Determination of physical parameters of NGC 2023 using the hyperfine NH3 spectrum

An improved approach is given for deriving the physical parameters of a molecular cloud by its NH₃ rotation-inversion hyperfine spectra. The optical depth τ₀(1, 1) of NH₃ (1,1) is obtained by considering the blending effect of the magnetic hyperfine spectral lines, the (1-1) excitation temperature T_ex (1, 1) is calculated by a two level model, the effect of different collision rate and the thermalization of the (1, 1) inversion lines are discussed, the rotation temperature T_R ( 2, 1) between the NH₃ levels (2, 2) and (1, 1) and the column density N( 1, 1) of the NH₃ (1, 1) inversion level are derived, the results of the total column density from different assumptions for the abundance ratio of ortho-NH₃ and para-NH₃ are also discussed.

This approach is used for the molecular cloud NGC 2023 by using the relevant observed data and its optical depth and other physical parameters are obtained.     

Extended dust emission in NGC 7465

We present SCUBA 850-μm, JCMT  CO( J =2→1)  , B -band imaging and VLA H  i observations of the NGC 7465/4/3 group of galaxies. The 850-μm emission associated with NGC 7465 extends to at least ∼2 R ₂₅ and is well correlated with the H  i . We investigate a range of possible mechanisms by which dust beyond R ₂₅ may be heated to give the observed extended submillimetre emission. By modelling the dust heating by stars in two extreme geometries, we fail to find any reasonable star formation scenario that is consistent with both the 850-μm and optical data. Furthermore, we do not detect any  CO( J =2→1)  emission coincident with the extended dust and atomic gas as would be expected if significant star formation were occurring. We show that shock-heating of dust via cloud–cloud collisions in the stripped interstellar medium of NGC 7465 could be sufficient to explain the extended 850-μm emission and lack of optical emission in the stripped gas, and suggest that cloud–cloud collisions may be an important dust heating mechanism in gas-rich systems.     

Star formation in NGC 6334 I and I(N)

The northern section of the molecular cloud complex NGC 6334 has been mapped in the CO and CS spectral line emission and in continuum emission at a wavelength of 1300 μm. Our observations highlight the two dominant sources, I and I(N), and a host of weaker sources. NGC 6334 I is associated with a cometary ultracompact H  ii region and a hot, compact core ≤10 arcsec in size. Mid-infrared and CH₃OH observations indicate that it is also associated with at least two protostellar sources, each of which may drive a molecular outflow. For region I we confirm the extreme high-velocity outflow first discovered by Bachiller & Cernicharo and find that it is very energetic with a mechanical luminosity of 390 L_⊙. A dynamical age for the outflow is ∼3000 yr. We also find a weaker outflow originating from the vicinity of NGC 6334 I. In CO and CS this outflow is quite prominent to the north-west, but much less so on the eastern side of I, where there is very little molecular gas. Spectral survey data show a molecular environment at position I which is rich in methanol, methyl formate and dimethyl ether, with lines ranging in energy up to 900 K above the ground state. NGC 6334 I(N) is more dense than I, but cooler, and has none of the high-excitation lines observed toward I. I(N) also has an associated outflow, but it is less energetic than the outflow from I. The fully sampled continuum map shows a network of filaments, voids and cores, many of which are likely to be sites of star formation. A striking feature is a narrow, linear ridge which defines the western boundary. It is unclear if there is a connection between this filament and the many potential sites of star formation, or if the filament existed prior to the star formation activity.     

