148 research outputs found
Mid-J CO Emission From NGC 891: Microturbulent Molecular Shocks in Normal Star Forming Galaxies
We have detected the CO(6-5), CO(7-6), and [CI] 370 micron lines from the
nuclear region of NGC 891 with our submillimeter grating spectrometer ZEUS on
the CSO. These lines provide constraints on photodissociation region (PDR) and
shock models that have been invoked to explain the H_2 S(0), S(1), and S(2)
lines observed with Spitzer. We analyze our data together with the H_2 lines,
CO(3-2), and IR continuum from the literature using a combined PDR/shock model.
We find that the mid-J CO originates almost entirely from shock-excited warm
molecular gas; contributions from PDRs are negligible. Also, almost all the H_2
S(2) and half of the S(1) line is predicted to emerge from shocks. Shocks with
a pre-shock density of 2x10^4 cm^-3 and velocities of 10 km/s and 20 km/s for
C-shocks and J-shocks, respectively, provide the best fit. In contrast, the
[CI] line emission arises exclusively from the PDR component, which is best
parameterized by a density of 3.2x10^3 cm^-3 and a FUV field of G_o = 100 for
both PDR/shock-type combinations. Our mid-J CO observations show that
turbulence is a very important heating source in molecular clouds, even in
normal quiescent galaxies. The most likely energy sources for the shocks are
supernovae or outflows from YSOs. The energetics of these shock sources favor
C-shock excitation of the lines.Comment: 18 pages, 2 figures, 6 tables, accepted by Ap
Strong C+ emission in galaxies at z~1-2: Evidence for cold flow accretion powered star formation in the early Universe
We have recently detected the [CII] 157.7 micron line in eight star forming
galaxies at redshifts 1 to 2 using the redshift(z) Early Universe Spectrometer
(ZEUS). Our sample targets star formation dominant sources detected in PAH
emission. This represents a significant addition to [CII] observations during
the epoch of peak star formation. We have augmented this survey with
observations of the [OI] 63 micron line and far infrared photometry from the
PACS and SPIRE Herschel instruments as well as Spitzer IRS spectra from the
literature showing PAH features. Our sources exhibit above average gas heating
efficiency, many with both [OI]/FIR and [CII]/FIR ~1% or more. The relatively
strong [CII] emission is consistent with our sources being dominated by star
formation powered PDRs, extending to kpc scales. We suggest that the star
formation mode in these systems follows a Schmidt-Kennicutt law similar to
local systems, but at a much higher rate due to molecular gas surface densities
10 to 100 times that of local star forming systems. The source of the high
molecular gas surface densities may be the infall of neutral gas from the
cosmic web. In addition to the high [CII]/FIR values, we also find high
[CII]/PAH ratios and, in at least one source, a cool dust temperature. This
source, SWIRE 4-5, bears a resemblance in these diagnostics to shocked regions
of Stephan's Quintet, suggesting that another mode of [CII] excitation in
addition to normal photoelectric heating may be contributing to the observed
[CII] line.Comment: Accepted for publication in Astrophysical Journal. To appear in
December 20, 2014, V797 - 2 issu
Chemically Distinct Nuclei and Outflowing Shocked Molecular Gas in Arp 220
We present the results of interferometric spectral line observations of Arp
220 at 3.5mm and 1.2mm from the Plateau de Bure Interferometer (PdBI), imaging
the two nuclear disks in HCN and , HCO and , and HNC as well as SiO and , HCN, and SO. The gas traced by SiO
has a complex and extended kinematic signature including a prominent P Cygni
profile, almost identical to previous observations of HCO. Spatial
offsets north and south of the continuum centre in the emission and
absorption of the SiO P Cygni profile in the western nucleus (WN)
imply a bipolar outflow, delineating the northern and southern edges of its
disk and suggesting a disk radius of pc, consistent with that found by
ALMA observations of Arp 220. We address the blending of SiO and
HCO by considering two limiting cases with regards to the
HCO emission throughout our analysis. Large velocity gradient (LVG)
modelling is used to constrain the physical conditions of the gas and to infer
abundance ratios in the two nuclei. Our most conservative lower limit on the
[HCN]/[HCO] abundance ratio is 11 in the WN, cf. 0.10 in the
eastern nucleus (EN). Comparing these ratios to the literature we argue on
chemical grounds for an energetically significant AGN in the WN driving either
X-ray or shock chemistry, and a dominant starburst in the EN.Comment: 28 pages, 17 figures, accepted to Ap
Development of Aluminum LEKIDs for Balloon-Borne Far-IR Spectroscopy
We are developing lumped-element kinetic inductance detectors (LEKIDs)
designed to achieve background-limited sensitivity for far-infrared (FIR)
spectroscopy on a stratospheric balloon. The Spectroscopic Terahertz Airborne
Receiver for Far-InfraRed Exploration (STARFIRE) will study the evolution of
dusty galaxies with observations of the [CII] 158 m and other atomic
fine-structure transitions at , both through direct observations of
individual luminous infrared galaxies, and in blind surveys using the technique
of line intensity mapping. The spectrometer will require large format
(1800 detectors) arrays of dual-polarization sensitive detectors with
NEPs of W Hz. The low-volume LEKIDs are fabricated
with a single layer of aluminum (20 nm thick) deposited on a crystalline
silicon wafer, with resonance frequencies of MHz. The inductor is a
single meander with a linewidth of 0.4 m, patterned in a grid to absorb
optical power in both polarizations. The meander is coupled to a circular
waveguide, fed by a conical feedhorn. Initial testing of a small array
prototype has demonstrated good yield, and a median NEP of
W Hz.Comment: accepted for publication in Journal of Low Temperature Physic
Spectroscopic FIR mapping of the disk and galactic wind of M82 with Herschel-PACS
[Abridged] We present maps of the main cooling lines of the neutral atomic
gas ([OI] at 63 and 145 micron and [CII] at 158 micron) and in the [OIII] 88
micron line of the starburst galaxy M82, carried out with the PACS spectrometer
on board the Herschel satellite. By applying PDR modeling we derive maps of the
