- ID:
- ivo://CDS.VizieR/J/A+A/608/A133
- Title:
- Gas and dust in star-forming region rho OphA
- Short Name:
- J/A+A/608/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. rho Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H_2_, H_2_O, NH_3_, N_2_H^+^, O_2_, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H_2_O and NH_3_, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S1. At the interface to the molecular core 0.05pc away, atomic hydrogen is rapidly converted into H_2_, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O_2_ in the core SM1, where X(O_2_)~5x10^-8^. There, the ratio of the O_2_ to H_2_O abundance [X(H_2_O)~5x10^-9^] is significantly higher than unity. Away from the core, O_2_ experiences a dramatic decrease due to increasing H_2_O formation. Outside the molecular core, on the far side as seen from S1, the intense radiation from the 0.5pc distant early B-type star HD147889 destroys the molecules. Towards the dark core SM1, the observed abundance ratio X(O_2_)/X(H_2_O)>1, which suggests that this object is extremely young, which would explain why O_2_ is such an elusive molecule outside the solar system.
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- ID:
- ivo://CDS.VizieR/J/A+A/578/A131
- Title:
- Gas and dust in the star-forming region rho OphA
- Short Name:
- J/A+A/578/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N_2_H^+^, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N_2_H^+^(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class-1 sources to low values close to 0 for the disk-dominated emission in ClassIII objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C^18^O, also N_2_H^+^ is frozen onto the grains.
- ID:
- ivo://CDS.VizieR/J/A+A/408/873
- Title:
- Gas and stellar kinematics in spirals
- Short Name:
- J/A+A/408/873
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measured the ionized-gas and stellar kinematics along the major and minor axis of a sample of 10 early-type spirals. Much to our surprise we found a remarkable gas velocity gradient along the minor axis of 8 of them. According to the kinematic features observed in their ionized-gas velocity fields, we divide our sample galaxies in three classes of objects. (i) NGC 4984, NGC 7213, and NGC 7377 show an overall velocity curve along the minor axis without zero-velocity points, out to the last measured radius, which is interpreted as due to the warped structure of the gaseous disk. (ii) NGC 3885, NGC 4224, and NGC 4586 are characterized by a velocity gradient along both major and minor axis, although non-zero velocities along the minor axis are confined to the central regions. Such gas kinematics have been explained as being due to non-circular motions induced by a triaxial potential. (iii) NGC 2855 and NGC 7049 show a change of slope of the velocity gradient measured along the major axis (which is shallower in the center and steeper away from the nucleus), as well as non-zero gas velocities in the central regions of the minor axis. This has been attributed to the presence of a kinematically-decoupled gaseous component in orthogonal rotation with respect to the galaxy disk, namely an inner polar disk. The case and origin of inner polar disks are discussed and the list of their host galaxies is presented.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/398
- Title:
- Gas and stellar metallicities in HII galaxies
- Short Name:
- J/MNRAS/421/398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the gas and stellar metallicities in a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. We eliminated all spectra with an insufficient signal-to-noise ratio, without strong emission lines and without the [OII] {lambda}3727{AA} line, which is necessary for the determination of the gas metallicity. This excludes galaxies with redshift ~<0.033. Our final sample contains ~700 spectra of HII galaxies.
