In an attempt to understand the findings presented in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), we followed their data analysis methodology, omitting the hot and ...cold‐load calibrations that are an important part of the standard SOFIA GREAT instrument calibration procedure. This process requires scaling of the Venus off‐source spectra by an arbitrary factor, which in turn introduces residuals of the intrinsic receiver bandpass shape as spurious components in the resulting line/continuum spectra. Although these additional artifacts can be reduced via Fourier‐domain spectral filtering, their removal depends on an ill‐constrained interpolation of the Venus continuum across the PH3 spectral line positions, resulting in an unreliable final spectrum. We therefore conclude that the PH3 lines claimed to be detected in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) originate from data/analysis artifacts, and confirm our original result that there is no evidence for phosphine in the SOFIA Venus data.
Plain Language Summary
We performed observations using a unique, flying telescope—the Stratospheric Observatory for Infrared Astronomy (SOFIA)—to search for a gas called phosphine in the atmosphere of Venus, which has been suggested to be an indicator for life. The observations, published by Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055), were analyzed carefully but showed no evidence of phosphine. Our findings were called into question in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), who claimed to find phosphine lines in the SOFIA observations after following an unconventional data analysis method. We have investigated their method, and conclude that it is likely to introduce spurious signals into the data, so the claimed phosphine detection is therefore not significant.
Key Points
The revised calibration procedure adopted by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) introduces additional receiver artifacts into the SOFIA 4G2 Venus spectra
The claimed PH3 detection is likely a result of this, combined with interpolation artifacts that occur during subsequent Fourier filtering
We confirm our original conclusion that there is no evidence for phosphine in the SOFIA GREAT Venus data
The unbearable opaqueness of Arp220 Martín, S.; Aalto, S.; Sakamoto, K. ...
Astronomy and astrophysics (Berlin),
06/2016, Letnik:
590
Journal Article
Recenzirano
Odprti dostop
Context. The origin of the enormous luminosities of the two opaque nuclei of Arp 220, the prototypical ultra-luminous infrared galaxy, remains a mystery because we lack observational tools to explore ...the innermost regions around the nuclei. Aims. We explore the potential of imaging vibrationally excited molecular emission at high angular resolution to better understand the morphology and physical structure of the dense gas in Arp 220 and to gain insight into the nature of the nuclear powering sources. Methods. The Atacama Large Millimeter/submillimeter Array (ALMA) provided simultaneous observations of HCN, HCO+, and vibrationally excited HCN v2 = 1f emission. Their J = 4–3 and 3–2 transitions were observed at a matching resolution of ~0.5′′, which allows us to isolate the emission from the two nuclei. Results. The HCN and HCO+ lines within the ground-vibrational state poorly describe the central ~100 pc region around the nuclei because there are strong effects of cool absorbing gas in the foreground and severe line blending that is due to the prolific molecular emission of Arp 220. Vibrationally excited emission of HCN is detected in both nuclei with a very high ratio relative to the total LFIR, higher than in any other observed galaxy and well above what is observed in Galactic hot cores. HCN v2 = 1f is observed to be marginally resolved in ~60 × 50 pc regions inside the dusty ~100 pc sized nuclear cores. Its emission is centered on our derived individual nuclear velocities based on HCO+ emission (VWN = 5342 ± 4 and VEN = 5454 ± 8 km s-1, for the western and eastern nucleus, respectively). With virial masses within r ~ 25–30 pc based on the HCN v2 = 1f line widths, we estimate gas surface densities (gas fraction fg = 0.1) of 3 ± 0.3 × 104 M⊙ pc-2 (WN) and 1.1 ± 0.1 × 104 M⊙ pc-2 (EN). The 4−3/3−2 flux density ratio could be consistent with optically thick emission, which would further constrain the size of the emitting region to >15 pc (EN) and >22 pc (WN). The absorption systems that may hide up to 70% of the HCN and HCO+ emission are found at velocities of −50 km s-1 (EN) and 6, −140, and −575 km s-1 (WN) relative to velocities of the nuclei. Blueshifted absorptions are the evidence of outflowing motions from both nuclei. Conclusions. Although vibrationally excited molecular transitions could also be affected by opacity, they may be our best tool to peer into the central few tens of parsecs around compact obscured nuclei like those of Arp 220. The bright vibrational emission implies the existence of a hot dust region radiatively pumping these transitions. We find evidence of a strong temperature gradient that would be responsible for both the HCN v2 pumping and the absorbed profiles from the vibrational ground state as a result of both continuum and self-absorption by cooler foreground gas.
