91 research outputs found
Resolving the masers in M82
Despite first being detected in the 1970s, surprisingly little is known about
the OH main line maser population in the nearby starburst galaxy M82. Sometimes
referred to as 'kilomasers', they have isotropic luminosities intermediate
between Galactic masers and those found in more distant megamasers. Several
observations have been carried by this group over the last ten years in an
attempt to get a better handle on their nature. High velocity resolution VLA
observations in 2006 showed that almost all of the maser spots, distributed
across the central arcminute of the galaxy, were apparently coincident with
background continuum features, and a handful displayed multiple velocity
components. The majority of those with velocity structure are located on a
blue-shifted arc in the pv-plane, spatially located on an arc northward of the
peculiar source known as B41.95+57.5. Now, new results from high spatial and
spectral resolution observations with the EVN have resolved several of these
masers into multiple spatial components for the first time. The maser emission
is compared with known continuum sources in the galaxy, and we conclude that at
least some of the maser emission is from high-gain maser action.Comment: Six pages, one table, one figure. To appear in proceedings of the
11th EVN Symposium (Bordeaux, 9-12 October 2012
Tracing the envelopes around embedded low-mass young stellar objects with HCO+ and millimeter-continuum observations
Interferometer observations of millimeter-continuum (OVRO) and single-dish
observations of HCO+ and H13CO+ J=1-0, 3-2, and 4-3 (JCMT, IRAM 30m) are
presented of nine embedded low-mass young stellar objects (YSOs) in Taurus. All
nine objects are detected at 3.4 and 2.7 mm, with fluxes of 4-200 mJy, and
consist of unresolved (<3 arcsec) point sources, plus, toward about half of the
objects, an extended envelope. The point sources likely are circumstellar
disks, showing that these are established early in the embedded phase.
Literature values of 1.1 mm continuum emission are used to trace the envelopes,
carrying 0.001-0.26 M(sol). In HCO+, the 1-0 lines trace the surrounding
clouds, while the 3-2 and 4-3 are concentrated toward the sources with
intensities well correlated with the envelope flux. An HCO+/H2 abundance of
1.2e-8 is derived. The HCO+ line strengths and envelope fluxes can be fit
simultaneously with the simple collapse model of Shu (1977), and related
density power laws with slopes p=1-3. As an indicator of the relative
evolutionary phase of a YSO, the ratio of HCO+ 3-2 line intensity over
bolometric luminosity is proposed, which is roughly proportional to the current
ratio of envelope over stellar mass. It is concluded that HCO+ 3-2 and 4-3 are
excellent tracers of the early embedded phase of star formation.Comment: 45 pages, 10 figures, ApJ/AASLaTeX. To be published in The
Astrophysical Journa
The eSMA: description and first results
The eSMA ("extended SMA") combines the SMA, JCMT and CSO into a single
facility, providing enhanced sensitivity and spatial resolution owing to the
increased collecting area at the longest baselines. Until ALMA early science
observing (2011), the eSMA will be the facility capable of the highest angular
resolution observations at 345 GHz. The gain in sensitivity and resolution will
bring new insights in a variety of fields, such as protoplanetary/transition
disks, high-mass star formation, solar system bodies, nearby and high-z
galaxies. Therefore the eSMA is an important facility to prepare the grounds
for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been
substantial progress toward making the eSMA into a working interferometer. In
particular, (i) new 345-GHz receivers, that match the capabilities of the SMA
system, were installed at the JCMT and CSO; (ii) numerous tests have been
performed for receiver, correlator and baseline calibrations in order to
determine and take into account the effects arising from the differences
between the three types of antennas; (iii) first fringes at 345 GHz were
obtained on August 30 2007, and the array has entered the science-verification
stage.
We report on the characteristics of the eSMA and its measured performance at
230 GHz and that expected at 345 GHz. We also present the results of the
commissioning and some initial science-verification observations, including the
first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located
along the line of sight to the lensed quasar PKS1830-211, and on the imaging of
the vibrationally excited HCN line towards IRC+10216.Comment: 12 pages, 7 figures, paper number 7012-12, to appear in Proceedings
of SPIE vol. 7012: "Ground-based and Airborne Telescopes II", SPIE conference
on Astronomical Instrumentation, Marseille, 23-28 June 200
Detection of CI in absorption towards PKS 1830-211 with the eSMA
We report the first science observations and results obtained with the
"extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT
(James Clerk Maxwell Telescope) and CSO (Caltech Submillimeter Observatory).