Star-forming regions in blue compact dwarf galaxies

We present near-infrared 2.1-μm continuum and Brγ and 1–0S(1) line images of three blue compact dwarf galaxies: II Zw 40, NGC 5253 and He 2-10. Comparison of the morphologies of the emission-line regions and continuum together with the line ratios shows that in these cases the starbursts are typified by strongly peaked Brγ and weak diffuse H₂ emission, indicating the presence of one or more compact nuclei, and also tidal tails. We consider the possible origins of the H₂ emission, and conclude that shock excitation in cloud collisions, and hence dynamical processes such as interactions or mergers, is important. By comparing models of the equivalent width of Brγ to other age constraints from the literature we show that the star formation must have occurred not only recently but in a short-duration burst. The current centres of star formation in all three galaxies are of a similar age but, whereas the hotspots in He 2-10 are coeval, we find phase differences between those in NGC 5253. We compare the masses and sizes of the star formation sites to those of present-day globular clusters.     

Ammonia observations of the nearby molecular cloud MBM 12

We present NH₃(1,1) and (2,2) observations of MBM 12, the closest known molecular cloud (65-pc distance), aimed at finding evidence for on-going star formation processes. No local temperature (with a T _rot upper limit of 12 K) or linewidth enhancement is found, which suggests that the area of the cloud that we have mapped (15-arcmin size) is not currently forming stars. Therefore this nearby 'starless' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation.
A radio continuum source has been found in Very Large Array archive data, close to but outside the NH₃ emission. This source is likely to be a background object.     

Ram-pressure stripping of the interstellar medium in NGC 4485

This paper describes submm, ¹²CO (J = 2–1) observations of the interacting pair of galaxies NGC 4490 and 4485, and together with high resolution H  i and multifrequency radio continuum data we investigate the evolution of the ISM in this system. We find the following. (i) The smaller member of the pair, NGC 4485, has had the atomic, molecular and dust components of its ISM stripped via ram pressure during its recent passage through the extended H  i distribution of NGC 4490. A bow-shock is identified in the H  i ahead of the stripped gas. (ii) Within the disc of NGC 4490 we find a very low H₂-to-H  i ratio as well as a strong correlation between thermal emission and mass of H₂ suggesting that the star formation rate is limited in this case by the conversion of H  i to H₂. (iii) ¹²CO emission from an H  i and radio-continuum bridge between the two galaxies is detected.     

H i and CO observations of Arp 104: a spiral–elliptical interacting pair

We present data probing the spatial and kinematical distribution of both the atomic (H  i ) and molecular (CO) gas in NGC 5218, the late-type barred spiral galaxy in the spiral–elliptical interacting pair, Arp 104. We consider these data in conjunction with far-infrared and radio-continuum data, and N -body simulations, to study the galaxies interactions, and the star formation properties of NGC 5218. We use these data to assess the importance of the bar and tidal interaction on the evolution of NGC 5218, and the extent to which the tidal interaction may have been important in triggering the bar. The molecular gas distribution of NGC 5218 appears to have been strongly affected by the bar; the distribution is centrally condensed with a very large surface density in the central region. The N -body simulations indicate a time-scale since perigalacticon of  ∼3 × 10⁸ yr  , which is consistent with the interaction having triggered or enhanced the bar potential in NGC 5218, leading to inflow and the large central molecular gas density observed. Whilst NGC 5218 appears to be undergoing active star formation, its star formation efficiency is comparable to a 'normal' SBb galaxy. We propose that this system may be on the brink of a more active phase of star formation.     

Gas-phase models for the evolved planetary nebulae NGC 6781, M4-9 and NGC 7293

We have studied the chemistry of the molecular gas in evolved planetary nebulae. Three pseudo-time-dependent gas-phase models have been constructed for dense (10⁴–10⁵ cm⁻³) and cool ( T ∼15 K) clumpy envelopes of the evolved nebulae NGC 6781, M4-9 and NGC 7293. The three nebulae are modelled as carbon-rich stars evolved from the asymptotic giant branch to the late planetary nebula phase. The clumpy neutral envelopes are subjected to ultraviolet radiation from the central star and X-rays that enhance the rate of ionization in the clumps. With the ionization rate enhanced by four orders of magnitude over that of the ISM, we find that resultant abundances of the species HCN, HNC, HC₃N and SiC₂ are in good agreement with observations, while those of CN, HCO⁺, CS and SiO are in rough agreement. The results indicate that molecular species such as CH, CH₂, CH₂⁺ , HCl, OH and H₂O are anticipated to be highly abundant in these objects.     

