- ID:
- ivo://CDS.VizieR/J/ApJ/833/248
- Title:
- Chemical properties of red MSX sources (RMSs)
- Short Name:
- J/ApJ/833/248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red Midcourse Space Experiment (MSX) Sources (RMSs) are regarded as excellent candidates of massive star-forming regions. In order to characterize the chemical properties of massive star formation, we made a systematic study of 87 RMSs in the southern sky, using archival data taken from the Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), the Australia Telescope Compact Array, and the Millimetre Astronomy Legacy Team Survey at 90GHz (MALT90). According to previous multiwavelength observations, our sample could be divided into two groups: massive young stellar objects and HII regions. Combined with the MALT90 data, we calculated the column densities of N_2_H^+^, C_2_H, HC_3_N, and HNC and found that they are not much different from previous studies made in other massive star-forming regions. However, their abundances are relatively low compared to infrared dark clouds (IRDCs). The abundances of N_2_H^+^ and HNC in our sample are at least 1mag lower than those found in IRDCs, indicating chemical depletions in the relatively hot gas. Besides, the fractional abundances of N_2_H^+^, C_2_H, and HC_3_N seem to decrease as a function of their Lyman continuum fluxes (N_L_), indicating that these molecules could be destroyed by UV photons when HII regions have formed inside. We also find that the C_2_H abundance decreases faster than HC_3_N with respect to N_L_. The abundance of HNC has a tight correlation with that of N_2_H^+^, indicating that it may be also preferentially formed in cold gas. We regard our RMSs as being in a relatively late evolutionary stage of massive star formation.
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- ID:
- ivo://CDS.VizieR/J/A+A/527/A88
- Title:
- Chemistry in infrared dark clouds
- Short Name:
- J/A+A/527/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars, the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, whether the molecular abundances in IRDCs are similar to the low-mass pre-stellar cores, or if they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93GHz using the 22-m Mopra radio telescope. In total, 13 molecular species comprising N_2_H^+^, ^13^CS, CH_3_CN, HC_3_N, HNC, HCO^+^, HCN, HNCO, C_2_H, SiO, H^13^CO^+^, H^13^CN, and CH_3_C_2_H were observed for all targets. Hence, we included in general species appropriate for elevated densities, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes.
- ID:
- ivo://CDS.VizieR/J/other/NatAs/5.684
- Title:
- CH3OH in the HD100546 disk
- Short Name:
- J/other/NatAs/5.
- Date:
- 17 Jan 2022 00:30:51
- Publisher:
- CDS
- Description:
- Quantifying the composition of the material in protoplanetary disks is paramount to determining the potential for exoplanetary systems to produce and support habitable environments. When considering potential habitability, complex organic molecules are of relevance, key among which is methanol (CH_3_OH). Methanol primarily forms at low temperatures via the hydrogenation of CO ice on the surface of icy dust grains and is a necessary basis for the formation of more complex species such as amino acids and proteins. We report the detection of CH_3_OH in a disk around a young, luminous A-type star, HD 100546. This disk is warm and therefore does not host an abundant reservoir of CO ice. We argue that the CH_3_OH cannot form in situ, and hence this disk has probably inherited complex-organic-molecule-rich ice from an earlier cold dark cloud phase. This is strong evidence that at least some interstellar organic material survives the disk formation process and can then be incorporated into forming planets, moons and comets. Therefore, crucial pre-biotic chemical evolution already takes place in dark star-forming clouds.
- ID:
- ivo://CDS.VizieR/J/ApJS/227/10
- Title:
- CH_3_OH & OH line emission from Galactic center
- Short Name:
- J/ApJS/227/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Class I methanol masers are collisionally pumped and are generally correlated with outflows in star-forming sites in the Galaxy. Using the Very Large Array in its A-array configuration, we present a spectral line survey to identify methanol J=4_-1_->3_0_E emission at 36.169GHz. Over 900 pointings were used to cover a region 66'x13' along the inner Galactic plane. A shallow survey of OH at 1612, 1665, 1667, and 1720MHz was also carried out over the area covered by our methanol survey. We provide a catalog of 2240 methanol masers with narrow line-widths of ~1km/s, spatial resolutions of ~0.14"x0.05", and rms noises ~20mJy/beam per channel. Lower limits on the brightness temperature range from 27000 to 10000000K, showing that the emission is of non-thermal origin. We also provide a list of 23 OH (1612), 14 OH (1665), 5 OH (1667), and 5 OH (1720MHz) masers. The origin of such a large number of methanol masers is not clear. Many methanol masers appear to be associated with infrared dark clouds, though it appears unlikely that the entire population of these masers traces the early phase of star formation in the Galactic center.
- ID:
- ivo://CDS.VizieR/J/ApJ/845/96
- Title:
- [CII] emission in the ISM of 20 nearby galaxies
- Short Name:
- J/ApJ/845/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The [CII]158{mu}m fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [CII] balances the heating, including that due to far- ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [CII] emission remains unclear because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [CII] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [NII]205{mu}m fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [CII]/[NII]122{mu}m. Using the FIR [CII] and [NII] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%-80% of [CII] emission originates from neutral gas. We find that the fraction of [CII] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [CII] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/105
- Title:
- [CII], [OI] and [OIII] line emission from z~6 gal.
