About the nature of Mercer 14

view Abstract Citations (99) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular and Atomic Hydrogen Line Emission from Star-forming Galaxies Puxley, P. J. ; Hawarden, T. G. ; Mountain, C. M. Abstract Models of the generation of molecular and atomic hydrogen line emission from star-forming regions are discussed. These take into account the variations in the efficiency with which fluorescent H_2_ emission is produced as the ratio of the incident soft UV to the gas density changes (the lower this ratio, the higher the efficiency). The models deal with hot stars embedded within molecular clouds, large compact clusters of young stars generating intense UV fields, and emission from clouds bathed in a relatively diffuse UV field. The results from the models are compared with the ratio of the observed intensities of the H_2_ v = 1-0 S(1) and Brγ lines from the nuclear regions for a sample of 29 galaxies whose optical spectra are dominated by H II regions. Unlike previous investigators, we find that the scatter in the ratio of the two lines is quite small, suggesting a common mechanism for the H_2_ excitation. The line ratios are found to be consistent with H_2_ emission from photodissociation zones and in most of the sample can be understood in terms of ensembles of hot stars intimately mixed with molecular clouds, and perhaps forming blisters at their surface, although a few galaxies require much higher ratios of the UV intensity to the gas density, conditions which imply the presence of large numbers of massive stars in compact clusters. Publication: The Astrophysical Journal Pub Date: November 1990 DOI: 10.1086/169386 Bibcode: 1990ApJ...364...77P Keywords: Atomic Spectra; Emission Spectra; Hydrogen; Molecular Spectra; Star Formation; Starburst Galaxies; Astronomical Models; Star Clusters; Stellar Mass; Ultraviolet Radiation; Astrophysics; GALAXIES: INTERSTELLAR MATTER; INTERSTELLAR: MOLECULES; RADIATION MECHANISMS; STARS: FORMATION full text sources ADS | data products NED (29) SIMBAD (28) Related Materials (1) Erratum: 1991ApJ...372..733P

Context. Understanding the physical conditions of circumstellar material around young stars is crucial to star and planet formation studies. In particular, very low-mass stars (M★ < 0.2 M⊙) are interesting sources to characterize as they are known to host a diverse population of rocky planets. Molecular and atomic hydrogen lines can probe the properties of the circumstellar gas. Aims. This work aims to measure the mass accretion rate, the accretion luminosity, and more generally the physical conditions of the warm emitting gas in the inner disk of the very low-mass star 2MASS-J16053215-1933159. We investigate the source mid-infrared spectrum for atomic and molecular hydrogen line emission. Methods. We present the full James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) spectrum of the protoplanetary disk around the very low-mass star 2MASS-J16053215-1933159 from the MINDS GTO program, previously shown to be abundant in hydrocarbon molecules. We analyzed the atomic and molecular hydrogen lines in this source by fitting one or multiple Gaussian profiles. We then built a rotational diagram for the H2 lines to constrain the rotational temperature and column density of the gas. Finally, we compared the observed atomic line fluxes to predictions from two standard emission models. Results. We identify five molecular hydrogen pure rotational lines and 16 atomic hydrogen recombination lines in the 5–20 µm spectral range. The spectrum indicates optically thin emission for both species. We use the molecular hydrogen lines to constrain the mass and temperature of the warm emitting gas. We derive a total gas mass of only 2.3 × 10−5 MJup and a temperature of 635 K for the warm H2 gas component located in the very inner disk (r < 0.033 au), which only accounts for a small fraction of the upper limit for the disk mass from continuum observations (0.2 MJup). The HI (7−6) recombination line is used to measure the mass accretion rate (4.0 × 10−10 M⊙ yr−1) and luminosity (3.1 × 10−3 L⊙) onto the central source. This line falls close to the HI (11−8) line, however at the spectral resolution of JWST MIRI we managed to measure both separately. Previous studies based on Spitzer have measured the combined flux of both lines to measure accretion rates. HI recombination lines can also be used to derive the physical properties of the gas using atomic recombination models. The model predictions of the atomic line relative intensities constrain the atomic hydrogen density to about 109−1010 cm−3 and temperatures up to 5000 K. Conclusions. The JWST-MIRI MRS observations for the very low-mass star 2MASS-J16053215-1933159 reveal a large number of emission lines, many originating from atomic and molecular hydrogen because we are able to look into the disk warm molecular layer. Their analysis constrains the physical properties of the emitting gas and showcases the potential of JWST to deepen our understanding of the physical and chemical structure of protoplanetary disks.

