32 research outputs found
First CO J=6-5, 4-3 detections in local ULIRGs: the dense gas in Mrk231, and its colling budget
We report on detections of the high-excitation CO J=6-5, J=4-3 lines in
Mrk231, a prototypical Ultra Luminous Infrared Galaxy (ULIRG) and Seyfert 1
QSO. These observations are combined with CO J=3-2, HCN J=4-3 (this work), and
CO J=2-1, J=1-0, 13CO J=2-1, HCN J=1-0 measurements taken from the literature
to provide better constraints on the properties of the molecular gas in an
extreme starburst/QSO in the local Universe. We find that the CO J=4-3 and
J=6-5 transitions trace a different gas phase from that dominating the lower
three CO transitions, with n(H_2) ~ (1-3)x10^4 cm-3 and Tk ~ (40-70) K. This
phase is responsible for the luminous HCN emission, and contains most of the H2
gas mass of this galaxy. The total CO line cooling emanating from this dense
phase is found similar to that of the [CII] line at 158 micron, suggesting a
very different thermal balance to that seen in lower IR-luminosity galaxies,
and one likely dominated by dense photon-dominated regions. Our dense
"sampling" of the CO rotational ladder and the HCN lines enables us to produce
well-constrained Spectral Line Energy Distributions (SLEDs) for the dense
molecular gas in Mrk231 and compare them to those of high redshift starbursts,
many of which have SLEDs that may be affected by strong lensing. Finally, we
use our local molecular line excitation template to assess the capabilities of
future cm and mm/sub-mm arrays in detecting CO and HCN transitions in similar
systems throughout the local and distant universe.Comment: accepted for publication in The Astrophysical Journal; 37 pages,
preprint format; 5 figures (2 in color
A Search for Dense Molecular Gas in High Redshift Infrared-Luminous Galaxies
We present a search for HCN emission from four high redshift far infrared
(IR) luminous galaxies. Current data and models suggest that these high IR
luminous galaxies represent a major starburst phase in the formation of
spheroidal galaxies, although many of the sources also host luminous active
galactic nuclei (AGN), such that a contribution to the dust heating by the AGN
cannot be precluded. HCN emission is a star formation indicator, tracing dense
molecular hydrogen gas within star-forming molecular clouds (n(H) cm). HCN luminosity is linearly correlated with IR luminosity for
low redshift galaxies, unlike CO emission which can also trace gas at much
lower density. We report a marginal detection of HCN (1-0) emission from the
QSO J1409+5628, with a velocity integrated line luminosity of
K km s pc, while we obtain
3 upper limits to the HCN luminosity of the QSO J0751+2716 of
K km s pc, K km s pc for the starburst galaxy
J1401+0252, and K km s pc for the QSO J1148+5251. We compare the HCN data on these sources, plus three
other high- IR luminous galaxies, to observations of lower redshift
star-forming galaxies. The values of the HCN/far-IR luminosity ratios (or
limits) for all the high sources are within the scatter of the relationship
between HCN and far-IR emission for low star-forming galaxies (truncated).Comment: aastex format, 4 figures. to appear in the Astrophysical Journal;
Revised lens magnification estimate for 1401+025
Dense molecular gas in quasar host galaxies: a search for HCN emission from BR B1202-0725 at z=4.695
We report on the results of a search using the VLA for redshifted HCN(1-0)
emission from the host galaxy of BR B1202-0725, an optically luminous quasar at
z=4.695. The host galaxy emits strongly in the rest-frame far-infrared, and
shows characteristics very similar to that of more local, ultraluminous
infrared galaxies, in which a significant fraction of the far-infrared emission
is powered by star formation. We find a 3-sigma upper limit to the HCN(1-0)
emission of 4.9 x 10^10 K kms^-1 pc^2, assuming a lambda-cosmology. This limit
is consistent with correlations derived from measurements of the HCN, CO, and
far-infrared emission for a sample of more local galaxies, including starbursts
(Solomon et al, 1992a)
A Study of CO Emission in High Redshift QSOs Using the Owens Valley Millimeter Array
Searches for CO emission in high-redshift objects have traditionally suffered
from the accuracy of optically-derived redshifts due to lack of bandwidth in
correlators at radio observatories. This problem has motivated the creation of
the new COBRA continuum correlator, with 4 GHz available bandwidth, at the
Owens Valley Radio Observatory Millimeter Array. Presented here are the first
scientific results from COBRA. We report detections of redshifted CO(J=3-2)
emission in the QSOs SMM J04135+10277 and VCV J140955.5+562827, as well as a
probable detection in RX J0911.4+0551. At redshifts of z=2.846, z=2.585, and
z=2.796, we find integrated CO flux densities of 5.4 Jy km/s, 2.4 Jy km/s, and
2.9 Jy km/s for SMM J04135+10277, VCV J140955.5+562827, and RX J0911.4+0551,
respectively, over linewidths of Delta(V_{FWHM}) ~ 350 km/s. These
measurements, when corrected for gravitational lensing, correspond to molecular
gas masses of order M(H_2) ~ 10^{9.6-11.1} solar masses, and are consistent
with previous CO observations of high-redshift QSOs. We also report 3-sigma
upper limits on CO(3-2) emission in the QSO LBQS 0018-0220 of 1.3 Jy km/s. We
do not detect significant 3mm continuum emission from any of the QSOs, with the
exception of a tentative (3-sigma) detection in RX J0911.4+0551 of S_{3mm}=0.92
mJy/beam.Comment: 18 pages, 5 figures, 2 tables, accepted to ApJ. Changes made for
version 2: citations added, 2 objects added to Table 2 and Figure
The SCUBA Bright Quasar Survey (SBQS): 850micron observations of the z>4 sample
We present initial results of a new, systematic search for massive
star-formation in the host galaxies of the most luminous and probably most
massive z>=4 radio-quiet quasars (M(B) 10^13Lsun).
