Brγ Emission Research Articles

A Near‐Infrared Survey of Radio‐selected Ultracompact H ii Regions

A near-infrared (NIR) survey of 63 radio-selected, ultracompact (UC) H II regions representing 47 different star-forming sites has been completed. The survey was obtained using H-band imaging and moderate-resolution, R = 1200, K-band spectroscopy, centered on the radio emission peak of the UC H II regions. The goal of this survey was to determine the fraction of radio-selected UC H II regions that can be studied with NIR observations and analysis. Approximately 50% of the 63 radio-selected UC H II regions appear to be detected at NIR wavelengths in Brγ emission (107 ergs s-1 cm-2 sr-1). Typical line-of-sight extinction toward the detected UC H II regions ranged from AV = 30 to 50, though one source was measured to have AV = 80. For a few of these UC H II regions, the central ionizing sources are detected through high signal-to-noise ratio NIR spectra of photospheric transitions. This preliminary survey suggests that perhaps 5%-10% of UC H II regions showing NIR counterparts will have directly detectable central ionizing sources. Using the ratio of He I 2.11 to Brγ, the effective temperatures of the central ionizing stars in 25 UC H II regions have been estimated. While He I is not always detected in UC H II regions, when it was found or a meaningful upper limit determined, the spectral type implied by the ratio of He I 2.11 to Brγ closely matched similar estimates of spectral type derived from radio. Model predictions based on mid-infrared measurements appear to underestimate the temperature of the central ionizing stars for which we have directly detected spectral types. The line ratios of H2 2-1 S(1) and 1-0 S(0) relative to the 1-0 S(1) line in our sample of UC H II regions are generally indicative of dense photodissociation regions rather than shocks, similar to what is seen in the Orion Bar. This was true even for UC H II regions showing very weak Brγ emission. While Brγ was generally found to be spatially correlated with the radio emission, H2 showed little correlation with the UC H II regions, typically lying 10'' from the central radio emission. A discussion of each UC H II region studied is included in an extensive appendix.

2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster

Canada-France-Hawaii-Telescope adaptive optics bonnette images through narrowband filters in the K band are presented for the Arches cluster. Continuum fluxes, line fluxes, and equivalent widths are derived from high angular resolution images, some nearly diffraction limited, for the well-known massive stars in the Arches cluster. Images were obtained in the lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19 μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. In addition, fluxes are presented for H I Pα (1.87 μm) and a nearby continuum position (1.90 μm) from Hubble Space Telescope archival data*. The 2 μm and Pα data reveal two new emission-line stars and three fainter candidate emission-line objects. Indications for a spectral change of one object between earlier observations in 1992–1993 and our data from 1999 are found. The ratio of He II 2.19 μm to Brγ emission exhibits a narrow distribution among the stars, suggesting a narrow evolutionary spread centered predominantly on spectral types O4 If or Wolf-Rayet stars of the WN7 subtype. From the approximate spectral types of the identified emission-line stars and comparisons with evolutionary models we infer a cluster age between ~2 and 4.5 Myr.

Adaptive Optics Integral Field Spectroscopy of the Young Stellar Objects in LkHα 225

Progress in understanding the embedded stars in LkHα 225 has been hampered by their variability, making it hard to compare data taken at different times, and by the limited resolution of the available data, which cannot probe the small scales between the two stars. In an attempt to overcome these difficulties, we present new near-infrared data on this object taken using the adaptive optics with a laser for astronomy adaptive optics system with the MPE 3D integral field spectrometer and the near-infrared camera Omega-Cass. The stars themselves have K-band spectra which are dominated by warm dust emission, analogous to classes I-II for low-mass young stellar objects (YSOs), suggesting that the stars are in a phase where they are still accreting matter. On the other hand, the ridge of continuum emission between them is rather bluer, suggestive of extinct and/or scattered stellar light rather than direct dust emission. The compactness of the CO emission seen toward each star argues for accretion disks (which can also account for much of the K-band veiling) rather than a neutral wind. In contrast to other YSOs with CO emission, LkHα 225 has no detectable Brγ emission. In addition, there is no H2 detected on the northern star, although we do confirm that the strongest H2 emission is on the southern star, where we find it is excited primarily by thermal mechanisms. A second knot of H2 is observed to its northeast, with a velocity shift of -75 km s-1 and a higher fraction of nonthermal emission. This is discussed with reference to the H2O maser, the molecular outflow, and [S II] emission observed between the stars.

