212 research outputs found
Resolving the Host Galaxy of the Nearby QSO I Zw 1 with Sub-Arcsecond Multi-Transition Molecular Line Observations
We present the first sub-kpc 0.7" (~ 850 pc) resolution 12CO(1-0) molecular
line observations of the ISM in the host galaxy of the QSO I Zw 1. The
observations were obtained with the BIMA mm-interferometer in its compact A
configuration. The BIMA data are complemented by new observations of the
12CO(2-1) and 13CO(1-0) line with IRAM Plateau de Bure mm-interferometer (PdBI)
at 0.9" and 1.9" resolution, respectively. These measurements, which are part
of a multi-wavelength study of the host galaxy of I Zw 1, are aimed at
comparing the ISM properties of a QSO host with those of nearby galaxies as
well as to obtain constraints on galaxy formation/evolution models. Our images
of the 12CO(1-0) line emission show a ring-like structure in the circumnuclear
molecular gas distribution with an inner radius of about 1.2 kpc. The presence
of such a molecular gas ring was predicted from earlier lower angular
resolution PdBI 12CO(1-0) observations. A comparison of the BIMA data with IRAM
PdBI 12CO(2-1) observations shows variations in the excitation conditions of
the molecular gas in the innermost 1.5" comprising the nuclear region of I Zw
1. The observed properties of the molecular cloud complexes in the disk of the
host galaxy suggest that they can be the sites of massive circumnuclear star
formation, and show no indications of excitation by the nuclear AGN. This all
indicates that the molecular gas in a QSO host galaxy has similar properties to
the gas observed in nearby low luminosity AGNs.Comment: to be published in ApJ 1 July 2004 issu
Dust formation, evolution, and obscuration effects in the very high-redshift universe
The evolution of dust at redshifts z>9, and consequently the dust properties,
differs greatly from that in the local universe. In contrast to the local
universe, core collapse supernovae (CCSNe) are the only source of
thermally-condensed dust. Because of the low initial dust-to-gas mass ratio,
grain destruction rates are low, so that CCSNe are net producers of
interstellar dust. Galaxies with large initial gas mass or high mass infall
rate will therefore have a more rapid net rate of dust production comported to
galaxies with lower gas mass, even at the same star formation rate. The dust
composition is dominated by silicates, which exhibit a strong rise in the UV
opacity near the Lyman break. This "silicate-UV break" may be confused with the
Lyman break, resulting in a misidentification of a galaxies' photometric
redshift. In this paper we demonstrate these effects by analyzing the spectral
energy distribution (SED) of MACS1149-JD, a lensed galaxy at z=9.6. A potential
2mm counterpart of MACS1149-JD has been identified with GISMO. While additional
observations are required to corroborate this identification, we use this
possible association to illustrate the physical processes and the observational
effects of dust in the very high redshift universe.Comment: Accepted for publication in ApJ Letter
Near-Infrared Photometry of the High-Redshift Quasar RDJ030117+002025: Evidence for a Massive Starburst at z=5.5
With a redshift of z=5.5 and an optical blue magnitude M_B ~ -24.2 mag (~4.5
10^12 L_sun), RDJ030117+002025 is the most distant optically faint (M_B > -26
mag) quasar known. MAMBO continuum observations at lambda=1.2 mm (185
micrometer rest-frame) showed that this quasar has a far-IR luminosity
comparable to its optical luminosity. We present near-infrared J- and K-band
photometry obtained with NIRC on the Keck I telescope, tracing the slope of the
rest frame UV spectrum of this quasar. The observed spectral index is close to
the value of alpha_nu ~ -0.44 measured in composite spectra of optically-bright
SDSS quasars. It thus appears that the quasar does not suffer from strong dust
extinction, which further implies that its low rest-frame UV luminosity is due
to an intrinsically-faint AGN. The FIR to optical luminosity ratio is then much
larger than that observed for the more luminous quasars, supporting the
suggestion that the FIR emission is not powered by the AGN but by a massive
starburst.Comment: 6 pages, APJ in pres
New constraints on dust emission and UV attenuation of z=6.5-7.5 galaxies from millimeter observations
We have targeted two recently discovered Lyman break galaxies (LBGs) to
search for dust continuum and [CII] 158 micron line emission. The strongly
lensed z~6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703, and the
spectroscopically confirmed z=7.508 LBG z8-GND-5296 in the GOODS-N field have
been observed with the Plateau de Bure interferometer (PdBI) at 1.2mm. These
observations have been combined with those of three z>6.5 Lya emitters (named
HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained
with the PdBI and ALMA. [CII] is undetected in both galaxies, providing a deep
upper limit for Abell1703-zD1, comparable to recent ALMA non-detections. Dust
continuum emission from Abell1703-zD1 and z8-GND-5296 is not detected with an
rms of 0.12 and 0.16 mJy/beam. From these non-detections we derive upper limits
on their IR luminosity and star formation rate, dust mass, and UV attenuation.