The Single Aperture Far-InfraRed (SAFIR) Observatory’s science goals are driven by the fact that the earliest stages of almost all phenomena in the universe are shrouded in absorption by and emission from cool dust and gas that emits strongly in the far-infrared (40μ–200μ) and submillimeter (200μ–1 mm). In the very early universe, the warm gas of newly collapsing, unenriched galaxies will be revealed by molecular hydrogen emission lines at these long wavelengths. High redshift quasars are found to have substantial reservoirs of cool gas and dust, indicative of substantial metal enrichment early in the history of the universe. As a result, even early stages of galaxy formation will show powerful far-infrared emission. The combination of strong dust emission and large redshift (1 < z < 7) of these galaxies means that they can only be studied in the far-infrared and submillimeter. For nearby galaxies, many of the most active galaxies in the universe appear to be those whose gaseous disks are interacting in violent collisions. The details of these galaxies, including the effect of the central black holes that probably exist in most of them, are obscured to shorter wavelength optical and ultraviolet observatories by the large amounts of dust in their interstellar media. Within our own galaxy, the earliest stages of star formation, when gas and dust clouds are collapsing and the beginnings of a central star are taking shape, can only be observed in the far-infrared and submillimeter. The cold dust that ultimately forms the planetary systems, as well as the cool “debris” dust clouds that indicate the likelihood of planetary sized bodies around more developed stars, can only be observed at wavelengths longward of 20μ.

: We report on 2 micrometers spectroscopy of three Seyfert and two star burst galactic nuclei. We have detected line emission from vibrationally excited H2 in the Seyfert galactic nuclei NGC 1275, NGC 3227, and NGC 4151. For NGC 1275 and NGC 4151, these detections are the first reported detections of molecular line emission. We have also measured the Br(gamma) line flux in NGC 4151 and obtained an upper limit on the Br(gamma) line flux in NGC 1275. There is large range in the observed S(1) to Br(gamma) line ratio for both Seyfert and starburst galaxies (measured in this work and by others). We rule out UV fluorescence based on the S(1) to Br(gamma) line ration and the H2 line ratios in the Seyfert galaxy NGC 1275. Shocks probably excite the H2 emission in this galaxy. UV fluorescence may be the excitation mechanism in the Seyfert 1 galaxies NGC 4151 and NGC 3227. The H2 lines are not formed in the broad-line regions these Seyfert 1 galaxies based on our measured upper limits on the S(1) line widths. Simple starburst models cannot account for the highest of the measured ratios of S(1) to Br(gamma) line flux, most notably in the starburst galaxy NGC 6240 and in the peculiar Seyfert NGC 1275. Since the galaxies with the largest values of this ratio also have strong morphological evidence of galaxy-galaxy interactions, global shocks rather than shocks within young stellar outflows and remnants may be responsible for the excitation of the molecular hydrogen in these galaxies.

The newly commissioned University of New South Wales Infrared Fabry–Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 μm in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1–0)/(2–1) S(1) ratio, suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1–0 S(1) intensities also tend to show the highest (1–0)/(2–1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H2. An isolated knot of emission discovered just outside P 18, and having both an unusually high (1–0)/(2–1) S(1) ratio and relative velocity, provides additional evidence for an outflow source associated with P 18.

The newly-commissioned University of New South Wales Infrared Fabry-Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 microns in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1-0)/(2-1) S(1) ratio suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes, and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1-0 S(1) intensities also tend to show the highest (1-0)/(2-1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H_2. An isolated knot of emission discovered just outside P 18, and having both an unusually high (1-0)/(2-1) S(1) ratio and relative velocity provides additional evidence for an outflow source associated with P 18.

We report detection of a Young Stellar Object with an evidence for an outflow in the form of knots in the molecular hydrogen emission line (2.121 micron) towards the massive star forming region IRAS 06061+2151. Near-infrared images reveal IRAS 06061+2151 to be a cluster of at least five sources, four of which seem to be early B type young stellar objects, in a region of 12 arcsec surrounded by a nebulosity. The presence of the knots that are probably similar to the HH objects in the optical wavelengths, suggests emerging jets from one of the cluster members. These jets appear to excite a pair of knot-like objects (Knot-NW and Knot-SE) and extend over a projected size of 0.5pc. The driving source for the jets is traced back to a member of the cluster whose position in the H-Ks/J-H color-color diagram indicates that it is a Class 1 type pre-mainsequence star. We also obtained K band spectra of the brightest source in the cluster and of the nearby nebular matter. The spectra show molecular hydrogen emission lines but do not show Brackett gamma line at 2.167 micron. These spectra suggest that the excitation of the molecular hydrogen lines is probably due to a mild shock.