Evidence for Extinction and Accretion Variability in T Tauri South

We present angularly resolved spectra of T Tau North and South in the 3 μm water-ice feature and K band. Most of the water-ice absorption lies along the line of sight toward T Tau South, confirming that it is viewed through stronger extinction. A decrease in ice-band absorption toward T Tau S between 1998 December and 2000 January, significant at the 2 σ level, was associated with an increase in its near-IR flux. Brγ emission is detected in T Tau North and South and H2 (2.12 μm) emission toward only T Tau South, consistent with previous studies of infrared companions to T Tauri stars. Our results suggest that the near-IR variability of T Tau S is probably caused by both variations in accretion rate and variable extinction along the line of sight.

Star Formation in NGC 4038/4039

We performed near infrared integral field spectroscopy of several star clusters and the nuclei of the prototypical merger NGC 4038/39 (“The Antennae”). Near infrared (NIR) images covered both galaxies. The collision of the two gas-rich spiral galaxies has triggered a starburst obvious from a large number of young star clusters. ISO data suggest that the most active star formation occurs in the region where the two galaxy disks overlap. A significant fraction of the total bolometric luminosity of the system is produced there. Since this region is heavily extincted in the optical, the investigation was made in the NIR. Using Brγ emission and CO absorption features as age indicators, we derive the ages and mass estimates of the star clusters from a comparison with stellar synthesis models. Extinction is calculated from the Brγ/Hα ratio. The young, bright star clusters have ages ranging from 4-12 Myrs, while the nuclear starbursts are much older (50-80 Myrs). The overlap region hosts most of the youngest star clusters below ∼8 Myrs, while the northwestern region is dominated by star clusters in the age range between 8 and 12 Myrs. Several regions, including the northern nucleus, show evidence for sequential star formation on small spatial scales (< 100pc).

Multiwalength Studies of Star Forming Regions in the Magellanic Clouds

We present a multiwavelength study of several star forming regions in the LMC and SMC. Broad and narrowband IR imaging in conjunction with cold molecular emission of CO lines and mid IR imaging by ISO are providing us the data to define the massive star content and formation processes in low metallicity environments (1/3 to 1/10 solar) for comparison with Galactic star forming regions. Our multiwavelength studies show a clear correlation between the 2.12 μm H2, the 6.7 μm AIBs, and 230 GHz CO(2-1) emission as predicted by PDR models towards N66 in the SMC and 30 Doradus in the LMC. We have found IR embedded sources toward the peaks of the CO emission detected toward both HII regions. We find that the molecular gas that has not yet been photo dissociated by the UV radiation field of the O stars is in hot, dense clumps with very small filling factors. The distribution and morphology of the excited molecular gas in 30 Doradus as seen in the H2 line is clumpy with numerous knots while that of the ionized gas in the 2.16 μm Brγ emission shows a filamentary structure. The 6.7 μm images show a good correlation to the Br γ emission as expected for warm gas. Towards N11 and N159 in the LMC we have also found several IR embedded sources associated to the presence of cold molecular gas. These are seen in the interfaces between the molecular material and the HII regions. Thus, either induced or trigered star formation occurs in these interfaces producing a PDR region.