Thanks to strong gravitational lensing the limit for Abell1703-zD1 is probing
the sub-LIRG regime ( Lsun) and very low dust
masses ( Msun). We find that all five galaxies are
compatible with the Calzetti IRX- relation, their UV attenuation is
compatible with several indirect estimates from other methods (the UV slope,
extrapolation of the attenuation measured from the IR/UV ratio at lower
redshift, and SED fits), and the dust-to-stellar mass ratio is not incompatible
with that of galaxies from z=0 to 3. For their stellar mass the high-z galaxies
studied here have an attenuation below the one expected from the mean relation
of low redshift (z<1.5) galaxies. More and deeper (sub)-mm data are clearly
needed to directly determine the UV attenuation and dust content of the
dominant population of high-z star-forming galaxies and to establish more
firmly their dependence on stellar mass, redshift, and other properties.Comment: 10 pages, 7 figures. Minor revisions. Accepted for publication in A&
The Galactic centre mini-spiral in the mm-regime
The mini-spiral is a feature of the interstellar medium in the central ~2 pc
of the Galactic center. It is composed of several streamers of dust and ionised
and atomic gas with temperatures between a few 100 K to 10^4 K. There is
evidence that these streamers are related to the so-called circumnuclear disk
of molecular gas and are ionized by photons from massive, hot stars in the
central parsec. We attempt to constrain the emission mechanisms and physical
properties of the ionized gas and dust of the mini-spiral region with the help
of our multiwavelength data sets. Our observations were carried out at 1.3 mm
and 3 mm with the mm interferometric array CARMA in California in March and
April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the
NIR Br-gamma with VLT NACO in August 2009. We present high resolution maps of
the mini-spiral, and obtain a spectral index of 0.5 for Sgr A*, indicating an
inverted synchrotron spectrum. We find electron densities within the range
0.8-1.5x10^4 cm-3 for the mini-spiral from the radio continuum maps, along with
a dust mass contribution of ~0.25 solar masses from the MIR dust continuum, and
extinctions ranging from 1.8-3 at 2.16 micron in the Br-gamma line. We observe
a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm
observations of the extended emission of the mini-spiral, which we interpret as
evidence that there are a range of contributions to the thermal free-free
emission by the ionized gas emission and by dust at 1.3 mm.Comment: 9 pages, 11 figures, accepted to A&
Design and Fabrication Highlights Enabling a 2mm, 128 Element Bolometer Array for GISMO
The design and fabrication of a background limited, 128 pixel Transition Edge Sensor (TES) bolometer array for the Goddard IRAM Super-conducting 2-mm Observer (GISMO) is presented
The Nearby QSO Host I Zw 1: NIR Probing of Structural Properties and Stellar Populations
The likely merger process and the properties of the stellar populations in
the I Zw 1 host galaxy are analyzed on the basis of multi-wavelength
observations (with the ISAAC camera at the Very Large Telescope (VLT/UT1) of
the European Southern Observatory (ESO), Chile (Paranal), with the
interferometer of the Berkeley-Illinois-Maryland Association (BIMA), USA (Hat
Creek/California), and with the IRAM Plateau de Bure Interferometer (PdBI),
France) and N-body simulations. The data give a consistent picture of I Zw 1,
with properties between those of ultra-luminous infrared galaxies (ULIRGs) and
QSOs as displayed by transition objects in the evolutionary sequence of active
galaxies.Comment: 4 pages, 2 figures, to be published in "The Dense Interstellar Medium
in Galaxies", proceedings of the 4th Cologne-Bonn-Zermatt-Symposium held
September 22-26, 2003, in Zermatt, Switzerlan
Implications of a High Angular Resolution Image of the Sunyaev-Zel'dovich Effect in RXJ1347-1145
The most X-ray luminous cluster known, RXJ1347-1145 (z=0.45), has been the
object of extensive study across the electromagnetic spectrum. We have imaged
the Sunyaev-Zel'dovich Effect (SZE) at 90 GHz (3.3 mm) in RXJ1347-1145 at 10"
resolution with the 64-pixel MUSTANG bolometer array on the Green Bank
Telescope (GBT), confirming a previously reported strong, localized enhancement
of the SZE 20" to the South-East of the center of X-ray emission. This
enhancement of the SZE has been interpreted as shock-heated (> 20 keV) gas
caused by an ongoing major (low mass-ratio) merger event. Our data support this
interpretation. We also detect a pronounced asymmetry in the projected cluster
pressure profile, with the pressure just east of the cluster core ~1.6 times
higher than just to the west. This is the highest resolution image of the SZE
made to date.Comment: 9 pages, 7 figures; accepted for publication in The Astrophysical
Journa
Stray Light Suppression in the Goddard IRAM 2-Millimeter Observer (GISMO)
The Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) is an 8xl6 Transition Edge Sensor (TES) array of bolometers built as a pathfinder for TES detector development efforts at NASA Goddard Space Flight Center. GISMO has been used annually at the Institut de Radioastronomie Millimetrique (IRAM) 30 meter telescope since 2007 under engineering time and was opened in the spring of 2012 to the general astronomical community. The spring deployment provided an opportunity to modify elements of the room temperature optics before moving the instrument to its new permanent position in the telescope receiver cabin. This allowed for the possibility to extend the cryostat, introduce improved cold baffling and thus further optimize the stray light performance for final astronomical use of the instrument, which has been completed and validated. We will demonstrate and discuss several of the methods used to quantify and limit the influence of stray light in the GISMO camera
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