation generated in a molecular shell due to the expansion of
the N11 nebula is suggested. The integrated line ratios CO/CO
show evidences of selective photodissociation of the CO, and probably
other mechanisms such as chemical fractionation. The CO contribution to the
continuum at 870 m was directly derived. The distribution of the
integrated line ratios CO J=3--2/2--1 show hints of stellar feedback in
N11B and N11D. The ratio between the virial and LTE mass (M/M) is higher than unity in all analyzed molecular clumps, which suggests
that the clumps are not gravitationally bounded and may be supported by
external pressure. A non-LTE analysis suggests that we are mapping gas with
densities about a few 10 cm.Comment: Accepted to be published in A&A. Figures were degrade
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