Circumnuclear star formation in M100

Near-infrared (JHK) images of the nucleus of the barred spiral galaxy M100 (NGC 4321) have been obtained using a high-bandwidth tip-tilt secondary and fast guider system on the 3.8 m United Kingdom Infrared Telescope (UKIRT). The resulting images, with a resolution of 0.34″ at K, reveal for the first time a host of compact ‘knots’, which appear to be the result of a recent burst (or bursts) of star formation. Confirmation of this comes from K-band spectroscopy of these knots with CGS4 on UKIRT, which shows Brγ emission and CO absorption features. A comparison with starburst evolutionary models suggests ages for these knots of between 17 and 27 Myr, and a stellar population dominated by late-type supergiants.

The infrared counterpart of the Z source GX 5-1

We have obtained UK Infrared Telescope infrared observations of the field of the bright Galactic Z source GX 5-1. From an astrometric plate solution tied to Tycho-ACT standards we have obtained accurate positions for the stars in our field which, combined with an accurate radio position, have allowed us to identify the probable infrared counterpart of GX 5-1. Narrow-band photometry marginally suggests excess Brγ emission in the counterpart, supporting its association with an accretion-disc source. No significant variability is observed in a limited number of observations. We compare the H and K magnitudes with those of other Z sources, and briefly discuss possible sources of infrared emission in these systems.

Near‐Infrared Line Observations of Arp 299 as a Tracer of Activity in the Nuclei

We have obtained images of the molecular hydrogen (H2) and Brγ emission lines in the interacting galaxy system Arp 299. In order to investigate the nuclear activities, we also have obtained H- and K-band spectra for three of its 2 μm continuum peaks and also J-band spectra for one of them. From the line ratios of Paγ, Paβ, Br10, and Brγ, and also those between [Fe II] 1.26 μm and [Fe II] 1.64 μm, we have successfully modeled the extinction for component A as a combination of AK = 2.6 mag region(s) and AK = 0.3 mag region(s). The extinction corrected Brγ luminosity requires 5 × 1054 s-1 of Lyman photons, which corresponds to 3 × 105 "O6 stars." The mean stellar density within its 100 pc core is comparable to those for the cores in blue compact dwarf galaxies even though the luminosity is almost 2 orders of magnitude larger. The starbursts at the nucleus of component A are probably the most dominant source for the far-infrared emission from this component. In this component, we have found large [Fe II]/H I ratios, which are at the higher end of starburst galaxies and are typical for AGNs or AGN/starburst composites. The nucleus must be in a starburst phase that includes many supernova remnants. The spatial distribution of the H2 emission for this interacting system is similar to that of the 12CO 1-0 emission mapped by Aalto et al. The H2 intensity, however, is not proportional to the CO intensity among components, because of the difference in the H2 excitation mechanism among them. We report the first possible detection of J-band H2 lines in infrared luminous galaxies in component A, which suggests a significant contribution of nonthermal excitation mechanisms.

Low‐Mass Star Formation and the Initial Mass Function in the ρ Ophiuchi Cloud Core

We have obtained moderate-resolution (R = 800-1200) K-band spectra for ~100 stars within and surrounding the cloud core of ρ Oph. We have measured spectral types and continuum veilings and have combined this information with results from new deep imaging. Using the latest evolutionary tracks of D'Antona & Mazzitelli to interpret the H-R diagram for ρ Oph, we infer ages ranging between 0.1 and 1 Myr for the class II and III sources (i.e., those that have emerged from their natal cocoons). A few stars may be slightly older. The initial mass function (IMF) peaks at about 0.4 M☉ and slowly declines to the hydrogen-burning limit with a slope of ~-0.5 in logarithmic units (Salpeter is +1.35). Our lower limits on the numbers of substellar objects demonstrate that the IMF probably does not fall more steeply below the hydrogen-burning limit, at least down to ~0.02 M☉. The derived IMF is consistent with previous findings that the ρ Oph IMF is roughly flat from 0.05 to 1 M☉. The exact shape of the mass function remains a function of the theoretical evolutionary tracks and, at the lowest masses, the conversion from spectral types to effective temperatures. We then make the first comparison of mass functions of stars and prestellar clumps measured in the same region. The similar behavior of the two mass functions in ρ Oph supports the suggestion of Motte et al. and Testi & Sargent that the stellar mass function in young clusters is a direct product of the process of cloud fragmentation. We have also studied the very young and often still embedded class I and flat-spectrum objects. After considering the effect of extinction on the SED classifications of the sample, we find that ~17% of the ρ Oph stars are class I, implying ~0.1 Myr for the lifetime of this stage. In spectra separated by 2 yr, we observe simultaneous variability in the Brγ emission and K-band continuum veiling for two stars, where the hydrogen emission is brighter in the more heavily veiled data. This behavior indicates that the disk may contribute significantly to continuous K-band emission, in contrast to the proposal that the infalling envelope always dominates. Our detection of strong 2 μm veiling (rK = 1-4) in several class II and III stars, which should have disks but little envelope material, further supports this proposition. We also detect absorption features in the spectra of ~25% of class I and flat-spectrum sources, demonstrating the feasibility of studying the photospheres of extremely young protostars.