- ID:
- ivo://CDS.VizieR/J/AZh/71/189
- Title:
- Gas Kinematics from Halpha line in NGC 4151
- Short Name:
- J/AZh/71/189
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nucleus spectra of the Seyfert galaxy NGC 4151 obtained in 1988-1991 were analyzed in order to study the profile variability of the Ha line resulting from ionizing continuum flux variations. At the time of this galaxy monitoring, the response of the integral flux of the Ha line was almost linear and the average profile shape did not change by more than 5%.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/80
- Title:
- Gas phase oxygen abundances for HII regions
- Short Name:
- J/ApJ/887/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 HII regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) optical integral field spectroscopy as part of the PHANGS-MUSE survey. After removing the first-order radial gradients present in each galaxy, we look at the statistics of the metallicity offset ({Delta}O/H) and explore azimuthal variations. Across each galaxy, we find low ({sigma}=0.03-0.05dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those HII regions that are 1{sigma} outliers toward both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher H{alpha} luminosity, lower H{alpha} velocity dispersion, younger star clusters, and associated molecular gas clouds showing higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased H{alpha} velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but cannot always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the interstellar medium.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A34
- Title:
- GC hot UV-bright stars model spectra
- Short Name:
- J/A+A/627/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch (AGB) stars, and post-early AGB stars. There are indications that old stellar systems like globular clusters produce fewer post-(early) AGB stars than currently predicted by evolutionary models, but observations are still scarce. We wish to derive effective temperatures, surface gravities, and helium abundances of the luminous hot UV-bright stars in these clusters to determine their evolutionary status and compare the observed numbers to predictions from evolutionary theory. We obtained FORS2 spectroscopy of 11 of these UV-selected objects (covering a range of -2.3<[Fe/H]<-1.0), which we (re-)analysed together with previously observed data. We used model atmospheres of different metallicities, including super-solar ones. Where possible, we verified our atmospheric parameters using UV spectrophotometry and searched for metal lines in the optical spectra. We calculated evolutionary sequences for four metallicity regimes and used them together with information about the HB morphology of the globular clusters to estimate the expected numbers of post-AGB stars. We find that metal-rich model spectra are required to analyse stars hotter than 40000 K. Seven of the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars, two are evolving away from the HB, one is a foreground white dwarf, and another is a white dwarf merger. Taking into account published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low. Spectroscopy is clearly required to identify the evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model spectra are required to reproduce their optical and UV spectra, which may affect the flux contribution of hot post-AGB stars to the UV spectra of evolved populations. Adding published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/L14
- Title:
- Gemini/FLAMINGOS-2 NIR spectra of V1047 Cen
- Short Name:
- J/ApJ/886/L14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14yr separating the CN and DN eruptions of V1047 Cen is the shortest of all instances recorded thus far. Explaining this rapid succession of CN and DN outbursts in V1047 Cen may be challenging within the framework of standard theories for DN outbursts. Following a CN eruption, the mass accretion rate is believed to remain high (dM/dt~10^-8^M_{sun}_/yr) for a few centuries, due to the irradiation of the secondary star by the still-hot surface of the white dwarf. Thus a DN eruption is not expected to occur during this high mass accretion phase as DN outbursts, which result from thermal instabilities in the accretion disk, and arise during a regime of low mass accretion rate (dM/dt~10^-10^M_{sun}_/yr). Here we present near-infrared spectroscopy to show that the present outburst is most likely a DN eruption, and discuss the possible reasons for its early occurrence. Even if the present re-brightening is later shown to be due to a cause other than a DN outburst, the present study provides invaluable documentation of this unusual event.
- ID:
- ivo://CDS.VizieR/J/ApJ/894/111
- Title:
- Gemini/GMOS-S spectra of the type IIn SN 2010jl
- Short Name:
- J/ApJ/894/111
- Date:
- 19 Jan 2022 13:05:54
- Publisher:
- CDS
- Description:
- The luminous Type IIn SN 2010jl shows strong signs of interaction between the SN ejecta and dense circumstellar material. Dust may be present in the unshocked ejecta; the cool, dense shell (CDS) between the shocks in the interaction region; or in the circumstellar medium (CSM). We present and model new optical and infrared photometry and spectroscopy of SN 2010jl from 82 to 1367 days since explosion. We evaluate the photometric and spectroscopic evolution using the radiative transfer codes MOCASSIN and DAMOCLES, respectively. We propose an interaction scenario and investigate the resulting dust formation scenarios and dust masses. We find that SN 2010jl has been continuously forming dust based on the evolution of its infrared emission and optical spectra. There is evidence for preexisting dust in the CSM as well as new dust formation in the CDS and/or ejecta. We estimate that 0.005-0.01M_{sun}_ of predominantly carbon dust grains has formed in SN 2010jl by ~1400 days post-outburst.
- ID:
- ivo://CDS.VizieR/J/ApJ/873/35
- Title:
- Gemini GNIRS NIR spectroscopy of 50 QSOs at z>~5.7
- Short Name:
- J/ApJ/873/35
- Date:
- 19 Jan 2022 09:09:09
- Publisher:
- CDS
- Description:
- We report initial results from a large Gemini program to observe z>~5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with simultaneous ~0.85-2.5{mu}m spectra covering the rest-frame ultraviolet and major broad emission lines from Ly{alpha} to MgII. We present spectral measurements for these quasars and compare with their lower redshift counterparts at z=1.5-2.3. We find that when quasar luminosity is matched, there are no significant differences between the rest-UV spectra of z>~5.7 quasars and the low-z comparison sample. High-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average Eddington ratio of ~0.3. There is no evidence for super-Eddington accretion or hypermassive (>10^10^M_{sun}_) black holes within our sample. We find a mild excess of quasars with weak CIV lines relative to the control sample. Our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts.