The identification of an optical counterpart to the super-Eddington X-ray source NGC 5204 X-1

We report the identification of a possible optical counterpart to the super-Eddington X-ray source NGC 5204 X-1. New Chandra data show that the X-ray source is point-like, with a luminosity of 5.2×10³⁹ erg s⁻¹ (0.5–8 keV) . It displays medium- and long-term X-ray variability in observations spanning a period of 20 yr. The accurate Chandra position allows us to identify a blue optical continuum source ( m _v =19.7) at the position of NGC 5204 X-1, using newly obtained optical data from the INTEGRAL instrument on the William Herschel Telescope. The X-ray and optical source properties are consistent with the scenario in which we are observing the beamed X-ray emission of a high-mass X-ray binary in NGC 5204, composed of an O star with either a black hole or neutron star companion.     

The early-type galaxies NGC 1407 and NGC 1400 – I. Spatially resolved radial kinematics and surface photometry

This is the first paper of a series focused on investigating the star formation and evolutionary history of the two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Here, we present new high signal-to-noise ratio long-slit spectroscopic data obtained at the ESO 3.6-m telescope and high-resolution multiband imaging data from the Hubble Space Telescope /Advanced Camera for Surveys and wide-field imaging from Subaru Suprime-Cam. We spatially resolved integrated spectra out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. The radial profiles of the kinematic parameters v _rot, σ, h ₃ and h ₄ are measured. The surface brightness profiles are fitted to different galaxy light models and the colour distributions analysed. The multiband images are modelled to derive isophotal shape parameters and residual galaxy images. The parameters from the surface brightness profile fitting are used to estimate the mass of the possible central supermassive black hole in NGC 1407. The galaxies are found to be rotationally supported and to have a flat core in the surface brightness profiles. Elliptical isophotes are observed at all radii and no fine structures are detected in the residual galaxy images. From our results, we can also discard a possible interaction between NGC 1400, NGC 1407 and the group intergalactic medium. We estimate a mass of  ∼1.03 × 10⁹ M_⊙  for the supermassive black hole in NGC 1407 galaxy.     

Exploring morphological correlations among H2CO, 12CO, MSX and continuum mappings

There are relatively few H₂CO mappings of large-area giant molecular cloud (GMCs). H₂CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of the study was to identify H₂CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature (CBT) data and H₂CO (1₁₁−1₁₀; Nanshan 25-m radio telescope), ¹²CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components on foreground clouds. We report simultaneous 6-cm H₂CO absorption lines and H110α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′), DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H₂CO and ¹²CO contours onto the MSX color map, we can compare correlations. The resolution for H₂CO, ¹²CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H₂CO and ¹²CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there are some discrepancies between ¹²CO and H₂CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H₂CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H₂CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the ΔV range from 1.206 to 5 km s⁻¹.     

Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151

We search for a direct signature of discrete 'clouds' in the broad-line region (BLR) of the Seyfert galaxy NGC 4151. For this purpose we apply cross-correlation (CC) analysis to a high-resolution Keck spectrum of the galaxy. No such signature is found in the data. In order for cloud models to be compatible with this result, there must be at least ∼3×10⁷ emitting clouds in the BLR, where the limit is based on simulation of a homogeneous cloud population. More realistic distributions increase the lower limit to above 10⁸. These numbers are an order-of-magnitude improvement on our previous limit from Mrk 335, where the improvement comes from higher signal-to-noise ratio (S/N), broader lines and refined simulations. Combined with the predicted upper limit for the number of emitting clouds in NGC 4151 (10⁶–10⁷), the derived lower limit puts a strong constraint on the cloud scenario in the BLR of this object. Similar constraints can be placed on models where the emission originates in streams and sheets. Thus, this investigation suggests that the broad emission lines (BELs) in NGC 4151, and by extension in all AGNs, are not made of an ensemble of discrete independent emitters.     