NIR Line Observations of Starburst Galaxies

We have obtained images of the H2and Brγ emission lines in the galaxy interacting system NGC 3690 + IC 694. We have also obtained simultaneous H- and K-band spectra for three of its 2μm continuum peaks. The most detectable line emission is concentrated at the continuum peaks. Therefore, the emission lines as well as stellar absorption lines can be used as tracers of the activity in the nuclei themselves. From the strong Brγ and marginal detection of Br10 at the nucleus of IC 694, we derive a large extinction for the fully ionized gas in this nucleus. If we adopt this extinction also for the [Fe II]1.64μm emission, the extinction-corrected [Fe II]1.64μm/Brγ ratio will lie at the higher end of starburst galaxies, and is typical for AGNs or AGN/starburst composites. This might imply that many SNRs are involved in the starburst at this nucleus, unless it includes an AGN. All of our results for Component C, including very little CO absorption in the K band, a largeEW(Brγ), a small H2/Brγ ratio, the effective temperature (Teff≃ 40,000K) derived from HeI 1.70μm/Br10 and HeI 2.06μm/Brγ, are consistent with a very young starburst.

Low‐Mass Star Formation and the Initial Mass Function in IC 348

We have performed deep infrared and optical spectroscopy of virtually the entire stellar population within the 5' × 5' core of IC 348, measuring K (2.2 μm) band and optical spectral types that are in good agreement. We have also identified several sources that may be substellar depending on the choice of temperature scales and evolutionary tracks, with three particularly late-type objects (M7.5-M8) that are likely bonafide brown dwarfs. In conjunction with the theoretical evolutionary tracks of D'Antona & Mazzitelli, the H-R diagram indicates a spread in ages from 0.5 to 10 Myr, with most of the core star formation occurring in the last 3 Myr. Using K-band imaging to provide a completeness correction to the spectroscopic sample, we arrive at an initial mass function (IMF) that matches that of Miller & Scalo from 0.25 to 3 M☉. The IMF appears to fall slowly from 0.25 M☉ to the hydrogen burning limit, slightly below the IMF of Miller & Scalo, which is flat in logarithmic units (as compared to slopes of ~1.35 and -2.6 for Salpeter and Scalo). Correction for unresolved binary systems could steepen the slope of the low-mass IMF by about 0.5, which implies a single-star IMF that is roughly flat below 0.25 M☉. The low-mass IMF in IC 348 is similar to that derived in studies of most other young clusters, implying that the IMF does not vary dramatically among clusters of differing environments; however, the derived IMF is dependent on the evolutionary tracks and the detailed shape of the IMF should be viewed with caution until these models are tested against observations, particularly at low masses ( 10 A) or Brγ (>1 A) emission or K-band continuum veiling (rK ≥ 0.5). Since no sources older than 3 Myr show evidence for massive disks, disk lifetimes in the core of IC 348 appear to be shorter than those observed in Taurus or in the outer regions of IC 348.