Aims. We study the feedback of star formation and nuclear activity on the chemistry of molecular gas in NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy, by analyzing whether the abundances of ...key molecular species such as ethynyl (C2H), which is a classical tracer of photon dominated regions (PDR), change in the different environments of the disk of the galaxy. Methods. We used the Atacama Large Millimeter Array (ALMA) to map the emission of the hyperfine multiplet of C2H(N = 1−0) and its underlying continuum emission in the central r ≃ 35″ (2.5 kpc) region of the disk of NGC 1068 with a spatial resolution 1.̋0 × 0.̋7 (≃ 50−70 pc). We used maps of the dust continuum emission obtained at 349 GHz by ALMA to derive the H2 gas column densities and combined these with the C2H map at matched spatial resolution to estimate the fractional abundance of this species. We developed a set of time-dependent chemical models, which include shocks, gas-phase PDRs, and gas-grain chemical models to determine the origin of the C2H gas. Results. A sizeable fraction of the total C2H line emission is detected from the r ≃ 1.3 kpc starburst (SB) ring, which is a region that concentrates the bulk of the recent massive star formation in the disk traced by the Paα emission complexes imaged by the Hubble Space Telescope (HST). However, the brightest C2H emission originates from a r ≃ 200 pc off-centered circumnuclear disk (CND), where evidence of a molecular outflow has been previously found in other molecular tracers imaged by ALMA. We also detect significant emission that connects the CND with the outer disk in a region that probes the interface between the molecular disk and ionized gas outflow out to r ≃ 400 pc. We derived the fractional abundances of C2H (X(C2H)) assuming local thermodynamic equilibrium (LTE) conditions and a set of excitation temperatures (Tex) constrained by the previous multiline CO studies of the galaxy. Our estimates range from X(C2H) ≃ a few 10-8 in the SB ring up to X(C2H) ≃ a few 10-7 in the outflow region. The PDR models that incorporate gas-grain chemistry are able to account for X(C2H) in the SB ring for moderately dense (n(H2) ≥ 104 cm-3) and moderately UV-irradiated gas (UV-field ≤ 10 × Draine field, where 1 Draine field ≡ 2.74 × 10-3 erg s-1 cm-2) in a steady-state regime, which depending on the initial and physical conditions of the gas may be achieved by 105 yr or as late as 107 yr. However, the high fractional abundances estimated for C2H in the outflow region can only be reached at very early times (T ≤ 102−3 yr) in models of UV or X-ray irradiated dense gas (n(H2) ≥ 104−5 cm-3). Conclusions. We find that the transient conditions required to fit the high values of X(C2H) in the outflow are likely due to UV or X-ray irradiated non-dissociative shocks associated with the highly turbulent interface between the outflow and molecular gas in NGC 1068. Although the inferred local timescales are short, the erosion of molecular clouds by the active galactic nucleus (AGN) wind and/or the jet likely resupplies the interface working surface continuously, making a nearly steady state persist in the disk of the galaxy.
Context.
In the nearby (
D
= 14 Mpc) AGN-starburst composite galaxy NGC 1068, it has been found that the molecular gas in the circumnuclear disk (CND) is outflowing, which is a manifestation of ...ongoing AGN feedback. The outflowing gas has a large spread of velocities, which likely drive different shock chemistry signatures at different locations in the CND.
Aims.
We performed a multiline molecular study using two shock tracers, SiO and HNCO, with the aim of determining the gas properties traced by these two species, and we explore the possibility of reconstructing the shock history in the CND.
Methods.
Five SiO transitions and three HNCO transitions were imaged at high resolution 0.″5 − 0.″8 with the Atacama Large Millimeter/submillimeter Array (ALMA). We performed both LTE and non-LTE radiative transfer analysis coupled with Bayesian inference process in order to characterize the gas properties, such as the molecular gas density and gas temperature.