main ISM physical parameters, including the [CII] optical depth, at
unprecedented spatial resolution (~300 pc). We can clearly kinematically
separate the disk from the outflow in all lines. The [CII] and [OI]
distributions are consistent with PDR emission both in the disk and in the
outflow. Surprisingly, in the outflow, the atomic and the ionized gas traced by
the [OIII] line both have a deprojected velocity of ~75 km/s, very similar to
the average velocity of the outflowing cold molecular gas (~ 100 km/s) and
several times smaller than the outflowing material detected in Halpha (~ 600
km/s). This suggests that the cold molecular and neutral atomic gas and the
ionized gas traced by the [OIII] 88 micron line are dynamically coupled to each
other but decoupled from the Halpha emitting gas. We propose a scenario where
cold clouds from the disk are entrained into the outflow by the winds where
they likely evaporate, surviving as small, fairly dense cloudlets (n_H\sim
500-1000 cm^-3, G_0\sim 500- 1000, T_gas\sim300 K). We show that the UV photons
provided by the starburst are sufficient to excite the PDR shells around the
molecular cores. The mass of the neutral atomic gas in the outflow is \gtrsim
5-12x 10^7 M_sun to be compared with that of the molecular gas (3.3 x 10^8
M_sun) and of the Halpha emitting gas (5.8 x 10^6 M_sun). The mass loading
factor, (dM/dt)/SFR, of the molecular plus neutral atomic gas in the outflow is
~ 2. Energy and momentum driven outflow models can explain the data equally
well, if all the outflowing gas components are taken into account.Comment: 26 pages, 23 figures, 4 Tables, Accepted for publication in Astronomy
& Astrophysic
ISM conditions in z~0.2 Lyman-Break Analogs
We present an analysis of far--infrared (FIR) [CII] and [OI] fine structure
line and continuum observations obtained with /PACS, and CO(1-0)
observations obtained with the IRAM Plateau de Bure Interferometer, of Lyman
Break Analogs (LBAs) at . The principal aim of this work is to
determine the typical ISM properties of Main Sequence (MS)
galaxies, with stellar masses between and ,
which are currently not easily detectable in all these lines even with ALMA and
NOEMA. We perform PDR modeling and apply different IR diagnostics to derive the
main physical parameters of the FIR emitting gas and dust and we compare the
derived ISM properties to those of galaxies on and above the MS at different
redshifts. We find that the ISM properties of LBAs are quite extreme (low gas
temperature, high density and thermal pressure) with respect to those found in
local normal spirals and more active local galaxies. LBAs have no [CII] deficit
despite having the high specific star formation rates (sSFRs) typical of
starbursts. Although LBAs lie above the local MS, we show that their ISM
properties are more similar to those of high-redshift MS galaxies than of local
galaxies above the main sequence. This data set represents an important
reference for planning future ALMA [CII] observations of relatively low-mass MS
galaxies at the epoch of the peak of the cosmic star formation.Comment: 19 pages, 12 Figures,8 Tables, Accepted for publication in A&
A deep Herschel/PACS observation of CO(40-39) in NGC 1068: a search for the molecular torus
Emission from high-J CO lines in galaxies has long been proposed as a tracer
of X-ray dominated regions (XDRs) produced by AGN. Of particular interest is
the question of whether the obscuring torus, which is required by AGN
unification models, can be observed via high-J CO cooling lines. Here we report
on the analysis of a deep Herschel-PACS observation of an extremely high J CO
transition (40-39) in the Seyfert 2 galaxy NGC 1068. The line was not detected,
with a derived 3 upper limit of . We apply an XDR model in order to
investigate whether the upper limit constrains the properties of a molecular
torus in NGC 1068. The XDR model predicts the CO Spectral Line Energy
Distributions for various gas densities and illuminating X-ray fluxes. In our
model, the CO(40-39) upper limit is matched by gas with densities , located at from the AGN,
with column densities of at least . At such high
column densities, however, dust absorbs most of the CO(40-39) line emission at
m. Therefore, even if NGC 1068 has a molecular torus
which radiates in the CO(40-39) line, the dust can attenuate the line emission
to below the PACS detection limit. The upper limit is thus consistent with the
existence of a molecular torus in NGC 1068. In general, we expect that the
CO(40-39) is observable in only a few AGN nuclei (if at all), because of the
required high gas column density, and absorption by dust.Comment: 22 pages, accepted for publication in Ap
Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and
H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at
least 285 and \sim200 K, respectively, are detected in both sources, indicating
radiative pumping and location in the high radiation density environment of the
nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei
of both sources. The inferred OH+ column and abundance relative to H nuclei are
(0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220,
an extended low excitation component around the nuclear region is found to have
OH+/H2O+\sim5-10. H3O+ is detected in both sources with
N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable
lines indicate a high rotational temperature of ~500 K, indicative of formation
pumping and/or hot gas. Simple chemical models favor an ionization sequence
dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+
production is most likely dominated by X-ray/cosmic ray ionization. The full
set of observations and models leads us to propose that the molecular ions
arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in
which case the ionization rate per H nucleus (including secondary ionizations)
is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate
estimates for Galactic regions. In Arp 220, our lower limit for zeta is
compatible with estimates for the cosmic ray energy density inferred previously
from the supernova rate and synchrotron radio emission, and also with the
expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray
ionization due to an AGN is responsible for the molecular ion production.Comment: 24 pages, 13 figures. Accepted for publication in Astronomy &
Astrophysic
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