Redshifted absorptions at z=0.886 of CI (^3P_1 - ^3P_0) were observed with the
eSMA with an angular resolution of 0.55"x0.22" at 1.1 mm toward the
southwestern image of the remarkable lensed quasar PKS 1830-211, but not toward
the northeastern component at a separation of ~1". Additionally, SMA
observations of CO, 13CO and C18O (all J=4-3) were obtained toward this object:
CO was also detected toward the SW component, but none of the isotopologues
were. This is the first time [CI] is detected in this object, allowing the
first direct determination of relative abundances of neutral atomic carbon to
CO in the molecular clouds of a spiral galaxy at z>0.1. The [CI] and CO
profiles can be decomposed into two and three velocity components respectively.
We derive C/CO column density ratios ranging from <0.5 (representative of dense
cores) to ~2.5 (close to translucent clouds values). This could indicate that
we are seeing environments with different physical conditions or that we are
witnessing chemical evolution of regions where C has not completely been
converted into CO.Comment: 6 pages using emulateapj, 3 tables, 2 figures ; accepted for
publication in ApJ
A Search for Molecular Gas in the Host Galaxy of FRB 121102
We present SMA and NOEMA observations of the host galaxy of FRB 121102 in the
CO 3-2 and 1-0 transitions, respectively. We do not detect emission from either
transition. We set upper limits to the CO luminosity for CO 3-2 and for CO 1-0. For
Milky-Way-like star formation properties, we set a upper limit on the
mass of , slightly less than the
predictions for the mass based on the star formation rate. The true
constraint on the mass may be significantly higher, however, because of
the reduction in CO luminosity that is common forlow-metallicity dwarf galaxies
like the FRB host galaxy. These results demonstrate the challenge of
identifying the nature of FRB progenitors through study of the host galaxy
molecular gas. We also place a limit of 42 Jy () on the continuum
flux density of the persistent radio source at 97 GHz, consistent with a
power-law extrapolation of the low frequency spectrum, which may arise from an
AGN or other nonthermal source.Comment: Accepted for publication in A
The Host Galaxy and Redshift of the Repeating Fast Radio Burst FRB 121102
The precise localization of the repeating fast radio burst (FRB 121102) has
provided the first unambiguous association (chance coincidence probability
) of an FRB with an optical and persistent radio
counterpart. We report on optical imaging and spectroscopy of the counterpart
and find that it is an extended ()
object displaying prominent Balmer and [OIII] emission lines. Based on the
spectrum and emission line ratios, we classify the counterpart as a
low-metallicity, star-forming, AB mag dwarf galaxy at a
redshift of , corresponding to a luminosity distance of 972 Mpc.
From the angular size, the redshift, and luminosity, we estimate the host
galaxy to have a diameter kpc and a stellar mass of
, assuming a mass-to-light ratio between 2 to
3. Based on the H flux, we estimate the star
formation rate of the host to be and a
substantial host dispersion measure depth .
The net dispersion measure contribution of the host galaxy to FRB 121102 is
likely to be lower than this value depending on geometrical factors. We show
that the persistent radio source at FRB 121102's location reported by Marcote
et al (2017) is offset from the galaxy's center of light by 200 mas and
the host galaxy does not show optical signatures for AGN activity. If FRB
121102 is typical of the wider FRB population and if future interferometric
localizations preferentially find them in dwarf galaxies with low metallicities
and prominent emission lines, they would share such a preference with long
gamma ray bursts and superluminous supernovae.Comment: 12 pages, 3 figures, Published in ApJ Letters. V2: Corrected mistake
in author lis
Tomography of Galactic star-forming regions and spiral arms with the Square Kilometer Array
© 2014 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence https://creativecommons.org/licenses/by-nc-sa/3.0/us/. Published by Proceedings of Science http://pos.sissa.it/Very Long Baseline Interferometry (VLBI) at radio wavelengths can provide astrometry accurate to 10 micro-arcseconds or better (i.e. better than the target GAIA accuracy) without being limited by dust obscuration. This means that unlike GAIA, VLBI can be applied to star-forming regions independently of their internal and line-of-sight extinction. Low-mass young stellar objects (particularly T Tauri stars) are often non-thermal compact radio emitters, ideal for astrometric VLBI radio continuum experiments. Existing observations for nearby regions (e.g. Taurus, Ophiuchus, or Orion) demonstrate that VLBI astrometry of such active T Tauri stars enables the reconstruction of both the regions' 3D structure (through parallax measurements) and their internal kinematics (through proper motions, combined with radial velocities). The extraordinary sensitivity of the SKA telescope will enable similar "tomographic mappings" to be extended to regions located several kpc from Earth, in particular to nearby spiral arm segments. This will have important implications for Galactic science, galactic dynamics and spiral structure theories
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