M. Simon

Infrared line and radio continuum emission of circumstellar ionized regions

We present new VLA observations at 1.3 cm wavelengths and new Br..gamma.., Pf..gamma.., and Br..cap alpha.. IR line observations of very compact molecular cloud IR sources that show evidence of ionized gas. We develop a model for their radio continuum and IR line emission in terms of a dense, ionized circumstellar envelope that is the result of mass loss. The effects of a finite radius of the ionized region of flow are specifically included in our analysis and prove to be important for interpreting the radio spectra of these objects. This analysis permits us to discriminate between those IR sources that seem to be ultracompact H II regions and those whose ionized regions are best characterized as flowing circumstellar envelopes with their ionized regions extending to only a few tens of AU from the central star. These flows apparently are often so massive that both their radio continuum and hydrogen IR line emission are optically thick. A model for the photoionization of the dense envelopes by the Balmer photon flux of the central stars of these objects is developed. It is shown that photoionization from the hydrogen n = 2 energy level can be an important ionization mechanism for thesemorexa0» very dense circumstellar envelopes. Thus, all the IR sources we have observed can be understood as powered by a nearly spectral type star on or near the main sequence. The different types among these IR sources may represent different stages of the stars interaction with its molecular cloud environment.«xa0less

High-velocity gas flows associated with H2 emission regions: how are they related and what powers them?

On presente les resultats de letude de la matiere moleculaire a grande vitesse proche des regions demission de H 2 excite par vibration dans les objets DR 21, W75N, NGC 7538, OMC-2, NGC 6334/Peak V et dans HH 2. On a utilise les transitions 12 CO(J=1-0) et 13 CO(J=1-0) comme traceurs. Toutes les sources H 2 sont associees a des ecoulements CO bipolaires a grande vitesse

Molecular hydrogen line emission in Seyfert galactic nuclei

Abstract : 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.

Near-infrared observations of the far-infrared source V region in NGC 6334

We have observed a very red near-infrared source at the center of NGC 6334 FIRS V, a far-infrared source suspected of variability by McBreen et al. The near-infrared source has deep ice and silicate absorption bands, and its half-power size at 20 ..mu..m is approx.15 x 10. Over the past 2 years we have observed no variability in the near-infrared flux. We have also detected an extended source of H/sub 2/ line emission in this region. The total luminosity in the H/sub 2/ v-1--0 S(1) line, uncorrected for extinction along the line of sight, is 0.3 L/sub sun/. Detection of emission in high-velocity wings of the J = 1--0 /sup 12/CO line suggests that the H/sub 2/ emission is associated with a supersonic gas flow.

A determination of the reddening of the H2 emission from the Orion molecular cloud

We have observed the V=1..-->..0 S (0), S (1), S (2), Q (2), Q (3), Q (4), O (5), O (6), and O (7) quadrupole lines of molecular hydrogen from the Orion Molecular Cloud at a position approx.30 southeast of BN in order to measure the extinction to the emitting region. From the relative line strengths, we find that the lines are strongly reddened, and thus the source of emission lies deep within the Orion Molecular Cloud. The visual extinction to the excited H/sub 2/ derived from the ratios of the S and Q lines is A/sub v/=40 +- 6. The O (5) and O (6) lines appear to suffer additional extinction beyond that predicted by the van de Hulst reddening curve; at least part of this absorption is probably attributable to water ices. If the H/sub 2/ lines are excited by a shock propagating through a molecular cloud, the de-reddened line intensities imply a shock velocity of 10--25 km s/sup -1/.

Observations of H2 emission from NGC 7538

Observations of the molecular hydrogen emission at 2 ..mu..m in NGC 7538 are presented. A map of the ..nu..=1-0S(1) line obtained at 24 resolution indicates that the peak of the molecular line emission occurs between the interface of the visible H II region and the dense molecular cloud and the infrared cluster within the molecular cloud. The apparent luminosity in the S(1) line of approx.1.2L/sub sun/ is similar to that measured for Orion, approx.2.5L/sub sun/, before correction for extinction by overlying dust.

Luminous molecular hydrogen emission in the galaxy system NGC 3690-IC 694

We report the detection of line emission of vibrationally excited H/sub 2/ from the galaxy system NGC 3690-IC 694. The line emission is distributed within the system. The total observed luminosity in the H/sub 2/..nu.. = 1-0 S(1) line alone is approximately 1.5 x 10/sup 7/ L/sub sun/. We also detected Br..gamma.. line emission of the system; its observed luminosity indicates that at least 4 x 10/sup 54/ ionizing photons per second are required to maintain ionization of the H II. The H/sub 2/ is probably heated by shocks, and the mass of hot H/sub d/2 exceeds 2 x 10/sup 4/ M/sub sun/.