The S140/L1204 cloud contains a deeply embedded region of star formation and a powerful molecular outflow. In this paper, we present images of the S140 region obtained in the light of the 2.12 m molecular hydrogen emission line and adjacent continuum. Our images reveal several knots of H2 line emission originating from shocked material close to IRS 1 as well as further out. Strong H2 shock emission is found north-east of IRS1 (at position angle of20{30), as well as to the south-west of IRS1 (at position angles around 190{ 220), clearly demonstrating the presence of outflow activity in the north-east/south-west direction. We also nd patches of H2 emission several arcminutes away from IRS1 at a position angles of 150 and 340, i.e. in directions consistent with the previously known north-west/south-east molecular outflow. Our results therefore provide evidence for the existence of two distinct bipolar outflow systems originating simultaneously from IRS 1. We also discuss general aspects of the star formation process in the S140 region. An inferred high ratio of stellar to gas mass suggests that the outflows have dispersed most of the cloud mass.

"Green fuzzies" or "extended green objects" were discovered in the recent Spitzer GLIMPSE survey data. These extended sources have enhanced emission in the 4.5um IRAC channel images (which are generally assigned to be green when making 3-color RGB images from Spitzer data). Green fuzzies are frequently found in the vicinities of massive young stellar objects, and it has been established that they are in some cases associated with outflows. Nevertheless, the spectral carrier(s) of this enhanced emission is still uncertain. Although it has been suggested that Br Alpha, H2, [Fe II], and/or broad CO emission may be contributing to and enhancing the 4.5um flux from these objects, to date there have been no direct observations of the 4-5um spectra of these objects. We report here on the first direct spectroscopic identification of the origin of the green fuzzy emission. We obtained spatially resolved L and M band spectra for two green fuzzy sources using NIRI on the Gemini North telescope. In the case of one source, G19.88-0.53, we detect three individual knots of green fuzzy emission around the source. The knots exhibit a pure molecular hydrogen line emission spectrum, with the 4.695um v=0-0 S(9) line dominating the emission in the 4-5um wavelength range, and no detected continuum component. Our data for G19.88-0.53 prove that green fuzzy emission can be due primarily to emission lines of molecular hydrogen within the bandpass of the IRAC 4.5um channel. However, the other target observed, G49.27-0.34, does not exhibit any line emission and appears to be an embedded massive young stellar object with a cometary UC HII region. We suggest that the effects of extinction in the 3-8um wavelength range and an exaggeration in the color stretch of the 4.5um filter in IRAC RGB images could lead to embedded sources such as this one falsely appearing "green".

We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high-velocity dispersion (∼870 km s -1) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal e

We present near-infrared (NIR) spectroscopic observations of the blue compact dwarf (BCD) galaxy Mrk 59, obtained with the TripleSpec spectrograph mounted on the 3.5m APO telescope. The NIR spectrum of Mrk 59, which covers the 0.90 - 2.40 micron wavelength range, shows atomic hydrogen, molecular hydrogen, helium, sulfur and iron emission lines. The NIR data have been supplemented by a SDSS optical spectrum. We found extinction in the BCD to be low [A(V)=0.24 mag] and to be the same in both the optical and NIR ranges. The NIR light does not reveal hidden star formation. The H2 emission comes from dense clumps and the H2 vibrational emission line intensities can be accounted for by photon excitation. No shock excitation is needed. A CLOUDY photoinization model of Mrk 59 reproduces well the observed optical and NIR emission line fluxes. There is no need to invoke sources of ionization other than stellar radiation.The [FeII] 1.257 and 1.643 micron emission lines, often used as supernova shock indicators in low-excitation high-metallicity starburst galaxies, cannot play such a role in high-excitation low-metallicity HII regions such as Mrk 59.

We present near-infrared (NIR) spectroscopic observations of five blue compact dwarf (BCD) galaxies, II Zw 40, Mrk 71, Mrk 930, Mrk 996 and SBS 0335-052E. The NIR spectra which cover the 0.90 micron - 2.40 micron wavelength range, show hydrogen, molecular hydrogen, helium, sulfur and iron emission lines. The NIR data for all BCDs have been supplemented by optical spectra. We found the extinction coefficient in all BCDs to be very similar in both the optical and NIR ranges. The NIR hydrogen emission lines do not reveal more star formation than seen in the optical. The same conclusion is reached from Spitzer data concerning the MIR emission lines. This implies that emission-line spectra of low-metallicity BCDs in the ~ 0.36 - 25 micron wavelength range are emitted by relatively transparent ionized gas. The large extinction derived from the MIR continuum emission in some BCDs implies that the latter arises not from the visible H II regions themselves, but from locations outside these H II regions. The H2 emission line fluxes can be accounted for by fluorescence. CLOUDY stellar photoinization models of all BCDs reproduce well the fluxes of most of the observed optical and NIR emission lines, except in Mrk 930 where shock ionization is needed to account for the [Fe II] emission lines. However, some contribution of shock ionization at the level of < 10% that of stellar ionization is required to reproduce the observed fluxes of high ionization species, such as He II 0.469 micron in the optical range and [O IV] 25.89 micron in the MIR range.