- Short Name:
- J/ApJ/846/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of the almost 40 star-forming galaxies at z>~5 (not counting quasi-stellar objects) observed in [CII] to date, nearly half are either very faint in [CII] or not detected at all, and fall well below expectations based on locally derived relations between star formation rate and [CII] luminosity. This has raised questions as to how reliable [CII] is as a tracer of star formation activity at these epochs and how factors such as metallicity might affect the [CII] emission. Combining cosmological zoom simulations of galaxies with SIGAME (SImulator of GAlaxy Millimeter/submillimeter Emission), we modeled the multiphased interstellar medium (ISM) and its emission in [CII], as well as in [OI] and [OIII], from 30 main-sequence galaxies at z~6 with star formation rates ~3-23M_{sun}_/yr, stellar masses ~(0.7-8)x10^9^M_{sun}_, and metallicities ~(0.1-0.4)xZ_{sun}_. The simulations are able to reproduce the aforementioned [CII] faintness of some normal star-forming galaxy sources at z>=5. In terms of [OI] and [OIII], very few observations are available at z>~5, but our simulations match two of the three existing z>~5 detections of [OIII] and are furthermore roughly consistent with the [OI] and [OIII] luminosity relations with star formation rate observed for local starburst galaxies. We find that the [CII] emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ~66% and ~27%, respectively. The molecular gas, which constitutes only ~10% of the total gas mass, is thus a more efficient emitter of [CII] than the ionized gas, which makes up ~85% of the total gas mass. A principal component analysis shows that the [CII] luminosity correlates with the star formation activity of a galaxy as well as its average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their [CII] faintness, and we suggest that these factors may also be responsible for the [CII]-faint normal galaxies observed at these early epochs.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/65
- Title:
- CI radial velocities with HST/STIS
- Short Name:
- J/ApJ/734/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed absorption features arising from interstellar neutral carbon that appeared in the UV spectra of 89 stars recorded in the highest resolution echelle modes of the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope so that we could determine the relative populations of collisionally excited fine-structure levels in the atom's electronic ground state. From this information, in combination with molecular hydrogen rotation temperatures, we derive the distribution of thermal pressures in the diffuse, cold neutral medium (CNM). We find a lognormal pressure distribution (weighted by mass) with a mean in log(p/k) equal to 3.58 and an rms dispersion of at least 0.175dex that plausibly arises from turbulence with a characteristic Mach number in the range 1<M<4.
- ID:
- ivo://CDS.VizieR/J/ApJS/146/353
- Title:
- Circumnuclear dust in galaxies
- Short Name:
- J/ApJS/146/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps of 123 nearby galaxies that show the distribution of the cold ISM, as traced by dust, with excellent spatial resolution. These observations reveal that nuclear dust spirals are found in the majority of active and inactive galaxies and they possess a wide range in coherence, symmetry, and pitch angle. We have used this large sample to develop a classification system for circumnuclear dust structures.
- ID:
- ivo://CDS.VizieR/J/ApJS/112/557
- Title:
- Classification of IRAS Sources
- Short Name:
- J/ApJS/112/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAS low-resolution spectra were extracted for 11,224 IRAS sources. These spectra were classified into astrophysical classes, based on the presence of emission and absorption features and on the shape of the continuum. Counterparts of these IRAS sources in existing optical and infrared catalogs are identified, and their optical spectral types are listed if they are known. The correlations between the photospheric/ optical and circumstellar/infrared classifications are discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/830/127
- Title:
- CLASSy: CARMA obs. in L1451 region of Perseus
- Short Name:
- J/ApJ/830/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 3mm spectral line and continuum survey of L1451 in the Perseus Molecular Cloud. These observations are from the CARMA Large Area Star Formation Survey (CLASSy), which also imaged Barnard 1, NGC1333, Serpens Main, and Serpens South. L1451 is the survey region with the lowest level of star formation activity-it contains no confirmed protostars. HCO^+^, HCN, and N_2_H^+^ (J=1->0) are all detected throughout the region, with HCO^+^ being the most spatially widespread, and molecular emission seen toward 90% of the area above N(H_2_) column densities of 1.9x10^21^cm^-2^. HCO^+^ has the broadest velocity dispersion, near 0.3km/s on average, compared with ~0.15km/s for the other molecules, thus representing a range of subsonic to supersonic gas motions. Our non-binary dendrogram analysis reveals that the dense gas traced by each molecule has a similar hierarchical structure, and that gas surrounding the candidate first hydrostatic core (FHSC), L1451-mm, and other previously detected single-dish continuum clumps has similar hierarchical structure; this suggests that different subregions of L1451 are fragmenting on the pathway to forming young stars. We determined that the three-dimensional morphology of the largest detectable dense-gas structures was relatively ellipsoidal compared with other CLASSy regions, which appeared more flattened at the largest scales. A virial analysis shows that the most centrally condensed dust structures are likely unstable against collapse. Additionally, we identify a new spherical, centrally condensed N_2_H^+^ feature that could be a new FHSC candidate. The overall results suggest that L1451 is a young region starting to form its generation of stars within turbulent, hierarchical structures.