A total of 38 z>=4 radio-quiet quasars have been observed at the JCMT using
SCUBA at 850microns: 8 were detected (>3sigma) with S(850microns)>~ 10mJy
(submillimetre-loud). The new detections almost triple the number of optically
selected, submillimetre-loud z>~4 radio-quiet quasars known to date. We include
a detailed description of how our quasar sample is defined in terms of radio
and optical properties.
There is no strong evidence for trends in either detectability or 850microns
flux with absolute magnitude, M(B). We find that the weighted mean flux of the
undetected sources is 2.0 +/- 0.6mJy, consistent with an earlier estimate of
\~3mJy based on more sensitive observations of a sample z>~4 radio-quiet
quasars (McMahon et al., 1999). This corresponds to an inferred starformation
rate of \~1000Msun/yr, similar to Arp220. The typical starformation timescale
for the submillimetre-bright sources is ~1Gyr, 10 times longer than the typical
accretion-driven e-folding timescale of ~5x10^7 years. Our 850micron detection
of the z=4.4 quasar PSS J1048+4407 when analysed in conjunction with 1.2mm
single-dish and interferometric observations suggests that this source is
resolved on angular scales of 1-2" (6-12 kpc). In addition, we present a new
optical spectrum of this source, identifying it as a broad absorption line
(BAL) quasar. The new redshift is outside that covered in a recent CO line
search by Guilloteau et al., (1999), highlighting the need for accurate
redshifts for the obervation and interpretation of high-redshift line studies.Comment: 16 pages, 11 figures. Accepted by Monthly Notices of the Royal
Astronomical Societ
Herschel/SPIRE Sub-millimeter Spectra of Local Active Galaxies
We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven
nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer
(SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as
well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461
GHz line. We used radiative transfer models to analyze the observed CO spectral
line energy distributions (SLEDs). The FTS CO data were complemented with
ground-based observations of the low-J CO lines. We found that the warm
molecular gas traced by the mid-J CO transitions has similar physical
conditions (n_H2 ~ 10^3.2 - 10^3.9 cm^-3 and T_kin ~ 300 - 800 K) in most of
our galaxies. Furthermore, we found that this warm gas is likely producing the
mid-IR rotational H2 emission. We could not determine the specific heating
mechanism of the warm gas, however it is possibly related to the star-formation
activity in these galaxies. Our modeling of the [CI] emission suggests that it
is produced in cold (T_kin 10^3 cm^-3) molecular gas.
Transitions of other molecules are often detected in our SPIRE/FTS spectra. The
HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in
emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or
collisional excitation with electrons are plausible excitation mechanisms
likely related to the AGN of this galaxy. In some galaxies few H2O emission
lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are
identified in NGC7130.Comment: Accepted for publication in ApJ; 20 pages, 9 figure
The molecular gas in Luminous Infrared Galaxies II: extreme physical conditions, and their effects on the X_{co} factor
In this work we conclude the analysis of our CO line survey of Luminous
Infrared Galaxies (LIRGs: L_{IR}>=10^{11}L_{sol}) in the local Universe
(Paper\,I), by focusing on the influence of their average ISM properties on the
total molecular gas mass estimates via the so-called X_{co}=M(H_2)/L_{co,1-0}
factor. One-phase radiative transfer models of the global CO Spectral Line
Energy Distributions (SLEDs) yield an X_{co} distribution with:
\sim(0.6+/-0.2) M_{sol}(K km s^{-1} pc^2)^{-1} over a significant range
of average gas densities, temperatures and dynamical states. The latter emerges
as the most important parameter in determining X_{co}, with unbound states
yielding low values and self-gravitating states the highest ones. Nevertheless
in many (U)LIRGs where available higher-J CO lines (J=3--2, 4--3, and/or
J=6--5) or HCN line data from the literature allow a separate assessment of the
gas mass at high densities (>=10^{4} cm^{-3}) rather than a simple one-phase
analysis we find that {\it near-Galactic X_{co} (3-6)\,
M_sol\,(K\,km^{-1}\,pc^2)^{-1} values become possible.} We further show that in
the highly turbulent molecular gas in ULIRGs a high-density component will be
common and can be massive enough for its high X_{co} to dominate the average
value for the entire galaxy. .........
...this may have thus resulted to systematic underestimates of molecular gas
mass in ULIRGs.Comment: 77 pages, 6 figures, one Table, accepted for publication at The
Astrophysical Journa
A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine Teff,â=4734±67Kâ , Râ=0.726±0.007Rââ , and Mâ=0.748±0.032Mââ . We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 Râ, and a mass of Mb=13.5+1.7â1.8 Mâ, whilst TOI-1064 c has an orbital period of Pc=12.22657+0.00005â0.00004 d, a radius of Rc = 2.65 ± 0.04 Râ, and a 3Ï upper mass limit of 8.5 Mâ. From the high-precision photometry we obtain radius uncertainties of âŒ1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of massâradius space, and it allow us to identify a trend in bulk densityâstellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.Publisher PDFPeer reviewe
Two warm Neptunes transiting HIP 9618 revealed by TESS and Cheops
peer reviewedHIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of 3.9 ± 0.044 R (HIP 9618 b) and 3.343 ± 0.039 R (HIP 9618 c). While the 20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M for HIP 9618 b, which, according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of 50 d, opening the door for the atmospheric characterization of warm (Teq < 750 K) sub-Neptunes