Results.
We found clear evidence of chemical differentiation between SiO and HNCO, with the SiO/HNCO ratio ranging from greater than one on the east of CND to lower than 1 on the west side. The non-LTE radiative transfer analysis coupled with Bayesian inference confirms that the gas traced by SiO has different densities – and possibly temperatures – than that traced by HNCO. We find that SiO traces gas affected by fast shocks while the gas traced by HNCO is either affected by slow shocks or not shocked at all.
Conclusions.
A distinct differentiation between SiO and HNCO has been revealed in our observations and our further analysis of the gas properties traced by both species confirms the results of previous chemical modelings.
We present a line survey of the ultraluminous infrared galaxy Arp 220, taken with the newly installed SEPIA (Swedish-European Southern Observatory PI receiver for APEX) Band 5 instrument on APEX ...(Atacama Pathfinder Experiment). We illustrate the capacity of SEPIA to detect the 183.3 GHz H2O 31,3–22,0 line against the atmospheric H2O absorption feature. We confirm the previous detection of the HCN(2–1) line, and detect new transitions of standard dense gas tracers such as HNC(2–1), HCO+(2–1), CS(4–3), C34S(4–3) and HC3N(20–19). We also detect HCN(2–1) v
2 = 1 and the 193.5 GHz methanol (4–3) group for the first time. The absence of time variations in the megamaser water line compared to previous observations seems to rule out an AGN nuclear origin for the line. It could, on the contrary, favour a thermal origin instead, but also possibly be a sign that the megamaser emission is associated with star-forming cores washed out in the beam. We finally discuss how the new transitions of HCN, HNC and HCO+ refine our knowledge of the interstellar medium physical conditions in Arp 220.
Context. The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory for exploring the molecular chemistry in the surroundings of an active galactic nucleus (AGN). Aims. Exploring the distribution ...of different molecular species allows us to understand the physical processes affecting the interstellar medium both in the AGN vicinity and in the outer star forming molecular ring. Methods. We carried out 3 mm ALMA observations that include seven different molecular species, namely HCN, HCO+, CCH, CS, HNCO, SiO, HC3N, and SO, as well as the 13C isotopologues of the first two. Spectra were extracted from selected positions and all species were imaged over the central 2 kpc (~30′′) of the galaxy at a resolution of ~2.2′′ × 1.5′′ (150 pc × 100 pc). Results. HCO+ and CS appear to be slightly enhanced in the star forming ring. CCH shows the largest variations across NGC 1097 and is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO, and HC3N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Conclusions. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO+ and HCN/CS differences observed between AGN-dominated and starburst (SB) galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally, we claim that lower HCN/CS is a combination of a small underabundance of CS in AGNs, together with excitation effects, where a high density gas component (~106 cm-3) may be more prominent in SB galaxies. However, the most promising are the differences found among the dense gas tracers that, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well-shielded gas in the disk, surrounding the dense material moderately exposed to the X-ray radiation traced by HC3N. Finally SiO might be the innermost molecule in the disk structure.
The presence of phosphine (PH3) in the atmosphere of Venus was reported by Greaves et al. based on observations of the J = 1–0 transition at 267 GHz using ground-based, millimeter-wave spectroscopy. ...This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of atmospheric phosphorous-bearing gases. Here we present results from a search for PH3 on Venus using the German REceiver for Astronomy at Terahertz Frequencies instrument aboard the Stratospheric Observatory for Infrared Astronomy aircraft, over three flights conducted in November 2021. Multiple PH3 transitions were targeted at frequencies centered on 533 and 1,067 GHz, but no evidence for atmospheric PH3 was detected. Through radiative transfer modeling, we derived a disk-averaged upper limit on the PH3 abundance of 0.8 ppb in the altitude range 75–110 km, which is more stringent than previous ground-based studies.
Context. Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission ...from vibrationally excited HCN (HCN-vib), which is thought to trace warm and highly enshrouded galaxy nuclei. It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. Aims. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (ultra)luminous infrared galaxies ((U)LIRGs). Methods. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 μm OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. Results. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission have fast and collimated outflows that can be seen in spectral lines at longer wavelengths, including in millimeter emission lines of CO and HCN (in its vibrational ground state) and in radio absorption lines of OH. Conclusions. We conclude that the galaxy nuclei with the highest LHCN − vib/LIR do not drive wide-angle outflows that are detectable using the median velocities of far-infrared OH absorption lines. This is possibly because of an orientation effect in which sources oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed.