Context. Winds in protoplanetary disks play an important role in their evolution and dispersal. However, the physical process that is actually driving the winds is still unclear (i.e. magnetically versus thermally driven), and can only be understood by directly confronting theoretical models with observational data. Aims. We aim to interpret observational data for molecular hydrogen and atomic oxygen lines that show kinematic disk-wind signatures in order to investigate whether or not purely thermally driven winds are consistent with the data. Methods. We use hydrodynamic photoevaporative disk-wind models and post-process them with a thermochemical model to produce synthetic observables for the spectral lines o–H2 1–0 S(1) at 2.12 µm and [OI] 1D2–3P2 at 0.63 µm and directly compare the results to a sample of observations. Results. We find that our photoevaporative disk-wind model is consistent with the observed signatures of the blueshifted narrow low-velocity component (NLVC) – which is usually associated with slow disk winds – for both tracers. Only for one out of seven targets that show blueshifted NLVCs does the photoevaporative model fail to explain the observed line kinematics. Our results also indicate that interpreting spectral line profiles using simple methods, such as the thin-disk approximation, to determine the line emitting region is not appropriate for the majority of cases and can yield misleading conclusions. This is due to the complexity of the line excitation, wind dynamics, and the impact of the actual physical location of the line-emitting regions on the line profiles. Conclusions. The photoevaporative disk-wind models are largely consistent with the studied observational data set, but it is not possible to clearly discriminate between different wind-driving mechanisms. Further improvements to the models are necessary, such as consistent modelling of the dynamics and chemistry, and detailed modelling of individual targets (i.e. disk structure) would be beneficial. Furthermore, a direct comparison of magnetically driven disk-wind models to the observational data set is necessary in order to determine whether or not spatially unresolved observations of multiple wind tracers are sufficient to discriminate between theoretical models.

Aims. We present near-infrared spectroscopy of the forbidden emission line (FEL) and molecular hydrogen emission line (MHEL) regions at the bases of Herbig-Haro (HH) jets from seven embedded protostars: SVS 13 (the HH 7-11 progenitor), HH 26-IRS, HH 34-IRS, HH 72-IRS, HH 83-IRS, HH 300-IRS (IRAS 04239+2436) and HH 999-IRS (IRAS 06047-1117) Methods. The integral field spectrograph, SINFONI, on the European Southern Observatory’s Very Large Telescope (VLT) was used to characterise jet parameters in these formative regions, where the jets are collimated and accelerated. Results. We find considerable differences in the spectra of HH 83-IRS when compared to the other six sources; CO bandhead and atomic permitted lines from Ca i ,N ai ,M gi and Al i are observed in emission in all but HH 83-IRS, where they are detected in absorption. It is likely that this source is more evolved than the others (or at the very least considerably less active). Strong CO bandhead emission is also detected in emission in the other six sources, while extended H2 ro-vibrational and [Fe ii] forbidden emission lines trace the outflows (only the HH jet from HH 83-IRS is undetected). CO bandhead and Brγ emission peaks are in most cases coincident with the jet source continuum position, consistent with excitation in an accretion disk or accretion flow. However, in the closest source, HH 300-IRS, we do find evidence for excitation in the outflow: here the emission peak is offset by 3.6(±0.7) AU along the flow axis. We also note a correlation between CO and Mg i ,N ai and Ca i intensities, which supports the idea that these atomic permitted lines are associated with accretion disks. From H2 and [Fe ii] images we measure jet widths and derive upper limits to flow component opening angles. Although we do not find that the ionised [Fe ii] component is consistently narrower than the H2 flow component, we do find that narrower H2 and/or [Fe ii] flow components are associated with higher radial velocities (as reported in the literature). Flow opening angles, over the first few hundred AU in each source, are measured to be in the range 21 ◦ –42 ◦ in both H2 and [Fe ii]. Finally, from our 3-D data we are also able to map the extinction and electron density at the base of the outflows from some of our targets: within a few hundred AU, both decrease sharply with distance from the source. Conclusions. It seems clear that collimated atomic and molecular jets, which may initially exhibit a wide opening angle, are a feature of outflows from Class I protostars, Class II T Tauri stars, and possibly even Class 0 sources, and that these jets can be traced to within a few hundred AU of the driving source. A common jet collimation and acceleration mechanism seems inescapable for all stages of low mass star formation.

Molecular hydrogen emission lines are associated with collimated outflows from young stellar objects. They have been measured near Herbig–Haro objects within jets as well as at the jet termination. Similarly to HH objects, the lines are produced from radiative shocks which may be in the form of oblique internal jet shocks or bow shocks. A J-shock can only be invoked in a dynamical model context since the H2 lines are often wide (&gt; 30 km s−1). The alternative is the MHD C–shock in which the ionisation level is sufficiently low so that the magnetic field and ions interact weakly with the neutrals. We have investigated C-shock flows by employing approximate forms for the ion-neutral drag, cooling and other processes with the following results.