S255‐2: The Formation of a Stellar Cluster

As part of an ongoing study of high-mass star formation regions, we have imaged the S255-2 triple H II region in near-infrared broadband wavelength bands J (1.23 μm), H (1.65 μm), K (2.23 μm), and at 3.3 μm. We have also obtained images in the Brγ and Brα hydrogen recombination lines, in the H2, v = 1 → 0 S(1) line, and in the 3.29 μm dust feature emission band. The region consists of a circular core of stars and young stellar objects, as well as nebulosity, and a more diffuse stellar cluster. The Brackett-line emission from the region is at least a factor of 10 greater than the value estimated from the radio continuum flux density, assuming case B recombination. The strongest Brα line emission object is IRS 1b, which appears to be an ionizing wind source. The central core region contains a narrow band of Brγ and H2 emission that we postulate is an ionized jet. The 3.29 μm and the H2 emission are found in a bubble-like region that overlaps and extends beyond the Brα and Brγ emission into the photodissociation region. S255-2 appears to be a young cluster of stars still in the process of forming.

Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars

view Abstract Citations (159) References (116) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars Morris, Patrick W. ; Eenens, P. R. J. ; Hanson, Margaret M. ; Conti, Peter S. ; Blum, R. D. Abstract We present an overview of the spectroscopic properties of several luminous stars belonging to Of supergiant, Ofpe/WN9, late-type nitrogen sequence Wolf-Rayet (WNL), B[e], Be supergiant, and luminous blue variable (LBV) classes at 2 μm and 1.6 μm, using recently published and new spectra of moderate to high resolution (500-1600). These objects are "transitional" in their optical classification and may be related in their evolution. The 2 μm spectrum of the LBV AG Car has changed from its 1984-1985 appearance as an Of/WN star, now appearing as a Be or B[e] star by comparison to new spectra of HD 72754 (B2Iape) and GG Car (B[e], whose spectrum has varied since 1984-1985). Further support for a link between B[e] stars and LBVs is seen in the case of the SMC B[e] star S18, which has changed its 1987-1989 spectrum from one of Brγ emission only to one in which emission lines of Fe II, Mg II, Na I, 12CO overtone, He I 2.112-3 μm, and He I 2.058 μm (strong) are present. As the earlier observations were not of a high signal-to-noise ratio, we confirm only the He I and 12CO as new emission, where the latter was previously expected on the basis of TiO emission but was undetected. The overall morphology of the atomic spectrum of S18, including the He I 2.112-3 μm emission, are shared by only one other B star, namely, the quiescent LBV P Cyg (B1 Ia+), but is shared also by the LBV and Ofpe/WN9 star HDE 269582. Only AG Car is observed to have also varied in the 2.112-3 μm line. We thus consider S18 a strong candidate LBV. Our new high-resolution 2 μm spectra also include HD 5980, a WN binary recently observed to undergo an LBV-like outburst in short-term brightness and spectroscopic variations. We provide a detailed K-band line identification of the probable LBV He 3-591 (WRA 751), which is rich in lines of permitted and forbidden iron (mainly Fe II) and includes new identification of [Ni II] at 2.308 μm and 2.369 μm. A significant degree of overlap in spectral morphology exists between the groups, where at least one example from each group may be classified as a member of another from its 2 μm spectrum. This has serious consequences for observations of hot, luminous objects in visually obscured regions. The overlapping infrared spectral morphology reinforces the notion that the objects in this study are interrelated in their evolution. We propose that "transitional" massive stars with hydrogen present at their surfaces (including the least extreme WN types) may not yet be in the stage of core-helium burning but rather are in a previous phase in which the stellar atmosphere/wind is sometimes dynamically unstable. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177892 Bibcode: 1996ApJ...470..597M Keywords: INFRARED: STARS; STARS: EARLY-TYPE; STARS: EMISSION-LINE; BE; STARS: WOLF-RAYET; STARS: SUPERGIANTS full text sources ADS | data products SIMBAD (43)