Context.
Phosphorus (P) is a crucial element for life given its central role in several biomolecules. P-bearing molecules have been discovered in different regions of the Milky Way, but not yet ...towards an extragalactic environment.
Aims.
We searched for P-bearing molecules outside the Milky Way towards the nearby starburst Galaxy NGC 253.
Methods.
Using observations from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) project, we used the MAdrid Data CUBe Analysis package to model the emission of P-bearing molecules assuming local thermodynamic equilibrium (LTE) conditions. We also performed a non-LTE analysis using SpectralRadex.
Results.
We report the detection of a P-bearing molecule, phosphorus nitride (PN), for the first time in an extragalactic environment, towards two giant molecular clouds (GMCs) of NGC 253. The LTE analysis yields total PN beam-averaged column densities
N
= (1.20 ± 0.09) × 10
13
cm
−2
and
N
= (6.5 ± 1.6) × 10
12
cm
−2
, which translate into abundances with respect to H
2
of
χ
= (8.0 ± 1.0) × 10
−12
and
χ
= (4.4 ± 1.2) × 10
−12
. We derived a low excitation temperature of
T
ex
= (4.4 ± 1.3) K towards the GMC with the brightest PN emission, which indicates that PN is sub-thermally excited. The non-LTE analysis results in column densities consistent with the LTE values. We also searched for other P-bearing molecules (PO, PH
3
, CP, and CCP), and upper limits were derived. The derived PO/PN ratios are < 1.3 and < 1.7. The abundance ratio between PN and the shock-tracer SiO derived towards NGC 253 follows the same trend previously found towards Galactic sources.
Conclusions.
Comparison of the observations with chemical models indicates that the derived molecular abundances of PN in NGC 253 can be explained by shock-driven chemistry followed by cosmic-ray-driven photochemistry.
Aiming to characterise the properties of the molecular gas in the ultra-luminous infrared galaxy Mrk 273 and its outflow, we used the NOEMA interferometer to image the dense-gas molecular tracers ...HCN, HCO+, HNC, HOC+ and HC3N at ∼86 GHz and ∼256 GHz with angular resolutions of 4ʺ̣9 × 4ʺ̣5 (∼3.7 × 3.4 kpc) and 0ʺ̣61 × 0ʺ̣55 (∼460 × 420 pc). We also modelled the flux of several H2O lines observed with Herschel using a radiative transfer code that includes excitation by collisions and far-infrared photons. The disc of the Mrk 273 north nucleus has two components with decoupled kinematics. The gas in the outer parts (R ∼ 1.5 kpc) rotates with a south-east to north-west direction, while in the inner disc (R ∼ 300 pc) follows a north-east to south-west rotation. The central 300 pc, which hosts a compact starburst region, is filled with dense and warm gas, and contains a dynamical mass of (4 −5) × 109 M⊙, a luminosity of L′HCN = (3–4) × 108 K km s−1 pc2, and a dust temperature of 55 K. At the very centre, a compact core with R ∼ 50 pc has a luminosity of LIR = 4 × 1011 L⊙ (30% of the total infrared luminosity), and a dust temperature of 95 K. The core is expanding at low velocities ∼50–100 km s−1, probably affected by the outflowing gas. We detect the blue-shifted component of the outflow, while the red-shifted counterpart remains undetected in our data. Its cold and dense phase reaches fast velocities up to ∼1000 km s−1, while the warm outflowing gas has more moderate maximum velocities of ∼600 km s−1. The outflow is compact, being detected as far as 460 pc from the centre in the northern direction, and has a mass of dense gas ≤8 × 108 M⊙. The difference between the position angles of the inner disc (∼70°) and the outflow (∼10°) indicates that the outflow is likely powered by the AGN, and not by the starburst. Regarding the chemistry in Mrk 273, we measure an extremely low HCO+/HOC+ ratio of 10 ± 5 in the inner disc of Mrk 273.
PDF