Ultra-high-resolution observations of circumstellar K i and C2 around the post-AGB star HD 56126

We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s⁻¹ (FWHM), to observe K  i and C₂ absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K  i , two of which are also present in C₂. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions ( b -values) of 0.2–0.3 km s⁻¹ for the K  i components, and 0.54±0.03 km s⁻¹ for the strongest (and best defined) C₂ component. These correspond to rigorous kinetic temperature upper limits of 211 K for K  i and 420 K for C₂, although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C₂ implies low kinetic temperatures ( T _k≈10 K) and high densities ( n ≈10⁶ to 10⁷ cm⁻³) within the shell responsible for the main C₂ component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell.     

On the possibility of observing H2 emission from primordial molecular cloud kernels

We study the prospects for observing H₂ emission during the assembly of primordial molecular cloud kernels. The primordial molecular cloud cores, which resemble those at the present epoch, can emerge around  1+ z ∼20  according to recent numerical simulations. The kernels form inside the cores, and the first stars will appear inside the kernels. A kernel typically contracts to form one of the first generation stars with an accretion rate that is as large as ∼0.01 M_⊙ yr⁻¹. This occurs owing to the primordial abundances, which result in a kernel temperature of order 1000 K, and the collapsing kernel emits H₂ line radiation at a rate ∼10³⁵ erg s⁻¹. Predominantly   J =5-3   ( v =0)  rotational emission of H₂ is expected. At redshift  1+ z ∼20  , the expected flux is ∼0.01 μJy for a single kernel. While an individual object is not observable by any facilities available in the near future, the expected assembly of primordial star clusters on subgalactic scales can result in fluxes at the sub-mJy level. This is marginally observable with ASTRO-F and ALMA. We also examine the rotational   J =2-0   ( v =0)  and vibrational   δv =1  emission lines. The former may possibly be detectable with ALMA.     

Limits on the 2.2-μm contrast ratio of the close-orbiting planet HD 189733b

We obtained 238 spectra of the close-orbiting extrasolar giant planet HD 189733b with resolution   R ∼ 15 000  during one night of observations with the Near-Infrared High-Resolution Spectrograph (NIRSPEC), at the Keck II Telescope. We have searched for planetary absorption signatures in the  2.0–2.4 μm  region where H₂O and CO are expected to be the dominant atmospheric opacities. We employ a phase-dependent orbital model and tomographic techniques to search for the planetary absorption signatures in the combined stellar and planetary spectra. Because potential absorption signatures are hidden in the noise of each single exposure, we use a model list of lines to apply a spectral deconvolution. The resulting mean profile possesses a signal-to-noise ratio (S/N) that is 20 times greater than that found in individual lines. Our spectral time series thus yields spectral signatures with a mean S/N = 2720. We are unable to detect a planetary signature at a contrast ratio of  log₁₀( F _p/ F _*) =−3.40  , with 63.8 per cent confidence. Our findings are not consistent with model predictions which nevertheless give a good fit to mid-infrared observations of HD 189733b. The 1σ result is a factor of 1.7 times less than the predicted 2.185-μm planet/star flux ratio of  log₁₀( F _p/ F _*) ∼−3.16  .     