High-Resolution Spectroscopy of BR gamma Emission in Young Stellar Objects

view Abstract Citations (71) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Resolution Spectroscopy of BR gamma Emission in Young Stellar Objects Najita, Joan ; Carr, John S. ; Tokunaga, Alan T. Abstract We have obtained high-resolution spectra of the Brγ emission line in a small sample of low-luminosity embedded young stellar objects (YSOs) and active T Tauri stars. We find line profiles which possess broad wings (400-700 km s-1 FWZI) but which conspicuously lack the blueshifted absorption components generally expected for emission from a wind. Even T Tauri stars that show strong wind absorption features in the Hα and Na D lines show no obvious evidence of a wind origin for the Brγ line. These results imply that the winds in these YSOs are likely cooler than previously estimated and that mass-loss rates derived from Brγ line strengths require reexamination. We also find a tendency for the centroid of the emission to be blueshifted with respect to the stellar velocity, as is often observed in the higher Balmer lines of T Tauri stars. This tendency is generally consistent with emission from infalling rather than outflowing gas. We discuss the physical origin of the infalling gas and the origin of the broad line wings. Publication: The Astrophysical Journal Pub Date: January 1996 DOI: 10.1086/176649 Bibcode: 1996ApJ...456..292N Keywords: ACCRETION; ACCRETION DISKS; INFRARED: STARS; STARS: MASS LOSS; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (8)

A Multiwavelength Study of 30 Doradus: The Interstellar Medium in a Low-Metallicity Galaxy

We report maps of the 158 microns [C II] fine-structure line, the 63 microns and 146 microns [O I] fine-structure lines, the 2.2 microns H I Brγ line, the 2.1 microns H<SUB>2</SUB> 1-0 S(1) ro-vibrational line, and the 2.6 mm CO (1-0) rotational line toward the 30 Doradus complex in the Large Magellanic Cloud. <P />Comparing our Brγ map with Hα and Hβ measurements, we find that visual to near-infrared extinction and reddening follow the standard dust extinction law and that the Brγ extinction is small, which allows for a reliable determination of the Lyman-continuum intensity. The Lyman continuum as derived from the Brγ emission and the far-UV derived from the far-infrared continuum match the average spectrum of the exciting stars in the 30 Doradus cluster. The observed H_{2 }line intensity may be produced in dense clumps exposed to the stellar radiation fields. <P />The maps of all tracers emphasize a shell-like structure of the 30 Doradus region, which is seen approximately edge-on. The warm molecular gas traced by the H<SUB>2</SUB> line and the ionized gas traced by the Brγ line are intermixed, while the cold molecular gas as traced by CO (1-0) and the photodissociated gas as traced by [C ii] are coextensive over tens of parsecs. This distribution can be explained only by a highly fragmented structure of the interstellar medium that allows UV radiation to penetrate deep into the molecular cloud. Clumpiness is also the key to understanding the extremely high [C II]/CO line intensity ratio. Depending on cloud geometry and physical conditions, the relative beam-filling factors of the partly atomic, partly molecular photodissociated gas as seen in the FIR tracers, and of the purely molecular gas traced by CO, can differ substantially in a clumpy, low-metallicity environment. This effect also leads to a greatly increased H<SUB>2</SUB>/CO conversion factor because a major part of the H<SUB>2</SUB> molecular gas may be contained in the photodissociation region where CO has been destroyed.

