We present the observations of the starburst galaxy M82 taken with the Herschel SPIRE Fourier-transform spectrometer. The spectrum (194–671 μm) shows a prominent CO rotational ladder from J = 4–3 to ...13–12 emitted by the central region of M82. The fundamental properties of the gas are well constrained by the high J lines observed for the first time. Radiative transfer modeling of these high-S/N 12CO and 13CO lines strongly indicates a very warm molecular gas component at ~500 K and pressure of ~3×106 K cm-3, in good agreement with the H2 rotational lines measurements from Spitzer and ISO. We suggest that this warm gas is heated by dissipation of turbulence in the interstellar medium (ISM) rather than X-rays or UV flux from the straburst. This paper illustrates the promise of the SPIRE FTS for the study of the ISM of nearby galaxies.
Submillimetre observations of z > 6 quasars Robson, Ian; Priddey, Robert S.; Isaak, Kate G. ...
Monthly notices of the Royal Astronomical Society,
06/2004, Letnik:
351, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report on submillimetre (submm) observations of three high-redshift quasars (z > 6) made using the SCUBA camera on the James Clerk Maxwell Telescope (JCMT). Only one of the sample was detected ...(>10σ significance) at 850 μm – SDSS J1148+5251 (z= 6.43). It was also detected at 450 μm (>3σ significance), one of the few quasars at z > 4 for which this has been the case. In combination with existing millimetric data, the 850- and 450-μm detections allow us to place limits on the temperature of the submm-emitting dust. The dust temperature is of no trivial importance given the high redshift of the source, since a cold temperature would signify a large mass of dust to be synthesized in the little time available (as an extreme upper limit in only 0.9 Gyr since z=∞). We find, however, that the combined millimetre and submm data for the source cannot simply be characterized using the single-temperature greybody fit that has been used at lower redshifts. We discuss the results of the observing and modelling, and speculate as to the origin of the deviations.
We present results of the first systematic search for submillimetre (submm) continuum emission from z∼ 2, radio-quiet, optically-luminous (MB < −27.5) quasars, using the SCUBA array camera on the ...James Clerk Maxwell Telescope (JCMT). We have observed a homogeneous sample of 57 quasars in the redshift range 1.5 < z < 3.0— the epoch during which the comoving density of luminous active galactic nuclei (AGN) peaks — to make a systematic comparison with an equivalent sample at high redshift (z > 4; Paper I). The target sensitivity of the survey, 3σ = 10 mJy at 850 μm, was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. Nine targets are detected with 3σ significance or greater, with fluxes in the range 7–17 mJy. Although the detection rate above 10 mJy is lower than that of the z > 4 survey, the weighted mean flux of the undetected sources, 1.9 ± 0.4 mJy, is similar to that at z > 4 (2.0 ± 0.6 mJy). The statistical significance of trends is analysed, and it is found that: (i) within the limited optical luminosity range studied, there is no strong evidence for a correlation between submm and optical luminosity; (ii) there is a suggestion of a variation of submm detectability with redshift, but that this is consistent with the K-correction of a characteristic far-infrared spectrum.
(Ultra) luminous infrared galaxies ((U)LIRGs) are objects characterized by their extreme infrared (8-1000 mu m) luminosities (L sub(LIRG) > 10 super(11) L sub(middot in circle) and L sub(ULIRG) > 10 ...super(12)L sub(middot in circle)). The Herschel Comprehensive ULIRG Emission Survey (PI: van der Werf) presents a representative flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of these objects (10 super(11)L sub(middo t in circle) < or =, slant L sub(IR) < or =, slant 10 super(13) L sub(middot in circle)). With the Herschel Space Observatory, we observe CII 157 mu m, OI 63 mu m, and OI 145 mu m line emission with Photodetector Array Camera and Spectrometer, CO J = 4-3 through J = 13-12, CI 370 mu m, and CI 609 mu m with SPIRE, and low-J CO transitions with ground-based telescopes. The CO ladders of the sample are separated into three classes based on their excitation level. In 13 of the galaxies, the OI 63 mu m emission line is self absorbed. Comparing the CO excitation to the InfraRed Astronomical Satellite 60/100 mu m ratio and to far infrared luminosity, we find that the CO excitation is more correlated to the far infrared colors. We present cooling budgets for the galaxies and find fine-structure line flux deficits in the CII, SiII, OI, and CI lines in the objects with the highest far IR fluxes, but do not observe this for CO 4 < or =, slant J sub(upp) < or =, slant 13. In order to study the heating of the molecular gas, we present a combination of three diagnostic quantities to help determine the dominant heating source. Using the CO excitation, the CO J = 1-0 linewidth, and the active galactic nucleus (AGN) contribution, we conclude that galaxies with large CO linewidths always have high-excitation CO ladders, and often low AGN contributions, suggesting that mechanical heating is important.
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes ...to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M 99 and M 100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.
We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC 6822 observed from 70 to 500 μm and clearly resolve the H ii regions with PACS and SPIRE. We find that the ratio ...250/500 is dependent on the 24 μm surface brightness in NGC 6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions H ii regions and less active regions across the galaxy and find that the SEDs of H ii regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used. The global G/D of NGC 6822 is finally estimated to be 186, using amorphous carbon.
We present a search for HCN emission from four high-redshift far-IR-luminous galaxies. Current data and models suggest that these high-z 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 (AGNs), 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 super(H2) similar to 10 super(5) cm super(-3)). 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 z = 2.5832 QSO J1409+5628, with a velocity-integrated line luminosity of L' sub(HCN) = (6.7 plus or minus 2.2) x 10 super(9) K km s super(-1) pc super(2), while we obtain 3 sigma upper limits to the HCN luminosity of the z = 3.200 QSO J0751+2716 of L' sub(HCN) = 1.0 x 10 super(9) K km s super(-1) pc super(2), L' sub(HCN) = 1.6 x 10 super(9) K km s super(-1) pc super(2) for the z = 2.565 starburst galaxy J1401+0252, and L' sub(HCN) = 1.0 x 10 super(10) K km s super(-1) pc super(2) for the z = 6.42 QSO J1148+5251. We compare the HCN data on these sources, plus three other high-z 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-z sources are within the scatter of the relationship between HCN and far-IR emission for low-z star-forming galaxies. These observations are consistent with dust heating by a massive starburst in these systems, with two important caveats. First, about half the measurements are strictly upper limits to the HCN luminosities. Second, the IR spectral energy distributions for most of the high-z sources are well constrained only on the Rayleigh-Jeans side of the thermal dust peak. We also present a spatially resolved 42 GHz continuum image of the gravitational lens J0751+2716.
We present Herschel-SPIRE observations at 250–500 μm of the giant elliptical galaxy M 86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. ...The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10 kpc to the south-east. We estimate that ~106 $M_\odot$ of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with M 86. The gas-to-dust ratio of the cold gas component ranges from ~20–80. We discuss the different heating mechanisms for the dust features.
Context.
A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. ...Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects.
Aims.
We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates.
Methods.
We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements.
Results.
We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2
σ
. The planet TOI-5678 b has a mass of 20 ± 4 Earth masses (
M
⊕
) and a radius of 4.91 ± 0.08
R
⊕
Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2
±1.7
−1.3
M
⊕
.
Conclusions.
TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11
S
⊕
). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.
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