Magnetically collimated jets with high mass flux

We present HST /WFPC2 observations of UGC 4483, an irregular galaxy in the M81/NGC 2403 complex. Stellar photometry was carried out with HSTphot, and is complete to V ≃26.0 and I ≃24.7. We measure the red giant branch tip at I =23.56±0.10, and calculate a distance modulus of μ ₀=27.53±0.12 (corresponding to a distance of 3.2±0.2 Mpc), placing UGC 4483 within the NGC 2403 subgroup. We were able to measure properties of a previously known young star cluster in UGC 4483, finding integrated magnitudes of V =18.66±0.21 and I =18.54±0.10 for the stellar contribution (integrated light minus H α and [O  iii ] contribution), corresponding to an age of ∼10–15 Myr and an initial mass of ∼10⁴ M_⊙. This is consistent with the properties of the cluster's brightest stars, which were resolved in the data for the first time. Finally, a numerical analysis of the galaxy's stellar content yields a roughly constant star formation rate of 1.3×10⁻³ M_⊙ yr⁻¹ and mean metallicity of [Fe/H]=−1.3 dex from 15 Gyr ago to the present.     

Multiperiodicity and physical nature of the δ Sct star GSC 2683-3076

We present the results of a CCD Johnson V and photoelectric Strömgren uvbyβ photometric study of the recently discovered multiperiodic δ Sct star GSC 2683-3076. Our data set mainly consists of 2874 differential measurements in V together with a few data collected into the uvbyβ system. Additional unfiltered CCD measurements were also carried out. A set of seven best-fitting pulsation frequencies representing the light variations of the variable has been detected. The spectral type of the variable is found to be A9V or F0V. Using the uvbyβ indices the following main physical parameters for the variable have been derived: T _eff=7230 K , M _V =1.95 mag , log  g =3.90 , M =1.85 M_⊙ , R =2.30 R_⊙ , ρ =0.16  ρ _⊙ , age =1.0 Gyr , metal abundance [Me/H]=0.16 and distance modulus =8.4 mag . GSC 2683-3076 is found to be a Population I δ Sct star, slightly metal-enriched, evolving on its main-sequence stage. A mixture of radial and non-radial modes seems to be present in the pulsation of this variable. This star is also known as H133 in the young open cluster NGC 6871, however arguments are given that address this star as a non-member of the cluster. The uvbyβ photometry available in the literature for NGC 6871 is also discussed.     

The coronal line regions of planetary nebulae NGC 6302 and 6537: 3–13 μm grating and echelle spectroscopy

We report on advances in the study of the cores of NGC 6302 and 6537 using infrared grating and echelle spectroscopy. In NGC 6302, emission lines from species spanning a large range of ionization potential, and in particular [Si  ix ] 3.934 μm, are interpreted using photoionization models (including cloudy ), which allow us to re-estimate the temperature of the central star to be about 250 000 K. All of the detected lines are consistent with this value, except for [Al  v ] and [Al  vi ]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154 eV). A similar depletion pattern is observed in NGC 6537. Echelle spectroscopy of IR coronal ions in NGC 6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (<22 km s⁻¹ FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [Ne  v ] 3426 Å. We note the absence of a hot bubble, or a wind-blown bipolar cavity filled with a hot plasma, at least on 1 arcsec and 10 km s⁻¹ scales. The systemic heliocentric velocities for NGC 6302 and 6537, measured from the echelle spectra of IR recombination lines, are found to be −34.8±1 km s⁻¹ and −17.8±3 km s⁻¹. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.     

Search for young stars with ir surveys: Regions of massive star formation

A near-IR survey of a selected number of OB star forming regions using large format array cameras is in progress at Las Campanas observatory. The results relative to the HII/molecular cloud complexes NGC 3576 and NGC 6334I-II are presented.     

Australia Telescope Compact Array H i observations of the NGC 6845 galaxy group

We present the results of Australia Telescope Compact Array (ATCA) H  i line and 20-cm radio continuum observations of the galaxy quartet NGC 6845. The H  i emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total H  i mass of at least  1.8 × 10¹⁰ M_⊙  , most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct H  i components and their relation to the known H  ii regions. No H  i emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA  J2001−4659  , was detected 4.4 arcmin NE from NGC 6845B and has an H  i mass of  ∼5 × 10⁸ M_⊙  . No H  i bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of  15–40 M_⊙ yr⁻¹  .