Infrared Imaging and Spectroscopy of the Molecular Shock in IC 443

view Abstract Citations (50) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Imaging and Spectroscopy of the Molecular Shock in IC 443 Richter, Matthew J. ; Graham, James R. ; Wright, Gillian S. Abstract We present observations of H_{2 }emission from the molecular shock in the supernova remnant IC 443. The 1-0 5(1) line of H_{2 }at 2.122 microns has been imaged at an angular resolution of 2" over a 10' x 10' area including the peak H2 emission near the southeast edge of the remnant and at 0"7 resolution over an area of 50" x 65" including the emission peak. At high resolution, the previously known sinuous ridge of emission is shown to contain a wealth of structure, consisting of features with sizes ranging from 1" up to scales extending beyond the edges of the image. Unlike the optical emission from supernova remnant shocks, the small-scale H2 emission cannot be well described as a filamentary structure, but is better portrayed as an assemblage of knots. Long-slit spectroscopy from 2 to 4 microns is used to examine the ro-vibrational excitation of H2. The H2 1-0 5(1): 2-1 5(1) line ratio shows little variation over a large range of emission strength, suggesting that column density variations are primarily responsible for brightness differences. The lowest surface brightness emission may include a significant contribution from formation-pumped H2. Upper limits on Brγ emission provide an upper limit to the shock speed, ruling out low Alfvén Mach number bow shocks. Comparing data from different regions of IC 443 with each other and with published Orion Peak 1 data, we find the range of gas temperatures producing emission to be surprisingly uniform. This uniformity rules out the two-shock model of Wang & Scoville which would produce distinctly different line ratios. Comparisons with calculations show that the postshock gas is likely to be in LTE. Arguments based on pressure balance within the remnant require that nH2 ≍4 × 103 cm-3 depending on the dissociation fraction and compression ratio. This preshock density is much lower than previously considered in shock models of H2 emission, but similar to estimates based on the CO observations of van Dishoeck et al. To reach LTE at such a low density, H must be the dominant collision partner for H2, indicating that the shocks in IC 443 must be dissociative. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176481 Bibcode: 1995ApJ...454..277R Keywords: INFRARED: ISM: LINES AND BANDS; SHOCK WAVES; ISM: SUPERNOVA REMNANTS; ISM: INDIVIDUAL ALPHANUMERIC: IC 443; ISM: MOLECULES full text sources ADS | data products SIMBAD (6)

Extended infrared line emission excited by starburst and Seyfert activity in NGC 3256 and NGC 4945

view Abstract Citations (70) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extended Infrared Line Emission Excited by Starburst and Seyfert Activity in NGC 3256 and NGC 4945 Moorwood, A. F. M. ; Oliva, E. Abstract We present visible and infrared images, 1.5-2.3 micron infrared spectra and [Fe II] 1.64 micron, H_2_(1-0)S(1)2.121 microns, and Brγ 2.165 micron infrared line contour maps obtained to investigate the nature of the activity and the origin of the infrared line emission in two relatively nearby infrared luminous galaxies. NGC 3256 is a merging system exhibiting starburst activity over a region several kpc across and a high infrared luminosity of ~3 x 10^11^ L_sun_. A specific search for [Si VI] 1.96 micron coronal line emission from a possibly visually obscured Seyfert nucleus proved negative. Extremely high star- formation and SN rates of ~20 M_sun_ yr^-1^ and ~1.5 yr^-1^, respectively, however, are estimated using the observed integrated Brγ line luminosities and He I 2.06 micron/Brγ ratios together with an existing starburst model. At this rate, the injection energy associated with SN explosions alone could account for the observed [Fe II] 1.64 micron and H_2_ (1-0)S(1) line luminosities. NGC 4945 is an almost edge-on spiral with an order of magnitude lower infrared luminosity which is powered by both a 400 Pc size starburst and a visually obscured Seyfert nucleus which is a variable source of hard X- ray emission and could substantially contribute to the total luminosity. Its star formation efficiency is higher than in NGC 3256 whereas its luminosity and star formation and SN rates of ~0.4 M_sun_ yr^-1^ and ~0.05 yr^-1^ are much lower although still adequate to account for the excitation of the observed [Fe II] 1.64 micron and H_2_ (1-0)S(1) lines. Based on previous survey work, however, the large integrated H_2_ (1-0)S(I)/Brγ ratio observed in this galaxy is also indicative of the presence of a Seyfert nucleus. Maps of the Brγ, [Fe II], and H_2_ (1-0)S(1) line emission reveal significantly different spatial distributions in the two galaxies. In NGC 3256 the emission extends over a region ~4 kpc across and shows similar [Fe II] and Brγ morphologies, whereas the H_2_(1-0)S(1) emission does not correlate in detail with either. In particular, it is less peaked on the nucleus and traces a spiral arm and embedded source to the south of the nucleus. This source is also prominent in our K' (2.1 micron) image but totally obscured by dust in the visible and is probably the nucleus of the merging companion. Additional evidence that the merger is not yet complete is also provided by the fact that the light distribution in the K' image does not correspond to that expected of a relaxed system. In NGC 4945 the Brγ emission is largely confined to a ~380 Pc diameter and <= 190 Pc thick disk in the plane of the galaxy whereas both the [Fe II] 1.64 micron and H_2_ (1-0)S(1) line emission extends over the full extent of the molecular complex which is a factor of 2 larger perpendicular to the plane. This morphology is consistent with additional excitation by an embedded active galactic nucleus and/or a starburst driven superwind. The similarity of the observed [Fe II] and H_2_ intensity profiles perpendicular to the plane suggests a common excitation mechanism for the "excess" emission which we propose can be attributed to partial ionization and heating of molecular gas respectively by X-rays from the nuclear source. The overall conclusion of this study is that NGC 4945 is probably at an advanced stage of its evolution from a starburst to a Seyfert galaxy whereas there is no evidence that such an evolution is occurring yet in the considerably more luminous, merging system, NGC 3256. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174347 Bibcode: 1994ApJ...429..602M Keywords: Infrared Imagery; Infrared Spectra; Light (Visible Radiation); Luminosity; Mapping; Seyfert Galaxies; Star Formation; Starburst Galaxies; Arrays; Calibrating; Cameras; Contours; Detectors; Infrared Spectrometers; Infrared Telescopes; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3256; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4945; GALAXIES: INTERACTIONS; GALAXIES: STARBURST; GALAXIES: SEYFERT; INFRARED: GALAXIES; GALAXIES: ISM full text sources ADS | data products SIMBAD (2) NED (2)

A hidden class of Be stars?

Recently, Brα and Brγ emission was detected in the infrared spectrum of the B0.2V star τ Scorpii, without noticeable emission in Hα (Waters et al. A&amp;A 272, L9-L12, 1993). Here we present simple HI recombination line calculations in the infrared and in the optical that demonstrate that there could be a class of B stars with low-density discs, a factor of 100 lower in density compared to normal Be stars, which may have escaped detection so far.

High Resolution NIR Imaging of the Starburst Galaxy NGC 1808

We report 0.6″ res. J, H, and K and 1.5″ res. imaging of 2.17 μm HI Brγ and 2.12 μm H2 1-0 S(1) line emission towards the nucleus of the starburst galaxy NGC 1808. In the K-band data we (partially) resolve the nucleus and see several small knots in the circumnuclear region. Further, our JHK continuum images show that a large fraction of the near infrared light in NGC 1808 is produced in young star forming clusters. The Brγ emission originates from a compact nuclear source and from several distinct emission knots in the circumnuclear region. These knots are spatially well correlated with a family of compact radio sources, but uncorrelated with the optical “hot spots”. We propose that the Brγ knots trace the actual sites of starburst activity, while the optical hot spots are just directions of low foreground extinction.We use our data together with radio and far-infrared continuum emission measurements to constrain the parameters of the individual starburst sites in NGC 1808. The data suggest that the starbursts are unsynchronized and prolonged (5 × 106–5 × 107 yrs). The star formation rates in the active sites range from ∼0.1 to ∼0.6 M⊙ yr−1, and the present rapid rate of star-formation in NGC 1808 can be maintained for at most another ∼7 × 107 yrs.Portions of this work are presently in press (Krabbe, Sternberg, and Genzel 1993), and a second paper is in preparation (Tacconi-Garman et al. 1993).